Final Report

Speed Control of Induction Motor For Pump Application Using SPWM method CHAPTER 2 INTRODUCTION As far as the machine efficiency, robustness, reliability, durability, power factor, ripples, stable output voltage and torque are concerned, three- phase induction motor stands at the a top of the order. Induction motors are widely used in many residential, industrial, commercial, and utility applications [1]. But they require much more complex methods of control, more expensive and higher rated power converters than DC and permanent magnet machines. Various techniques are in practice for induction motor speed control today. S. Dam and A. Saha were proposed closed loop control of L-matrix based induction motor using V/F method using PID controller [1]. S.V. Ustun tuned the PI coefficients using fuzzy genetic control [3]. Neural network based control of induction motor speed control developed in [4-6]. M. Suetake and I. N. Da Silva were proposed DSP-Based Compact Fuzzy system for V/f control of induction motor in [7]. Artificial Intelligence (AI) techniques, such as Expert Systems, Fuzzy Logic, Neural Networks or Biologically Inspired and Genetic Algorithm have recently been applied in motor drives for V/f speed control [8]. Neuro-Fuzzy controller also designed for induction motor speed control [9, 10]. The most popular technique for induction motor speed control is by generating variable frequency supply, which has constant voltage to frequency ratio. This technique is popularly known as V/F control which has large applications in industry. The control strategy consists of keeping constant the Voltage/Frequency ratio of the induction motor supply source. In this paper for speed control of induction motors, a closed loop system utilizing PI controller and constant V/F ratio have been used and the performance of two kinds of PWM based inverter including sinusoidal PWM and space vector PWM have been compared. Induction motor are widely used for appliances, industrial control, and automation, they are often called the workhorse of the motion industry. They are robust, reliable, and durable. When power is supplied to an induction motor at the recommended specifications, it runs at its rated speed. However, many applications need variable speed operations. Historically, mechanical gear systems were used to obtained variable speed. Recently, electronic power and control system have matured tallow these component to be used for motor control in place of mechanical gears. These electronics not only control Dept of EEE, TOCE, Bangalore

Page 7

Speed Control of Induction Motor For Pump Application Using SPWM method the speed, but can improve the motor‘s dynamic and steady state characteristics. In addition, electronics can reduce the system‘s average power consumption and noise generation of the motor. Induction motor control is complex due to its nonlinear characteristics. While there are different method for control, variable voltage variable frequency or volts/hurtz to the most common method of speed control in close loop. This method is most suitable for applications without position control requirements or the need for high accuracy of speed control. For this purpose the generated 220 volts ac is fixed or sometimes is dependent on output load or battery voltage. We will regulate the output ac for induction motor so as to control the speed of induction motor by getting the sample of output and feeding it to the input as reference so that by fixing a fix voltage as comparator voltage we will regulate the speed of induction motor. II. SPEED CONTROL There are two speed terms are synchronous speed and rated speed used in the electric machine. Synchronous speed is the speed at which a motor's magnetic field rotates. Synchronous speed is the motor's theoretical speed if there was no load on the shaft and friction in the bearings. The two factors affecting synchronous speed are the frequency of the electrical supply and the number of magnetic poles in the stator. The synchronous speed is given by Where, f = Frequency in Hz P = Number of Poles The rotor speed of an Induction machine is different from the speed of Rotating magnetic field. The shaft speed (rotor speed) of induction motor when driving load will always be lass than the synchronous speed. The percent difference in synchronous speed and shaft speed is called slip as shown in equation Ns = Synchronous speed Nr = Rotor speed Below relation states that synchronous speed of induction motor is directly proportional to the frequency and inversely proportional to the number of poles of the motor .Since the number of poles is fixed by design, the best way to vary the speed of the induction motor is by varying the supply frequency. The speed of the motor shaft with rated voltage and line frequency applied at full load is so called base speed. By changing the frequency to the motor above or below 50Hz; the motor can operate above or below base speed. Volts - Per - Hertz Ratio This term describes a relationship that is fundamental to the operation of motors using adjustable frequency control. An ac induction motor produces torque by virtue of the flux in its rotating field. Keeping the flux constant will enable the motor to produce full load Dept of EEE, TOCE, Bangalore

Page 8

Speed Control of Induction Motor For Pump Application Using SPWM method torque. Below base speed, this is accomplished by maintaining a constant voltage-tofrequency ratio applied to the motor when changing the frequency for speed control. For 460 and 230 Volt motors, the ratio is 460/60 = 7.6 and 230/60 = 3.8. If this ratio rises as the frequency is decreased to reduce the motor speed, the motor current will increase and may become excessive. If it reduces as the frequency is increased, the motor torque capabilities will decrease. There are some exceptions to this rule which are described below. The base speed of the motor is proportional to supply frequency and is inversely proportional to the number of stator poles. So, by changing the supply frequency; the motor speed can be changed. Above base speed, this ratio will decrease when constant voltage (usually motor rated voltage) is applied to the motor. In these cases, the torque capabilities of the motor decrease above base speed. At approximately 30 Hertz and lower, the Volts-per-Hertz ratio is not always maintained constant. Depending on the type of load, the voltage may be increased to give a higher ratio, in order for the motor to produce sufficient torque, especially at zero speed. This adjustment is usually called "Voltage Boost". At base speed and below, the Volts-per-Hertz ratio can be adjusted lower to minimize motor current when the motor is lightly loaded. This adjustment, which lowers the voltage to the motor, will reduce the magnetizing current to the motor. Consequently, the motor will produce less torque which is tolerable. This control is the most popular in industries and is popularly known as the constant V/f control. The VFD is a system made up of active/passive power electronics devices; figure 1 shows electronic speed control of the motor supply frequency. The basic concept of these drives, figure 1, is that a rectifier converts the fixed frequency supply to d.c. (which converts commercial power into a direct current). A d.c. link stage smoothes the rectified output to a stable d.c. voltage (or current).This d.c. is then inverted to provide a synthesized a.c. waveform at the motor terminals. The frequency and power of the a.c. supply delivered to the motor is controlled by inverter [3]. Induction motors were used in the past mainly in applications requiring constant speed because conventional methods of IM speed control has either been expensive or inefficient. Variable speed applications have been dominated by DC drives. Availability of thyristors, IGBT, GTO have allowed the development of variable speed induction motor drives. The presence of commutator and brushes is the main disadvantage of DC motor, which require frequent maintenance and make them unsuitable for environments Dept of EEE, TOCE, Bangalore

Page 9

Speed Control of Induction Motor For Pump Application Using SPWM method which involve explosive and dirt. On the other hand, induction motors, particularly squirrelcage are rugged, cheap, light, small, and more efficient, require lower maintenance and can operate in dirty and explosive environments. Although speed control of induction motor drives are generally expensive than DC drives, they are used in number of applications such as pump, steel mills, cranes, hoist drives, conveyors, traction etc. because of the advantage of induction motor. Dominant of them is the traction system which is used in auto mobiles and locomotives [1].Induction motor drives have gained equal importance as BLDC motor drives in automotive industries. Both have their advantages and disadvantages. in this we try to see the better parts of induction motor drives. In auto mobile applications speed control is the most important crucial part. Hence in this we have discussed efficient way of controlling induction motor which is discussed in later sections. Following methods are employed for speed control of induction motors: i. Pole changing ii. Supply frequency control iii. Stator voltage control iv. Rotor resistance control In this we go for frequency controlled induction motor drive. There are again two types of variable frequency drive: a) Scalar control b) Vector control In this we discuss scalar control of induction motor due to its simplicity compared to vector controlled methods. We go for Volt/hertz control which is a scalar control method for variable frequency drive. II. VOLT/HERTZ CONTROL Due to the advancement in solid state power devices and microprocessors, speed control of Induction motor controlled by switched power converter are getting popular. Switched power converters offer an easy way to regulate both the frequency and magnitude of the voltage applied to a motor. As a result higher efficiency and performance can be achieved by these motor drives with less noise. The most common principle of this is the constant V/Hz principle which requires that frequency and the magnitude of the voltage applied to the stator of a motor maintain a constant ratio. So by this, the magnetic field in the stator is kept almost constant for all operating points. Thus, constant torque is maintained. Also allows the motor to achieve faster dynamic response.

Dept of EEE, TOCE, Bangalore

Page 10

Speed Control of Induction Motor For Pump Application Using SPWM method CHAPTER 3 LITERATURE SURVEY In modern industrialized countries, more than half the total electrical Energy used is converted to mechanical energy through AC induction motors. Induction motors are extensively used in industrial and household appliances and consume more than 50% of the total generated electrical energy. Single-phase induction motors are widely used in home appliances and industrial control. During the last few years, the concept of speed and torque control of asynchronous motor drives has gained significant popularity. This way, it has been possible to combine the induction-motor structural robustness with the control simplicity and efficiency of a direct current motor. This evolution resulted to the replacement of the dc machines by induction motors in many applications in the last few years.Earlier only dc motors were employed for drives requiring variable speedsdue to facilitate of their speed control methods [1]. The conventional methods of speed control of aninduction motor were either too extravagant or too inefficient thus limiting their application to only constantspeed drives. They are used to drive pumps, fans, compressors, mixers, agitators, mills, conveyors, crushers, machine tools, cranes, etc. This type of electric motor is so popular due to its simplicity, reliability, less maintenance and low cost. Today, with advancements in power electronics, microcontrollers, and digital signal processors(DSPs), electric drive systems have improved drastically. Initially the principle of speed control was based on steady state consideration of the induction motor. V/f control was the commonly used one for the open-loop speed control of drives with low dynamic requirements. In this paper, literature review on speed controlled techniques of induction machine drive and the strategies for pulse width modulation technique are narrated. Approaches for sensorless operation of induction motor and field weakening control are reviewed. Analysis of research contributions in propulsion applications are also carried out. Finally, the research gap in propulsion application with induction motor require an intensive and time-consuming effort for the tuning of their electrical parameters in order to achieve satisfactory performance is presented in open literatures. Various technique methods are now available for the control of induction motor drives; a brief classification of the available drive types is given in figure 2.1

Dept of EEE, TOCE, Bangalore

Page 11

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 3.1 Available drives Such as the popular constant Volts per Hertz control [1] or the ever more popular fieldoriented, or vector, control method [2]-[4]. Recently, ABB has introduced direct torque control (DTC), a speed sensorless control approach [5]. There has also been some investigation into the application of neural networks to various aspects of induction motor control such as adaptive control [6], sensorless speed control [7]–[10], inverter current regulation [11]– [13], as well as for motor parameter identification purposes [14], [15] and flux estimation purposes [8], [9]. There has been less attention devoted to the implementation of neural-network-based field-oriented control in induction motor drives [12], [13].

Dept of EEE, TOCE, Bangalore

Page 12

Speed Control of Induction Motor For Pump Application Using SPWM method

CHAPTER 4 BLOCK DIAGRAM Figure 4.1 represents the block diagram of the proposed system. The proposed system has been in MATLAB/Simulink for the three phase system and the hardware implementation was done for the single phase system.

As represented in block diagram, the energy is supplied from the solar panel to the charge controller. The power from the charge controller flows to the battery and from there to the single phase inverter. It uses a boost converter to boost the voltage from the 12V DC to 24V DC. This is given to the inverter. The inverter converts DC power to AC power. This is stepped up to the single phase system and given to the load. Load in this case being the bulb. The whole system is simulated in MATLAB/Simulink and the hardware prototype has also been implemented for the same proposed system. This system can be used for pump application in field of agriculture or in aerospace applications.

4.1.1 Induction Motor An induction motor or asynchronous motor is an AC electric motor in which the electric current in

the rotor needed

to

produce

torque

is

obtained

by electromagnetic

induction from the magnetic field of the stator winding. An induction motor can therefore be made without electrical connections to the rotor. An induction motor's rotor can be either wound type or squirrel-cage type. Three-phase squirrel-cage induction motors are widely used as industrial drives because they are self-starting, reliable and economical. Single-phase induction motors are used extensively for smaller loads, such as household appliances like fans. Although traditionally used in fixed-speed service, induction motors are increasingly being used with variable-frequency drives (VFDs) in variable-speed service. VFDs offer especially Dept of EEE, TOCE, Bangalore

Page 13

Speed Control of Induction Motor For Pump Application Using SPWM method important energy savings opportunities for existing and prospective induction motors in variable-torque centrifugal fan, pump and compressor load applications. Squirrel cage induction motors are very widely used in both fixed-speed and variable-frequency drive (VFD) applications. The induction motor with a wrapped rotor was invented by Nikola Tesla Nikola Tesla in 1882 in France but the initial patent was issued in 1888 after Tesla had moved to the United States. In his scientific work, Tesla laid the foundations for understanding the way the motor operates. The induction motor with a cage was invented by Mikhail DolivoDobrovolsky about a year later in Europe. Technological development in the field has improved to where a 100 hp (74.6 kW) motor from 1976 takes the same volume as a 7.5 hp (5.5 kW) motor did in 1897. Currently, the most common induction motor is the cage rotor motor. An electric motor converts electrical power to mechanical power in its rotor (rotating part). There are several ways to supply power to the rotor. In a DC motor this power is supplied to the armature directly from a DC source, while in an induction motor this power is induced in the rotating device. An induction motor is sometimes called a rotating transformer because the stator (stationary part) is essentially the primary side of the transformer and the rotor (rotating part) is the secondary side. Induction motors are widely used, especially polyphase induction motors, which are frequently used in industrial drives. Induction motors are now the preferred choice for industrial motors due to their rugged construction, absence of brushes (which are required in most DC motors) and the ability to control the speed of the motor. 2 CONSTRUCTION A typical motor consists of two parts namely stator and rotor like other type of motors. 1. An outside stationary stator having coils supplied with AC current to produce a rotating magnetic field, 2. An inside rotor attached to the output shaft that is given a torque by the rotating field.

Dept of EEE, TOCE, Bangalore

Page 14

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 4.1 Motor Construction

Figure 4.2 Rotor Construction

Stator construction The stator of an induction motor is laminated iron core with slots similar to a stator of a synchronous machine. Coils are placed in the slots to form a three or single phase winding. 3 Figure. Single phase stator with windings. Figure. Induction motor magnetic circuit showing stator and rotor slots Type of rotors Rotor is of two different types. 1. Squirrel cage rotor 2. Wound rotor Squirrel-Cage Rotor In the squirrelDept of EEE, TOCE, Bangalore

Page 15

Speed Control of Induction Motor For Pump Application Using SPWM method cage rotor, the rotor winding consists of single copper or aluminium bars placed in the slots and short-circuited by end-rings on both sides of the rotor. Most of single phase induction motors have Squirrel-Cage rotor. One or 2 fans are attached to the shaft in the sides of rotor to cool the circuit. 4 Figure. Squirrel cage rotor Wound Rotor In the wound rotor, an insulated 3-phase winding similar to the stator winding wound for the same number of poles as stator, is placed in the rotor slots. The ends of the star-connected rotor winding are brought to three slip rings on the shaft so that a connection can be made to it for starting or speed control. It is usually for large 3 phase induction motors. Rotor has a winding the same as stator and the end of each phase is connected to a slip ring. Compared to squirrel cage rotors, wound rotor motors are expensive and require maintenance of the slip rings and brushes, so it is not so common in industry applications.

Figure 4.3 Squirrel Cage IM Construction

PRINCIPLE OF OPERATION An AC current is applied in the stator armature which generates a flux in the stator magnetic circuit. This flux induces an emf in the conducting bars of rotor as they are “cut” by the flux while the magnet is being moved (E = BVL (Faraday’s Law)) A current flows in the rotor circuit due to the induced emf, which in term produces a force, (F = BIL) can be changed to the torque as the output. In a 3-phase induction motor, the threeDept of EEE, TOCE, Bangalore

Page 16

Speed Control of Induction Motor For Pump Application Using SPWM method phase currents ia, ib and ic, each of equal magnitude, but differing in phase by 120°. Each phase current produces a magnetic flux and there is physical 120 °shift between each flux. The total flux in the machine is the sum of the three fluxes. The summation of the three ac fluxes results in a rotating flux, which turns with constant speed and has constant amplitude. Such a magnetic flux produced by balanced three phase currents flowing in thee-phase windings is called a rotating magnetic flux or rotating magnetic field (RMF).RMF rotates with a constant speed (Synchronous Speed). Existence of a RFM is an essential condition for the operation of an induction motor. If stator is energized by an ac current, RMF is generated due to the applied current to the stator winding. This flux produces magnetic field and the field revolves in the air gap between stator and rotor. So, the magnetic field induces a voltage in the short circuited bars of the rotor. This voltage drives current through the bars. The interaction of the rotating flux and the rotor current generates a force that drives the motor and a torque is developed consequently. The torque is proportional with the flux density and the rotor 6 bar current (F=BLI). The motor speed is less than the synchronous speed. The direction of the rotation of the rotor is the same as the direction of the rotation of the revolving magnetic field in the air gap. However, for these currents to be induced, the speed of the physical rotor and the speed of the rotating magnetic field in the stator must be different, or else the magnetic field will not be moving relative to the rotor conductors and no currents will be induced. If by some chance this happens, the rotor typically slows slightly until a current is reinduced and then the rotor continues as before. This difference between the speed of the rotor and speed of the rotating magnetic field in the stator is called slip. It is unitless and is the ratio between the relative speed of the magnetic field as seen by the rotor the (slip speed) to the speed of the rotating stator field. Due to this an induction motor is sometimes referred to as an asynchronous machine. SLIP The relationship between the supply frequency, f, the number of poles, p, and the synchronous speed (speed of rotating field), ns is given by 120 s f n p = The stator magnetic field (rotating magnetic field) rotates at a speed, ns , the synchronous speed. If, n= speed of the rotor, the slip, s for an induction motor is defined as s s n n s n − = At stand still, rotor does not rotate , n = 0, so s = 1. At synchronous speed, n= nS, s = 0 The mechanical speed of the rotor, in terms of slip and synchronous speed is given by, n=(1-s) ns Frequency of Rotor Current and Voltage With the rotor at stand-still, the frequency of the induced voltages and currents is the same as that of the stator (supply) frequency, fe. If the rotor rotates at speed of n, then the relative speed is Dept of EEE, TOCE, Bangalore

Page 17

Speed Control of Induction Motor For Pump Application Using SPWM method the slip speed: nslip=ns-n nslip is responsible for induction. 7 Hence, the frequency of the induced voltages and currents in the rotor is, fr= sfe. SPEED CONTROL OF INDUCTION MACHINES We have seen the speed torque characteristic of the machine. In the stable region of operation in the motoring mode, the curve is rather steep and goes from zero torque at synchronous speed to the stall torque at a value of slip s = ˆs. Normally ˆs may be such that stall torque is about three times that of the rated operating torque of the machine, and hence may be about 0.3 or less. This means that in the entire loading range of the machine, the speed change is quite small. The machine speed is quite stiff with respect to 16 load changes. The entire speed variation is only in the range ns to (1 − s)ns, ns being dependent on supply frequency and number of poles. The foregoing discussion shows that the induction machine, when operating from mains is essentially a constant speed machine. Many industrial drives, typically for fan or pump applications, have typically constant speed requirements and hence the induction machine is ideally suited for these. However, the induction machine, especially the squirrel cage type, is quite rugged and has a simple construction. Therefore it is good candidate for variable speed applications if it can be achieved. 1.Speed control by changing applied voltage From the torque equation of the induction machine, we can see that the torque depends on the square of the applied voltage. The variation of speed torque curves with respect to the applied voltage is shown in figure below. These curves show that the slip at maximum torque remains same, while the value of stall torque comes down with decrease in applied voltage. The speed range for stable operation remains the same. Further, we also note that the starting torque is also lower at lower voltages. Thus, even if a given voltage level is sufficient for achieving the running torque, the machine may not start. This method of trying to control the speed is best suited for loads that require very little starting torque, but their torque requirement may increase with speed. 2. Rotor resistance control From the expression for the torque of the induction machine, torque is dependent on the rotor resistance. The maximum value is independent of the rotor resistance. The slip at maximum torque is dependent on the rotor resistance. Therefore, we may expect that if the rotor resistance is changed, the maximum torque Dept of EEE, TOCE, Bangalore

Page 18

Speed Control of Induction Motor For Pump Application Using SPWM method point shifts to higher slip values, while retaining a constant torque. Figure below shows a family of torque-speed characteristic obtained by changing the rotor resistance. Note that while the maximum torque and synchronous speed remain constant, the slip at which maximum torque occurs increases with increase in rotor resistance, and so does the starting torque. whether the load is of constant torque type or fan-type, it is evident that the speed control range is more with this method. Further, rotor resistance control could also be used as a means of generating high starting torque. For all its advantages, the scheme has two serious drawbacks. Firstly, in order to vary the rotor resistance, it is necessary to connect external variable resistors (winding resistance itself cannot be changed). This, therefore necessitates a slip-ring machine, since only in that case rotor terminals are available outside 3. Stator frequency control The expression for the synchronous speed indicates that by changing the stator frequency also it can be changed. This can be achieved by using power electronic circuits called inverters which convert dc to ac of desired frequency. Depending on the type of control scheme of the inverter, the ac generated may be variable-frequency-fixedamplitude or variable-frequency variable-amplitude type. Power electronic control achieves smooth variation of voltage and frequency of the ac output. This when fed to the machine is capable of running at a controlled speed. However, consider the equation for the induced emf in the induction machine. V = 4.44NØmf where N is the number of the turns per phase, _m is the peak flux in the air gap and f is the frequency. Note that in order to reduce the speed, frequency has to be reduced. If the frequency is reduced while the voltage is kept constant, thereby requiring the amplitude of induced emf to remain the same, flux has to increase. This is not advisable since the 21 machine likely to enter deep saturation. If this is to be avoided, then flux level must be maintained constant which implies that voltage must be reduced along with frequency. The ratio is held constant in order to maintain the flux level for maximum torque capability. Actually, it is the voltage across the magnetizing branch of the exact equivalent circuit that must be maintained constant, for it is that which determines the induced emf. Under conditions where the stator voltage drop is negligible compared the applied voltage, the above equation is valid.

4.1.2 Three Phase Inverter Dept of EEE, TOCE, Bangalore

Page 19

Speed Control of Induction Motor For Pump Application Using SPWM method Three Phase DC-AC Converters Three phase inverters are normally used for high power applications. The advantages of a three phase inverter are: o The frequency of the output voltage waveform depends on the switching rate of the swtiches and hence can be varied over a wide range. o The direction of rotation of the motor can be reversed by changing the output phase sequence of the inverter. o The ac output voltage can be controlled by varying the dc link voltage. The general configuration of a three phase DC-AC inverter is shown in Figure 1. Two types of control signals can be applied to the switches: • 180° conduction • 120° conduction

Figure 4.4: Configuration of a Three-Phase DC-AC Inverter 180-Degree Conduction with Star Connected Resistive Load The configuration of the three phase inverter with star connected resistive load is shown in Figure 3.5. The following convention is followed:

Dept of EEE, TOCE, Bangalore

Page 20

Speed Control of Induction Motor For Pump Application Using SPWM method • A current leaving a node point a, b or c and entering the neutral point n is assumed to be positive. • All the three resistances are equal,

.

In this mode of operation each switch conducts for 180°. Hence, at any instant of time three switches remain on . When S1 is on , the terminal a gets connected to the positive terminal of input DC source. Similarly, when S4 is on , terminal a gets connected to the negative terminal of input DC source. There are six possible modes of operation in a cycle and each mode is of 60° duration and the explanation of each mode is as follows:

Figure 4.5: Three-Phase DC-AC Inverter with star connect resistive load Mode

1: In

interval

this

mode

the

switches S5 , S6 and S1 are

turned on for

time

. As a result of this the terminals a and c are connected to the positive

terminal of the input DC source and the terminal b is connected to the negative terminal of the DC source. The current flow through Ra, Rb and Rc is shown in Figure 3a and the equivalent circuit is shown in Figure 3b. The equivalent resistance of the circuit shown in Figure 3b is Dept of EEE, TOCE, Bangalore

Page 21

Speed Control of Induction Motor For Pump Application Using SPWM method

(1) The current i delivered by the DC input source is

(2) The currents ia and ib are

(3) Keeping the current convention in mind, the current ib is

(4) Having determined the currents through each branch, the voltage across each branch is

(5)

Dept of EEE, TOCE, Bangalore

Page 22

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 4.6 (a): Current through the load in Mode 1

Figure 4.6(b): Equivalent circuit in Mode 1 Mode-2 : In interval

this

mode

the

switches S6 , S1 and S2 are

turned on for

time

. The current flow and the equivalent circuits are shown in Figure

4a and Figure 4b respectively. Following the reasoning given for mode 1 , the currents through each branch and the voltage drops are given by

Dept of EEE, TOCE, Bangalore

Page 23

Speed Control of Induction Motor For Pump Application Using SPWM method

(6)

(7)

Figure 4.7(a): Current through the load in Mode 2

Dept of EEE, TOCE, Bangalore

Page 24

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 4.7(b): Equivalent circuit in Mode 2

Mode 3 : In this mode the switches S1 , S2 and S3 are on for

. The current flow

and the equivalent circuits are shown in Figure 5a and figure 5b respectively. The magnitudes of currents and voltages are:

(8)

(9)

Dept of EEE, TOCE, Bangalore

Page 25

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 4.8(a): Current through the load in Mode 32

Figure 4.8 (b): Equivalent circuit in Mode 3 For modes

4,

5 and 6 the

equivalent

circuits

will

be

same

as modes

1,

2 and 3 respectively. The voltages and currents for each mode are:

Dept of EEE, TOCE, Bangalore

Page 26

Speed Control of Induction Motor For Pump Application Using SPWM method

for mode 4

(10)

for mode5

(11)

for mode 6

(12)

The plots of the phase voltages (van, vbn and vcn) and the currents ( ia, ib and ic) are shown in Figure 4.9 . Having known the phase voltages, the line voltages can also be determined as:

(13) The plots of line voltages are also shown in Figure 4.9 and the phase and line voltages can be expressed in terms of Fourier series as:

(14)

Dept of EEE, TOCE, Bangalore

Page 27

Speed Control of Induction Motor For Pump Application Using SPWM method

(15)

Dept of EEE, TOCE, Bangalore

Page 28

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 4.9: Voltage waveforms for Resistive load for 180°

Dept of EEE, TOCE, Bangalore

Page 29

Speed Control of Induction Motor For Pump Application Using SPWM method

180-Degree Conduction with Star Connected R-L Load In mode

1 the

switches S5, S4 and S1are

turned on.

The

mode

previous

to mode1 was mode 6and the in mode 6 the switches S4, S5 and S6 were on. In the transition from mode 6 to mode 1the switch S4 is turned off and S1 turned on and the current ia changes its direction (outgoing phase). When the switch S4 was on, the direction of current was from point n to point a, the circuit configuration is shown in Figure 7a and the equivalent circuit is shown in Figure 7b. When S1 is turned on the direction of current should be from point a to point n. However, due to the presence of inductance, the current cannot change its direction instantaneously and continues to flow in the previous direction through diode D1(Figure 7c) and the equivalent circuit of the configuration is shown in Figure 7d. Once ia = 0 , the diode D1 ceases to conduct and the current starts flowing through S1 as shown already in Figure 3a and Figure 3b. Whenever one mode gets over and the next mode starts, the current of the outgoing phase cannot change its direction immediately due to presence of the inductance and hence completes its path through the freewheeling diode.

Dept of EEE, TOCE, Bangalore

Page 30

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 3.8(a): Current through the load in Mode 6

The phase currents are determined as follows:

(16) Dept of EEE, TOCE, Bangalore

Page 31

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 3.8(b): Equivalent circuit for Mode 6

Dept of EEE, TOCE, Bangalore

Page 32

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 7d: Current through the load during transition from Mode 6 to Mode 1

Figure 3.8 (c): Equivalent circuit during transition from Mode 6 to Mode 1

Dept of EEE, TOCE, Bangalore

Page 33

Speed Control of Induction Motor For Pump Application Using SPWM method CHAPTER 5 SIMULATION AND HARDWARE SYSTEM Figure 5.1 represents the simulation system of the three phase induction motor in a closed loop. The induction motor is controlled in a closed loop condition by the three phase inverter and the user defined speed.

Figure 5.1 Simulation system for closed loop control of IM The simulation presented, takes in the solar panel power form the MPPT control to the three phase inverter through the DC link. The PV panel presented is a subsystem shown in figure 5.2. It produces the voltage and current for the inverter. The DC bus is just a link between the inverter and the panel which reduces the ripples and the harmonics in it. The inverter is a three phase inverter represented in figure 5.3. It takes in 6 gate pulses for the six switches. The speed controller is a sub system which converts the actual speed with the reference speed and produce gate pulses through the SPWM controller. The speed controller sub system is shown in figure 5.4.

Dept of EEE, TOCE, Bangalore

Page 34

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 5.2 (a) Sub system of PV Panel with MPPT Boost converter

Figure 5.2 (b) PV panel system

Dept of EEE, TOCE, Bangalore

Page 35

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 5.3 Three Phase Inverter

Figure 5.4 Speed Controller sub system

5.2 Hardware Implementation The figure 5.5 represents the hardware prototype of the proposed system for the open loop single phase system.

As represented, The system generates a 230V form the 12V renewable system which in this case is a solar panel. The solar panel used here is of 12V, which is given to the solar charge controller of 12V DC. The solar charge controller is used to control the power going from the solar array to the battery. If the voltage in the battery is less, the power is Dept of EEE, TOCE, Bangalore

Page 36

Speed Control of Induction Motor For Pump Application Using SPWM method delivered from the solar cell or else it is kept in OFF position. The power from the charge controller is passed to the battery. The battery supplies power to the boost converter which supplies boosted voltage, in this case 24V DC to the single phase inverter. The Inverter converts this 24VDC to 12VAC which is given to the step up transformer. This steps up the voltage to 230V is given to the load. The detailed explanation of the system is given below.

5.2.1 ATMEGA328 The project uses Arduino microcontroller board the Arduino ecosystem consists of software and hardware. The microcontroller board used in the project is Arduino mega2560. A microcontroller is a self-contained system with peripherals, memory and a processor that can be used as an embedded system for processing signals. Most programmable microcontrollers that are used today are embedded in other consumer products or machinery including phones, peripherals, automobiles and household appliances for computer systems. Due to that, another name for a microcontroller is "embedded controller." Some embedded systems are more sophisticated, while others have minimal requirements for memory and programming length and a low software complexity. Input and output devices include solenoids, LCD displays, relays, switches and sensors for data like humidity, temperature or light level, amongst others. Microcontrollers are used in automatically controlled products and devices, such as automobile engine control systems, implantable medical devices, remote controls, office machines, appliances, power tools, toys and other embedded systems. By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control even more devices and processes. Mixed signal microcontrollers are common, integrating analog components needed to control non-digital electronic systems.

Some microcontrollers may use four-bit words and operate at clock rate frequencies as low as 4 kHz, for low power consumption (single-digit mill watts or microwatts). They will generally have the ability to retain functionality while waiting for an event such as a button press or other interrupt; power consumption while sleeping (CPU clock and most peripherals off) may be just nanowatts, making many of them well suited for long lasting Dept of EEE, TOCE, Bangalore

Page 37

Speed Control of Induction Motor For Pump Application Using SPWM method battery applications. Other microcontrollers may serve performance-critical roles, where they may need to act more like a digital signal processor (DSP), with higher clock speeds and power consumption. The microcontroller used in this project is Arduino Mega consisting of at mega 2560. At mega 2560 features The high-performance, low-power Atmel 8-bit AVR RISC-based microcontroller combines 256KB ISP flash memory, 8KB SRAM, 4KB EEPROM, 86 general purpose I/O lines, 32 general purpose working registers, real time counter, six flexible timer/counters with compare modes, PWM, 4 USARTs, byte oriented 2-wire serial interface, 16-channel 10-bit A/D converter, and a JTAG interface for on-chip debugging. The device achieves a throughput of 16 MIPS at 16 MHz and operates between 4.5-5.5 volts. By executing powerful instructions in a single clock cycle, the device achieves a throughput approaching 1 MIPS per MHz, balancing power consumption and processing speed. buggies and small robots. Others are electrically equivalent but change the form factor sometimes retaining compatibility with shields, sometimes not.

Figure 5.8: An Official Arduino ATmega2560 Types of Arduino: •

Arduino Uno

•

Arduino Leonardo

•

Arduino LilyPad

•

Arduino Mega

•

Arduino Nano

Dept of EEE, TOCE, Bangalore

Page 38

Speed Control of Induction Motor For Pump Application Using SPWM method •

Arduino Mini

•

Arduino Mini Pro

Table 5.1 :Features of ATmega2560

POWER

The Arduino Mega2560 can be powered via the USB connection or with an external power supply. The power source is selected automatically. External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack. Leads from a battery can be inserted in the Gnd and Vin pin headers of the POWER connector. The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts. The Mega2560 differs from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega8U2 programmed as a USB-to-serial converter. The power pins are as follows: • VIN. The input voltage to the Arduino board when it's using an external power source (as Dept of EEE, TOCE, Bangalore

Page 39

Speed Control of Induction Motor For Pump Application Using SPWM method opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin. • 5V. The regulated power supply used to power the microcontroller and other components on the board. This can come either from VIN via an on-board regulator, or be supplied by USB or another regulated 5V supply. • 3V3. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA. • GND. Ground pins. MEMORY The ATmega2560 has 256 KB of flash memory for storing code (of which 8 KB is used for the bootloader), 8 KB of SRAM and 4 KB of EEPROM INPUT AND OUTPUT Each of the 54 digital pins on the Mega can be used as an input or output, using pinMode(), digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can provide or receive a maximum of 40 mA and has an internal pull-up resistor (disconnected by default) of 20-50 kOhms. In addition, some pins have specialized functions: • Serial: 0 (RX) and 1 (TX); Serial 1: 19 (RX) and 18 (TX); Serial 2: 17 (RX) and 16 (TX); Serial 3: 15 (RX) and 14 (TX). Used to receive (RX) and transmit (TX) TTL serial data. Pins 0 and 1 are also connected to the corresponding pins of the ATmega8U2 USB-toTTL Serial chip . • External Interrupts: 2 (interrupt 0), 3 (interrupt 1), 18 (interrupt 5), 19 (interrupt 4), 20 (interrupt 3), and 21 (interrupt 2). These pins can be configured to trigger an interrupt on a low value, a rising or falling edge, or a change in value. See the attachInterrupt() function for details. PWM: 0 to 13. Provide 8-bit PWM output with the analog Write() function. • SPI: 50 (MISO), 51 (MOSI), 52 (SCK), 53 (SS). These pins support SPI communication, which, although provided by the underlying hardware, is not currently included in the Arduino language. The SPI pins are also broken out on the ICSP header, which is physically compatible with the Duemilanove and Diecimila. Dept of EEE, TOCE, Bangalore

Page 40

Speed Control of Induction Motor For Pump Application Using SPWM method LED: 13. There is a built-in LED connected to digital pin 13. When the pin is HIGH value, the LED is on, when the pin is LOW, it's off. • I 2C: 20 (SDA) and 21 (SCL). Support I2C (TWI) communication using the Wire library (documentation on the Wiring website). Note that these pins are not in the same location as the I2C pins on the Duemilanove.

The Mega2560 has 16 analog inputs, each of which provide 10 bits of resolution (i.e. 1024 different values). By default they measure from ground to 5 volts, though is it possible to change the upper end of their range using the AREF pin and analogReference() function. There are a couple of other pins on the board:

AREF. Reference voltage for the analog inputs. Used with analogReference().

Reset. Bring this line LOW to reset the microcontroller. Typically used to add a reset button to shields which block the one on the board

COMMUNICATION The Arduino Mega2560 has a number of facilities for communicating with a computer, another Arduino, or other microcontrollers. The ATmega2560 provides four hardware UARTs for TTL (5V) serial communication. An ATmega8U2 on the board channels one of these over USB and provides a virtual com port to software on the computer (Windows machines will need a .inf file, but OSX and Linux machines will recognize the board as a COM port automatically. The Arduino software includes a serial monitor which allows simple textual data to be sent to and from the board. The RX and TX LEDs on the board will flash when data is being transmitted via the ATmega8U2 chip and USB connection to the computer (but not for serial communication on pins 0 and 1). A SoftwareSerial library allows for serial communication on any of the Mega's digital pins. The ATmega2560 also supports I2C (TWI) and SPI communication. The Arduino software includes a Wire library to simplify use of the I2C bus; see the documentation on the Wiring website for details Dept of EEE, TOCE, Bangalore

Page 41

Speed Control of Induction Motor For Pump Application Using SPWM method

AUTOMATIC SOFTWARE RESET: Rather then requiring a physical press of the reset button before an upload, the Arduino Mega2560 is designed in a way that allows it to be reset by software running on a connected computer. One of the hardware flow control lines (DTR) of the ATmega8U2 is connected to the reset line of the ATmega2560 via a 100 nanofarad capacitor. When this line is asserted (taken low), the reset line drops long enough to reset the chip. The Arduino software uses this capability to allow you to upload code by simply pressing the upload button in the Arduino environment. This means that the bootloader can have a shorter timeout, as the lowering of DTR can be well-coordinated with the start of the upload. This setup has other implications. When the Mega2560 is connected to either a computer running Mac OS X or Linux, it resets each time a connection is made to it from software (via USB). For the following half-second or so, the boot loader is running on the Mega2560. While it is programmed to ignore malformed data (i.e. anything besides an upload of new code), it will intercept the first few bytes of data sent to the board after a connection is opened. If a sketch running on the board receives onetime configuration or other data when it first starts, make sure that the software with which it communicates waits a second after opening the connection and before sending this data. The Mega contains a trace that can be cut to disable the auto-reset. The pads on either side of the trace can be soldered together to re-enable it. It's labeled "RESET-EN". You may also be able to disable the auto-reset by connecting a 110 ohm resistor from 5V to the reset line.

Dept of EEE, TOCE, Bangalore

Page 42

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 5.9: Pin Diagram of AT MEGA2560 Dept of EEE, TOCE, Bangalore

Page 43

Speed Control of Induction Motor For Pump Application Using SPWM method

5.2.2. TLP 250 MOSFET Driver: Mosfet driver is main component of power electronics circuits. Mosfet drivers are dedicated integrated circuits which are used to drive Mosfets in low side and high side configuration. Mosfet driver TL250 like other MOSFET drivers have input stage and output stage. It also have power supply configuration. TLP250 is more suitable for MOSFET and IGBT. The main difference between TLP250 and other MOSFET drivers is that TLP250 MOSFET driver is optically isolated. Its mean input and output of TLP250 mosfet driver is isolated from each other. Its works like a optocoupler. Input stage have a light emitting diode and output stage have photo diode. Whenever input stage LED light falls on output stage photo detector diode, output becomes high.

Pin layout of TLP250 is given below. It is clearly shown in figure that led at input stage and photo detector diode at output stage is used to provide isolation between input and ouput. Pin number 1 and 4 are not connected to any point. Hence they are not in use. Pin 2 is anode point of input stage light emitting diode and pin 3 is cathode point of input stage. Input is provided to pin number 2 and 3. Pin number 8 is for supply connection. Pin number 5 is for ground of power supply.

5.2.3. Pin configuration: Pin number one and four is not connected to any point physically. Therefore they are not in use. 

Pin number 8 is use to provide power supply to TLP250 and pin number 5 is ground pin which provides return path to power supply ground. Maximum power supply voltage between 15-30 volt dc can be given to TLP250. But it also depends on temperature of environment in which you are using TLP250.



Pin number 2 and 3 are anode and cathode points of input stage LED. It works like a normal light emitting diode. It has similar characteristics of forward voltage and input current. Maximum input current is in the range of 7-10mA and forward

Dept of EEE, TOCE, Bangalore

Page 44

Speed Control of Induction Motor For Pump Application Using SPWM method voltage drop is about 0.8 volt. TLP250 provides output from low to high with minimum threshold current of 1.2mA and above. 

Pin number six and seven is internally connected to each other. Ouput can be taken from either pin number 6 and 7. Totem pole configuration of two transistor is used in TLP250. In case of high input , output becomes high with output voltage equal to supply voltage and in case of low input, output become low with output voltage level equal to ground.



Mosfet driver TLP250 can be used up to 25khz frequency due to slow propagation delay.

Figure 5.10: pin configurations

Low side of MOSFET Driver: Circuit diagram of low side mosfet driver using tlp250 is shown below. In this circuit diagram, tlp250 is used as non inverting low side mosfet driver. you should connect an electrolytic capacitor of value 0.47uf between power supply. It provide protection to tlp250 by providing stabilize voltage to IC.

Dept of EEE, TOCE, Bangalore

Page 45

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 5.11: circuit low flow side of MOSFET driver As shown in figure above input is drive signal that drives the output. Vin is according to signal ground. It should not be connected with supply ground and output ground. It is clearly shown in above figure TLP250 and load ground is referenced to the power ground and it is isolated from input signal reference ground. When input is high, MOSFET Q1 get high signal from TLP250 and it is driven by power supply and current flows through the load. When input is low, MOSFET Q1 get low signal from TLP250 output pin and mosfet Q1 remains off and there is no current flow to load. Value of supply voltage ranges between 10-15 volt. Input resistor at gate of MOSFET is used depend on amplitude of input signal. Usually input signal is provided through microcontroller and microcontroller input signal level is in the order of 5 volt. Capacitor C1 is used as decoupling capacitor.

High side of MOSFET Driver: Circuit diagram of MOSFT driver tlp250 used as high side driver is shown below. It is used as non inverting high side mosfet driver. Because input signal ground is connected to cathode of input stage light emitting diode. Therefore it is used as a non inverting high side mosfet driver. In high side configuration there are three grounds as shown in figure above. Ground of input signal, ground of supply voltage and ground of power supply voltage. Remember that while using TLP250 as high side MOSFET driver, all grounds should be isolated from each other.

Dept of EEE, TOCE, Bangalore

Page 46

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 5.12: circuit high flow side of MOSFET driver 5.2.4 Inverter –MOFET / IRFZ44N IRF-Z44N basically belongs to the family of Metal Oxide Semiconductor Field Effect Transistor(MOSFET). It is a power MOSFET. There are two types of MOSFET i.e. N-channel and P-channel. IRF-Z44N belongs to the N-channel family. It uses “Trench” technology and is enveloped in a plastic structure. It has very low on state resistance. It has zener diode which provides ESD protection up to 2 kilo-volt. It is a low cost device and provides higher efficiency. It is easily available in the market these days and is mostly known because of its vast applications. IRF-Z44N has several different amazing features. It’s features include ultra low on resistance, advance processing technology, dynamic rating, avalanche rated completely, quick switching process and many more. It has a wide range of real life applications including full bridge, push pull applications, consumer full bridge and a lot more.  IRFZ44N belongs to the family of N-channel Power MOSFETs, covered in plasteic body and uses “Trench” technology.  Similar

to

other

transistors,

it

has

three

terminals

named

as Gate,

Drain andSource. They are denoted by the alphabets G, D and S respectively.  Its features include very low on state resistance, high speed processing technology, completely avalanche rated etc. Dept of EEE, TOCE, Bangalore

Page 47

Speed Control of Induction Motor For Pump Application Using SPWM method  Push pull systems and full bridge are few of its real life applications.

Figure 5.13: IR Sensor

Pinout: 

It has total three (3) pins having different individual functions.



IRFZ44N Pinout is as follows: o

Pin # 1: Gate.

o

Pin # 2: Drain.

o

Pin # 3: Source.

Table 5.2: pin configuration

Dept of EEE, TOCE, Bangalore

Page 48

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 5.14: Pinout

Table 5.3: IRFZ44N Ratings

Dept of EEE, TOCE, Bangalore

Page 49

Speed Control of Induction Motor For Pump Application Using SPWM method

Table 5.4: IRFZ44N Features

Table 5.5: IRFZ44N Applications

Dept of EEE, TOCE, Bangalore

Page 50

Speed Control of Induction Motor For Pump Application Using SPWM method 5.2.5 Solar panel

Figure 5.15: Solar panel

Small, compact, all weather and built to high standards. This 6V Solar panel is ideal for steady battery charging and maintenance of 6V projects. Ideal for Trickle charging Motorcycles, Classic cars, Power tools and Water pumps This high quality 5w monocrystalline 6v solar panel works in both sunny and overcast conditions and is fully weatherproof. Comes supplied with 2 meters of cable, a blocking diode to prevent reverse charging and crocodile clips for easy battery connection

Specification  Dimensions: 200mm (w) 265mm(H) 25mm (D)  Open Circuit Voltage: 10.80V  Short Circuit Current: 0.74A  Max Power Voltage: 9.00V  Max System Current: 0.56A  Max System Voltage: 600V  Year electronic component warranty  25 year efficiency guarantee @ >80%

Dept of EEE, TOCE, Bangalore

Page 51

Speed Control of Induction Motor For Pump Application Using SPWM method

5.2.6 Solar Charge Controller A charge controller, charge regulator or battery regulator limits the rate at which electric current is added to or drawn from electric batteries.[1] It prevents overcharging and may protect against overvoltage, which can reduce battery performance or lifespan, and may pose a safety risk. It may also prevent completely draining ("deep discharging") a battery, or perform controlled discharges, depending on the battery technology, to protect battery life.[2][3] The terms "charge controller" or "charge regulator" may refer to either a standalone device, or to control circuitry integrated within a battery pack, battery-powered device, or battery charger.

Figure 5.16 Stand-alone charge controllers

Charge controllers are sold to consumers as separate devices, often in conjunction with solar or wind power generators, for uses such as RV, boat, and off-the-grid home battery storage systems. In solar applications, charge controllers may also be called solar regulators. Some charge controllers / solar regulators have additional features, such as a low voltage disconnect (LVD), a separate circuit which powers down the load when the batteries become overly discharged (some battery chemistries are such that overdischarge can ruin the battery). A series charge controller or series regulator disables further current flow into batteries when they are full. A shunt charge controlleror shunt regulator diverts excess electricity to an auxiliary or "shunt" load, such as an electric water heater, when batteries are full. Simple charge controllers stop charging a battery when they exceed a set high voltage level, and re-enable charging when battery voltage drops back below that level. Pulse width modulation (PWM) and maximum power point Dept of EEE, TOCE, Bangalore

Page 52

Speed Control of Induction Motor For Pump Application Using SPWM method tracker (MPPT) technologies are more electronically sophisticated, adjusting charging rates depending on the battery's level, to allow charging closer to its maximum capacity. A charge controller with MPPT capability frees the system designer from closely matching available PV voltage to battery voltage. Considerable efficiency gains can be achieved, particularly when the PV array is located at some distance from the battery. By way of example, a 150 volt PV array connected to an MPPT charge controller can be used to charge a 24 or 48 volt battery. Higher array voltage means lower array current, so the savings in wiring costs can more than pay for the controller. Charge controllers may also monitor battery temperature to prevent overheating. Some charge controller systems also display data, transmit data to remote displays, and data logging to track electric flow over time.

5.2.7 Step up Transformer A transformer that increases the voltage from primary to secondary (more secondary winding turns than primary winding turns) is called a step-up transformer. Conversely, a transformer designed to do just the opposite is called a step-down transformer.

Figure 5.17 Transformer This is a step-down transformer, as evidenced by the high turn count of the primary winding and the low turn count of the secondary. As a step-down unit, this transformer converts high-voltage, low-current power into low-voltage, high-current power. The larger-gauge wire used in the secondary winding is necessary due to the increase in current. The primary winding, which doesn’t have to conduct as much current, may be made of smaller-gauge wire

Dept of EEE, TOCE, Bangalore

Page 53

Speed Control of Induction Motor For Pump Application Using SPWM method Reversibility of Transformer Operation In case you were wondering, it is possible to operate either of these transformer types backward (powering the secondary winding with an AC source and letting the primary winding power a load) to perform the opposite function: a step-up can function as a stepdown and visa-versa. However, as we saw in the first section of this chapter, efficient operation of a transformer requires that the individual winding inductances be engineered for specific operating ranges of voltage and current, so if a transformer is to be used “backward” like this it must be employed within the original design parameters of voltage and current for each winding, lest it prove to be inefficient (or lest it be damaged by excessive voltage or current!). Transformer Construction Labels Transformers are often constructed in such a way that it is not obvious which wires lead to the primary winding and which lead to the secondary. One convention used in the electric power industry to help alleviate confusion is the use of “H” designations for the higher-voltage winding (the primary winding in a step-down unit; the secondary winding in a step-up) and “X” designations for the lower-voltage winding. Therefore, a simple power transformer will have wires labeled “H1”, “H2”, “X1”, and “X2”. It is usually significant to the numbering of the wires (H1 versus H2, etc.), which we’ll explore a little later in this chapter. Practical Significance of Step-Up and Step-Down Transformers The fact that voltage and current get “stepped” in opposite directions (one up, the other down) makes perfect sense when you recall that power is equal to voltage times current, and realize that transformers cannot produce power, only convert it. Any device that could output more power than it took in would violate the Law of Energy Conservation in physics, namely that energy cannot be created or destroyed, only converted. As with the first transformer example we looked at, power transfer efficiency is very good from the primary to the secondary sides of the device.

Analysis of Step-up and Step-down Transformer Operation Dept of EEE, TOCE, Bangalore

Page 54

Speed Control of Induction Motor For Pump Application Using SPWM method Looking closely at the numbers in the SPICE analysis, we should see a correspondence between the transformer’s ratio and the two inductances. Notice how the primary inductor (l1) has 100 times more inductance than the secondary inductor (10000 H versus 100 H), and that the measured voltage step-down ratio was 10 to 1. The winding with more inductance will have a higher voltage and less current than the other. Since the two inductors are wound around the same core material in the transformer (for the most efficient magnetic coupling between the two), the parameters affecting inductance for the two coils are equal except for the number of turns in each coil. If we take another look at our inductance formula, we see that inductance is proportional to the square of the number of coil turns. Transformer used in this circuit is of 12V to 230V of 500mA as shown below.

Figure 5.18 Step Up Transformer

5.2.8 Boost Converter

As with the buck converter, the boost or step-up converter circuit consists of a switch, a diode, an inductor and a capacitor. Their positions in the circuit vary in comparison to the buck converter. In this case the switch is in parallel with the input voltage source, the capacitor and the load. The inductor is placed between the input voltage source and the switch and the diode is placed in-between the switch and the capacitor. A simple boost circuit with the components mentioned above is pictured in Figure 7. The switch is pictured as a transistor.

Dept of EEE, TOCE, Bangalore

Page 55

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 5.20: Boost Converter Circuit

Just like in the buck converter case there are two separate states in this boost converter topology. When the switch is on or closed the input voltage is used to increase the inductor current as energy is stored in the inductor. The switch acts as short circuit path to disable the RC part of the circuit on the right side of the diode. The diode prevents the capacitor from discharging the output voltage to ground. The second state is encountered when the switch is opened or off. The inductor’s tendency to resist changes in current enables the boost in voltage. When the inductor is charging it acts as a load and stores energy. In this state the inductor acts as an energy source and the output voltage produced during its discharge is related to the current’s rate of change, not the input voltage, therefore allowing a difference between the two voltages. The inductor current is used to charge the capacitor and in turn boost the output voltage. As the output voltage increases the current decreases. The Boost converter used is XL6009 in this system shown below.

Figure 5.21 XL6009 Boost Converter

Dept of EEE, TOCE, Bangalore

Page 56

Speed Control of Induction Motor For Pump Application Using SPWM method This DC-DC Module is based on IC XL6009E1 which is a high-performance step-up switching current (BOOST) module. The module uses the second generation of highfrequency switching technology XL6009E1 core chip that offers superior performance over the first generation technology LM2577. XL6009 replaces LM2577 module as LM2577 is about to be phased out. Features 

Wide input voltage range of 3V – 32V (optimum operating voltage range is 5 – 32V)



Wide Output voltage range of 5V – 35V (Adjustable using on board preset)



Built in 4A MOSFET switches enables efficiency of up to 94% (LM2577 current is 3A)



High switching frequency of 400KHz, can use a small-capacity filter capacitors that can achieve very good results (LM2577 switching frequency is only 50KHz)

Specifications

Value

Type

Non-Isolated Boost ( BOOST )

Rectification

Non-synchronous rectification

Input Range

3V ~ 32V

Output Range

5V ~ 35V

Input Current

4A (maximum), load 18mA ( 5Vinput, 8V output, no-load is less than 18mA . The higher the voltage, the load current increases.)

Conversion efficiency

<94% (the greater the current, the lower the efficiency)

Switching frequency

400KHz

Output ripple

50mV (the higher the voltage, the greater the current, the greater ripple)

Load Regulation ± 0.5% Voltage Regulation

± 0.5%

Working temperature

-40 ° C ~ +85 ° C

Dimensions

43mm * 21mm * 14mm (length * width* height)

Dept of EEE, TOCE, Bangalore

Page 57

Speed Control of Induction Motor For Pump Application Using SPWM method

Pins 

IN+ input positive



IN- input negative!



OUT+ output positive



OUT- output negative

Module Schematic

Dept of EEE, TOCE, Bangalore

Page 58

Speed Control of Induction Motor For Pump Application Using SPWM method

CHAPTER 6 RESULTS AND DISCUSSIONS 6.1 Simulation Results The simulation done for the closed loop control of Induction motor fetches very good results and accurate speed as it follows closed loop control by comparing the actual and reference speed.

Dept of EEE, TOCE, Bangalore

Page 59

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 6.1 Output actual speed and reference speed along with electromagnetic torque The actual speed and the reference speed are in coordination with each other which can be observed from the graph. The electromagnetic torque always stays approximately close to 0 when the required speed is achieved. Figure 5.2 represents the stator voltages Vq and Vs out of the induction motor.

Figure 6.2 Stator Voltages Dept of EEE, TOCE, Bangalore

Page 60

Speed Control of Induction Motor For Pump Application Using SPWM method

6.2 Hardware Results The hardware prototype has been designed for 12V voltage. The solar panel of 12V is attached to charge controller as shown in figure 5.5. The charge controller allows the voltage to flow through it to the battery. The battery is of 12V DC. The power from the battery is given to the Boost converter of 24V. This is given to the Inverter which converts my DC power to AC power of 12V. The gate pulses to the hardware or the inverter is given through the ATMEGA328 microcontroller. The 12V AC voltage is stepped up and given to the step up transformer and to the load. Figure 6.3 represents the gate pulses for inverter and the figure 6.4 represents the inverter output voltage.

Figure 6.3 Gate pulses for Inverter

Dept of EEE, TOCE, Bangalore

Page 61

Speed Control of Induction Motor For Pump Application Using SPWM method

Figure 6.4 Inverter Output

CHAPTER 7 7.1CONCLUSION The machine efficiency, robustness, reliability, durability, power factor, ripples, stable output voltage and torque are concerned, three- phase induction motor stands at the a top of the order. Induction motors are widely used in many residential, industrial, commercial, and utility applications. But they require much more complex methods of control, more expensive and higher rated power converters than DC and permanent magnet machines. Various techniques are in practice for induction motor speed control today. In this project, a closed loop simulation of IM was performed along with the open

Dept of EEE, TOCE, Bangalore

Page 62

Speed Control of Induction Motor For Pump Application Using SPWM method loop single phase system in hardware prototype. The results were in accordance with each other.

7.2 FUTURE SCOPE This system can be implemented for real world applications by proper designing for the future purpose. If properly designed, the system can be also applied to other applications such aerospace, industries etc.

CHAPTER 8 REFRENCES 1. IEC 60050 (Publication date: 1990-10). Section 411-31: Rotation Machinery General, IEV ref. 411-31-10: "Induction Machine - an asynchronous machine of which only one winding is energized". 2. ^ Jump up to:a b Babbage, C.; Herschel, J. F. W. (Jan 1825). "Account of the Repetition of M. Arago's Experiments on the Magnetism Manifested by Various Substances during the Act of Rotation". Philosophical Transactions of the Royal Society. 115: 467–496. doi:10.1098/rstl.1825.0023. Retrieved 2 December 2012.

Dept of EEE, TOCE, Bangalore

Page 63

Speed Control of Induction Motor For Pump Application Using SPWM method 3. ^ Thompson, Silvanus Phillips (1895). Polyphase Electric Currents and AlternateCurrent Motors (1st ed.). London: E. & F.N. Spon. p. 261. Retrieved 2 December 2012. 4. ^ Baily,

Walter

(June

28,

1879). "A

Mode

of

producing

Arago's

Rotation". Philosophical Magazine. Taylor & Francis. 5. ^ Jump up to:a b Vučković, Vladan (November 2006). "Interpretation of a Discovery" (PDF). The

Serbian

Journal

of

Electrical

Engineers. 3(2).

Retrieved 10 February 2013. 6. ^ The Electrical engineer, Volume 5. (February, 1890) 7. ^ The Electrician, Volume 50. 1923 8. ^ Official gazette of the United States Patent Office: Volume 50. (1890) 9. ^ Eugenii Katz. "Blathy". People.clarkson.edu. Archived from the original on June 25, 2008. Retrieved 2009-08-04. 10. ^ Ricks, G.W.D. (March 1896). "Electricity Supply Meters". Journal of the Institution

of

Electrical

Engineers. 25 (120):

57–77. doi:10.1049/jiee-

1.1896.0005. 11. ^ Ferraris, G. (1888). "Atti della Reale Academia delle Science di Torino". Atti della R. Academia delle Science di Torino. XXIII: 360–375. 12. ^ Jump up to:a b c d e f g Alger, P.L.; Arnold, R.E. (1976). "The History of Induction Motors in America". Proceedings of the IEEE. 64 (9): 1380– 1383. doi:10.1109/PROC.1976.10329. 13. ^ Froehlich,

Fritz

E.

Editor-in-Chief; Allen

Kent Co-Editor

(1992). The

Froehlich/Kent Encyclopedia of Telecommunications: Volume 17 - Television Technology to Wire Antennas (First ed.). New York: Marcel Dekker, Inc. p. 36. ISBN 978-0-8247-2902-8. 14. ^ The Electrical Engineer (21 Sep 1888). . . . a new application of the alternating current in the production of rotary motion was made known almost simultaneously by two experimenters, Nikola Tesla and Galileo Ferraris, and the subject has attracted general attention from the fact that no commutator or connection of any kind with the armature was required. . . . Volume II. London: Charles & Co. p. 239.

Dept of EEE, TOCE, Bangalore

Page 64

Speed Control of Induction Motor For Pump Application Using SPWM method 15. ^ Ferraris, Galileo (1885). "Electromagnetic Rotation with an Alternating Current". Electrician. 36: 360–375.

Dept of EEE, TOCE, Bangalore

Page 65