Rashid Ch17 Images
This document was uploaded by user and they confirmed that they have the permission to share it. If you are author or own the copyright of this book, please report to us by using this DMCA report form. Report DMCA
Overview
Download & View Rashid Ch17 Images as PDF for free.
More details
- Words: 2,495
- Pages: 69
Loading documents preview...
POWER ELECTRONICS Devices, Circuits, and Applications FOURTH EDITION
CHAPTER CHAPTER
17
Protections of Devices and Circuits
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Learning Outcomes
After completing this chapter, students should be able to do the following: Describe the electrical analog of thermal models and the methods for cooling power devices. Describe the methods for protecting the devices from excessive di/dt and dv/dt, and transient voltages due to load and supply disconnection. Select fast-acting fuses for protecting power devices. List the sources of electromagnetic interference (EMI) and the methods of minimizing EMI effects on receptor circuits.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Symbols and Their Meanings
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.1
Electrical analog of heat transfer.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.1
Cooling and Heat Sinks
• The junction temperature of a device TJ is
given by
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.2
Thermal resistance characteristics. (Courtesy of EG&G Wakefield Engineering.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.3
Heat sinks. (Courtesy of Wakefield-Vette Thermal Solutions.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.4
Heat pipes.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.5
Water-cooled ac switches. (Courtesy of Powerex, Inc.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.6
Assembly units. (Courtesy of Powerex, Inc.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.7
Junction temperature with rectangular power pulses.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.2 and 17.3
Junction Temperature with Rectangular Power Pulses
• If Z0 is the steady-state junction case
thermal impedance, the instantaneous thermal impedance can be expressed as
• where τth is the thermal time constant of
the device. If the power loss is Pd, the instantaneous junction temperature rise above the case is Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.4
Junction Temperature with Rectangular Power Pulses
• If P1, P2, P3, . . . are the power pulses
with P2 = P4 = . . . = 0, the junction temperature at the end of mth pulse can be expressed as
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.8
Approximation of a power pulse by rectangular pulses.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.5
Approximation of a Power Pulse
• The junction temperature at the end of
mth pulse can be found from
where Zn is the impedance at the end of nth pulse of duration tn = δt.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.9
Device power loss.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.10
Junction temperature rise for Example 17.1.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Table 17.1
Equivalencies between the Electrical and Thermal Variables
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.11
Electrical transmission line equivalent circuit or modeling heat conduction.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.12
Thermal equivalent elements for modeling heat conduction. [Ref. 1, M. März]
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Table 17.2
Thermal Data for Common Materials [Ref. 1]
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.13
Simple mathematical equivalent circuit, Ref. 1.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.6 and 17.7
Mathematical Thermal Equivalent Circuit
• Using the partial fractional representation,
the step response of the thermal impedance can be expressed as given by
• The equivalent input impedance at the
input terminals can be expressed as
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.8
Mathematical Thermal Equivalent Circuit
• This cooling curve can be used to find the
transient thermal impedance of the device.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.14
Simple mathematical equivalent circuit, Ref. 1.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.9
Coupling of Electrical and Thermal Components
• This cooling curve can be used to find the
transient thermal impedance of the device.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.15
Device mounted on a heat sink and its thermal equivalent circuit. [Ref. 1, M. März]
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.16
Snubber networks.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.17
Equivalent circuit during recovery.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.12 and 17.13
Reverse Recovery Transients
• For an underdamped case, the solutions of
Eqs. (17.10) and (17.11) yield the reverse voltage across the device as
• where
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.14 and 17.15
Reverse Recovery Transients
• The undamped natural frequency is
• The damping ratio is
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.16
Reverse Recovery Transients
• and the damped natural frequency is
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.18
Recovery transient.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.19 and 17.20
Recovery Transient
• The initial reverse voltage and dv/dt can
be found from Eqs. (17.12) and (17.17) by setting t = 0:
• where the current factor (or ratio) d is
given by
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.22 and 17.23
Recovery Transient
• The time t1, which can be obtained by
setting Eq. (17.17) equal to zero, is found as
• and the peak voltage can be found from
Eq. (17.12):
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.19 Optimum snubber parameters for compromise design. (Reproduced from W. McMurray, "Optimum snubbers for power semiconductors," IEEE Transactions on Industry Applications, Vol. 1A8, No. 5, 1972, pp. 503–510, Fig. 7, © 1972 by IEEE.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.20
Nondissipative snubber.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.21
Switching off transient.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.41 and 17.42
Supply- and Load-Side Transients
• The transient voltage vo(t) is the same as
the capacitor voltage vc(t).
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.43 and 17.44
Supply- and Load-Side Transients
• where
• and
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.45
Supply- and Load-Side Transients
• If ω0 < ω, the transient voltage in Eq.
(17.42) that is maximum when cos θ = 0 (or θ = 90°) is
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.22
Equivalent circuit during switching on the supply.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.46 and 17.47
Equivalent Circuit During Switching on the Supply
• In practice, ω0 < ω, and the transient
voltage, which is maximum when cos θ = 0 (or θ = 0°) is
• The required amount of capacitance to
limit the transient voltage can be determined from
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.48
Equivalent Circuit During Switching on the Supply
• Substituting ω0 from Eq. (17.46) into Eq.
(17.47) gives us
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.23
Equivalent circuit due to load disconnection.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.24
Characteristics of selenium diode.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.25
Voltage-suppression diodes.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.49
Voltage-suppression Diodes
• The current is expressed as
where K is a constant and V is the applied voltage. The value of α varies between 30 and 40.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.26
Protection of power devices.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.27
Individual protection of devices.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.28
Semiconductor fuses. (Image is courtesy of Eaton's Bussmann Business.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.29
Fuse current.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.50
Fuse Current
• If R is the resistance of the fault circuit
and i is the instantaneous fault current between the instant of fault occurring and the instant of arc extinction, the energy fed to the circuit can be expressed as
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.30
Current–time characteristics of device and fuse.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.31
Protection by crowbar circuit.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.32
RL circuit.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.51
Fault Current with Ac Source
• Redefining the time origin, t = 0, at the
instant of closing the switch, the input voltage is described by νs = Vm sin(ωt + θ) for t ≥ 0. Eq. (11.6) gives the current as
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.33
Fault in ac circuit.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.52 and 17.53
Fault in Ac Circuit
• If there is a fault across the load, applying
an initial current of I0 at the beginning of the fault, gives the fault current as
• For a highly inductive fault path, ϕ = 90°
and e-Rt/L = 1, and Eq. (17.52) becomes
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.54
Fault in Ac Circuit
• If the fault occurs at θ = 0, that is, at the
zero crossing of the ac input voltage, ωt = 2nπ. Eq. (17.53) becomes
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.34
Transient voltage and current waveforms.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.35
Dc circuit.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.55
Fault Current with Dc Source
• The current of a dc circuit in Figure 17.35
is given by
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.36
Fault in dc circuit.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.56
Fault in Dc Circuit
• With an initial current of I0 at the
beginning of the fault current, as shown in Figure 17.36, the fault current is expressed as
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.37
Fault in ac circuit for PSpice simulation.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.38
PSpice plot for Example 17.7.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Table 17.3
FCC EMI Limits [Ref. 10]
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Table 17.4
European EN 55022 EMI Limits [Refs. 10, 11]
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
CHAPTER CHAPTER
17
Protections of Devices and Circuits
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Learning Outcomes
After completing this chapter, students should be able to do the following: Describe the electrical analog of thermal models and the methods for cooling power devices. Describe the methods for protecting the devices from excessive di/dt and dv/dt, and transient voltages due to load and supply disconnection. Select fast-acting fuses for protecting power devices. List the sources of electromagnetic interference (EMI) and the methods of minimizing EMI effects on receptor circuits.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Symbols and Their Meanings
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.1
Electrical analog of heat transfer.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.1
Cooling and Heat Sinks
• The junction temperature of a device TJ is
given by
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.2
Thermal resistance characteristics. (Courtesy of EG&G Wakefield Engineering.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.3
Heat sinks. (Courtesy of Wakefield-Vette Thermal Solutions.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.4
Heat pipes.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.5
Water-cooled ac switches. (Courtesy of Powerex, Inc.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.6
Assembly units. (Courtesy of Powerex, Inc.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.7
Junction temperature with rectangular power pulses.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.2 and 17.3
Junction Temperature with Rectangular Power Pulses
• If Z0 is the steady-state junction case
thermal impedance, the instantaneous thermal impedance can be expressed as
• where τth is the thermal time constant of
the device. If the power loss is Pd, the instantaneous junction temperature rise above the case is Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.4
Junction Temperature with Rectangular Power Pulses
• If P1, P2, P3, . . . are the power pulses
with P2 = P4 = . . . = 0, the junction temperature at the end of mth pulse can be expressed as
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.8
Approximation of a power pulse by rectangular pulses.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.5
Approximation of a Power Pulse
• The junction temperature at the end of
mth pulse can be found from
where Zn is the impedance at the end of nth pulse of duration tn = δt.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.9
Device power loss.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.10
Junction temperature rise for Example 17.1.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Table 17.1
Equivalencies between the Electrical and Thermal Variables
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.11
Electrical transmission line equivalent circuit or modeling heat conduction.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.12
Thermal equivalent elements for modeling heat conduction. [Ref. 1, M. März]
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Table 17.2
Thermal Data for Common Materials [Ref. 1]
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.13
Simple mathematical equivalent circuit, Ref. 1.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.6 and 17.7
Mathematical Thermal Equivalent Circuit
• Using the partial fractional representation,
the step response of the thermal impedance can be expressed as given by
• The equivalent input impedance at the
input terminals can be expressed as
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.8
Mathematical Thermal Equivalent Circuit
• This cooling curve can be used to find the
transient thermal impedance of the device.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.14
Simple mathematical equivalent circuit, Ref. 1.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.9
Coupling of Electrical and Thermal Components
• This cooling curve can be used to find the
transient thermal impedance of the device.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.15
Device mounted on a heat sink and its thermal equivalent circuit. [Ref. 1, M. März]
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.16
Snubber networks.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.17
Equivalent circuit during recovery.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.12 and 17.13
Reverse Recovery Transients
• For an underdamped case, the solutions of
Eqs. (17.10) and (17.11) yield the reverse voltage across the device as
• where
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.14 and 17.15
Reverse Recovery Transients
• The undamped natural frequency is
• The damping ratio is
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.16
Reverse Recovery Transients
• and the damped natural frequency is
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.18
Recovery transient.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.19 and 17.20
Recovery Transient
• The initial reverse voltage and dv/dt can
be found from Eqs. (17.12) and (17.17) by setting t = 0:
• where the current factor (or ratio) d is
given by
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.22 and 17.23
Recovery Transient
• The time t1, which can be obtained by
setting Eq. (17.17) equal to zero, is found as
• and the peak voltage can be found from
Eq. (17.12):
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.19 Optimum snubber parameters for compromise design. (Reproduced from W. McMurray, "Optimum snubbers for power semiconductors," IEEE Transactions on Industry Applications, Vol. 1A8, No. 5, 1972, pp. 503–510, Fig. 7, © 1972 by IEEE.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.20
Nondissipative snubber.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.21
Switching off transient.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.41 and 17.42
Supply- and Load-Side Transients
• The transient voltage vo(t) is the same as
the capacitor voltage vc(t).
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.43 and 17.44
Supply- and Load-Side Transients
• where
• and
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.45
Supply- and Load-Side Transients
• If ω0 < ω, the transient voltage in Eq.
(17.42) that is maximum when cos θ = 0 (or θ = 90°) is
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.22
Equivalent circuit during switching on the supply.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.46 and 17.47
Equivalent Circuit During Switching on the Supply
• In practice, ω0 < ω, and the transient
voltage, which is maximum when cos θ = 0 (or θ = 0°) is
• The required amount of capacitance to
limit the transient voltage can be determined from
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.48
Equivalent Circuit During Switching on the Supply
• Substituting ω0 from Eq. (17.46) into Eq.
(17.47) gives us
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.23
Equivalent circuit due to load disconnection.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.24
Characteristics of selenium diode.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.25
Voltage-suppression diodes.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.49
Voltage-suppression Diodes
• The current is expressed as
where K is a constant and V is the applied voltage. The value of α varies between 30 and 40.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.26
Protection of power devices.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.27
Individual protection of devices.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.28
Semiconductor fuses. (Image is courtesy of Eaton's Bussmann Business.)
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.29
Fuse current.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.50
Fuse Current
• If R is the resistance of the fault circuit
and i is the instantaneous fault current between the instant of fault occurring and the instant of arc extinction, the energy fed to the circuit can be expressed as
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.30
Current–time characteristics of device and fuse.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.31
Protection by crowbar circuit.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.32
RL circuit.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.51
Fault Current with Ac Source
• Redefining the time origin, t = 0, at the
instant of closing the switch, the input voltage is described by νs = Vm sin(ωt + θ) for t ≥ 0. Eq. (11.6) gives the current as
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.33
Fault in ac circuit.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equations 17.52 and 17.53
Fault in Ac Circuit
• If there is a fault across the load, applying
an initial current of I0 at the beginning of the fault, gives the fault current as
• For a highly inductive fault path, ϕ = 90°
and e-Rt/L = 1, and Eq. (17.52) becomes
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.54
Fault in Ac Circuit
• If the fault occurs at θ = 0, that is, at the
zero crossing of the ac input voltage, ωt = 2nπ. Eq. (17.53) becomes
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.34
Transient voltage and current waveforms.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.35
Dc circuit.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.55
Fault Current with Dc Source
• The current of a dc circuit in Figure 17.35
is given by
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.36
Fault in dc circuit.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Equation 17.56
Fault in Dc Circuit
• With an initial current of I0 at the
beginning of the fault current, as shown in Figure 17.36, the fault current is expressed as
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.37
Fault in ac circuit for PSpice simulation.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Figure 17.38
PSpice plot for Example 17.7.
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Table 17.3
FCC EMI Limits [Ref. 10]
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Table 17.4
European EN 55022 EMI Limits [Refs. 10, 11]
Power Electronics: Devices, Circuits, and Applications, 4e Muhammad H. Rashid
Copyright ©2014 by Pearson Education, Inc. All rights reserved.
Related Documents
Rashid Ch17 Images
March 2021 0
Rashid Ch14 Images
March 2021 0
Rashid Ch04 Images
March 2021 0
Rashid Ch13 Images
March 2021 0
Rashid Ch11 Images
March 2021 0
Rashid Ch09 Images
March 2021 0More Documents from "Atiq Ur Rehman"
Rashid Ch13 Images
March 2021 0
Rashid Ch11 Images
March 2021 0
Rashid Ch14 Images
March 2021 0
Rashid Ch04 Images
March 2021 0
60152341_a4-p________1.0_en
February 2021 0