Power Electronic Switch Component
For PSCAD Version 5.0
January 30, 2020
Initial
Power Electronic Switch Component
CONTENTS
1. OVERVIEW ....................................................................................................................... 1
1.1. DIODE ....................................................................................................................................... 1
1.2. THYRISTOR................................................................................................................................. 2
1.3. GTO/IGBT/TRANSISTOR ............................................................................................................ 3
2. PSCAD/EMTDC EXAMPLE DESCRIPTION ............................................................................ 4
2.1. EXAMPLE 1 ................................................................................................................................ 4
2.2. EXAMPLE 2 ................................................................................................................................ 6
2.3. EXAMPLE 3 ................................................................................................................................ 7
2.4. EXAMPLE 4 ................................................................................................................................ 8
2.5. EXAMPLE 5 ................................................................................................................................ 9
2.6. EXAMPLE 6 .............................................................................................................................. 10
3. REFERENCE .................................................................................................................... 11
Power Electronic Switch Component
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1. OVERVIEW
1.1. Diode
The diode ON and OFF states are controlled by the voltage and current conditions across the device
itself. The diode assumes a fixed small ON and a large OFF resistance. Conduction commences when the
device is forward biased and the forward voltage exceeds the Forward Voltage Drop input parameter.
The diode turns OFF at current zero and remains OFF as long as it is reverse biased.
The V-I characteristic for the diode model is shown in Figure 1.
Figure 1: Diode V-I characteristic Curve
Both ON and OFF events use the Interpolation Algorithm to calculate the instant of switching. Thus,
turn ON occurs exactly when forward voltage reaches the Forward Voltage Drop and turn OFF occurs
exactly when current reaches zero.
NOTE: Reverse recovery time (i.e. the time for which a finite reverse current flows in the device,
following a turn OFF) of the diode is assumed zero. If the ON resistance is zero or smaller than the
switching threshold value, the closed state will be modeled as an ideal short circuit.
Power Electronic Switch Component
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1.2. Thyristor
The thyristor is usually latched ON by a firing pulse supplied to the gate terminal, but is turned OFF
according to voltage and current conditions across the device itself. An external control signal is
required to generate the gate firing pulses.
The thyristor assumes a fixed small ON and a large OFF resistance. The thyristor state will change under
the following conditions:
1. The forward bias voltage across the device is greater than or equal to the Forward Voltage Drop
parameter input AND the gate signal goes from 0 to 1 (i.e. firing pulse is issued).
2. The forward bias voltage across the device is greater than or equal to the Forward Voltage Drop
parameter input AND the gate signal is pre-set to 1 (i.e. firing angle = 0°). A turn ON under this
situation is NOT interpolated (for an interpolated turn ON with firing angle = 0°, use the Diode).
3. The forward bias voltage across the device is greater than or equal to Forward Break-Over
Voltage parameter input.
4. Turning OFF occurs with the device current reaching zero.
The V-I characteristic for the thyristor model is shown in Figure 2.
Figure 2: Thyristor V-I characteristic Curve
The Interpolation Algorithm is automatically invoked during all naturally commutated turn ON and turn
OFF events (including Forward Break-Over), to calculate the exact instant of switching. Please note
however, that the user is provided a choice to interpolate the incoming gate signal.
Power Electronic Switch Component
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The extinction time is also represented. The thyristor therefore, will re-fire following a turn OFF if the
Minimum Extinction Time parameter input has not elapsed before the forward voltage rises above the
Forward Voltage Drop parameter input. This will occur even in the absence of a turn on signal.
NOTE: Reverse recovery time (i.e. the time for which a finite reverse current flows in the device,
following a turn OFF) of the Thyristor is assumed zero. If the ON resistance is zero or smaller than the
Switching Threshold value, the closed state will be modeled as an ideal short circuit.
1.3. GTO/IGBT/Transistor
The GTO, IGBT, and Transistor models are essentially the same. The GTO/IGBT/Transistor is usually
turned ON and OFF by firing signals supplied to the gate terminal. An external control signal is required
to generate the gate firing pulses.
The characteristics of the GTO/IGBT/Transistor are very similar to that of the Thyristor except that a
GTO/IGBT/Transistor can be forced to turn OFF with a gate pulse of 0, while the device is forward biased
and conducting current.
The V-I characteristic for the GTO/IGBT/Transistor model is shown in Figure 3.
Figure 3: GTO, IGBT, and Transistor V-I characteristic Curve
The Interpolation Algorithm is automatically invoked during all naturally commutated turn ON and turn
OFF events (including Forward Break-Over), to calculate the exact instant of switching. Please note
however, that the user is provided a choice to interpolate the incoming gate signal.
NOTE: Reverse recovery time (i.e. the time for which a finite reverse current flows in the device,
following a turn OFF) of the diode is assumed zero. If the ON resistance is zero or smaller than the
Switching Threshold value, the closed state will be modeled as an ideal short circuit.
