Implement thyristor model
Fundamental Blocks/Power Electronics
The thyristor is a semiconductor device that can be turned on via a gate signal. The thyristor model is simulated as a resistor Ron, an inductor Lon, and a DC voltage source representing the forward voltage Vf, connected in series with a switch. The switch is controlled by a logical signal depending on the voltage Vak, the current Iak, and the gate signal g.
The Thyristor block also contains a series Rs-Cs snubber circuit that can be connected in parallel with the thyristor device.
The static VI characteristic of this model is shown below.
The thyristor device turns on when the anode-cathode Vak voltage is greater than Vf and a positive pulse signal is applied at the gate input (g > 0). The pulse height must be greater than 0 and last long enough to allow the thyristor anode current to become larger than the latching current Il.
The thyristor device turns off when the current flowing in the device becomes 0 (Iak = 0) and a negative voltage appears across the anode and cathode for at least a period of time equal to the turnoff time Tq. If the voltage across the device becomes positive within a period of time less than Tq, the device turns on automatically even if the gate signal is low (g = 0) and the anode current is less than the latching current. Furthermore, if during turn-on, the device current amplitude stays below the latching current level specified in the dialog box, the device turns off after the gate signal level becomes low (g = 0).
The turnoff time Tq represents the carrier recovery time: it is the time interval between the instant the anode current has decreased to 0 and the instant when the thyristor is capable of withstanding positive voltage Vak without turning on again.
To optimize simulation speed, two models of thyristors are available:
the thyristor model and the detailed thyristor model. For the thyristor
model, the latching current Il and recovery time Tq are
assumed to be
The thyristor internal resistance Ron, in ohms (Ω). Default
0.001. The Resistance Ron parameter
cannot be set to
0 when the Inductance
Lon parameter is set to
The thyristor internal inductance Lon, in henries (H). Default
0 for Thyristor blocks and
1e–3 for Detailed
Thyristor blocks. The Inductance Lon parameter
is normally set to
0 except when the Resistance
Ron parameter is set to
The forward voltage of the thyristor, in volts (V). Default
When the Inductance Lon parameter is greater
0, you can specify an initial current flowing
in the thyristor. It is usually set to
0 to start
the simulation with the thyristor blocked. Default is
You can specify an Initial current Ic value corresponding to a particular state of the circuit. In such a case all states of the linear circuit must be set accordingly. Initializing all states of a power electronic converter is a complex task. Therefore, this option is useful only with simple circuits.
The snubber resistance, in ohms (Ω). Default is
Set the Snubber resistance Rs parameter to
eliminate the snubber from the model.
The snubber capacitance in farads (F). Default is
Set the Snubber capacitance Cs parameter to
eliminate the snubber, or to
inf to get a resistive
If selected, add a Simulink® output to the block returning the thyristor current and voltage. Default is selected.
The latching current of the detailed thyristor model, in amperes
(A). Default is
0.1. This parameter is specific
to Detailed Thyristor blocks.
The turnoff time Tq of the detailed thyristor model, in amperes
(A). Default is
100e–6. This parameter is
specific to Detailed Thyristor blocks.
Simulink signal to control the gate of the Thyristor.
The Simulink output of the block is a vector containing two signals. You can demultiplex these signals by using the Bus Selector block provided in the Simulink library.
The Thyristor block implements a macro model of the real thyristor. It does not take into account either the geometry of the device or complex physical processes that model the behavior of the device [1, 2]. The forward breakover voltage and the critical value of the derivative of the reapplied anode-cathode voltage are not considered by the model.
Depending on the value of the inductance Lon, the Thyristor block is modeled either as a current source (Lon > 0) or as a variable topology circuit (Lon = 0). The Thyristor block cannot be connected in series with an inductor, a current source, or an open circuit, unless its snubber circuit is in use.
The inductance Lon is forced to 0 if you choose to discretize your circuit.
a single-pulse thyristor rectifier is used to feed an RL load. The
gate pulses are obtained from a pulse generator synchronized on the
source voltage. The following parameters are used:
The firing angle is varied by a pulse generator synchronized on the voltage source. Run the simulation and observe the load current and load voltage, as well as the thyristor current and voltage.
 Rajagopalan, V., Computer-Aided Analysis of Power Electronic Systems, Marcel Dekker, Inc., New York, 1987.
 Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics: Converters, Applications, and Design, John Wiley & Sons, Inc., New York, 1995.