Implement a gate turn off (GTO) thyristor model
The gate turn off (GTO) thyristor is a semiconductor device that can be turned on and off via a gate signal. Like a conventional thyristor, the GTO thyristor can be turned on by a positive gate signal (g > 0). However, unlike the thyristor, which can be turned off only at a zero crossing of current, the GTO can be turned off at any time by the application of a gate signal equal to 0.
The GTO thyristor is simulated as a resistor Ron, an inductor Lon, and a DC voltage source Vf connected in series with a switch. The switch is controlled by a logical signal depending on the voltage Vak, current Iak, and the gate signal g.
The Vf, Ron, and Lon parameters are the forward voltage drop while in conduction, the forward conducting resistance, and the inductance of the device. The GTO block also contains a series Rs-Cs snubber circuit that can be connected in parallel with the GTO device (between terminal ports A and K).
The GTO thyristor turns on when the anode-cathode voltage is greater than Vf and a positive pulse signal is present at the gate input (g > 0). When the gate signal is set to 0, the GTO thyristor starts to block but its current does not stop instantaneously.
Because the current extinction process of a GTO thyristor contributes significantly to the turnoff losses, the turnoff characteristic is built into the model. The current decrease is approximated by two segments. When the gate signal becomes 0, the current Iak first decreases from the value Imax (value of Iak when the GTO thyristor starts to open) to Imax/10, during the fall time (Tf), and then from Imax/10 to 0 during the tail time (Tt). The GTO thyristor turns off when the current Iak becomes 0. The latching and holding currents are not considered.
Dialog Box and Parameters
infto eliminate the snubber from the model.
0to eliminate the snubber, or to
infto get a resistive snubber.
Inputs and Outputs
The input port (g) is a Simulink signal applied to the gate of the GTO thyristor. The output port (m) is a Simulink measurement vector [Iak Vak] returning the GTO thyristor current and voltage.
Assumptions and Limitations
The GTO block implements a macromodel of a real GTO thyristor. It does not take into account either the geometry of the device or the underlying physical processes of the device .
The GTO block requires a continuous application of the gate signal (g > 0) in order to be in the on state (with Iak > 0). The latching current and the holding current are not considered. The critical value of the derivative of the reapplied anode-cathode voltage is not considered.
The GTO block is modeled as a current source. It cannot be connected in series with an inductor, a current source, or an open circuit, unless its snubber circuit is in use. In order to avoid an algebraic loop, you cannot set the inductance Lon to 0.
Each GTO block adds an extra state to the electrical circuit model. See the Advanced Topics chapter for more details on this topic.
You must use a stiff integrator algorithm to simulate circuits containing GTO blocks.
ode15s with default parameters usually gives the best simulation speed.
psbbuckconv.mdl demo illustrates the use of the GTO block in a buck converter topology. The basic polarized snubber circuit is connected across the GTO block. The snubber circuit consists of a capacitor Cs, a resistor Rs, and a diode Ds. The parasitic inductance Ls of the snubber circuit is also taken into consideration.
The parameters of the GTO block are those found in the dialog box section, except for the internal snubber, which is not used (
Rs = Inf Cs = 0). The switching frequency is 1000 Hz and the pulse width is 216 degrees (duty cycle: 60%).
Run the simulation. Observe the GTO block voltage and current as well as the load voltage and current.
 Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics: Converters, Applications, and Design, John Wiley & Sons, Inc., New York, 1995.
IGBT, MOSFET, Thyristor
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