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GTO

Implement gate turn off (GTO) thyristor model

Library

Power Electronics

Description

The gate turnoff (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, the 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

Resistance Ron

The internal resistance Ron, in ohms (Ω). The Resistance Ron parameter cannot be set to 0 when the Inductance Lon parameter is set to 0.

Inductance Lon

The internal inductance Lon, in henries (H). The Inductance Lon parameter is normally set to 0 except when the Resistance Ron parameter is set to 0.

Forward voltage Vf

The forward voltage of the GTO thyristor device, in volts (V).

Current 10% fall time

The current fall time Tf, in seconds (s). This parameter is not modeled when the Enable use of ideal switching devices parameter of the Powergui block is selected.

Current tail time

The current tail time Tt, in seconds (s). This parameter is not modeled when the Enable use of ideal switching devices parameter of the Powergui block is selected.

Initial current Ic

You can specify an initial current flowing in the GTO thyristor. It is usually set to 0 in order to start the simulation with the device blocked.

If the Initial Current IC parameter is set to a value greater than 0, the steady-state calculation considers the initial status of the GTO as closed. Initializing all states of a power electronic converter is a complex task. Therefore, this option is useful only with simple circuits.

Snubber resistance Rs

The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs parameter to inf to eliminate the snubber from the model.

Snubber capacitance Cs

The snubber capacitance, in farads (F). Set the Snubber capacitance Cs parameter to 0 to eliminate the snubber, or to inf to get a resistive snubber.

Show measurement port

If selected, add a Simulink® output to the block returning the GTO current and voltage.

Inputs and Outputs

g

Simulink signal to control the gate of the GTO.

m

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.

Signal

Definition

Units

1

GTO current

A

2

GTO voltage

V

Assumptions and Limitations

The GTO block implements a macro model 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 [1].

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.

Depending on the value of the inductance Lon, the GTO is modeled either as a current source (Lon > 0) or as a variable topology circuit (Lon = 0). The GTO block cannot be connected in series with an inductor, a current source, or an open circuit, unless its snubber circuit is in use.

Use the Powergui block to specify either continuous simulation or discretization of your electrical circuit containing GTO blocks. When using a continuous model, the ode23tb solver with a relative tolerance of 1e-4 is recommended for best accuracy and simulation speed.

The inductance Lon is forced to 0 if you choose to discretize your circuit.

Example

The power_buckconvpower_buckconv example 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 voltage and current as well as the load voltage and current.

References

[1] Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics: Converters, Applications, and Design, John Wiley & Sons, Inc., New York, 1995.

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