Documentation

# Thyristor Converter

Implements single or three-phase thyristor converter for DC motor drives

## Library

Simscape / Electrical / Specialized Power Systems / Electric Drives / Fundamental Drive Blocks

## Description

The Thyristor Converter block represents a standard two-leg (single-phase) or three-leg (three-phase) thyristor bridge model (detailed mode). It has two operating modes to represent a detailed or average-value converter.

### Detailed mode

In detailed mode, this block is an instance of the Universal Bridge model configured as a single- (two arms) or three-phase (three arms) thyristor bridge converter. For more details, see Universal Bridge. For four-quadrant operation, two thyristor bridge converters can be connected in antiparallel through circulating current inductors.

### Average mode

In average mode, the Thyristor Converter block implements an average-value thyristor bridge model for two- or four-quadrant DC drives. The average-value model can be one of these types:

• Single phase, four-quadrant DC drive

• Three phases, two-quadrant DC drive

The converter is composed of one controlled current source on the AC side and one controlled voltage source on the DC side, as shown in the figure.

The AC current source allows the representation of the fundamental single-phase current (Ia) given by

${I}_{\alpha }=\sqrt{2}{I}_{d}\mathrm{sin}\left(2\pi ft+\alpha +{\alpha }_{0}\right),$

with α being the firing angle value, α0 the phase angle of the AC side, f the AC frequency, and Id the rectified output current value. The DC voltage source represents the average voltage value of the rectified voltage waveform given by

${V}_{d}=\frac{2\sqrt{2}}{\pi }{V}_{rms}\mathrm{cos}\alpha -4fL{I}_{d},$

with Vrms being the input RMS voltage value and L being the source inductance value.

This model is similar to the single-phase, two-quadrant DC drive model, except that another controlled current source is required on the DC side, as shown in the figure.

The additional controlled current source represents the circulation current due to the instantaneous voltage difference between both converter outputs of the dual converter. The circulation current is given by

${I}_{circ}=\frac{\sqrt{2}}{{\pi }^{2}f{L}_{circ,tot}}{V}_{rms}\left(\mathrm{sin}\alpha -\alpha \mathrm{cos}\alpha \right),$

with Lcirc,tot being the total circulation inductance of the circulation current loop.

This model is composed of two controlled current sources on the AC side and one controlled voltage source on the DC side, as shown in the figure.

The AC current sources allow the representation of the fundamental three-phase current behaviors. The average voltage value of the rectified voltage waveform is given by

${V}_{d}=\frac{3\sqrt{6}}{\pi }{V}_{rms}\mathrm{cos}\alpha -6fL{I}_{d}.$

In this model, an additional current source is required on the DC side to represent the circulation current in the dual-converter, as shown in the figure.

## Parameters

Model detail level

Specify the model detail level to use:

• Detailed (default)

• Average

Supply

Specify the number of phases to use:

• Single-phase (default)

• Three-phase

Specify the number of quadrants to use. This parameter is available only when the Model detail level parameter is set to Average. The default value is 2.

Sample Time

The sample time of the thyristor converter, in seconds. The default value is 2e-6.

Ron (Ohms)

Internal resistance of the selected device, in ohms. The default value is 1e-3.

Snubber resistance Rs (Ohms)

The snubber resistance, in ohms. Set the Snubber resistance Rs parameter to inf to eliminate the snubbers from the model. The default value is 10e3.

Snubber capacitance Cs (F)

The snubber capacitance, in farads. Set the Snubber capacitance Cs parameter to 0 to eliminate the snubbers, or to inf to get a resistive snubber. The default value is 900e-9.

Forward voltage Vf (V)

The forward voltage of the thyristors, in volts. The default value is 1.3.

Line RMS voltage (V)

RMS voltage, in volts, of the supply connected to the A+ or A– (or A, B, C for a three-phase supply) terminals of the drive. This parameter is available only when the Model detail level parameter is set to Average. The default value is 460.

Line frequency (Hz)

Frequency, in hertz, of the supply connected to the A+ or A– (or A, B, C for a three-phase supply) terminals of the drive. This parameter is available only when the Model detail level parameter is set to Average. The default value is 60.

Phase (deg)

Phase angle, in degrees, of the supply connected to the A+ or A– (or A, B, C for a three-phase supply) terminals of the drive. This parameter is available only when the Model detail level parameter is set to Average. The default value is 0.

Source inductance (H)

Source inductance, in henry, of the supply connected to the A+ or A– (or A, B, C for a three-phase supply) terminals of the drive. This parameter is available only when the Model detail level parameter is set to Average and the Number of quadrants parameter is set to 2. The default value is 0.1e-3.

Circulation current inductance (H):

The inductance of the circulating current inductors, in henry. This parameter is visible only when the Model detail level parameter is set to Average and the Number of quadrants parameter is set to 4. The default value is 0.

Nominal power (W)

Motor nominal power, in watts. This parameter is available only when the Model detail level parameter is set to Average. The default value is 5*746.

Fraction of nominal power dissipated in input resistances

Fraction of nominal power to be dissipated in input resistances. These input resistors are needed due to the converter current sources in series with an inductive motor. This parameter is available only when the Model detail level parameter is set to Average. The default value is 0.025.

## Inputs and Outputs

g

The gate input for the controlled switch devices. Pulses are sent to upper and lower switches of inverter legs A+ or A– (or A, B, and C for a three-phase converter). This input is visible only when the Model detail level parameter is set to Detailed.

A+

The single-phase terminals on the AC side. The applied voltage must be adequate for the motor size. This input is visible only when the Supply type parameter is set to Single-phase.

A-

The single-phase terminals on the AC side. The applied voltage must be adequate for the motor size. This input is visible only when the Supply type parameter is set to Single-phase.

A, B, C

The three-phase terminals on the AC side. The applied voltage must be adequate for the motor size. This input is visible only when the Supply type parameter is set to Three-phase.

Alpha

Converter firing angle. This input is visible only when the Model detail level parameter is set to Average.

+

The positive terminal on the DC side.

-

The negative terminal on the DC side.

## Examples

The Thyristor Converter block is used in the DC1, DC2, DC3, and DC4 blocks of the Electric Drives library.

## References

[1] Bose, B. K. Modern Power Electronics and AC Drives, NJ: Prentice-Hall, 2002.