Documentation

Bridge Firing Unit (DC)

Generate gate signals for single- or three-phase thyristor bridge

Library

Electric Drives/Fundamental Drives

Description

The Bridge Firing Unit (DC) block generates gate signals for a standard two-leg or three-leg thyristor bridge. It features two operating modes: detailed and average. In detailed mode, the block outputs synchronized pulses for each thyristor. In average mode, it outputs the firing angle for the thyristor bridge.

Detailed Mode

In detailed mode, the Bridge Firing Unit (DC) block converts the firing angle provided by the current/voltage controller to pulses to control the thyristor gates. The block contains a low-pass filter on voltage measurement to remove voltage harmonics.

The output of the block is a vector of four pulses (or six pulses for a three-phase supply) individually synchronized with the supply voltage. The pulses are generated alpha degrees (firing angle) after the zero crossings of the thyristor commutation voltages.

The figures show the synchronization of the six pulses for a firing angle of 30 degrees and pulse width of 10 degrees. The pulses are generated at exactly 30 degrees after the zero crossings of the three line-to-line synchronization voltages.

Two pulses (double-pulsing) are sent to each thyristor: a first pulse when the alpha angle is reached, and a second pulse 60 degrees later, when the next thyristor is fired. For the four-quadrant DC drives, the block outputs an additional set of pulses for the antiparallel thyristor converter.

Average Mode

The average model outputs the firing angle value needed by the thyristor converter. For four-quadrant DC drives, the block also outputs a second firing angle for the antiparallel converter.

Parameters

Model detail level

Specify the model detail level to use:

  • Detailed (default)

  • Average

Supply phases

Specify the number of phases—single-phase or three-phase—of the supply device connected at the input of the unit. Choose between 1 and 3. The default value is 1.

Number of quadrants

Specify the operating mode of the unit—2-quadrant or 4-quadrant. Choose between 2 and 4. The default value is 2.

Frequency of synchronization voltages (Hz)

The frequency of the synchronization voltages, in hertz. It usually corresponds to the frequency of the supply. The default value is 60.

Pulse width (deg.)

The width of the pulse, in degrees. The default value is 10.

Sample time (s)

The sample time of the bridge fire unit, in seconds. The default value is 2e-6.

Inputs and Outputs

Alpha

Converter firing angle.

Alpha_1

Converter firing angle. This input is visible only when the Number of quadrants parameter is set to 4.

Alpha_2

Converter firing angle. This input is visible only when the Number of quadrants parameter is set to 4.

A, B, C

Connect these inputs to the three-phase terminals of the supply. This input is visible only when the Supply phases parameter is set to 3.

A+, A-

Connect these inputs to the single-phase terminals of the supply. This input is visible only when the Supply phases parameter is set to 1.

Pulse

The gate pulses for the thyristor bridge. This output is visible only when the Model detail level parameter is set to Detailed.

Pulse_1

The gate pulse for the thyristor bridge. This output is visible only when the Model detail level parameter is set to Detailed and the Number of quadrants parameter is set to 4.

Pulse_2

The gate pulse for the thyristor bridge. This output is visible only when the Model detail level parameter is set to Detailed and the Number of quadrants parameter is set to 4.

Examples

The Bridge Firing Unit (DC) block is used in the DC1, DC2, DC3, and DC4 blocks from the Electric Drives library.

References

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

Introduced in R2015b

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