Bridge Firing Unit (AC)

Implement six pulse firing unit with notch filters for three-phase thyristor bridge


Electric Drives/Fundamental Drives


The Bridge Firing Unit (AC) block converts the firing angle, typically provided by a current/voltage controller, to pulses applied to the thyristor gates. The block uses notch filters on voltage measurement to remove voltage harmonics.

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

The figures show the synchronization of the six pulses for an alpha 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.


Network frequency (Hz)

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

Sample time

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

Inputs and Outputs


Converter firing angle.


Control signal to disable or enable the output pulses.

A, B, C

Three-phase terminals of the supply.


Gate pulses for the thyristor bridge.


The Bridge Firing Unit (AC) block is used in the AC1 block of the Electric Drives library.


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

Introduced in R2015b

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