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Synchronized 12-Pulse Generator

Implement a synchronized pulse generator to fire the thyristors of a twelve-pulse converter

Library

Extras / Control Blocks

Description

The Synchronized 12-Pulse Generator block generates two vectors of six pulses synchronized on a three-phase commutation voltage. The first set of pulses, denoted PY, is generated alpha degrees after the zero crossing of the phase-to-phase synchronization voltages. The second set of pulses, denoted PD, lags the PY pulses by 30 degrees.

The figures below display the synchronization for the three first pulses of the two output vectors.

The phase-to-ground A,B, and C voltages are provided to the generator, and the phase-to-phase synchronization voltages are generated internally.

The Synchronized 12-Pulse Generator block can be used to control two six-pulse thyristor converters connected in series on the secondary terminals of a Y-Y-Delta transformer.

The PY pulses are used to fire the six thyristors of the converter connected to the Y secondary terminal and the PD pulses are used to fire the thyristors of the converter connected at the Delta terminal of the transformer.

The ordering of the pulses in the two outputs of the block corresponds to the natural order of commutation of a three-phase thyristor bridge. When you connect the Synchronized 12-Pulse Generator block outputs to the pulse inputs of the Universal Bridge blocks (with the thyristor device), the pulses are sent to the thyristors in the following way:

Dialog Box and Parameters

Frequency of synchronization voltages (Hz)
The frequency, in hertz, of the synchronization voltages. It usually corresponds to the frequency of the network.
Pulse width (degrees)
The width of the pulses, in degrees.
Double pulsing
If selected, the generator sends to each thyristor a first pulse when the alpha angle is reached, and then a second pulse 60 degrees later when the next thyristor in the sequence is fired. The double pulsing is applied separately on the two vectors of pulses.

Inputs and Outputs

alpha_deg

Input 1 is the alpha firing signal, in degrees. This input can be connected to a Constant block, or it can be connected to a controller system to control the pulses of the generator.

A, B, C

Inputs 2, 3, and 4 are the phase-to-ground synchronization voltages Va, Vb, and Vc. The synchronization voltages should be measured at the primary side of the converter transformer.

block

Input 5 allows you to block the operation of the generator. The pulses are disabled when the applied signal is greater than zero.

PY

Output 1 contains the six-pulse signals to be sent to the six-pulse thyristor converter connected to the Y secondary winding of the converter transformer.

PD

Output 2 contains the six-pulse signals to be sent to the six-pulse thyristor converter connected to the Delta (D) secondary winding of the converter transformer.

Example

In the psbtwelvepulses.mdl demo a Synchronized 12-Pulse Generator block is used to fire the thyristors of a twelve-pulse thyristor bridge built with two six-pulse bridges. The bridge is fed by a three-winding three-phase transformer. The Y-connected secondary fed the first six-pulse bridge. The Delta secondary fed the second bridge.

The two bridge rectifiers are connected in series and a 300 Km line is connected to the DC side of the rectifiers.

A first simulation is performed with an alpha angle of 0 degrees. Open the Constant block connected at input 1 of the Synchronized 12-Pulse Generator block and set its value to 0. Start the simulation. The voltages of the thyristors of the D thyristor Converter block are displayed in the next figure. The resulting DC voltage at the input terminal of the transmission line is also displayed.

Compare the DC voltage generated by the Synchronized 12-Pulse Generator and its associated rectifier bridges to the results you obtained with the Synchronized 6-Pulse Generator. Notice that the ripple in the DC waveform is softer when 12 thyristors are used to rectify the three-phase AC voltage.


  Synchronized 6-Pulse Generator Synchronous Machine