Implement synchronized pulse generator to fire thyristors of twelve-pulse converter
A discrete version of this block is available in the Extras/Discrete Control Blocks library.
The Synchronized 12-Pulse Generator block generates two vectors of six pulses synchronized on the twelve thyristor commutation voltages. The first set of pulses, denoted PY, is sent to the six-pulse bridge connected to the wye (Y) secondary winding of the Y/Y/Delta converter transformer. The second set of pulses, denoted PD, is sent to the six-pulse bridge connected to the delta secondary winding of the converter transformer.
The synchronization voltages provided to the generator are the three phase-to-ground voltages Va, Vb, Vc measured on the primary side (Y) of the Y/Y/Delta converter transformer. The PY pulses are generated alpha degrees after the zero crossing of the phase-to-phase voltages generated from the synchronization voltages. The PD pulses can be set to lead or lag the PY pulses by 30 degrees.
The following figure shows the synchronization and internal phase-to-phase voltages plus the first three pulses of the PY and PD output vectors. In this example the PY pulses are generated 20 degrees (alpha angle) after the zero crossing of the phase-to-phase voltages and the PD pulses lag the PY pulses by 30 degrees.
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:
If set to D1 (lagging), the PD pulses lag the PY pulses by 30 degrees. If set to D11 (leading), the PD pulses lead the PY pulses by 30 degrees.
The frequency, in hertz, of the synchronization voltages. It usually corresponds to the frequency of the network.
The width of the pulses, in degrees.
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.
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.
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.
Available only with the discrete version of the Synchronized 6-Pulse Generator. This input should be connected to a constant block containing the fundamental frequency, in hertz, or to a PLL tracking the frequency of the system.
Input 5 allows you to block the operation of the generator. The pulses are disabled when the applied signal is greater than zero.
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.
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.
In the power_twelvepulsespower_twelvepulses example 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 (500 kV / 200 kV / 200 kV). The Y-connected secondary feeds the first six-pulse bridge. The Delta secondary feeds the second bridge. The transformer is assumed to be ideal (no leakage reactances, no resistance). The expected DC voltage obtained for alpha = 0 is
The two bridge rectifiers are connected in series and a 300 km DC line is connected to the rectifier.
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 (average value = 540 kV).
Compare the DC voltage generated by the Synchronized 12-Pulse Generator with the DC voltage you obtained with the Synchronized 6-Pulse Generator. Notice that the ripple in the DC voltage waveform is lower. The rectifier voltage contains the harmonics 12*k (k = 1,2,...).