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Pulse Generator (Thyristor)

Generate pulses for twelve-pulse and six-pulse thyristor converters

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Control and Measurements/Pulse & Signal Generators

Description

The Pulse Generator (Thyristor) block generates two pulse trains. These control a twelve-pulse thyristor converter made of two three-phase full-wave thyristor bridges (also called Graetz bridges). In steady-state condition, each pulse train consists of six equidistant square pulses with 60 degrees shift between them.

The first set of pulses (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 (PD) is sent to the six-pulse bridge connected to the delta secondary winding of the converter transformer. The PD pulses can be set to lead or lag the PY pulses by 30 electrical degrees, depending on the configuration of the delta connection of the converter transformer.

The following figure shows an example of a Pulse Generator (Thyristor) block connected to a twelve-pulse thyristor converter.

The Pulse Generator (Thyristor) block can be programmed to control a six-pulse thyristor converter made of one three-phase full-wave thyristor bridge. In this configuration, the PD pulse train is not generated and the block outputs only the PY pulse train. The pulse train, renamed P, is suitable for a Graetz bridge connected to a converter transformer, with no phase shift between primary and secondary windings.

The pulse ordering in the pulse trains corresponds to the natural order of commutation of a three-phase thyristor bridge, as shown in the following figure.

The table below gives the commutating voltages for the thyristors according to the transformer connexion. The transformer connexion reflects the phase shift between the AC source and the thyristors.

Thyristor to be ignited123456
Thyristor to be extinguished561234
Commutating voltage for a Y-Y connexionVacVbcVbaVcaVcbVab
for a Y-D1 (lagging)-VcVb-VaVc-VbVa
for a Y-D11 (leading)Va-VcVb-VaVc-Vb

The Pulse Generator (Thyristor) block is controlled by the alpha angle reference signal and by the synchronisation signal wt. The wt signal is an angle varying between 0 and 2*pi radians, synchronized on zero crossings of the fundamental (positive-sequence) of phase A of the primary voltage of the converter transformer. The wt signal is normally obtained from a phase locked loop (PLL) system.

The Pulse Generator (Thyristor) block generates internal wt ramps to control the pulses. The alpha delay angle is expressed in electrical degrees by which the pulse is delayed relative to angle zero of its commutating voltage. The figure shows how the PY pulse train is generated.

The Pulse Generator (Thyristor) block can be configured to work in double-pulsing mode. In this mode two pulses are sent to each thyristor: a first pulse when the alpha angle is reached, and then a second pulse 60 degrees later, when the next thyristor is fired. This figure shows the double pulses in a PY pulse train.

Dialog Box and Parameters

Generator type

Select the type of thyristor converter to control. When set to 6-pulse, the PD pulse train output is not generated, and the PY output is renamed to P.

Delta winding connection

Specify the type of delta secondary winding connection of the converter transformer. When set to D1(lagging), the PD pulses lag the PY pulses by 30 degrees. When set to D11(leading), the PD pulses lead the PY pulses by 30 degrees.

Pulse width (deg)

Specify the width of the pulses, in degrees.

Double pulsing

When this check box is selected, the Pulse Generator (Thyristor) block implements the double-pulsing technique.

Sample time

Specify the sample time of the block, in seconds. Set to 0 to implement a continuous block.

Inputs and Outputs

alpha

The alpha delay angle 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.

wt

Angle, in radians, varying between 0 and 2*pi, synchronized on zero crossings of the fundamental (positive-sequence) of phase A of the primary voltage of the converter transformer. The wt signal is normally obtained from a phase locked loop (PLL) system.

Block

When set to true (Boolean 1), blocks the operation of the generator. The pulses are disabled and block the operation of the generator.

PY, P

Outputs the six-pulse signals to be sent to the six-pulse thyristor converter connected to the Y secondary winding of the converter transformer. The output is named PY when the Generator type parameter is set to 12-pulse, and named PY when the Generator type parameter is set to 6-pulse.

PD

Outputs the six-pulse signals to be sent to the six-pulse thyristor converter connected to the Delta (D) secondary winding of the converter transformer. This output does not exist when the Generator type parameter is set to 6-pulse.

Characteristics

Sample TimeSpecified in the Sample Time parameter
Scalar ExpansionNo
DimensionalizedNo
Zero-Crossing DetectionYes

Example

The power_PulseGeneratorpower_PulseGenerator example shows various uses of the pulse generator.

The model sample time is parameterized with the variable Ts (default value Ts = 50e-6). To simulate continuous mode, specify Ts = 0 in the MATLAB® Command Window.

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