# Bridge Cycloconverter Voltage Controller (Three-Phase)

RMS Voltage PI control for three-phase bridge cycloconverters

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• Simscape / Electrical / Control / Converter Control

## Description

The Bridge Cycloconverter Voltage Controller (Three-Phase) block implements a PI-based root-mean-square (RMS) voltage controller for three-phase bridge cycloconverters.

To convert a three-phase signal directly from a higher frequency to a lower frequency, use this block with a three-phase bridge cycloconverter. Refer to Three-Phase Bridge Cycloconverter for an example of such a conversion.

### Operating Principle

The controller regulates the cycloconverter line-to-neutral RMS voltage to a given value and a given electrical frequency. The structure of the cycloconverter controller is illustrated in this diagram.

In the diagram:

• The controller integrates the desired output frequency fref to produce the reference electrical angle θe_ref.

• The Signal Conditioning block filters the cycloconverter line-to-neutral voltage vcyc and current icyc to produce the per-unit RMS voltage vrms_cyc and smoothed current signal icyc_lpf.

• The PI Controller generates a reference phase voltage in the q-axis from the error between the desired output RMS voltage Vref and vrms_cyc.

• The Inverse Park Transform block converts the reference phase voltage in dq0-coordinates to a phase voltage vabc_ref in abc-coordinates.

• The Sinusoidal Power Measurement (PLL, Three-Phase) block estimates the phase angle θ of the input voltage signal vabc.

The Modulator and Bank Selector blocks create the 36 pulses to drive the cycloconverter using the reference phase voltage vabc_ref, estimated phase angle θ, and filtered cycloconverter current icyc_lpf. To generate the firing angles, the controller uses the cosine wave crossing method.

This diagram shows the signal conditioning logic.

In the diagram:

• The Park Transform blocks convert the measured cycloconverter voltage vcyc and current icyc into d- and q-axis components (vd,vq,id,iq) using the reference electrical angle θe_ref.

• The Low-Pass Filter (LPF) blocks remove the high-frequency noise from each of the d- and q-axis voltage and currents to produce the filtered components (vd_lpf, vq_lpf, id_lpf, iq_lpf).

• The block calculates the cycloconverter per-unit RMS voltage vrms_cyc by taking the squared sum of the dq components, dividing by $\sqrt{2}$, and finally converting from SI to per-unit representation.

• The Inverse Park Transform converts the dq filtered current back to the abc-axis and outputs it as icyc_lpf.

The cycloconverter reference line-to-neutral rms voltage output is given in per-unit representation.

### Visualization

The block outputs a bus containing six signals for visualization:

• The estimated phase angle θ of the input voltage signal vabc

• The desired RMS voltage Vref of the output signal

• The reference phase voltages vabc_ref of the desired output signal

• The filtered line-to-neutral cycloconverter RMS voltage vrms_cyc

• The filtered cycloconverter phase currents icyc_lpf

• The filtered cycloconverter phase voltages vcyc_lpf

## Ports

### Input

expand all

Reference line-to-neutral RMS voltage, expressed in per-unit representation.

Data Types: `single` | `double`

Reference electrical frequency, in Hz.

Data Types: `single` | `double`

Measured phase voltages of the source, in V.

Data Types: `single` | `double`

Measured cycloconverter phase voltages, in V.

Data Types: `single` | `double`

Measured cycloconverter phase currents, in A.

Data Types: `single` | `double`

### Output

expand all

Thyristor pulse vector to control a three-phase bridge cycloconverter.

Data Types: `single` | `double`

Bus containing internal signals for visualization. For a full list of signals, refer to the Visualization section.

Data Types: `single` | `double`

## Parameters

expand all

Rated RMS voltage for per-unit conversion calculations, in V.

Loop filter proportional gain for the phase-locked loop (PLL) estimating the phase of the input signal. This value determines the aggressiveness of the PLL in tracking and locking to the phase angle. Increase this value to improve reaction time of the tracking to step changes in the phase angle.

Loop filter integral gain for the phase-locked loop (PLL) estimating the phase of the input signal. Increase this value to increase the rate at which steady-state error is eliminated in the phase angle. This value also determines the aggressiveness of the PLL in tracking and locking to the phase.

Time constant of the low-pass filters in the Signal Conditioning block of the controller. These filters reduce undesired high-frequency noise in the cycloconverter phase voltage and current measurements.

Proportional gain for the PI-controller that generates the reference phase voltage for the cycloconverter. Increase this value to increase the aggressiveness of the controller.

Integral gain of the PI-controller that generates the reference phase voltage for the cycloconverter. Increase this value to increase the rate at which steady-state error is eliminated in the phase voltage signal.

Anti-windup gain of the PI-controller that generates the reference phase voltage for the cycloconverter.

Angular width of pulses sent to the cycloconverter.

Current threshold for switching between positive and negative converters.

Strategy used for the ordering of generated pulses.

Sample time for the block (-1 for inherited). If you use this block inside a triggered subsystem, set the sample time to `-1`. If you use this block in a continuous variable-step model, set the sample time explicitly.

## References

[1] Chen, H., M. H. Johnson, and D. C. Aliprantis. "Low-frequency AC transmission for offshore wind power." IEEE Transactions on Power Delivery. Vol. 28, Number 4, 2013, pp. 2236–2244.

## Extended Capabilities

### C/C++ Code GenerationGenerate C and C++ code using Simulink® Coder™.

Introduced in R2017b