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RMS Voltage PI control for three-phase bridge cycloconverters

**Library:**Simscape / Electrical / Control / Converter Control

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.

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

*f*to produce the reference electrical angle_{ref}*θ*._{e_ref}The Signal Conditioning block filters the cycloconverter line-to-neutral voltage

*v*and current_{cyc}*i*to produce the per-unit RMS voltage_{cyc}*v*and smoothed current signal_{rms_cyc}*i*._{cyc_lpf}The PI Controller generates a reference phase voltage in the

*q*-axis from the error between the desired output RMS voltage*V*and_{ref}*v*._{rms_cyc}The Inverse Park Transform block converts the reference phase voltage in

*dq0*-coordinates to a phase voltage*v*in_{abc_ref}*abc*-coordinates.The Sinusoidal Power Measurement (PLL, Three-Phase) block estimates the phase angle

*θ*of the input voltage signal*v*._{abc}The Modulator and Bank Selector blocks create the 36 pulses to drive the cycloconverter using the reference phase voltage

*v*, estimated phase angle_{abc_ref}*θ*, and filtered cycloconverter current*i*. To generate the firing angles, the controller uses the cosine wave crossing method._{cyc_lpf}

This diagram shows the signal conditioning logic.

In the diagram:

The Park Transform blocks convert the measured cycloconverter voltage

*v*and current_{cyc}*i*into_{cyc}*d*- and*q*-axis components (*v*,_{d}*v*,_{q}*i*,_{d}*i*) using the reference electrical angle_{q}*θ*._{e_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 (*v*,_{d_lpf}*v*,_{q_lpf}*i*,_{d_lpf}*i*)._{q_lpf}The block calculates the cycloconverter per-unit RMS voltage

*v*by taking the squared sum of the_{rms_cyc}*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*i*._{cyc_lpf}

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

The block outputs a bus containing six signals for visualization:

The estimated phase angle

*θ*of the input voltage signal*v*_{abc}The desired RMS voltage

*V*of the output signal_{ref}The reference phase voltages

*v*of the desired output signal_{abc_ref}The filtered line-to-neutral cycloconverter RMS voltage

*v*_{rms_cyc}The filtered cycloconverter phase currents

*i*_{cyc_lpf}The filtered cycloconverter phase voltages

*v*_{cyc_lpf}

[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.