Controlling the circulating current in naturally commutated static power converters
AssigneeWestinghouse Electric Corp.
InventorsEric J. Stacey, Donal E. Baker, Charles L. Doughman, Ralph D. Jessee
Life of this patent
Estimating the term…
Abstract
The firing pulses to the nonload carrying bank only of the naturally commutated thyristor power circuit of a static power converter are retarded to reduce or eliminate the interbank circulating current. In one form of the invention, half wave rectified load current signals are summed with the output waveform reference signal applied to the positive and negative bank firing pulse generators in a sense to retard the pulses in the nonload carrying bank. In another form of the invention, the inversion end stops are used to generate the retarded firing pulses in the nonload carrying bank.
Claims11
A method of synthesizing an output waveform from a multiphase AC voltage source comprising the steps of:
- generating firing pulses to sequentially fire a plurality of thyristors arranged in positive and negative banks in a naturally commutated power circuit inserted between the AC voltage source and a load;
- determining which bank of thyristors is carrying the load current;
- and
- retarding the firing pulses to the nonload current carrying bank independently of the timing of the firing pulses to the other bank to reduce the circulating current in the thyristor banks.
A static power converter for generating an output waveform from a multiphase AC source voltage, comprising:
- a naturally commutated power circuit comprising a positive and a negative bank of thyristors connected across the AC voltage source;
- control means for generating firing pulses to sequentially fire said thyristors to generate said output waveform;
- detector means for determining which bank of thyristors is carrying the load current;
- and
- circulating current suppressor means responsive to said detector means and operative to modify the operation of said control means to retard the firing pulses to the thyristor bank not carrying the load current without affecting the timing of the firing pulses to the other bank.
A cycloconverter for generating from a multiphase AC voltage source a desired output waveform to be applied to a load, said cycloconverter comprising:
- a naturally commutated power circuit having positive and negative thyristor banks connected between the phases of said AC voltage source and the load for supplying the positive and negative half cycles of output current to the load;
- means for generating a reference signal;
- first and second control means for sequentially generating firing pulses for the thyristors in the positive and negative thyristor banks respectively at intervals determined as a function of the reference signal and the source voltages;
- means for generating positive and negative half wave rectified bias signals from the output current;
- and
- means for summing the half wave rectified bias signal having a magnitude greater than zero when the output current is negative to the reference signal applied to said first control means and in a sense which retards the firing pulses generated by the first control means and means for summing the other half wave rectified bias signal with the reference signal applied to the second control means in a sense which retards the firing pulses generated by the second control means.
Dependencies are inferred from the claim text.