Apparatus and method for cycloconverter bank selection

Claim 2

In a cycloconverter system having a positive and a negative bank of gate controlled switching elements, the gating of said switching elements by firing circuits converting an AC waveform of an input supply source into a desired AC output waveform for application to a load, the combination comprising, first circuit means for developing an electrical signal proportional to the fundamental component of the cycloconverter AC output current waveform, and a bank selector circuit means responsive to said first circuit means for controlling the conduction of said positive and said negative banks relative to the zero crossover points of the fundamental AC component of the cycloconverter output waveform to minimize cycloconverter output waveform distortion.

Claim 3

In a cycloconverter system as claimed in claim 1 including second circuit means operatively connected to said bank selector circuit means to control the transfer of conduction between said banks as a function of load conditions in order to maintain a continuous cycloconverter load current.

Claim 4

In a cycloconverter system as claimed in claim 2 wherein said second circuit means responds to the magnitude and power factor of the load to vary the transfer of bank conduction between an overlap mode of bank conduction and a nonoverlap mode of bank conduction as a function of the load conditions.

Claim 5

In a cycloconverter system as claimed in claim 1 wherein said first circuit means for developing an electrical signal proportional to said fundamental component of the AC output current of the cycloconverter includes a current transformer circuit for monitoring the cycloconverter output current and developing a voltage signal proportional to the cycloconverter AC output current, and a filter means operatively connected to said current transformer circuit to derive a voltage signal corresponding to the fundamental component of the cycloconverter AC output current.

Claim 6

In a cycloconverter system as claimed in claim 4 wherein said bank selector circuit means includes, a first null detector circuit means having an input and an output, said input operatively connected to the output of said filter means, a signal inverter means having an input and an output, said input operatively connected to the output of said filter means, and a second null detector circuit means having an input and an output, said input operatively connected to the ouTput of said signal inverter means, said first and second null detector circuit means responding to alternate polarity half cycles of the fundamental AC component of the cycloconverter output waveform by generating square waves of opposite phase, the square wave output of said first null detector circuit means controlling the conduction of said positive bank, and the square wave output of said second null detector circuit means controlling the conduction of said negative bank.

Claim 7

In a cycloconverter system as claimed in claim 3 wherein said second circuit means includes a variable bias voltage circuit, said bias voltage circuit operatively connected to the inputs of said first and second null detector circuit means, said variable bias voltage circuit capable of producing zero, positive, and negative output bias voltages at the inputs of said null detector circuit means as required by the load conditions to establish a mode of bank conduction transfer sufficient to maintain a continuous cycloconverter mode current.

Claim 10

A method as claimed in claim 7 including developing an interbank circulating current under no load and relatively light load conditions to insure a continuous cycloconverter load current.

Claim 11

A method as claimed in claim 7 including, inhibiting the development of an interbank circulating current under relatively heavy load conditions.