Method and circuit for controlling a hybrid contactor
AssigneeGeneral Electric Company
InventorsWilliam P. Kornrumpf, Joseph L. Ciccone
Life of this patent
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Abstract
A method and circuit for minimizing DC current offset generated by the voltage-integrating property of an inductive load. First, second and third hybrid contactors connect first, second, and third output lines of an AC power source to first, second, and third input lines of an inductive load. Each hybrid contactor includes a pair of relay contacts in parallel with a semiconductor switching unit having two antiparallel-connected silicon-controlled-rectifiers. A latching circuit and several delay circuits are used to turn on and off the hybrid contactors; the timing of the turn-on points is controlled relative to a zero-crossing of a voltage from the AC power source such that minimal DC offset current occurs.
Claims25
A method of controlling the flow of power from an AC power source to an inductive load by way of a switching circuit comprising a control circuit operably connected to a first hybrid contactor having a pair of relay contacts connected in parallel with a switching unit including at least one switching device, the AC power source having at least one output line and the inductive load having at least one input line, said first hybrid contactor switchably electrically connecting said at least one output line to said at least one input line, the steps comprising:
- I. turning on the flow of power by:
- (a) generating a turn-on signal,
- (b) sensing a relative waveform from the output line of the AC power source,
- (c) generating an indicating signal based on said relative waveform,
- (d) switching the switching unit of the first hybrid contactor to an on state responsive to said turn-on signal and at a point in time determined by, and other than at a zero crossing of, the sensed relative waveform to cause a minimal DC offset current to be generated by the integrating property of the inductive load, and
- (e) switching the pair of relay contacts of the first hybrid contactor to assume a closed state only after the switching unit is in an on state;
- and
- II. turning off the flow of power by:
- (a) generating a turn-off signal,
- (b) switching the pair of relay contacts of the first hybrid contactor to an open state responsive to the turn-off signal, and
- (c) switching the switching unit of the first hybrid contactor to an off state only after the pair of relay contacts are opened, to halt the flow of power from the AC power source to the inductive load.
A circuit system having at least a switching circuit for switchably supplying power from first, second, and third output lines of a three-phase AC power source to respectively corresponding first, second, and third input lines of an inductive load, said switching circuit comprising:
- two switching means, each switching means for independently switchably electrically connecting a different output line of the AC power source to a corresponding different input line of the inductive load;
- and
- a control circuit including a detect circuit for sensing the relative voltage between two of the three output lines of the AC power source and for generating an indicating signal circuit for generating a turn-on signal, said control circuit causing a first-closing one of said two switching means to close responsive to the turn-on signal and at a point in time determined by the sensed relative voltage to cause a minimal DC offset current to be generated by the integrating property of the inductive load, and said control circuit causing a second-closing one of said two switching means to close at a point in time after the closing of the first-closing one of said switching means to cause a minimal DC offset current to be generated by the integrating property of the inductive load.
Dependencies are inferred from the claim text.