×

Control system for controlling an SCR network to regulate three-phase A-C power flow

  • US 4,499,534 A
  • Filed: 10/12/1982
  • Issued: 02/12/1985
  • Est. Priority Date: 10/12/1982
  • Status: Expired due to Term
First Claim
Patent Images

1. A control system for controlling the conduction angles of three pairs of SCR'"'"'s, to each of which pairs is applied a respective assigned one of the three alternating sinusoidal phase voltages of a three-phase A-C power supply, in order to regulate the power flow from the power supply to a load circuit, comprising:

  • a transformer for deriving the corresponding line-to-neutral voltage for a predetermined one of the alternating phase voltages;

    a band-pass filter for attenuating, in the derived line-to-neutral voltage, frequencies above and below the voltage'"'"'s fundamental frequency, while at the same time introducing no phase shift to that fundamental frequency, the output signal from the band-pass filter thereby being sinusoidal shaped and identical to the predetermined phase voltage except that any harmonics, noise, transients or other distortions in the phase voltage are not present in the filter'"'"'s output signal;

    means for effectively detecting the zero voltage crossings in the filter'"'"'s sinusoidal output signal and producing a square wave signal which constitutes a reference voltage waveform having the same frequency as said phase voltages and having amplitude excursions which are precisely synchronized to the zero voltage crossings of the predetermined phase voltage;

    means for developing, from said reference voltage waveform, three phase-displaced square wave signals which are phase-displaced with respect to each other by 120° and

    have the same frequency as said phase voltages, each of the three phase-displaced square wave signals having its amplitude excursions occurring in exact time coincidence with the zero voltage crossings of a respective one of the three line-to-neutral voltages for the three phase voltages;

    means responsive to the three phase-displaced square wave signals for developing three phase-displaced, ramp-shaped analog signals each of which corresponds to and is in phase with a respective associated one of the three square wave signals, each ramp-shaped analog signal having a linearly changing ramp-shaped pulse during each half cycle of its associated square wave signal;

    means for supplying a d-c analog control voltage representing a desired power flow to the load circuit;

    and means for comparing said d-c control voltage to each of the three ramp-shaped analog signals and for producing, from the comparisons, gating signals for triggering the six SCR'"'"'s into conduction at the angles necessary to delivery the desired power flow to the load circuit.

View all claims
  • 6 Assignments
Timeline View
Assignment View
    ×
    ×