Dual speed control circuit for power flow through an inverter

• US 4,251,735 A
• Filed: 07/23/1979
• Issued: 02/17/1981
• Est. Priority Date: 07/23/1979
• Status: Expired due to Term

• Current Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Coleman, Allen K.
• Primary Examiner(s): Griffin, Donald A.
• Assistant Examiner(s): Dwyer, James L.
• Application Number:
  US06/059,724
• Time in Patent Office: 575 Days
• Field of Search: 307/44, 307/45, 307/46, 307/48, 307/66, 307/72, 307/87, 363/95, 363/96, 363/97
• US Class Current: 307/46
• CPC Class Codes: H02J 3/32 using batteries with converting means
• CPC Class Codes: H02M 7/48 using discharge tubes with control electrode or semiconductor devices with control electrode

Abstract

A control circuit for a force-commutated inverter connected intermediate a regenerative DC power source and a power grid, the power source/inverter combination operative to supply AC electrical energy to, or receive AC electrical energy from or adjust the power factor of, the AC electrical energy of the power grid. The control circuit of the present invention varies the real power component and the reactive power component of the electrical energy flowing between the electrochemical cell and the power grid through the use of two feedback loops with separate time constants. The first feedback loop allows for the independent control of the magnitude and direction of both the real power component and the reactive power component of the AC electrical energy flowing to or from the power grid. The first feedback loop also has a relatively slow time constant so that the power flow between the DC source and the power grid is substantially unaffected by transients. The second feedback loop has a fast time constant for rapidly adjusting the effective magnitude and phase of the voltage waveform from the inverter to compensate for instantaneous or short duration voltage surges which periodically appear on the power grid.

Claims

1. A control circuit for an inverter which can be connected between an electrochemical cell and a power grid for electrical energy flow therebetween, comprising:

first feedback loop means having a relatively slow time constant for receiving an adjustable power command signal, said adjustable power command signal including a reactive power command signal and a real power command signal, which are indicative of desired electrical energy flow with said power grid, and for receiving sensed signals indicative of the actual electrical energy flow with the power grid, and for providing a power error signal in response thereto;

a second feedback loop means having a fast time constant for receiving said reactive power command signal and said real power command signal, and for sensing the phase of the signal waveform on said power grid, and for providing an output signal for varying the amplitude of the fundamental signal supplied to said power grid, and also for varying the phase of said fundamental signal to said power grid; and

switching waveform generator means connected to said second feedback loop means for providing a switching waveform to aid inverter of a pattern adjusted in accordance with said power error signal thereby varying the power flow between said power grid and said electrochemical cell.

2. A control circuit for an inverter according to claim 1, wherein said first feedback loop means includes a first comparator means for receiving said reactive power command signal indicative of a desired magnitude and direction of reactive power flow of said electrical energy, and for combining said aforementioned signal with a signal indicative of the actual magnitude and direction of reactive power flow to said power grid, for providing a reactive power error signal to said second feedback loop means indicative of the difference between the reactive power command signal and the actual reactive power flowing to said power grid, and wherein said first feedback loop means also includes a second comparator means for receiving said real power command signal indicating a desired level of real power flow, and also for receiving a signal indicative of the actual electrical power flow and for providing an output signal indicating the difference between the desired power level and the actual power level.

3. A control circuit for an inverter according to claim 2, wherein said first feedback loop further includes a first integration means coupled to the output of said first comparator for integrating the reactive power error signal over a relatively long time period, and wherein said first feedback means also includes a second integrator connected to the output of said second comparator means for integrating the real power error signal over a relatively long time period.

5. A control circuit for an inverter according to claim 1, wherein said second feedback loop means includes a phase controller for receiving said real power error signal from said first feedback loop and also for receiving a signal proportional to the fundamental waveform of said power grid, and for providing a phase offset signal to said switching waveform generator in which the sensed signal has been offset by an amount proportional to the real power error signal received from said first feedback loop means.

7. A control circuit for an inverter according to claim 5, wherein said phase controller includes a detector means for providing a signal corresponding to the zero crossover point of said voltage waveform of said power grid, and further including a phase comparison means responsive to the signal from said detector means and also responsive to a feedback signal for providing an error signal proportional to any phase difference between the zero crossover signal and the feedback signal, and further including a voltage controlled oscillator means connected to the output of said phase comparison means for providing an output signal whose frequency is proportional to the magnitude of said phase error signal, and further including a phase shift means disposed in said feedback loop from the output of said voltage controlled oscillator means to said phase comparison means for phase shifting said feedback signal in response to the real power error signal received from said first feedback loop.

8. A control circuit for an inverter according to claim 1, wherein said switching waveform generator means includes a lookup table in which the notch width information of the end notches versus the effective amplitude of the switching waveform pattern is stored, and further including a ring counter means for providing a series of pulse trains related to the frequency of the fundamental out of said inverter, and wherein said switching waveform generator further includes a digital comparator means for receiving a series of pulse trains from said ring counter means and offsetting said series of pulse trains in accordance with said signal received from said lookup table.

4. A control circuit for an inverter according to claim 4, wherein said second feedback loop means includes a voltage controller for receiving said reactive power error signal and for providing an output signal to said switching waveform generator for changing the effective magnitude of the fundamental voltage out of said inverter.

6. A control circuit for an inverter according to claim 4, wherein said voltage controller comprises a comparator circuit having a first input for receiving the reactive power error signal from said first feedback loop means, and a second input for receiving a signal proportional to the effective amplitude of the voltage waveform of said power grid, and a third input for receiving a feedback signal, said comparator providing an output signal to an integrating A/D means which integrate the aforementioned signal over approximately one-half cycle of the fundamental waveform of said power grid, and means for feeding back a scaled version of the signal from said integrating means to said third output of said comparator.