Abstract: A control circuit for a static VAR generator measures appropriate circuit current and voltage during consecutive half cycles. This information is utilized to determine the firing angles of the VAR generator thyristors for providing compensating current to the line for keeping line current in phase with line voltage and for balancing the line currents in three phase electrical systems. A non-linear frequency dependent dynamic gain adjuster is provided in the control system of the VAR generator to automatically and rapidly reduce the gain of the VAR generator circuit as the frequency of load disturbance exceeds the VAR generator frequency response range.

Abstract: A control circuit for a static VAR generator measures appropriate circuit variables during consecutive half cycles of line voltage. This information is utilized to determine the firing angles of the VAR generator thyristors for providing compensating current to the line for keeping the source current in phase with the source voltage, for balancing source current in three-phase electrical systems and for reducing the line voltage fluctuation. A time-related-error minimizer is provided in the control system of the VAR generator to reduce the deviation between the amount of compensating current which is predicted for proper compensation during a given half cycle and the actual amount of compensating current needed at the time of application. The error is related to the differential between the time of the calculation of the value of current needed and the time it is actually applied. In one case, an open loop-type computational technique is utilized to determine the required inductor current.

Abstract: A control circuit for a static VAR generator measures load power during consecutive half cycles of the source voltage. This information, together with load voltage and load current information is used to determine the firing angles of the VAR generator thyristors for providing compensating current for keeping the source current in phase with the source voltage and for balancing the source currents in a three-phase electrical system. The total computation time for determining the firing angles extends into the half cycle in which correction is to be applied beyond a fixed minimum firing angle.

Abstract: A voltage regulator is taught for maintaning the terminal voltage of a three phase transmission line at a fixed reference value. The voltage regulator system utilizes the inductive reactance of the transmission line in conjunction with reactive current from a VAR generator to compensate for the voltage effect of line current as it flows through the inductive reactance. The VAR generator is of the parallel capacitor-inductor type where the inductor is controlled by a thyristor switch. The firing range for the thyristor switch is determined by a fast acting static control system which utilizes line-to-line voltage and line-to-ground voltage as an input. A signal related to the latter voltages is processed and compared against a reference. The integrated difference thereof is utilized to determine the firing angle for the thyristor switch.

Abstract: A set-reset flip-flop is taught utilizing NAND gate logic elements and an internally connected resistor-capacitor circuit. The time constant of the resistor-capacitor network is such that valid triggering pulses for the input terminal of the flip-flop will not be propagated through the flip-flop to change the output state thereof unless the pulses are of a minimum duration. The duration of such pulses are chosen to be significantly larger than the duration of expected random noise which may appear on the input terminal of the flip-flop. Such being the case, noise signals are not propagated through the flip-flop to change the state thereof. A discharge network is provided for the capacitor to quickly discharge the capacitor at the termination of each input pulse, whether noise or triggering, so that an accummulaton of noise pulses will not cause a shift in the output of the flip-flop.

Abstract: A static VAR generator is taught for use with a source of electrical power and a rapidly varying load. The static VAR generator comprises thyristor switched inductors connected across a capacitor. The gate of the thyristor switch is fired each half cycle in accordance with a predetermined firing angle to provide sufficient inductive current to cancel a portion of the capacitive current to thus provide a net reactive current for the system served. This is done on a half cycle by half cycle basis. A main disconnect switch is connected in parallel with the series combination of a secondary disconnect switch, a diode and a large resistor. The latter combination is connected in series with the parallel combination of the compensating inductor and the compensating capacitor.

Abstract: Apparatus provided for utilization with the control circuit of a static VAR generator to determine the presence of a DC component in the output of the VAR generator which component is not desirable because it may effect certain AC power components such as transformers. There is provided apparatus for determining the presence of the DC component in the VAR generator which utilizes a feedback loop which includes the VAR generator control system as part thereof to insure that the positive and negative half cycles of the VAR generator output current generally remain equal.

Abstract: A static VAR generator circuit having a control system adapted to utilize the values of three phase load currents to generate time delayed firing angles for thyristor controlled inductors which are utilized with parallel capacitors to provide unity power factor and balanced electrical currents to the AC source. The time delayed firing angles are calculated from integrating furnace load currents over prescribed intervals during real time to thus maintain balanced load current at specified phase angles, usually zero, in the three phase system.

Abstract: An over current shutdown apparatus for protecting the power circuit of a static VAR generator flicker compensator. The apparatus incorporates a two stage current sensing means and attempts to provide system recovery by limiting the firing angles of thyristors in the flicker compensator for prescribed intervals.

Abstract: A tachometerless motor drive of the induction motor type is obtained by synthesizing the motor slip frequency from analog signals sensed at the input of the motor. The slip frequency signal so derived is used as one of the parameters for control, beside voltage and/or frequency or current and frequency at the input of the motor.Analog circuitry is used involving the derivation of a numerator N characteristic of E.sub.1 I.sub.1 Cos .theta., where E.sub.1, I.sub.1 and .theta..sub.1 are given by the vectorial representation of the input current and voltage, and of a denominator D = E.sub.1.sup.2 /.omega..sub.1where .omega..sub.1 is the frequency of the motor supply.

Abstract: Apparatus for significantly reducing the drift and increasing the accuracy of a firing phase angle determination device for the control circuit of a static VAR generator. A phase locked loop is utilized for providing accurate phase information and rapid capture. The phase locked loop utilizes a ripple cancelling digital phase detector and a dual mode amplifier/filter.