Abstract: A capacitor unit including a capacitive element connected in parallel with a discharge resistor is provided with a switch in series with the resistor. This switch responds to power frequency current flowing through the capacitive element such that it opens to remove the discharge resistor from the circuit when power frequency current is flowing through the capacitor unit and closes when power frequency current stops, thus reinserting the discharge resistor to eliminate any residual charge remaining on the capacitive element.

Abstract: The switching intervals for the power transistors in a three-phase inverter are generated by a microprocessor. DC content control is provided separately for each phase by modulation of the duration of the switching intervals through adjustment of the length of the sequences of instructions carried out by the microprocessor.

Abstract: Negative sequence filters employing one to three operational amplifiers and a single reactive element generate the negative sequence voltage of a three phase AC power system by generating two line-to-line voltages, phase shifting one of them to bring them into phase and summing the resultant signals. The phase shifting circuit includes a potentiometer, one end of which serves as the input to the circuit and the other end of which is connected to the inverting input of an operational amplifier. A capacitor is connected between the tap point of the potentiometer and ground and the values of the components are selected so that the tap point of the potentiometer can be positioned to compensate for variations in the capacitive reactance of the capacitor without affecting the magnitude of the phase shifted signal.

Abstract: A controller system using high frequency switching by providing a bilateral switch gated on and off at a frequency about ten times the source frequency and the duty cycle determined by pulse width modulation of the high frequency waveform in accordance with window heater temperature.