Abstract: An apparatus and method for generating a sensing signal from a generally periodic AC signal. The apparatus includes a first integrating circuit (125) for generating a first integrated signal by integrating the AC signal during a time period between positive transitions of the AC signal. The first integrating circuit (125) is reset by pulses from a pulse generator (100) at negative transitions of the AC signal. The apparatus further includes a second integrating circuit (135) for generating a second integrated signal by integrating the AC signal during the time period between positive transitions of the AC signal. The second integrating circuit (135) is reset by a further pulse generator at positive transitions of the AC signal. The sensing signal is generated by taking the difference in magnitude between the first and second integrated output signals.

Abstract: Apparatus and method for eliminating or reducing to a filterable minimum the relevant harmonic frequencies which otherwise occur in an AC output voltage from a multi-phase static inverter circuit operating from a symmetrically notched source of DC input voltage. The inverter circuit is electronically switched and controlled to provide notched phase voltages with the notch positioning being optimally variably placed in the periodically occurring waveform and with a controlled interval of the notch for controlling the fundamental component independently of the source voltage, while substantially eliminating the 11th and 13th harmonic components of the fundamental output voltage. A harmonic neutralizing transformer circuit includes paired wye, delta, or wye-delta configurations is connected between the inverter circuit and a composite output transformer circuit which couples or connects paired windings of the harmonic neutralizing circuit.

Abstract: Apparatus and method for a twelve-pole inverter for eliminating all of the relevant low-order harmonic component frequencies, except the fundamental for an AC output from a source of DC input voltage. The inverter circuit provides four separate three-phase sets of constantly phase displaced pole voltages from controlled six-pulse bridge inverter circuits. Additional phase displacements for straddled paired-sets of the pole voltages are introduced with a first and second predetermined phase displacement proportion of 2:1 or 15 degrees. One paired-set of pole voltages is input to a transformer configuration of a wye with a delta, and the other paired-set of pole voltages is input to a neutralizing transformer with a truncated delta paired configuration for low-order cancellation of harmonics.

Abstract: This invention controls the operation of solid state swithing devices in an output stage of an electronic inverter by using a counter to maintain a fixed delay between transition points in a switching command signal and a modified switch operation signal. The counter begins counting clock pulses following a transition in the switch command signal and produces a transition point in a switch drive signal when it reaches a predetermined count. The solid state switching device changes conduction states in response to the transition points in the switch drive signal. This produces a transition point in a switch operation signal. Those transition points are time-shifted by an amount corresponding to the level of DC voltage in the inverter output to produce the modified switch operation signal. The counter stops counting in response to one of the transition points in that modified switch operation signal.

Abstract: An electric generating system having a discharge circuit for a DC filter capacitor includes an electric power source for producing a DC voltage on a pair of conductors and a DC filter capacitor electrically connected between the conductors. A voltage indicating signal, representative of the actual output voltage of the generator, is combined with a reference signal to obtain a control signal which varies in proportion to the difference between the desired output voltage of the power source and the actual output voltage. Power source output voltage is controlled in response to the control signal. A branch circuit with a solid state switching device is connected across the DC filter capacitor. The solid state switching device is turned on for a limited time in response to a change in the magnitude of the control signal resulting from an increase in the actual output voltage of the power source, thereby discharging the DC filter capacitor.

Abstract: A transistor drive circuit includes a driver transistor and a power switching transistor connected in a Darlington configuration which receives turn-on and turn-off signals from a drive transformer. A capacitor is provided for connection between the driver transistor base and the switching transistor emitter during a turn-off period such that the voltage on the capacitor hastens turn-off of the driver transistor and the switching transistor. A diode connected between the emitter and the base of the driver transistor provides for continuing current flow from the capacitor following turn-off of the driver transistor but prior to turn-off of the switching transistor. After the switching transistor has turned off, the capacitor is recharged prior to the presence of a turn-on signal from the drive transformer.

Abstract: A pole switch firing control for a pulse width modulated inverter controls pole switch operation under steady-state operating conditions such that the inverter output duplicates a reference signal waveform after a fixed time delay. Pole switch operating time for a given pulse in an inverter output cycle is measured by counting a sequence of clock pulses to get a count equivalent to the delay time of the pole switch. This count then serves as the starting point for a presettable counter which begins to count upon the occurrence of a transition point in the reference waveform. When the presettable counter reaches a preselected count, the pole switch operating cycle is initiated, thereby causing the pole switch to operate at a fixed time following a transition point in the reference signal.

Abstract: A pole switch firing control for a pulse width modulated inverter controls pole switch operation under steady state operating conditions such that the inverter output duplicates a reference signal waveform after a fixed time delay. Average pole switch operating time for a given pulse in an inverter output cycle is measured by obtaining an average number of clock pulses which occur during the delay time of the associated pole switch for a given number of preceding inverter output cycles. This average count then serves as a starting point for a presettable counter which begins to count upon the occurrence of a transition point in the reference waveform. When the presettable counter reaches a preselected count, the pole switch operating cycle is initiated, thereby causing the pole switch to operate at a fixed time following a transition point in the reference signal.

Abstract: A pole switch firing control for a pulse width modulated inverter controls pole switch operation under steady state operating conditions such that the inverter output duplicates a reference signal waveform after a fixed time delay. Pole switch operating time for a given pulse in an inverter output cycle is measured and subtracted from a fixed time interval to get a delay time. In the succeeding output cycle, the corresponding pulse is produced by initiating the pole switch operating sequence after the delay time, thereby causing the pole switch to operate a fixed time following the reference signal.

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: Firing signals for the power switches in static power frequency changers are generated by comparing the integral of the output waveform ripple voltage to a repetitively generated stabilizing signal phase locked to, but having a time dependent magnitude independent of, the component waveforms of the output voltage. The stabilizing signal which changes in magnitude in one direction with time is reset to an initial level each time a firing signal is generated.

Abstract: The firing pulses to the nonload carrying bank only of the naturally commutated thyristor power circuit of a static power converter are retarded to reduce or eliminate the interbank circulating current. In one form of the invention, half wave rectified load current signals are summed with the output waveform reference signal applied to the positive and negative bank firing pulse generators in a sense to retard the pulses in the nonload carrying bank. In another form of the invention, the inversion end stops are used to generate the retarded firing pulses in the nonload carrying bank.