Abstract:
Speed control of an a-c motor is accomplished with back-to-back thyristors coupled between the power line and the motor. A gate circuit (1) selects which of the thyristors can be gated on, and (2) determines the actual time of thyristor conduction in each half-cycle. In turn the gate circuit is regulated, as to thyristor selection, by a countdown arrangement including frequency control and multivibrator circuits. The gate circuit is also regulated, to determine the actual conduction time, by a voltage control circuit coupled to the frequency control circuit. Thus the frequency control circuit regulates motor speed as a function either of the fundamental power line frequency, or a subharmonic of the line frequency.
Abstract:
An impulse commutated, variable output frequency, multiphase inverter type of power switching system employing main SCRs to handle the primary output currents and auxiliary SCRs to aid in commutating the main SCRs is disclosed wherein the firing of the SCRs is done by using isolated direct current supplies. Each SCR is fired by a separate driving circuit which includes individual isolated direct current supply and a switch unit to connect that supply directly to the gate-cathode circuit of the associated SCR. The control circuitry includes an oscillator whose output frequency is selectively variable, and a three-phase square-wave generator driven by the oscillator which produce two squarewaves, one the inverse of the other, for each phase. Each of these six outputs of the generator drives a pulse and a delay pulse circuit which respectively produce a first pulse and a delayed second pulse in response to each change of polarity of the particular square-wave input. These pulse and delay pulse are inductively coupled to different ones of the multivibrator circuits to turn on the switch unit and to ''''fire'''' an SCR in accordance with a predetermined sequence so as to generate a three-phase a.c. output from the inverter. This arrangement allows for short rise times and fast turn-off of the SCR gate drive and also allows the output frequency to be varied over a large range from d.c. to large values.
Abstract:
An inverter circuit includes a pair of conventional commutating capacitors, coupled in series between the input conductors. Additional pair of commutating capacitors is provided, and an inductor is coupled between the common connection of the additional capacitors and the common connection of the conventional commutating capacitors.
Abstract:
AN OSCILLATOR APPLIES TIMING SIGNALS TO AN INVERTER LOGIC ARRANGEMENT FOR GOVERNING THE FREQUENCY OF THE INVERTER OUTPUT A-C VOLTAGE SUPPLIED TO A MOTOR. THE AMPLITUDE OF THE A-C VOLTAGE APPLIED TO THE MOTOR IS ADJUSTED BY SUITABLE CONTROL MEANS WHICH RECEIVES A REGULATING SIGNAL FROM A COMPARATOR. A FIRST SIGNAL CHANNEL INCLUDES A FEEDBACK NETWORK, AND APPLIES TO THE COMPARATOR A FIRST CONTROL SIGNAL WHICH INDICATES THE EFFECTIVE AMPLITUDE OF THE INVERTER VOLTAGE. A SECOND SIGNAL CHANNEL IS CONNECTED BETWEEN THE OSCILLATOR AND THE COMPARATOR TO PROVIDE A SECOND CONTROL SIGNAL RELATED TO THE FREQUENCY OF THE OSCILLATOR OUTPUT. THE COMPARATOR OUTPUT SIGNAL IS A FUNCTION OF BOTH AMPLITUDE AND FREQUENCY, AND DRIVES THE CONTROL MEANS TO MAIN A PRESET RATIO BETWEEN AMPLITUDE AND FREQUENCY OF THE A-C VOLTAGE PASSED TO THE MOTOR.
Abstract:
A PNPN-thyristor has an extra gate connection added in the Nregion adjacent the outer P-region. A pulse generator applies a turnoff control signal to the added gate when turnoff across the anode-cathode connections is initiated, to sweep out the carriers at the center junction rather than allow the carriers to normally recombine over a longer time period. The connection to the added gate can be extended in area, either in the operation by which the extra connection is added to a conventionally produced PNPNthyristor, or by varying the manufacturing process by which the PNPN-thyristor is produced.
Abstract:
A static transfer system includes a first switch for connecting a normally used AC source to a lead and a second switch for connecting a standby source to the lead. A sensor is connected to an AC sine wave reference source for comparing at every instant of time the normal AC sine wave signal to the reference source signal and feeding an error signal to a logic circuit at any instant in time when the normal source signal falls below the reference signal. The logic circuit is effective to instantaneously connect the load to the standby source and disconnect the load from the normal source irrespective of the load power factor, and to reconnect the load to the normal source and disconnect the standby source from the load when the normal source is again capable of handling the load.