Abstract: A DC voltage converter apparatus is provided to convert a fluctuating input DC voltage into an isolated and regulated output DC voltage by operation of a first switch device for charging a capacitor through one primary winding of a transformer and a second switch device for discharging the capacitor through a second primary winding of that transformer. A load is energized by an output voltage from a first secondary winding when the first switch is conducting and is energized by an output voltage from a second secondary winding when the second switch is conducting. The first and second switching devices are controlled in response to the voltage change across the capacitor.

Abstract: A voltage converter apparatus is provided to energize a first load and a second load from a power supply connected through an inverter and a coupling transformer, with the transformer having a first secondary winding energizing the first load with first voltage pulses having a variable width determined by the operational frequency of the inverter and having a second secondary winding energizing the second load with second voltage pulses having a variable width determined by a phase controlled switching apparatus responsive to one of the voltage and the current of the second voltage pulses.

Abstract: A vehicle propulsion motor control apparatus includes a motor current regulating chopper apparatus and a free wheeling diode in the motor circuit. It is desired that the chopper apparatus not be commutated OFF when the free wheeling diode is conducting motor current to prevent damage to the free wheeling diode. A current detector is provided to prevent commutation of the chopper apparatus in response to sensing a current flow through the free wheeling diode.

Abstract: A transient voltage suppression apparatus is disclosed for application in conjunction with a power supply line to protect the chopper thyristor in the transit vehicle propulsion motor control apparatus, wherein an electrolytic capacitor is provided to absorb the inductive stored energy of that power supply line in the zener mode of operation of that capacitor upon the occurrence of a system fault condition involving that power supply line.

Abstract: An electronic sensing circuit monitoring the voltage on each of two alternating current power lines indicates when a load may be transferred from one of the power lines to the other without generating undesirable transient voltages or currents in the load.

Abstract: A three phase undervoltage monitor separately converts the voltage on each phase to a D.C. voltage, compares each of the separate D.C. voltages with a reference voltage, and operates an output signal whenever one or more of the voltages drops below the reference voltage.

Abstract: A method and apparatus are disclosed for reducing effective inductance and providing balanced line-to-line voltages in induction machine dynamic braking circuits which utilize braking resistors to substantially increase the full torque braking range of the machine. The current phase lag caused by the inductive property of conventional braking resistors, is substantially reduced by rectifying the current provided to the braking resistor through a three-phase rectifier bridge. This reduction of the current phase lag permits a reduction in the capacitance required to compensate for the effective inductance in the dynamic braking circuit. Furthermore, because the braking currents flow through a common braking resistor, the line-to-line stator motor voltages are inherently balanced. If the prior art braking impedance control is also employed, the rectifier bridge need carry current only if dynamic braking is required when motor voltage is greater than the maximum voltage of the inverter supplying the machine.