Showing papers by "Robert Louis Steigerwald published in 1979"

Analysis of a Novel Forced-Commutation Starting Scheme for a Load-Commutated Synchronous Motor Drive

Abstract: A load-commutated inverter synchronous motor drive system employing a simple auxiliary commutation circuit for machine startup analyzed, and results hybrid computer simulation are presented. The commutation circuit employs a single commutation capacitor connected to the neutral of the machine and two auxiliary thyristors, which are used only during machine starting. A practical operating scheme is developed for the forced commutated inverter, which insures commutation over all load currents by actively allowing the commutation capacitor to charge to a voltage proportional to load, current. Results of key computer runs are given including inverter waveforms, transient waveforms during transition from forced to load commutation, as well as the effect of forced commutation and load commutation on pulsating torque. The forced-commutation circuit is used only for synchronous machine startup. However, due to its simplicity it also is an attractive alternative to be considered for other types of current-fed inverter ac drives.

Phase controlled rectifier circuit for rapidly charging batteries

Abstract: An improved battery charger circuit for rapidly charing a battery by increasing the rate of battery charge acceptance through periodic battery discharge during the charging process includes a pair of first and second controlled rectifier circuits coupled to an AC source and adapted for coupling to a battery. The first controlled rectifier circuit is rendered conductive during the charging intervals to supply the battery with charge current from the AC source. The second controlled rectifier circuit is rendered conductive during battery discharge intervals to discharge the battery in a substantially lossless manner by conducting battery discharge current through the AC source, thus realizing a highly efficient battery charger.

Characteristics of a Current-Fed Inverter with Commutation Applied Through Load Neutral Point

Abstract: A current-fed inverter which is commutated by an auxiliary commutating circuit acting through the load neutral point is investigated. The auxiliary commutation circuit consists of a single commutating capacitor and two auxiliary thyristors which are used to sequentially commutate the main thyristors. The properties of the inverter are considered for the case of an ac machine load, although the results are general and can be easily applied to cases where the inverter is interconnected with an ac power system. A ``voltage behind subtransient reactance'' model results in a good prediction of the inverter operating modes for either a synchronous or an induction machine. It is shown that if conventional simple-sequential gating is used, the inverter can only operate in the motoring region, while a commutation failure will result in the generating region. This negative feature is overcome by introducing a ``delayed gating'' scheme for the thyristor, which allows the peak commutating capacitor voltage to be actively controlled; thus, commutation for various inverter conditions is maintained. A scheme of parallel commutation circuits is introduced which allows the value of commutating capacitance to be actively selected as a function of load condition. While the main thyristors are subjected to approximately 50 percent more applied voltage compared to the more conventional auto-sequential type of inverter in present use, the thyristors may be rectifier grade since a substantial di/dt inductance is naturally provided by the motor leakage inductance: a fact which means that negligible snubber components are needed compared to the auto-sequential circuit.

Induction cooking system

Abstract: An induction cooking system comprises at least one induction surface unit which includes an induction coil operatively positioned adjacent to a metallic, food-containing utensil. A switching means is coupled in series with the coil across a source of rectified AC and is rendered conductive at a prescribed rate to energize the coil, causing the coil to generate magnetic flux which, in turn, causes eddy currents to be circulated in the utensil surface. The circulating eddy currents in the utensil surface result in joule losses causing food heating. Reactive energy present in the induction coil during intervals when the switching means is non-conductive is stored in a reactive power converter for subsequent discharge across the source of rectified AC. Selectively discharging the reactive power converter during the valleys of the AC input wave to the induction coil allows the coil to be energized during the entire 360° of the AC input wave, thus realizing an efficient induction cooking system.

Third harmonic auxiliary commutated inverter having selectable commutation capacitance as a function of load current

Abstract: Three pairs of series-connected inverter main thyristors are coupled in parallel across a unidirectional current source with the junction between thyristors of each pair being adapted for coupling to a respective phase of a three phase wye-connected inductive load. A first and second pair of serially-connected auxiliary thyristors are coupled in parallel across the current source, with the junction between thyristors of the first and second auxiliary pairs coupled by a first and second commutating capacitance, respectively, to the load neutral. Control means, responsive to conduction of a main thyristor, render a respective one of the thyristors of the first and second auxiliary thyristor pairs conductive in accordance with inverter load current to commutate a conductive main thyristor by coupling a respective one of the first and second commutating capacitances in series with a respective load phase across the conductive main thyristor. Inverter commutation capacitance is thus varied in accordance with load current, thereby extending inverter operating range and reducing likelihood of inverter commutation failure.

Combination field chopper and battery charger

Abstract: A power transistor used in a chopper circuit to control field excitation of a vehicle motor when in a power mode is also used to control charging current from an a-c to d-c rectifier to the vehicle battery when in a battery charging mode. Two isolating diodes and a small high frequency filter inductor are the only elements required in the chopper circuit to reconfigure the circuit for power or charging modes of operation.