Abstract: Quasi-harmonic neutralized inverter systems are provided with interphase transformers connected in a waffle tree configuration and each having a pair of inputs for receiving staggered voltage waveforms, wherein the stagger angle of the voltage waveforms reduces a harmonic component of an output voltage on an output terminal of each interphase transformer. Inverters produce voltage waveforms at phase angles necessary to provide the required stagger angles at the inputs of the interphase transformers in a first stage of the waffle tree configuration. A method for quasi-harmonic neutralization of voltages in an inverter system is also provided, in which interphase transformers, each having a pair of inputs for receiving staggered voltage waveforms, are connected in a waffle tree configuration, such that the stagger angle of the voltage waveforms reduces a harmonic component of an output voltage on an output terminal of each interphase transformer.

Abstract: A UPS system which operates initially in a commutation mode allowing commutation of the static transfer switch provided on the primary supply lines, and wherein the standby source is kept energized so as to operate to commutate such transfer switch through the inverter just before initiating UPS mode of operation.

Abstract: An AC/DC or DC/AC converter includes a single hexagon transformer with each side connected to opposite polarity DC terminals through two pairs of SCR devices gated in sequence synchronously with the frequency of the AC lines, gating in a pair lagging gating of the next SCR device in the adjoining pair, to create a 24-pulse output, while minimizing AC line harmonic contents, especially the 11th and 13th harmonics.

Abstract: A load commutated inverter (LCI) a-c drive system includes a synchronous motor with two 30 degree angularly displaced sets of three-phase windings. Each set of motor windings is powered by a three-phase inverter fed by a three-phase rectifier in a separate d-c loop. The three-phase rectifiers are fed by either a generator with two angularly displaced sets of three-phase windings or by a transformer with a three-phase primary winding, and delta and wye secondary windings separately supplying the two rectifiers. Twelve-pulse operation in the line commutated mode with substantially constant d-c link currents significantly reduces torque pulsations. At low speeds, sinusoidal segment pulsed d-c currents in the d-c links are gated to pairs of windings in the two sets of motor windings which generate component MMFs either 90 degrees or 150 degrees displaced to produce a resultant rotating motor MMF of constant magnitude to completely eliminate torque pulsations.

Abstract: In a 12-pulse AC/DC converter of the hexagon type the rectifier switches are distributed in three groups for each polarity and for each polarity three coils are joined to the common pole and connected separately to the pairs of rectifier switches of a corresponding group. As a result, the capability of the hexagon is extended to commutation of diodes, instead of controlled rectifier switches, by the effect of such interposed commutation inductance.

Abstract: A two-pole inverter bridge has an inductor mounted between the two controlled switches in each pole and a resonant load is connected across the poles between ends of the inductors which are similarly situated relative to the terminals. In each pole one antiparallel circuit includes an auxiliary controlled switch and another antiparallel circuit includes only a diode. Fault protection is provided with an auxiliary source mounted between opposite ends of the inductors for applying reverse bias to the controlled switches of the poles whenever a fault in the inverter is detected.

Abstract: An adjustable speed machine-commutated inverter-synchronous motor drive includes control of the inverter at a selected rate without positioning. The line converter is controlled so as to maintain a relation I=f(T) and the relation E/l=g(T) is established by applying to the field regulator loop a reference which is a function of T, where T is the torque, I the current drawn by the motor drive and E the excitation voltage. Accordingly, the torque is not sensed. The functions are chosen so that the commutation margin angle is safe under natural commutation by the EMF of the motor and also chosen to improve drive operation.

Abstract: In a transformer-rectifier converter system, at least one inductance is inserted in the commutation path of two adjacent diode or thyristor devices in a cluster of three devices related to a common DC polarity pole, the reactance due to such inductance being sufficient to lengthen the commutation overlap thereby to minimize AC line harmonics. The invention is applicable to AC/DC as well as to DC/AC conversion.

Abstract: In a thyristor-controlled converter system the non-canonical harmonics are minimized by active filtering through control of the firing angle of the thyristors in accordance with the undesired harmonic component.

Abstract: Electrical apparatus such as a VAR generator or convertor is taught for high-voltage application. The electrical apparatus includes series stacked silicon controlled rectifiers, some of which operate at high electrical potential. Switching information is provided to the thyristors by way of insulating light pipes. The energy for actuating the gate of the thyristor in each case is provided by a current transformer which in some instances is interconnected with the anode of the thyristor in question to monitor the anode current thereof in a previous half cycle of conduction. In other instances, anode current of another thyristor are monitored. The anode current is converted to stored charge which is later released through a light actuated switch to the gate for energization of the thyristor in question. This means that a thyristor may be repeatedly energized even after many intervals of full cycle conduction where no anode to cathode potential is available for charging a capacitor.

Abstract: A three-phase transformer having a delta-connected primary and two identical secondary windings per phase connected in hexagon, has symmetrical taps on each secondary winding connected to rectifying devices for generating DC energy from a first group of six symmetrical AC voltages at 60.degree. with respect to the virtual neutral for one polarity and from a second group of six symmetrical AC voltages at 60.degree. with respect to the virtual neutral for the other polarity, the first and second groups being at 30.degree. phase shift to one another.

Abstract: Tap changing apparatus including a plurality of electrical inductive windings, each having an intermediate tap which divides each winding into two sections with the voltage of one section being twice that of the other section. Gate-controlled electronic switches, disposed between the ends and the intermediate tap of each winding and each of two output terminals, are selectively triggered to form a conductive path which will cause either or both sectons of each tapped winding to be connected into a circuit so that it will aid, oppose or bypass the circuit. The switching sequences provide a full range of positive to negative output voltage magnitudes for each winding in incremental unit steps.

Abstract: The static VAR generator of the fixed capacitor switch-controlled inductor type is taught. The inductive element has a break point in its inductive characteristic. That is, below a certain predetermined current, the inductance is one value and above the latter current the inductance is another value. This has the effect of providing a reduced value of inductive reactance above a certain inductive current level thus making it possible to significantly increase the inductive current above its normal range with a small increase of the switch conduction interval. In one case a saturable iron core reactor is utilized to achieve the break point and in another case two inductive elements are provided--one of which is controlled by a switch which places the latter inductor into circuit arrangement with the first at the time that the current exceeds the predetermined value.

Abstract: Disclosed is a force commutated static switch composed of inverse parallel connected thyristors. A bilateral commutation circuit is connected across the thyristors. The commutation circuit includes a switched capacitor which, during a current commutation interval, provides the dual functions of contributing to the current commutation operation and of acting as a current source for one of the thyristors. The capacitor discharge current interacts with the intrinsic resistance of the thyristor to provide a relatively low forward voltage drop which is a reverse voltage drop for the other thyristor. The low reverse voltage is known as soft biasing voltage. This voltage is utilized in conjunction with the most recently turned off thyristor to prevent reconduction thereof during the critical recovery time of the thyristor. The commutation circuit cooperates with its control circuit to provide an abort capability for its current limiting operation.

Abstract: A dual converter for use in a static direct current motor drive is operated with circulating current and the circulating current is adjusted by firing angle control to automatically maintain reactive power compensation during varying torque and speed conditions of the load.

Abstract: An AC/AC frequency changer operating under a one to one frequency ratio has its input coupled to a power system of same frequency and voltage, with an inductor connected between its output and input terminals. The output voltage is controlled so as to deviate by a predetermined amount from the input voltage so that reactive power flows from the output to the input which, owing to the inherent phase inversion in the frequency changer, causes reactive input current and reactive output current to be summed up directly at the input terminals. As a result, the frequency changer requires only a power rating which is half the reactive power which it can supply to the power system.

Abstract: A variable speed drive is provided for a polyphase induction motor. The motor is connected through a contactor to a constant frequency polyphase alternating current power source for starting and for full speed operation but is supplied by a variable frequency source in a single phase operating mode when reduced speed levels are desired. In the single phase operating mode, low speed operation is provided by driving the motor with a cycloconverter which converts power from the polyphase source to single phase alternating current of a predetermined lower frequency. The motor speed decreases from a higher level to a lower level by coasting, with gate signals of the cycloconverter suppressed until a desired lower speed is reached. Initiation of contactor and cycloconverter operation is coordinated by motor speed sensing means.

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.