Commutated Inverter Research Articles

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

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.

Current-Source Double DC-Side Forced Commutated Inverter

DC-side commutated inverters are very attractive due to their simplicity and efficient use of the commutation circuit. A new current-source commutated inverter of this type equally applicable to both single and multiphase bridge configurations is considered. Simultaneous turn-off of all bridge thyristors allows ample possibilities for programming the commutation sequence. The behavior of a threephase bridge is analized, and the optimum values of the commutation components are obtained. Guidelines for analysis under any commutation condition, as well as general programming rules and suggestions for snubber design are given. Results obtained in a 8-kVA variable speed drive prototype are shown and discussed.

Design Methods for Current Source Inverter/Induction Motor Drive Systems

A current source inverter combined with a controlled slip induction motor is a reliable and rugged ac drive system. The majority of the inverters in use today are the voltage source type using auxiliary impulse commutation. However, recent advances in SCR blocking voltage capability are making the complementary impulse commutated current source inverter a viable competitor

Analysis of a Forced Commutation Circuit for Design of a Class or Thyristor Inverters

The literature contains a variety of inverter circuits with forced commutation. In general, the auxiliary circuit for switching off the load current carrying thyristors is composed of a number of energy storage components and semiconductor switches which are affected by losses. These circuits demonstrate specific advantages under certain conditions. The analysis of a forced commutated inverter with a series LC-resonant circuit is presented in this article. The peak capacitor voltage depends on the quality of the resonant circuit and the ratio of the peak capacitor current vs. the maximum load current. This can cause high stresses on all the components of the inverter circuit. The set of equations for the circuit is established and used for the computation of results. The peaks of stored energy and the losses in the commutation circuit are calculated and given in a normalized form. Design parameters in normalized form are derived therefrom and presented in this article.

Optimum Design of an Input-Commutated Inverter for AC Motor Control

In any forced commutated inverter scheme, a certain amount of energy is "trapped" at the end of the commutation interval. It is desirable to minimize this level of trapped energy for best circuit component utilization. An input commutation circuit, suitable for single or three-phase inverter circuits, is introduced as a model. A mathematical analysis of the circuit yields expressions for circuit component values in terms of the load impedance at the instant of commutation. Optimizing procedures produce direct expressions for the components to yield the most efficient operation and minimum trapped energy.