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The paper describes the effects of changes in the triggering frequency on the maximum working frequency of a series inverter. Inverters differ in the type of load and in the mutual coupling existing between two commutation inductors in the circuit. It has been shown that the transient state is a result of changes in thyristor commutation from natural or critical to overlapping, and is dependent on the mode of change of the triggering frequency. The region of overlapping commutation has been determined by using two types of frequency change: fast (by keying modulation) and slow (by frequency modulation). The results show that slow changes in thyristor commutation permit a higher maximum working frequency than do fast changes. The region of overlapping commutation of thyristors is defined by new limit curves. The results may, for example, be applied in the design of an ultrasonic generator operating with frequency modulation. [ABSTRACT FROM AUTHOR]

The paper presents the results of theoretical analysis as well as numerical calculations of the maximum output frequency in a series inverter working with overlapping commutation of the thyristors. The changes from natural or critical thyristor commutation to overlapping commutation were fast. The region of overlapping commutation is limited by new extreme curves which ave dependent on the type of load as well as on the mutual coupling value between the two commutation inductors. Resonance shaping load-current edges have also been considered in this paper. [ABSTRACT FROM AUTHOR]

A novel coupled-inductor commutation circuit is described. The circuit may also be used for inverters. It uses only two auxiliary thyristors, each operating in alternate cycles and eliminating the need for reversal of the commutating capacitor voltage. Trapped energy is fed back to the source. The output voltage is controllable from zero to the full input voltage. The commutation circuit can be connected to a voltage source other than that feeding the load. A DC chopper using this commutation scheme has been analysed and experimentally verified. [ABSTRACT FROM AUTHOR]

A McMurray commutation circuit with a (di/dt) inductor in series with the main thyristors is analysed. Analysis shows that advanced firing on the commutation current ring is necessary in order to avoid the commutation failure in case of sudden loading of the inverter. Advanced firing boosts the commutation capacitor voltage. Hence, the operating conditions should be adjusted so as to control the commutation capacitor voltage in a narrow range from no-load to full-load conditions. At the same time, the commutation energy corresponding to these conditions should not deviate much from the minimum commutation energy. [ABSTRACT FROM AUTHOR]

This paper explains the requirements of thyristor chopper circuits to operate without any commutation limits and also explains the commutation processes of a thyristor chopper which satisfies these requirements. The practical design equations for the selection of components are derived and the complete design of the chopper circuit to meet typical drive specifications is presented. [ABSTRACT FROM AUTHOR]

The paper presents the effects of source inductance and discontinuous conduction in the load on the commutation, and voltage ratings of thyristors, diodes and capacitors of some commonly used chopper circuits. [ABSTRACT FROM AUTHOR]

This paper explains the methods for determining the commutation losses of a thyristor chopper circuit, derives analytical expressions for each component of commutation losses and demonstrates the importance of commutation losses on the design of the thyristor chopper to guarantee the minimum reverse bias time of the main thyristor. [ABSTRACT FROM AUTHOR]

The three-phase stepped-wave inverter is based on a new method of synthesizing waveforms. The proposed system comprises a 120° conduction type three phase bridge inverter and a single-phase triple-frequency square-wave inverter. The triple-frequency inverter used for wave-shaping is of low power and is used in the neutral circuit of the three-phase inverter. A special complementary impulse commutation circuit realizes the above system with only eight thyristors. The output voltage waveform has three steps per quarter cycle and has a total harmonic distortion of 15-1%. The kVA ratings of the wound components are derived. The experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

In this paper the influence of the dynamic parameters of real thyristors on the properties of series inverters operating in the region of overlapping commutation has been presented. The formal SCR model has been used based on the rise time (t[sub r]) characterizing the thyristor turn-on process and on the reverse recovery time (t[sub rr]) and the total stored charged (Q[sub rr]) characterizing the thyristor turn-off process. [ABSTRACT FROM AUTHOR]

There are two important problems that arise in the design of bi-directional thyristors, particularly for high-current applications. These are the problem of (1) gate isolation and (2) commutation. The former arises in bi-directional thyristors with two gates, one to fire in the 1st quadrant and the other to fire in the 3rd quadrant of the device's characteristics. The normal requirement is that the 1st quadrant gate should not fire in the 3rd quadrant and vice versa. Successful gate isolation consists of meeting this requirement.
The problem of commutation arises when a bi-directional thyristor which has been carrying current in one quadrant is switched rapidly into the other quadrant, where it is expected to present a blocking characteristic. Under some circumstances stored charge effects can cause the device to turn on in the other quadrant (i.e. fail to commutate).
In this paper analyses are made of both these problems, some practical results are given, and the implication in actual device design is examined. [ABSTRACT FROM AUTHOR]