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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]