A generalized circuit topology of multilevel voltage source inverter is proposed, which is based on a direct extension of the three-level inverter to higher level, and the circuit topologies up to five-level are presented. The proposed multilevel inverter can realize any multilevel pulsewidth modulation(PWM) scheme which leads to harmonic reduction and provides full utilization of semiconductor devices like GTOs especially in high power range where high voltage could be applied. Capacitor voltage balancing problem is pointed out and a circuit remedy for such a problem is also given.

A new modeling technique based on phasor transformation that provides the unified model of series resonant converters (SRC) is proposed. The proposed approach gives explicit and simple equations with fruitful physical insight. In the case that the switching frequency deviates from the resonant frequency, the SRC is modeled as the first order, and in the case of resonance the SRC is modeled as the second order. It is shown that the frequency band in which the SRC is modeled as the second order is very narrow' in practice. The time constant, small signal gains, and system order are highly depend on the switching frequency, load resistor, and output capacitor.

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