Optimal Double-Halfbridge Pulse Width Modulation by Current-Dispersion Criterion

Abstract

The paper discusses an analytical approach to optimal pulse width modulation. Modulation error is understood to mean the difference between the currents generated by the modulated voltage function and by the modulating voltage function. Modulation quality value is interpreted as the numerical integral characteristic of standard modulation error (dispersion) in a time interval. Two-phase modulation is understood to mean double-halfbridge modulation. Load-current dispersion equation has been derived for a bridged electronic gate circuit. The research team has synthesized formulae for the switching functions of halfbridges. It is demonstrated that the minimum load-current dispersion can be found by three variables; the load is a low-frequency filter. The paper introduces the concept of zero potential function as one of the optimization variables. The variable is found; it corresponds to the minimum current dispersion in case of two-phase modulation. The paper derives formulae for finding the parameters describing the location of halfbridge-potential pulses in the PWM interval. It is demonstrated that optimizing the location of pulses in this interval considerably reduces the current dispersion as long as the relative modulation frequency is less than 40. If the relative modulation frequency exceeds the value, the optimal solution consists in centrally symmetric pulse location in the modulation interval. The paper describes a versatile approach to two-phase optimal pulse width modulation, which can be generalized for multiphase PWM.