Load independent hysteresis current control of a three level single phase inverter with constant switching frequency

Two level single-phase hysteresis current controllers have the major limitations of a variable switching frequency and a harmonic performance that varies with load inductance. This paper describes a method for digitally implementing three level modulation of a single phase inverter with a constant switching frequency, by using the zero crossing time error of the phase current error to vary either the hysteresis bands or the active pulse widths of the modulator. The approach makes the algorithm performance independent of the load inductance, and achieves a stable switching frequency within two switching periods after a transient event. Simulation and experimental results are presented in the paper.