Constant frequency three-phase hysteresis current regulator with extended modulation depth

This paper presents a novel approach to hysteresis current regulation that extends the modulation range of a three-phase voltage source inverter to 1.15 while simultaneously maintaining an essentially constant switching frequency. The strategy uses the average of the phase leg switched output voltages, to both vary the hysteresis band to maintain a constant switching frequency and to inject a third harmonic offset to achieve the increased modulation range. The approach also provides a soft transition into the overmodulation region. The controller fully uses the DC bus voltage, and achieves a similar harmonic performance as conventional space-vector PWM (SVPWM). The work is confirmed by simulation and matching experimental results.