Improved constant-frequency hysteresis current control of VSI inverters with simple feed-forward bandwidth prediction

An improved implementation of the constant-frequency hysteresis current control of three-phase voltage source inverters is presented. A simple, self adjusting analog prediction of the hysteresis band is added to the phase-locked-loop control to ensure constant switching frequency even at high rate of output voltage change, such as required in active filters, fast drives and in other high demanding applications. This provision also improves the relative position of phase modulation pulses, thus reducing the current ripple. The prediction method is robust and uses a small number of inexpensive components. It does not require trimming or tunings, giving the whole system the capability to adjust itself to different load conditions. Thus the control becomes suitable to hybrid or monolithic integration. In the paper, the basic principles are described, and a detailed stability analysis is done. The control performance is illustrated both by simulated and experimental results.