Improved constant-frequency hysteresis current control of VSI inverters with simple feedforward 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 a high rate of output voltage change, such as required in active filters, fast drives and other highly 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 tuning, giving the whole system the capability to adjust itself to different load conditions. Thus, the control becomes suitable for hybrid or monolithic integration. In this paper, the basic principles are described, and a detailed stability analysis is carried out. The control performance is illustrated, both by simulated and experimental results.