Single-phase, three-level, constant frequency current hysteresis control for UPS applications

The characteristics of hysteresis current control of voltage source inverters make this solution particularly suitable for high precision, high performance UPS, and for similar high demanding applications, like fast response drives. The extension of hysteresis techniques to three-level modulation, which is common in high-performance inverters, is usually quite critical and complex to implement. In this paper a new hysteresis control system is presented, which is capable of producing constant frequency, three-level modulation. The technique is based on the concept of decoupling the contributions to the current error of the inverter phase legs and of the load midpoint voltage. A robust, simple control is obtained. In the paper the decoupling theory is developed and the control implementation is described in detail. Experimental results are reported which confirm the excellent performance of the proposed control