A three-phase four-line soft switched inverter for UPS applications

As the heart of UPS systems, the inverter is required to cope with stringent voltage regulation and distortion constraints in the presence of unbalanced and nonlinear loads. This paper presents a four-leg soft switched inverter topology to provide a four-line output including the neutral point. The adoption of a resonant DC link inverter (RDCLI) technique, which makes the four-line output possible, offers the potential of substantially higher switching frequency resulting in high reliability, high power densities and high quality AC power. A novel controller is proposed to achieve excellent static and transient performance characteristics. This inverter system has been studied in detail by simulation, including the use of an active clamp circuit, a new kind of discrete pulse current regulator, a load current feedforward strategy under different load conditions