Design and implementation of a single phase inverter with sine wave tracking method for emergency power supply with high performance reference

Uninterruptible power supplies (UPS) play an important role in supplying critical loads. The majority of UPS systems employ batteries as a mean of energy storage. Since typical loads are supplied by AC voltage, an inverter is an indispensable part of a UPS to convert DC voltage to AC. Conventional control methods for single phase inverters suffers from many drawbacks like slow dynamic/transient response, oscillatory no-load behavior and distorted waveform in presence of non-linear loads. This paper in concerned with the control loop design for a single-phase voltage source inverter when employed in UPS applications. The regulation of the output voltage is done based on reference tracking to ensure good steady-state and dynamic performance. The control loop is designed taking into consideration the low damping during light loads. Three control strategies are proposed. The first is based on modified PID controller which demonstrated moderate performance and is suitable for low cost applications. The second method is based on an additional current control loop which has the benefit of inherent inverter protection. The last method is based on the theory of "internal model controller" which gives nearly ideal steady-state regulation. Key points in implementing controllers with digital controllers are addressed. An experimental system is built to verify the validity of theoretical results