Analysis and design of a series-connected PWM voltage regulator for single-phase AC sources

Regulation of load voltage in single-phase applications is becoming an important issue for critical loads. This paper proposes a method to regulate a single-phase AC source by using a series connected auxiliary voltage source. A voltage source inverter, connected in series with the AC supply through a transformer, is used to compensate the input voltage variations to achieve a regulated load voltage. Input power factor improvement can also be obtained, when operating with reactive load, by phase-shifting the compensating voltage with respect to the input voltage. The operation of the compensator in all four quadrants allows the compensation of any voltage drop, and not only the reactive voltage drop within the same path. The total kVA rating for the system is a fraction of the load total power, and is determined by the maximum allowable line voltage variations. The use of a series connection associated with a high-performance modulation technique results in a high-quality output with a small size filter. This paper includes a description of the proposed method, implementation principles, design equations and a design example. Steady-state performance features are investigated. Simulated and experimental results confirm the concept and feasibility of the proposed system