Digital-Controlled Single-Phase Transformer-Based Inverter for Non-Linear Load Applications

The paper presents a new digital-controlled single-phase transformer-based inverter for non-linear load applications. A capacitive full-bridge circuit is added to provide instant current under non-linear load condition and thereby reducing the harmonics significantly to meet the required harmonic standard, IEEE 519-1992, even under non-linear load condition. The redundant capacity, cost, size and weight of line frequency transformer can therefore be dramatically reduced. Moreover, a new integrated controller for inverter control is proposed to eliminate both DC current component and steady state error even under heavy load condition. The proposed integrated controller consists of a Proportional (P) controller acts as voltage controller, DC offset canceller, an RMS compensator and non-linear load compensator. Experimental results derived from a DSP-based inverter system will be presented. The inverter rating is 1.5 kVA. It will be shown that both redundant capacity of line frequency transformer and voltage harmonics are significantly reduced even with non-linear load. It will also be demonstrated that the DC current component and steady state error are eliminated even under heavy load condition. These experimental results therefore confirm the superb performance of the proposed inverter and control techniques.