Compensation of magnetic core saturation for grid connected single-phase power converters

This paper proposes a saturation compensation strategy for single phase grid-connected power converters based on line frequency transformer. High power quality operations requires the direct control of injected grid current providing zero steady-state error at grid frequency. A zero steady-state error at grid frequency can be obtained by a control in a synchronous reference frame that ensures an infinite open loop gain at fundamental frequency and a superior disturbance rejection. However, the direct control of grid current is archived providing that transformer core saturation is avoided. Since the transformer blocks out the DC components the feedback loop closed on the transformer output current can lead to core saturation. This paper presents a compensation strategy based only on the monitoring of the output current distortion around voltage zero crossings. The proposed solution is free from offset problems, since no DC measurement is required. Experimental results confirm the effectiveness of the proposed control architecture and of the strategy adopted to avoid transformer core saturation.