Digital control strategy for harmonic compensation of dynamic voltage restorer

To make dynamic voltage restorer (DVR) compensate the low-order harmonic voltage, overcome the effects on system performance of digital control, and improve the voltage compensation effect, a dual closed-loop digital PR control strategy, consisting of voltage outer loop fundamental proportional resonant (PR) control and current inner loop low-order harmonic PR control is proposed. The discretization methods of PR controller are analysed, a detailed analysis and parameter design of the fundamental PR controller and the 3rd, 5th and 7th harmonic PR controller in the discrete domain are carried out. The analysis shows that the harmonic PR controller can effectively compensate for the 3rd, 5th and 7th harmonic voltage, the fundamental PR controlled can achieve zero steady-state error tracking and inhibit the effects on output voltage of load current, and digital control system has good dynamic response characteristics. Based on the theoretical analysis, 11KVA DVR prototype is developed and tested. The effectiveness and feasibility of the proposed control strategy are verified by experimental results.