Tham khảo tài liệu 'renewable energy part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Single-Phase Grid Connected Converters for Photovoltaic Plants 99 Fig. 12. Effect of a positive DC bias on the current at transformer input. Core flux green solid line transformer input blue solid line and output red solid line currents. Fig. 13. Computation of saturation indexes. Core flux green trace current set point black trace and transformer output current red one . Fig. 14. Block diagram of the saturation compensation scheme. Experimental Results Several experiments were made in order to evaluate the performances of the saturation compensation strategy. Experiments were made with the prototype described in section . The saturation compensation strategy is applied to two different current controllers PI feed forward and d-q synchronous reference frame controllers. The amplitude of the desired grid current . the set-point of the current controller is 8A in both cases. Figure 15a shows the grid voltage with an intrinsic distortion not correlated to the PV system the grid current transformer output current and the transformer input current in case of PI regulator and feed-forward without saturation compensation. As it can be noted 100 Renewable Energy current distortion appears in correspondence of the voltage zero crossing at the end of a positive voltage semi-period hence saturation is due to a positive DC bias at the transformer input. Figure 15b shows the effects of the saturation compensation strategy. b PI regulator feed forward control with saturation compensation a PI regulator feed forward control without saturation compensation d d-q control with saturation compensation c d-q control without saturation compensation Fig. 15. Experimental Results. Time waveforms of grid voltage violet solid line grid current red solid line and transformer input current blue solid line . The same experimental results are made using the d-q control without Figure 15c and with Figure 15d saturation compensation. As expected in this case the steady-state error is .
