In order to test the performance of grid-connected inverters, a testing platform is proposed, which takes back to back PWM converter as its circuit topology. The rectifier side adopts a three-phase voltage LC rectifier and the inverter side takes three single-phase H-bridge inverters to output three-phase voltage separately. The testing platform can simulate various power quality conditions such as voltage sags, three-phase imbalance, voltage harmonics and frequency offset, etc. To improve the dynamic response, voltage and current double-loop control strategy is adopted. A modified PR controller is proposed to improve the control static accuracy. The control parameters are designed through pole assignment method. The validity and feasibility of the proposed method is demonstrated via experimental results.