Two-Stage DVR Control with Improved Dynamic Performance under Nonlinear Load Condition

The dynamic voltage restorer (DVR) provides continuous and stable power supply to the load during grid voltage sags. Under nonlinear load conditions, when the load suddenly changes, if the dynamic response speed of the system is insufficient, it may cause the overvoltage protection of the front-stage DC/DC converter, and reduce the output power quality of the back-stage DC/AC converter. In this paper, a two-stage DVR control strategy is designed, which can improve the dynamic performance of the system under nonlinear load condition. The harmonic components extracted by the bandpass filter are subtracted from the load current, and the difference after the subtraction is used as the load current feedforward, which is superimposed respectively on the current inner loop of the front-stage DC/DC converter and the back-stage DC/AC converter. In order to improve the DVR output power quality, the proportional integral resonance (PIR) controller is used in this paper. By setting the appropriate resonance angular frequency, the PIR controller can effectively solve the output voltage waveform distortion caused by the harmonic current. Finally, the effectiveness of the control strategy is verified by simulations and experiments.