Dynamic Voltage Restorer Detection And Control Method Research

Disturbances in the power grid can cause temporary voltage drops in the grid,causing abnormal operation or tripping of voltage sensitive equipment for customers.This voltage anomaly is one of the common serious power supply quality problems.Dynamic Voltage Restorer(DVR)is an ideal voltage compensation device for voltage transient problems,which can effectively maintain load voltage stability and reduce the harm caused by voltage transients when voltage transients occur in the grid.At present,there are few theoretical studies on DVR of medium-voltage high-capacity structure in China,and it has not been applied in industry,so it is of great theoretical and practical significance to study the key technology of mediumvoltage high-capacity DVR.In the paper,the detection method,control strategy and cascaded multilevel inverter modulation strategy of the DVR are studied based on the topology and basic parameters of the medium-voltage high-capacity DVR as the development target.Based on the analysis of the voltage transient detection method based on the Second-Order General Integrator(SOGI)phase-locked loop,an improved voltage transient detection method based on the SOGI unit is proposed to address the problem that the voltage waveform distortion is serious during voltage transients and the phase-locked loop cannot work normally,thus affecting the detection accuracy.The DC component of the voltage is filtered out by adding a differencing node,and the harmonic component of the voltage is filtered out by averaging sliding filtering method.The simulation model is built in Matlab/Simulink to verify the feasibility of the detection method.To address the shortcomings of the existing control strategy,a dual closed-loop composite control strategy with inductor current and load voltage feedback and grid voltage feedforward is adopted.The proportional resonance controller is improved to make the DVR have the function of suppressing the specific order harmonics in response to the problem that more harmonics are present in the voltage transient,and a Hybrid Pulse Width Modulation(HPWM)strategy is adopted.The simulation results show that the HPWM modulation strategy can effectively reduce the switching losses while ensuring the output voltage waveform quality.In order to verify the effectiveness of the proposed DVR topology,detection method,control strategy and modulation strategy,a medium voltage 10 k V power supply system and the corresponding DVR simulation model are established in Matlab/Simulink.The simulation results show that the improved SOGI phase-locked loop-based voltage transient detection method of the DVR can quickly and accurately detect the voltage transients and calculate the output voltage reference value when the voltage transients and voltage distortions are severe.The dual-loop composite control strategy and HPWM modulation strategy can accurately compensate the fundamental wave while suppressing the high harmonics,and greatly reduce the switching losses,which can effectively maintain the load voltage stability and achieve the expected results.