Research On Control Strategy Of Single Phase Series Voltage Compensator

With the continuous development of the industry,more and more power electronic devices based on computers and digital signal processors are used.These devices are very sensitive to fluctuations and interferences in the power grid,which puts higher requirements on the power quality of the power supply system and the sag or interruption has the greatest impact on the equipment.In this context,it is necessary to study the compensation equipment and control methods that can effectively compensate for the sudden change of voltage.The voltage compensator is a series-type voltage compensation device,When the grid voltage drops,swells,harmonic distortion,etc.,the compensation amount is output to the power line to ensure the normal load voltage.This paper studies the single-phase series voltage compensator.In this paper,the structure and basic principle of the voltage compensator are analyzed firstly.The transformerless full bridge structure is used to reduce the volume of the equipment,reduce the cost,and accelerate the dynamic response speed of the compensation.The three SPWM modulation methods are compared and analyzed,and the equivalent switch is selected.The frequency-doubled unipolar modulation method is designed according to the project requirements,and the system main circuit and control system hardware are designed,and the whole hardware system is subjected to open-loop simulation and experiment to verify the correctness of the hardware parameters calculation of the whole system.The fast and accurate detection of the characteristic quantity of the grid voltage dip is a prerequisite for the operation of the voltage compensator.In order to accurately obtain the grid voltage phase information,this paper firstly designs a single-phase phase-locked loop with reference to the three-phase phase-locked loop based on the dq rotating coordinate system.Comparing the two voltage sag detection methods of instantaneous voltage dq conversion method and defect voltage method,the real-time defect voltage method is selected and optimized.On the basis of ensuring its real-time performance,it can also avoid false triggering of the device caused by grid voltage flicker.For the harmonic voltage detection,the instantaneous voltage dq conversion method is used,and the sampling compensation program is prepared for the case where the conditioning circuit has attenuation for the high-order harmonic voltage detection.The simulation and experimental results show that the improved defect voltage method has better real-time performance in voltage sag detection.The harmonic voltage detection method based on instantaneous voltage dq conversion method can accurately detect harmonics.Secondly,in order to accurately track the output voltage,the control method of single-phase series voltage compensator is studied.The quasi-proportional resonance(PR)controller is chosen,and the control strategy of output voltage and output current double closed loop combined with load current feedforward is designed.The theoretical analysis shows good stability.Simulation and experiments verify that the compensation strategy has good effects in response speed and compensation accuracy.Thirdly,the logic of the switching device is analyzed and designed for the start and stop of the voltage compensator.On this basis,four working modes of the voltage compensator are proposed,and the fast switching technology from the hot standby state to the compensation state is proposed.For detailed analysis,the protection logic is designed for the particularity of the series voltage compensator fault.The effectiveness of the system level control strategy is verified by simulation and experiment.Finally,on the basis of the achievements,the shortcomings of the research work are discussed,and the prospects for further research are proposed.