Research On The Shunt Active Power Filter

With the development of power electronic technology,a variety of power electronic devices such as rectifiers,inverters,motor speed control devices and other nonlinear loads have been widely used.A large amount of harmonic current is injected into the power grid,leading to a serious current waveform distortion of the power grid,and a deterioration of power quality,which has a negative effect on the electrical equipment operation.Therefore,it has great practical significance to the restraination and compensation harmonics.The traditional passive filter is easily to be affected by the grid parameters,which means is easily resonate with the grid impedance and amplify the harmonic current.Compared with the passive filter,the active power filter show a less effect of the grid impedance.Active power filter,with its own advantages,has become an important trend of harmonic suppression.Especially,the emergence of hybrid active power filter,which has widened the application of active power filter,makes the application in medium and high voltage occasions become more economical and effective.Therefore,the active power filter was taken as the research object to study the current control strategies of active power filter and to optimize the design of shunt hybrid active power filter system,which will provide a guidance for the practical application of active filtering technology.In this paper,the mathematical model of shunt active power filter was established.Based on the topology,the harmonic current was detected by d-q harmonic detection method and the PI double closed loop control system was designed.Lastly,PI double closed loop control system was verified by the simulation and experiment.The simulation and experimental results show that the double closed loop control system based on PI control was limited by the bandwidth,and the compensation effect was unsatisfactory.Aiming at the problem mentioned above,a composite current control strategy based on PI control and repetitive control was proposed.The stability and dynamic properties of the system were simulated and experimented under the composite control mode.The results of simulation and experiment show that the current compensation system has a high precision stable compensation,and can solve the problem of the low stable accuracy under the single PI control mode.But its dynamic response is still too slow.In view of the problem mentioned above,the sliding mode variable structure control strategy was proposed.The sliding mode controller of active power filter was also designed.Lastly,the simulation and experimental were carried out.The results show that the sliding mode variable structure control has a fast dynamic response and strong robustness.In order to improve the voltage and capacity of the active power,a hybrid active power filter was proposed.The mathematical model of the hybrid active power filter was established,and the filtering characteristics of the hybrid active power filter under different control modes were analyzed.In order to improve the steady state accuracy of the system,a double loop control strategy based on repetitive control was proposed.Lastly,the proposed control strategy was simulated and experimented.The simulation and experimental results show that the current double closed loop control strategy based on repetitive control can improve the steady state accuracy of the system and achieve the target of harmonic suppression.The hybrid active power filter reduces the capacity of the active filter to a great extent,and is suitable for the occasions of high voltage and large capacity.