Research Of Harmonic Detection And Control Strategy In Shunt Active Power Filters

With the development of the society,more and more non-linear power electronic device is put into the distribution network,which improving the quality of people's life,while it also brings a lot of harmonic pollution,causing deterioration of the power grid' power quality.The active power filter has multiple compensation functions,which can realize the dynamic compensation aiming at load current whose frequency and size change timely,and its compensation performance won't be affected by the frequency change of grid.The good compensation performance of APF is welcomed by the users,and it also becomes a hotspot in research of harmonic suppression.Parallel Active Power Filter based on three-phase three-wire system is regarded as the research object in this article,firstly,the basic principle and main circuit topology structure of the APF(Active Power Filter)is introduced,its mathematical model is established under three kinds of coordinate system.Then,carrying on the thorough research aiming at the related key technology,the main research contents are as follows:(1)The research of Harmonic detection strategy: The rapid and accurate detection of harmonic current is extremely important for the compensation performance of APF,the harmonic detection strategy based on instantaneous power theory is mainly improved in this article,using the current average method instead of the digital low-pass filter under the testing link,which improved the real-timing of detection.By improving the phase-locked loop circuit,which can get the unit sinusoidal voltage who has the same phase angle with the network voltage,applying it to the improved ip-iq detection algorithm,without tedious coordinate transformation,it can reduce the amount of calculation,at the same time improve the accuracy of detection.Through the comparison of several harmonic detection strategies under simulation,the results show that the improved ip-iq detection algorithm can short the delay time and precision is also improved.(2)The research of tracking and control strategy: first,analyze the advantages and disadvantages of hysteresis control and triangle wave comparison control.On this basis,the double closed-loop hybrid control strategy based on d – q coordinate system was proposed;due to the traditional PI control strategy can only realize the no difference tracking for straight flow,the inner adopts the parameter self-adjusting fuzzy PI with repetitive control in parallel,the outer adopt fuzzy-PI dual-mode control strategy,the simulation show that the hybrid control strategy is effective.At the same time,considering the nonlinear characteristics of APF,predictive control will be introduced to the controller design of APF.For current control strategy,through the establishment of cost function to evaluate the predicted value that need to control,choosing the switch states that can minimize the cost function of the predicted value to drive the inverter,which will get the minimum error.Aiming at the existence that the switch frequency of traditional direct power control is not fixed,while the model of existing predictive direct power control is not accurate,an improved predictive direct power control strategy with constant switching frequency is proposed in this article.The strategy uses a precise prediction algorithm to calculate the reference voltage vector,and use the space voltage vector pulse width modulation(SVPWM)strategy to track the reference voltage.The simulation results show that the improved strategy show a better static and dynamic performance.(3)The parameters of main circuit are designed based on the actual industrial power system.Adopting the PLECS that owns ideal switch characteristics,it is fast and efficient and robust.Hybrid programming with Matlab to make full use of its characteristics,which can make more close to the simulation results with the actual situation.