| With the increased use of power electronics devices,people’s life is more convenient.But these power electronic device is nonlinear,lots of harmonic inject into power grid.Those harmonic will reduce the quality of the electrical energy,increase the loss of transmission line,and reduce the life of the equipment.Because of the simple structure and low cost,the PF has been widely used.However,because of the poor dynamic performance,the PF falls into resonance with the power grid.While APF has a batter dynamic performance than PF.Unfortunately,the capacity of APF is low.Combining the advantages of APF and PF,HAPF not only has a good dynamic performance but also has large capacity.In fact,there are many problems remained to be solved in process of application.In this paper,we will focus on some problems for further research.The emphasis and achievement of the paper mainly manifested in the follows aspects:(1)The harmonic resonance prevention and compensation capabilities of the HAPF are investigated.The PF may fall into resonance when the operating conditions of the power grid change,which results in harmonic current application phenomena at the power system side.First of all,a single-phase harmonic circuit model of HAPF will be deduced and built.Base on this circuit model,the harmonic resonance prevention and compensation capabilities are analyzed when PF and HAPF are used.Then through the simulation results demonstrate that the resonance disappears when the HAPF is operated.What’s more,the filtering performance will be improved.(2)The impact of the filtering performance is analyzed when HAPF has delay.The delay is mainly divided into the detection process algorithm delay and digital control delay when HAPF is operating.During detecting harmonic currents,LPF is usually used to extract the fundamental current.However,the accuracy of the reference current will be reduced,because of the delay of LPF.To solve those problems,a tracking differentiator is used to compensate the delay.On the other hand,the delay caused in digital information processing will cause that the compensation and harmonic current can’t be synchronized.As for this problem,a modified repetitive control algorithm is used to solve it.(3)A new protection scheme is proposed to bring higher work efficiency and reliability.The compensation current will be boosted when the power grid fault occurs or the load suddenly increases,if the compensation current is more than the capacity of the converter,the converter will be damaged.However,the protection way is achieved by examining the compensation current,if the compensation current is more than the capacity of the converter,the APF will latch the pulse and quit operation.HAPF back into operation when the fault is removed.During this time,the system can’t compensate the harmonic current even if the fault is instantaneous.In this paper,a novel protection method is proposed,which can not only resist the disturbance of the power system,but also proportionally reduce the amplitude of compensation current.It is worth mentioning that the method has no impact on the system when the system is stable.(4)The validity of the method was verified through experiments.In this paper,an improved algorithm of detection is provided to advance the precision of compensation current.Then through the experiments the effectiveness of the proposed method is verified. |
