Research On The Improvement Of Power Quality Of Distribution Network Based On LCL Type D-STATCOM

Nowadays,under the background of energy policy such as"environmental protection"and"renewable energy use",how to produce electricity,transmit electricity and use electricity cleanly and environmentally-friendly has become a hot topic.There are various kinds of power quality problems in the distribution network.Compared with other power equipments,D-STATCOM device has the remarkable advantages of fast dynamic response and so on.Therefore,this dissertation uses D-STATCOM device to finish the adjustment of the reactive power,the harmonic suppression and the compensation of three-phase unbalance,so as to improve the power quality of the distribution network.The specific content of the work is as follows:(1)This dissertation establishes the mathematical model of D-STATCOM based on LCL filter.(2)The performance of LCL filter is analyzed,and LCL filter is compared with L filter.It is concluded that LCL filter has better inhibition effect on high-frequency harmonic current under the condition of the same total inductance.In order to suppress the system resonance generated by LCL filter,the passive damping method and the active damping method is analyzed,and the passive damping method of capacitor branch series resistance is finally selected.The parameters of LCL filter are designed,and the effect of each parameter for the performance of the system is analyzed.The simulation in Matlab shows that when the total inductance value is the same,LCL filter has stronger suppression ability for harmonic current in high frequency compared with L filter.(3)This dissertation focuses on the control strategy of D-STATCOM based on LCL.The double-closed loop PI control method is designed.Aimed at the problems such as the unreasonable method of error generation caused by PID controller,this dissertation proposed ADRC technology(Active Disturbance Rejection Control,ADRC)to improve it,and aimed at the defects of complex adjustment and setting caused by ADRC controller,Linear Active Disturbance Rejection Controllor(LADRC)is finally used to design the current inner loop of D-STATCOM.And the tuning method of its parameters is given.The simulation shows LADRC controller used in the current inner loop can enhance the rapidity and robustness of the system response.The h harmonic compensation term is superimposed on the quasi-PR controller to form the multiple harmonic quasi-PR controller,and it is applied to the current inner loop of power grid,to utilize the characteristic of the infinite gain at the resonant frequency,to compensate emphatically the low order harmonic in the distribution network.The simulation shows that the current inner loop adopted multiple harmonic quasi-PR controller can obviously improve the tracking precision of the compensation current.In order to improve the rapidity and robustness of the system,LADRC controller is finally selected to control D-STATCOM based on LCL in this dissertation,so as to improve the power quality of the distribution network.(4)The operation state of D-STATCOM under unbalanced condition is analyzed.A detection method of i_p-i_q reactive power and harmonic current without phase-locked loop is proposed to detect the output compensation current under unbalanced condition,so as to improve the dynamic response speed of the system.The simulation shows that when LADRC control mode is used,D-STATCOM based on LCL can compensate reactive current,harmonic current and negative-sequence current in distribution network at the same time,so as to effectively improve the power quality of distribution network.And the i_p-i_q reactive power and harmonic current detection method without PLL has obvious effect for improving the dynamic response speed of the system.