Research And Design Of DSTATCOM With LCL Filter Under Unbalanced Three-phase Voltage

In distribution network, the unbalance degree of the user terminal access point voltage is an important measure of the quality of distribution network power supply. The installation of DSTATCOM in distribution network is an effective way to reduce the voltage unbalance of the access point. In order to reduce the second pollution of the power distribution network caused by the switching harmonics, this paper uses the LCL type filter instead of the traditional L type filter. Aiming at the problem that traditional double positive and negative sequence current inner loop control strategy superimposed computationally intensive and LCL systems decoupling is difficult, this paper uses the phase control strategy based on the PR controller. Under three-phase unbalanced condition, the p-q method and the p qi-i method are difficult to detect the reactive power and negative sequence current. Therefore, this paper uses the positive sequence voltage synchronous transform generalized reactive current detection based on the scheme to solve this problem.The mathematical model of DSTATCOM type LCL based on PR controller is 5 order system, which makes it difficult to design the controller parameters. To solve this contradiction, a novel method is proposed which based on generalized reactive current detection scheme of positive sequence voltage synchronous transform, and also based on split phase control strategy of PR controller.The influence of system current loop made by capacitive feedback coefficient and PR controller parameters can be analyzed by frequency response analysis. System stability margin and compensation capability are chosen as indexes to design the value range of its parameters. Then, according to frequency characteristic, we can get the prioritization scheme of the parameter value selection, which conforms with actual operation. The method has the advantages of simple design and small computation. In the design process, it is not necessary to repeat the parameters to meet the performance indicators, which can ensure the system to operate stably in complex conditions, and has high compensation ability.In the Matlab/Simulink simulation environment, the test scheme, the control strategy and the parameter design method are verified by the reactive power compensation, load mutation and three-phase voltage unbalance. Compared to the traditional method, the proposed method is better in three-phase voltage unbalance experiment.A prototype of the experimental principle, which takes the DSP TMS320F2812 as the main control chip and the power as the 3kVA, is designed in the end. The traditional decoupling control strategy and the phase splitting control strategy based on PR are implemented in the prototype. The physical experiment results further demonstrate the effectiveness of the proposed control strategy and its parameter design method.