Research On Control Strategy Of Inverters Under Grid Faults

With the advancement of high-power switching devices and digital signal processor technology, all kinds of distributed generation system is widely used and development which makes up for the shortcomings of the traditional power energy. Actually,grid is not ideal and it is a dynamic and complex system. In order to guarantee the distributed power generation systems under the condition of power grid failure to maintain normal grid work but also to ensure the quality of electric energy, inverters must be required to ensure the quality of injected into power grid electricity under the condition of unbalanced power grid failure, not to take off in the power grid voltage drop failure of network, and to restrain instantaneous large current shock occurs, protecting device from being damaged. So in this paper, the inverter grid control strategy of the power grid failure is studied thoroughly.(1) Studying and analyzing voltage vector which under a grid failure. Studying and analyzing positive sequence, negative sequence and zero sequence component extraction algorithms when grid voltage unbalance fault occurs, which provides the reference for the improvement of single synchronous coordinate system control structure discussed in the third chapter; Studying the classification of the voltage and derived when power grid voltage drop failures occur, which laying the ground for the low voltage through the control algorithm of the fourth chapter and simplifying the analysis of the control strategy.(2) Analyzing grid-connected inverter control strategy under the unbalanced power grid failure. Firstly modeling and analyzing for the grid-connected inverter under ideal conditions, which leads to impacts on the traditional single synchronous inverter control structure coordinates under the power grid voltage unbalance condition, meanwhile it is concluded that the traditional single synchronous frame PI controller structure can not track the positive sequence and negative sequence components at the same time, so shocks of the twice fundamental frequency occur; And then based on this conclusion, and raising the double synchronous frame PI control structure that can adapt to unbalanced power grid failure and eliminate the influence of twice the fundamental frequency of the oscillation; Finally according to different control objectives and user needs, putting forward the different control strategy, in order to meet the requirements of injection grid current balance or power balance, meanwhile simulating and verifying the effectiveness of the theoretical analysis.(3) Studying and analyzing the low voltage through the control algorithm under grid voltage drop failure. Studying and analyzing controlling difficulties of grid-connected inverter under grid voltage drop failures, at the same time, putting forward the control strategy. Detecting the state and drop depth of the grid voltage according to the instantaneous value of dv+ which is obtained by double synchronous coordinate decoupling phase-locked loop. Besides, assigning and controlling reasonably the injection power grid power during the power grid voltage drops, to prevent the flow; Proposing the instantaneous feed-forward control strategy to restrain large current shock when power grid voltage drops instantly; Getting the inevitability of current shock and the effectiveness of the instantaneous feed forward control by the theoretical analysis; Verifying the effectiveness of the low voltage control algorithm by simulation experiment. Conducting low voltage ride through experiments on 50 k W dc inverter device at inverter commissioning area which belongs to the Dongfang electric automatic control co., LTD. Besides, it not only passed project certification and acceptance, but also completed the experiment of the zero voltage through.