Research On Power Control And Power Quality Improvement Of Micro-grid

As the world’s energy problems become more and more serious, and the development of distributed power generation(DG) technology, a large number of distributed energy generation that is connecting to the power grid cause a series of problems. The problem of the power generation and consumption of DG can be solved by Micro-grid. Also, it could improve the performance of distributed power generation. Therefore, it is practically significant to research on power control and power quality of Micro-grid.In the thesis, the photovoltaic(PV) Micro-grid of a university is the prototype of the simulation which is modeling on the Matlab/Simulink. Besides, the power control strategies of Micro-grid and its power quality issues are lucubrated in the thesis. The main contents are as follows:Firstly, the photovoltaic array is modeled in detail which is controlled by incremental conductance method of maximum power point tracing(MPPT) The study mainly focus on its output characteristics from different temperatures and solar irradiancy.Secondly, the strategy of PQ control which is accomplished by dual-loop control, an inner current-loop and an outer power-loop control, is applied in two kinds of working conditions of balanced and unbalanced three-phase voltage respectively to study its control characteristics. Also, the strategy of V/f control which is carried out by voltage and current double-loop control is taken advantage to Micro-grid in island mode to learn its control performance. Moreover, the strategy of Droop control which is achieved by three-loop control, an inner current-loop, a middle voltage-loop and an outer power-loop control, is putted into the operating conditions of commissioning/resecting load in Micro-grid in island mode Micro-grid in grid mode and in island mode respectively and the operating conditions of operation modes of Micro-grid switched to each other to study its control characteristics. The results of the simulations testified the validity of the three kinds of strategy.Thirdly, a model of Micro-grid with many DGs is established. Strategies of master-slave control and peer-to-peer control are utilized into this Micro-grid to control its active power and reactive power. Especially, importance is attached to study the characteristics of the control strategies, when they are applying to the working stations of Micro-grid switched the operation modes to each other and the working stations of commissioning/resecting load in Micro-grid of island mode. The simulation results justified that the two strategies can coordinate DGs to share the total power production. Also, combined with actual situation, the strategy of master-slave control is adopted as the control strategy of the Micro-grid through the comparison.Finally, aiming at power quality of Micro-grid, the harmonic is mainly analyzed. An alternate classification of the nonlinear load is presented, which classify the nonlinear load into three categories: the voltage source type, the current source type, and the complex source type.Harmonic current from three kinds of nonlinear load is detected by the ip-iq method of the theory of instantaneous power, and removed by APF. Besides, to limit the amplification of load harmonic current, and to improve the APF compensation characteristics, a method, using series inductance in AC side of the load to increase impedance ratio, is putted forward. The validity of the method has been proved through the simulation, and it improves the power quality of the Micro-grid.