Simulation Study On Micro-grid Power Inverter Control System Based On Fuzzy Control Strategy

At present, power system accident has already brought huge impact to the safe and stable operation of large power grid, the UHV power grid has developed a lot to interconnect power optimal allocation of resources, meanwhile, as a useful complement of the large power grid, the micro-grid has become an important supplementary for most of the countries to solve the security and reliability problems in power system, it has a very practical significance to manage and accept new energy in shape of micro-grid. But people found that it is difficult to coordinate safe and stable operation between micro-grid and the large power grid, especially when the micro-grid has power system fault, it may brought greater impact to the large power grid, therefore, it is particularly important to design accurate and effective control system. Based on the research of micro-grid, PQ control strategy and V/f control strategy have been discussed in detail, meanwhile the control strategies of different structure and different operation mode of the micro-grid has been supplied in reason. The detailed researches are as follows:(1) The working principles of PQ control and V/f control have been introduced preliminarily. In the PQ control mode, the voltage and frequency of micro-grid is supplied by large power grid to maintain stable operation, micro-grid only need to delivery or absorb active power and reactive power follow the instructions to complementary shortfall with the large power grid; in the V/f control mode, the voltage and frequency of micro-grid is not supplied by large power grid any more, based on P-f、Q-U droop characteristic, the micro-source supply reference voltage and frequency of its own after get the output power of every micro-source, then adjust the voltage and frequency in turn. The mathematical mode of micro-source has been established, because micro-source is mainly distribute power, it is uncontrollable for the large power grid, so the micro-source is accessed by the power electronic devices generally, through the control of electronic devices, to realize the control of micro-source. Three-phase full-bridge voltage inverter has been applied in the paper.(2) The PQ control system has been designed, include two core part mainly, the current calculation module and current regulator, considering about the stability and accuracy, PI controller has been applied in the paper as the current regulator. The parameter is obtained by pole placement method, and the mode of the control system has been established and simulated in MATLAB/Simulink. The simulation result shows:the designed controller satisfied the dynamic performance. At last, simulate against the situation of single micro-source with load, the result shows:under the premise of stable voltage and frequency, when load changed, the designed micro-grid PQ control system can supply constant power to large power grid.(3) The V/f control system has been designed, include three core part mainly, the power calculation module、the droop module and the voltage and current control module. In the voltage and current controller design, the paper take two different method:PID single-loop feedback and double-loop PI feedback, The parameter is still obtained by pole placement method. The two modes of the control systems have been established and simulated in MATLAB/Simulink. The simulation result shows:the dynamic performance of double-loop PI feedback is better than PID single-loop feedback. At last, simulate against the situation of single micro-source with load, the result shows: when load changed, the designed controller can make the micro-grid restoration the voltage and frequency of its own, thus to maintain the stable operation.(4) The PI controller is taken in both PQ control system and V/f control system, in order to get better effect, the paper introduce fuzzy PI controller to replace the traditional PI controller further. The PQ control system mode and the V/f control system mode which based on FPI are established in MATLAB/Simulink. The simulation result shows:the dynamic performance and static performance of FPI is better than traditional PI controller.