Research On Island Microgrid Load Reduction Strategy

As a clear and sustainable energy,distributed power is widely applied to micro-grid. It can enhance the utilization efficiency of traditional energy. Meanwhile, it can make full use of various renewable energy sources. Combined with distributed power, load and energy conversion device, the micro-grid is a new type of gird with both interconnection and islanding. On the condition of islanding, unbalanced power may be caused because its capacity is small and its load demand is greater than the output of distributed power. And finally, that will cause decreased frequency, severely influencing the stability of system operation and the safety running of micro-grid. Consequently, corresponding load curtailment strategy should be developed. In case of power shortage in the islanding micro-grid, it is especially important that part of unconsidered load be curtailed in time,the main work of the dissertation is performed as follows:1. This thesis studies the basic principles and operating characteristics of photovoltaic cell, micro gas turbine and energy storage device (e.g. battery) of micro-grid. A mathematical model and PSCAD simulation model is established through equivalent circuit. On that basis, it analyzes the control methods adopted by various distributed powers in islanding micro-grid. The stable operation of islanding micro-grid can be guaranteed through P/Q control in photovoltaic cells and storage batteries as well as V/f control in micro gas turbines. Therefore, it lays a solid foundation for; the future verification of load curtailment strategy.2. It analyzes the advantages and disadvantages of the load curtailment strategy in the current islanding micro-grid. Because of the inaccuracy caused by power shortage method using frequency change rate and equivalent moment of inertia, an improved algorithm is proposed to enhance accuracy of the power shortage of micro-grid in this paper. To begin with, the load capacity to be curtailed for the first time is calculated according to the frequency change rate and the approximate equivalent moment of inertia of micro-gird.And then, the second load curtailment is conducted in line with the frequency change information from the micro-grid after the first time. As a result,safe and stable micro-grid operation can be achieved by two times of load curtailment. The improved algorithm can calculate the power shortage without depending on the accurate parameters of equivalent moment of inertia of micro-grid.3. In the simulation system of islanding micro-grid based on PSCAD/EMTDC platform, an analysis of simulation comparison is carried out in various load curtailment strategy. The result indicates the improved strategy can curtail partial load timely in case of power shortage in islanding micro-gird. In addition, it turns out to be more precise load curtailment, ensuring the rapid recovery of stable frequency to safe and stable operation of micro-grid.