Research On Microgrid PCC Power Quality Measurement And Control Technology

The current power system at home and abroad is the traditional distribution network based on centralized power, long distance transmission and distribution. Traditional network has the advantages of large capacity, high redundancy and strong stability; at the same time, the cost is high and it is difficult to operate, the power supply lacks of diversity, especially when the electric energy quality of emergency emerges, it is possible to appear cascading failure etc. In contrast, the micro-grid can meet the diversity needed of electricity and improve power quality. Especially when the power fails, micro grid enters into the island-state operation and supplies continuous power to local areas, thereby reducing the blackout area. In view of this, the combination of grid and the traditional distribution network can be more effective for the user to use electricity.There will be two ways of supplying energy to the loads when micro grid combines to the power grid. On one condition, both the micro grid and power grid supply the power needed by the loads; on the other condition, micro grid not only offers the power the load need but also the extra energy to the traditional power grid. As for the latter, the power quality issues of the point of common coupling falls on the side of micro grid. When micro grid is off-grid, power system sends the energy to the load, the power quality issues falls on the power system side. According to the second condition, this paper studies the power quality issues of the point of common coupling during the course of wind generating sets separate from the power system.To the power quality caused during the course of withdrawing the wind generating sets from the power grid, using four-leg active power filter to solve the question of power quality caused by nonlinear load of three-phase four wires as the background, under the environment of MATLAB-Simulink, a main circuit and control circuit is proposed, which is made up of device components from SimPowerSystem libraries and adopts the model of Fcn to program to fulfill the detecting algorithm of the current instruction and sets up a dynamic and real-time simulation model of four-leg active power filter. Based on this, an algorithm of real-time detecting harmonic current based on improved instantaneous active current and reactive current theory is studied, firstly, remove the zero sequence of the three phase current and then get rid of the fundamental active current by the mean method of dynamic timer window so as to obtain the compensation instructions of the harmonic current.Besides, this paper also compensates the neutral line current based on the fact that the national electric power industry ministry issued by the transformer operation rules regulation, the running transformer line current shall not exceed25%of the rated current transformer of low voltage side.To the power quality caused during the course of withdrawing the wind generating sets from the power grid, the simulation result shows that the detective algorithm of the harmonic current of nonlinear load of the four-leg active power filter is correct.