The Study Of Motor Starting Effects And The Countermeasures To Improve The Power Quality In Islanded Micro-grid

With the intensification of energy crisis and air pollution, promoting energy conservation and developing clean energy sources achieve more attentions all over the world. So micro-grid, an ideal means of making full use of new energy utilization, will be widely used in the near future. Also, the micro-grid can make up for the shortcomings of the traditional large power supply, and be of great meaning to develop electrical energy market. But at present, the micro-grid technology is relatively immature, which affects its application. For a mature micro-grid, high power quality is one of its characteristics. Based on the previous studies, this paper analyzed the power quality problems brought by the starting of motor in the islanded micro-grid, and gave some strategies to improve the power quality.Firstly, the control strategies of the energy storages were improved to avoid the voltage decline when the motor starts. In the islanded micro-grid, the voltage and frequency levels are supported by the energy storage, which is of great difference from the grid-connected mode. So the islanded micro-grid is more susceptible to the load disturbances. The motor is one of unavoidable load types in the islanded micro-grid. But the motor needs large power during it starts, which may lead to the drop of voltage and frequency. By comparing of the characteristics of various energy storage elements, this paper identified the mating scheme of batteries and super capacitors. And by improving the control strategy of the super capacitors, the impulse power brought by the motor can be compensated timely, which means the drop of voltage can be avoided. At last, the simulation in Matlab/Simulink environment verifies that these control strategies are effective to improve the power quality.Secondly, combined with the characteristics of the islanded micro-grid, a new control method of the active power filter(APF) is proposed to compensate harmonic. The soft start equipment is used to deal with the motor impulse power furtherly but it causes harmonic pollution in the micro-grid. It is necessary to adopt advanced harmonic governance programs to coped with these harmonics. By comparing of the APF and traditional passive filter, this paper determined the use of APF with inverter program. By improving control algorithm of the APF, the shortcomings of the traditional APF in terms of voltage imbalance are made up, which increases its applicability in islanded micro-grid. Then the improving control algorithm simplifies the calculation of the command signal, thus the new APF works more efficiently. Also The improved control algorithm bases on compensating the harmonic according to different harmonic orders,which strengthens the stability of the new APF. Through simulation in Matlab/Simulink environment, the excellent performance of the new APF in improving power quality wasproven.