Research On Power Quality Control Strategy In Low Voltage Microgrid

As an important part of the smart grid and energy internet in third industrial revolution,Microgrid technology combined different types of distributed generation, enhanced thereliability and flexibility of the power supply and reduced the pollution of the environment, ithas attracted much attention both at home and abroad in recent years. But Microgrid closes tothe user, belongs to distribution network, its voltage level is low and the capacity of thedistributed generation is small, so as to its stable operation easily affected by the disturbanceof the system or the load, one solution to the problem is designing reasonable control strategyto provide high-quality electricity for users. Good control strategy not only can make the newenergy and renewable energy generation effectively used, also can realize the optimaleconomic operation inside the microgrid, ensure the power quality and maximize the value ofMicrogrid at the same time. Therefore, in-depth study on the control strategy of Microgridpower quality has vital significance.First, this paper elaborated the research background, significance and related concepts ofMicrogrid and analyzed the overseas and domestic research status of Microgrid, the types ofthe power quality control strategy of Microgrid and the applicable occasions of each strategy,among them the hierarchical control strategy contains upper Microgrid central controller withthe under droop control, combined the advantages of various control strategies, has goodprospects for development. Then analyzed the key technologies of the Microgrid powerquality control strategy, mainly including the mathematical model of inverters, space vectormodulation (SVPWM) algorithm, the phase lock loop (PLL) technique, etc.In view of thegeneral droop control is highly dependent on the line resistance, which is difficult to realizethe effective control of power quality in low voltage microgrid as the line resistance is oftenresistive or resistor-inductance. Based on the general droop control theory, this paperproposed an universal PQ-fV power coupling droop control method and designed a modifiedPQ-fV multi-loop control strategy by combining the upper energy optimization managementand introducing the Proportional Complex Integral (PCI) voltage control technology. Thiscontrol strategy not only can achieve flexible and effective control of power quality in lowvoltage microgrid with resistor-inductance characteristic and is suitable for both grid andisland operation mode, meanwhile it can also fast track reference instructions given by the upper energy management system and realize the reasonable distribution of the distributedgeneration output power.Taking the two parellel grid-connected inverters as an example, builed up the simulationmodel of Microgrid power quality control strategy mentioned above in Matlab/Simulink, andcompared with the conventional droop control with PI adjust, the results analysis show thesuperiority of the improved droop control strategy proposed in this paper.