Font Size: a A A

Research On Operation And Coordination Control Strategy Of Microgrids

Posted on:2016-04-02Degree:MasterType:Thesis
Country:ChinaCandidate:C ZhuangFull Text:PDF
GTID:2272330479984649Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
With the growing electricity demand of human society, the requirement of power supply reliability and power quality from consumers also increase continually. But the traditional energy structure and power system still need much improvement in aspect of safety, reliability and flexibility. In the meantime, we would also face the gradual occurrence of environment crisis and the increasing severity of global energy situation. In recent years, people have done much research and exploration in distributed generation technology including new energy with some progress. And the rapid development of microgrids is acting as a key role in integrating multiple distributed resources. It can not only make full use of new energy, but also improve power supply reliability and power quality by flexible and varied control strategy. So the research of microgrids is becoming a hot spot in power system. Microgrids is a small power system including distributed resources, energy storing devices and load. It can operate both in grid-connected and islanded mode. With its different characteristics from traditional grid, the operation and coordination control of microgrids is one of its key technologies, which is an important premise for microgrids to play its own advantages.This paper gives a brief introduction about the occurrence and definition of microgrids, and classify the main coordination control methods. Three main control strategies of DG inverter have been researched: PQ control, V/f control and droop control. PQ control which are mostly used in grid-connected mode has been briefly introduced. Voltage and current double loop feedback structure is constructed in the part of V/f control. The theory of P-ω, Q-V control has been paid much attention. Coordination control theory of voltage, frequency and power between parallel DGs in microgrids has been introduced. SPWM basic theory is presented. SPLL is used to detect phase with its modeling presented. In the modeling of droop controller, power calculation module is built with measured voltage and current. Droop coefficient calculated basis are presented with reference of DG capacity. At last, droop control module are built based on droop curve in Matlab/Simulink.Steady-state error exists in reactive power sharing due to the line impedance mismatch between distributed generation units. Meanwhile voltage and frequency deviation problem caused by droop control also exists in islanded microgrids system. This paper proposed an improved droop control strategy with frequency autonomous restorable regulation based on the analyze of parallel inverters power sharing and droop deviation mechanism. Reactive power coordination sharing problem is improved by adding redesigned virtual impedance loop. Frequency autonomous restoration control loop is added to ensure that frequency can restore to nominal value autonomously. The simulation results demonstrate the effectiveness of the proposed control strategy.Finally, to the unsolved error of reactive power sharing, an improved power sharing strategy is proposed. A redesigned method of Q-V droop control is presented. Power coordination sharing problem is solved by adding a reactive power error integral term. Grid synchronization control of islanded microgrid is built with system small signal model. Stability of the control system adopting improved power sharing and grid synchronization strategy is analyzed.. The simulation results show good performance of power sharing, smooth and stable transient process of grid synchronization. Coordination control and grid synchronization process of DG parallel inverters perform well under islanded mode.
Keywords/Search Tags:Islanded microgrid, Droop control, Virtual impedance loop, Frequency autonomous restoration control, Improved power sharing, Grid synchronization control
PDF Full Text Request
Related items