Research On The Voltage Control And Reactive Power Sharing Strategys In Microgrids

The aggravation of global energy crisis and environmental problem boost the booming of renewable energy sources (RES). Microgrid technology with flexible operation modes emerges to balance the conflict between power grid and distributed generations (DGs) and take the most advantage of the benefits brought by DGs to the power system and the users. Based on the introduction and analysis of research status of Microgrid coordinate control, the thesis studies voltage control and reactive power allocation problem belonging to the coordinate control of microgrid, toward single source microgrid, milti-source microgrid and milti-icrogrid system apparently. The main content of this thesis is as follows:Firstly, three kinds of common control strategy, which are PQ control. V/f control and droop control is introduced for inverter-based grid-connected micro source; voltage-var control method is analyzed for microgrid under typical operation mode (including peer to peer and master-slave mode). The feature and existing methods for reactive power regulation is introduced from two aspects of single source and multi-source coordination. Reactive power control strategy for multi-source coordination therein is divided into two classes, namely communication-based way and communication-less way, of each way the advantages and disadvantages are compared.Then, on the level of single grid-connected micro-source voltage-var control, methods are presented from two aspect taking photovoltaic power generation systems as example.existing control strategy is analyzed and a modified voltage control method for grid-connected micro-source is proposed, having the capability to limit voltage rise caused by active power output of Photovoltaic power generation, and of dynamic reactive power support, from the aspect of improving control strategy; from the aspect of improving topology, a grid-connected micro-source topology with reactive power compensation and voltage regulation is designed, an inverter dynamic remain capacity based reactive power allocation strategy is proposed and control algorithm for both paralleled inverters and series-connected inverters is designed. Both of the aforementioned improvement approaches are simulated and validated by PSCAD/EMTDC.In the next parts, paralleled multi-sources voltage-var drooping characteristic is analyzed and a drooping control tactic based on hybrid/compound virtual impedance and self-adaptive drooping coefficients, by adding feedbacks of active power and reactive power output into drooping coefficients. The proposed method is able to increase the reactive power allocation accuracy among micro-sources and reduce voltage deviation. The result of small signal analysis and time domain simulation show that the proposed method features high stability and accuracy.Lastly, aspect to multi-microgrid system coordinate control rely on communication, power limitation and allocation among multi-microgrid is realized by MMGCC, an Online Control Policies based on Voltage Sensitivity Analysis for micro-source inside multi mircogrid system is proposed, which can accomplish online voltage regulation. The automated generation control (AGC) optimization mode for micro-sources is establish and solved by an enhanced immune bimodal particle swarm algorithm. The proposed policy and algorithm is simulated and validated by matlab-PSCAD combined platform toward a real case.