Research On Microgrid Control And Power Quality Improvement

Microgrid is a kind of system composed of the distributed generators (DGs) andloads, which can be used to weaken the negative effects of DGs and give full play ofDGs. This paper makes researches on microgrid control strategy, power quality andnetwork configuration with distributed generation which is accessed to the network inthe form of microgrid. The main achievements are as follows:1. The most popular microgrid control strategies are analyzed, and the droopcontrol is improved based on the analysis. The setting theory of droop coefficients ispresented firstly. And then the droop control strategy is improved by adding penaltyvalue to force DG to change its droop characteristics to vertical characteristics whenthe power output overruns its limit, which is consistent with the DG actual operation.Finally to eliminate the harmonics and get better control performance, filters areadopted to active power, reactive power and voltage control blocks.2. Based on the different types of Microsources, the interfaces of the microsourcescould be divided into two types: voltage source inverter (VSI) interface andSynchronous generator interface. This paper proposes the control strategy ofMicrogrid which contains the two interfaces. For VSI interface, the set rules ofexternal inductance value is presented and the gate pulse generator control block isdesigned based on the improved droop control and space vector modulation theory,which can be as theoretical guide for future VSI practical use. From the network pointof view，the inverter can be represented by an ideal and balanced voltage source withonly the fundamental component in simulation. The output of improved droop controlcan be as the input of the controlled voltage sources block, therefore the whole controlstrategy of VSI interface is achieved in simulation.For SG interface, the angular velocity output from the improved control strategyand the measured angular velocity are as the input of the equivalent speed controlsystem to output the desired mechanical active power, and the voltage amplitudeoutput from the improved control strategy and the measured voltage amplitude are asthe input of the equivalent field system to output the desired field voltage. The desiredmechanical active power and field voltage can be as the input of SG to make thegenerator operate smoothly.Static switch is designed to make the microgrid only connect with the grid whentheir voltages are closely with the same frequency and amplitude. The simulationresults testify the effectiveness of the proposed control strategy and SS. 3. This paper analyzes the power quality problems of microgrid. For harmonicscaused by electronic devices and voltage variation caused by high reactive powerrequirement, a combined system constructed by SVC and SAPF is proposed based oneconomy and compensation performance, in which SAPF is adopted near themicrosource to mitigate harmonic currents and SVC near the load to compensatereactive power so as to relieve the voltage variation. To avoid coupling, the control ofSVC and SAPF are independent. To get better tracking performance, the repetitivecontrol and PI control combined together are applied to APF control.4. When the DG is used in the form of microgrid, it can be equivalent as a negativeload node. Distribution network reconfiguration model containing DGs andconsidering three running modes is established. Binary particle swarm optimizationalgorithm (BPSO) with dynamic inertia weight adaptation strategy is applied to solvethis model. Case results justify that the improved BPSO can solve distributionnetwork reconfiguration effectively with better results which can be used to guidedistribution networks operation.