The Research Of Microgrid Operation And Control Strategies

Microgrid is a relatively small power grid compared to traditional power grid that has a great variety of devices. Microgrid can operate in grid-connected mode or islanded mode under external power grid failure. No matter in which mode, the operation control goal of microgrid is to guaranteethe stability of the system. Then its operation economic efficiency is sufficiently considered. This thesis concentrates on distributed energy resources (DERs) modeling, design of inverter current loop and microgrid control strategies. The main contents are as follows:Firstly,according to mathematic models of photovoltaic generation, microturbine generation and battery energy storage system, their simulation models have been developed in PSCAD/EMTDC.Secondly, as the link between microsource and grid, the good design of inverter can not only guarantee microgrid power output, but also play a very important role in the micro grid operation. A mathematical model of inverter output is established in this paper and the current control loop is deduced on the d-q rotating coordinate system. Making full use of the characteristics of coupling terms,an improved function coupling method is proposed. The quality of the inverter modulating voltage wave-form can be improved by adjusting the proportion of the feedback current and the reference current.Then, the three parts of microgrid energy management system are introduced. The master-slave control mode and peer-to-peer control mode are closely compared. The improved current controller is applied to three typical control methods, active and reactive power control, voltage and frequency control, droop control. A new islanding detection method is put forward. Frequency deviation is caused by a small reactive power margin between micro source output and load consumption.Finally, a microgrid simulation system in master-slave control mode is created based on the improved current controller. The simulation results show that the microgrid in grid-connected mode and isolated mode can operate well and the switching process is smoothly. The micro-grid model is available and efficient in describing the dynamic and static characteristics of the power resources. The voltage waveform comparison of the original and improved current controller show that the latter controller can reduce the harmonics and has better voltage waveform. The islanding detection method utilizing a small reactive power margin is proved efficiently in microturbine generation system simulation.