Operating Characteristics Analysis And Control Strategy Research Of Microgrid Stability Controller

Microgrid, as an important form of utilization of renewable energy, taking advantage of the characteristics of renewable energy, such as dispersive distribution and variety of forms, manage the energy in one network, which greatly improves the efficiency and reliablity. Domestic and oversea research indicate the importance of energy storage in microgrid. Energy storage can control the power exchange with main grid by compensating the power fluctuation of renewable in grid-connected mode, and also can establish voltage and frequency for loads and distributed generator and maintain the steady operation of microgrid in islanding mode. The control performance of the energy storage-based inverter can influence the power quality of microgrid. This thesis conducts the thorough research on operating characteristics and control strategy of energy storage-based inverter which is named microgrid stability controller here.1、Based on the basic structure of microgrid and main topology of microgrid stability controller, mathematical model of microgrid stability controller in islanding mode is established. Three control strategies utilized in islanding mode when connecting with linear loads are compared, the results of simulation and experiment validate the correctness of the control strategy.2、Mathematical mode of microgrid stability controller in grid-connected mode is established, based on which control strategy and islanding detection method in ideal grid voltage condition are designed, the results of simulation and experiment verify the effectiveness of the control strategies.3、Control strategy of microgrid stability controller when connecting with nonlinear load in islanding mode is studied. The structure and drawback of repetitive control are analyzed, improved method is proposed, Finally the proposed method is validated by simulation and experiment results.4、Phase locked loop(PLL) method is analyzed under unbalanced grid voltage. Based on the mathematical mode of PLL under unbalanced voltage, new PLL method is proposed and verified by simulation and experiment results.5、Dual-PI control scheme in dq reference frame under unbalanced condition is analyzed, control strategy to eliminate the double-frequency ripple in active power and reactive power by employing rational reference current is proposed, repetitive control is used to improve the performance of control strategy. The results of simulation validate that the proposed method has better performance than dual-PI control scheme in dq reference frame.