Research On Control Strategy For Power Sharing And Power Quality Of Semi-Autonomous Distributed Compact Power Supply System

With the global energy and environmental issues facing unprecedented challenges, countries in the world are actively developing and utilizing the renewable energy resources to deal with the challenges. The modern power system is developing rapidly towards the distributed generation (DG) under the drive of future smart grid. Containing mainly the primary energy of clean energy and renewable energy, microgrid system as a new and special kind of distributed generation technology will play a key role in future smart grid, which has attracted more and more attention and has become a global hot research topic recently. It is the key technical issues that load power sharing among DGs and power quality issues are in the microgrid. Therefore, in this thesis, control strategies for power sharing and power quality problems of the micrgrid have been researched in-depth, which is of great and profound significance for the development and application of microgrid.1. The development status, trends and the latest research achievements of advanced control strategies and power quality control of distributed generation and microgrid technology are firstly introduced and reviewed. Then the definition and characteristics of the semi-autonomous distributed compact power supply system are given combined with the characteristics of the operation mode of microgrid in the future smart grid and the actual situation in our country. And in order to overcome the drawbacks of the conventional droop control applied in the low voltage microgrid, a modified droop control method is proposed with the consideration of voltage restoration, secondary frequency regulation and accurate power sharing, enhancing the performance of droop controller;2. Based on chapter 2 and with the consideration of nonlinearity and uncertainties of the inverter in the distributed generation system and the DC voltage uncertainty, the MIMO nonlinear uncertain model of the inverter system is modeled, which is strict parameter feedback form. Then the modified adaptive backstepping method is adopted to design the nonlinear voltage and current controller of the parallel inverter, enhancing the static and dynamic performance and robustness of the system;3. According to the actual situation of the distributed generation system, control strategy of operation and power sharing is proposed for the single-phase back-to-back converter (SPBTB) based hybrid compact power supply system which operates in the islanding mode. The independent operation of the three-phase and single-phase systems is also proposed. And then the study is focused on the control of load power sharing among phases for single-phase system in islanded mode. Finally, the methods both modified adaptive backstepping and sliding mode control are combined to design the controllers of the SPBTB system, and good results are obtained;4. Based on chapter 4, unbalance compensation and harmonic suppression strategy of the voltage at the point of common coupling (PCC) is proposed for the hybrid compact power supply system in grid connected mode which is connected to the utility grid through the fuel cell-based DG-powered back-to-back converter (BTB). The controller of the compensating DG converter is also designed. With the proposed method, the low bandwidth communication can be avoided as well as the sacrifice of other DGs’output power quality. This method can ensure the voltage quality at PCC;Finally, main concluding remarks are summarized and presented at the end of this thesis as well as some interesting problems which deserve further study.