Study And Implementation On Key Technologies Of Micro-grid Synthetic Control

Microgrid has got increasingly attentions these years as it is an effective way to take advantages of renewable sources such as wind, solar and so on. However, a number of problems exists because of the complexity and variety of microgrid structure. This dissertation takes the demonstration project of the sea-island microgrid as the study subject, aiming at the key and difficult the problems of the microgrid. The main work of the dessertation is summerized as follows:Firstly, an integrated control and protection designing scheme based on three levels and two networks is proposed aiming at the demonstration project of microgrid. The structure of the three levels which are optimal control of substation, coordination control and protection, and local control and protection is illustrated to achieve security and stability of microgrid. On this basis, an application which is "the control strategy of black-start of multi PCS" has been illustrated. Lastly, the feasibility of the system structure proposed in this paper has been proved via simulation and field test.Secondly, control strategy of converter under steady state operation has been studied. In this dissertation, the s-domain model of converter controller has been build. At the same time, the problem that influence of the output current caused by both DC and AC bus voltage has been studied. To solve this problem, a current control strategy which contains proportional-integral as well as dual repetitive control (PI-DRC) is proposed to suppress harmonics of output current of two-stage PCS. In the end, the simulation and experiment has been done to prove the feasibility of the controller strategy proposed in this dissertation.Thirdly, the strategy of converter and loads under abnormal state has been studied. The characters of negative sequence of system voltage has been analyzed. Moreover, an improved control strategy based on droop control is proposed to solve the problems caused by voltage unbalance of microgrid. The feasibility of the method has been improved via simulation based on PSCAD. At the same time, a design method of abnormal voltage ride through of transducer has been introduced. In this part, a topological structure of triple CUK circuit in parallel is proposed to guarantee the constant of the rotate speed, torque, and output power of transducers during abnormal voltage occurs in microgrids. In the end, a prototype machine is produced to prove the effectiveness of the scheme.Finally, the study focuses on the problem of connection and disconnection of two sub-microgrid. In this part, the boundedness that caused by traditional droop control during the process of connection and disconnection of two sub-microgrid has been analysed. Aiming at the worse response performance and the lower control accuracy, an improved droop control strategy of δ-P-Q/V-P-Q is proposed. In additional, the control process based on the improved droop control has been introduced. At last, the effectiveness of the proposed method has been proved via simulation and field test.