Research On Hybrid Microgrid Operation Control Strategy

Microgrid is a new form of power grid with distributed generations, energy storages, controllable loads and other units included, which can be connected to utility grid or operate independently to satisfy the needs of supply diversity and reliability of users. Regarded as a special form of microgrid, hybrid microgrid fully takes advantage of the feature of AC microgrid and DC microgrid, which can be supplied to both AC and DC loads as well as reduce the number of power converters so as to make the structure simpler and control more flexible.The operation control of hybrid microgrid is focused not only on the stability of voltage and frequency in AC microgrid, but also on the stability of voltage in DC microgrid and power balance in the whole system. Simple control strategies can not satisfy the control requirements in variety of operation conditions in hybrid microgrid. Therefore, a hierarchical control structure is proposed, which includes the local control, distributed coordination control and central control, based on the different time scales. The main contents of this paper are as follows.1) The development and research status of AC microgrid, DC microgrid and hybrid microgrid are analyzed in detail. Then, this paper focuses on the operation control of hybrid microgrid. Finally, the project background of this paper is well introduced.2) A small hybrid microgrid system is constructed in this paper. Then, the information of equipment and components in the electrical system is well introduced. At last, hybrid microgrid hierarchical control structure based on the different time scales is proposed in the constructed system.3) Local control strategy in AC microgrid is studied, which can mainly be divided into master-slave mode and peer to peer mode, including PQ control, V/f control and droop control. In the meanwhile, master-slave mode and peer to peer mode in DC microgrid are also researched. Then, local control strategies in hybrid microgrid are well introduced. Finally, the strategies are validated by simulations and experiments.4) A hybrid microgrid dual mode distributed control strategy is proposed in this paper which includes the free control mode as well as the forced control mode. First of all, the organizational mechanism, command generating mechanism and coordinating mechanism are well designed. Furthermore, the function applications are researched in different operating conditions, including smoothing tie-line power fluctuation, zeroing of tie-line power, optimal power allocation between energy storage systems and restoration of system state. Then the flexibility and engineering applicability of proposed control strategy in different operating conditions is validated through the experimental platform. At last, the influences of system topology, communication delay and stability are carefully analyzed.5) Hybrid microgrid operation control system is well designed in this chapter, including the design of communication and control system as well as energy management system. Firstly, based on EtherCAT bus, the communication and control system is constructed through CX8090 controllers, EtherCAT terminals and soft PLC based TwinCAT. Secondly, the energy management system is designed, in which the call relationship of software is introduced and the strategy of EMS based on the different time scales is proposed. Finally, the software of hybrid microgrid control system is well designed.