Study On Multi-port Bi-directional Energy Router In Energy Internet

In recent years, new energy technologies and energy storage technologies have been developed rapidly with the increasing demand of the global electricity and the shortage of the traditional fossil fuels. However, the conventional grid and devices can not meet the variety of the electrical interfaces and multi-directional power flow, as the renewable energy generation, storage devices and uncertain loads like electric vehicles penetrate into the existing electrical grid. The concept of energy internet comes into being. In this thesis, energy router as the key component of energy internet is studied, focusing on its topology and coordinated control strategy.This thesis proposes a multi-port bi-directional energy router topology. This device mainly consists of high-voltage grid side converter port, low-voltage AC load port and low-voltage DC load port.The high-voltage grid side converter port is comprised of three-phase cascaded H-bridge converter and bi-directional isolated half-bridge DC/DC converter. The basic principles, control mode and power transmission characteristics of each port have been analyzed. Combined with the design objectives and simulation, the main circuit topology structure of energy router and the main parameters have been determined.In this thesis, decentralized autonomous control strategy of port converters is proposed. Without a centralized controller for real-time information collection and power allocation of each port, the multi-port energy router judges the internal system power flow and real-time energy balance by monitoring the relative changes of the DC bus voltage. On this basis, this thesis introduces the control strategies of each port in detail. The direct current decoupling control and three stage DC voltage stabilizing control are adopted for the cascade H-bridge converter. The DC/DC part utilizes phase shift control to ensure the dynamic balance of active power and maintain the DC bus voltage constant. For the AC and DC ports on the load side, constant voltage control strategies are utilized to provide standardized interfaces. Each converter can achieve full and bi-directional power control only according to its own port informations and the DC bus voltage. And finally, the energy router can achieve decentralized autonomous control and improve the reliability and availability of the whole device.A simulation model of multi-port energy router is constructed in PSCAD/EMTDC platform. Simulations and analyses on the start process, low-voltage ports with loads only, AC load port with extra PV, DC load port with extra PV and both load ports with extra PV conditions are conducted. The simulation results show that the multi-port energy router proposed in this thesis can realize the interconnection and energy bi-directional flow between different AC and DC standards and different voltage levels. It can provide standardized interfaces for the AC and DC load side. When the load side ports are connected with the distributed generation devices whose output power is large enough, the energy router can automatically realize the bi-directional power transmission between the high-voltage grid side converter port and the load side ports, and finally achieve plug and play.