Power Conversion And Control Of Dual Energy Source Uninterruptible Power Supply

Nowadays,(Uninterruptible power supply) UPS has been widely used in critical loads such as IDC center, traffic hubs, precision manufacturing industry and so on. Diesel generator is generally used for realizing longer back up time. However a oil storage tank is necessary and the oil in the tank needs to be replaced with certain periods, which causes higher maintenance cost and emission pollution.In dual-energy-source (DES) UPS, diesel generator is replaced by natural gas (NG) generator. Since these two distinctive energy sources have the independent common infrastructures respectively, the configuration of dual energy source provides good redundancy in power supply and increases the reliability of the UPS system. The power conversion and control of DES UPS is studied in this paper.The development of UPS is introduced and the schemes of increasing the power supply reliability by adopting renewable energy and fuel cell are retrospected in the first chapter. Then the background and current research situation of NG generation is introduced. Finally, the configuration of DES UPS is introduced and its characteristics are presented.NG generator is inserted into DES UPS by AC/DC rectifier. So power conversion unit is the basis of the system operation. Power conversion unit and energy management scheme are designed in the second chapter. The output performance of a NG generator is analyzed by experimental results firstly. Then power conversion unit is designed based on the requirments in DES UPS. Aimed at the efficiency of converter, switching frequency and power device is selected. Then power circuit parameters, control scheme and protection are designed. Besides, allowed for the problem of cold start delay in NG generator, the energy management based on the cooperative control of generator and super-capacitor is presented. Load power is supported by super-capacitor during the cold start period, which achieves the uninterruptible power supply. UPS ought to guarantee sustained load power. So during the condition of grid failure, the energy transfer scheme is the premise of realizing redundant power supply. Energy transfer control scheme is investigated in the third chapter. The operation modes and the transfer conditons between different operation modes of DES UPS are analyzed fistly. Based on the energy management scheme, the seamless transfer control between grid operation mode and NG operation mode is designed. Uninterruptible load power is achieved both in power failure and power recovery during the process of mode transfer.The analysis and design are validated by the experiment on a lOkW DES UPS prototype.