Electronic Power Transformer & Its Application To Transmission System

Electronic Power Transformer (EPT) based on power electronic conversion is a new type of transformer, which aims at the voltage regulation and power transmission of power net. Compared with traditional transformer, EPT has a lot of advantages. A significant advantage is that the voltage of the primary side, the current of the second side and the power of both sides can be flexibly controlled. With EPT applied to power system, firstly the power quality and the power system stability can be improved. Then, the flexible transmission mode and the power flows control in real-time are possible. Furthermore, a variety of distributed power resources can expect to be conformed. Thus, the researches on EPT are significant for the Green & Digital Grid construction. The basic theory and the present state of EPT are introduced in this paper. Then, by comparing and analyzing the existing topologies, a new one with three-stages of EPT is proposed, in which the input, isolation and output stages are included. The undertake voltage of input stage is improved with the cascade multilevel modules, and their redundancy has greater flexibility to system design and harmonic can be reduced greatly. The cascade topology is expected to hold stronger voltage-sharing ability in theory, and experiments confirm it, furthermore, each module has good voltage and current waveform. All of the above show the feasibility of EPT's new topology. For Pulse Width Modulation (PWM) technique applied to rectify modules of Input stage, power flowing in both directions can be realized. The basis theory and characteristics of PWM rectifier are analyzed firstly, then, the mathematic model of EPT is deduced. At last, the current control strategies of PWM rectifier are proposed in this paper, the input power factor of EPT can be adjusted from 0 to 1 in theory. Simulation results confirm the control strategy's efficiency. The snubbers of power devices, the lightening protection and heat sinks selection of EPT are discussed in this paper. At last, this paper concentrates on EPT's application to power system and the co-control between EPT and power system. Simulation results show that EPT can effectively improve the stability and performance of power system.