The Research On The Efficiency Optimization Control Of Modular Power Electronic Transformer

Due to the active promotion of the national energy development strategy,the renewable energy has rapidly and comprehensively developed,the high-penetrated renewable energy brings new challenges and requirements to power grid in efficiency,security and sustainability.At present,a lot of renewable energy access to AC distribution network,but it has many AC/DC conversion,which reduces efficiency and affects the convenience of system,and traditional distribution network has insufficient active control capability,which limits the renewable energy in consumption and efficient use.The AC/DC hybrid system has become a new development trend based on power electronic transformer,which can achieve voltage conversion like the traditional transformer,but also can regulate the voltage,current and the power flow of the distribution grid rapidly and the function of intelligent management.This paper based on the modular cascaded power electronic transformer,which is widely used in resent years,and take the operation efficiency of power electronic transformer in AC/DC hybrid distribution network as the research content.the efficiency optimization of power electronic transformer under different operating conditions is studied.Firstly,the topology structure and working principle of the cascaded H-bridge of the modular cascaded power electronic transformer are analyzed in detail,and describe the implementation form of the hybrid modulation technology adopted in the pre-stage cascaded H-bridge circuit in detail.The topology of the isolated bidirectional DC/DC converter and the operation principle under single phase shift control are described,at the same time the loss models of the H-bridge module and the isolated bidirectional DC/DC converter are analyzed detailedly.Then,for the power electronic transformer which is used in the AC-DC hybrid distribution network under light load operation,and the feasibility of power optimization allocation is verified by experimental data,combining the output characteristics of cascaded H-bridge circuit with hybrid pulse width modulation,an active power unbalanced control strategy is proposed.In this paper,an active power unbalanced control strategy is proposed,which reduces system loss compared to traditional power equalization control.For the condition that the power electronic transformer in high-power operation,a fixed rotation hybrid PWM algorithm is proposed,which can reduce the switching loss of the system and ensure the balanced output of each power unit.Finally,a modular cascaded power electronic transformer experimental platform is developed to verify the efficiency optimization control method.The experimental results show that in different load condition,the proposed active power unbalanced control strategy and fixed rotation hybrid PWM algorithm can effectively improve the system efficiency,they are simple and easy to implement.