Research On Medium Frequency Cascaded H-bridge Rectifier For Aviation Applications

With the increase of the capacity of the aircraft systems and the load complexity of the equipments,the traditional energy,such as gas and hydraulic pressure,can not meets the needs of aviation developments.Multi-electric aircraft uses electricity as its secondary energy.It can effectively reduce environmental pollutions and improve energy utilization.Howerver,it asks for higher requirements,such as electric energy quality,power density and efficiency.Cascaded H-bridge rectifier improves the power factor of the system,reduces the voltage stress of the power devices,improves the overall equivalent switching frequency,and reduces the volume and weight of the capacitors and inductors.This paper studies the principle and control of cascaded H-bridge rectifier on the background of medium frequency aviation application.In this paper,the topology and mathematical model of the single-phase full-bridge voltage-type PWM rectifier and cascaded H-bridge rectifier are introduced at first.Then,it analyzes the principle of unipolar double-frequency carrier phase shifted SPWM,and how it increases the equivalent switching frequency.According to the particularity of aircraft electricity,all control methods are by means of analogy methods.Using 400 Hz as the fundamental frequency,the model of the system adopts doubleloop control.The cascaded H-bridge rectifier has dynamic performance and stable performance at the range of aviation medium frequency.Capacitor voltage balancing is the key problem of cascaded Hbridge rectifier.Based on the loss model,several factors causing the DC capacitor voltage unbalance are verified.Taking into account of the aviation analogy control mode,this paper presents three control strategies of capacitor voltage which base on active power or output voltage of each H-bridge unit.The range of load balancing for one of the control strategies is gived.Finally,simulation and an experimental prototype of a 3kW two units cascaded H-bridge rectifier verify the correctness of the theory.