Optimization Research On Medium Voltage Drives Based On Cascaded H Bridge

In recent years,multilevel conversion technology has become a research hotspot with the fast development of power electronic devices in medium voltage and high power situation.In multilevel technology families,diode clamped and flying capacitor firstly arise.But with increasing numbers of output levels,the number of semiconductor devices and the capacitors are increased rapidly.At the same time,the main control system and capacitor voltage balance control will be more complex and difficult to design.Therefore,these two topologies can only be used in low voltage systems.With the rapid development of the module integration of power circuit,the idea of series module is developed.In this paper,the main study object is the medium voltage drives based on cascaded mutilevel structure.There exist different kinds of cascaded power module,such as the traditional H bridge module,T-type module,diode clamped module and matrix converter module,etc..In this paper,the advantages and disadvantages of the medium voltage converter based on these four kinds of power module are analyzed.And the corresponding simulation results are given in MATLAB/Simulink.Finally,the most widely used cascaded multilevel H bridge topology is chosen as the research object in this paper.A optimization strategy is put forward to restrain the DC-link voltage ripple in the H bridge module with no affect exists in the medium voltage side current.This paper firstly analyzes the causes of DC link voltage ripple;secondly,the optimized control system of active front-end circuit based on three-phase PWM rectifier are analyzed and the fluctuation component of power module's output power is proposed to restrain the DC link voltage ripple;finally,the function of four quadrant operation is realized in the power module.In addition,this paper also gives the design of vector control system based on rotor flux orientation,and A simulation based on two quadrant cascaded H bridge topology is built to verify the speed adjusetment system.At the same time,another simulation based on four quadrant CHB-MVD is carried out to validate the feasibility of the optimization strategy and the function of four quadrant operation.