Research On Control And Parallel Techniques For 400Hz Inverters

The 400Hz power supplies,as the important aircraft supporting equipments at airports and on ships,are required to provide large-capacity,high quality and reliable power.Therefore,it is significant to research the control and parrellel techniques for 400Hz inverters.In this thesis,the400Hz inverter based on T-NPC double-bridge topology is studied combined with theoretical analysis as well as simulation and experiment verification.The 400Hz inverter has higher output voltage harmonics in both low frequency band and high frequency band because of its high fundamental frequency.Firstly,the strategy to inhibit the low-frequency harmonics is studied.The paper analyzes the deadtime's effect on output waveform and points out that the dead-time effect is the key factor of increasing low-frequency odd harmonics.The inhibition method is put forward from perspective of control and circuit design.One method is using low-order harmonics resonant control to enhance the gain in low frequency band.Another method is decreasing switching frequency to reduce the impact of deadtime.However,the latter method increases the digital control delay and may lead to unstability.So the approaches which can reduce digital control delay are studied and a solution is proposed.The strategy to inhibit the high-frequency harmonics is also studied.A combination of passive damper and harmonic trap is used to optimize the LC filter which is commonly used in inverter.This paper points out that R_d-C_d damper can inhibit the resonant peak,ensure system's robustness as well as maintain the filter's damping capacity in high frequency band.The method of selecting damping parameters is put forward considering its damping effect and power loss.The harmonic traps can be classified into serial trap and parallel trap.The serial trap provides high impedance in switching frequency and can inhibit the high-frequency harmonics of both output voltage and inductor current.The design of LC_trap-LC-RC filter is presented in this paper.The parameters are selected and the stability of inverter with this filter is verified.Then,the parallel techniques for 400Hz inverter are studied in this paper.The principle of master-slave parallel control is introduced and the implementation scheme is presented based on DSP and CPLD control.In conventional master-slave parallel system,the reliability of system depends on the reliability of master module.So the master-slave parallel control is optimized by adding auto-selecting master fuction.This paper also analyzes the circulating current caused by difference between modules and communication delay when decreasing switching frequency and adding serial harmonic trap.The expression of circulating current of parallel system is derived and the factors that affect the fundamental circulating current and the high frequency circulating current are analyzed.Based on the analysis,it is found that the high-frequency circulating current can be reduced by adding a serial harmonic trap.At last,the model of 400Hz inverter based on T-NPC double bridge topology is established in MATLAB/Simulink and SABER and two 15kVA inverter modules are developed.The simulation and experiment results of single-phase operation and parallel operation are presented,which demonstrate the proposed control method and the correctness of the analysis.