Research On Medium Frequency Inverter And Harmonic Suppression Technique Of DC Bus

Due to the high output voltage frequency and small output filter, medium friquency power supply has a unique advantage in power density over power frequency inverter, so it is widely used in the area of aviation, vessels, casting and other special occasions. However, compared with power frequency inverter, the requierment of improving bandwith makes the controller, which can make medium frequency inverter achieve good output performance, more difficult. At the same time, as load of high voltage DC power system, the DC bus of inverter will be consisted of different kinds of harmonic currents, which will cause pollution to the DC system. Therefore, in order to reduce the damage of harmonic currents, harmonic suppression should be took into account when designing medium frequency inverter to ensure the entire power system safe and stable.Firstly, the input current of single phase inverter under unipolar SPWM modulation is deeply analyzed. The influence of modulation on harmonic currents and its loss are also analyzed. According to the characteristics of medium frequency inverter, the fullbridge topoiogy is selected as the main circuit structure. The small- signal model of main circuit is built and double closed-loop controllers based on instantaneous feedback is designed. For the adverse impact of phase leg caused by digtal control and output filter on medium frequency inverter, PR controller with phase lead correction in voltange control loop is introduced to improve the output performance. Simulation results show that the system is stable and responses fast.For the DC bus harmonic currents, a DC active power filter topology operating in staggered Boost-Buck is deeply studied, its harmonic suppression principle is analyzed in detail. With key parameters of the main circuit designed, the mathematical model of it is built. Finally, a compnesator for DC active power filter is built and the simulation based on it is also presented, the simulation results confirm the compensation effect of DC active power filter.Based on the above theoretical analysis and simulation verification, a 1kVA medium frequency inverter and a DC power active filter prototypes are produced, the DSP chip TMS320F28035 of Texas Instruments is used as systerm controller. The experimental results are in accordance with simulation results, which confirms the theoretical analysis and system design.