Study Of A Novel Cascade Inverter Topology And Application Based On PSM Technology

With the emergence of the high-power electronic devices, power electronic equipment has been widely used in power system. Traditional inverter topology cannot be directly in parallel with the power system and the quality of its output voltage is low so that its application in power system is limited. But the cascaded multilevel inverter has high quality of its output voltage. It distributes the grid voltage evenly to each power device through the cascade so that these power devices can be directly connected with the grid when their pressure values are fixed. A sufficient number of power semiconductor devices are needed in the inverter to achieve shunt connection with the grid which has very high voltage level and significant challenges are brought to the control strategy. By adopting SVPWM control strategy, the output voltage of the inverter has a high content of fundamental, so this control strategy is widely used. But with the increase of cascaded devices, switching vectors as well as switching redundant vectors dramatically increase to increase the difficulty of the implementation of SVPWM.A new single-phase space vector is proposed on the basis of the traditional single-phase cascaded H-bridge in this paper. The validity of SVPWM control strategy is proved by theoretical analysis and simulation results. Then based on the basic principle of carrier phase shift modulation, the single-phase SVPWM control strategy can be extended to the three-phase system through the introduction of three rotation vectors which have a difference of120degrees in proper order. Implementation process of the new SVPWM strategy in the three-phase system is analyzed in detail and the effectiveness of its algorithm is verified through simulation.A large amount of H bridges are needed to achieve sufficient high-level output voltage and small voltage variation rate in traditional cascaded H-bridge inverter. As researches continue, a new asymmetric cascaded H-bridge structure is proposed in this paper to make up for shortcomings of the traditional structure. Transformer is used in the output of the new asymmetric cascaded multilevel inverter to achieve isolation. The transformer is the ordinary frequency transformer and can output sufficient high power. At the same time, the output voltage of the H-bridge unit can be boosted by changing the variable ratio of the transformer to achieve parallel connection with the grid. A new PSM strategy which is the combination of the SM and the PWM strategy is adopted in the new asymmetric cascaded multilevel inverter. Simplify the control of cascaded multilevel inverter which the output voltage level is more.Finally, the new asymmetric multilevel topology is applied to active power filter in this paper. The voltage source part and the current source part are controlled separately in the new topology. Compensation is entirely completed in the current source part and a large number of levels with high enough voltage are output in the voltage part so that the current source part can work in a low-pressure environment, then the compensation power of active power filter substantially increases and the compensation effect is improved. Simulation and experiment results verify that this new topology.