Topology Of A Class Of Hybrid CHB Inverter And Optimization Of Its Modulation Method

The demand for high voltage and power inverters bring opportunities to the development and application of hybrid cascaded multilevel inverters,and also put forward new requirements for the research and optimization of topology and modulation method of hybrid cascaded multilevel inverters.The topology and modulation method should be simple,reliable and efficient.This paper first introduces the development and research status of topologies and modulation methods of multilevel inverters.Second,taking several common topologies and modulation methods of hybrid cascaded multilevel inverters as examples,the working principles and characteristics of these topologies and modulation methods are introduced.The mechanism of reverse current and the essence of their elimination methods are explained,and the shortcomings of these topologies and modulation methods are analyzed.For capacitor-clamped and diode-clamped hybrid cascaded multilevel inverter,although more levels and higher output voltage quality can be obtained with fewer DC sources and switches,the balance control of capacitor voltage is required for the normal operation of the inverter.For hybrid cascaded H-bridge(CHB)inverter,in order to eliminate reverse current and ensure output voltage quality,the high-voltage cells must operate at high frequency.The design and implementation difficulty of modulation method also sharply increases with the number of cascaded cells.From the perspective of engineering applications,these complex topologies and modulation methods are not conducive to the improvement of power level and reliability of hybrid CHB multilevel inverters.Therefore,it is necessary to get a simple,reliable and efficient new topology and a modulation method of hybrid CHB inverters to promote its industrial application.Based on this,this paper proposes a new scheme of hybrid CHB multilevel inverter.Firstly,by optimizing the DC voltage distribution rule,a new topology of hybrid CHB inverter with a simple structure and easy expansion is proposed.Secondly,by combining the idea of step-wave modulation and carrier modulation,a hybrid phase-shifted modulation method and a hybrid level-shifted pulse width modulation method are proposed.Among them,the hybrid PS-PWM method also has double-frequency performance.Thirdly,a power balance method based on logic operation is provided for the power balance problem.This power balance method can realize the power balance between high-voltage cells and low-voltage cells in the II-type hybrid CHB 13-level inverter.The new topology and modulation method enhances the expansibility of high-voltage cells and low-voltage cells,realizes the operation of high-voltage cells at fundamental frequency,eliminates reverse current and ensures output voltage quality under the lower modulation difficulty.Finally,a hybrid CHB 13-level inverter simulation and experiment platform with a voltage ratio of 1: 1: 2: 2 and 1: 1: 1: 3 was built,which verified the correctness and feasibility of the proposed new scheme.