Topology Research Of Single-input Extended Switched Capacitor Multilevel Inverter

With the global energy crisis and the awakening of environmental protection awareness,building an energy supply system dominated by renewable clean energy has become a general consensus of human society.Solar energy has the character-istics of ease of use,universality and cleanliness,and has become the best alterna-tive to fossil energy.Therefore,the photovoltaic power generation industry has developed rapidly.In the photovoltaic power generation system,the photovoltaic inverter plays a vital role,and its performance affects the stability of the entire power supply system.The multilevel inverter has the advantages of being able to output an approximate sine staircase waveform,reducing the total harmonic dis-tortion,reducing the peak inverse voltage,a smaller du/dt and reducing electro-magnetic interference.Therefore,it is widely used in the field of micro-grid such as photovoltaic power generation.Aiming at the problems of complex structure,capacitor voltage imbalance and difficult modulation of traditional multilevel in-verters,combined with the development needs of photovoltaic inverters,the topol-ogy of multilevel inverters based on switched capacitor structure was studied.In this paper,a variety of single-input extended switched capacitor multilevel invert-ers are proposed.The proposed topology has the advantages of capacitor voltage self-balancing,less power devices,high power density,modular expansion,high voltage gains and so on.It has significant significance for the research of inverter integration and lightweight.The main research contents of the subject are:（1）Aiming at the disadvantages of traditional multilevel inverters such as the use of many power devices and complex structure,a switched capacitor multilevel inverter with step-charging and self-balancing is proposed.The switched capacitor module of the proposed topology adopts a combination of double capacitors.The series-parallel conversion of the switched capacitor module and the step-charging of the double capacitor increase the output level and boost gain of the inverter,and reduce the use of power devices.In addition,the synchronous discharge of the dual capacitors helps to reduce the capacitor voltage ripple and improve the output volt-age quality.（2）The above-mentioned multilevel inverter uses an H-bridge circuit at the terminal to obtain bipolar levels.The H-bridge switches needs to withstand the cumulative voltage of the previous capacitors and the power supply.The larger peak inverse voltage is not conducive to reducing the inverter losses.Therefore,a modular extended switched capacitor multilevel inverter topology is proposed.The switched capacitor module of the proposed topology has an inherent level inversion capability,avoids the use of terminal H-bridge,and significantly reduces the peak inverse voltage of the switches.The capacitor of the proposed topology still adopts the working mode of step charging,which allows the inverter to use fewer power devices to output more levels.（3）Although the switch of the topology mentioned in（2）has a lower peak inverse voltage,as the topology expands,the peak inverse voltage also increases.To solve the above problems,an X-type low-stress switched capacitor multilevel inverter is proposed.The proposed topology obtains more output levels through the expansion of the X-type bipolar module,but the maximum peak inverse voltage of the switch does not exceed 4V_dc,and this characteristic will not change with the expansion of the inverter.Low voltage stress will provide opportunities for inverter applications in medium-high voltage scenarios.In this paper,the topology,operation principle and modulation strategy of a series of single-input extended switched capacitor multilevel inverters are de-scribed in detail.In addition,related parameters such as capacitance was calculated and comparative analysis of topologies were performed.Finally,a small laboratory prototype was built to conduct steady-state experiments and dynamic experiments on the above-mentioned inverters,and the results verified the feasibility of the in-verter topology and the correctness of the modulation strategy.