Research On Cascade Multilevel Inverter Topology And Its Control Strategy

With the negative impact of fossil fuels increasing in recent years,renewable energies are gaining widespread interest because of their unique advantages.Inverters play an essential role in renewable energy system,represented by photovoltaics systems.Good performance inverters are important for improving the efficiency and reliability of photovoltaic systems.Therefore,scholars are focusing on the research of inverters.Non-isolated inverters are popular for their more obvious advantages compared to isolated inverters.This paper proposes a new multilevel inverter topology,which is a non-isolated inverter and can effectively reduce the number of devices required for the inverter,around which the following research is carried out.This paper presents a multilevel inverter that can effectively reduce the number of switches by taking a non-isolated inverter as the object of study.Firstly,the development of the multilevel inverter is introduced,several traditional multilevel inverters and new topologies proposed in recent years are analysed and compared with the proposed multilevel inverter to analyse the advantages and disadvantages of the proposed topology from various aspects.The proposed new multilevel inverter topology is described in detail and the operating principle,the switching states and the corresponding output levels of the proposed topology are analysed using an eleven-level inverter as an example.Among other things,the topology consists of an inner ring,an outer ring and an H-bridge.The modulation method is a simplified one-dimensional space vector modulation,where the number of inverter output levels can be controlled by changing the modulation system.The control system of the whole system is also designed.The controller is a proportional resonance controller with a single phase-locked loop based on second order generalised integration for grid-connected control.In addition,the design of the hardware and software of the experimental platform is also highlighted.Finally,a multilevel inverter experimental platform is built and the feasibility of the proposed scheme is further demonstrated by the experimental results.