Research On Modulation Strategy Of NPC Three Level Inverter

With the development of economy and technology in China,the application of inverter in AC variable frequency speed regulation system has become a hot research field.Multi-level inverters have low voltage requirements for devices,which has the advantages of high switching frequency,smooth waveform and so on.Diode Clamping(NPC)Three-Level Inverter Has Clear Advantage Over Other Inverters,which has made it become the research hotspot of peoplegradually.It has been widely applied to many large capacity transmission occasions.First of all,this paper studies the research background and current development of multilevel inverters,as well as the main problems,by referring to the relevant literature and periodicals at home and abroad.At the same time,the topology of the diode clamped three level inverter and the working principle of its main circuit are introduced and analyzed,and the corresponding mathematical model of the NPC three level inverter is set up.Secondly,the modulation strategy of multilevel inverter is analyzed,and the SVPWM algorithm is derived based on NPC three level inverter.The problem of neutral point potential imbalance in the operation of NPC three level inverter is studied.The mechanism of midpoint potential fluctuation and the strategy of VSVPWM modulation are analyzed.In view of the complexity of the VSVPWM modulation strategy and the high switching loss of the device two problems,a hybrid modulation method which combines the three-dimensional space vector(3D-SVPWM)with the virtual space vector pulse width modulation is proposed.Finally,a Simulink platform is built,and a simulation model of a three-level inverter is established using MATLAB software for a hybrid modulation method and a virtual space vector pulse width modulation method,respectively.The simulation results show that the proposed hybrid modulation method can effectively control the balance of the neutral point potential and reduce the loss of the inverter switch device to a certain extent.The correctness of the proposed algorithm is verified.