Research And Design Of NPC Three-level Inverter Based On SVPWM Modulation Technology

With the rapid development of my country’s industry,the field of power electronics has made great progress.With the increase in voltage levels,low-voltage and low-power devices represented by two-level inverters can no longer meet the needs of the society.Instead,the three-level inverter is the representative high-voltage and high-power device.Because the three-level inverter has the advantages of high DC side voltage utilization,high switching frequency,and low output harmonics,it is currently widely used in the fields of medium and high voltage inverters,photovoltaic energy storage,and motor traction.This article takes the neutral point clamped(NPC)three-level inverter as the research object.According to the circuit topology,the working principle and dynamic commutation state are analyzed,and the modulation effect of the space voltage vector pulse width modulation(SVPWM)technology on the diode-clamped three-level inverter is studied and improved.The traditional space voltage vector PWM technology is complex and difficult to control in real time.This paper proposes a space vector PWM technology in a 60° coordinate system,which simplifies the control method.The neutral point potential unbalance is a research hotspot of the NPC type threelevel inverter,and the space voltage vector PWM technology can improve the neutral point potential unbalance.In order to investigate the cause of the midpoint potential imbalance and improve its problems,this paper analyzes the principle of virtual space vector.The improved virtual space vector PWM technology simulates the virtual small vector and the virtual middle vector through the small vector and the middle vector,and controls the midpoint voltage in the 60° coordinate system,which greatly simplifies the calculation process and effectively controls the midpoint voltage balance.On this basis,a simulation platform of a three-level inverter based on SVPWM technology is built,and the output waveform is consistent with the theoretical result.Under laboratory conditions,the experimental platform of the three-level inverter is built,the hardware circuit is designed,and the software is compiled.Through the experimental waveform analysis of the prototype,the feasibility of the above modulation algorithm and midpoint voltage control technology is verified.