| Along with the development of technology of power electronics, technology of high-voltage and high-power multi-level inverter is studied more and more. Multi-level inverters are used in Frequency Adjustable Speed System, Reversible PWM Rectifier, Active Filter of Power System and Flexible AC Transmission Systems because of the advantages of high dielectric strength, high equivalent switch frequency, no dynamic equalizing and good output waveform.There are several kinds of topologies and control strategies of multi-level inverter. This paper studied how the diode clamped three-level inverter works, the theory of Space Vector Pulse Width Modulation (SVPWM), and problem of neutral point potential balancing.At the beginning, this paper analyses the theories of NPC three-level inverter, SVPWM, the influence of imbalanced neutral point potential, the reasons of imbalanced neutral point potential, the characteristics of imbalanced neutral point potential. Then, several strategies of controlling the neutral point potential are given. Based on the charging and discharging of capacitances balances neutral point potential, two circuits with assistant leg are introduced. Based on the arithmetic of SVPWM, a software strategy by adjusting the work times of active and negative small vectors is introduced.After the studying of theory, this paper simulates the NPC three-level inverter with SVPWM and the several neutral point potential balancing strategies as above, and the emulational waveforms validate that they are correct.At last, the NPC three-level inverter is established with MOSFETs and diodes to finish the experiments, and the DSP of TMS320LF2407A is used to create PWM drive signals. The whole hardware system contains main circuit, isolating and driving circuit, detecting circuit and snubber circuit. Through analyzing the waveforms and data of experiments, conclusions of the strategy of SVPWM and adopted strategy of neutral point potential balancing are correct.
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