Research On NPC Three-level Inverter And Its Neutral-point Voltage Balance

The development of three-level inverter provides effective solutions for thepower conversion in the large-capacity and high-voltage situations. Therefore, thethree-level technology has become a research hotspot nowadays. As the advantages oflarge output capacity, low current harmonics and low withstand voltage of switchingelement,the diode clamped three-level inverters have been widely applied.Neutral-point clamped (NPC) three-level inverter is deeply studied in thisdissertation. And the Space Vector Pulse Width Modulation (SVPWM) algorithm isanalyzed and simulated. On this basis, the inherent problem of neutral voltage balanceof NPC inverter is discussed in detail. Firstly, the basic principle of NPC inverter isintroduced and the advantages and disadvantages of NPC inverter are summarized.Then, the control principle of SVPWM algorithm is analyzed and the calculation stepsof SVPWM are given. Besides, based the reason of neutral voltages fluctuation, theneutral voltage is mathematically analyzed and explored. Last, making use of thesmall vectors’ opposite influence to the offset of neutral voltage, the voltage balancestrategy is put forward.Based the theory study, the SVPWM algorithm and voltage balance strategy issimulated under the Matlab/Simulink. The validity of SVPWM and neutral voltagebalance strategy under different circumstance is verified.