Research On Neutral-Point Potential Balance Technology Of Three-Level Inverter

Recent years,product of under the 1140V voltage multi-level inverter with independent intellectual property rights increasingly grow in China,the multi-level inverter's advantage of less output voltage harmonic content,power tube pressure resistance and other aspects compared to two-level inverter is obvious,currently it has become a research hotspot in the field of power transmission.In this paper,described the basic working principle of three-level inverter and studied the vector control system of asynchronous motor oriented by rotor flux.The dynamic mathematical model of asynchronous motor is analyzed in detail,and designed the block diagram of control principle,the specific parameters of rotor flux amplitude and space angle are analyzed by indirect magnetic field orientation method.The simulation circuit of asynchronous motor vector control system is built.on this basis,the space vector modulation algorithm based on ??? coordinate system and the space vector modulation algorithm based on simplified 600 coordinate system are compared and analyzed.The simulation results show that the vector control system of asynchronous motor has good performance.The simplified space vector modulation algorithm in 60° coordinate system is easier to realize digital control.For the diode clamp three-level inverter,this paper makes a qualitative and quantitative analysis to the voltage imbalance in the course of operation,by introducing the distribution factor into the small vector pair to effectively suppress the Neutral-Point Potential offset problem,but there are still some potential fluctuations,this paper performed appropriate improvement on the basis,adding of charge control method,the switching function of the control algorithm is established so that the Neutral-Point Potential is effectively suppressed in terms of offset and fluctuation.The simulation platform of Neutral-Point Potential balance control is built,and the output results are consistent with the theory.The experimental prototype platform of the three-level inverter system is completed in the laboratory environment,and the DSP is the core control unit,which mainly includes The main circuit of the system,the driving circuit,the Neutral-Point Potential detection circuit,the voltage and current sampling circuit and so on.The relevant experimental waveforms were tested.The experimental results further verified the validity and feasibility of the designed simplified SVPWM algorithm and the Neutral-Point Potential balance control strategy.