Neutral-point Voltage Balancing Control With Narrow Pulse Suppression

With the increase in car ownership,the problems of energy and environment brought by traditional fuel vehicles have become increasingly prominent.Electric vehicles consume renewable energy and enable energy recycling,which have become a trend in the automotive industry.The core of electric vehicles lies in the three-electric system,and the inverter has received extensive attention as an important part of the motor control unit.Existing two-level inverters are difficult to meet the requirements of low harmonic distortion,high power density and low electromagnetic interference of electric vehicles.Therefore,three-level inverters have broad application prospects in electric vehicles.The most widely used diode-clamped three-level inverter has a problem of narrow pulse and neutral-point voltage unbalancing due to its switching tube characteristics and structural characteristics.The cause of the neutral-point voltage unbalancing,the influence on neutral-point voltage of different voltage vectors and the ability to balance the neutral-point voltage of the nearest three vector pulse width modulation algorithm and virtual space vector pulse width modulation algorithm are analyzed.The process of AC motor vector control is analyzed,and the influence of the neutral-point voltage unbalancing on the voltage vectors in the two-axis AC coordinate system is analyzed.Different pulse width modulation methods have different effects on the narrow pulse generated in the modulation process.The narrow pulse distribution of the two-level inverter under different pulse width modulation methods is analyzed in this paper.Besides,the narrow pulse distribution of the three-level inverter under different pulse width modulation method is analyzed.An improved virtual space vector pulse width modulation algorithm is designed.The method of narrow pulse suppressed by the common mode voltage or differential mode voltage in the range of 0 to 60 degrees of electrical angle is analyzed in detail.The voltage injected is corrected according to the feedback value of the neutral-point voltage so that the output voltage waveform is not affected by the neutral-point voltage unbalancing and the neutral-point voltage can be controlled within a certain range.The simulation control model of simulink was built,and the open-loop control was used to verify the balance ability of the neutral-point voltage and the phase voltage output waveform of the nearest three vector pulse width modulation algorithm and the virtual space vector pulse width modulation algorithm.The improved virtual space vector pulse width modulation algorithm can effectively suppress narrow pulse,control neutral-point voltage balance and make output phase voltage without distortion.An experimental platform for AC induction motor control was built,using an I-type inverter.The experiment compared between the original virtual space vector pulse width modulation algorithm and the improved virtual space vector pulse width modulation algorithm is designed to verify that the improved virtual space vector pulse width under different modulation ratios can suppress most narrow pulses and control neutral-point voltage within a given range.Fourier analysis of the phase current shows the total harmonic distortion is not increased,which verifies the effectiveness of the method.