| In high-voltage and high-power applications,the three-level inverter has become a popular research point compared to the two-level inverter.The switch of each phase hold lower voltage and the inverter has lower output current harmonics.The research object is the T-type three-level inverter where the control strategy is studied.The topology and operational principle of T-type three-level inverter is analyzed,and the mathematical model is deduced.The SVPWM algorithm under traditional coordinate system and 60-degree coordinate system is discussed in detailed,including the judgement of sectors,the time of basic vectors in operation and the division of switch sequence,etc.The calculation of the 60-degree coordinate system with no trigonometric function and less division operation is largely simplified.In terms of the control of the neutral voltage imbalance,the operation time of positive small vector and negative small vector can be adjusted according to the neutral voltage deviation,so that the deviation will be quickly sustained within ±2V.Based on the current polarity detection,a dead-time compensation strategy on the basis of voltage vector is proposed.As for the control strategy of dead-time and dead-time compensation in three-level inverter,the principle and effect of dead-time are analyzed in detail,and the dead-time compensation is related to the detection of current polarity.The dead-time compensation can be realized only by adjusting the reference voltage vector.And the strategy of over-modulation is given and extended to a general formula.The MATLAB is used to simulate the modulation strategy of each module.Eventually,the mentioned above control strategy is verified by the experimental platform,including SVPWM,neutral point voltage control and dead-time compensation.The experimental results show that the fluctuation of the neutral point voltage can be controlled within ±2V,and the dead time compensation can reduce the harmonics of the output voltage and output current. |
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