Neutral point voltage control method for neutral point clamped (NPC) type three-level inverter based on carrier amplitude shift

Abstract

The invention discloses a method for controlling the midpoint voltage of an NPC three-level inverter based on carrier amplitude shift. K×m and 1-K×m, K is the carrier amplitude adjustment coefficient, m is the modulation ratio, the carrier amplitude is adjusted by adjusting the carrier amplitude adjustment coefficient in real time, and the carrier obtained after the amplitude adjustment is compared with the modulated wave Output PWM signal. The adjustment method of K is: when Unp is greater than Udc / 2, then -1≤K<0; if Unp is equal to Udc / 2, then K=0; if Unp is less than Udc / 2, then 0<K≤1; If Unp is greater than Udc / 2, then 0<K≤1, if Unp is equal to Udc / 2, then K=0, if Unp is less than Udc / 2, then -1≤K<0; where, is the power factor angle , Unp is the inverter midpoint voltage, Udc is the DC bus voltage. The present invention achieves the balance of the midpoint potential by keeping the frequency of the modulating wave and the upper and lower carrier waves unchanged, and changing the amplitudes of the upper and lower carrier waves. The method has the advantages of simple calculation and easy implementation.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and in particular relates to a method for controlling the midpoint voltage of an NPC type three-level inverter based on carrier amplitude shift. Background technique [0002] Compared with the traditional two-level inverter, the diode-clamped (NPC) three-level inverter has the advantages of lower requirements on the withstand voltage level of switching devices, high equivalent switching frequency, and small output waveform harmonics. It is widely used in medium and high voltage high power conversion circuits. But the midpoint potential balance problem is its inherent outstanding problem. The imbalance of the midpoint potential will increase the harmonics of the output voltage, and it will also damage the switching devices and filter capacitors. [0003] Inconsistent DC bus capacitor parameters, unbalanced loads and different modulation strategies may cause unbalanced midpoint voltage....

AI Technical Summary

Problems solved by technology

However, the selection of zero-sequence components requires high skills. The calculation of zero-sequence components often requires parameters such as three-phase reference voltage, output current, DC bus capacitor voltage and capacitance value. A large number of parameters make the calculation of zero-sequence components complicated. It is also not conducive to the realization of real-time control system, while increasing the cost

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