A midpoint potential equalization control method for three-level npc inverters based on midpoint current

Abstract

The invention discloses a middle-point potential equalization control method of a three-level NPC inverter based on the middle-point current. Real-time sampling of the upper and lower capacitor voltages and the midpoint current, and compare the upper and lower capacitor voltages to obtain the capacitor voltage difference. According to the capacitor voltage difference, the midpoint current polarity and the polarity of the original modulation wave of the three phases, the voltage equalization adjustment amount is calculated to adjust the three phases. Phase original modulation waves vma, vmb, vmc are adjusted to obtain three-phase modulation waves vma', vmb', vmc', compare the three-phase modulation waves with the triangular carrier wave Cup and Cdown respectively, and output PWM signals to control the inverter Switching state of the switching tube, so as to realize the adjustment of the midpoint potential. In the method of the present invention, since the pulsation frequency of the voltage equalization adjustment value is greater than the carrier frequency, the adjustment of the midpoint potential by this method has high-frequency characteristics, and the adjustment of the midpoint potential of the NPC inverter can be realized in a very short time. Good real-time performance and high control precision.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and in particular relates to a midpoint potential equalization control method of a three-level NPC inverter based on midpoint current. Background technique [0002] Compared with the two-level topology, the three-level neutral point clamp (NPC) inverter has the advantages of effectively reducing the harmonic content of the output voltage, reducing the voltage stress of the switch tube, and reducing electromagnetic interference, etc., and is widely used in For new energy power generation, active power filter (APF), flexible AC transmission (FACTS), motor drive and other high-voltage and high-power occasions, the topology structure is as follows: figure 1 shown. [0003] Three-level NPC converter topology DC side bus must use two capacitors in series, the AC side can output three-level phase voltage and five-level line voltage. Theoretically, the voltage of each capacitor is half of the...

AI Technical Summary

Problems solved by technology

The mid-point potential DC imbalance will introduce a large number of even harmonic components, especially the second harmonic component, into the output voltage of the AC side of the three-level NPC inverter, which reduces the waveform quality of the inverter output voltage

At the same time, the DC imbalance will lead to inconsistent voltage stress on the power switching devices of the three-level NPC inverter, which may damage the switching devices and affect the normal operation of the system.

Images