Three-level NPC inverter neutral point potential equalization control method based on neutral point current

Abstract

The invention discloses a three-level NPC inverter neutral point potential equalization control method based on neutral point current. Upper and lower capacitor voltage and neutral point current are sampled in real time, the upper capacitor voltage and the lower capacitor voltage are compared to obtain a capacitor voltage difference value, voltage equalizing regulating quantities are obtained according to the capacitor voltage difference value, neutral point current polarity and three-phase original modulating wave polarity to regulate the three-phase modulating waves v<ma>, v<mb> and v<mc>, thereby obtaining three-phase modulating waves v<ma'>, v<mb'> and v<mc'>, the three-phase modulating waves are compared with triangular carriers C<up> and C<down>, and a PWM signal is output to control the on-off state of an inverter switching tube, thereby realizing regulation of neutral point potential. In the method provided by the invention, since pulsation frequency of the voltage equalizing quantities is larger than carrier frequency, the method for regulating the neutral point potential has a high frequency characteristic, can realize regulation of the neutral point potential in an NPC inverter in a very short time, and is good in real-time performance and high in 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.

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