Parallel control method employing selective harmonic elimination pulse width modulation (SHEPWM) for multiple T-type three-level inverters

Abstract

The invention discloses a parallel control method employing selective harmonic elimination pulse width modulation (SHEPWM) for multiple T-type three-level inverters. The parallel control method comprises the following steps of determining the quantity of switching angles of each period according to the quantity of harmonic orders needed to be eliminated; figuring out a switching angle of SHEPWM based on a multi-object particle swarm optimization method, and generating a corresponding SHEPWM signal; acquiring a neutral-point voltage and a zero-sequence loop current of a T-type three-level inverter parallel system; setting a time sequence, carrying out small vector control on the SHEPWM signal according to the neutral-point voltage or the zero-sequence loop current and the time sequence, and rewriting the SHEPWM signal. The neutral-point voltage or the zero-sequence loop current is controlled according to the set time sequence. Since the neutral points of the multiple inverters are connected, the neutral-point voltage of the system is balanced only by controlling the neutral-point voltage of an arbitrary inverter at a certain moment.

Description

technical field [0001] The invention relates to a parallel control method for multiple T-type three-level inverters using SHEPWM. Background technique [0002] With the large-scale access of distributed energy sources including photovoltaic power generation systems to the low-voltage distribution network, the power grid puts forward higher requirements on the output current waveform quality of grid-connected inverters. It is difficult for traditional two-level grid-connected inverters to meet large-scale Grid high power quality requirements. The emergence of T-type three-level grid-connected inverters solves the above problems, such as figure 2 As shown, compared with the traditional two-level inverter, the inverter has the advantages of small harmonics, low switching loss, and small electromagnetic interference; compared with the traditional diode-clamped three-level inverter, the inverter has The number of switches is small, the conduction loss is small, and the power lo...

AI Technical Summary

Problems solved by technology

Therefore, T-type three-level inverters have been widely used in distributed power generation occasions such as photovoltaic power generation and micro-grid, but capacity has always been the bottleneck restricting its rapid development.

[0003] The parallel connection of multi-unit T-type three-level grid-connected inverters can increase system capacity, reliability and efficiency, and has become an important choice for high-power distributed power generation. However, hardware mismatch between modules, dead time and control algorithm execution Time and other differences will produce circulation

Circulating current will increase system loss and cause grid-connected current distortion, seriously affecting the life of IGBT switch tubes, so it is of great significance to study the circulating current suppression of parallel T-type three-level inverters

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