A control method for a flying capacitor type three-level inverter device

Abstract

The invention discloses a control method of a flying capacitive type three-level inverter device adopting an improved carrier wave overlapped PWM method. According to the control method of the flying capacitive type three-level inverter device, the states of '1' '0' and '-1' needed for controlling an inverter are obtained, a zero-level vector quantity selecting link is added by utilizing the redundancy characteristics of on-off states of a flying capacitor, the zero-level vector quantity states '0+' and '0-' are reasonably distributed after an initial value is set, and the voltage of the flying capacitor is controlled and balanced through the switchover of the two zero-level states. The control method of the flying capacitive type three-level inverter device has lower line voltage harmonic, is more favorable for grid-connected operation of the inverter, is high in flexibility, is simple to achieve, and has low requirements for hardware; is additionally provided with the zero-level selecting link, can manually control voltage balance of the flying capacitor, and has better control performance; utilizes the flying capacitor to replace a complex clamping diode, reduces the number of devices, can carry out decoupling control over active power and reactive power, is favorable for grid connection of the inverter, and is popularized in higher-level applications more easily.

Description

technical field [0001] The invention relates to the technical field of inverters for grid-connected power generation, in particular to a control method for a flying capacitor type three-level inverter device. Background technique [0002] In recent years, multi-level inverters have been used more and more in high-voltage and high-power fields. Now there are three main topologies that are relatively mature: diode clamped, cascaded, and flying capacitor. The diode-clamped multilevel inverter topology has disadvantages such as difficult voltage equalization of capacitors on the DC bus side and uneven voltage stress. The cascaded multi-level inverter topology requires multiple independent DC power supplies without a common ground when active power needs to be provided. Compared with the other two, the flying-capacitor multilevel inverter topology overcomes the inherent defects of the diode-clamped inverter by using the capacitor clamp; it overcomes the inherent defects of the c...

AI Technical Summary

Problems solved by technology

The diode-clamped multilevel inverter topology has the disadvantages of difficult voltage equalization and uneven voltage stress on the capacitors on the DC bus side.

However, when the PDPWM method is applied to a flying-capacitor inverter, the voltage on the capacitor will change, and the flying-capacitor inverter uses capacitor clamping to ensure that the voltage on the capacitor is stable. Therefore, the traditional PDPWM method is not suitable for flying capacitor inverters. Transcapacitive Multilevel Inverter

[0010] Only the carrier phase-shift PWM method (PSPWM) is applicable to the flying capacitor type multilevel inverter, but when the traditional PSPWM method is applied to the flying capacitor type multilevel inverter, due to the inherent characteristics of this algorithm, it will Larger line voltage harmonics are generated on the output side of the inverter, which is not conducive to power generation and grid connection; due to the automatic balance of the flying capacitor voltage, human intervention and adjustment cannot be performed, which will cause a certain voltage deviation of the flying capacitor voltage and cannot be changed.

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