Harmonic compensation control method of cascade H bridge photovoltaic grid-connected inverter

Abstract

The present invention discloses a harmonic compensation control method of a cascade H bridge photovoltaic grid-connected inverter, belonging to the photovoltaic generation field. The method mainly comprises the following steps: (1) performing independent control of capacitor voltages at direct current sides of all the H bridge units, and obtaining an active instruction value of a power grid current; (2) realizing astatic control of the power grid current, and generating total modulation voltage of an inverter and modulation degrees of all the H bridge units; and (3) calculating a modulation wave of each H bridge module according to a harmonic wave compensation strategy. Compared to literatures disclosed in the prior art, the harmonic compensation control method of the cascade H bridge photovoltaic grid-connected inverter can ensure normal operation of inverter unit power factors and small fluctuation of capacitor voltages at the direct current sides when the input power of the H bridgephotovoltaic grid-connected inverter is severely imbalance.

Description

technical field [0001] The invention belongs to the photovoltaic power generation technology in the field of electrical engineering, and in particular relates to a harmonic compensation control method for cascaded H-bridge photovoltaic grid-connected inverters. Background technique [0002] Compared with the traditional inverter, the cascaded H-bridge multilevel inverter has the advantages of low harmonic content of grid current, low switching frequency, small filter size and easy modularization, etc., so it has attracted the attention of many scholars. In addition, the DC side of each H-bridge unit of the cascaded H-bridge multi-level inverter can be independently powered by a photovoltaic cell, making its independent maximum power point tracking (MPPT—Maximum Power Point Tracking) control possible, so the level The H-bridge multilevel topology is especially suitable for photovoltaic grid-connected inverters. [0003] Although each H-bridge unit of the cascaded H-bridge ph...

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Problems solved by technology

[0008] 1) When the output power of each H-bridge module is seriously unbalanced, although the reactive power compensation control strategy can ensure that all H-bridge modules are not modulated, the system power factor is low and cannot meet the grid-connected standard

[0009] 2) Although the hybrid modulation strategy can expand the operating range of the system to a certain extent, the DC side capacitor voltage fluctuates greatly, which will reduce the power generation of the system

[0010] 3) Although the third harmonic compensation strategy can make the system operate at unity power factor and the DC side capacitor voltage fluctuation is small, the ability to deal with system imbalance is weak

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