Control method of single-phase cascaded photovoltaic grid-connected inverter

Abstract

The invention discloses a control method of a single-phase cascaded photovoltaic grid-connected inverter, and belongs to the field of photovoltaic power generation. According to the method, a workingscene that the output power of the photovoltaic module is seriously unbalanced is dealt with, and compared with an existing single-phase cascaded H-bridge photovoltaic grid-connected inverter, by using the method of the invention, the operation range of the system can be expanded to a large extent. The method comprises the following steps: controlling the average value of the DC bus capacitor voltage of the H-bridge converter; controlling a grid-connected current; using improved nearest level approximation modulation; and controlling a single-phase active filter and controlling the input DC bus voltage of a four-switch tube Buck-Boost converter. By the adoption of the method, even in the working scene that the output power of the photovoltaic assemblies is seriously unbalanced, all the photovoltaic assemblies can still work at the maximum power points of the photovoltaic assemblies, and the power generation capacity of the system is maximized.

Description

technical field [0001] The invention belongs to photovoltaic power generation technology in the field of electrical engineering, and in particular relates to a control method for a single-phase cascaded photovoltaic grid-connected inverter. Background technique [0002] In 2017, the National Electrical Code of the United States formulated new standards, requiring all photovoltaic facilities on buildings to have the ability to quickly shut down at the component level in emergency situations, which will surely promote the rapid development and widespread use of component-level power electronics technology application. Since each power unit of a single-phase cascaded H-bridge (Cascaded H-bridge, CHB) photovoltaic grid-connected inverter can be independently powered by a photovoltaic module, it is easy to achieve maximum power point tracking (Maximum Power Point Tracking, MPPT) at the module level, Component-level monitoring and components can be shut down, so the single-phase ...

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Problems solved by technology

[0009] (1) The reactive power compensation strategy can deal with serious power imbalances, but this method will reduce the power factor of the system, and its practical application may be limited

[0010] (2) The improved hybrid modulation strategy can expand the linear modulation range of the H-bridge converter from 1 to 4 / π, but the DC bus capacitor voltage of the H-bridge converter fluctuates greatly and there is a static error in the control, which will reduce the power generation of the system and MPPT efficiency

[0011] (3) The third harmonic compensation strategy will neither aggravate the fluctuation of the DC bus capacitor voltage of the H-bridge converter nor ensure the unit power factor operation of the system, but this method has a weak ability to deal with power imbalance

[0012] (4) The harmonic compensation strategy retains the advantages of the third harmonic compensation strategy and further expands the linear modulation range of the H-bridge converter. system is greater than 4 / π), the harmonic compensation strategy will also fail

[0013] (5) Although the improved MPPT control strategy can cope with severe power imbalance scenarios, this method reduces the power generation of the system

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