A photovoltaic grid-connected inverter and its control method

Abstract

The invention discloses a photovoltaic grid-connected inverter which comprises a first direct current bus capacitor branch, a second direct current bus capacitor branch, a boost converting circuit, a direct current bypass branch, a full-bridge inverter circuit and an alternating current filtering circuit, wherein the first direct current bus capacitor branch, the boost converting circuit, the second direct current bus capacitor branch, the full-bridge inverter circuit and the alternating current filtering circuit are sequentially connected in series; the input end of the first direct current bus capacitor branch is externally connected with a photovoltaic modules string; the output end of the alternating current filtering circuit is externally connected with a power grid; the direct current bypass branch is connected in parallel between the input end of the first direct current bus capacitor branch and the output end of the full-bridge inverter circuit. Meanwhile, the invention also discloses a control method for the photovoltaic grid-connected inverter. According to the photovoltaic grid-connected inverter and the control method thereof disclosed by the invention, the direct current bypass branch is introduced, so the problems in the prior art are solved.

Description

technical field [0001] The invention relates to a photovoltaic grid-connected inverter and a control method thereof, belonging to the technical field of power electronic converters. Background technique [0002] Due to the renewable and clean nature of solar energy, photovoltaic grid-connected power generation technology has developed rapidly. The output DC voltage of the photovoltaic module string is usually lower than the peak value of the AC grid voltage, so it needs to go through a first-stage boost circuit and then connect to the inverter to realize grid-connected operation, such as figure 1 shown. However, when the instantaneous absolute value of the AC grid voltage is lower than the output DC voltage of the photovoltaic module string, the electric energy output by the photovoltaic module still needs to be converted by a booster circuit, so the literature "K.Orgura, T.Nishida, E.Hiraki, M.Nakaoka , and S.Nagai.Time-sharing boost chooper cascaded dual mode single-phas...

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Problems solved by technology

However, when the instantaneous absolute value of the AC grid voltage is lower than the output DC voltage of the photovoltaic module string, the electric energy output by the photovoltaic module still needs to be converted by a booster circuit, so the literature "K.Orgura, T.Nishida, E.Hiraki, M.Nakaoka , and S.Nagai.Time-sharing boost chooper cascaded dual mode single-phase sinewave inverter for solar photovoltaic power generation system.IEEEPESC 2004,pp.4763-4767" proposed that when the output voltage of the photovoltaic module string is lower than the absolute value of the instantaneous value of the grid voltage value, so that the DC bus capacitor voltage between the boost converter and the inverter is equal to the absolute value of the instantaneous value of the grid voltage; and when the output voltage of the photovoltaic module string is higher than the absolute value of the instantaneous value of the grid voltage, the boost circuit Not working

However, this control method limits the capacity of the DC bus capacitor, so the voltage ripple of the DC bus capacitor is relatively large, and the control is more complicated and difficult to implement.

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