Grid-connected startup method for photovoltaic grid-connected inverter

Abstract

The invention discloses a grid-connected startup method for a photovoltaic grid-connected inverter. The grid-connected startup method comprises the following steps of: a, keeping an off state of an alternating current switch; b, respectively detecting the bus voltage and power grid voltage through a direct current (DC) voltage sensor and an alternating current (AC) voltage sensor, and transmitting a detection result to a control circuit; c, judging whether the bus voltage is higher than the peak voltage of the power grid through the control circuit, and switching on the AC switch if the bus voltage is higher than the peak voltage of the power grid; d, calculating inverter modulation waves with the same frequency and phase as the power grid voltage through the control circuit according to the amplitude, phase and frequency of the detected power grid voltage; and e, judging whether the power grid voltage crosses the zero point through the control circuit, and if the power grid voltage crosses the zero point, applying the inverter modulation waves to the photovoltaic grid-connected inverter, starting the operation of the photovoltaic grid-connected inverter and starting the grid-connected operation. According to the method, the condition that high phase deviation occurs between the inverter voltage and power grid voltage can be effectively avoided, high impact current is avoided, and the stability of the system is guaranteed.

Description

technical field [0001] The invention relates to the technical field of photovoltaic grid-connected inverters, in particular to a grid-connected startup method for photovoltaic grid-connected inverters. Background technique [0002] Such as figure 1 As shown, it is a grid-connected circuit diagram of a common photovoltaic grid-connected inverter at present. The DC input side of the photovoltaic grid-connected inverter 11 is connected with a DC voltage sensor 13 for detecting the bus voltage, while the AC output side is connected with a AC switch 15, and an AC voltage sensor 17 for detecting the grid voltage is connected to the side of the AC switch 15 close to the grid, and the control circuit 19 controls the photovoltaic grid connection according to the detection results of the DC voltage sensor 13 and the AC voltage sensor 17 The operation of the inverter 11 and the switching of the AC switch 15 . [0003] In the invention patent application with the application number 20...

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Problems solved by technology

[0004] Compared with the traditional grid-connected start-up method, although the grid-connected start-up method disclosed in the above-mentioned patent application documents has some improvements, it has the following defects: when the grid-connected start-up, the actual grid-connected grid voltage and theoretical grid-connected There is a certain deviation in the phase of the grid voltage at that time, resulting in a large phase deviation between the inverter voltage and the grid voltage, so that a large inrush current will be generated, which will have an adverse effect on the photovoltaic grid-connected inverter

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