A control method and system for parallel connection of photovoltaic inverter AC side

Abstract

The present invention provides a method and system for controlling the parallel connection of the AC side of photovoltaic inverters, which is applied to an inverter system in which the AC sides are connected in parallel and the DC side is independent. The input end of the first inverter is connected to the first PV array. The input end of the second inverter is connected to the second PV array. Both the first PV array and the second PV array have parasitic capacitance to the ground. The first inverter and the second inverter are coupled through the parasitic capacitance to form a common mode loop; including the following steps: detecting the first DC voltage of the first inverter and the second DC voltage of the second inverter; obtaining the difference between the first DC voltage and the second DC voltage; adjusting the DC voltage of the inverter The difference is controlled within a predetermined range, so that the common-mode voltage in the common-mode loop is controlled within a predetermined common-mode voltage range. When the difference between the inverters is smaller, the common-mode voltage difference between the inverters is smaller, so the common-mode current is also smaller, thereby suppressing the common-mode circulating current between the inverters.

Description

technical field [0001] The invention relates to the technical field of photovoltaic power generation, in particular to a control method and system for parallel connection of alternating current side of photovoltaic inverters. Background technique [0002] With the continuous expansion of the capacity of new energy power stations, in order to realize the optimal allocation of grid-connected inverter capacity and realize the single-machine WM-level solution, the parallel connection of inverters has become a trend of technological development. Parallel connection of the AC side of the inverter has the following advantages: [0003] The double-split transformer can be replaced by a double-winding transformer on the AC side, saving system investment costs; the original maximum power point tracking MPPT is not lost, and there are few changes in system layout and structure. [0004] see figure 1 , which is a schematic diagram of inverters connected in parallel on the AC side in t...

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Problems solved by technology

[0007] Although the inverters connected in parallel on the AC side have advantages, there are parasitic capacitances between the positive and negative poles of the PV array to the ground, which causes coupling on the DC side of each inverter in the parallel system, thereby forming a common-mode loop and causing common-mode circulation problems.

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