Method and device for inhibiting and eliminating leakage current of photovoltaic grid connection system without transformer

Abstract

The invention relates to a method and a device for inhibiting and eliminating leakage current of a photovoltaic grid connection system without a transformer. The device is composed of a leakage current detector, a central controller and a waveform generator, wherein, the central controller is provided with a waveform analyzing circuit, a command current computing circuit and a current tracking control circuit; the waveform generator is provided with a drive circuit and a power module; the leakage current detector is arranged on the direct-current side of an inverter and is connected with the central controller; the central controller is used for analyzing and processing the leakage current waveform and generating compensatory current control signals; and the waveform generator is arrangedin a photovoltaic array and is connected with the output end of the current tracking control circuit of the central controller, and is used for injecting the corresponding compensatory current generated according to the command of the central controller into a photovoltaic system. In the invention, the compensating current the size of which is the same as that of the leakage current, and the phase position of which is opposite to that of the leakage current is generated through detecting, analyzing and processing the leakage current waveform. The compensating current is overlaid and offset with the leakage current after being injected with circuit, thus achieving the purpose of inhibiting and eliminating the leakage current; and the method and device provided by the invention has the characteristics of real-time monitoring, tracking, less dynamic compensation power consumption and smaller environment influence, can effectively inhibit and eliminate the leakage current, and has large application prospects and economic effect.

Description

technical field [0001] The invention belongs to the technical field of photovoltaic grid-connected system inverters, and in particular relates to a method and device for suppressing and eliminating the leakage current of a transformerless photovoltaic grid-connected system. Background technique [0002] In recent years, people's demand for energy is increasing, and the requirements for energy saving are also getting higher and higher. As a clean and renewable energy source, solar energy has broad application prospects, and grid-connected photovoltaic systems will become a trend. In the past, the cost of photovoltaic systems mainly depended on the price of solar cell chips, but with the improvement of chip production capacity and the decline of prices, inverters have increasingly become a factor restricting the cost of photovoltaic systems. [0003] In order to ensure personal safety and avoid leakage current, photovoltaic grid-connected systems often use isolated inverters ...

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Problems solved by technology

[0004] However, in a photovoltaic grid-connected system without a transformer, there is direct electrical contact between the AC grid and the DC photovoltaic array. Due to the inevitable parasitic capacitance between the photovoltaic array and the ground, it provides a channel for the leakage current. The parasitic capacitance The changing voltage will stimulate the corresponding leakage current, causing problems such as EMI and causing safety hazards and malfunctions of protection equipment, etc.

[0005] Since the frequency and size of the leakage current vary greatly depending on the control method, device characteristics, weather conditions and other environmental factors, traditional filtering techniques such as LC filters, H5 circuit or H6 circuit improvement methods are all effective in suppressing dynamic leakage. There are certain limitations in terms of current

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