Double-frequency transformer-free type single-phase photovoltaic grid-connected inverter

Abstract

The invention relates to the technical field of inverters, in particular to a double-frequency transformer-free single-phase photovoltaic grid-connected inverter which comprises an inverter shell, a circuit board is arranged in the inverter shell, and a control unit and a main loop unit are arranged on the circuit board, the main loop unit is divided into a power unit and a resonance elimination unit, and the resonance elimination unit and the power unit are connected to two sides of a single-phase power grid in parallel; the bus cathode of the resonance elimination unit is connected with thebus cathode of the power unit through a connecting capacitor; the LA terminal and the LB terminal of the power unit are connected to the L terminal and the N terminal of a power grid through a power filter. The HA terminal and the HB terminal of the resonance elimination unit are connected to the L terminal and the N terminal of the power grid through a resonance elimination filter to form the main loop unit; through a novel topological structure and a control algorithm, the ground leakage current of the transformerless grid-connected inverter is effectively suppressed, and meanwhile, the overall efficiency and the power density of the inverter are improved.

Description

【Technical field】 [0001] The invention relates to the technical field of inverters, in particular to a dual-frequency transformerless single-phase photovoltaic grid-connected inverter. 【Background technique】 [0002] The development of renewable energy is an important means to solve environmental problems, and photovoltaic grid-connected power generation system is an important form of renewable energy, photovoltaic grid-connected inverter is an important part of it, how to further improve the performance of grid-connected inverter Efficiency and quality of grid-connected current, while reducing size and cost, have received a lot of attention. The transformerless grid-connected inverter does not require a single-phase transformer between the inverter and the grid, so it has advantages in terms of cost, reliability, structural simplicity, and efficiency, and has been widely used in 2.5kW~ In the distributed photovoltaic power generation system within the power range of 8kW. ...

AI Technical Summary

Problems solved by technology

In order to improve the efficiency of the inverter, it is necessary to use a lower switching frequency, but this increases the volume of the passive filter; conversely, in order to reduce the volume of the passive filter, it is necessary to increase the switching frequency, which will reduce the inverter The efficiency of the inverter, while increasing the design difficulty of the cooling system

At the same time, reducing the switching frequency for the H5 structure and HERIC structure will also increase the amplitude of the high-frequency component of the negative (positive) voltage of the DC bus, thereby increasing the amplitude of the ground leakage current

[0007] In terms of the complexity of the structure and control algorithm, in order to further reduce the leakage current level, various improvement schemes have been proposed from the aspects of modulation strategy, increasing the number of switches to improve the topology, clamping the neutral point voltage, and blocking the leakage current loop. Compared with the topologies of H5 and HERIC basic transformerless grid-connected inverters, they all increase the difficulty of the topology or (and) control strategy to varying degrees, and increase the cost of the system to a certain extent.

[0008] It can be seen that although the transformerless grid-connected inverter has been widely used, it still needs further improvement in terms of leakage current, efficiency and implementation complexity.

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