Photovoltaic inverter unit and three-phase photovoltaic grid-connected generation device

Abstract

The invention discloses a photovoltaic inverter unit and three-phase photovoltaic grid-connected generation device. The photovoltaic inverter unit comprises an in-series connected inverter module and a transformer module, wherein the in-series connected inverter module a comprises two parallel-connected three-phase invertors and the transformer module comprises a transformer and the primary side of the transformer is connected to the output end through the series winding connected by Y and the secondary side of the transformer is connected to the alternating current side of the two three-phase inverters respectively through series winding connected by Y and D. The three-phase photovoltaic grid-connected generation device comprises a photovoltaic array and the photovoltaic inverter unit, wherein the photovoltaic array is connected to the direct current side of the photovoltaic inverter unit and the alternating current side of the photovoltaic inverter unit is connected to the grid. The photovoltaic array outputs the direct current and transforms to the three-phase alternating current through the photovoltaic inverter unit and then output to grid. The output voltage low frequency harmonics is capable of being eliminated by utilizing phase-shifting technique and the primary current is consistent with the secondary side current. The photovoltaic inverter unit and three-phase photovoltaic grid-connected generation device have the advantages of being simple in structure, being low in cost, being small in volume and being high in conversion efficiency and the like.

Description

technical field [0001] The invention relates to the technical field of photovoltaic power generation, in particular to a photovoltaic inverter unit and a three-phase photovoltaic grid-connected power generation device. Background technique [0002] The cost of photovoltaic power generation is usually higher than the cost of conventional energy. Research on inverter products with better performance, lower cost and greater adaptability is of great significance for reducing the cost of photovoltaic power generation. The increase of the single inverter capacity can reduce the cost per watt, reduce the space occupied by the inverter and reduce the installation cost. At present, the single inverter capacity has been continuously increased from the earliest 250kW to 500kW, and some container type The inverter has been able to reach 1MW. However, at present, the increase of inverter capacity is achieved by connecting multiple modules in parallel or simply increasing the operating v...

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Problems solved by technology

However, at present, the increase of inverter capacity is achieved by connecting multiple modules in parallel or simply increasing the operating voltage level of the inverter. Affected by factors such as the cost of IGBT power devices and main circuit switching devices, the capacity of a single unit and the integration There is limited space for improving the degree of integration, which cannot meet the needs for higher capacity and integration.

[0003] Some practitioners proposed to use transformer cascading technology to realize high-power three-phase photovoltaic inverter, but in this type of scheme, the primary side and secondary side of the transformer use the same connection method, such as D / Y, D / D, Y / Y, Y One of the / D connections, that is, the connection groups of the primary side and the secondary side are consistent, and the transformation ratios of each transformer are the same. To eliminate the fundamental harmonic and improve the output voltage waveform, one method is to increase the switch Frequency implementation, this method will increase the system loss and the difficulty of heat dissipation design; another method is to use high-level inverter power modules or through the series superposition of the secondary side of multiple output transformers, and the secondary sides of multiple output transformers are superimposed in series The method usually adopts the PWM modulation method of sawtooth wave phase shifting, and superimposes in series through the secondary side of the output transformer, so that the superimposed output voltage becomes a multi-level ladder wave voltage to achieve the purpose of eliminating fundamental harmonics. High-level inverter power modules or the above-mentioned multi-output transformer secondary side series superposition method will increase the complexity of the system, and the actual implementation is difficult

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