Non-isolated intermediate-point clamping photovoltaic grid connected inverter and modulation method thereof

Abstract

The invention provides a non-isolated intermediate-point clamping photovoltaic grid connected inverter and a modulation method thereof. The non-isolated intermediate-point clamping photovoltaic grid connected inverter is arranged between a photovoltaic array output unit and an AC power grid, and comprises a capacitor bank, a clamping unit, a freewheeling unit and first and second legs; the first leg is in parallel connection with the capacitor bank, second leg and photovoltaic array output unit; the positive end of the clamping unit is connected with the freewheeling unit and the second leg, and the negative end of the clamping unit is connected to the intermediate point of the capacitor bank; one end of the freewheeling unit is connected with the positive end of the clamping unit, and theother end of the freewheeling unit is connected with the intermediate point of the first leg; and a point a of the first leg and a point b of the second leg form an AC voltage output end of the non-isolated intermediate-point clamping photovoltaic grid connected inverter. Thus, common-mode voltage oscillation caused by a switch junction capacitance parameter can be eliminated, and common-mode grounding leakage current caused by the switch junction capacitor is inhibited effectively.

Description

technical field [0001] The invention relates to the field of electric energy conversion and new energy distributed grid-connected power generation, and specifically relates to a non-isolated neutral point clamp photovoltaic grid-connected inverter and a modulation method thereof. Background technique [0002] Distributed photovoltaic power generation has the advantages of decentralized power generation, local use, avoiding investment and loss in power transmission and distribution, and no need to occupy additional land, and has been valued by countries all over the world. According to the function, photovoltaic inverters are divided into off-grid inverters and grid-connected inverters; the output of off-grid inverters is voltage, which is mainly used for energy storage systems and places that cannot be reached by the grid in remote areas; grid-connected inverters The output of the inverter is current, which is mainly used in the grid-connected system to obtain income or self...

AI Technical Summary

Problems solved by technology

(1) The power frequency isolated inverter can realize the electrical isolation between the photovoltaic side and the grid side to suppress the leakage current, but it increases the problems of cost, volume and loss, and there are many deficiencies in industrial applications

(2) High-frequency isolated inverters reduce system volume and cost, but the power level is divided into several levels, which affects reliability and does not significantly improve the overall efficiency of the system

However, due to the existence of switch junction capacitance, the leakage current loop cannot be completely cut off, causing the ground voltage at the midpoint of the inverter output bridge arm to be in a suspended and uncertain state during the grid-connected current continuous flow stage, and the common-mode voltage cannot be guaranteed to be constant, thus Generates common mode leakage current

The generation of common-mode leakage current will cause problems such as grid-connected current distortion and electromagnetic interference, especially posing a threat to personal safety

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