Photovoltaic grid-connected inverter and control method

Abstract

The invention discloses a photovoltaic grid-connected inverter. The photovoltaic grid-connected inverter comprises a photovoltaic array, a plurality of unit bodies, three unit body series branches, an alternating current reactor, a grid-connected switch, unit body controllers and a master controller, wherein the preceding stage of each unit body is respectively connected with the photovoltaic array; the unit body series branches are connected into a power grid after being connected with the alternating current reactor and the grid-connected switch in series; and each unit body comprises one of the unit body controllers. The invention also discloses a photovoltaic grid-connected inverter control method. In the inverter and the control method disclosed by the invention, the unit bodies are connected in series instead of directly connecting power devices in series, so that the problem of voltage-sharing of devices are solved; the power level is high; the limitation of load capacity of power electronic devices is overcome; a unit phase shift wave overlapping technology is adopted, so that an output harmonic wave is small; because of the action of an energy storage battery, when illumination disappears suddenly, a system cannot be off-grid and standby suddenly; and because of adopting a unit body automatic bypass technology, the security of the system is improved.

Description

technical field [0001] The invention relates to the technical field of photovoltaic power generation, in particular to a photovoltaic grid-connected inverter and a control method. Background technique [0002] Solar energy is one of the most dynamic new energy sources in the 21st century. Photovoltaic power generation is developing from small-scale off-grid power generation to large-scale grid-connected power generation. The capacity of photovoltaic grid-connected power generation systems is increasing, and megawatt-level systems are the direction of future development. Therefore, it is of great significance to study high-power high-voltage photovoltaic grid-connected inverters and their control methods. [0003] Photovoltaic grid-connected inverters based on various topologies and control methods have been widely studied, but it is still difficult to meet the requirements of stability, safety, economy and high power quality, as follows: [0004] Because the output power o...

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Problems solved by technology

[0004] Because the output power of the photovoltaic system depends on the lighting conditions, and the lighting is uncertain, the grid-connected power fluctuates greatly, especially when the lighting is suddenly blocked, the system has to go off-grid and stand by, and the operation is unstable; a switch tube in the system Partial failures such as battery panels and other local faults often lead to downtime, and the safety of the system is low; the output voltage level of the photovoltaic system is low, and the grid connection generally needs to be boosted by a transformer, which increases the cost of the system; limited to the load capacity of current power electronic devices , it is difficult to further increase the power level of photovoltaic grid-connected inverters, especially to achieve the level of a single megawatt; moreover, as the power level increases, the operating frequency of the switching tube will inevitably decrease, which will lead to current harmonics wave problem

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