A power balance control method for cascaded h-bridge photovoltaic grid-connected inverters

Abstract

The invention discloses a power balance control method for cascaded H-bridge photovoltaic grid-connected inverters, the purpose of which is to enable three-phase common DC bus cascaded H-bridge photovoltaic grid-connected inverters to output power between photovoltaic arrays It can still operate normally when it is seriously unbalanced. The steps are: control the voltage of N public DC buses; select the output power command value of N public DC buses; control the grid current without static difference; judge the working mode of the system, and use different modulation wave calculation methods , Calculate the modulation waves of all H-bridges; control the output voltages of all three-level full-bridge LLC converters. Using this method, the system can still operate normally when the modulation degree of some H-bridge converters is greater than 1.155, which greatly improves the ability of the three-phase common DC bus cascaded H-bridge photovoltaic grid-connected inverters to cope with power imbalance.

Description

technical field [0001] The invention belongs to photovoltaic power generation technology in the field of electrical engineering, and in particular relates to a power balance control method for cascaded H-bridge photovoltaic grid-connected inverters. Background technique [0002] According to the "Global Renewable Energy Status Report 2019", the new installed capacity of photovoltaic power generation in 2018 was about 100GW, of which photovoltaic power plants with a power level greater than 5WM contributed about 50% of the installed capacity. In the future, large-scale photovoltaic power plants will still occupy a large market share. This is because the power generation cost per watt of high-power systems is lower than that of low-power systems, which will help realize photovoltaic power grid parity and become more commercially attractive. Compared with the centralized and string topology, the three-phase isolated cascaded H-bridge photovoltaic inverter has outstanding advant...

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Problems solved by technology

[0004] However, the common DC bus cascaded H-bridge photovoltaic grid-connected inverter introduced above still has the problem of power imbalance between modules in the phase, the literature "Xing Zhang, Mingda Wang, Tao Zhao, Wang Mao, Yuhua Hu, Renxian Cao. Topological Comparison and Analysis of Medium-Voltage and High-Power Direct-linked PV inverter[J]. CES Transactions on Electrical Machines and Systems, 2019, 3(4): 327-334. (Xing Zhang, Mingda Wang, Tao Zhao , Wang Mao, YuhuaHu, Renxian Cao, Topology comparison and analysis of medium-voltage high-power direct-mounted photovoltaic grid-connected inverters, CES Journal of Electric Machines and Systems, 2019, Volume 3, Issue 4, Pages 327 to 334)” No detailed analysis of the power imbalance between modules in the phase of this topology has been carried out, and no relevant control strategy has been proposed to solve this problem

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