Module power equalization control method for cascade photovoltaic solid-state transformer

Abstract

The invention discloses a module power equalization control method for a cascade photovoltaic solid-state transformer and is to realize equalization control of active power between modules when a system operates under non-unit power factor and the number of modules contained in the three phases is not equal. The method comprises the following main steps: controlling average DC side capacitor voltage of all H-bridge converters and obtaining an active current instruction value; controlling grid current and compensating three-phase modulation voltage with the calculated zero-sequence voltage to realize module power equalization control; controlling the output voltage of a two-level full-bridge LLC converter; and controlling input bus voltage of a Boost converter to realize maximum power pointtracking control of a pre-stage photovoltaic array. Compared with existing technologies, the method can ensure that all modules transmit the same active power when the number of three-phase modules is not equal regardless of whether the system operates under unit power factor, thereby facilitating modular design.

Description

technical field [0001] The invention belongs to photovoltaic power generation technology in the field of electrical engineering, and in particular relates to a module power balance control method of cascaded photovoltaic solid-state transformers. Background technique [0002] Due to the limitations of semiconductor switching devices, it is practically challenging and uneconomical to increase the power rating of conventional centralized inverters above 1WM. One of the methods can use a three-phase solid-state transformer topology based on cascaded H-bridge multilevel converters. The modular structure can use common low-voltage components on the market to expand the entire system to higher voltage and power levels, making it possible to connect the entire power station to the medium-voltage grid with only a single converter. Since the high-frequency transformer in the isolated DC / DC converter can provide electrical isolation, bulky power-frequency transformers are no longer n...

AI Technical Summary

Problems solved by technology

[0009] 1) It is necessary to add additional auxiliary devices to make the system operate under fault conditions, which will increase the cost and complexity of the system and reduce the reliability of the system

[0010] 2) The existing literature mentions the module power balance control of cascaded photovoltaic solid-state transformers under fault conditions, but the proposed method is not suitable for converters operating under non-unity power factors

Images