Method and system for neutral point potential balance of two-stage three-level three-phase four-wire energy storage converter

Abstract

The invention discloses a method and system for balancing the midpoint potential of a two-stage three-level three-phase four-wire energy storage converter, comprising: according to the low voltage in the three-level Buck / Boost circuit in the energy storage converter Side inductor current reference value i Lref , control the three-level Buck / Boost circuit to work in Boost mode or Buck mode; refer to Δu according to the midpoint potential ref The difference from the midpoint potential offset Δu is used to adjust the duty cycle of each switch in the Buck / Boost circuit in Boost mode or Buck mode, so that the total DC bus voltage is constant and the midpoint potential is balanced. The invention has the advantages of constant total voltage of the DC bus, balanced midpoint potential, and improved operation stability of the converter.

Description

technical field [0001] The invention mainly relates to the technical field of energy storage, in particular to a method and system for balancing the midpoint potential of a two-stage three-level three-phase four-wire energy storage converter. Background technique [0002] Energy storage technology has broad application prospects in the fields of improving power grid reliability, demand side management, and new energy access. The integration of energy storage into the power system can improve the security and stability of the power grid, alleviate the load peak-to-valley difference, improve power quality, and promote the application of renewable energy; it forms an independent microgrid with distributed power sources, which can improve the stability of the microgrid system. Electrochemical energy storage systems mainly include battery management systems (BMS) and bidirectional energy conversion systems (Power Conversion System, PCS). It mainly has the following functions: 1)...

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Problems solved by technology

[0004] Among them, the unbalanced component of the midpoint potential of the three-level inverter circuit includes a DC component and an AC component, which will cause many problems: 1) cause output voltage waveform distortion, and increase the content of low-order harmonics; 2) increase the voltage stress of the device, It is easy to cause overvoltage damage to the device

In the above method, the introduction of "transition vector" and the decomposition of zero level lead to an increase in the number of switches participating in the neutral point potential balance phase in a control cycle, which increases the switching loss, and for the case of a large load imbalance, the medium Limited ability to suppress point potential oscillations

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