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SOC equalization control method for energy-storage MMC under unbalanced network pressure

A technology of balanced control and balanced network, applied in the power field, can solve the problems of inconsistent SOC change rate of sub-modules, unbalanced three-phase grid-connected power, etc., to achieve rapid SOC balance and avoid waste.

Inactive Publication Date: 2020-02-14
CHANGSHA UNIVERSITY OF SCIENCE AND TECHNOLOGY
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Problems solved by technology

However, the modular multilevel converter also has shortcomings. In terms of its control, the balance of the sub-module capacitor voltage and the circulation problem between the bridge arms have always been the focus of research

Method used

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  • SOC equalization control method for energy-storage MMC under unbalanced network pressure
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  • SOC equalization control method for energy-storage MMC under unbalanced network pressure

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Embodiment Construction

[0022] The topology of the MMC is as figure 2 As shown, according to its topology and Kirchhoff's current-voltage law, the expressions of bridge arm current and bridge arm voltage can be obtained:

[0023]

[0024]

[0025] where L a Inductance of the bridge arm; j = a, b, c; u j is the phase output voltage; i j Measure the output current for AC; u jp and u jn are the equivalent voltages of the upper and lower bridge arms respectively; i jp and i jn Respectively, the upper and lower bridge arm currents; U dc is the DC bus voltage.

[0026] i diffj is j-phase circulation, its expression is:

[0027]

[0028] where i diffj_dc is the DC component in the j-phase circulating current; i diff_m Is the amplitude of the i-time circulating current in the j-phase.

[0029] The analysis of the internal circulation mechanism of MMC shows that under symmetrical working conditions, the circulation current of MMC mainly contains the second harmonic component of the curre...

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Abstract

The invention discloses an SOC equalization control method for an energy-storage MMC under unbalanced network pressure. The method can enable the energy-storage MMC to carry out stable SOC equalization control under unbalanced network pressure. Firstly, circulation components in the three-phase circulation expression and instantaneous power expressions of sub-modules under unbalanced network pressure are analyzed. It is found that the difference of three-phase AC power is the cause of SOC imbalance and the 2-fold frequency doubling component in the circulation will affect SOC equalization control. Therefore, 2-fold frequency circulation is taken as the target to set a circulation reference value to suppress the 2-fold frequency doubling component to 0 by a quasi-PR controller. By using theimproved droop control to equalize the SOC value of the sub-module, the equalization time can be shortened, waste in the aspect of energy distribution due to too long equalization time is avoided, and finally SOC equalization between phases and within phases is achieved.

Description

technical field [0001] The patent of the invention relates to an SOC balance control method of an energy storage type MMC under unbalanced network voltage in flexible direct current transmission, which belongs to the field of electric power technology. Background technique [0002] The high-voltage flexible DC transmission technology based on Modular Multilevel Converter (MMC), as a new type of DC transmission technology for contemporary voltage source converters, is the focus of research on flexible DC transmission technology today. Compared with the traditional DC transmission technology, the MMC-based flexible DC transmission technology does not have the problems of reactive power compensation and commutation failure, and can supply power for passive systems, and has the ability to independently adjust active and reactive power. However, the modular multilevel converter also has deficiencies. In terms of its control, the balance of the sub-module capacitor voltage and the...

Claims

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Application Information

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IPC IPC(8): H02J3/32H02J3/26H02J3/36H02M7/483
CPCH02J3/26H02J3/32H02J3/36H02M7/483Y02E40/50Y02E60/60
Inventor 夏向阳徐雷刘奕玹
Owner CHANGSHA UNIVERSITY OF SCIENCE AND TECHNOLOGY