Voltage-sharing and current-sharing control method for chopper of superconducting magnetic energy storage system

Abstract

The invention relates to a voltage-sharing and current-sharing control method for a chopper of a superconducting magnetic energy storage system. An adopted chopper comprises n + m chopper sub-moduleswith the same structure, the middle terminal of the chopper sub-module SM1 is connected with the positive electrode of the direct current bus, the middle terminal of the chopper sub-module SMk is connected with the lower terminal of the chopper sub-module SMk-1, and the lower terminal of the chopper sub-module SMn + m is connected with the negative electrode of the direct current bus; the n + m chopper sub-modules are sorted according to the magnitude of the current of the superconducting magnet after each control period; when the superconducting magnetic energy storage system is charged, n chopper sub-modules are sequentially selected according to the current of the superconducting magnet from small to large, and for each selected chopper sub-module, the charging power of the superconducting magnet Lsc is kept equal to the charging power of the capacitor C, so that the voltage of the capacitor C is kept constant; and the remaining m chopper sub-modules are controlled, and the superconducting magnet Lsc are kept in a follow current state all the time in a control period.

Description

technical field [0001] The invention relates to the field of superconducting magnetic energy storage systems, in particular to a chopper. Background technique [0002] Superconducting Magnetic Energy Storage (SMES) system is a fast and efficient energy storage device that stores energy in superconducting magnets. Compared with energy storage devices such as mechanical energy storage and electrochemical energy storage, the SMES system has the advantages of fast response, high cycle times, high power density, and high energy conversion rate, and can be used to suppress the grid-connection of new energy sources such as photovoltaics and wind power. frequency fluctuation of the power system; improve the transient stability of the power grid; enhance the reliability of power supply for important loads, etc. [0003] As the core part of the SMES system, the chopper's main function is to realize the controllable energy exchange between the superconducting magnet and the grid. At ...

AI Technical Summary

Problems solved by technology

At present, most SMES systems use single-phase choppers. Due to the limitation of the cut-off voltage of switching devices, single-phase choppers are only suitable for occasions with low voltage levels.

The turn-off voltage of each switching device of the neutral-point clamped single-phase chopper is only half of the pole-to-pole voltage of the DC bus, which is suitable for occasions with high voltage levels, but the control logic of this type of structure is complex and the scalability is poor , and prone to midpoint potential drift

[0004] It is technically difficult to significantly increase the voltage level of single-phase choppers. Connecting multiple single-phase choppers in series to a higher voltage level is an effective measure to solve this problem. At the same time, connecting multiple single-phase choppers in series The chopper formed can be connected to multiple superconducting magnets, which can effectively increase the energy storage of the SMES system as a whole, but the reliability of the chopper is low, and a failure of a single-phase chopper will cause the chopper to exit as a whole At the same time, it is difficult to ensure that the parameters of each capacitor and each superconducting magnet in the chopper are completely consistent in actual engineering, and it is difficult to maintain the voltage balance of each capacitor and the current balance of each superconducting magnet.

The unbalanced capacitor voltage may cause overvoltage of some devices, and the unbalanced superconducting magnet current will cause some superconducting magnets to complete the charging and discharging process first, while the remaining superconducting magnets are forced to stop charging and discharging, thereby weakening the overall discharge depth of the SMES system

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