Balance control strategy for unbalanced current among multiple MMC converters in extra-high voltage hybrid cascaded DC power transmission system
A DC power transmission system and hybrid cascade technology, applied in power transmission and AC networks, etc., can solve problems such as unbalanced current, overcurrent damage to equipment, etc., and achieve the effects of improving reliability, speeding up fault recovery time, and simplifying operations.
Active Publication Date: 2020-02-21
NORTH CHINA ELECTRIC POWER UNIV (BAODING)
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Problems solved by technology
[0003] In the case of LCC step-down on the inverter side or faults on the AC side that lead to commutation failure of the LCC on the inverter side, unbalanced currents will be generated between the MMCs connected in parallel at the inverter station due to different control methods, and even overcurrent will occur in severe cases. damage equipment
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[0033] The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.
[0034] The present invention provides a balanced control strategy for unbalanced current among multi-MMC converters in an UHV hybrid cascaded direct current transmission system. The control strategy determines the amount of unbalanced current by the following formula:
[0035]
[0036] The calculated unbalanced current is:
[0037] Such as figure 1 Shown is when n=3, the block diagram of the balanced control strategy of unbalanced current among many MMC converters in a kind of UHV hybrid cascaded direct current transmission system described in the present invention, now unbalanced current amount is
[0038] Such as figure 2 As shown, the topology (unipolar structure) of the UHV hybrid cascaded DC transmission system, the rectifier side adopts the series structure of two 12-pulse LCCs, and the inverter side adopts the stru...
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The invention provides a balance control strategy for unbalanced current among multiple MMC converters in an extra-high voltage hybrid cascaded DC power transmission system. The rectification side ofthe extra-high voltage hybrid cascaded DC power transmission system adopts a double 12-pulse LCC structure, and the inversion side of the extra-high voltage hybrid cascaded DC power transmission system adopts a structure in which one LCC is connected in series with a plurality of parallel-connected MMCs. The control strategy provided by the invention is suitable for the unbalanced current generated when the LCC voltage of the inversion side is greatly reduced or the commutation failure voltage is reduced to zero under an AC side fault of the inversion side of the equalization system. Compensation is made to an active power outer loop of constant power control MMCs on the inversion side according to the calculated unbalanced current conversion success rate, so as to achieve the purpose of current power balancing, reduce the over-current level during voltage reduction and shorten the fault recovery time. Under the condition that imbalance detection is not needed, current equalization among multiple MMCs is simply and quickly realized, and the stability of the system is improved. The attached drawing of the abstract is an unbalanced current balance control block diagram taking three MMCs as an example.
Description
technical field [0001] The invention relates to a device in the technical field of power transmission and distribution, in particular to a balancing control strategy for unbalanced current among multiple MMC converters in an UHV hybrid cascaded direct current transmission system. Background technique [0002] Based on the Baihetan-Jiangsu UHV hybrid cascaded DC transmission system currently planned in my country, it is planned to adopt a structure in which the sending-end LCC and the receiving-end LCC are connected in series with three parallel MMCs, and the three parallel MMCs can provide the LCC of the inverter station Reactive power support can reduce the risk of commutation failure to a certain extent. At the same time, the unidirectional conduction of LCC converter current can also block the fault current of MMC when a DC fault occurs, so it has good technical and economic advantages. [0003] In the case of LCC step-down on the inverter side or faults on the AC side tha...
Claims
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IPC IPC(8): H02J3/36
CPCH02J3/36Y02E60/60
Inventor 郭春义吴张曦杨硕赵成勇
Owner NORTH CHINA ELECTRIC POWER UNIV (BAODING)