MMC AC side near-end asymmetric fault short-circuit current calculation method
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A technology of short-circuit current and calculation method, which is applied in the directions of reducing the asymmetry of polyphase networks, eliminating/reducing asymmetry of polyphase networks, power transmission AC networks, etc. MMC and other issues
Pending Publication Date: 2022-04-01
STATE GRID FUJIAN POWER ELECTRIC CO ECONOMIC RES INST
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Considering that the system structure and control system characteristics of MMC are completely different from those of LCC, the existing LCC AC side fault current analysis and calculation methods cannot be directly applied to MMC
In addition, the current research on the MMC-HVDC system in th
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Embodiment 1
[0090] Please refer to figure 1 , Embodiment 1 of the present invention is:
[0091] A method for calculating the short-circuit current of an asymmetric fault near the MMC AC side, which is used to analyze the characteristics and influencing factors of the short-circuit current when the AC grid side of the MMC-HVDC system is faulty, especially in the case of an asymmetric fault, including steps :
[0092] S1. Use the phase sequence separation module to convert the AC voltage u at the common coupling point PCC of the MMC to s and the alternating current i s Separated into positive and negative sequence dq axis components, we get
[0093] S2. Calculate the real-time active power P and real-time reactive power Q transmitted by the MMC when an asymmetrical fault occurs according to the instantaneous power theory;
[0094] S3. Determine the type of the power outer loop controller, and calculate the command value of the dq axis current of the MMC positive sequence according to...
Embodiment 2
[0099] Such as Figure 2 to Figure 7 , the second embodiment of the present invention is:
[0100] A method for calculating the asymmetric fault short-circuit current at the near end of the MMC AC side, on the basis of the first embodiment above, in this embodiment, step S1 specifically includes the following steps:
[0101] S11, collect the AC voltage u of the common coupling point PCC s and the alternating current i s ;
[0102]S12. Calculate the AC voltage u according to formulas (1) and (2) s and the alternating current i s The voltage component u in the two-phase stationary coordinate system α , u β and current component i α i β ;
[0103]
[0104] where u s,a , u s,b , u s,c is the AC voltage u s The three-phase component;
[0105]
[0106] where i s,a i s,b i s,c is the three-phase component of the alternating current;
[0107] S13. Calculate the positive and negative sequence components of the voltage in the two-phase stationary coordinate syste...
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Abstract
The invention provides an MMC alternating-current side near-end asymmetric fault short-circuit current calculation method. The method comprises the steps that alternating-current voltage and current at a PCC are decomposed into positive-sequence dq-axis components and negative-sequence dq-axis components through a phase sequence separation module; calculating real-time active power and reactive power transmitted by the MMC when an asymmetric fault occurs according to an instantaneous power theory; judging the type of a power outer loop controller, calculating a positive sequence dq-axis current instruction value, and converting the positive sequence dq-axis current instruction value into a positive sequence dq-axis current instruction value and a negative sequence dq-axis current instruction value; according to the MMC mathematical model of the positive and negative sequence dq-axis components and the mathematical model of the positive and negative sequence decoupling inner loop current controller, solving a transfer function of the positive and negative sequence current output by the MMC and the instruction value of the positive and negative sequence dq-axis current; and calculating the short-circuit current fed into the short-circuit point by the MMC according to the positive and negative sequence current. According to the method, reference is provided for MMC controller parameter setting and alternating current system relay protection parameter setting, and the method can be used for analyzing the active power and reactive power characteristics of MMC transmission after an asymmetric fault occurs on the near-end alternating current side of the MMC.
Description
technical field [0001] The invention relates to the technical field of flexible direct current transmission systems, in particular to a calculation method for asymmetric fault short-circuit current at the near end of an MMC AC side. Background technique [0002] Compared with conventional DC transmission, flexible DC transmission does not have the problems of commutation failure and reactive power compensation of the grid, and can independently adjust active and reactive power. Its harmonic level is low, and it is easy to build a multi-terminal system. It can supply power for weak systems and even passive systems. , especially suitable for grid connection of renewable energy power generation. The modular multilevel converter (MMC) has greatly improved the transmission capacity and voltage level of the flexible direct current transmission system, making flexible direct current transmission more widely used, such as Nanhui, Xiamen, Zhoushan, Nanao The construction of seven so...
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IPC IPC(8): H02J3/36H02J3/26H02J3/38H02H7/26
CPCY02E40/50Y02E60/60
Inventor 林毅林威魏鑫薛静玮唐雨晨刘崇茹朱睿林章岁吴威
Owner STATE GRID FUJIAN POWER ELECTRIC CO ECONOMIC RES INST
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