Current differential protection method, device and system for grid-connection tie lines of large-scale inverter type power supply

Abstract

The invention discloses a current differential protection method, device and system for grid-connection tie lines of a large-scale inverter type power supply based on a negative sequence component. The current differential protection method comprises the steps of S1, collecting current flowing through protection 1 and protection 2 at two ends of a tie line PQ, and calculating the corresponding current phasor; S2, respectively calculating a positive sequence component, a negative sequence component and a zero sequence component of the current phasor at two ends of the tie line; S3, respectivelycalculating synthesis current of the system side and the inverter type power supply side so as to give prominence to the negative sequence current difference of the two ends of the tie line; S4, calculating a differential ratio coefficient; S5, respectively calculating differential current Idiff.phi of phase lines in three phases; S6, setting a protection action threshold Krel and a segregated phase current differential protection set value Iset, and determining that there is a fault in the tie line area when one of the following conditions is met: the differential ratio coefficient Cdiff isless than or equal to the protection action threshold Kref, or the differential current Idiff.phi is greater than the segregated phase current differential protection set value Iset; and S7, if it isjudged that there is a fault in the tie line area, sending a trip signal by the protection so as to isolate the tie line fault area from the system. The current differential protection method can reliably differentiate faults inside or outside the area from the normal operation condition, and overcomes a problem of low sensitivity of the traditional current differential protection.

Description

technical field [0001] The invention relates to the technical field of electric power system relay protection, in particular to a method, device and system for current differential protection of large-scale inverter power grid-connected tie lines. Background technique [0002] Inverter-interfaced generators (IIG) represented by photovoltaic cells and permanent magnet direct-drive wind turbines are being integrated into the grid on a large scale. Compared with the traditional AC synchronous generator set, the inverter power supply is mainly composed of power electronic devices. On the one hand, the ability of these power electronic devices to withstand overvoltage and overcurrent is weaker. On the other hand, the transient response time of the inverter power supply Short, with the characteristics of nonlinear and strong coupling, its fault characteristics are mainly determined by the control strategy during the fault period. These flexible fault control strategies lead to sig...

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Problems solved by technology

[0005] The technical problem to be solved in the present invention is: based on the fault current characteristics of the inverter power supply under the positive sequence component control strategy, a large-scale inverter power supply grid-connected tie line current differential protection method based on the negative sequence component is proposed to overcome Under the characteristics of large-scale inverter power supply fault current limiting, the sensitivity of the traditional current differential protection of the inverter power supply tie line is low, and the protection may have the problem of failure to operate due to faults in the area, so as to ensure the safe and reliable operation of large-scale inverter power supply grid-connected

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