Current rate of change and incremental protection method for bidirectional converter flexible direct current power supply system

Abstract

The application provides a current change rate and increment protection method of a bidirectional converter flexible direct current power supply system, comprising the following steps: step S1: continuously monitoring di / dt, when the value of di / dt reaches a starting value S and the duration meets an anti-shake delay tS, starting protection, and starting to count a reset delay tR at the same time; step S2: simultaneously performing protection of a quick action section, a blocked pulse action section and an unblocked pulse action section, when the quick action section, the blocked pulse action section and the unblocked pulse action section meet an action condition, tripping the outlet, and the quick action section, the blocked pulse action section and the unblocked pulse action section are not provided with a condition for determining whether to reset by judging the size of di / dt; step S3: after the reset delay tR is exceeded, all protections are reset. The application can correctly identify whether a fault point occurs at a near end, a middle end, a far end or a terminal of cross-zone power supply.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of rail transit, and particularly relates to a current rate of change and increment protection method for a bidirectional converter HVDC power supply system. BACKGROUND

[0002] With the emergence of global climate change posing a major threat to human society, more and more countries have raised "carbon neutrality" as a national strategy and proposed a vision of a carbon-free future. In the field of urban rail transit, the bidirectional converter HVDC power supply system, which has green and low-carbon characteristics such as bidirectional energy flow, controllable DC characteristics, adjustable power factor, and small harmonic content, has gradually entered the stage of popularization and application from development and trial, and accordingly, the relay protection for ensuring the safe and reliable operation of the power supply system has also brought new problems and challenges.

[0003] A bidirectional converter HVDC power supply system is shown in Figure 1 According to the simulation results of different short-circuit points of the bidirectional converter HVDC power supply system under various operating conditions, when a short circuit occurs, as the short-circuit current increases, the bidirectional converter will enter an uncontrollable state when the voltage decreases to a certain value (about 1400V in a 1500V system), and the IGBT will block the pulse; the converter outputs current through the freewheeling diode of the IGBT module, at which time the voltage is no longer controlled, and it transitions to a large-impedance rectifier device. During the transient transition process, di / dt and the current amplitude will fluctuate, and as the short-circuit point approaches the end of the large double-sided zone, the initial time of pulse blocking is distributed between 0-200ms after the short circuit, and when the short-circuit point is close to the end of the large double-sided zone, as the short-circuit current decreases, the amount of bus voltage decrease caused by the short circuit decreases, and the bidirectional converter does not enter the pulse blocking state.

[0004] Taking the short-circuit simulation waveform at one point as an example, the current and voltage waveforms of a single 3MW bidirectional converter short-circuit at 2km are shown in Figure 2 , and the di / dt waveform is shown in Figure 3 . Among them, the cursor 1 is the blocking point, and the cursor 2 is the peak point. From the simulation graph, it can be seen that the current waveform fluctuation amplitude is not large, and the voltage and di / dt waveforms have obvious sawtooth fluctuations during the transient transition process.

[0005] The existing DC power supply system relay protection is provided with: large current tripping protection (circuit breaker body), current quick-break protection, overcurrent protection, di / dt & delta I protection, catenary thermal overload protection, double-sided tie-in protection, low voltage protection (alarm), etc. Among these protections, the di / dt & delta I protection is the most affected during the transient fluctuation change process of the bidirectional converter pulse blocking, and due to the up and down fluctuations of di / dt near zero, it may directly cause partial or complete protection functions of the di / dt & delta I protection of different manufacturers to fail due to reset.

[0006] For di / dt & ΔI fast section, ΔI value is relatively large because it is matched with adjacent near-end short circuit, and is mainly used as protection for near-end to intermediate section. di / dt reset value is included in protection action judgment logic of each manufacturer, which is used to filter some false start signals of non-true short circuit, such as di / dt reset value is same as start value in Sitras PRO of Siemens, and the value is generally 40-60 A / mS, and reset delay can be set to 1-4 mS. The principles of SPCOS-NG of Xishu Long and ZJK-11 of 712 are basically same, di / dt reset value F is independent of start value, and the value is generally 15 A / mS, and if di / dt < F, it is reset immediately without delay. Reset value of Bao Fu DCP3 is independent of start value (similar to SPCOS-NG), and reset delay can be set to 1-10 mS. In summary, if short circuit point ΔI action value falls in transient fluctuation process of pulse blocking of bidirectional converter, it may be reset, and thus the action result of this section protection is affected, and the protection range of ΔI protection is relatively reduced.

[0007] For di / dt & ΔI delay section, principles of each manufacturer are also different, and delay di / dt value is generally 40-60 mS, and except that ΔI and delay setting value are different, di / dt value for judging whether protection is reset and reset delay logic are basically similar to fast section. For short circuit section falling in or across transient fluctuation process of pulse blocking during protection delay, protection may be reset in advance, or repeated start, reset and export failure may occur.

[0008] In DC power supply system, di / dt & ΔI protection can cover near, intermediate, far-end and cross-zone large bidirectional power supply mode, and losing it means that main protection or backup protection is lost in some cases, and power supply system cannot guarantee that relay protection can meet basic requirements of reliability, selectivity, sensitivity and speed in various operation modes when short circuit fault occurs. Therefore, a new di / dt & ΔI protection suitable for bidirectional converter flexible DC power supply system needs to be developed, and reset characteristics can avoid transient change process of pulse blocking of bidirectional converter. SUMMARY

[0009] The present application aims at the technical problems existing in the prior art, and provides a current change rate and increment protection method of a bidirectional converter flexible direct power supply system, which can correctly identify the fault point occurring in a near end, a middle end, a far end or a terminal of cross-zone power supply, and can quickly trip before a blocking pulse in a short-circuit current, cannot act in a transient state process of a pulse blocking of the bidirectional converter, and can act to trip after the transient state, and can safely and reliably act to trip before a stable state in a short-circuit current.

[0010] The technical scheme adopted by the present application is as follows:

[0011] Step S1: continuously monitoring di / dt, and starting protection when the value of di / dt reaches a starting set value S and the duration meets an anti-jitter delay tS, while: ① recording a current reference value I0 at the starting moment, continuously monitoring the current I at the current moment and calculating ΔI, ΔI=I-I0; ② continuously monitoring a feeder voltage Uf; ③ starting a reset delay tR timing; the protection is protection of a quick-acting section, a blocked pulse acting section and an unblocked pulse acting section;

[0012] Step S2: simultaneously performing protection of the quick-acting section, the blocked pulse acting section and the unblocked pulse acting section, and tripping when the quick-acting section, the blocked pulse acting section and the unblocked pulse acting section meet an action condition, and the quick-acting section, the blocked pulse acting section and the unblocked pulse acting section not being provided with a condition for determining whether to reset by judging the size of di / dt;

[0013] Step S3: resetting all protections after the reset delay tR is exceeded.

[0014] Further, the protection process of the quick-acting section is as follows: when it is monitored that ΔI reaches a set value ΔIins, starting a delay tins timing, and continuously meeting ΔI>ΔIins and di / dt>R during the delay tins, the quick-acting section trips;

[0015] Wherein, R is a di / dt reset set value.

[0016] Further, the protection process of the blocked pulse acting section is as follows: when it is monitored that the feeder voltage Uf<Vth and continuously meets an anti-jitter delay tV, starting a transient process delay tra timing, and after tra, judging whether ΔI reaches a set value ΔIdel1, if ΔI reaches the set value ΔIdel1, starting a delay tdel1 timing, and continuously meeting ΔI>ΔIdel1 during the delay tdel1, the blocked pulse acting section trips.

[0017] Wherein, Vth is pulse blocking voltage judgment value.

[0018] Further, the protection process of the non-blocking pulse action section is as follows: when di / dt > R is monitored, the delay tdel2 is started to be counted, if di / dt > R is continuously met within tdel2, and when tdel2 time is up, ΔI > ΔIdel2, the non-blocking pulse action section outlet is tripped;

[0019] Wherein, R is di / dt reset value, and ΔIdel2 is a constant value.

[0020] Compared with the prior art, the present application has the beneficial effects that:

[0021] The present application adopts the fast action section to ensure the rapidity of the action when the short-circuit current is large; the delay section is divided into two cases of having blocking pulse and not having blocking pulse, the voltage criterion is added in the blocking pulse action section, so as to ensure the flexibility and reliability; and the reset characteristic avoids the transient process of the blocking pulse of the bidirectional converter. The present application can be used as the all-around protection of the bidirectional converter flexible power supply system in the near-end, middle-end, far-end and cross-zone power supply modes.

[0022] The present application can solve the problem that the di / dt protection of the DC feeder in the bidirectional converter flexible power supply system of the rail transit may be reset due to the transient change process of the thyristor blocking caused by short circuit, fill the technical blank in this field, and provide guarantee for the development and application of the green and environmentally-friendly flexible power supply technology. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a schematic diagram of the bidirectional converter flexible power supply system of the prior art;

[0024] Figure 2 It is a current and voltage simulation waveform schematic diagram of the single 3MW bidirectional converter 2km short circuit;

[0025] Figure 3 It is a di / dt simulation waveform schematic diagram of the single 3MW bidirectional converter 2km short circuit;

[0026] Figure 4 It is a flowchart of the embodiment of the present application;

[0027] Figure 5 It is an action characteristic curve diagram of the fast action section and the delay section 2 of the embodiment of the present application;

[0028] Figure 6 It is an action characteristic curve diagram of the delay section 1 of the embodiment of the present application. DETAILED DESCRIPTION

[0029] For those skilled in the art to better understand the technical solutions of the present application, the present application will be described in detail below in combination with the drawings and specific embodiments.

[0030] The embodiments of the present application provide a current rate of change and incremental protection method for a bidirectional converter flexible direct current power supply system, as shown in the formula (1), which comprises the following steps: Figure 4

[0031] Step S1: protection starting: continuously monitoring di / dt, when the value of di / dt reaches the starting constant value S and the duration meets the anti-jitter delay tS, the protection starts, the protection is the protection of the quick action section, the blocked pulse action section (delay section 1) and the unblocked pulse action section (delay section 2); at the same time, recording the current reference value I0 at the starting time, continuously monitoring the current I and calculating ΔI, ΔI = I-I0; continuously monitoring the feeder voltage Uf; and starting the reset delay tR timing. The above current is only positive effective.

[0032] Step S2: multi-section protection: simultaneously performing the protection of the quick action section, the blocked pulse action section and the unblocked pulse action section, specifically:

[0033] The protection process of the quick action section is: when it is monitored that ΔI reaches the constant value ΔIins, starting the delay tins, during the delay tins, continuously meeting ΔI>ΔIins and di / dt>R, the quick action section exits and trips.

[0034] The protection process of the blocked pulse action section is: when it is monitored that the feeder voltage Uf<Vth and continuously meets the anti-jitter delay tV, starting the transient process delay tra, after tra, judging whether ΔI reaches the constant value ΔIdel1, if ΔI reaches the constant value ΔIdel1, starting the delay tdel1, during the delay tdel1, continuously meeting ΔI>ΔIdel1, the blocked pulse action section exits and trips.

[0035] The protection process of the unblocked pulse action section is: when it is monitored that di / dt>R, starting the delay tdel2, if during tdel2, continuously meeting di / dt>R and when tdel2 time is up, ΔI>ΔIdel2, the unblocked pulse action section exits and trips.

[0036] Step S3: protection reset condition: after the protection starts, when the reset delay tR is exceeded, all protections are reset.

[0037] The protection setting parameters are as follows:

[0038]

[0039] The protection action characteristics of the present embodiment are as shown in the formula (2). Figures 5-6

[0040] ​​The fast acting section has the same ΔI protection action characteristic as the direct current power supply system, and the difference is that the positive logic judgment condition is adopted, and when the action condition is not met, no export and no reset are performed. The fast acting section is mainly used for normal large double-sided near-end short circuit, and can reach the protection action condition before the transient process of pulse blocking.

[0041] The delay section 2 has the same di / dt protection action characteristic as the direct current power supply system, and the difference is that the positive logic judgment condition is adopted, and when the action condition is not met, no export and no reset are performed. The delay section 2 is mainly used for normal large double-sided middle and far-end short circuit, and can reach the protection action condition before the transient process of pulse blocking, and the end of the cross-zone power supply cannot reach the pulse blocking in the whole short circuit process.

[0042] The delay section 1 is mainly used for short circuit conditions that may appear pulse blocking, fully combines the waveform characteristics of the flexible direct current power supply system in the pulse blocking state, and uses the additional voltage as the fault judgment condition, so that the disturbance wave, filter capacitor charging and discharging, and locomotive starting and braking can be prevented from being mis-operated in the normal operation condition.

[0043] The reset characteristic fully avoids that the protection does not reset when the pulse blocking transient process appears, and the whole reset is performed after all protection sections are operated.

[0044] The above describes the application in detail through the embodiments, but the content described can only be the exemplary embodiments of the application, and cannot be considered to limit the implementation range of the application. The protection range of the application is limited by the claims. Any technical solution using the technical solution described in the application, or inspired by the technical solution of the application, within the essence and protection range of the application, designed to achieve the above technical effects, or equivalent changes and improvements to the application range, should still belong to the patent coverage protection range of the application.

Claims

1. A method for current rate of change and incremental protection for a bidirectional converter HVDC power supply system, characterized in that: The method comprises the following steps: Step S1: continuously monitoring di / dt, when the value of di / dt reaches a starting value S and the duration meets the anti-shake delay tS, starting the protection, while: ① recording the current reference value I0 at the starting moment, continuously monitoring the current I and calculating ΔI, ΔI=I-I0; ② continuously monitoring the feeder voltage Uf; ③ starting the reset delay tR timing; the protection is the protection of the fast acting section, the blocked pulse action section and the unblocked pulse action section; Step S2: simultaneously performing the protection of the fast acting section, the blocked pulse action section and the unblocked pulse action section, when the fast acting section, the blocked pulse action section and the unblocked pulse action section meet the action conditions, the outlet trips, and the fast acting section, the blocked pulse action section and the unblocked pulse action section are not provided with the condition for determining whether to reset by judging the size of di / dt; Step S3: after the reset delay tR is exceeded, all protections are reset; The protection process of the fast acting section is: when it is monitored that ΔI reaches the value ΔIins, the delay tins is started, and during the delay tins, ΔI>ΔIins and di / dt>R are continuously met, the outlet of the fast acting section trips; Wherein, R is the di / dt reset value. The protection process of the unblocked pulse action section is: when it is monitored that di / dt>R, the delay tdel2 is started, if during the tdel2 time, di / dt>R is continuously met, and when the tdel2 time is up, ΔI>ΔIdel2, the outlet of the unblocked pulse action section trips; Wherein, R is the di / dt reset value, and ΔIdel2 is a constant value.

2. The current rate of change and incremental protection method for a bidirectional converter HVDC power supply system according to claim 1, characterized in that: The protection process of the fast acting section is: when it is monitored that ΔI reaches the value ΔIins, the delay tins is started, and during the delay tins, ΔI>ΔIins and di / dt>R are continuously met, the outlet of the fast acting section trips; Wherein, R is the di / dt reset value. The protection process of the fast acting section is: when it is monitored that ΔI reaches the value ΔIins, the delay tins is started, and during the delay tins, ΔI>ΔIins and di / dt>R are continuously met, the outlet of the fast acting section trips;

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