Inter-station Coordination Processing Method for Faults in Parallel Multi-terminal UHVDC Transmission System

Abstract

The present invention discloses a method for inter-station coordination processing of a parallel multi-terminal ultra-high voltage direct current transmission system fault. The fault-end converter station selects to execute one of the following according to the current fault type: exit the fault converter, exit the pole where the fault converter is located, and all the poles of the multi-terminal direct current transmission system stations are locked, and a signal is sent to the non-fault station; after receiving the signal, the non-fault-end converter station immediately performs phase shifting or zero voltage control operation, and within the set detection time and delay time, according to the type of fault measures received, takes the same measures as the fault-end converter station, or takes fault handling measures according to the type of consecutive fault measures received; after the fault handling measures are completed, the remaining operating converters will release the phase shifting or zero voltage control measures and resume normal operation. The present invention realizes the conversion of different types of handling measures after consecutive faults through inter-station coordination, so that the range of exiting the operation of the DC system after the consecutive faults is small and the transmission power loss is small.

Description

Technical Field

[0001] The present invention relates to an inter-station coordination processing method for transmission system faults, and particularly to an inter-station coordination processing method for faults in a parallel multi-terminal UHV DC transmission system. Background Art

[0002] A parallel multi-terminal DC transmission system includes three or more converter stations. The converters of the same pole at each end are connected across the earth and the DC transmission line of this pole, forming a DC transmission system with a parallel structure of multi-terminal converter stations. A parallel multi-terminal UHV DC transmission system refers to a DC transmission system in which each pole of each station contains two or more converters connected in series. Figure 1 That is, an N-terminal parallel UHV DC transmission system formed by two converters connected in series at each pole of each station.

[0003] When a fault occurs at a converter station at a certain end of a parallel multi-terminal UHV DC transmission system, resulting in the blocking of the converter, depending on the type of the fault and design requirements, the measures that can be taken include blocking the faulty converter at this station and the corresponding converters of the same pole at all other converter stations, or blocking the pole where the faulty converter is located at this station while the poles of other converter stations continue to operate, or blocking the poles of all converter stations at both ends. If successive faults occur, the above fault handling measures may be successively enabled, and during the execution of the previous fault handling measure, it may be necessary to switch to another fault handling measure.

[0004] The existing fault handling methods for parallel multi-terminal UHV DC transmission systems only take preset measures for single faults, without considering the situation of successive faults, nor do they involve the conversion of different types of fault handling measures and their inter-station coordination processing methods. However, the structure of a parallel multi-terminal UHV DC transmission system is complex, the probability of successive faults is relatively high, and if not properly handled, it is easy to cause the expansion of faults, resulting in more power transmission losses. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide an inter-station coordination processing method for faults in a parallel multi-terminal UHV DC transmission system that can handle successive faults in the parallel multi-terminal UHV DC transmission system and has less power transmission loss after successive faults occur.

[0006] Technical Solution: The inter-station coordination processing method for faults in a parallel multi-terminal UHV DC transmission system according to the present invention, the parallel multi-terminal UHV DC transmission system includes at least three converter stations, each pole of each station contains two converters connected in series, and the converter type is a line-commutated converter (LCC) or a voltage-source converter (VSC), and the method includes the following steps:

[0007] (1) When a fault occurs at a certain converter station, the faults and corresponding measures are classified into three categories according to the types of measures required to clear the fault: Category A faults correspond to Category A measures, and the faulty converter is withdrawn; Category B faults correspond to Category B measures, and the pole where the faulty converter is located at the converter station at that end is withdrawn; Category C faults correspond to Category C measures, and the poles of all stations in the multi-terminal DC transmission system are blocked; after the fault occurs, the local station immediately executes the corresponding type of measure and immediately sends the signal for executing this type of measure to other converter stations at each end; the priority of the three types of measures is from high to low as Category C, Category B, and Category A; when a high-priority measure appears at the same converter station, the measures of the lower-priority fault types that appear later are blocked;

[0008] (2) After receiving the signal for executing a certain type of fault handling measure sent by a converter station at a certain end, the non-faulty converter station records the moment when the signal is received; if the corresponding pole of the non-faulty end is a line-commutated converter (LCC), the phase-shifting operation is immediately executed; if the corresponding pole of the non-faulty end is a voltage-source converter (VSC), the DC voltage of the converter is immediately controlled to zero, that is, the zero-voltage control operation is executed;

[0009] (3) The non-faulty converter stations classify the types of received fault handling measures, and the classification measures are as follows:

[0010] (a) If it is a Category A measure, starting from the moment when the Category A fault handling signal is received, maintain the phase-shifting or zero-voltage control state within the first detection time t1, and continuously monitor whether there is a Category B measure signal from the same faulty end or a Category A measure signal from the other converter of the same pole at this end. If there is, it is determined that it is equivalent to receiving the Category B measure signal of the same pole at the faulty end, and the handling measures at the non-faulty end are executed according to (b); if not, after the first detection time t1 ends, start the Category A measure of the corresponding converter at the local end, and the other converter of the same pole at the local end maintains the phase-shifting or zero-voltage control state within the first delay time t2 starting from the moment when the Category A measure signal is received;

[0011] (b) If it is a Category B measure, block the Category A measure signal of the same pole sent by the same faulty end starting from T time before the Category B measure signal; starting from the moment when the Category B measure signal from the faulty end is received, maintain the phase-shifting or zero-voltage control state within the second delay time t3;

[0012] (c) If it is a Category C measure, block any type of measure signal of the same pole at any converter station and immediately execute the pole blocking;

[0013] (4) For the remaining operating converters at the local end, after the delay conditions of all the phase-shifting or zero-voltage control executed in step (3) end, the phase-shifting or zero-voltage control measures are released and normal operation is restored.

[0014] Further, in the process (a) of step (3), before the end of the first delay time t2 during which the other converter of this pole at the local end maintains the phase shift or zero voltage control state, if a Class B measure sent by another faulty end is received, starting from the moment when the Class B measure signal from this faulty end is received, it continues to maintain the phase shift or zero voltage control state within the second delay time t3.

[0015] Further, in the process (b) of step (3), if a signal of the fault handling measure for this pole sent by another faulty end is received within the second delay time t3, according to the type of the fault handling measure:

[0016] (b1) If it is a Class B measure, and the signal comes from the last converter station that takes the Class B measure among all converter stations operating in the rectification state or the last converter station that takes the Class B measure among all converter stations operating in the inversion state, it is determined that it is equivalent to receiving a signal for this pole of this faulty end to execute a Class C measure, and the local converter station immediately executes the pole blocking of this pole;

[0017] (b2) If it is a Class B measure, and there is at least one converter station operating in the rectification state and at least one converter station operating in the inversion state that have not sent the Class B measure for this pole except for the converter stations that have already sent the Class B measure, starting from the moment when the Class B measure signal for this pole of the latest received faulty end is received, it maintains the phase shift or zero voltage control state within the second delay time t3;

[0018] (b3) If it is a Class A measure, it is monitored in real time within the first detection time t1 whether there is a Class A measure signal from the other converter of this pole of the same faulty end. If there is, it is determined that it is equivalent to receiving a signal for this pole of this faulty end to execute a Class B measure, and the measures of the non-faulty end are executed according to the above (b1) and (b2); if not, after the end of the first detection time t1, the Class A measure of the corresponding converter at the local end is started, and the other converter of this pole at the local end maintains the phase shift or zero voltage control state within the first delay time t2 starting from the moment when the Class A measure signal is received.

[0019] Further, in (b) of step (3), starting from the moment when the local converter station receives the Class B measure signal from a certain faulty end, within the second delay time t3, if a fault occurs at this pole of the local converter station, the measures according to its fault type are as follows:

[0020] If it is a Class A fault, the Class A measure of the faulty converter at this station of this pole is immediately started, and the signal for executing this type of measure is immediately sent to the other converter stations at each end; the other converter of this pole at the local end maintains the phase shift or zero voltage control state until both the first delay time t2 starting from the moment when the Class A measure signal is received and the second delay time t3 starting from the moment when the Class B measure signal from a certain faulty end in (b) of step (3) end, and then the phase shift or zero voltage control measure is released and the normal operation is restored;

[0021] For Class B faults, if all other converter stations at the same rectifier or inverter operating state as the local converter station have withdrawn or are implementing Class B measures for the same pole, it is determined that the local station implements Class C measures for this pole and immediately sends the signal of implementing Class C measures to all other converter stations; otherwise, the local station implements Class B measures for this pole and immediately sends the signal of implementing Class B measures to all other converter stations.

[0022] Furthermore, in step (3)(a), within the first delay time t2 starting from the moment when the local converter station receives the Class A measure signal from a faulty station, if another converter of this pole at the local converter station fails, the measures are as follows according to its fault type:

[0023] If it is a Class A fault, it is determined that the local station implements Class B measures for this pole;

[0024] For Class B faults or cases where it is determined that the local station implements Class B measures for this pole, if all other converter stations at the same rectifier or inverter operating state as the local converter station have withdrawn or are implementing Class B measures for the same pole, it is determined that the local station implements Class C measures for this pole and immediately sends the signal of implementing Class C measures to all other converter stations; otherwise, the local station implements Class B measures for this pole and immediately sends the signal of implementing Class B measures to all other converter stations.

[0025] Furthermore, T time before the Class B measure signal in step (3)(b), where T time is not greater than the first detection time t1, and the value range of T is 0ms - 50ms.

[0026] Furthermore, in step (3), the first detection time t1 is less than the first delay time t2 and the second delay time t3. The value range of the first detection time t1 is 0ms - 50ms, the value range of the first delay time t2 is 50ms - 350ms, and the value range of the second delay time t3 is 50ms - 650ms.

[0027] Furthermore, in step (1), when a Class A fault occurs at a certain pole of a converter station and the inter-station communication between this pole of the local converter station and other converter stations is also faulty during the occurrence of the Class A fault, the faulty pole of this converter station does not implement the Class A fault handling measures and switches to implementing Class B measures.

[0028] Compared with the prior art, the present invention has the following remarkable effects: 1. When high-priority measures occur at the same converter station in the present invention, measures of lower-priority fault types that occur later are shielded, and it can handle successive faults in a parallel multi-terminal UHVDC transmission system. Through inter-station coordination, the conversion of different types of treatment measures after successive faults is achieved, so that the range of the DC system exiting operation after successive faults is as small as possible, and the lost transmission power is as small as possible, improving the reliability and availability of the parallel multi-terminal UHVDC transmission system; 2. A method for inter-station coordinated processing of faults in a parallel multi-terminal UHVDC transmission system is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic structural diagram of a parallel multi-terminal UHVDC transmission system;

[0030] Figure 2 It is a schematic structural diagram of a parallel three-terminal UHVDC hybrid transmission system;

[0031] Figure 3 It is a flowchart of the inter-station coordinated processing method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention will be further described in detail below with reference to the accompanying drawings of the specification and the specific embodiments.

[0033] Figure 1 It is a schematic diagram of a typical parallel multi-terminal UHVDC transmission system. The whole system includes a total of N converter stations, namely converter station 1, converter station 2,..., converter station N-1, and converter station N; each converter station includes two poles, and the two poles are connected by wires, and the wire connecting the two poles is grounded; each pole of each converter station includes two series-connected converters, which are connected across the DC line and the grounding electrode lead of each pole. The converter close to the DC line is called the high-voltage terminal converter, and the converter close to the grounding electrode lead is called the low-voltage terminal converter; in this way, pole 1 and pole 2 of N converter stations respectively form an inter-station parallel structure.

[0034] In the parallel multi-terminal UHVDC transmission system of the present invention, the converter type can be either a conventional DC converter LCC or a flexible DC converter VSC. For example, Figure 2 In a shown parallel three-terminal UHVDC hybrid transmission system, converter station 1 and converter station 2 adopt conventional DC converters LCC, and converter station 3 adopts a flexible DC converter VSC.

[0035] The specific embodiments of the present invention include the following steps:

[0036] Step 1: When a fault occurs at a converter station at one end, the faults and corresponding measures are classified into three categories according to the types of measures required to clear the fault: Class A faults correspond to Class A measures, and the faulty converter is withdrawn; Class B faults correspond to Class B measures, and the pole where the faulty converter is located at this end of the converter station is withdrawn; Class C faults correspond to Class C measures, and the poles of all stations in the multi-terminal DC power transmission system are blocked. After the fault occurs, this station immediately executes the corresponding type of measure and immediately sends the signal for executing this type of measure to other converter stations at each end. The priority of the three types of measures is the highest for Class C, followed by Class B, and then Class A. When a higher-priority measure appears at the same converter station, the measures of lower-priority fault types that appear later are blocked.

[0037] Step 2: After receiving the signal for executing a certain type of fault handling measure sent from a converter station at one end, the non-faulty converter station records the moment when the signal is received. If the corresponding pole of the non-faulty end is an LCC converter, the phase-shifting operation is immediately executed. If the corresponding pole of the non-faulty end is a VSC converter, the DC voltage of the converter is immediately controlled to zero, which is simply referred to as executing the zero-voltage control operation.

[0038] Step 3: The non-faulty converter station distinguishes the types of received fault handling measures, and the processing flow chart is as Figure 3 shown, and the measures are as follows:

[0039] (a) If it is a Class A measure, starting from the moment when the Class A fault handling signal is received, maintain the phase-shifting or zero-voltage control state within the first detection time t1, and continuously monitor whether there is a Class B measure signal from the same faulty end or a Class A measure signal from the other converter of the same pole at this end. If there is, it is determined that it is equivalent to receiving the Class B measure signal of the same pole of this faulty end, and the measures of the non-faulty end are the same as those in Step 3(b). If not, after the first detection time t1 ends, start the Class A measure of the corresponding converter at this end, and the other converter of the same pole at this end maintains the phase-shifting or zero-voltage control state within the first delay time t2 starting from the moment when the Class A measure signal is received.

[0040] (b) If it is a Class B measure, block the Class A measure signal of the same pole sent from the same faulty end starting from T time before the Class B measure signal; starting from the moment when the Class B measure signal of this faulty end is received, maintain the phase-shifting or zero-voltage control state within the second delay time t3.

[0041] (c) If it is a Class C measure, block any type of measure signal of the same pole of any converter station and immediately execute the pole blocking.

[0042] Step 4: For the remaining operating converters at this end, after the delay conditions of all the phase-shifting or zero-voltage control in Steps 1 and 2 that have been executed end, the phase-shifting or zero-voltage control measures are released and normal operation is restored.

[0043] In the process of the above step 3(a), before the end of the first delay time t2 during which the other converter of this pole at the local end maintains the phase shift or zero voltage control state, if a type B measure sent by another faulty end is received, starting from the moment when the type B measure signal of this faulty end is received, it continues to maintain the phase shift or zero voltage control state within the second delay time t3.

[0044] In the process of the above step 3(b), if a signal of the fault handling measure for this pole sent by another faulty end is received within the second delay time t3, according to the type of the fault handling measure:

[0045] (b1) If it is a type B measure, and the signal comes from the last converter station that takes the type B measure among all converter stations operating in the rectification state or the last converter station that takes the type B measure among all converter stations operating in the inversion state, it is determined that it is equivalent to receiving a signal for this pole of this faulty end to execute a type C measure, and the local converter station immediately executes the pole blocking of this pole.

[0046] (b2) If it is a type B measure, and in addition to the converter stations that have sent the type B measure, there is at least one converter station operating in the rectification state and at least one converter station operating in the inversion state on this pole that have not sent the type B measure, starting from the moment when the type B measure signal of this pole of the latest received faulty end is received, it maintains the phase shift or zero voltage control state within the second delay time t3.

[0047] (b3) If it is a type A measure, it is monitored in real time within the first detection time t1 whether there is a type A measure signal of the other converter of this pole from the same faulty end. If there is, it is determined that it is equivalent to receiving a signal for this pole of this faulty end to execute a type B measure, and the measures of the non-faulty ends are executed according to the above (b1) and (b2); if not, after the end of the first detection time t1, the type A measure of the corresponding converter at the local end is started, and the other converter of this pole at the local end maintains the phase shift or zero voltage control state within the first delay time t2 starting from the moment when the type A measure signal is received.

[0048] In the above step 3(b), starting from the moment when the local converter station receives the type B measure signal of a certain faulty end, within the second delay time t3, if a fault occurs at this pole of the local converter station, the measures according to its fault type are as follows:

[0049] If it is a type A fault, the type A measure of the faulty converter is immediately started at this pole of this station, and the signal for executing this type of measure is immediately sent to the other converter stations at each end; the other converter of this pole at the local end maintains the phase shift or zero voltage control state until after the end of both the first delay time t2 starting from the moment when the type A measure signal is received and the second delay time t3 starting from the moment when the type B measure signal of a certain faulty end described in step 3(b) is received, and the phase shift or zero voltage control measure is released and the normal operation is restored.

[0050] For Class B faults, if all other converter stations at the same rectifier or inverter operating state as the local converter station have withdrawn or are implementing Class B measures for the relevant pole, it is determined that the local converter station implements Class C measures for this pole and immediately sends the signal of implementing Class C measures to all other converter stations; otherwise, the local converter station implements Class B measures for this pole and immediately sends the signal of implementing Class B measures to all other converter stations.

[0051] In step (a) of the above step 3, within the first delay time t2 starting from the moment when the local converter station receives the Class A measure signal from a faulty end, if another converter of this pole at the local converter station fails, the measures are as follows according to the type of the fault:

[0052] If it is a Class A fault, it is determined that the local converter station implements Class B measures for this pole;

[0053] For Class B faults or situations where it is determined that the local converter station implements Class B measures for this pole, if all other converter stations at the same rectifier or inverter operating state as the local converter station have withdrawn or are implementing Class B measures for the relevant pole, it is determined that the local converter station implements Class C measures for this pole and immediately sends the signal of implementing Class C measures to all other converter stations; otherwise, the local converter station implements Class B measures for this pole and immediately sends the signal of implementing Class B measures to all other converter stations.

[0054] Before the Class B measure signal in step (b) of the above step 3, there is a time T, where the time T is not greater than the first detection time t1, and the typical value range of T is 0 ms - 50 ms.

[0055] The above first detection time t1 is less than the first delay time t2 and the second delay time t3. The typical value range of the first detection time t1 is 0 ms - 50 ms, the typical value range of the first delay time t2 is 50 ms - 350 ms, and the typical value range of the second delay time t3 is 50 ms - 650 ms.

[0056] In step 1 of the above, when a Class A fault occurs at a certain pole of a converter station and the inter-station communication between this pole of the local converter station and other converter stations is also faulty when the Class A fault occurs, the faulty pole of the local converter station does not implement the Class A fault handling measures and instead implements Class B measures.

[0057] The following takes Figure 2 an example of a parallel three-terminal UHV hybrid HVDC transmission system shown to illustrate the specific implementation manners of the present invention.

[0058] Embodiment 1

[0059] Before time 0, the parallel three-terminal UHVDC hybrid transmission system operates normally. At time 0, a fault occurs in the converter at the high-voltage terminal of Pole 1 of Station 2, and Class A measures are immediately initiated to withdraw this converter. Ignoring the inter-station communication time, after receiving this information, according to Step 3(a), Pole 1 of Station 1 immediately shifts phase, and Pole 1 of Station 3 immediately controls to zero voltage. The typical value of the first detection time t1 is set to 20 ms. At the 10 ms moment, a fault occurs in Pole 1 of Station 2 again, resulting in the immediate initiation of Class B measures for Pole 1 of Station 2. After receiving the information that Pole 1 of Station 2 executes Class B measures, with T taken as 20 ms, according to what is described in Step 3(b), the Class A measure signal of the converter at the high-voltage terminal of Pole 1 of Station 2 received at time 0 is shielded and no longer continued to be executed. Starting from the 10 ms moment, the phase shift or zero-voltage control state is continued until after the second delay time t3 (the typical value is taken as 450 ms), that is, at the 460 ms moment, Pole 1 of Station 1 and Station 3 resumes operation.

[0060] Embodiment 2

[0061] Before time 0, the parallel three-terminal UHVDC hybrid transmission system operates normally. At time 0, a fault occurs in the converter at the high-voltage terminal of Pole 1 of Station 2, and Class A measures are immediately initiated to withdraw this converter. Ignoring the inter-station communication time, after receiving this information, according to Step 3(a), Pole 1 of Station 1 immediately shifts phase, and Pole 1 of Station 3 immediately controls to zero voltage. The typical value of the first detection time t1 is set to 20 ms. At the 20 ms moment, the converters at the high-voltage terminals of Pole 1 of Station 1 and Pole 1 of Station 3 execute the measure of withdrawing the converter. The converter at the low-voltage terminal of Pole 1 of Station 1 maintains phase shift, and the converter at the low-voltage terminal of Pole 1 of Station 3 maintains zero-voltage control. At the 30 ms moment, a fault occurs in Pole 1 of Station 2 again, resulting in the immediate initiation of Class B measures for Pole 1 of Station 2. After receiving the information that Pole 1 of Station 2 executes Class B measures, with T taken as 20 ms, according to Step 3(b), Station 1 and Station 3 do not shield the Class A measure signal received before 30 ms. The converters at the high-voltage terminals of Pole 1 of Station 1 and Station 3 continue to execute the measure of withdrawing the converter, while their converters at the low-voltage terminals of Pole 1 start from the 30 ms moment and continue to maintain the phase shift or zero-voltage control state until after the second delay time t3 (the typical value is taken as 450 ms), that is, at the 480 ms moment, the converters at the low-voltage terminals of Pole 1 of Station 1 and Station 3 resume operation.

[0062] Embodiment 3

[0063] Before time 0, the parallel three-terminal UHV hybrid DC transmission system operates normally. At time 0, a Class B fault occurs at Pole 1 of Station 2, and the Class B measures are immediately initiated to withdraw Pole 1 of Station 2; ignoring the inter-station communication time, after receiving this information, according to Step 3(b), Pole 1 of Station 1 immediately shifts phase, and Pole 1 of Station 3 immediately controls to zero voltage and maintains the second delay time t3 (the typical value is taken as 450 ms); at the moment of 30 ms, a fault occurs in the high-end converter of Pole 1 of Station 3, and the Class A measures are immediately initiated to withdraw this converter. After Station 1 receives this information, according to (b3), and after the first detection time of 20 ms, that is, at the moment of 50 ms, it initiates to withdraw the high-end converter of Pole 1 of Station 1. From the moment of 30 ms, after the first delay time t2 (the typical value is taken as 200 ms), the process of withdrawing the converter ends, but the low-end converter of Pole 1 of Station 1 still maintains phase shift, and the low-end converter of Pole 1 of Station 3 still maintains zero voltage control until the Class B fault handling process of Pole 1 of Station 2 is completed at the moment of 450 ms, and then the low-end converters of Pole 1 of Station 1 and Pole 1 of Station 3 resume operation.

[0064] The above embodiments are only used to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the present invention.

Claims

1. A method for coordinating and processing faults of a parallel multi-terminal ultra-high voltage direct current transmission system between stations, wherein the parallel multi-terminal ultra-high voltage direct current transmission system comprises at least three-terminal converter stations, each station and each pole comprising two converters connected in series, and the converter type is a DC converter LCC or a flexible DC converter VSC, Features: The following steps are involved: (1) When a fault occurs at a converter station at one end, the fault and corresponding measures are divided into three categories according to the type of measures needed to clear the fault: Class A faults correspond to Class A measures, which is to exit the faulty converter; Class B faults correspond to Class B measures, which means exiting the pole where the faulty converter is located at the converter station at that end; Class C faults correspond to Class C measures, and the poles of all stations in the multi-terminal DC transmission system are locked; after a fault occurs, the station immediately executes the corresponding type of measures, and immediately sends the signal for executing such measures to the converter stations at other ends; the priorities of the three types of measures are Class C, Class B, and Class A from high to low; when a high-priority measure of the converter station at the same end occurs, the measures of the lower-priority fault type that appear afterwards are shielded; (2) After the non-fault-end converter station receives a signal from a converter station at a certain end to execute a certain type of fault handling measure, it records the time when the signal is received; if the corresponding pole of the non-fault-end is a DC converter LCC, the phase shift operation is immediately performed; if the corresponding pole of the non-fault-end is a flexible DC converter VSC, the zero voltage control operation is immediately performed; (3) The types of fault handling measures received by the non-fault-end converter station are classified as follows: (a) If it is a Class A measure, starting from the moment when the Class A fault processing signal is received, the phase shift or zero voltage control state is maintained within the first detection time t1, and real-time monitoring is performed to see whether there is a Class B measure signal from the same fault end or a Class A measure signal from another converter of the same pole. If there is, it is determined to be equivalent to receiving the signal of the Class B measure of the fault end, and the processing measures of the non-fault end are executed according to (b); if not, after the first detection time t1 ends, the Class A measure of the corresponding converter of the same end is started, and the other converter of the same pole of the same end maintains the phase shift or zero voltage control state within the first delay time t2 starting from the receipt of the Class A measure signal; (b) If it is a Class B measure, shield the Class A measure signal sent by the same fault end from the time T before the Class B measure signal; from the moment the Class B measure signal of the fault end is received, maintain the phase shift or zero voltage control state within the second delay time t3; (c) If it is a Class C measure, shield any type of measure signal of the local pole of any terminal converter station and immediately execute the local pole locking; (4) After all the delay conditions for phase shifting or zero voltage control in step (3) have been completed, the remaining operating converters at this end release the phase shifting or zero voltage control measures and resume normal operation.

2. The method for inter-station coordination processing of a parallel multi-terminal ultra-high voltage direct current transmission system fault according to claim 1, Features: In the process (a) of step (3), before the end of the first delay time t2 during which the other converter of this pole at the local end maintains the phase shift or zero voltage control state, if a type B measure sent by another faulty end is received, starting from the moment when the type B measure signal from this faulty end is received, it continues to maintain the phase shift or zero voltage control state within the second delay time t3.

3. The inter-station coordination processing method for faults in a parallel multi-terminal UHVDC transmission system according to claim 1, characterized in that: in the process (b) of step (3), if a signal of the fault handling measure for this pole sent by another faulty end is received within the second delay time t3, according to the type of the fault handling measure: (b1) If it is a type B measure and the signal comes from the last converter station that has taken the type B measure among all converter stations operating in the rectification state or the last converter station that has taken the type B measure among all converter stations operating in the inversion state, it is determined that it is equivalent to receiving a signal for the local converter station to execute a type C measure for this pole, and the local converter station immediately executes the pole blocking for this pole; (b2) If it is a type B measure and there is at least one converter station operating in the rectification state and at least one converter station operating in the inversion state that have not sent the type B measure for this pole except for the converter stations that have already sent the type B measure, starting from the moment when the type B measure signal for this pole from the latest received faulty end is received, it maintains the phase shift or zero voltage control state within the second delay time t3; (b3) If it is a type A measure, it is continuously monitored within the first detection time t1 whether there is a type A measure signal from the other converter of this pole of the same faulty end. If there is, it is determined that it is equivalent to receiving a signal for the local converter station to execute a type B measure, and the measures of the non-faulty end are executed according to the above (b1) and (b2); if not, after the end of the first detection time t1, the type A measure of the corresponding converter at the local end is started, and the other converter of this pole at the local end maintains the phase shift or zero voltage control state within the first delay time t2 starting from the moment when the type A measure signal is received.

4. The inter-station coordination processing method for faults in a parallel multi-terminal UHVDC transmission system according to claim 1, characterized in that: in (b) of step (3), starting from the moment when the local converter station receives the type B measure signal from a certain faulty end, within the second delay time t3, if a fault occurs in this pole of the local converter station, the measures according to its fault type are as follows: If it is a type A fault, the type A measure of the faulty converter is immediately started at this station for this pole, and the signal for executing this type of measure is immediately sent to the converter stations at other ends; the other converter of this pole at the local end maintains the phase shift or zero voltage control state until both the first delay time t2 starting from the moment when the type A measure signal is received and the second delay time t3 starting from the moment when the type B measure signal from a certain faulty end in (b) of step (3) end, and then the phase shift or zero voltage control measure is released and normal operation is restored; For Class B faults, if all other pole ends of converter stations in the same rectifier or inverter operation state as the local converter station have exited or are implementing Class B measures, it is determined that the local pole end implements Class C measures, and the signal for implementing Class C measures is immediately sent to all other converter stations; otherwise, the local pole end implements Class B measures, and the signal for implementing Class B measures is immediately sent to all other converter stations.

5. The method for inter-station coordinated handling of faults in a parallel multi-terminal UHVDC transmission system according to claim 1, wherein: In (a) of step (3), within the first delay time t2 starting from the moment when the local converter station receives the Class A measure signal from a certain fault end, if another converter of the local converter station for this pole has a fault, the measures are as follows according to the fault type: If it is a Class A fault, it is determined that the local pole end implements Class B measures; For Class B faults or cases where it is determined that the local pole end implements Class B measures, if all other pole ends of converter stations in the same rectifier or inverter operation state as the local converter station have exited or are implementing Class B measures, it is determined that the local pole end implements Class C measures, and the signal for implementing Class C measures is immediately sent to all other converter stations; otherwise, the local pole end implements Class B measures, and the signal for implementing Class B measures is immediately sent to all other converter stations.

6. The method for inter-station coordinated handling of faults in a parallel multi-terminal UHVDC transmission system according to claim 1, wherein: Before the Class B measure signal in (b) of step (3), there is a time T, where the time T is not greater than the first detection time t1, and the value range of T is 0ms - 50ms.

7. The method for inter-station coordinated handling of faults in a parallel multi-terminal UHVDC transmission system according to claim 1, wherein: In step (3), the first detection time t1 is less than the first delay time t2 and the second delay time t3. The value range of the first detection time t1 is 0ms - 50ms, the value range of the first delay time t2 is 50ms - 350ms, and the value range of the second delay time t3 is 50ms - 650ms.

8. The method for inter-station coordinated handling of faults in a parallel multi-terminal UHVDC transmission system according to claim 1, wherein: In step (1), when a Class A fault occurs at a certain pole end of a converter station, and the inter-station communication between the local pole end of this converter station and other converter stations is also in a fault state during the occurrence of the Class A fault, the local faulty pole end does not implement the Class A fault handling measures and instead implements Class B measures.

Images