Multi-infeed direct current cooperative control method comprising controllable commutation converter and phase modifier

Abstract

The invention discloses a multi-infeed direct current cooperative control method comprising a controllable commutation converter and a phase modifier, and the method comprises the steps: starting a commutation failure prediction control module, and adjusting the Gamma angles of a conventional converter and the controllable commutation converter, and the excitation reference voltage and duration of the phase modifier according to a commutation failure severity signal. The commutation failure prediction control module adopts various criteria, such as alternating voltage zero sequence, alpha / beta conversion, direct current instruction deviation and alternating current and direct current difference. The commutation failure influence factor is used for evaluating the influence degree of commutation failure of the converter and is in direct proportion to the electrical coupling degree. The method aims to prevent or reduce commutation failures and guarantee safe and stable operation of a power grid.

Description

Technical Field

[0001] The present invention relates to the technical field of high - voltage direct - current transmission, and particularly relates to a multi - infeed DC coordinated control method including a controllable commutation converter and a synchronous condenser. Background Art

[0002] For a high - voltage direct - current transmission (Line Commutated Converter High - Voltage Direct Current, LCC - HVDC) project based on a line - commutated converter, the LCC - HVDC transmission system depends on the AC system to provide commutation voltage in principle, and there is a commutation failure problem. When the AC system fails, etc., commutation failure is likely to occur, resulting in a surge in current and a rapid and large loss of DC transmission power.

[0003] To solve the inherent commutation failure problem of LCC - HVDC, in recent years, topologies based on a controllable line - commutated converter (CLCC) and a hybrid line - commutated converter (HLCC) have been proposed. The turn - off ability of the auxiliary - branch IGBT is used to cut off the arm current to complete commutation between arms, and the commutation failure problem is solved in principle.

[0004] Whether it is an LCC, a CLCC or an HLCC, a large amount of reactive power is consumed. A synchronous condenser is a reactive - power compensation device used in a DC converter station, and its main function is to provide dynamic reactive - power support for the DC converter station. The latest research shows that the new - generation synchronous condenser has excellent transient characteristics and overload capacity. It can not only provide a certain amount of reactive - power output under steady - state conditions, but also has good transient reactive - power support performance. In addition, maintaining the steady - state reactive - power voltage level is also very helpful for improving transient voltage stability. In short, the new - generation synchronous condenser makes it possible to provide both steady - state and transient reactive - power regulation.

[0005] However, at present, there is only a simple steady - state reactive - power instruction coordination between the reactive - power voltage control of the UHV DC system and the reactive - power control of the synchronous condenser, lacking an overall coordinated control strategy. The synchronous condenser hardly participates in the reactive - power exchange of the system, and only provides transient support when the system is disturbed, failing to fully utilize this advantage of the new - generation synchronous condenser. As a new topology, CLCC / HLCC currently lacks a multi - DC overall coordinated control strategy.

[0006] The above information disclosed in the background - art section is only used to enhance the understanding of the background of the present invention, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0007] The present invention provides a multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser. Through an effective coordinated control method in a multi-DC power transmission system, the DC control system, the controllable phase-shifting converter, and the synchronous condenser work together to fully utilize the potential of these advanced devices.

[0008] A multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser comprises:

[0009] S1: Monitoring the phase failure prediction control module in the converters of each DC converter station in the operating state; when the phase failure prediction control module is triggered, generating a phase failure prediction control module start signal and a phase failure severity signal, and sending the signals to the control systems of other operating converters and synchronous condensers in the same station through the in-station communication system of the DC converter station, and at the same time sending the signals to the control systems of operating converters and synchronous condensers in other DC converter stations through the inter-station communication system of the DC converter station;

[0010] S2: The converter receiving the phase failure prediction control module start signal performs Gamma angle adjustment operations according to its type and current operating mode:

[0011] If it is a conventional converter, increase the Gamma angle;

[0012] If it is a controllable phase-shifting converter and in the non-controllable phase-shifting mode, increase the Gamma angle; if in the controllable phase-shifting mode, decrease the Gamma angle;

[0013] S3: The control system of the synchronous condenser receiving the signal modifies the excitation reference voltage and the duration command according to the phase failure impact factor and the phase failure severity signal to implement emergency control actions.

[0014] In the multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser, the phase failure prediction control module adopts one or more of an AC voltage zero-sequence criterion, an AC voltage α / β conversion criterion, a DC current command deviation criterion, or an AC-DC current difference criterion.

[0015] In the multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser, the phase failure impact factor is used to characterize the influence degree of phase failure of each converter, and is proportional to the electrical coupling degree of the converter and the synchronous condenser. If other operating converters in the in-station of the DC converter station are in the non-layered mode, its phase failure impact factor is the largest. If after the converter has a phase failure, the AC system voltage and current of the operating converters and synchronous condensers in other DC converter stations are not affected, its phase failure impact factor is the smallest.

[0016] In the multi - infeed DC coordinated control method including a controllable phase - shifting converter and a synchronous condenser, the commutation failure prediction control module adopts the zero - sequence criterion of AC voltage. When the zero - sequence value of the AC voltage exceeds a set value, the commutation failure prediction control module is activated, and the commutation failure severity signal is proportional to the zero - sequence value of the AC voltage.

[0017] In the multi - infeed DC coordinated control method including a controllable phase - shifting converter and a synchronous condenser, the commutation failure prediction control module adopts the α / β conversion criterion of AC voltage. When the α / β conversion criterion of the AC voltage exceeds a set value, the commutation failure prediction control module is activated, and the commutation failure severity signal is proportional to the α / β conversion value of the AC voltage.

[0018] In the multi - infeed DC coordinated control method including a controllable phase - shifting converter and a synchronous condenser, the commutation failure prediction control module adopts the criterion of DC current command deviation. When the deviation between the measured value of the DC current and the DC current command exceeds a set value, the commutation failure prediction control module is activated, and the commutation failure severity signal is proportional to the DC current command deviation.

[0019] In the multi - infeed DC coordinated control method including a controllable phase - shifting converter and a synchronous condenser, the commutation failure prediction control module adopts the criterion of AC - DC current difference. When the AC - DC current difference criterion exceeds a set value, the commutation failure prediction control module is activated, and the commutation failure severity signal is proportional to the AC - DC current difference.

[0020] In the multi - infeed DC coordinated control method including a controllable phase - shifting converter and a synchronous condenser, the commutation failure influence factor adopts the multi - infeed interaction factor.

[0021] In the multi - infeed DC coordinated control method including a controllable phase - shifting converter and a synchronous condenser, when two or more criteria are satisfied simultaneously, the following processing strategy is executed: the severity signals of all parallel trigger criteria will be output through a maximum selector as the final commutation failure severity signal.

[0022] In the multi - infeed DC coordinated control method including a controllable phase - shifting converter and a synchronous condenser, the larger the commutation failure severity signal is, the larger the change amount of the Gamma angle of the converter and the emergency control adjustment amount of the synchronous condenser are; the smaller the commutation failure severity signal is, the smaller the change amount of the Gamma angle of the converter and the emergency control adjustment amount of the synchronous condenser are.

[0023] Compared with the prior art, the present invention has the following advantages: realizing the coordinated control of a multi-control system of a conventional DC, a thyristor controlled phase converter (TCPC), and a synchronous condenser. This method fully utilizes the advantages of the TCPC and the synchronous condenser in resisting commutation failures. By real-time monitoring the bus voltage, AC current, DC current and their command values of the DC converter station, when the relevant electrical quantities reach the preset criteria for coordinated control, the system will respond quickly: the conventional DC increases the gamma angle, the TCPC decreases the gamma angle, and the synchronous condenser starts the strong excitation measure. This synergistic effect among multiple devices can be adjusted according to the severity of the commutation failure and its influencing factors, effectively preventing or reducing the risk of simultaneous or consecutive commutation failures in a multi-DC system, ensuring the safe and stable operation of a multi-infeed DC power grid, and bringing significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] By reading the following detailed description of the preferred specific embodiments, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only for the purpose of showing the preferred embodiments and are not considered as a limitation of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts. Moreover, throughout the drawings, the same reference numerals are used to represent the same components.

[0025] In the drawings:

[0026] Att Figure 1 is a schematic diagram of a multi-infeed DC regional power grid in a specific embodiment;

[0027] Att Figure 2 is a schematic diagram of the control system communication in a multi-infeed DC power grid including a thyristor controlled phase converter and a synchronous condenser.

[0028] The following further explains the present invention in conjunction with the drawings and embodiments. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The specific embodiments of the present invention will be described in more detail below with reference to the drawings. Although the specific embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be completely conveyed to those skilled in the art.

[0030] It should be noted that in the specification and claims, certain terms are used to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. The specification and claims do not distinguish components based on the difference in nouns, but rather on the functional differences of the components. As mentioned throughout the specification and claims, the term "comprising" or "including" is an open-ended term and should be interpreted as "including but not limited to". The subsequent description in the specification is the preferred embodiment for implementing the present invention, but the description is for the purpose of the general principles of the specification and is not intended to limit the scope of the present invention. The protection scope of the present invention shall be subject to what is defined by the appended claims.

[0031] For the convenience of understanding the embodiments of the present invention, the following will further explain with specific embodiments in conjunction with the accompanying drawings, and each accompanying drawing does not constitute a limitation on the embodiments of the present invention.

[0032] As Figures 1 to 2 shown, a multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser comprises the following steps:

[0033] S1: The multi-infeed DC regional power grid includes multiple DC converter stations and synchronous condensers. The DC converter station includes a control system for monitoring the operating state of the DC converter station. The control system includes a commutation failure prediction control module. After starting the commutation failure prediction control module for monitoring the operating state of each DC converter station, the commutation failure prediction control module start signal and the commutation failure severity signal are sent to the control systems of other operating converters and synchronous condensers within the same DC converter station.

[0034] Further, the control system refers to the DC control system within the DC converter station.

[0035] S2: After the commutation failure prediction control module is started, the operating converter takes the following steps according to the commutation failure severity signal.

[0036] S2-1: If the operating converter is a converter of a non-controllable phase-shifting converter, increase the Gamma angle.

[0037] S2-2: If the operating converter is a controllable phase-shifting converter, if the controllable phase-shifting converter is in the non-controllable commutation mode, increase the Gamma angle; if the controllable phase-shifting converter is in the controllable commutation mode, decrease the Gamma angle.

[0038] S3: After the control systems of other converters and synchronous condensers in the same HVDC converter station that are in the operating state receive the start signal of the commutation failure prediction control module, according to the commutation failure impact factor and the commutation failure severity signal, where the commutation failure impact factor is used to characterize the impact degree of commutation failure of each converter and is proportional to the electrical coupling degree between the converter and the synchronous condenser, the following steps are taken:

[0039] S3-1: If the other converter in the same HVDC converter station that is in the operating state is a converter with non-controllable commutation, increase the Gamma angle.

[0040] S3-2: If the other converter in the same HVDC converter station that is in the operating state is a converter with controllable commutation, if the converter with controllable commutation is in the non-controllable commutation mode, increase the Gamma angle, and if the converter with controllable commutation is in the controllable commutation mode, decrease the Gamma angle.

[0041] S3-3: The control system of the synchronous condenser modifies the excitation reference voltage and the duration command to complete the emergency control of the synchronous condenser.

[0042] S4: After the control systems of the converters and synchronous condensers in other HVDC converter stations that are in the operating state receive the start signal of the commutation failure prediction control module, according to the commutation failure impact factor and the commutation failure severity signal, the following steps are taken:

[0043] S4-1: If the converter in other HVDC converter stations that are in the operating state is a converter with non-controllable commutation, increase the Gamma angle.

[0044] S4-2: If the converter in other HVDC converter stations that are in the operating state is a converter with controllable commutation, if the converter with controllable commutation is in the non-controllable commutation mode, increase the Gamma angle, and if the converter with controllable commutation is in the controllable commutation mode, decrease the Gamma angle.

[0045] S4-3: The control system of the synchronous condenser sends a command to modify the excitation reference voltage and the duration to complete the emergency control of the synchronous condenser.

[0046] In the preferred implementation of the multi-infeed DC coordinated control method including a converter with controllable commutation and a synchronous condenser, the commutation failure prediction control module adopts one or more of the AC voltage zero-sequence criterion, the AC voltage α / β conversion criterion, the DC current command deviation criterion, or the AC-DC current difference criterion.

[0047] In the preferred implementation of the multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser, the commutation failure impact factor is used to characterize the impact degree of commutation failure of each converter, which is proportional to the electrical coupling degree between the converter and the synchronous condenser. If other converters in the same DC converter station in the operating state are in a non-hierarchical mode, its commutation failure impact factor is the largest. If the converter experiences commutation failure and there is no impact on the AC system voltage and current of the converters and synchronous condensers in the operating state of other DC converter stations, its commutation failure impact factor is the smallest.

[0048] In the preferred implementation of the multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser, the commutation failure prediction control module uses the AC voltage zero-sequence criterion. When the AC voltage zero-sequence exceeds a set value, the commutation failure prediction control module is activated, and the commutation failure severity signal is proportional to the AC voltage zero-sequence value.

[0049] In the preferred implementation of the multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser, the commutation failure prediction control module uses the AC voltage α / β conversion criterion. When the AC voltage α / β conversion criterion exceeds a set value, the commutation failure prediction control module is activated, and the commutation failure severity signal is proportional to the AC voltage α / β conversion value.

[0050] In the preferred implementation of the multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser, the commutation failure prediction control module uses the DC current command deviation criterion. When the deviation between the measured DC current value and the DC current command exceeds a set value, the commutation failure prediction control module is activated, and the commutation failure severity signal is proportional to the DC current command deviation.

[0051] In the preferred implementation of the multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser, the commutation failure prediction control module uses the AC-DC current difference criterion. When the AC-DC current difference criterion exceeds a set value, the commutation failure prediction control module is activated, and the commutation failure severity signal is proportional to the AC-DC current difference.

[0052] In the preferred implementation of the multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser, the commutation failure impact factor uses the multi-infeed interaction factor.

[0053] In the preferred implementation of the multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser, when two or more criteria are simultaneously satisfied, the following processing strategy is executed: the severity signals of all parallel trigger criteria will be output through a maximum selector as the final commutation failure severity signal.

[0054] In the preferred embodiment of the multi-infeed DC coordinated control method with a controllable phase-shifting converter and a synchronous condenser, the larger the commutation failure severity signal is, the larger the change amount of the Gamma angle of the converter and the emergency control adjustment amount of the synchronous condenser are; the smaller the commutation failure severity signal is, the smaller the change amount of the Gamma angle of the converter and the emergency control adjustment amount of the synchronous condenser are.

[0055] In one embodiment, the method includes:

[0056] Step 1: Monitor the commutation failure prediction control module in the control system of the converters in operation at each DC converter station. After the commutation failure prediction control module is started, send the start signal of the commutation failure prediction control module and the commutation failure severity signal to the control systems of other converters and synchronous condensers in operation within the same DC converter station through the communication of the in-station control system of the DC converter station, and send them to the control systems of the converters and synchronous condensers in operation at other DC converter stations through the communication of the inter-station control system of the DC converter station.

[0057] Step 2: After the commutation failure prediction control module is started, the converter in operation adopts the following method according to the commutation failure severity signal:

[0058] 1): If the converter in operation is a conventional converter, increase the Gamma angle.

[0059] 2): If the converter in operation is a controllable phase-shifting converter, when the controllable phase-shifting converter is in the non-controllable commutation mode, that is, the conventional commutation mode, increase the Gamma angle; when the controllable phase-shifting converter is in the controllable commutation mode, decrease the Gamma angle.

[0060] Step 3: After receiving the start signal of the commutation failure prediction control module, the control systems of other converters and synchronous condensers in operation within the same DC converter station adopt the following method according to the commutation failure impact factor and the commutation failure severity signal:

[0061] 1): If the other converters in operation within the same DC converter station are conventional converters, increase the Gamma angle.

[0062] 2): If the other converters in operation within the same DC converter station are controllable phase-shifting converters, when the controllable phase-shifting converter is in the non-controllable commutation mode, that is, the conventional commutation mode, increase the Gamma angle; when the controllable phase-shifting converter is in the controllable commutation mode, decrease the Gamma angle.

[0063] 3): The control system of the synchronous condenser modifies the excitation reference voltage and the duration command to complete the emergency control of the synchronous condenser.

[0064] Step 4: After receiving the start signal of the commutation failure prediction control module, the control systems of the converters and synchronous condensers in the other DC converter stations in the operating state adopt the following methods according to the commutation failure impact factor and the commutation failure severity signal.

[0065] 1): If the converter in the other DC converter station in the operating state is a conventional converter, increase the Gamma angle.

[0066] 2): If the converter in the other DC converter station in the operating state is a controllable commutation converter, when the controllable commutation converter is in the non-controllable commutation mode, that is, the conventional commutation mode, increase the Gamma angle; when the controllable commutation converter is in the controllable commutation mode, decrease the Gamma angle.

[0067] 3): The control system of the synchronous condenser sends a command to modify the excitation reference voltage and the duration by the excitation system to complete the emergency control of the synchronous condenser.

[0068] The commutation failure prediction control module includes an AC voltage zero-sequence criterion, or an AC voltage α / β conversion criterion, or a DC current command deviation criterion, or an AC-DC current difference criterion. Specifically:

[0069] 1) AC voltage zero-sequence criterion

[0070] Add the three-phase AC voltages to obtain the zero-sequence voltage. When a single-phase AC voltage fails, the zero-sequence value is greater than the AC voltage unbalance zero-sequence value in the steady state. This criterion is mainly used to identify asymmetrical faults in the AC system.

[0071]

[0072] In the formula, , , are the A, B, and C phase AC voltages respectively, is the set value of the AC voltage zero-sequence criterion, and the typical set value is 0.3 pu.

[0073] 2) AC voltage α / β conversion criterion

[0074] Detect three-phase voltage faults through α / β transformation. When all three-phase voltages fail, the output value of the α / β transformation is less than the output value of the α / β transformation in the steady state. This criterion is mainly used to identify symmetrical faults in the AC system.

[0075]

[0076] In the formula, is the α / β transformation value of the current three-phase AC voltage is the α / β transformation value of the three-phase AC voltage before time t0 (such as the α / β transformation value 2 s ago), and is used to represent the α / β transformation value under steady-state conditions is the set value of the α / β conversion criterion for the AC voltage, and the typical set value is 0.2 pu

[0077] 3) DC current command deviation criterion

[0078] Compare the DC current measurement value with the DC current command value. This criterion is mainly used to prevent commutation failure caused by sudden increase in current

[0079]

[0080] In the formula is the DC current measurement value is the DC current command value is the set value of the DC current command deviation criterion, and the typical set value is 0.16 pu

[0081] 4) AC-DC current difference criterion

[0082] Compare the DC current with the AC current. This criterion is mainly used as a backup criterion for commutation failure prediction

[0083]

[0084] In the formula is the DC current measurement value and are respectively the maximum values of the absolute values of the AC currents of the Y-bridge and D-bridge and the DC current command value is the set value of the AC-DC current difference criterion, and the typical set value is 0.1 pu

[0085] The commutation failure impact factor is used to indicate the impact degree of commutation failure of each converter, and is proportional to the electrical coupling degree between the converter and the synchronous condenser. If other converters in the same DC converter station in the operating state are in a non-layered mode, its commutation failure impact factor is the largest. If after the converter has a commutation failure, there is no impact on the AC system voltage and current of the converters and synchronous condensers in the operating state of other DC converter stations, its commutation failure impact factor is the smallest. The typical commutation failure impact factor adopts the multi-infeed interaction factor

[0086] The multi-infeed interaction factor (MIIF) is an index proposed by the CIGRE WG B4 working group to measure the strength of the interaction between converter stations in a multi-infeed HVDC system. Its definition is: when a symmetric three-phase reactor is connected to converter bus i, causing the voltage on this bus to drop by 1%, the voltage change rate of converter bus j is

[0087]

[0088] wherein, is the multi-infeed interaction factor of converter bus j relative to converter bus i, is the voltage change of converter bus j, is the bus voltage of converter bus i before the reactor is put into operation.

[0089] , The larger the value is, the stronger the interaction between converter station i and converter station j. When The smaller the value is, the weaker the interaction between converter station i and converter station j. The magnitude of the multi-infeed interaction factor (MIIF) has nothing to do with the size of the symmetric three-phase reactor put into operation at the converter bus, and only relates to the parameters of the receiving-end AC system. The multi-infeed interaction factor of the multi-infeed HVDC system can be obtained through theoretical calculation (node self-impedance and mutual impedance) or modeling and simulation.

[0090] The start signal of the commutation failure prediction and control module and the commutation failure severity signal are described in detail as follows:

[0091] 1) If the commutation failure prediction and control module adopts the zero-sequence criterion of AC voltage, when the zero-sequence of AC voltage exceeds the set value, the commutation failure prediction and control module starts, and the commutation failure severity signal is proportional to the zero-sequence value of AC voltage.

[0092]

[0093] wherein, is the commutation failure severity. The larger this value is, the more serious the possible commutation failure is. is the parameter associated with the zero-sequence criterion of AC voltage, and the typical set value is 0.15.

[0094] 2) If the commutation failure prediction and control module adopts the α / β conversion criterion of AC voltage, when the α / β conversion criterion of AC voltage exceeds the set value, the commutation failure prediction and control module starts, and the commutation failure severity signal is proportional to the α / β conversion value of AC voltage.

[0095]

[0096] wherein, is the parameter associated with the zero-sequence criterion of AC voltage, and the typical set value is 0.15.

[0097] 3) If the commutation failure prediction control module adopts the DC current command deviation criterion, when the deviation between the measured DC current value and the DC current command exceeds a certain value, the commutation failure prediction control module is activated, and the commutation failure severity signal is proportional to the DC current command deviation.

[0098]

[0099] In the formula, is the associated parameter of the AC voltage zero-sequence criterion, and the typical fixed value is 1.0.

[0100] 4) For the start signal of the commutation failure prediction control module and the commutation failure severity signal, if the commutation failure prediction control module adopts the AC-DC current difference criterion, when the AC-DC current difference criterion exceeds a certain value, the commutation failure prediction control module is activated, and the commutation failure severity signal is proportional to the AC-DC current difference.

[0101]

[0102] In the formula, is the associated parameter of the AC voltage zero-sequence criterion, and the typical fixed value is 1.0.

[0103] For the above commutation failure prediction control module, when two or more criteria are satisfied simultaneously, the following processing strategy is executed: The severity signals of all parallel trigger criteria will be output through a maximum selector as the final commutation failure severity signal. The larger the commutation failure severity signal, the larger the change in the Gamma angle of the converter and the emergency control adjustment amount of the synchronous condenser; the smaller the commutation failure severity signal, the smaller the change in the Gamma angle of the converter and the emergency control adjustment amount of the synchronous condenser.

[0104] In one embodiment, as shown in the appendix Figure 1 In a certain multi-infeed DC regional power grid, there are 5 DC lines connected, and there is also 1 group of synchronous condensers. The 5 DC converter stations are as follows: Converter station 1, 500 kV conventional DC; Converter station 2, 800 kV UHV DC; Converter station 3: 500 kV conventional DC; Converter station 4: 500 kV CCC converter DC, adopting CLCC technology; Converter station 5: 800 kV UHV CCC converter DC, adopting HLCC technology.

[0105] Before this solution was used, each converter station adopted its own control method to suppress commutation failure, and the synchronous condenser adopted its own control method to provide reactive power support.

[0106] Converter stations 1 to 5 are configured with commutation failure prediction modules. The commutation failure prediction criterion is one or several of the following four criteria: AC voltage zero-sequence criterion, AC voltage α / β conversion criterion, DC current command deviation criterion, and AC-DC current difference criterion (when multiple criteria are used, it is an OR relationship. If any one criterion is met, the commutation failure prediction control module will be activated, and the activation signal of the commutation failure prediction control module is 1). The detailed description of each criterion is as follows:

[0107] 1) AC voltage zero-sequence criterion

[0108]

[0109]

[0110] In the formula, , , are the AC voltages of phases A, B, and C respectively, is the set value of the AC voltage zero-sequence criterion, and the typical set value is 0.3 pu; is the severity of commutation failure. The larger this value, the more severe the possible commutation failure, is the associated parameter of the AC voltage zero-sequence criterion, and the typical set value is 0.15.

[0111] 2) AC voltage α / β conversion criterion

[0112]

[0113]

[0114] In the formula, is the current three-phase AC voltage α / β transformation value, is the three-phase AC voltage α / β transformation value before time t0 (such as the α / β transformation value 2 s ago), which is used to represent the α / β transformation value in the steady state, is the set value of the AC voltage α / β conversion criterion, and the typical set value is 0.2 pu; is the associated parameter of the AC voltage zero-sequence criterion, and the typical set value is 0.15.

[0115] 3) DC current command deviation criterion

[0116] Compare the DC current measurement value and the DC current command value. This criterion is mainly used to prevent commutation failure caused by a sudden increase in current.

[0117]

[0118]

[0119] In the formula, is the DC current measurement value, is the DC current command value, is the fixed value of the DC current command deviation criterion, and the typical fixed value is 0.16 pu; is the associated parameter of the AC voltage zero-sequence criterion, and the typical fixed value is 1.0.

[0120] 4) AC-DC current difference criterion

[0121] Compare the DC current and the AC current. This criterion is mainly used as a backup criterion for predicting commutation failure.

[0122]

[0123]

[0124] In the formula, is the DC current measurement value, , are respectively the maximum values of the absolute values of the AC currents of the Y-bridge and the D-bridge, the DC current command value, is the fixed value of the AC-DC current difference criterion, and the typical fixed value is 0.1 pu; is the associated parameter of the AC voltage zero-sequence criterion, and the typical fixed value is 1.0.

[0125] The commutation failure impact factor, which is used to measure the impact degree of commutation failure of each converter, is proportional to the electrical coupling degree between the converter and the synchronous condenser. If other converters in the same DC converter station in the operating state are in a non-layered mode, its commutation failure impact factor is the largest. If after the converter has a commutation failure, there is no impact on the AC system voltage and current of the converters and synchronous condensers in the operating state of other DC converter stations, its commutation failure impact factor is the smallest. The typical commutation failure impact factor adopts the Multi-Infeed Interaction Factor (MIIF).

[0126] The size of the Multi-Infeed Interaction Factor has nothing to do with the size of the symmetrical three-phase reactor connected at the commutation bus, and only relates to the parameters of the receiving-end AC system. The Multi-Infeed Interaction Factor of the multi-infeed DC power transmission system can be obtained through theoretical calculation (node self-impedance and mutual impedance) or modeling and simulation. The MIIF matrix is:

[0127]

[0128] In the formula, is the Multi-Infeed Interaction Factor of the commutation bus j relative to the commutation bus i.

[0129] A specific implementation scheme of a multi-infeed DC collaborative control method including a controllable commutation converter and a synchronous condenser is as follows:

[0130] Step 1: Monitor the commutation failure prediction control module in the control system of the converters in operation at each HVDC converter station. After the commutation failure prediction control module is started, send the start signal of the commutation failure prediction control module and the commutation failure severity signal to the control systems of other converters and synchronous condensers in operation within the same HVDC converter station through the in-station control system communication of the HVDC converter station, and send them to the control systems of converters and synchronous condensers in operation at other HVDC converter stations through the inter-station control system communication of the HVDC converter station. (As shown in Appendix Figure 2 shown)

[0131] Step 2: After the commutation failure prediction control module is started, the converter in operation shall, according to the commutation failure severity signal, adopt the following methods

[0132] 1): If the converter in operation is a conventional converter, increase the Gamma angle

[0133] 2): If the converter in operation is a phase-controllable converter, when the phase-controllable converter is in the non-phase-controllable commutation mode, i.e., the conventional commutation mode, increase the Gamma angle; when the phase-controllable converter is in the phase-controllable commutation mode, decrease the Gamma angle.

[0134] Step 3: After receiving the start signal of the commutation failure prediction control module, the control systems of other converters and synchronous condensers in operation within the same HVDC converter station shall, according to the commutation failure impact factor and the commutation failure severity signal, adopt the following methods

[0135] 1): If the other converter in operation within the same HVDC converter station is a conventional converter, increase the Gamma angle

[0136] 2): If the other converter in operation within the same HVDC converter station is a phase-controllable converter, when the phase-controllable converter is in the non-phase-controllable commutation mode, i.e., the conventional commutation mode, increase the Gamma angle; when the phase-controllable converter is in the phase-controllable commutation mode, decrease the Gamma angle

[0137] 3): The control system of the synchronous condenser shall modify the excitation reference voltage and the duration command to complete the emergency control of the synchronous condenser.

[0138] Step 4: After receiving the start signal of the commutation failure prediction control module, the control systems of converters and synchronous condensers in operation at other HVDC converter stations shall, according to the commutation failure impact factor and the commutation failure severity signal, adopt the following methods

[0139] 1): If the converter in operation at other HVDC converter stations is a conventional converter, increase the Gamma angle

[0140] 2): If the converter in other DC converter stations in the operating state is a controllable commutation converter, and if the controllable commutation converter is in the non - controllable commutation mode, that is, the conventional commutation mode, increase the Gamma angle; if the controllable commutation converter is in the controllable commutation mode, decrease the Gamma angle.

[0141] 3): The control system of the synchronous condenser sends commands to modify the excitation reference voltage and the duration to complete the emergency control of the synchronous condenser.

[0142] After implementing the multi - DC collaborative control method proposed by the present invention, which includes a controllable commutation converter and a synchronous condenser, the coordinated control of a multi - element control system of a conventional DC, a controllable commutation converter, and a synchronous condenser can be achieved. The advantages of the controllable commutation converter and the synchronous condenser in resisting commutation failures are fully utilized, effectively preventing or reducing the risk of simultaneous or consecutive commutation failures in a multi - DC system, and ensuring the safe and stable operation of a multi - infeed DC power grid.

[0143] In one embodiment, a multi - infeed DC collaborative control method including a controllable commutation converter and a synchronous condenser realizes the coordinated control between multiple DC converters and the synchronous condenser through a commutation failure prediction control module in the converter station. The method includes: starting the commutation failure prediction control module, adjusting the Gamma angles of the conventional converter and the controllable commutation converter, as well as the excitation reference voltage and duration of the synchronous condenser according to the commutation failure severity signal. The commutation failure prediction control module uses multiple criteria, such as AC voltage zero - sequence, α / β conversion, DC current command deviation, and AC - DC current difference. The commutation failure impact factor is used to evaluate the impact degree of the converter commutation failure and is proportional to the electrical coupling degree. The purpose of this method is to prevent or reduce commutation failures and ensure the safe and stable operation of the power grid.

[0144] The commutation failure prediction control module (CFP) of the present invention

[0145] Multiple criteria are adopted (such as AC voltage zero-sequence criterion, α / β conversion criterion, DC current command deviation criterion, AC-DC current difference criterion) for commutation failure prediction. Early warning function: By monitoring the system status in real time, abnormal trends can be detected before commutation failure occurs, realizing the forward-looking control of commutation failure. Improve discrimination accuracy and robustness: Multiple criteria are used in parallel, which can adapt to different types of faults (symmetrical / asymmetrical), enhancing the reliability of the system under various operating conditions. Output severity signal: It not only judges whether commutation failure may occur, but also reflects its severity, providing a quantitative basis for subsequent adjustment strategies. Maximum value selection mechanism: When multiple criteria are triggered simultaneously, the maximum severity is selected as the final signal to ensure the response to the most serious threat and avoid missing key risks. The Gamma angle control strategy adopts different Gamma angle adjustment strategies for different types of converters (conventional converter vs. controllable commutation converter) according to the commutation failure severity signal. For conventional converters: increase the Gamma angle; for controllable commutation converters, increase the Gamma angle in the non-controllable mode (i.e., conventional mode); decrease the Gamma angle in the controllable mode. Enhance commutation margin: Increasing the Gamma angle can extend the turn-off angle time and improve the probability of successful commutation, especially suitable for conventional converters. Dynamically optimize commutation performance: For controllable commutation converters, decreasing the Gamma angle in the controllable mode provides reactive power support for the system, which is beneficial to fault recovery and improves the response speed and efficiency. Differentiated control strategy: Flexibly adjust the control strategy according to the converter type and the current operating mode to achieve refined control and enhance the stability and flexibility of the overall system. The commutation failure impact factor (CFIF) uses indicators such as the multi-infeed interaction factor (MIIF) to measure the degree of mutual influence between converter stations, and CFIF is proportional to the electrical coupling degree. Quantify the impact range: Clearly define the impact degree on other converter stations and synchronous condensers after commutation failure occurs at a certain DC converter station. Implement differentiated coordinated control: Based on the magnitude of CFIF, determine whether other converters and synchronous condensers need to participate in coordinated control and their control intensity, avoiding over-response or under-response. Enhance the overall resilience of the system: Through the dynamic analysis of the impact factor, the control system can make optimal decisions from a global perspective, preventing chain reactions caused by local disturbances. The synchronous condenser emergency control strategy modifies the excitation reference voltage and the duration command according to the start signal and severity signal of the commutation failure prediction module. Fast reactive power support ability: In the pre-judgment stage of commutation failure, the synchronous condenser can quickly provide or absorb reactive power by adjusting the excitation to stabilize the AC voltage. Enhance the voltage stability of the system: Especially in the case of a weak AC system or insufficient short-circuit capacity, the synchronous condenser can effectively suppress voltage dips and reduce the risk of commutation failure.Cooperate with the DC system: The synchronous condenser is no longer an independent operating device, but becomes a part of the protection of the entire DC system, forming an integrated control system of "DC + synchronous condenser". Cross-converter station communication and coordinated control, and commutation failure prediction signals and severity signals are transmitted to all relevant converters and synchronous condenser controllers through in-station and inter-station communication networks. Achieve wide-area coordinated control: Break through the limitations of traditional single-station independent control, and build an information sharing and linkage mechanism between multiple DC converter stations and synchronous condensers. Improve the system's self-healing ability: Through cross-station coordination, when a potential fault occurs in one converter station, other stations can make preparations in advance to jointly resist risks. Optimize resource scheduling and allocation: Reasonably allocate the action intensity and direction of each converter and synchronous condenser to avoid resource waste or conflicts. The Controllable Line Commutated Converter (CLCC / Hybrid LCC, HLCC) can switch control strategies according to the operating mode and actively intervene in the commutation process in the controllable commutation mode. Break through the inherent defects of traditional LCC: Traditional LCC relies on the natural zero-crossing of the grid voltage for commutation and is vulnerable to AC system disturbances; while CLCC can actively control the commutation moment when necessary. Improve the anti-interference ability: It can still maintain a high commutation success rate when the AC system voltage fluctuates or is unbalanced. Flexible operation mode switching: Support switching between the conventional mode and the controllable mode, taking into account economy and safety.

[0146] Although the embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments and application fields. The above specific embodiments are merely illustrative and guiding, rather than restrictive. Those of ordinary skill in the art can also make many forms under the inspiration of this specification and without departing from the scope protected by the claims of the present invention, and all of these fall within the scope of protection of the present invention.

Claims

1. A multi-infeed DC coordinated control method including a thyristor controlled phase shifter and a synchronous condenser, characterized in that, It includes the following steps: S1: Monitor the phase failure prediction control module in the converters of each DC converter station in the operating state; when the phase failure prediction control module is triggered, generate a phase failure prediction control module start signal and a phase failure severity signal, and send the signals to the control systems of other operating converters and synchronous condensers in the same station through the in-station communication system of the DC converter station, and at the same time send the signals to the control systems of the operating converters and synchronous condensers in other DC converter stations through the inter-station communication system of the DC converter station; S2: The converter that receives the phase failure prediction control module start signal performs Gamma angle adjustment operations according to its type and current operating mode: If it is a conventional converter, increase the Gamma angle; If it is a controllable phase commutation converter and is in the non-controllable phase commutation mode, increase the Gamma angle; if it is in the controllable phase commutation mode, decrease the Gamma angle; S3: The control system of the synchronous condenser that receives the signal modifies the excitation reference voltage and the duration command according to the phase failure impact factor and the phase failure severity signal to achieve emergency control actions.

2. The multi-infeed DC collaborative control method with a controllable phase-shifting converter and a synchronous condenser according to claim 1, characterized in that, The phase failure prediction control module adopts one or more of the AC voltage zero-sequence criterion, the AC voltage α / β conversion criterion, the DC current command deviation criterion, or the AC-DC current difference criterion.

3. A multi-infeed DC collaborative control method including a controllable phase-shifting converter and a synchronous condenser according to claim 1, characterized in that, The phase failure impact factor is used to characterize the impact degree of phase failure of each converter, and is proportional to the electrical coupling degree of the converter and the synchronous condenser. If the other operating converters in the DC converter station are in the non-stratified mode, its phase failure impact factor is the largest. If there is no impact on the AC system voltage and current of the operating converters and synchronous condensers in other DC converter stations after the converter has a phase failure, its phase failure impact factor is the smallest.

4. A multi-infeed DC collaborative control method including a controllable commutation converter and a synchronous condenser according to claim 1, characterized in that, The phase failure prediction control module adopts the AC voltage zero-sequence criterion. When the AC voltage zero-sequence exceeds the set value, the phase failure prediction control module starts, and the phase failure severity signal is proportional to the AC voltage zero-sequence value.

5. A multi-infeed DC collaborative control method including a controllable commutation converter and a synchronous condenser according to claim 1, characterized in that The phase failure prediction control module adopts the AC voltage α / β conversion criterion. When the AC voltage α / β conversion criterion exceeds the set value, the phase failure prediction control module starts, and the phase failure severity signal is proportional to the AC voltage α / β conversion value.

6. The multi-infeed DC coordinated control method with a controllable phase-shifting converter and a synchronous condenser according to claim 1, wherein The phase failure prediction control module adopts the DC current command deviation criterion. When the deviation between the measured DC current value and the DC current command exceeds the set value, the phase failure prediction control module starts, and the phase failure severity signal is proportional to the DC current command deviation.

7. A multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser according to claim 1, characterized in that The phase failure prediction control module adopts the AC-DC current difference criterion. When the AC-DC current difference criterion exceeds the set value, the phase failure prediction control module starts, and the phase failure severity signal is proportional to the AC-DC current difference.

8. A multi-infeed DC collaborative control method including a controllable phase-shifting converter and a synchronous condenser according to claim 1, characterized in that, The phase failure impact factor adopts the multi-infeed interaction factor.

9. A multi-infeed DC coordinated control method including a controllable commutation converter and a synchronous condenser according to claim 1, characterized in that, When two or more criteria are satisfied simultaneously, the following processing strategy is executed: The severity signals of all parallel trigger criteria will be output through the maximum selector as the final phase failure severity signal.

10. A multi-infeed DC coordinated control method including a controllable phase-shifting converter and a synchronous condenser according to claim 1, characterized in that, The greater the commutation failure severity signal, the greater the change in the gamma angle of the converter and the emergency control adjustment amount of the synchronous condenser. The smaller the commutation failure severity signal, the smaller the change in the gamma angle of the converter and the emergency control adjustment amount of the synchronous condenser.

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