Valve side fault protection configuration method and device based on active neutral point potential deviation

Abstract

The invention discloses a valve side fault protection configuration method and device based on active neutral point potential deviation, and belongs to the field of large-scale collection and centralized transmission of new energy. The configuration method comprises the following steps: measuring the neutral point voltage of the DC side of the MMC; judging whether the neutral point voltage has significant offset or not; if the voltage of the neutral point deviates remarkably, the fault converter is locked; otherwise, judging whether the neutral point voltage has significant offset or not again; connecting a parallel supplementary capacitor; judging whether the interface circuit breaker is opened or not; if the interface circuit breaker is opened, the energy consumption device is started; otherwise, whether the interface circuit breaker is opened or not is judged again; starting power coordination control, and performing adaptive power adjustment of the wind power plant and rebalancing of the capacitor voltage of the converter station; waiting for the HVDC system to enter single / double-pole full-power operation; compared with a classic valve side fault protection configuration method, the number of required current sensors is small, and the sensors and circuit elements are prevented from being subjected to over-current and over-voltage risks.

Description

Technical Field

[0001] The present invention belongs to the field of large-scale collection and centralized transmission of new energy, and in particular relates to a valve-side fault protection configuration method and device based on active neutral point potential shift. Background Art

[0002] A valve-side fault in a converter station in a high voltage direct current (HVDC) system refers to an AC fault that occurs between the converter and the interface transformer. It is usually caused by temporary / permanent insulation breakdown of the transformer and is considered a serious AC fault. Considering that the fault point is closest to the converter, the valve-side fault has a great impact on the normal operation of the converter and may even endanger the safe and stable operation of the entire AC system. For this reason, when a valve-side fault occurs, it is usually required to detect the fault as early as possible and achieve rapid locking of the converter. However, even so, it may still cause problems such as overvoltage of submodule capacitors and system divergence, and there is a lack of recovery and operation strategies for the system after the fault. Summary of the invention

[0003] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a valve-side fault protection configuration method and device based on active neutral point potential shift, which solves the problems in the prior art.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] A valve-side fault protection configuration method based on active neutral point potential shift is applied to an HVDC system, wherein the HVDC system includes: a WPP, a WPP-side transformer, an AC line, an interface circuit breaker, an MMC-side transformer and an MMC connected in sequence, an energy dissipation device and a parallel compensation capacitor are connected between the AC line and the interface circuit breaker; one end of the MMC DC side is electrically connected to a grounding point through a DC-side grounding impedance, and the other end of the MMC DC side is electrically connected to a DC system through a DC-side smoothing reactor;

[0006] The configuration method comprises the following steps:

[0007] Measure the neutral point voltage on the DC side of the MMC;

[0008] Determine whether the neutral point voltage has a significant deviation; if the neutral point voltage has a significant deviation, lock the faulty converter; otherwise, determine again whether the neutral point voltage has a significant deviation;

[0009] Connect the supplementary capacitor in parallel;

[0010] Determine whether the interface circuit breaker is already opened; if the interface circuit breaker is already opened, start the energy consumption device; otherwise, determine again whether the interface circuit breaker is already opened;

[0011] Start power coordination control to perform adaptive power regulation of wind farms and rebalance of capacitor voltage at converter stations;

[0012] Waiting for the HVDC system to enter unipolar / bipolar full power operation.

[0013] Furthermore, the neutral point voltage is a DC side grounding impedance voltage.

[0014] Furthermore, the significant voltage deviation refers to that the measured neutral point voltage is greater than 0.05 times the rated DC voltage.

[0015] Furthermore, at the moment of starting the energy dissipation device, the energy dissipation resistor needs to be cut in to reverse the output power of the converter station, and then the energy dissipation resistor is gradually cut out; during this process, the output power of the WPP continues to decrease, and the injection power of the MMC continues to increase until they overlap and the energy dissipation device completely exits.

[0016] Furthermore, the specific expression of the adaptive power regulation of the wind farm is:

[0017]

[0018] Among them, P s , P sN , P sref are the output power, rated power and reference power of the wind farm respectively, k pcut is the regulation speed of active power, ω pll is the output angular frequency of the phase-locked loop, U s and U sN are the measured value and rated value of the voltage amplitude at the grid connection point, and s is the Laplace operator.

[0019] Furthermore, the process of rebalancing the capacitor voltage of the converter station is: achieving inter-phase energy balance through single-phase power injection, and achieving sub-module voltage balance between upper and lower bridge arms within the phase through fundamental frequency injection.

[0020] Further, the HVDC system includes: a WPP, a WPP side transformer, an AC line, an interface circuit breaker, an MMC side transformer and an MMC connected in sequence, an energy dissipation device and a parallel compensation capacitor are connected between the AC line and the interface circuit breaker; one end of the MMC DC side is electrically connected to a grounding point through a DC side grounding impedance, and the other end of the MMC DC side is electrically connected to a DC system through a DC side smoothing reactor;

[0021] The configuration device comprises:

[0022] Voltage measurement unit: measures the neutral point voltage on the DC side of the MMC;

[0023] The deviation judging unit is used to judge whether the neutral point voltage has a significant deviation; if the neutral point voltage has a significant deviation, the faulty converter is locked; otherwise, the neutral point voltage is judged again whether the neutral point voltage has a significant deviation;

[0024] Capacitor connection unit: connects parallel supplementary capacitors;

[0025] Energy consumption device starting unit: determines whether the interface circuit breaker is already opened; if the interface circuit breaker is already opened, starts the energy consumption device; otherwise, determines again whether the interface circuit breaker is already opened;

[0026] Coordination control unit: Starts power coordination control, performs adaptive power regulation of wind farms and rebalances the capacitor voltage of converter stations;

[0027] And, operating unit: waiting for the HVDC system to enter unipolar / bipolar full power operation.

[0028] A computer storage medium stores a readable program, which can execute the above-mentioned valve side fault protection configuration method based on active neutral point potential shift when the program is running.

[0029] An electronic device, comprising: a processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other through the communication bus;

[0030] The memory is used to store at least one executable instruction, and the executable instruction enables the processor to execute operations corresponding to the above-mentioned valve-side fault protection configuration method based on active neutral point potential offset.

[0031] A computer program product includes computer instructions, wherein the computer instructions instruct a computing device to execute operations corresponding to the above-mentioned valve-side fault protection configuration method based on active neutral point potential shift.

[0032] Beneficial effects of the present invention:

[0033] 1. Rapid fault detection is achieved through indirect DC side neutral point grounding, the existence of the working point of the AC system after blocking is improved through parallel filter capacitors, the lower arm commutation of the faulty converter is coupled to the upper arm through the DC side grounding resistor to suppress the overvoltage of the submodule capacitor, and the inter-pole transient power transfer of the bipolar system is achieved through energy dissipation devices to prevent overload of the converter station after the fault is cleared. The self-balancing of the AC system after the fault is achieved through coordinated control of the wind farm and the converter station. After the fault occurs, the single / bipolar full power operation of the HVDC system can be achieved, which can greatly reduce the power loss caused by the fault.

[0034] 2. Compared with the classic valve side fault protection configuration method, the method of the present invention requires fewer current sensors and does not expose sensors and circuit components to overcurrent and overvoltage risks.

[0035] 3. Improves the existence of the operating point of the AC system during faults, helping to prevent system divergence.

[0036] 4. It suppresses the overvoltage of the submodule capacitor of the converter and prevents the switching device from facing overcurrent. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0038] Figure 1 is a block diagram of the HVDC system structure to which the method of the present invention is applied;

[0039] Figure 2 is a flow chart of the method proposed by the present invention;

[0040] Figure 3 It is a fast fault detection block diagram of the method proposed by the present invention;

[0041] Figure 4 is a schematic diagram of transient power transfer of the method proposed in the present invention;

[0042] Figure 5 It is a submodule capacitor voltage rebalancing control diagram of the method proposed in the present invention.

[0043] In the figure: 1- Wind Power Plant (WPP), 2- WPP side transformer, 3- AC line, 4- energy consumption device, 5- parallel compensation capacitor, 6- interface circuit breaker, 7- MCC side transformer, 8- Modular Multilevel Converter (MMC), 9- DC side grounding impedance, 10- DC side smoothing reactor. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Example 1

[0046] like Figure 1 As shown, the HVDC system includes: a wind farm 1, a WPP side transformer 2, an AC line 3, an interface circuit breaker 6, an MMC side transformer 7 and a modular multilevel converter 8 connected in sequence; an energy dissipation device 4 and a parallel compensation capacitor 5 are connected between the AC line 3 and the interface circuit breaker 6; one end of the MMC DC side is electrically connected to the grounding point through a DC side grounding impedance 9, and the other end of the MMC DC side is electrically connected to the DC system through a DC side smoothing reactor 10.

[0047] Example 2

[0048] based on Figure 1 In the HVDC system in the present embodiment, a valve side fault protection configuration method based on active neutral point potential shift is proposed, such as Figure 2 As shown, the specific steps include:

[0049] S1, measure the neutral point voltage on the DC side of the MMC,

[0050] The neutral point voltage of the MMC DC side is measured as follows: the MMC DC side is grounded via the DC side grounding impedance 9, and then the voltage of the DC side grounding impedance 9 is measured in real time;

[0051] S2, determining whether the neutral point voltage has a significant deviation;

[0052] The significant voltage deviation is specifically when the measured neutral point voltage is greater than 0.05 times the rated DC voltage.

[0053] S3, if the neutral point voltage deviates significantly, the faulty converter is locked; otherwise, it is determined again whether the neutral point voltage deviates significantly;

[0054] like Figure 3 As shown, the voltage u of the DC side grounding impedance 9 is monitored in real time. dcg , if it deviates significantly from 0, it indicates that a valve side fault has occurred in the system; where u dcg Significant deviation from 0 means that the measured voltage is greater than 0.05 times the rated DC voltage.

[0055] And through MMC p and MMC n Different signal markers are superimposed in the modulation link to judge whether the valve side fault occurs in the MMC. p Still MMC n .

[0056] S4, connected in parallel with supplementary capacitor 5;

[0057] The specific value of the parallel compensation capacitor 5 needs to be obtained by calculating the steady-state power flow after the faulty converter is locked. The calculation steps of the parallel compensation capacitor 5 are:

[0058] 1) Set a reference point in the HVDC system and set the phase of the voltage at this point to 0.

[0059] 2) Set the value of the parallel compensation capacitor as an unknown number, solve the voltage and current of each circuit component, and then obtain the voltage and current expressions of all nodes in the HVDC system, thereby obtaining the model of the HVDC system.

[0060] 3) Solve the HVDC system model in combination with the following constraints: the voltage amplitude of each node cannot exceed 1.1 times its rated value, and the current amplitude of each branch cannot exceed 1.1 times its rated value.

[0061] 4) Optimize the value of the parallel compensation capacitor based on the solution of the HVDC system model.

[0062] S5, determining whether the interface circuit breaker 6 is open;

[0063] S6, if the interface circuit breaker 6 is already opened, the energy consumption device 4 is started; otherwise, it is determined again whether the interface circuit breaker 6 is already opened;

[0064] like Figure 4 As shown, at the moment of starting the energy dissipation device 4, the energy dissipation resistor needs to be switched in to reverse the output power of the converter station, and then the energy dissipation resistor is gradually switched out; during this process, the output power of the wind farm 1 continues to decrease, and the injection power of the modular multilevel converter 8 continues to increase until they overlap and the energy dissipation device 4 is completely withdrawn.

[0065] S7, start power coordination control, perform adaptive power regulation of the wind farm and rebalance the capacitor voltage of the converter station;

[0066] The specific expression of adaptive power regulation of wind farm is:

[0067]

[0068] Among them, P s , P sN , P sref are the output power, rated power and reference power of the wind farm respectively, k pcut is the regulation speed of active power, ω pll is the output angular frequency of the phase-locked loop, U s and U sN are the measured and rated values ​​of the grid-connected point voltage amplitude, and s is the Laplace operator.

[0069] like Figure 5As shown in Figure 2, the rebalancing process of the converter station capacitor voltage is:

[0070] Through single-phase power injection, phase-to-phase energy balance is achieved. As shown in the first branch, there are only measurement and calculation links, which can achieve rapid regulation of the total energy in the phase. At the same time, the sub-module voltage balance between the upper and lower bridge arms in the phase is achieved through baseband injection. There is only one PI link in each phase, and the voltage balance between the bridge arms will not interfere with the total energy regulation in the phase, which improves the transient performance of the circulating current control.

[0071] S8, waiting for the HVDC system to enter unipolar / bipolar full power operation.

[0072] The method of the present invention may be implemented in hardware, firmware, or as software or computer code that may be stored in a recording medium (such as a CDROM, RAM, floppy disk, hard disk, or magneto-optical disk), or as computer code that is originally stored in a remote recording medium or a non-temporary machine-readable medium downloaded over a network and will be stored in a local recording medium, so that the method described herein may be stored in such software processing on a recording medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware (such as an ASIC or FPGA). It is understood that a computer, processor, microprocessor controller, or programmable hardware includes a storage component (e.g., RAM, ROM, flash memory, etc.) that can store or receive software or computer code, and when the software or computer code is accessed and executed by a computer, processor, or hardware, the method described herein is implemented. In addition, when a general-purpose computer accesses the code for implementing the method shown herein, the execution of the code converts the general-purpose computer into a dedicated computer for executing the method shown herein.

[0073] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A valve side fault protection configuration method based on active neutral point potential shift, applied to HVDC system, characterized in that: The HVDC system includes: a WPP, a WPP side transformer, an AC line, an interface circuit breaker, an MMC side transformer and an MMC connected in sequence, an energy dissipation device and a parallel compensation capacitor are connected between the AC line and the interface circuit breaker; one end of the MMC DC side is electrically connected to a grounding point through a DC side grounding impedance, and the other end of the MMC DC side is electrically connected to a DC system through a DC side smoothing reactor; The configuration method comprises the following steps: Measure the neutral point voltage on the DC side of the MMC; Determine whether the neutral point voltage has a significant deviation; if the neutral point voltage has a significant deviation, lock the faulty converter; otherwise, determine again whether the neutral point voltage has a significant deviation; Connecting parallel supplementary capacitors: Determine whether the interface circuit breaker has been opened; if the interface circuit breaker has been opened, start the energy consumption device; otherwise, determine again whether the interface circuit breaker has been opened; Start power coordination control to perform adaptive power regulation of wind farms and rebalance of capacitor voltage at converter stations; Waiting for the HVDC system to enter unipolar / bipolar full power operation.

2. The valve side fault protection configuration method based on active neutral point potential shift according to claim 1, characterized in that: The neutral point voltage is the DC side grounding impedance voltage.

3. The valve side fault protection configuration method based on active neutral point potential shift according to claim 1, characterized in that: The significant voltage deviation means that the measured neutral point voltage is greater than 0.05 times the rated DC voltage.

4. The valve side fault protection configuration method based on active neutral point potential shift according to claim 1, characterized in that: At the moment of starting the energy dissipation device, the energy dissipation resistor needs to be cut in to reverse the output power of the converter station, and then the energy dissipation resistor is gradually cut out; during this process, the output power of the WPP continues to decrease, and the injection power of the MMC continues to increase until they overlap and the energy dissipation device is completely withdrawn.

5. The valve side fault protection configuration method based on active neutral point potential shift according to claim 1, characterized in that: The specific expression of the adaptive power regulation of the wind farm is: Among them, P s , P sN , P sref are the output power, rated power and reference power of the wind farm respectively, k pcut is the regulation speed of active power, ω pll is the output angular frequency of the phase-locked loop, U s and U sN are the measured value and rated value of the voltage amplitude at the grid connection point, and s is the Laplace operator.

6. The valve side fault protection configuration method based on active neutral point potential shift according to claim 1, characterized in that: The process of rebalancing the capacitor voltage of the converter station is: achieving inter-phase energy balance through single-phase power injection, and achieving sub-module voltage balance between the upper and lower bridge arms within the phase through fundamental frequency injection.

7. A valve side fault protection configuration device based on active neutral point potential shift, applied to HVDC system, characterized in that: The HVDC system includes: a WPP, a WPP side transformer, an AC line, an interface circuit breaker, an MMC side transformer and an MMC connected in sequence, an energy dissipation device and a parallel compensation capacitor are connected between the AC line and the interface circuit breaker; one end of the MMC DC side is electrically connected to a grounding point through a DC side grounding impedance, and the other end of the MMC DC side is electrically connected to a DC system through a DC side smoothing reactor; The configuration device comprises: Voltage measurement unit: measures the neutral point voltage on the DC side of the MMC; The deviation judgment unit is used to judge whether the neutral point voltage has a significant deviation; if the neutral point voltage has a significant deviation, the faulty converter is locked; otherwise, it is judged again whether the neutral point voltage has a significant deviation: Capacitor connection unit: connects parallel supplementary capacitors; Energy consumption device starting unit: determines whether the interface circuit breaker has been opened; if the interface circuit breaker has been opened, the energy consumption device is started; otherwise, determines again whether the interface circuit breaker has been opened; Coordination control unit: Starts power coordination control, performs adaptive power regulation of wind farms and rebalances the capacitor voltage of converter stations; And, operating unit: waiting for the HVDC system to enter unipolar / bipolar full power operation.

8. A computer storage medium storing a readable program, characterized in that: When the program is running, the valve-side fault protection configuration method based on active neutral point potential shift as described in any one of claims 1 to 6 can be executed.

9. An electronic device, characterized in that: include: A processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other via the communication bus; The memory is used to store at least one executable instruction, and the executable instruction enables the processor to perform operations corresponding to the valve-side fault protection configuration method based on active neutral point potential shift as described in any one of claims 1-6.

10. A computer program product comprising computer instructions, characterized in that: The computer instructions instruct the computing device to execute operations corresponding to the valve-side fault protection configuration method based on active neutral point potential shift as described in any one of claims 1-6.

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