A method, system and device for reactive power control of an AC-DC system in a converter station and a storage medium

Abstract

The application discloses a kind of converter station ac-dc system reactive power control method, system, equipment and storage medium, the method includes: obtaining the reactive power exchange value of converter station receiving end ac-dc system;Determine the reference value corresponding to ac-dc system in reactive power exchange zero state, to reference value reactive power exchange value is corrected, and reactive power exchange difference value is obtained;To reactive power exchange difference value is handled, and the instruction value corresponding to the off angle obtained by processing is sent to the sending end of converter station;Based on instruction value adjustment the triggering angle of the sending end of converter station;According to the direct current power transmitted by direct current system, construct segmented function, to limit the off angle and triggering angle by segmented function, and obtain limit condition;According to limit condition, the switching of filter is judged, to control reactive power balance.The embodiment of the application can greatly reduce the reactive exchange between the sending and receiving end converter station ac-dc system, and improve the operation stability of ac-dc system.

Description

Technical Field

[0001] This invention relates to the field of power transmission system technology, and in particular to a reactive power control method, system, device and storage medium for AC / DC systems in converter stations. Background Technology

[0002] With the goals of carbon peaking and carbon neutrality being proposed, accelerating the construction of a new power system dominated by new energy sources and addressing the constraints on the transformation from a traditional energy consumption structure dominated by coal power to one dominated by new energy sources are impacting the process of my country's low-carbon energy transition. High-voltage direct current (HVDC) transmission projects, as the backbone of my country's energy resource optimization, will play an increasingly prominent role in meeting the future demand for new energy consumption.

[0003] In existing technologies, the design of AC filters is a crucial aspect of high-voltage direct current (HVDC) transmission projects. Conventional HVDC transmission systems use a dead zone for reactive power in AC filters to control their switching, thus limiting the reactive power exchange between the AC and DC systems within this dead zone. However, with the large-scale development of new energy sources and the increasing trend of grid integration, both insufficient reactive power supply from the AC system and excessive reactive power injection from the DC system into the AC system can negatively impact the safe and stable operation of the AC and DC systems.

[0004] Therefore, how to effectively control reactive power has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention provides a method, system, device, and storage medium for reactive power control in AC / DC systems of converter stations, in order to solve the problem of how to effectively control the reactive power of power transmission systems and improve the safety and stability of AC / DC system operation in DC power transmission projects.

[0006] To address the aforementioned technical problems, embodiments of the present invention provide a reactive power control method for AC / DC systems in converter stations.

[0007] Obtain the reactive power exchange value of the AC / DC system at the receiving end of the converter station;

[0008] Determine the reference value corresponding to the AC / DC system in the reactive power exchange junction zero state, and use the reference value to correct the reactive power exchange value to obtain the reactive power exchange difference;

[0009] The reactive power exchange difference is processed, and the instruction value corresponding to the processed shutdown angle is sent to the sending end of the converter station.

[0010] The firing angle of the sending end of the converter station is adjusted based on the instruction value;

[0011] A piecewise function is constructed based on the DC power transmitted by the DC system, and the cut-off angle and the firing angle are constrained by the piecewise function to obtain the constraint conditions;

[0012] The switching of the filter is determined based on the aforementioned constraints in order to control the reactive power balance.

[0013] Further, obtaining the reactive power exchange value of the AC / DC system at the receiving end of the converter station includes:

[0014] Obtain the first reactive power provided by the AC system and the second reactive power consumed by the DC system;

[0015] The difference between the first reactive power and the second reactive power is calculated to obtain the reactive power exchange value.

[0016] Further, the step of processing the reactive power exchange difference and sending the command value corresponding to the processed turn-off angle to the sending end of the converter station includes:

[0017] The reactive power exchange difference is used as an input signal to a proportional-integral converter for signal processing, and an adjustment command for the turn-off angle is output.

[0018] In response to the adjustment command, the shut-off angle of the converter station is adjusted.

[0019] Further, adjusting the firing angle of the sending end of the converter station based on the instruction value includes:

[0020] Based on the adjustment process of the shut-off angle, the DC voltage of the DC system is corrected, and the corrected DC voltage adjustment command is output.

[0021] In response to the DC voltage regulation command, the firing angle of the sending end of the converter station is adjusted.

[0022] Furthermore, the step of constructing a piecewise function based on the DC power transmitted by the DC system includes:

[0023] The fluctuation of the DC power of the converter station is monitored in real time to obtain the first adjustment range of the DC power;

[0024] With the reactive power exchange junction at zero as the target, the switching angle and the triggering angle are adjusted to obtain the second adjustment range of the converter station's angle;

[0025] Based on the first adjustment range and the second adjustment range, a piecewise function is constructed; the piecewise function is represented by the following formula:

[0026] γ=f(P d )

[0027] Where γ is the shut-off angle, P d This is DC power.

[0028] Furthermore, the step of determining the switching of the filter based on the aforementioned constraints to control reactive power balance includes:

[0029] Based on the aforementioned constraints, obtain the upper and lower limits of the angles of the shutdown angle and the trigger angle;

[0030] With the goal of achieving zero reactive power exchange, a first reactive power exchange control value corresponding to the upper limit value and a second reactive power exchange control value corresponding to the lower limit value are set respectively.

[0031] The switching of the filter is determined by using the first reactive power exchange control value and the second reactive power exchange control value.

[0032] Furthermore, it also includes:

[0033] According to the upper limit value, when the AC / DC system of the converter station reaches the preset first reactive power exchange target value, the filter is disconnected;

[0034] According to the lower limit value, when the AC / DC system of the converter station reaches the preset second reactive power exchange target value, the filter is activated.

[0035] Another embodiment of the present invention provides an AC / DC reactive power control system for a converter station, comprising:

[0036] The data acquisition module is used to acquire the reactive power exchange value of the AC / DC system at the receiving end of the converter station;

[0037] The data processing module is used to determine the reference value corresponding to the AC / DC system in the reactive power exchange junction zero state, and to correct the reactive power exchange value with the reference value to obtain the reactive power exchange difference.

[0038] The instruction sending module is used to process the reactive power exchange difference and send the instruction value corresponding to the processed shutdown angle to the sending end of the converter station.

[0039] An angle adjustment module is used to adjust the firing angle of the sending end of the converter station based on the instruction value;

[0040] An angle limiting module is used to construct a piecewise function based on the DC power transmitted by the DC system, and to limit the turn-off angle and the trigger angle using the piecewise function to obtain the limiting conditions;

[0041] The filter switching module is used to determine the switching of the filter according to the aforementioned constraints in order to control the reactive power balance.

[0042] Another embodiment of the present invention provides a computer device, including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein the processor executes the computer program to implement the reactive power control method of the AC / DC system of the converter station as described above.

[0043] In another embodiment of the present invention, a computer-readable storage medium is provided, the computer-readable storage medium storing a computer program, wherein when the device containing the computer-readable storage medium executes the computer program, it implements the reactive power control method of the AC / DC system of the converter station as described above.

[0044] Compared with the prior art, the beneficial effects of the embodiments of the present invention are at least one of the following:

[0045] (1) When the filter is switched on or off, the power rises or falls, and the AC system voltage changes, the reactive power at the receiving end is reduced by adjusting the turn-off angle, which further affects the DC voltage and causes the trigger angle at the sending end to be adjusted synchronously. This causes the trigger angle at the sending end to change synchronously, thereby adjusting the reactive power at the sending end and reducing the AC and DC reactive power exchange values ​​at both the sending and receiving ends, thus achieving safe and stable operation of the AC and DC system.

[0046] (2) Limit the values ​​of the firing angle and the shut-off angle to reduce the reactive power injected into the AC system to maintain reactive power balance, ensure the stable operation of the AC system, and set the switching judgment principle of the AC filter to reduce the reactive power exchange value after the angle is limited and improve the stability of the system operation. Attached Figure Description

[0047] Figure 1 This is a schematic flowchart of a reactive power control method for an AC / DC system in a converter station according to one embodiment of the present invention;

[0048] Figure 2 This is a control block diagram of reactive power control measurement in one embodiment of the present invention;

[0049] Figure 3 This is a block diagram of the reactive power control system of the AC / DC system of the converter station in one embodiment of the present invention;

[0050] Figure 4 This is a block diagram of a computer device structure in one embodiment of the present invention. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0052] In the description of this application, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0053] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. The terms "vertical," "horizontal," "left," "right," "upper," "lower," and similar expressions used herein are for illustrative purposes only and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0054] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the invention. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0055] One embodiment of the present invention provides a reactive power control method for AC / DC systems in converter stations. For details, please refer to [link to relevant documentation]. Figure 1 , Figure 1 This is a schematic flowchart of a reactive power control method for an AC / DC system in a converter station according to one embodiment of the present invention.

[0056] This invention proposes a constant reactive power exchange control strategy that uses the reactive power exchange junction of the AC / DC system to zero as the control object. This strategy achieves zero reactive power at the receiving end by adjusting the turn-off angle during filter switching, power fluctuations, and AC system voltage changes. It further influences the DC voltage, causing synchronous adjustment of the sending end's trigger angle, which in turn adjusts the sending end's reactive power, thereby reducing the reactive power exchange value at both the sending and receiving ends. The specific steps include:

[0057] S1. Obtain the reactive power exchange value of the AC / DC system at the receiving end of the converter station. Specifically,

[0058] A converter station is a station built in a high-voltage direct current (HVDC) transmission system to convert alternating current (AC) to direct current (DC) or vice versa, in order to meet the power system's requirements for safety, stability, and power quality. The main equipment or facilities that a converter station should include include: converter valves, converter transformers, smoothing reactors, AC switchgear, AC filters and AC reactive power compensation devices, DC switchgear, DC filters, control and protection devices, external grounding electrodes, and remote communication systems.

[0059] In this embodiment, firstly, the first reactive power provided by the AC system and the second reactive power consumed by the DC system are obtained.

[0060] In this embodiment of the invention, the reactive power data obtained from the AC system and DC system at the receiving end of the converter station are respectively recorded as the first reactive power and the second reactive power.

[0061] Next, the difference between the first reactive power and the second reactive power is calculated to obtain the reactive power exchange value.

[0062] In this embodiment of the invention, it is necessary to monitor the reactive power exchange between the AC system and the DC system at the receiving end of the converter station in real time. This usually involves measuring the reactive power on the AC side and the DC side and calculating the difference between them.

[0063] In this embodiment, the reactive power on the AC side is set to Q. ac The reactive power on the DC side is Q. dc The reactive power exchange value ΔQ is expressed by the following formula:

[0064] ΔQ=Q ac -Q dc

[0065] Based on the above formula, it can be understood that this difference ΔQ represents the net exchange of reactive power between the AC system and the DC system. If ΔQ > 0, it means that the AC system provides excess reactive power to the DC system; if ΔQ < 0, it means that the DC system needs additional reactive power, which may be provided by the AC system or other reactive power compensation equipment; if ΔQ = 0, it means that the reactive power between the two systems is balanced.

[0066] S2. Determine the reference value corresponding to the AC / DC system in the state of zero reactive power exchange, and correct the reactive power exchange value with the reference value to obtain the reactive power exchange difference.

[0067] Zero reactive power exchange refers to a state where reactive power is completely balanced between the AC and DC systems, meaning there is no net exchange of reactive power. This state is typically closely related to stable grid operation, power factor correction, and reactive power compensation measures. In this state, ΔQ should equal 0.

[0068] However, in practical systems, perfect reactive power balance may be difficult to achieve due to various factors (such as equipment losses and control errors). Therefore, in this embodiment of the invention, it may be necessary to define a threshold value that is "close to zero" as a reference value, such as ΔQ. ref = ±∈, where ∈ is a very small positive number.

[0069] In this embodiment, it is assumed that the conditions under the completely zero-junction state can be accurately determined or simulated, and ΔQ is set accordingly. ref =0.

[0070] The reactive power exchange difference ΔQ can then be calculated using simple subtraction. f It actually represents the "difference" from the zero-state deviation, expressed by the following formula:

[0071] ΔQ f =ΔQ - ΔQ ref

[0072] Due to ΔQ ref =0, therefore:

[0073] ΔQ f =ΔQ

[0074] But the key here is understanding the concepts of correction and difference. In practical applications, if ΔQ ref If it is not 0 (i.e., the tolerance of the zero state is considered), then ΔQ f This will reflect the deviation between the actual exchange value and the ideal junction zero state.

[0075] S3-S4: Process the reactive power exchange difference and send the instruction value corresponding to the processed shutdown angle to the sending end of the converter station; adjust the firing angle of the sending end of the converter station based on the instruction value.

[0076] Specifically, it is understood that during the commutation process of a high-voltage direct current (HVDC) converter, the turn-off angle is the time from the moment when the positive current of the controllable valve decreases to zero to the positive zero-crossing point of the ideal sinusoidal commutation voltage applied to the valve, which directly affects the reactive power consumption of the converter.

[0077] The firing angle refers to the angle corresponding to the time interval from a fixed reference point (usually the voltage zero-crossing point or peak point) of the AC side voltage of the converter station to the time when the thyristor is triggered to conduct. It is a key parameter for controlling the converter to absorb power from the AC system or inject power into the AC system. Therefore, by adjusting the firing angle, the DC current, DC voltage and reactive power absorbed or injected by the converter can be controlled.

[0078] First, the reactive power exchange difference is used as an input signal to a proportional-integral converter for signal processing, and an adjustment command for the turn-off angle is output; in response to the adjustment command, the turn-off angle of the converter station is adjusted.

[0079] In this embodiment of the invention, the reactive power exchange difference needs to be processed. This processing may include filtering (i.e., noise removal), integration (accumulating the deviation for control), proportional-integral (PI) control, or other more complex control algorithms to generate a control signal. In this embodiment, the reactive power exchange difference can be sent as an input signal to a PI controller, which consists of a proportional part and an integral part, used to process the input signal and generate a control signal.

[0080] After receiving a new firing angle command value at the sending end of the converter station, the control system will adjust the firing angle of the converter to match this command value.

[0081] Secondly, based on the adjustment of the turn-off angle, the DC voltage of the DC system is corrected, and a corrected DC voltage adjustment command is output; in response to the DC voltage adjustment command, the firing angle of the sending end of the converter station is adjusted.

[0082] Specifically, by adjusting the turn-off angle, the DC voltage is further affected. Since the ultimate goal of this embodiment is to achieve "zero reactive power", when the DC voltage is affected and changed, it will further cause the trigger angle of the converter station to change synchronously, thereby realizing the adjustment of the reactive power at the sending end.

[0083] In this embodiment, the above-mentioned adjustment and control process is actually a process of continuously monitoring the DC voltage, calculating the deviation, generating adjustment commands, adjusting the firing angle, and correcting the DC voltage to achieve a balance in the reactive power exchange of the AC / DC system.

[0084] S5. Construct a piecewise function based on the DC power transmitted by the DC system, and use the piecewise function to restrict the turn-off angle and the firing angle to obtain the restriction conditions.

[0085] For specific reactive power requirements, taking increased power output as an example, when the DC power is relatively low, to increase the reactive power consumption of the converter station, it is necessary to significantly increase the firing angle of the converter and reduce the reactive power injected into the AC system to maintain reactive power balance and ensure the stable operation of the AC system. As the DC transmission power increases, the angle increased by the converter to consume the same amount of reactive power is less than the angle increased by the converter when the power is low. Based on this, angle limit values ​​for each power point can be designed.

[0086] The angle limit value at each power point is related to the parameters of a single AC filter. The larger the capacity of the single AC filter, the higher the angle limit value at each power point.

[0087] To maintain reactive power balance and stable operation of the AC system, especially when DC power changes, it is necessary to reasonably adjust the firing angle or shutdown angle of the converter. The following is a detailed process for establishing a piecewise function based on the angle constraints of each power point:

[0088] First, monitor the fluctuation of the DC power of the converter station in real time to obtain the first adjustment range of the DC power;

[0089] This embodiment uses a real-time monitoring system to track the DC power (P) of the converter station. d The fluctuations in DC power are analyzed, and their range or trend is calculated. Based on this data, the first adjustment range of DC power can be determined, that is, the range in which DC power may vary.

[0090] Then, with the reactive power exchange junction at zero as the target, the switching angle and the triggering angle are adjusted to obtain the second adjustment range of the converter station's angle;

[0091] To maintain the reactive power balance of an AC system, it is necessary to ensure that the converter station does not generate or absorb excessive reactive power during operation. This is typically achieved by adjusting the converter's firing angle (α) and shut-off angle (γ). When the reactive power exchange junction is zero, the converter neither generates nor absorbs reactive power, which is an ideal operating state.

[0092] To find this state, a series of experiments or calculations are needed to determine the optimal combination of firing and turning-off angles for a given DC power. In this process, it can be found that for different DC power values, the turning-off angle needs to be adjusted to a specific range to maintain reactive power balance.

[0093] Finally, based on the first adjustment range and the second adjustment range, a piecewise function is constructed; the piecewise function is represented by the following formula:

[0094] γ=f(P d )

[0095] Where γ is the shut-off angle, P d For DC power, P d = 0.1~1.0PdN, with a step size of 0.1PdN.

[0096] S6. Filter switching is determined according to the aforementioned constraints in order to control reactive power balance.

[0097] This embodiment sets two principles for filter switching: 1. The angle reaches the upper or lower limit; 2. The sum of reactive power exchange in the AC / DC systems of the sending and receiving converter stations reaches the target value, thus satisfying both conditions for filter switching.

[0098] Specifically, based on the aforementioned constraints, the upper and lower limits of the angles of the shutdown angle and the trigger angle are obtained;

[0099] With the goal of achieving zero reactive power exchange, a first reactive power exchange control value corresponding to the upper limit value and a second reactive power exchange control value corresponding to the lower limit value are set respectively.

[0100] The switching of the filter is determined by using the first reactive power exchange control value and the second reactive power exchange control value.

[0101] Furthermore, according to the upper limit value, when the AC / DC system of the converter station reaches the preset first reactive power exchange target value, the filter is disconnected;

[0102] According to the lower limit value, when the AC / DC system of the converter station reaches the preset second reactive power exchange target value, the filter is put into operation.

[0103] When the constant reactive power control strategy fails to achieve the zero-junction target of the AC / DC system, i.e., the angle limit is reached, the reactive power exchange value begins to accumulate. When increasing power, the angle reaches its lower limit. The reactive power exchange control target of the AC / DC system is Q. acf +Q aciWhen the angle is -K, the filter is activated to reduce the reactive power exchange value after angle limitation; when reducing power, the angle reaches its upper limit, and the reactive power exchange of the AC / DC system reaches its control target of Q. acf +Q aci When the value is K, the filter is removed to reduce the reactive power exchange value after the angle is limited.

[0104] In summary, this invention provides a method to effectively reduce the reactive power exchange between the sending and receiving end converter stations and the AC system, ensuring the stable operation of the AC system. It constructs a piecewise function with preset angles under a constant reactive power control strategy to adjust the turn-off angle to achieve zero reactive power at the receiving end of the converter station, further influencing the DC voltage to synchronously adjust the sending end trigger angle, thereby adjusting the sending end reactive power and reducing the reactive power exchange value between the sending and receiving ends. Furthermore, it proposes switching conditions for AC filters under a constant reactive power control strategy to reduce the reactive power exchange value after angle limitation, controlling the reactive power balance of the AC and DC systems.

[0105] The above solution will be described in detail below with a specific implementation case:

[0106] Taking the Fujian-Guangdong DC transmission project as an example, the design results of the project will be explained.

[0107] The Fujian-Guangdong DC transmission project has a DC transmission capacity of 2×1000MW and a DC voltage of ±100kV. The Fujian side filter configuration is 2×HAPF (140MVA) + 7×SC (150MVA), while the Guangdong side passive filter configuration is 3×BP1113 (140MVA) + 3×HP2436 (140MVA) + 2×HP3 (140MVA) + 1×SC (150MVA). The sending end is equipped with 3 sets of 60Mvar impedance. The rated voltage of the converter buses on both the rectifier and inverter sides is 525kV, with a voltage range of [500, 550]kV.

[0108] For conventional DC projects, constant current control is typically used on the rectifier side at the sending end, while constant turn-off angle control is used on the inverter side at the receiving end. The tap changer at the sending end is controlled within the angle range of [12.5, 17.5] degrees, and adjusted by one level if the angle exceeds this range. The receiving end typically uses a constant Udi0 control strategy. For back-to-back projects, constant power control is typically used for rectification, while other controls remain unchanged. Specifically, the main circuit parameters under this strategy are shown in Table 1. The reactive power exchange difference between the AC and DC systems is consistently 120 Mvar (0.8 × 150 = 120 Mvar).

[0109] Table 1. Main circuit characteristics under Udi0 control.

[0110] Power(pu) Pd Id UdR Udi Udi0R Udi0I Angle Gamma TCR TRI 0.1 100 0.46 109.69 109.60 114.73 115.30 15.00 17.00 0.4 0.0 0.2 200 0.92 108.91 108.72 114.89 115.30 15.00 17.00 0.3 0.0 0.3 300 1.39 108.11 107.83 115.05 115.30 15.00 17.00 0.2 0.0 0.4 400 1.87 107.30 106.93 115.22 115.30 15.00 17.00 0.0 0.0 0.5 500 2.36 106.47 106.00 115.39 115.30 15.00 17.00 -0.1 0.0 0.6 600 2.86 105.63 105.06 115.56 115.30 15.00 17.00 -0.2 0.0 0.7 700 3.36 104.78 104.10 115.74 115.30 15.00 17.00 -0.3 0.0 0.8 800 3.88 103.90 103.13 115.92 115.30 15.00 17.00 -0.4 0.0 0.9 900 4.41 103.01 102.13 116.11 115.30 15.00 17.00 -0.6 0.0 1 1000 4.95 102.10 101.11 116.30 115.30 15.00 17.00 -0.7 0.0 1.1 1100 5.50 101.17 100.07 116.30 115.30 14.64 17.00 -0.7 0.0

[0111] This embodiment proposes a reactive power control strategy for the aforementioned Fujian-Guangdong DC transmission project:

[0112] First, establish a control block diagram with the reactive power exchange of the AC / DC system as the target. Please refer to [reference needed] for details. Figure 2 , Figure 2 This is a control block diagram of reactive power control measurement in one embodiment of the present invention.

[0113] The constant reactive power control strategy is adopted, and its control objective is the reactive power exchange between the AC and DC systems, that is, the difference Q between the reactive power provided by the filter at the receiving end and the reactive power consumed by the DC system. i To control the target value, zero is used as a reference value. The difference between the two values ​​is calculated and fed into the PI controller, which outputs the turn-off angle command value. The turn-off angle command value further affects the DC voltage, thus influencing the sending-end angle.

[0114] Depend on Figure 2 It can be seen that the final output value of the shut-off angle command is directly related to the angle limit at each power point.

[0115] Secondly, a piecewise function for the angle constraints of each power point will be established for the above strategy. The specific construction process is as follows:

[0116] The first step is to adopt the above-mentioned constant reactive power control strategy, with both the sending and receiving ends using the constant Udi0 control mode. The specific requirements are as follows:

[0117] 1) The rectifier-side Udio remains constant;

[0118] 2) Udi0 on the inverter side remains constant;

[0119] 3) The DC current is controlled by the firing angle α of the rectifier.

[0120] By increasing the turn-off angle γ, the DC voltage is reduced, thereby controlling reactive power.

[0121] The angle limit value α / γ is:

[0122] Power / pu Sending and receiving end angle limitations 0-0.3 17°～53° 0.3 and above 17°～25°

[0123] The converter's angle range is as follows: 0.1–0.3 pu, α / γ range (17°–53°); 0.3–1 pu, α / γ range (17°–25°). The upper limit of α / γ is a linear change with active power: 53° for 0.1 pu, 25° for 0.3 pu, and 23.5° for 1 pu.

[0124] The angle control piecewise function is as follows:

[0125]

[0126] It is worth noting that this piecewise function is only applicable to the current project. Different projects should take into account the corresponding transmission power, reactive power configuration, and converter valve capacity.

[0127] Next, in practical applications, the reactive power dead zone of a conventional UHV converter station AC filter is approximately 0.8 times the capacity of a single AC filter group. Therefore, the reactive power exchange with the AC / DC system is controlled at 0.8 × Q. c (Capacity of a single capacitor bank)

[0128] When the constant reactive power control strategy fails to achieve the zero-load target of the AC / DC system, it means that the angle limit has been reached, and from this point onwards, the reactive power exchange value begins to accumulate. This strategy can be applied to single-sided converter stations or both-sided converter stations simultaneously.

[0129] When applied to a single-sided converter station, the voltage control target value on the other side may change due to the large increase in the angle between the stations, which in turn leads to a large adjustment of the tap changer. To avoid this situation, it is recommended to apply it to both sides simultaneously.

[0130] Applied to dual-sided converter stations, when increasing power, the angle reaches its lower limit. The reactive power exchange control target of the AC / DC system is set as Q. r +Q i When the value is -K, the AC filter is activated; when the power is reduced, the angle reaches its upper limit, and the reactive power exchange of the AC / DC system is set to achieve its control target of Q. r +Q i When the value is K, the AC filter is turned off.

[0131] This strategy can effectively reduce reactive power exchange between the DC and AC systems at the sending and receiving ends. If the reactive power exchange at the sending end Q... r Reactive power exchange at the receiving end Q i Using the sum as the target value may result in a situation where the sending end experiences positive reactive power exchange, the receiving end experiences negative reactive power exchange, and the sum equals zero. To avoid such a situation, the value of K should be a small but specific value, usually less than 20% of the group capacity, in order to minimize the reactive power exchange of the AC / DC system as much as possible.

[0132] Based on this principle, taking a converter unit in the Fujian-Guangdong power transmission project as an example, two sets of filters are started during unlocking, and both the sending and receiving ends have AC system parameters of 500kV / 525kV / 550kV main circuit. K < 0.2 * 140 = 28Mvar, so we take 20Mvar. Power increase process: Q r +Q i =-20, the shut-off angle reaches 17 degrees, and one set of ACF is put into both sides at the same time.

[0133] Specifically, the calculation results of the main loop parameters and the filter switching results are shown in Tables 2 to 4. Based on the data in the tables above, Q... r and Q i The reactive power exchange is 48.61 Mvar and 42.77 Mvar, both less than 120 Mvar. When the voltages on both sides are close, the maximum reactive power exchange is about 20 Mvar, which greatly reduces the reactive power value between AC and DC systems.

[0134] Table 2 shows the control main circuit parameters of a converter unit under a constant reactive power strategy, with 525kV transmission and receiving ends.

[0135]

[0136] Table 3 shows the control main circuit parameters of a converter unit under a constant reactive power strategy, with 500kV transmission and receiving ends.

[0137]

[0138]

[0139] Table 4 shows the control main circuit parameters of a converter unit under a constant reactive power strategy, with 550kV transmission and receiving ends.

[0140]

[0141] Analysis shows that during unbalanced operation of the AC systems at both ends (one at its highest and the other at its lowest), the power increase process is as follows: Q r +Q i = -20, the turn-off angle reaches 17 degrees, and one set of ACF is simultaneously put into operation on both sides. The calculation results of the main circuit parameters and the filter switching results are shown in Table 5.

[0142] Table 5 shows the control main circuit parameters of a converter unit under a constant reactive power strategy, with a sending end voltage of 500kV and a receiving end voltage of 550kV.

[0143]

[0144]

[0145] Furthermore, it is worth noting that the essential purpose of applying the constant reactive power control strategy is to reduce reactive power exchange between the converter station and the system. Therefore, in this embodiment of the invention, it is also considered that the above strategy should be exited under certain circumstances, specifically:

[0146] If a sudden change occurs in the AC systems at both ends, such as a sudden change from 500kV to 550kV on one side and a sudden change from 550kV to 500kV on the other side, the reactive power compensation direction on both sides will change synchronously, and the strategy must be abandoned.

[0147] The voltage operation of the AC system at both ends always maintains a large error. In severe cases, such as the sending end always operating at 550kV and the receiving end always operating at 500kV, the reactive power difference is proportional to the number of filter groups put into operation.

[0148] Based on the current single-group capacity, HP1224 has a group capacity of 140Mvar, and SC has a group capacity of 150Mvar.

[0149] The AC system voltage is [500, 550] kV, the capacity of the HP1224 group varies from [127, 154], and ΔQ = 27 Mvar.

[0150] The AC system voltage is [500, 550] kV, the SC group capacity varies from [136, 165], and ΔQ = 29 Mvar.

[0151] This strategy can be applied before three filters are put into operation under extreme voltage conditions. After four filters are put into operation, this strategy can be smoothly phased out.

[0152] Taking a 550kV sending end and a 500kV receiving end as an example, as shown in Table 6, the main circuit parameter table for the two converter units, although it can reduce Q... r +Q i While the reactive power exchange is kept within the required range, the reactive power exchange on one side reaches as high as 170 Mvar at high power levels. This is mainly due to the significant fundamental error of the reactive power compensation device caused by different AC system voltages. The difference when the 9th filter group is activated is 1459.68 - 1206.35 = 253 Mvar. Under such extreme voltage conditions, this strategy can be applied up to the point where 3 filter groups are activated. After 4 filter groups are activated, this strategy can be smoothly phased out.

[0153] Table 6 shows the control main circuit parameters of a converter unit under a constant reactive power strategy, with a sending end voltage of 500kV and a receiving end voltage of 550kV.

[0154]

[0155]

[0156] In this embodiment, a platform for the Fujian-Guangdong project can be built on RTDS to conduct research on reactive power switching and main circuit characteristics under a constant reactive power control strategy. The specific implementation process includes the following steps:

[0157] 1) Test conditions: Both sides are controlled by fixed Udi0, rectifier side 525kV, inverter side 525kV, automatic control. Filter capacity 140Mvar, automatic reactive power control, Qpc reactive power control function is enabled, Qpc and filter control are controlled by zeroing the sum of reactive power exchange on both sides, power increase.

[0158] Control strategy: At the unlocking moment, two sets of passive filters and two sets of low reactance are activated on both sides. As the power increases, when the angle reaches 17 degrees, Q... r +Q i When the power is -20 Mvar, with one passive filter group in operation, as the power increases, after the fourth ACF group is in operation and the angle reaches 17 degrees, Q... r +Q i When the reactive power exchange rate reaches 20 Mvar, the two low-resistance groups are gradually phased out. Specific examples are shown in Table 7, demonstrating that the reactive power exchange rate changes from ±120 Mvar to within ±5 Mvar.

[0159] power 1002 926 899 799 750 702 671 600 500 398 299 201 100 DC current 4786.2 4415 4292.3 3933 3627 3447.7 3099.3 2793.8 2434 1792 1411 1073.7 784.5 DC voltage 209.4 210.1 209.5 203.5 206.9 203.5 216.5 215.3 205.9 222 212.2 187.6 126.2 Number of filters 2 2 2 2 3 3 3 4 4 4 4 4 4 Resistance quantity 2 2 2 2 2 2 2 2 2 2 1 0 0 Reactive power exchange quantity R / Mvar 2 0 3 5 0 4 0 -4 -4 -1 0 0 0 AC voltage R / kV 524.6 523.8 522.9 522.5 521.4 521.4 520.4 519.4 519.4 518.4 518 516.8 516.8 Trigger angle R / o 54.8 36.1 23.9 15.5 29.5 25 19.2 35.2 24.6 19.2 19.1 17.6 16.6 gear R 14 14 14 14 14 14 15 15 15 15 15 15 15 Udi0R / kV 121.3 121.1 120.9 120.9 120.7 120.7 121.8 121.7 121.7 121.4 121.2 121.1 121.1 Reactive power exchange quantity I -2 0 -3 -5 0 -3 0 4 4 1 0 0 0 AC voltage I / Mvar 525.7 526.2 526.4 526.4 526.5 526.5 527.1 527.1 527.1 527.1 527.4 526.3 526.3 Extinguishing angle I / o 57.4 37.2 25.8 17.8 30.8 26.9 20.3 26.3 25.7 20.8 20.7 19.7 18.8 Gear I 14 13 13 13 13 13 13 13 13 13 13 13 13 Udi0_I / Mvar 121.5 120.1 120.1 120.1 120.1 120.1 120.2 120.3 120.3 120.3 120.3 120.1 120.1

[0160] Table 7 shows the switching of the boost filter and reactive power exchange under a converter unit control system under a constant reactive power strategy.

[0161] 2) Test conditions: Both sides are controlled by fixed Udi0, rectifier side 540kV, inverter side 510kV, automatic control. Filter capacity 140Mvar, automatic reactive power control, Qpc reactive power control function is enabled, Qpc and filter control are controlled by zeroing the sum of reactive power exchange on both sides, power increase.

[0162] Control strategy: At the unlocking moment, two sets of passive filters and two sets of low reactance are activated on both sides. As the power increases, when the angle reaches 17 degrees, Q... r +Q i When the power is -20 Mvar, with one passive filter group in operation, as the power increases, after the fourth ACF group is in operation and the angle reaches 17 degrees, Q... r +Q i When the reactive power exchange rate is -20 Mvar, the two low-resistance groups are gradually phased out. Specific examples are shown in Table 8, demonstrating that the reactive power exchange rate changes from ±120 Mvar to within ±5 Mvar.

[0163] Table 8 shows the switching of the power reduction filter and reactive power exchange in a converter unit under a constant reactive power strategy.

[0164]

[0165] 3) Test conditions: Initial voltage at the sending end is 540kV, initial voltage at the receiving end is 510kV, filter capacity is 140Mvar, after switching the fifth group of filters, the low reactance is switched on, and the power is reduced according to the sum of reactive power on both sides.

[0166] Control strategy: Under 1.0 PU, with no low-voltage input, DC power decreases, and the angle gradually increases. When the upper limit of the angle is reached, Q... r +Q i=20Mvar, one filter group is removed. As the power continues to decrease, after the fifth filter group is removed, as the angle gradually increases, when the upper limit of the angle is reached, Q r +Q i =20Mvar, two groups of low-resistance reactors were put into operation successively. The Qpc function increases the upper limit setting of the gamma angle: from 1000MW to 100MW, it is set to 5, 5, 10, 10, 10, 10, 15, 20, 20, 25, 25. Specific examples are shown in Table 9. It can be seen that the reactive power exchange has changed from ±120 to within ±40Mvar.

[0167] Table 9 shows the switching of the power reduction filter and reactive power exchange of a converter unit under a constant reactive power strategy at different AC voltages at the sending and receiving ends.

[0168] power 989 941 900 865 801 702 665 601 500 404 300 100 DC current 4720 4431 4273 4017 3778.3 3427.7 3023.7 2775 2405 1811 1413.9 785.2 DC voltage 209.7 212.4 210.6 215.5 212 204.7 219.6 216.7 208 222.9 212 127.7 Number of filters 4 4 4 4 4 4 3 3 3 2 2 2 Resistance quantity 0 1 1 2 2 2 2 2 2 2 2 2 Reactive power exchange quantity R 37 34 33 31 29 26 25 21 18 18 15 11 AC voltage R 533 533.6 533.7 534.2 534.5 535.6 535.4 535.4 536.6 538.5 537.9 540 Trigger angle R 17.2 15.8 18 15.6 19.1 24.4 14.9 18.9 25.5 14.5 23.6 55 gear R 13 13 13 13 13 13 13 13 13 12 12 12 Udi0_R 121.6 121.8 121.8 121.9 122 122.2 122.2 122.2 122.5 121.2 121.2 121.6 Reactive power exchange quantity I -37 -34 -33 -31 -29 -26 -25 -21 -18 -19 -16 -10 AC voltage I 508.6 509.1 509.1 509.5 509.9 510.3 510.5 510.5 510.8 510.4 510.7 510.1 Extinguishing angle I 19.3 18 19.9 17.8 20.9 35.7 17.2 20.7 26.5 18.1 26.1 57.4 Gear I 16 16 16 16 16 16 16 16 16 16 16 16 Udi0_I 120.8 120.9 120.9 120.9 121.1 121.2 121.3 121.3 121.3 121.2 121.3 121.1

[0169] In summary, by adopting the constant reactive power strategy, the reactive power exchange in the AC / DC system is reduced from 120 Mvar to 5 Mvar. Under extreme AC voltage conditions, the reactive power exchange can also be controlled within 40 Mvar, which greatly reduces the reactive power exchange between the system and the AC system.

[0170] One embodiment of the present invention provides a reactive power control system for an AC / DC system in a converter station. For details, please refer to [link to relevant documentation]. Figure 3 , Figure 3 The diagram shown is a block diagram of the reactive power control system of the AC / DC system of the converter station in one embodiment of the present invention.

[0171] Data acquisition module M1 is used to acquire the reactive power exchange value of the AC / DC system at the receiving end of the converter station;

[0172] Data processing module M2 is used to determine the reference value corresponding to the AC / DC system in the reactive power exchange junction zero state, and to correct the reactive power exchange value with the reference value to obtain the reactive power exchange difference.

[0173] The instruction sending module M3 is used to process the reactive power exchange difference and send the instruction value corresponding to the processed turn-off angle to the sending end of the converter station.

[0174] Angle adjustment module M4 is used to adjust the firing angle of the sending end of the converter station based on the instruction value;

[0175] Angle limiting module M5 is used to construct a piecewise function based on the DC power transmitted by the DC system, and to limit the turn-off angle and the trigger angle using the piecewise function to obtain the limiting conditions;

[0176] The filter switching module M6 is used to determine the switching of the filter according to the aforementioned constraints in order to control the reactive power balance.

[0177] like Figure 4 As shown, this embodiment of the invention also provides a computer device. Figure 4 This is a structural block diagram of a preferred embodiment of a computer device provided by the present invention. The computer device includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the reactive power control method of the AC / DC system of the converter station as described above.

[0178] Preferably, the computer program can be divided into one or more modules / units (such as computer program 1, computer program 2, ...), and the one or more modules / units are stored in the memory and executed by the processor to complete the present invention. The one or more modules / units can be a series of computer program instruction segments capable of performing specific functions, and the instruction segments are used to describe the execution process of the computer program in the computer device.

[0179] The processor can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor, or the processor can be any conventional processor. The processor is the control center of the terminal device, connecting various parts of the terminal device through various interfaces and lines.

[0180] The memory mainly includes a program storage area and a data storage area. The program storage area can store the operating system, applications required for at least one function, etc., while the data storage area can store related data, etc. Furthermore, the memory can be a high-speed random access memory, or a non-volatile memory, such as a plug-in hard drive, a SmartMedia Card (SMC), a Secure Digital (SD) card, and a Flash Card, or other volatile solid-state storage devices.

[0181] It should be noted that the aforementioned terminal devices may include, but are not limited to, processors and memory, as will be understood by those skilled in the art. Figure 4The structural block diagram is merely an example of a terminal device and does not constitute a limitation on the terminal device. It may include more or fewer components than shown, or combine certain components, or use different components. Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium may be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc.

[0182] Accordingly, embodiments of the present invention provide a computer-readable storage medium, the computer-readable storage medium including a stored computer program, wherein, when the computer program is executed, it controls the device where the computer-readable storage medium is located to perform steps in the reactive power control method of the converter station AC / DC system as described in the above embodiments, for example... Figure 1 Steps S1 to S6 as described above.

[0183] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A reactive power control method for an AC / DC system in a converter station, characterized in that, include: Obtain the reactive power exchange value of the AC / DC system at the receiving end of the converter station; Determine the reference value corresponding to the AC / DC system in the reactive power exchange junction zero state, and use the reference value to correct the reactive power exchange value to obtain the reactive power exchange difference; The reactive power exchange difference is processed, and the instruction value corresponding to the processed shutdown angle is sent to the sending end of the converter station. The firing angle of the sending end of the converter station is adjusted based on the instruction value; A piecewise function is constructed based on the DC power transmitted by the DC system, and the cut-off angle and the firing angle are constrained by the piecewise function to obtain the constraint conditions; The switching of the filter is determined based on the aforementioned constraints in order to control the reactive power balance.

2. The reactive power control method for AC / DC systems in converter stations as described in claim 1, characterized in that, The acquisition of reactive power exchange values ​​of the AC / DC system at the receiving end of the converter station includes: Obtain the first reactive power provided by the AC system and the second reactive power consumed by the DC system; The difference between the first reactive power and the second reactive power is calculated to obtain the reactive power exchange value.

3. The reactive power control method for AC / DC systems in converter stations as described in claim 1, characterized in that, The step of processing the reactive power exchange difference and sending the command value corresponding to the processed shut-off angle to the sending end of the converter station includes: The reactive power exchange difference is used as an input signal to a proportional-integral converter for signal processing, and an adjustment command for the turn-off angle is output. In response to the adjustment command, the shut-off angle of the converter station is adjusted.

4. The reactive power control method for AC / DC systems in converter stations as described in claim 3, characterized in that, The adjustment of the firing angle of the sending end of the converter station based on the instruction value includes: Based on the adjustment process of the shut-off angle, the DC voltage of the DC system is corrected, and the corrected DC voltage adjustment command is output. In response to the DC voltage regulation command, the firing angle of the sending end of the converter station is adjusted.

5. The reactive power control method for AC / DC systems in converter stations as described in claim 3, characterized in that, The step of constructing a piecewise function based on the DC power transmitted by the DC system includes: The fluctuation of the DC power of the converter station is monitored in real time to obtain the first adjustment range of the DC power; With the reactive power exchange junction at zero as the target, the switching angle and the triggering angle are adjusted to obtain the second adjustment range of the converter station's angle; Based on the first adjustment range and the second adjustment range, a piecewise function is constructed; the piecewise function is represented by the following formula: γ=f(P d ) Where γ is the shut-off angle, P d This is DC power.

6. The reactive power control method for AC / DC systems in converter stations as described in claim 1, characterized in that, The step of determining the switching of the filter based on the aforementioned constraints to control reactive power balance includes: Based on the aforementioned constraints, obtain the upper and lower limits of the angles of the shutdown angle and the trigger angle; With the goal of achieving zero reactive power exchange, a first reactive power exchange control value corresponding to the upper limit value and a second reactive power exchange control value corresponding to the lower limit value are set respectively. The switching of the filter is determined by using the first reactive power exchange control value and the second reactive power exchange control value.

7. The reactive power control method for AC / DC systems in converter stations as described in claim 6, characterized in that, Also includes: According to the upper limit value, when the AC / DC system of the converter station reaches the preset first reactive power exchange target value, the filter is disconnected; According to the lower limit value, when the AC / DC system of the converter station reaches the preset second reactive power exchange target value, the filter is activated.

8. A converter station AC / DC reactive power control system, characterized in that, include: The data acquisition module is used to acquire the reactive power exchange value of the AC / DC system at the receiving end of the converter station; The data processing module is used to determine the reference value corresponding to the AC / DC system in the reactive power exchange junction zero state, and to correct the reactive power exchange value with the reference value to obtain the reactive power exchange difference. The instruction sending module is used to process the reactive power exchange difference and send the instruction value corresponding to the processed shutdown angle to the sending end of the converter station. An angle adjustment module is used to adjust the firing angle of the sending end of the converter station based on the instruction value; An angle limiting module is used to construct a piecewise function based on the DC power transmitted by the DC system, and to limit the turn-off angle and the trigger angle using the piecewise function to obtain the limiting conditions; The filter switching module is used to determine the switching of the filter according to the aforementioned constraints in order to control the reactive power balance.

9. A computer device, characterized in that, The system includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein the processor, when executing the computer program, implements the reactive power control method for AC / DC systems of converter stations as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, wherein when the device containing the computer-readable storage medium executes the computer program, it implements the reactive power control method for AC / DC systems of converter stations as described in any one of claims 1 to 7.

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