Wind power plant staged reactive power coordination control method for coordinating SVG and distributed phase modifier

Abstract

The invention discloses a wind power plant staged reactive power coordination control method for coordinating an SVG and a distributed phase modifier, and belongs to the field of electric power regulation and control. Firstly, reactive power compensation characteristics of the distributed phase modifier, the SVG and a wind power plant are analyzed, characteristic differences are considered, and a transient voltage support strategy for heterogeneous reactive power resource coordination is provided; the active power output of the wind power plant during the fault period can be improved while the reactive power supporting capability of the system is enhanced. A wind-thermal bundled conventional high-voltage direct-current delivery system is established in the PSCAD / EMTDC, and the effectiveness of the proposed control scheme is verified by simulation results under near-area alternating-current short circuit and direct-current locking.

Description

Technical Field

[0001] This invention relates to the field of power regulation, specifically to a method for phased reactive power coordination control of wind farms that coordinates SVG and distributed synchronous condensers. Background Technology

[0002] Wind power-rich areas are often distributed in the opposite direction to load centers, requiring long-distance transmission and consumption via ultra-high-voltage AC / DC channels, resulting in a high proportion of wind power connected to weak power grids. In this scenario, due to the weak voltage support capabilities of both wind farms and the power grid, severe transient under / overvoltages will occur at the wind power grid connection point in the event of a near-field short circuit or DC blocking, potentially triggering a chain reaction of wind turbine disconnection. Related accident cases have been reported both domestically and internationally, seriously threatening the reliable transmission of wind power and the safe and stable operation of the power grid.

[0003] Optimizing the control strategy of wind farms is one feasible solution to improve system voltage response under AC / DC faults. Existing technologies treat wind farm voltage support as a constrained optimization problem, using intelligent algorithms to obtain control commands with multiple objectives, such as maximizing voltage support and improving imbalance. A scheme based on a linearized wind turbine model has been proposed to improve the stability of the voltage support strategy by adding cross-decoupling terms to the control loop. However, due to the limited capacity of wind farms, there is still a risk of voltage exceeding limits under severe faults. Therefore, this scheme is usually used as an auxiliary measure in conjunction with other measures to support voltage.

[0004] Configuring distributed synchronous condensers or static var generators (SVG) at wind farm junctions is a more effective measure to improve the system's transient voltage support capability. Existing technologies consider the differences in response characteristics between SVG and wind turbines, proposing a coordinated strategy where SVG first provides partial rapid reactive power support, followed by the wind turbine providing the main reactive power output. Other voltage control strategies have been proposed for coordinating direct-drive and doubly-fed induction generator (DFIG) turbines with SVG. These strategies prioritize SVG reactive power support, switching the wind turbine to reactive power support mode only when the grid connection voltage exceeds a preset threshold, primarily utilizing the wind turbine for reactive power. Although SVG offers fast response and flexible control, its reliance on power electronic converters limits its transient support performance under fault conditions.

[0005] Distributed synchronous condensers (SCMs), as synchronous rotating components, possess excellent instantaneous dynamic reactive power response characteristics and short-circuit capacity support capabilities. Existing technologies have analyzed the impact of SCM connection on the short-circuit ratio of wind farms and proposed SCM configuration methods that simultaneously consider short-circuit ratio improvement and transient overvoltage suppression. Existing technologies have effectively suppressed transient overvoltage problems by configuring distributed SCMs at wind turbine terminals with low short-circuit ratios. Furthermore, existing technologies use particle swarm optimization to search for optimal configuration schemes of distributed SCMs, which can suppress transient overvoltage levels under multi-fault scenarios. However, the support capability of distributed SCMs is affected by the excitation control system, exhibiting two stages with different response speeds; improper control may actually exacerbate the severity of overvoltage.

[0006] Therefore, for wind farms equipped with both distributed synchronous condensers and SVG, considering the differences in the response characteristics of each reactive power compensation device, in order to avoid the potential risk of weakening the voltage support effect due to control action offsetting and to suppress the transient voltage disturbance level of the system under severe faults, it is necessary to analyze the reactive power compensation characteristics of each device and design a heterogeneous reactive power resource coordination voltage support control strategy that adapts to the reactive power demand of transient processes. Summary of the Invention

[0007] To address the aforementioned shortcomings in the existing technology, this invention provides a phased reactive power coordination control method for wind farms that coordinates SVG and distributed synchronous condensers.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for phased reactive power coordination control of wind farms that coordinates SVG and distributed synchronous condensers includes the following steps: S1. Real-time monitoring of wind farm grid connection point voltage, DC converter bus voltage and system power parameters, and calculation of total reactive power deficit after a fault. S2. Based on the reactive resource response characteristics, the post-fault transient process is divided into the spontaneous response stage of the synchronous condenser, the coordinated support stage between the synchronous condenser and the SVG, and the reactive power participation stage of the wind farm. S3. During the spontaneous response phase of the synchronous condenser, the instantaneous spontaneous reactive power characteristics of the synchronous condenser are used first to support voltage, and reactive power instructions for subsequent phases are pre-allocated. S4. During the coordinated support phase of the synchronous condenser and SVG, the reactive power deficit is allocated according to the principle of prioritizing the synchronous condenser and supplementing the SVG. The precise control of the reactive power of the synchronous condenser is achieved through dual-loop control. S5. During the reactive power participation phase of the wind farm, reactive power commands for the wind turbine units are allocated according to the principle of equal power factor based on the remaining reactive power demand, and reactive power output is achieved through rotor current control. S6. Through three stages of reactive power coordination control, the synergistic optimization of transient voltage support and active power transmission capacity is achieved.

[0009] Furthermore, the formula for calculating the total reactive power deficit of the system after a fault in S1 is as follows:

[0010] In the formula, This represents the total reactive power deficit of the system. This refers to the DC transmission reactive power during periods of large disturbances. This refers to the active power transmitted via DC during periods of large disturbances. U To adjust the voltage on the 35 kV side of the step-up transformer for the camera, To match the reactive power generated by thermal power plants, Reactance for transmission lines connecting thermal power plants to high-voltage DC converter busbars.

[0011] Furthermore, the phase division in S2 is as follows: Phase 1 is the spontaneous response phase of the synchronous condenser from 0 to 10 ms after the fault; Phase 2 is the coordinated support phase of the synchronous condenser and SVG from 10 to 40 ms after the fault; and Phase 3 is the reactive power participation phase of the wind farm after 40 ms after the fault.

[0012] Furthermore, in the S3 phase, the reactive power output during the spontaneous response phase of the synchronous condenser is determined by the subtransient reactance, and its reactive power change is expressed as follows:

[0013] In the formula, Inject reactive power changes into the synchronous condenser before and after the disturbance. I d0 This refers to the direct-axis current component of the camera before the fault occurred. U To adjust the voltage on the 35 kV side of the step-up transformer of the synchronous condenser, Δ U This represents the change in direct-axis current before and after the fault. For adjusting the camera's subtransient reactance.

[0014] Furthermore, the coordination principle between the camera and the SVG in S4 is: when ΔQ≤Q sc_max The time adjustment is prioritized by the synchronous condenser when ΔQ > Q. sc_max The remaining portion is handled by SVG, where Q sc_max To adjust the camera's overload capacity limit; when ΔQ > Q sc_max +Q svg_max At that time, the wind farm participated in reactive power support, of which Q svg_max ΔQ represents the maximum reactive power output capability of the SVG, and ΔQ represents the total reactive power deficit of the system.

[0015] Furthermore, in S5, the reactive power command allocation for the wind farm adopts the equal power factor principle, and the reactive power command for a single wind turbine is expressed as follows:

[0016] In the formula, This is a reactive power command for a single wind turbine. For the total reactive power deficit of the system, These are the reactive power of the camera and the SVG, respectively. P DFIG_i For the first i Rated active power of the unit For the first k The rated active power of the generator set is n, where n is the total summation.

[0017] Furthermore, the SVG adopts a constant reactive power control mode, and the reactive power command is directly attached to the power outer loop to achieve a fast response.

[0018] Furthermore, the coordinated control strategy prioritizes suppressing transient overvoltages under DC blocking faults, and balances low-voltage support and post-fault overvoltage suppression under AC short-circuit faults.

[0019] The present invention has the following beneficial effects: Based on the priority order of reactive power support, this invention proposes a segmented reactive power allocation method after large disturbances. By designing a coordination controller and modifying the equipment control strategy, the invention enables each device to better execute the instructions issued by the coordination controller. The control strategy of this invention can effectively suppress transient overvoltage problems under DC blocking faults, improve the low voltage level during faults under AC faults, reduce the overvoltage level after faults, and ensure that the wind farm generates more active power to guarantee power supply. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the wind farm phased reactive power coordination control method for coordinating SVG and distributed synchronous condensers according to the present invention.

[0021] Figure 2 This is a topology diagram of a wind power DC transmission system according to an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram showing the comparison results of camera reactive power output and overload limit under near-field AC faults in an embodiment of the present invention.

[0023] Figure 4 This is a block diagram of the SVG control according to an embodiment of the present invention.

[0024] Figure 5 This is a timing diagram of reactive power control for each device after a large disturbance, according to an embodiment of the present invention.

[0025] Figure 6 This is a schematic diagram of the reactive power response of various devices after a power grid fault, according to an embodiment of the present invention.

[0026] Figure 7 This is a schematic diagram of the voltage coordination control architecture according to an embodiment of the present invention.

[0027] Figure 8 This is a schematic diagram of the DC blocking simulation results for various schemes in the embodiments of the present invention.

[0028] Figure 9 This is a schematic diagram of the simulation results of DC near-field AC short-circuit faults in various embodiments of the present invention. Detailed Implementation

[0029] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0030] A phased reactive power coordination control method for wind farms that coordinates SVG and distributed synchronous condensers, such as... Figure 1 As shown, it includes the following steps: S1. Real-time monitoring of wind farm grid connection point voltage, DC converter bus voltage and system power parameters, and calculation of total reactive power deficit after a fault. Considering that ultra-high voltage direct current (UHVDC) transmission is the main mode for large-scale wind power development and utilization in my country, and that transient voltage problems are more prominent in such systems than in AC transmission scenarios, this embodiment takes... Figure 2 The typical high-proportion wind power DC transmission system shown is used as an example for research.

[0031] The doubly-fed induction generator (DFIG) wind farm uses single-unit aggregated equivalent modeling and is connected to the 500 kV main grid via step-by-step voltage boosting; the SVG (Static Var Generator) and synchronous condenser are connected to the 35 kV collection bus within the wind farm; the supporting thermal power unit is connected to the 500 kV DC converter bus via voltage boosting. (See figure.) P , Q These represent active and reactive power, respectively. The subscripts svg, w, sc, and m represent the power generated by SVG, wind farm, synchronous condenser, and associated thermal power, respectively. X The subscripts L1 and L2 represent the transmission lines from the wind farm and its associated thermal power plant to the high-voltage DC converter bus, respectively.

[0032] When the installed capacity of the supporting thermal power plant is small or the transmission line of the wind farm is long, a transient low / overvoltage will occur at the wind power grid connection point after a near-area AC short-circuit fault or DC system fault. In severe cases, this may lead to the wind farm being disconnected from the grid due to failure to ride through the fault. Figure 2 Connecting reactive power compensation devices such as SVG and distributed synchronous condensers in parallel on the 35 kV busbar of a wind farm, as well as utilizing the wind farm to provide voltage support, are common solutions to improve system voltage stability under grid fault conditions.

[0033] Despite this, the voltage at the wind farm's grid connection point still poses a risk of exceeding limits after a fault. There are two main reasons for this: firstly, due to cost constraints, the capacity of reactive power compensation devices cannot fully suppress transient voltage; secondly, there are significant differences in the response speed, overload capacity, and support capacity of SVG, distributed synchronous condensers, and wind farms, and a lack of coordination among these devices leads to poor suppression of transient voltage disturbances after grid faults. Therefore, this embodiment first provides a detailed analysis of the reactive power response characteristics of these three types of electrical equipment.

[0034] As a synchronous rotating motor operating under no-load conditions, distributed synchronous condensers possess the ability to quickly and stably absorb / generate reactive power, effectively enhancing system strength upon connection. For transient analysis, they can be equivalently considered as a voltage source with adjustable internal electromotive force (EMF), and their response can be divided into two stages: ① a spontaneous response stage with a constant internal EMF, where reactive power output varies with the voltage of the connected bus; ② a dynamic response stage where the internal EMF is controlled by the excitation system, where reactive power output is jointly determined by the voltage at the synchronous condenser terminals and the excitation system.

[0035] (1) Spontaneous response stage: Distributed synchronous condensers consume very little active power, usually negligible, therefore their power angle is considered negligible. δ ≈0. Therefore, the voltage of the synchronous condenser connected to the bus and the reactive power injected can be expressed as follows: (1) In the formula, U , U d , U q These are the 35 kV side voltage of the synchronous condenser's step-up transformer and its direct and quadrature axis components, respectively. I d and I q These are the direct-axis and quadrature-axis current components, respectively. Q sc Reactive power injected into the power grid for synchronous condensers.

[0036] When the voltage connected to the synchronous condenser changes, the change in reactive power injected into the synchronous condenser before and after the disturbance is Δ Q sc It can be represented as: (2) In the formula, Q sc0 , I d0 These represent the reactive power and direct-axis current component of the camera before the fault; Δ U Δ I dThese represent the changes in voltage and direct-axis current before and after the fault, respectively.

[0037] Eliminate the change in reactive current Δ I d Equation (2) can be further simplified to: (3) In the formula, For adjusting the camera's subtransient reactance.

[0038] As can be seen from equation (3), during the spontaneous response phase of the subtransient process after a fault, the reactive power output of the synchronous condenser mainly depends on the severity of the fault and its initial direct-axis current. Since equation (3) is independent of the excitation control parameters, this process is called the instantaneous spontaneous response of the synchronous condenser, and its duration is usually no more than 20 ms. The reactive power compensation capability during this phase mainly depends on the direct-axis subtransient reactance. .

[0039] (2) Dynamic response stage under excitation system control: After a spontaneous response process of approximately 20 ms, the reactive power output of the synchronous condenser will be mainly determined by the excitation system. At this time, Δ in equation (2) I d The relationship between the excitation system control parameters and the excitation system control parameters is as follows:

[15] : (4) In the formula s Represents a complex frequency variable. X Indicates reactance parameters, T Represents the time constant. a , b For intermediate calculation parameters, K A This is the transfer function of the excitation system.

[0040] Synchronous condensers possess strong overload capacity, capable of reaching 4.5 times the rated current for at least 15 seconds. Under excitation control, synchronous condensers can generate more reactive power; however, excitation control has a time delay, and existing excitation control methods cannot fully utilize the reactive power compensation capacity of synchronous condensers. Figure 3 The figure shows the reactive power simulation results of the synchronous condenser under conventional control. Q during the excitation response stage... sc_max It can be obtained by substituting equation (4) into equation (2).

[0041] contrast Figure 3 The diagram shows the reactive power output and overload limit of the synchronous condenser under near-area AC fault conditions, revealing its untapped potential for reactive power support. Therefore, the transient reactive voltage support capability of the synchronous condenser can be further explored, enabling it to undertake more reactive power support tasks and reduce the severity of low / overvoltage at the wind farm's grid connection point.

[0042] The SVG structure is similar to the grid-side converter (GSC) structure of a doubly-fed induction generator (DFIG), both being based on voltage source inverters, but the SVG has a larger capacity. Furthermore, the SVG has a faster reactive power control response, typically with a delay of around 10 ms, while DFIGs require tens of milliseconds. my country's wind power grid connection standards stipulate that this time cannot exceed 60 ms.

[0043] The active power circuit of the SVG is controlled by constant DC voltage, while the reactive power control has two control modes: constant voltage and constant power. Its control block diagram is shown below. Figure 4 As shown. Normally, the SVG operates in constant voltage mode, and the reactive power it generates depends on equation (5), while the speed depends on the PI control parameters.

[0044] (5) In the formula, δ 1 is U svg Compared to U The phase.

[0045] Compared to constant voltage mode, constant power mode offers a faster reactive power response and better utilizes the reactive power potential of the SVG. Therefore, this embodiment primarily selects constant power mode for the SVG during fault periods. The overload capacity of the SVG is typically between 1.2 and 1.5 times the rated current, from which Q can be calculated. svg_max and Q svg_min .

[0046] For a doubly fed induction generator (DFIG) wind turbine, under grid voltage-oriented vector control, the q-axis voltage is 0, and the stator side of the turbine outputs reactive power. Q s It can be represented as: (6) In the formula, U s For the stator voltage of the wind turbine, i sq This represents the q-axis stator current.

[0047] Doubly fed induction generators (DFIGs) achieve reactive power control by adjusting the rotor q-axis current command. Furthermore, the reactive power output capacity of a DFIG is limited by the capacity of the rotor-side converter (RSC), and the upper / lower limits can be expressed as: (7) (8) In the formula, i rmax This is the maximum current that the RSC can output, typically between 1.2 and 1.5 times the rated value.

[0048] In summary, immediately after a large disturbance, the synchronous condenser first spontaneously outputs or absorbs reactive power to suppress voltage changes. After a brief control delay, the SVG and the synchronous condenser control system respond successively, initiating reactive power output control. Tens of milliseconds later, the wind farm's reactive current responds, and all three enter reactive power support mode. The typical reactive power control timing sequence of each device after a large disturbance is as follows: Figure 5 As shown. Among them, t 0 represents the start time of the fault. t 1 represents the start time of SVG reactive power control. t 2 represents the start time of the synchronous condenser excitation control. t 3 represents the start time of reactive power control in the wind farm.

[0049] Figure 6 The simulation results show the reactive power response of each device after the fault. It can be seen that after the fault occurs, the synchronous condenser responds spontaneously instantaneously, switching to excitation control response after approximately 20 ms, resulting in a significant increase in reactive power output. The SVG response time is approximately 10 ms, close to the excitation control response speed of the synchronous condenser. About 60 ms after the fault occurs, the wind farm enters reactive power support mode, outputting stable reactive power. The simulation results are consistent with... Figure 5 This is consistent with the reactive power control timing theory.

[0050] S2. Based on the reactive resource response characteristics, the post-fault transient process is divided into the spontaneous response stage of the synchronous condenser, the coordinated support stage between the synchronous condenser and the SVG, and the reactive power participation stage of the wind farm. The coordination principles for the reactive power response characteristics of SVG, synchronous condensers, and wind farms are designed based on their differences, and then reactive power control commands are allocated according to the quantified reactive power demand of the power grid. First, it is necessary to solve for the total reactive power deficit of the system after a large disturbance.

[0051] The active power loss of synchronous condensers and SVG is typically less than 1%, therefore, in this embodiment, their active power output is approximately negligible. According to Figure 2 In the equivalent circuit, the system power flow satisfies the following relationship: (9) (10) In the formula, Δ P DC Δ Q DC Δ represents the change in active and reactive power during DC transmission during a large disturbance. Q The total reactive power deficit of the sending-end system includes the reactive power changes of wind farms, SVG, and distributed synchronous condensers after large disturbances.

[0052] Combined equations (8) and (9), Figure 2 The grid connection voltage of the wind farm after a medium-to-large disturbance can be calculated as follows: (11) Assume the total reactive power generated by the wind farm, SVG, and synchronous condenser during the fault period is Δ. Q If the grid connection voltage of the wind power can be made 1 pu, then Δ is defined. Q The total reactive power deficit of the system can be obtained by solving equation (11): (12) In this formula, only the active and reactive power provided by the AC system, the active and reactive power consumed by the DC system, and the DC converter bus voltage need to be measured. These parameters can be obtained in real time through local measurement.

[0053] The foregoing analysis shows that the total reactive power demand of the system can be calculated based on the measured voltage of the HVDC converter bus, the active and reactive power of DC transmission, and the active and reactive power provided by the AC system. Coordinated control can be achieved by allocating this reactive power demand to various reactive power resources according to certain principles.

[0054] To maintain power system voltage stability, grid connection standards require wind farms to output reactive power during short-circuit faults. Due to inherent control delays in wind turbines, reactive power output from wind farms may exceed actual grid demand for a short period after the fault is cleared, leading to temporary overvoltage issues. Simultaneously, the limited capacity of converters and the prioritization of reactive power control during wind farm faults also restrict active power transmission. Considering the stronger overload capacity of synchronous condensers and the faster response speed of SVG (Static Var Generator), the principle of voltage coordination follows the basic principle of prioritizing reactive power support from synchronous condensers, supplemented by reactive power support from SVG, while maximizing active power generation from wind farms.

[0055] Specifically, in the initial stage of a fault, the synchronous condenser's spontaneous reactive power response characteristics with no delay should be fully utilized to quickly absorb or support reactive power at the grid connection point. Considering that the spontaneous reactive power component of the synchronous condenser will decay after a period of time, the synchronous condenser transitions to the excitation control stage. During this stage, the backup reactive power supplementation capability of the SVG should be utilized to increase reactive power generation.

[0056] Simultaneously, the reactive power deficit of the wind farm is calculated in real time, and reactive power commands are allocated based on the current operating status and power limits of the synchronous condenser. When the current reactive power deficit does not reach the synchronous condenser's power limit, it is entirely allocated as reactive power commands to the synchronous condenser and sent to its excitation system. If the reactive power deficit exceeds the synchronous condenser's overload range, the remaining reactive power deficit is allocated as reactive power commands to the SVG (Static Var Generator), which provides the remaining reactive power. If the synchronous condenser and SVG still cannot fully meet the reactive power demand, the remaining reactive power is provided by the wind farm.

[0057] Since SVG uses constant reactive power control, reactive power commands are appended to it. Figure 4 The control can be achieved on the outer power loop shown. The following analysis mainly focuses on the control of the synchronous condenser and the fan.

[0058] Combining equations (2) to (4), it can be seen that the reactive power output of the synchronous condenser in the sub-transient stage can be quantified, but since the voltage is the control target in the transient stage, it is difficult to directly control the power. Therefore, this embodiment draws on the dual-loop control method and uses the method of adding command values ​​to the inner power loop to achieve reactive power regulation.

[0059] The reactive power output of each turbine in a wind farm follows the principle of equal power factor distribution.

[25] Assuming there are wind farms n Taiwan unit, then the first i Reactive power compensation of the generator set It can be represented as: (13) In the formula, P DFIG_i For the first i Rated active power of the unit.

[0060] DFIG stator and rotor q The relationship between the shaft currents is as follows: (14) In the formula, L s , L m These are the stator and the magnetizing inductor, respectively. ω s Synchronous angular velocity; u s0 This is the terminal voltage before the fault.

[0061] Therefore, by combining equations (6), (13), and (14), the reference value of the rotor current can be obtained as follows: (15) By setting the current reference value command of each fan during the fault period to the calculation result of equation (15), the desired reactive power can be achieved.

[0062] In summary, the voltage coordination control architecture designed in this embodiment is as follows: Figure 7 As shown. S3. During the spontaneous response phase of the synchronous condenser, the instantaneous spontaneous reactive power characteristics of the synchronous condenser are used first to support voltage, and reactive power instructions for subsequent phases are pre-allocated. When the system detects a fault, the reactive power coordination strategy enters Phase 1. This phase primarily relies on the spontaneous response of the synchronous condenser, without regulating the reactive power of the SVG and wind farm values. Simultaneously, according to equation (12), the calculation unit collects key parameters such as the grid connection point voltage and the reactive power output of each device in real time to calculate Δ. Q Based on this, a preliminary allocation of reactive power command values ​​is performed. Considering the characteristic that the spontaneous reactive power component of the synchronous condenser decays over time, the first stage should not be too long; in this invention, 10 ms is chosen.

[0063] S4. During the coordinated support phase of the synchronous condenser and SVG, the reactive power deficit is allocated according to the principle of prioritizing the synchronous condenser and supplementing the SVG. The precise control of the reactive power of the synchronous condenser is achieved through dual-loop control. Considering both the SVG control delay and the synchronous condenser excitation control delay, this invention sets the entry point for stage two to be 10 ms after a fault occurs. By comparing Δ... Q With the adjustment camera ΔQ sc_max and the maximum reactive power output capability ΔQ of SVG svg_max Reactive power is allocated according to the principle of adjusting the camera first, then the SVG, and controlling the SVG only after the camera has reached full capacity. During this stage, the wind farm still maintains the active power priority control strategy.

[0064] S5. During the reactive power participation phase of the wind farm, reactive power commands for the wind turbine units are allocated according to the principle of equal power factor based on the remaining reactive power demand, and reactive power output is achieved through rotor current control. Referring to the grid connection standard requirement that the reactive power response time of wind farms should not exceed 60 ms, this invention sets up a phase three stage 40 ms after a fault occurs. In this stage, the wind farm switches to a reactive power priority control mode. The controller determines whether the wind farm needs to generate additional reactive power based on the total reactive power demand of the system and the power output of the synchronous condenser and SVG. If so, the controller converts the remaining reactive power deficit into a wind farm current command value and sends it to each wind turbine control link, further improving the system's voltage support capability. Conversely, the wind farm can generate as much active power as possible to maintain the system's active power transmission.

[0065] S6. Through three stages of reactive power coordination control, the synergistic optimization of transient voltage support and active power transmission capacity is achieved.

[0066] Considering the control delay, the instructions for each stage need to be allocated in advance. That is, the synchronous condenser and SVG instructions for stage 2 are calculated in stage 1; and the wind farm control instructions for stage 3 are calculated in advance in stage 2 to ensure the timeliness of reactive power control under the transient time scale of each device.

[0067] Under the proposed control strategy, the rapid reactive power compensation capabilities of the synchronous condenser and SVG can be fully utilized, and wind power can generate as much active power as possible during faults, thus ensuring the power supply of the system.

[0068] according to Figure 2 The system shown was simulated in PSCAD / EMTDC, with both thermal power and wind farm outputs set at 2500 MW (corresponding to a 50% wind power ratio); the LCC-HVDC rated power was 5000 MW and the rated voltage was ±800 kV; six 50 MVar distributed synchronous condensers and one 300 Mvar SVG were configured at the 35kV substation of the wind farm. Specific parameters of the synchronous condensers are shown in Table 1.

[0069] Different simulation scenarios and control schemes were set up to compare and verify the effectiveness and superiority of the proposed coordination strategy: Option 1: SVG, distributed synchronous condensers, and wind farms all use default basic control, with no coordination between reactive resources; Option 2: Adopt an SVG, synchronous condenser and wind farm coordination scheme, that is, the reactive power resources are coordinated according to the preset action sequence and output; Option 3: The coordination scheme proposed in this invention.

[0070] Table 1 Parameters of Distributed Synchronous Condenser name numerical values unit Rated capacity 50 MVar Rated stator voltage 10.5 kV Rated stator current 1.65 kA stator winding resistance 0.38 % Direct-axis synchronous reactor 111.5 % Direct-axis transient reactance 10 % Direct-axis subtransient reactance 8.5 % quadrature axis synchronous reactor 111.5 % quadrature axis transient reactance 10 % quadrature axis subtransient reactance 8.5 % Direct-axis transient open-circuit time constant 6.913 s Direct-axis subtransient open-circuit time constant 0.035 s Quadrature axis transient open circuit time constant 6.913 s Quadrature axis subtransient open-circuit time constant 0.035 s equivalent reactance of step-up transformer 6.67 % With a 2-2.3 s bipolar blockade for the DC converter, both the active and reactive power of the high-voltage DC power supply drop to zero. However, the reactive power compensation device within the converter station remains active, resulting in surplus reactive power being fed back to the sending-end AC system, causing a temporary overvoltage. Simulation results for the three schemes are compared below. Figure 8 As shown.

[0071] Figure 8 Simulation results show that after DC blocking, the peak voltage at the wind farm's grid connection point reaches 1.394 pu when using Scheme 1, posing a risk of grid disconnection. This is because the reactive power potential of the equipment under basic control is not fully utilized. Under the coordinated control of Scheme 2, the peak voltage at the grid connection point drops to 1.323 pu, but still exceeds the high voltage ride-through limit of 1.3 pu, indicating a risk of wind farm disconnection. This is because the equipment potential under this scheme is not fully utilized. However, when using the coordinated scheme proposed in this invention, the peak voltage at the grid connection point is reduced to 1.243 pu. The synchronous condenser can absorb approximately 4.5 times the rated reactive power during the excitation phase, and the SVG quickly responds to absorb approximately 1.5 times the rated reactive power after receiving the reactive power command. The wind farm absorbs approximately 40% of its rated reactive power, effectively ensuring power supply during faults, with minimal fluctuations in active power. Therefore, the control effect of Scheme 3 is significantly better than Schemes 1 and 2.

[0072] The rectifier-side converter bus is set to experience a three-phase ground fault within 2 to 2.3 seconds, with a fault resistance of 2 Ω. Simulation results for three control schemes are as follows: Figure 9 As shown. In addition to the voltage drop during the fault, a temporary overvoltage problem will also occur after the fault is cleared because the wind turbine unit does not promptly exit the low-voltage ride-through state. [ . Depend on Figure 9It is known that under Scheme 1, the effective voltage at the wind farm's grid connection point drops to 0.704 pu. During a fault, both the synchronous condenser (RCD) and the SVC will generate reactive power to support the voltage, but the amount of reactive power generated is relatively small compared to their rated capacity. At this time, the wind farm mainly undertakes the task of reactive power support, with reactive power output reaching 1000 MVar, while active power output decreases to around 0.6 times the rated value. In addition, due to the control delay of the wind turbine units, the wind farm continues to generate a large amount of reactive power after the fault ends, resulting in an overvoltage phenomenon at the grid connection point with an amplitude exceeding 1.15 pu. Under Scheme 2, the grid connection point voltage rises to 0.759 pu because the SVG and the RCD generate more reactive power. However, this scheme actively limits the output of the RCD and SVG in the early stage of the fault to ensure the reactive power reserve of the RCD. The wind farm still needs to generate a large amount of reactive power to raise the voltage, which limits the active power generated by the wind farm. Under this scheme, overvoltage will still occur after the fault is cleared. When Scheme 3 is adopted, the grid connection voltage is raised to 0.816 pu during the fault. It can be seen that the proposed coordinated control down-regulating camera and SVG generate a large amount of reactive power, while the wind farm does not need to provide reactive power and can continue to generate more than 80% of its rated active power. Furthermore, there is no surplus reactive power from the wind farm after the fault is cleared, and the voltage can recover smoothly. Therefore, Scheme 3's control effect under short-circuit faults is still significantly better than other schemes.

[0073] When using Scheme 1, the effective voltage at the wind farm's grid connection point drops to 0.704 pu. To suppress the transient low voltage, the wind farm generates a large amount of reactive power, while the reactive power output of the synchronous condenser and SVG is relatively low, failing to fully utilize the reactive power compensation capabilities of these two devices. Simultaneously, because reactive power output is prioritized during the fault, the active power output of the wind farm is limited to around 0.6 times its rated value, failing to maintain power transmission effectively. Furthermore, due to the delay in wind power control, the wind power continues to generate significant reactive power after the fault ends, resulting in reactive power redundancy at the grid connection point and causing significant overvoltage. Scheme 2 raises the low voltage at the grid connection point to approximately 0.759 pu during the steady-state phase of the fault. However, to ensure sufficient reactive power reserves for the synchronous condenser, this scheme limits the output of the synchronous condenser and SVG in the initial stage of the fault, requiring the wind farm to generate even more reactive power to suppress the voltage drop, which is detrimental to the active power transmission of the wind farm under fault conditions. When Scheme 3 is adopted, the grid connection voltage can be maintained at 0.816 pu during the steady-state period of the fault. The synchronous condenser and SVG quickly generate a large amount of reactive power, and the wind farm does not need to output reactive power. It can maintain the transmission of active power output of more than 80% of the rated value, which effectively ensures the power supply during the fault. Furthermore, under this condition, the amount of reactive power support for the wind farm is reduced due to the delayed shutdown, which also greatly reduces the severity of overvoltage after the fault. Therefore, the control effect of Scheme 3 is significantly better than that of Scheme 1 and Scheme 2.

[0074] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0075] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0076] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0077] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

[0078] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for phased reactive power coordination control of wind farms that coordinates SVG and distributed synchronous condensers, characterized in that, Includes the following steps: S1. Real-time monitoring of wind farm grid connection point voltage, DC converter bus voltage and system power parameters, and calculation of total reactive power deficit after a fault. S2. Based on the reactive resource response characteristics, the post-fault transient process is divided into the spontaneous response stage of the synchronous condenser, the coordinated support stage between the synchronous condenser and the SVG, and the reactive power participation stage of the wind farm. S3. During the spontaneous response phase of the synchronous condenser, the instantaneous spontaneous reactive power characteristics of the synchronous condenser are used first to support voltage, and reactive power instructions for subsequent phases are pre-allocated. S4. During the coordinated support phase of the synchronous condenser and SVG, the reactive power deficit is allocated according to the principle of prioritizing the synchronous condenser and supplementing the SVG. The precise control of the reactive power of the synchronous condenser is achieved through dual-loop control. S5. During the reactive power participation phase of the wind farm, reactive power commands for the wind turbine units are allocated according to the principle of equal power factor based on the remaining reactive power demand, and reactive power output is achieved through rotor current control. S6. Through three stages of reactive power coordination control, the synergistic optimization of transient voltage support and active power transmission capacity is achieved.

2. The method for phased reactive power coordination control of a wind farm by coordinating SVG and distributed synchronous condensers according to claim 1, characterized in that, The formula for calculating the total reactive power deficit of the system after a fault in S1 is as follows: In the formula, This represents the total reactive power deficit of the system. This refers to the DC transmission reactive power during periods of large disturbances. This refers to the active power transmitted via DC during periods of large disturbances. U To adjust the voltage on the 35 kV side of the step-up transformer for the camera, To match the reactive power generated by thermal power plants, Reactance for transmission lines connecting thermal power plants to high-voltage DC converter busbars.

3. The method for phased reactive power coordination control of a wind farm coordinating SVG and distributed synchronous condensers according to claim 1, characterized in that, The specific stage division in S2 is as follows: Stage 1 is the spontaneous response stage of the synchronous condenser from 0 to 10 ms after the fault; Stage 2 is the coordinated support stage of the synchronous condenser and SVG from 10 to 40 ms after the fault; and Stage 3 is the reactive power participation stage of the wind farm after 40 ms after the fault.

4. The method for phased reactive power coordination control of a wind farm by coordinating SVG and distributed synchronous condensers according to claim 1, characterized in that, The reactive power output during the spontaneous response phase of the synchronous condenser in S3 is determined by the subtransient reactance, and its reactive power change is expressed as follows: In the formula, Inject reactive power changes into the synchronous condenser before and after the disturbance. I d0 This refers to the direct-axis current component of the camera before the fault occurred. U To adjust the voltage on the 35 kV side of the step-up transformer of the synchronous condenser, Δ U This represents the change in direct-axis current before and after the fault. For adjusting the camera's subtransient reactance.

5. The method for phased reactive power coordination control of a wind farm by coordinating SVG and distributed synchronous condensers according to claim 1, characterized in that, The coordination principle between the camera and the SVG in S4 is as follows: when ΔQ≤Q sc_max The time adjustment is prioritized by the synchronous condenser when ΔQ > Q. sc_max The remaining portion is handled by SVG, where Q sc_max To adjust the camera's overload capacity limit; When ΔQ>Q sc_max +Q svg_max At that time, the wind farm participated in reactive power support, of which Q svg_max ΔQ represents the maximum reactive power output capability of the SVG, and ΔQ represents the total reactive power deficit of the system.

6. The method for phased reactive power coordination control of a wind farm by coordinating SVG and distributed synchronous condensers according to claim 1, characterized in that, The reactive power command allocation for wind farms in S5 adopts the principle of equal power factor, and the reactive power command for a single wind turbine is expressed as follows: In the formula, This is a reactive power command for a single wind turbine. For the total reactive power deficit of the system, These are the reactive power of the camera and the SVG, respectively. P DFIG_i For the first i Rated active power of the unit For the first k The rated active power of the generator set is n, where n is the total summation.

7. The method for phased reactive power coordination control of a wind farm by coordinating SVG and distributed synchronous condensers according to claim 1, characterized in that, The SVG adopts a constant reactive power control mode, and the reactive power command is directly attached to the power outer loop to achieve fast response.

8. The method for phased reactive power coordination control of wind farms by coordinating SVG and distributed synchronous condensers according to claim 1, characterized in that, The coordinated control strategy prioritizes suppressing transient overvoltages under DC blocking faults, while balancing low-voltage support and post-fault overvoltage suppression under AC short-circuit faults.

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