A fast frequency response method that coordinates wind farm unit response and overall control

Abstract

The present invention discloses a fast frequency response method that coordinates the unit response and overall control of a wind farm station. First, it is necessary to collect the frequency value of the grid connection point in real time for frequency detection, and secondly, evaluate the frequency regulation potential based on the operating conditions of the wind turbines in the station themselves. When the frequency drops, some of the wind turbines in the wind farm are first started to perform unit response to suppress the frequency drop. When the frequency drops to a set critical value, the power increase of the cluster in the second part of the wind farm station is distributed according to the received power increase through an overall control method to optimize the power increase. The present invention can enhance the frequency response capability of the wind farm station, thereby enhancing the stability of the power system, and has important academic significance and engineering practical value.

Description

Technical Field

[0001] The present invention relates to the field of new energy, and in particular to a fast frequency response method for coordinating wind farm station unit response and overall control. Background Art

[0002] With the introduction of a high proportion of power electronic equipment and renewable energy generation, the power system is gradually transforming into a new type of power system with high uncertainty. At the same time, as traditional thermal power units are largely replaced by renewable energy generation, the power system is gradually exhibiting low inertia characteristics. However, the latest grid stability guidelines require renewable energy power plants to have certain frequency regulation capabilities.

[0003] Currently, the primary frequency regulation capacity of most new energy power stations is insufficient. Therefore, as the proportion of new energy gradually increases, studying how to use new energy power stations for frequency regulation is a key technology. Summary of the Invention

[0004] In response to the above problems, the present invention proposes a fast frequency response method that coordinates the unit response and overall control of a wind farm, which can play a role in recovering from frequency drops and has important academic significance and engineering practical value.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0006] The present invention is a fast frequency response method that coordinates wind farm unit response and overall control, specifically as follows:

[0007] Step 1: Detect the overall status of the wind farm and collect relevant information from the power grid in real time. Evaluate the frequency regulation capability of the wind turbines.

[0008] Among them, the collected data includes the rotation speed of each wind turbine, wind speed conditions and grid connection frequency.

[0009] The purpose is to evaluate the primary frequency regulation capability of all wind turbines based on the existing wind speed and wind turbine speed. The frequency regulation capability can be expressed by the amount of power that can be increased within the primary frequency regulation time window.

[0010] Step 2: When the frequency starts to drop, the wind farm unit response is started; if the frequency does not drop to the set frequency threshold, the overall control is not started;

[0011] Step 3: When the frequency still drops to the warning value, start the overall control method; until the frequency returns to normal.

[0012] A further improvement of the present invention is that: the information collected in step 1 includes the rotational speed of each wind turbine, receives the wind speed and the grid-connected frequency, and evaluates the primary frequency regulation capability of all wind turbines based on the existing wind speed and wind turbine rotational speed. The frequency regulation capability is represented by the amount of additional power that can be generated within the primary frequency regulation time window. Since the wind farm participates in primary frequency regulation, the wind turbines need to operate in a load reduction mode. Assuming the load reduction level is d%, the method for evaluating the frequency regulation capability is as follows:

[0013] According to the current wind speed, the frequency modulation method is determined:

[0014] Since the wind energy utilization coefficient is related to the pitch angle and the blade tip speed ratio (ωR / v), when v≤v lim When the fan uses overspeed standby to perform a frequency adjustment, when v base ≥v≥v lim When v≥v base When , the wind turbine only uses variable pitch control to perform frequency regulation once;

[0015] Among them, v base is the rated wind speed;

[0016] Critical wind speed v lim The calculation formula is obtained according to the following formula:

[0017] (1-d%)C Popt -C Pde =(1-d%)C P (ω opt R / v lim ,0)-C P (ω max R / v lim ,0)=0, R is the blade radius of the fan, ω is the fan speed, v is the wind speed, C Pde is the wind energy utilization coefficient of the fan after load reduction, C Popt is the wind energy utilization coefficient when the wind turbine is performing maximum power tracking, v lim is the only critical wind speed corresponding to the reserved load reduction level d%, ω opt is the unique speed corresponding to the optimal tip speed ratio, ω max is the maximum speed of the wind turbine rotor, and 0 means the pitch angle is 0 degrees;

[0018] In the time scale of a frequency regulation, the power increase is provided by the rotor kinetic energy and the wind energy increase. Therefore, the frequency regulation potential of the frequency-regulated wind turbine is expressed as:

[0019]

[0020] Among them, V Wis the current wind speed, Δt is the time scale of a frequency modulation, ΔP r is the increase in rotor kinetic power, ΔP m is the power increase caused by the increase in wind energy utilization, ω(t0) is the initial speed, and C Pde The corresponding speed is given, and (1-d%)C Popt =C Pde ω(t0+Δt) is the speed after frequency modulation, and C Popt Given, H D is the inertia of the fan, ρ is the air density, typically 1.225 km / m 3 , A is the blade area, A=πR 2 .

[0021] Due to the existence of the wake effect, the wind speed received by each wind turbine is different, and the measured wind speed of each wind turbine is different, so the frequency regulation capability of each wind turbine also presents a different size relationship.

[0022] A further improvement of the present invention is that: a portion of wind turbines with frequency modulation capability are used as wind turbine units for unit response, and when the frequency begins to drop, the frequency drop is responded to in real time through integrated inertia control or droop control;

[0023] The specific formula for the droop formula is:

[0024] ΔP=-k p Δf

[0025] The formula corresponding to the comprehensive inertia control is:

[0026]

[0027] Where k p is the droop coefficient, Δf is the frequency change, ΔP is the wind turbine power change, k d is the coefficient of inertia.

[0028] A further improvement of the present invention is that in step 3, some fans are used as standby fans for overall control, and when the frequency drops but does not reach the warning value, they operate normally without frequency modulation, and only the fans that respond to the units are frequency modulated.

[0029] A further improvement of the present invention is that in step 3, when the frequency drops and drops to the warning value, the following operations are performed:

[0030] The other part of the wind farm with frequency regulation capability is used as a whole to control the wind turbines. When a power shortage occurs and the frequency drops to the rated value, the total power required for frequency regulation, ΔP, is provided by the upper-level control personnel and allocated to each wind turbine for power generation through optimization. The specific method is as follows:

[0031] When the total power required for frequency regulation is greater than the frequency regulation potential of the wind farm, the frequency-adjustable power of all wind turbines will be directly emitted;

[0032] When the total power involved in frequency regulation is less than the frequency regulation potential of the wind farm, the power allocation is constrained by the following equation:

[0033] min(∑E ki )=min(∑H Di ω i 2 )

[0034] sT i ≤P imax

[0035] ΣP i =ΔP

[0036]

[0037] Among them, E ki is the rotor kinetic energy of the i-th fan, Δt is the time scale of a frequency modulation, ω i is the speed of the i-th fan, P imax is the maximum value of the frequency regulation capability of the i-th fan, P i is the power increase of the i-th wind turbine, H Di is the inertia of the i-th fan, ω i (t0) is the initial speed of fan i, ω i (t0+Δt) is the speed after frequency modulation, ρ is the air density, A is the blade area, Δt is the time scale of one frequency modulation, H Di is the inertia of fan i.

[0038] The beneficial effects of the present invention are: 1. Compared with simple unit response, the overall control characteristics are increased and the frequency protection capability is improved.

[0039] 1. Compared with simple overall control, it improves the real-time performance and flexibility of frequency regulation. It also reduces the number of control orders and speeds up the response to frequency events. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of a permanent magnet direct-drive wind farm in an embodiment of the present invention.

[0041] Figure 2 2 is a comparison chart of the results of three frequency modulation methods in an embodiment of the present invention.

[0042] Figure 3 For extraction Figure 1 Image of a wave crest.

[0043] Figure 4 Schematic diagram showing output of three control strategies when the frequency drops in an embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0045] like Figure 1 As shown, the present invention is a fast frequency response method that coordinates wind farm unit response and overall control, specifically as follows:

[0046] The wind turbines in the wind farm are divided into real-time unit response wind turbines and overall control wind turbines for overall control. The wind turbines have the function of stabilizing the frequency. Under normal circumstances, they do not perform frequency adjustment during normal operation, but are in a load-reducing operation mode. The unit response wind turbines are used for the first quick action when a frequency drop occurs, and the overall control wind turbines take centralized action when the frequency drops to the warning value.

[0047] Step 1: Detect the overall condition of the wind farm, collect frequency-related information in real time through the grid connection point, and evaluate the frequency regulation capability of the wind turbines;

[0048] The collected data includes the speed of each wind turbine, wind speed conditions, and grid frequency. The goal is to assess the primary frequency regulation capability of all wind turbines based on the existing wind speed and turbine speed. Frequency regulation capability can be expressed as the amount of power that can be generated within the primary frequency regulation time window.

[0049] Step 2: When the frequency starts to drop, the wind farm units are activated to respond to the wind turbines. If the frequency does not drop to the set frequency threshold, the overall control is not activated.

[0050] Step 3: When the frequency drops to the warning value, the overall control method is used to start the overall control wind turbines of the wind farm until the frequency returns to normal.

[0051] like Figure 1 The three wind turbines shown are used as unit response units, and the six wind turbines are used for overall control, using a command-based overall control mode.

[0052] Assume the external system wind speed is 10 m / s and the equivalent grid uses a permanent magnet synchronous wind turbine. The unit response frequency threshold is 49.8 Hz, and overall control is initiated when the frequency drops to 49.5 Hz.

[0053] When the frequency begins to drop, the unit response mode is integrated inertia control, k p is the droop coefficient k d is the coefficient of inertia.

[0054] ΔP=-k p Δf-k d (dΔf / dt)

[0055] k p Set to 0.5, k d Set to 0.005.

[0056] The information collected in step 1 includes the speed of each wind turbine, the wind speed conditions, and the grid-connected frequency. Based on the existing wind speed and wind turbine speed conditions, the primary frequency regulation capability of all wind turbines is evaluated. The frequency regulation capability is represented by the amount of power that can be increased within the primary frequency regulation time window. Since the wind farm participates in primary frequency regulation, the wind turbines need to operate in a load reduction mode. Assuming the load reduction level is d%, the method for evaluating the frequency regulation capability is as follows:

[0057] According to the current wind speed, the frequency modulation method is determined:

[0058] Since the wind energy utilization coefficient is related to the pitch angle and the blade tip speed ratio (ωR / v), when v≤v lim When the fan uses overspeed standby to perform a frequency adjustment, when v base ≥v≥v lim When v≥v base When , the wind turbine only uses variable pitch control to perform frequency regulation once;

[0059] Among them, v base is the rated wind speed;

[0060] Critical wind speed v lim The calculation formula is obtained according to the following formula:

[0061] (1-d%)C Popt -C Pde =(1-d%)C P (ω opt R / v lim ,0)-C P (ω max R / v lim ,0)=0, R is the blade radius of the fan, ω is the fan speed, v is the wind speed, C Pde is the wind energy utilization coefficient of the fan after load reduction, C Popt is the wind energy utilization coefficient when the wind turbine is performing maximum power tracking, v lim is the only critical wind speed corresponding to the reserved load reduction level d%, ω optis the unique speed corresponding to the optimal tip speed ratio, ω max is the maximum speed of the wind turbine rotor, and 0 means the pitch angle is 0 degrees;

[0062] In the time scale of a frequency regulation, the power increase is provided by the rotor kinetic energy and the wind energy increase. Therefore, the frequency regulation potential of the frequency-regulated wind turbine is expressed as:

[0063]

[0064] Among them, V W is the current wind speed, Δt is the time scale of a frequency modulation, ΔP r is the increase in rotor kinetic power, ΔP m is the power increase caused by the increase in wind energy utilization, ω(t0) is the initial speed, and C Pde The corresponding speed is given, and (1-d%)C Popt =C Pde ω(t0+Δt) is the speed after frequency modulation, and C Popt Given, H D is the inertia of the fan, ρ is the air density, typically 1.225 km / m 3 , A is the blade area, A=πR 2 .

[0065] Due to the existence of the wake effect, the wind speed received by each wind turbine is different, and the measured wind speed of each wind turbine is different, so the frequency regulation capability of each wind turbine also presents a different size relationship.

[0066] When a frequency drop occurs, the fan that responds first adopts integrated inertia control to respond.

[0067] When a frequency drop occurs and drops to the warning value, the total power ΔP required for additional frequency regulation is first provided by the upper-level control personnel, and then ΔP is allocated to each wind turbine through an optimization method. Here, the power of the overall controlled wind turbines is increased.

[0068] It can be seen from the figure that the coordinated control scheme can optimize the frequency response capability due to the unregulated and individual unit responses.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific implementation methods of the present invention may still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims.

Claims

1. A fast frequency response method for wind farm station with coordinated unit response and overall control, characterized by: The details are as follows: Step 1: Detect the overall status of the wind farm and collect relevant information from the power grid in real time to evaluate the frequency regulation capability of the wind turbines; Step 2: When the frequency starts to drop, start the unit response of the wind farm station; Step 3: If the frequency recovers in time, the overall control method is not started. If the frequency still drops to the warning value after the unit response is started, the overall control method is started until the frequency returns to normal; In step 2: a portion of wind turbines with frequency modulation capability is used as a unit-responding wind turbine set, and when the frequency begins to drop, the frequency drop is responded to in real time through integrated inertia control or droop control; The specific formula for droop control is: ΔP=-k p Δf The corresponding formula for comprehensive inertia control is: Where k p is the droop coefficient, Δf is the frequency change, ΔP is the wind turbine power change, k d is the coefficient of inertia; In step 3: another part of the wind turbines in the wind farm that have frequency modulation capability is used as a whole to control the wind turbine group, and when the frequency drops but does not reach the warning value, it operates normally without frequency modulation, and only the wind turbines that respond to the unit are frequency modulated; In step 3: when the frequency drops and drops to the warning value, perform the following operations: The other part of the wind farm with frequency regulation capability is used as a whole to control the wind turbines. When a power shortage occurs and the frequency drops to the rated value, the total power required for frequency regulation provided by the upper-level control personnel is allocated to each wind turbine through an optimization method for power generation. The specific method is as follows: When the total power required for frequency regulation is greater than the frequency regulation potential of the wind farm, the frequency-adjustable power of all wind turbines will be directly emitted; When the total power required for frequency regulation is less than the frequency regulation potential of the wind farm, the power allocation is constrained by the following equation: min(∑E ki )=min(∑H Di oh i 2 ) s.t.P i ≤P imax ∑P i =ΔP Among them, E ki is the rotor kinetic energy of the i-th fan, Δt is the time scale of a frequency modulation, ω i is the speed of the i-th fan, P imax is the maximum value of the frequency regulation capability of the i-th fan, P i is the power increase of the i-th wind turbine, H Di is the inertia of the i-th fan, ω i (t0) is the initial speed of fan i, ω i (t0+Δt) is the speed after frequency modulation, ρ is the air density, A is the blade area, C Pde is the wind energy utilization coefficient of the fan after load reduction, C Popt is the wind energy utilization coefficient when the wind turbine is tracking its maximum power, V W is the current wind speed, and t0 is the initial time.

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