Synthetic inertia control method and system of wind driven generator

Abstract

The synthetic inertia control method comprises the following steps: executing maximum power point tracking control; detecting the frequency deviation of the power system; when the frequency deviation is larger than a specified value, the maximum power point tracking control is converted into temporary frequency support control, and the temporary frequency support control comprises a specified first time period starting from a time point of conversion from the maximum power point tracking control to the temporary frequency support control. Calculation and control are performed according to an active power reference value added to the original reference value in accordance with the maximum power point tracking control at the conversion time point, and the active power reference value added according to the temporary frequency support control can be calculated by a function of the frequency deviation and the rotor speed of the wind generator. According to the present invention, after the power system is disturbed, the output is increased by multiplying the control gain which is proportional to the frequency deviation and varies according to the rotor speed, and therefore, when the rotor speed is high, the output increase amount becomes large, and the lowest frequency increase effect is obvious.

Description

Technical Field

[0001] This invention relates to a synthetic inertia control method and system for a wind turbine, and more specifically to a synthetic inertia control method and system for a wind turbine. When a disturbance such as generator disconnection occurs in the power system, causing a sharp drop in system frequency, the minimum frequency is increased by temporarily releasing the kinetic energy stored in the rotating body of the wind turbine, thereby ensuring system stability. Background Technology

[0002] When disturbances such as generator disconnection occur in a power system, the kinetic energy stored in the rotating body of the synchronous generator is naturally released, and the system frequency drops sharply. This phenomenon is called the inertia response of the synchronous generator.

[0003] When the frequency drops below 59.964Hz, the governor of the online synchronous generator increases the output proportionally to the frequency deviation; this is called primary frequency control. If the output of the online synchronous generator increases by the same amount as the capacity of the off-grid generator, the frequency will reach its lowest point. This frequency is called the minimum frequency. After the frequency recovers, it will converge to a certain value, which is called the stabilizing frequency.

[0004] When the power system frequency drops below 59.8 Hz, the Automatic Generation Control (AGC), which is activated during normal operation to maintain the frequency at the rated frequency, will stop operating. After an disturbance occurs, if the stabilized frequency converges back above 59.8 Hz, the AGC will restart, and the frequency will return to 60 Hz. This type of control is called Second Frequency Control.

[0005] According to South Korea's power system reliability and power quality maintenance standards, when one generator is disconnected from the grid, the minimum frequency should be above 59.7 Hz, and the stabilization frequency should be above 59.8 Hz. Furthermore, when two generators are disconnected from the grid, the minimum frequency should be above 59.2 Hz, the stabilization frequency should rise to above 59.5 Hz within one minute, and to above 59.8 Hz within ten minutes.

[0006] In existing systems consisting only of synchronous generators, the synchronous generator is the primary entity responsible for frequency control in the event of an disturbance. In other words, the synchronous generator possesses primary and secondary reserve power as specified in reliability standards, which are released during disturbances to prevent the frequency from dropping and returning to the rated frequency.

[0007] To produce maximum energy, wind turbines employ Maximum Power Point Tracking (MPPT) control, adjusting the rotor speed to the optimal level based on varying wind speeds. For this purpose, the baseline value for active power is set to be proportional to the cube of the rotor speed. MPPT operation means that the wind turbine's active power is adjusted based on the rotor speed, not the system frequency. When multiple wind turbines are connected to the system, synchronous generators are isolated to match supply and demand. In this case, if only MPPT control is implemented for the wind turbines, the inertial response and primary frequency control capability of the synchronous generators will decrease in the event of disturbances. Consequently, the minimum frequency will be reduced, failing to meet reliability standards and potentially leading to power outages.

[0008] To address this issue, a synthetic inertial technology is proposed. During normal operation, the wind turbine performs MPPT control, temporarily releasing the kinetic energy stored in the rotating body after a disturbance. Wind turbine synthetic inertial technology is divided into frequency-based synthetic inertial methods and stepped synthetic inertial methods.

[0009] Non-patent literature 0001 proposes a method to reduce active power with a certain inclination to solve the problem of second frequency dip (SFD) phenomenon that occurs when the active power is reduced instantaneously to restore rotor speed in a stepped synthesis method.

[0010] Figure 1 The active power reference value (P) in non-patent document 0001 is shown. ref It can be observed that the active power decreases at a certain angle within the B'C interval. However, in order to restore the rotor speed, the active power at C must be less than the mechanical input of the wind turbine. The problem is that in order to determine this, C must be found through trial and error.

[0011] Furthermore, this method, even at low wind speeds, can increase the active power set at high wind speeds. Therefore, during synthetic inertial control, an over-deceleration (OD) phenomenon may occur, where the rotor speed reaches the minimum rotor speed. If OD occurs, the rotor speed of the wind turbine will further decrease, leading to stall and causing the turbine to stop rotating. To prevent stall, the active power of the wind turbine must be reduced rapidly, and the intersection with the MPPT control curve must also be reduced. This requires a significant reduction in output, which may result in a secondary frequency dip, lower than the primary minimum frequency.

[0012] Unlike non-patent document 0001, which sets a reference value for the active power of a wind turbine within a time region, non-patent document 0002 proposes a method such as... Figure 2 The figure shows the setting of the active power reference value (P) on the active power-rotor speed plane. ref (in the manner of)

[0013] Figure 2 The process is illustrated in the interval (AB') where the active power output increases instantaneously by a certain value and is maintained, the interval (B'C) where the rotor speed decelerates by reducing the active power, the interval (CD) where the rotor speed recovers to the MPPT control curve, and the interval (DA) where the rotor speed recovers to the speed before the disturbance along the MPPT control curve.

[0014] exist Figure 2 In the middle, P TFS P represents the active power reference value used for synthetic inertial control when a disturbance occurs. Tlim Pm represents the active power value calculated based on the torque limit of the rotating body, and P represents the external input obtained from the rotating body of the wind turbine. MPPT This represents the active power value based on the maximum power point tracking control of the wind turbine generator.

[0015] The advantage of non-patent document 002 is that it allows the rotor speed to converge to a stable range, thereby effectively preventing over-the-top (OD). However, after an interference occurs (AB, BB'), regardless of the size of the interference, a certain amount of active power will be increased and output. Therefore, when the interference is small, the increase in active power of the wind turbine is relatively large. The problem is that the frequency decreases again after exceeding 60Hz, resulting in repeated frequency fluctuations of exceeding and decreasing. Furthermore, the disadvantage is that at low wind speeds, the increase in active power is small, and the improvement in the lowest frequency is low.

[0016] [Preliminary Technology Documents]

[0017] [Non-patent literature]

[0018] (Non-Patent Document 0001) SE Itani, U.D. Annakkage, and G. Joos, “Short-term Frequency Support Utilizing Inertial Response of DFIG Wind Turbines,” IEEE Power and Energy Society General Meeting, vol. 23, no. 2, 2011

[0019] (Non-Patent Document 0002) D. Yang, J. Kim, YCKang, E. Muljadi, N. Zhang, J. Hong, S.-H. Song, and T. Zheng, “Temporary Frequency Support of a DFIG for High Wind Power Penetration”, IEEE Trans. Power Syst., vol. 33, no. 3, pp. 3428-3437, May 2018. Summary of the Invention

[0020] The technical problem to be solved by this invention is to provide a synthetic inertial control method and system for wind turbines, which can adjust the active power differently according to the magnitude of the disturbance, thereby improving the minimum frequency.

[0021] Another technical challenge that this invention aims to address is to provide a synthetic inertial control method and system for a wind turbine, which can prevent a secondary frequency drop during the rotor speed recovery process after an increase in active power output.

[0022] Another technical challenge that this invention aims to solve is to provide a synthetic inertial control method and system for a wind turbine, which does not use an additional energy storage device but only utilizes the kinetic energy stored in the rotating body of the wind turbine, thereby improving system stability at a low cost without incurring additional costs to increase the minimum frequency.

[0023] To address the aforementioned technical challenges, an embodiment of the present invention provides a synthetic inertial control method for a wind turbine generator, comprising the following steps: executing Maximum Power Point Tracking (MPPT) control; detecting the frequency deviation of the power system; and when the frequency deviation exceeds a predetermined value, converting the MPPT control to Temporary Frequency Support (TFS) control. The TFS control includes a first step of calculating and controlling, for a predetermined first time period starting from the point of transition from MPPT control to TFS control (the transition time point), based on an increase in active power reference value between the MPPT control and the original reference value at the transition time point. The increase in active power reference value based on the TFS control can be calculated as a function of the frequency deviation and the rotor speed of the wind turbine generator.

[0024] To address the aforementioned technical challenges, a synthetic inertial control system for a wind turbine according to another embodiment of the present invention includes: a frequency deviation detection unit that detects the frequency deviation of the power system from a reference frequency and a measured system frequency; a rotor speed detection unit that detects the rotor speed of the wind turbine; a switching unit that switches between maximum power point tracking (MPPT) control and temporary frequency support (TFS) control; an active power reference value calculation unit that calculates an active power reference value for wind turbine output control using the frequency deviation and rotor speed; and a control unit that controls the output control of the wind turbine based on the calculated active power reference value. The value is used to control the wind turbine. When the switch unit switches to Temporary Frequency Support (TFS) control, the active power reference value calculation unit calculates the active power reference value that is increased by the maximum power point tracking (MPPT) control compared to the original reference value at the time point of switching to Temporary Frequency Support (TFS) control (the switch time point). The increased active power reference value is calculated as a function of frequency deviation and rotor speed. During a predetermined first time period starting from the switch time point, the control unit performs the first step of control based on the active power reference value calculated as a function of frequency deviation and rotor speed.

[0025] Frequency deviation and rotor speed are detected at specified time intervals, and the active power reference value increased in the first step can be repeatedly calculated by each detected frequency deviation and rotor speed.

[0026] In one or more embodiments, the first time can be the time after the system frequency has recovered from its lowest frequency and the system frequency deviation is within a specified reference value.

[0027] In one or more embodiments, a second step is further included, which involves continuously reducing the active power reference value to converge the rotor speed, and the active power reference value in the second step can be calculated as a function of the rotor speed.

[0028] In one or more embodiments, a third step is further included: reducing the active power reference value during the second time period so that the rotor speed reaches the rotor speed on the MPPT (Maximum power point tracking) control curve, and the active power reference value in the third step can be calculated as a function of rotor speed and time.

[0029] In one or more embodiments, when the rotor speed reaches the rotor speed on the MPPT control curve, the step of terminating the Temporary Frequency Support (TFS) control and resuming MPPT control may also be included.

[0030] In one or more embodiments, the formula for calculating the active power reference value in the first step may include a value obtained by multiplying the control gain, which varies according to the rotor speed, by the frequency deviation.

[0031] In one or more embodiments, the active power reference value in the first step is calculated by the following formula:

[0032] P ref (ω r ,Δf)=k*F(ω r )+a(ω r )*Δf, for t0 <t≤t0+T set

[0033] Here, k is an arbitrary constant, ω r Let F(ω) be the speed of the rotor. r ω is the value that varies with the rotor speed. r The function, α(ω) r ) represents the control gain that varies according to the rotor speed, Δf represents the deviation between the reference frequency and the measured system frequency, and T set For the first time.

[0034] In one or more embodiments, (k g (A constant used for MPPT operations).

[0035] In one or more embodiments, F(ω) r )=ω r n (n is 0 or a natural number).

[0036] In one or more embodiments, the control gain α(ω) varies according to the rotor speed. r This can be expressed by the following formula:

[0037]

[0038] Here, ω max ω is the maximum rotor speed of the wind turbine. min For the minimum rotor speed, G max For ω max The control gain.

[0039] In one or more embodiments, in the second step, on the active power-rotor speed plane, along the curve below the Pm curve connecting a point in the first time step and ω r <ω Tset The line connecting one point within the area reduces the baseline value of active power.

[0040] In one or more embodiments, the active power reference value in the second step is calculated using the following formula:

[0041]

[0042] Here, P ref (T set ) and ω Tset ω represents the baseline value of active power and rotor speed at the point in time after the first time interval. r ω represents the speed of a rotor. min This is the minimum rotor speed.

[0043] In one or more embodiments, the active power reference value for the third step is calculated using the following formula:

[0044]

[0045] Here, ω r k is the speed of the rotor. g ΔP is a constant used for MPPT operations. c The point of convergence of the rotor velocity in the second step ( Figure 5 The active power and k at point C) g ω c 3 The difference, t c ΔT is the time at point C, and ΔT is the second time set at point C to achieve the rotor speed on the MPPT control curve.

[0046] In one or more embodiments, ΔT can be 45 seconds or more.

[0047] In one or more embodiments, the active power reference value calculation unit calculates the active power reference value of the second step that is continuously decreasing as a function of the rotor speed, and the control unit executes the second step control to continuously decrease the active power based on the active power reference value of the second step, thereby converging the rotor speed.

[0048] In one or more embodiments, the active power reference value calculation unit calculates the active power reference value of the third step as a function of rotor speed and time, and in order to make the rotor speed reach the rotor speed on the MPPT control curve, the control unit performs the control of the third step according to the active power reference value of the third step during the second time period.

[0049] In one or more embodiments, when the rotor speed reaches the rotor speed on the MPPT control curve, the switching unit terminates the Temporary Frequency Support (TFS) control and switches back to MPPT control.

[0050] Specific details of other embodiments are included in the detailed description and accompanying drawings.

[0051] The synthetic inertial control method and system for wind turbines according to embodiments of the present invention have the following effects.

[0052] First, after being disturbed, the output is increased by multiplying it by a control gain that is proportional to the frequency deviation and varies according to the rotor speed. Therefore, when the rotor speed is high, the output increase is large, and the minimum frequency rise is significant.

[0053] Second, even when the rotor speed is low, the output is increased according to the magnitude of the interference and OD is prevented, so the minimum frequency rise effect is obvious.

[0054] Third, based on the reduced rotor speed through synthetic inertial control, the control gain will also decrease, thereby reducing the increase in active power output and significantly preventing over-limit (OD) effects.

[0055] Fourth, when performing synthetic inertial control, the MPPT reference value (k g ω r 3 The value also decreases as the rotor speed decreases, thus improving the effect of preventing OD.

[0056] Fifth, compared with existing methods, a lower frequency drop occurs during the recovery of rotor speed.

[0057] The effects of this invention are not limited to those mentioned above, and those skilled in the art can clearly understand other effects not mentioned from the description in the claims. Attached Figure Description

[0058] Figure 1 These are diagrams used to illustrate the prior art of the present invention.

[0059] Figure 2 This is a diagram illustrating another prior art technique of the present invention.

[0060] Figure 3 This is a block diagram illustrating a synthetic inertial control system for a wind turbine according to an embodiment of the present invention.

[0061] Figure 4 This is a sequence diagram illustrating a synthetic inertial control method for a wind turbine according to an embodiment of the present invention.

[0062] Figure 5 This is a diagram illustrating a synthetic inertial control method for a wind turbine according to an embodiment of the present invention on the active power-rotor speed plane.

[0063] Figure 6 This shows the rotor speed ω in mathematical formula 2. r and control gain α(ω) r A diagram showing the relationship between ).

[0064] Figure 7 A test system is shown for verifying the performance of a synthetic inertial control method and system for a wind turbine according to an embodiment of the present invention.

[0065] Figures 8a to 8c These are graphs used to illustrate the results related to Verification Test Example 1 of the present invention.

[0066] Figures 9a to 9c These are graphs used to illustrate the results related to verification test example 2 of the present invention.

[0067] Figures 10a to 10c These are graphs used to illustrate the results related to verification test example 3 of the present invention.

[0068] Label Explanation

[0069] 110: Frequency Deviation Detection Unit; 120: Rotor Speed ​​Detection Unit

[0070] 130: MPPT / TFS control conversion unit; 140: Active power reference value calculation unit.

[0071] 150: Control Department Detailed Implementation

[0072] The advantages, features, and methods of implementing the present invention will become apparent when referring to the accompanying drawings and the detailed embodiments described below. However, the present invention is not limited to the embodiments disclosed below, but is implemented in many different and varied forms. These embodiments are provided only to ensure the completeness of the disclosure of the invention and to fully inform those skilled in the art of the scope of the invention, which is defined solely by the scope of the claims.

[0073] Throughout the instruction manual, the same reference numeral refers to the same constituent element.

[0074] "and / or" includes all combinations of each and more than one of the mentioned items.

[0075] The terminology used in this specification is for illustrative purposes and is not intended to limit the invention. Singular forms in this specification also include plural forms unless specifically stated otherwise. The use of the words "comprising" and / or "comprising..." to refer to constituent elements, steps, operations, and / or components does not preclude the presence or addition of one or more other constituent elements, steps, operations, and / or components.

[0076] Furthermore, throughout the instruction manual, when a part is referred to as being "connected" to other parts, this includes not only "direct connection" but also "indirect" or "electrical connection" with other components or elements in between.

[0077] Furthermore, throughout the specification, descriptions of the formation of each layer (film), region, pattern, or structure on the substrate, each side (film), region, pad, or pattern "on" or "under", include direct formation or formation by intervening with other layers. The references to the upper / lower or lower / upper layers for each layer are explained with reference to the accompanying drawings.

[0078] In addition, expressions such as "the first" and "the second" are only used to distinguish multiple components and do not limit the order or other characteristics between the components.

[0079] Unless otherwise defined, any terminology used in this specification (including technical and scientific terms) may be used in the sense that is commonly understood by one of ordinary skill in the art to which this invention pertains. Unless explicitly defined, terms as defined in commonly used dictionaries should not be interpreted ideally or excessively.

[0080] The present invention will now be described in detail with reference to the accompanying drawings.

[0081] Figure 3This diagram illustrates a synthetic inertial control system for a wind turbine according to an embodiment of the present invention. The wind turbine controlled by the synthetic inertial control system of the present invention may include a wind turbine based on a full converter (Type D) and a wind turbine based on a doubly-fed induction generator (Type C), etc., but the present invention is not limited thereto.

[0082] Reference Figure 3 According to an embodiment of the present invention, the synthetic inertial control system of a wind turbine generator may include a frequency deviation detection unit 110, a rotor speed detection unit 120, an MPPT / TFS control conversion unit 130, an active power reference value calculation unit 140, and a control unit 150.

[0083] The frequency deviation detection unit 110 detects the difference between the reference frequency and the actual measured frequency of the system, i.e., the frequency deviation (Δf). In this invention, although frequency deviation is used, the frequency change rate can be used instead, or a combination of both can be used. Therefore, even if someone replaces the frequency deviation of this invention with the frequency change rate or a combination of both, it remains an equivalent of this invention.

[0084] The rotor speed detection unit 120 detects the rotor speed of the wind turbine.

[0085] When the frequency deviation detected by the frequency deviation detection unit is greater than the specified value, the MPPT / TFS control conversion unit 130 converts the maximum power point tracking (MPPT) control to temporary frequency support (TFS) control.

[0086] Here, a detected frequency deviation greater than the specified value can be considered as an interference in the system. If interference occurs, the kinetic energy of the rotating body of the synchronous generator in the system will be released, the rotor speed of the synchronous generator will decrease, and ultimately the system frequency will decrease.

[0087] In this invention, in order to mitigate this frequency drop, the MPPT control of the wind turbine is converted to TFS, thereby performing output control different from the normal operation described below.

[0088] The active power reference value calculation unit 140 calculates the active power reference value for TFS control based on the frequency deviation detected by the frequency deviation detection unit 110 and the rotor speed detected by the rotor speed detection unit 120.

[0089] The active power reference value calculation unit 140 can calculate the active power reference value for each step of controlling the wind turbine in the following order to deal with the disturbance: the step of increasing active power by releasing rotor kinetic energy (first step), the rotor speed convergence step (second step), the step of moving the rotor speed along the MPPT (Maximum Power Point Tracking) curve (third step), and the step of moving the active power and rotor speed along the MPPT curve to the operating point before the disturbance occurs.

[0090] The control unit 150 controls the active power output of the wind turbine generator based on the active power reference value calculated by the active power reference value calculation unit 120. The control signal from the control unit 150 may include, for example, the form of a current command value, but the present invention is not limited thereto.

[0091] Figure 3 The terms 110 for frequency deviation detection, 130 for MPPT / TFS control conversion, and 140 for active power reference value calculation shown refer to at least one unit of processing function or operation, which can be implemented by software and / or hardware.

[0092] The control unit 150 may be composed of a computing device including a memory that stores a program and a processor that runs the program stored in the memory. The memory may include at least one type of storage medium from various known types. Alternatively, it may operate with web storage or a cloud server that performs storage functions on the Internet.

[0093] The synthetic inertial control system of the wind turbine according to the present invention senses the disturbances generated in the power system, releases the kinetic energy of the rotor according to the magnitude of the disturbance, and adjusts the increase in active power, thereby achieving the effect of increasing the minimum frequency, i.e., reducing the maximum drop in system frequency. The rotor speed recovery does not rely solely on the operating characteristics of AGC (Automatic Generation Control), but rather on a rotor speed convergence step, thus enabling rapid speed recovery. To this end, utilizing... Figure 4 and Figure 5 More detailed explanations will follow.

[0094] Figure 4 This is a sequence diagram illustrating a synthetic inertial control method for a wind turbine according to an embodiment of the present invention. Figure 5 This is a diagram illustrating a synthetic inertial control method for a wind turbine according to an embodiment of the present invention on the active power-rotor speed plane.

[0095] Reference Figure 4According to an embodiment of the present invention, a synthetic inertial control method for a wind turbine may include:

[0096] The steps are as follows: 1) When an disturbance is detected during normal operation of Maximum Power Point Tracking (MPPT) control, switch to Temporary Frequency Support (TFS) control; 2) Control the wind turbine generator with an active power reference value that is increased compared to MPPT control during a specified first time period (first step); 3) After the first time period, continuously reduce the active power reference value to achieve rotor speed convergence (second step); 4) Reduce the active power reference value during a second time period so that the rotor speed after convergence in the second step reaches the rotor speed on the MPPT control curve (third step).

[0097] After the second time interval, the TFS control is switched back to MPPT control, which allows the active power output and rotor speed before the disturbance to be restored along the MPPT curve.

[0098] Figure 5 The reference value (P) of the active power controlled by the synthetic inertial control method of the wind turbine according to an embodiment of the present invention is shown on the active power-rotor speed plane. ref (Charts)

[0099] Simultaneously refer to Figure 4 and Figure 5 During normal operation of wind turbines using maximum power point tracking (MPPT) control, the system's frequency deviation and the wind turbine rotor speed are periodically monitored.

[0100] When it is determined that the power system is disturbed due to the detected frequency deviation, the maximum power point tracking (MPPT) control is converted to temporary frequency support (TFS) control. After conversion to TFS control, the wind turbine is controlled according to the special active power reference value of the present invention.

[0101] The interference referred to here is, for example, a drop in system frequency due to reasons such as the disconnection of generators connected to the power system from the grid, which may cause the system frequency to exceed the deadband. If such interference is detected, the series of processes of this invention for frequency stabilization can be executed. However, this invention is not limited to this; of course, interference occurring in the power system can be detected by other devices besides the system frequency.

[0102] In one or more embodiments, when the power system experiences a disturbance and switches to TFS control, the active power reference value calculation unit 140 calculates the active power reference value based on the rotor speed ω. r The active power reference value (P) for wind turbine output control is calculated as a function of the frequency deviation Δf, i.e., the following mathematical formula 1. ref ).

[0103] [Mathematical Expression 1]

[0104]

[0105] Here, k g It is a constant used for MPPT operations, α(ω) r ) is the control gain based on the rotor speed variation, and T set It refers to the maintenance period of phase AB, i.e., the first moment.

[0106] like Figure 1 and Figure 2 As shown, after interference from non-patent documents 0001 and 0002, the active power P ref It is set as the active power value P0 at the moment of interference plus a certain output increase ΔP, i.e., P ref (t) is calculated as P0 + ΔP. Conversely, according to the synthetic inertial control method of the present invention, it is calculated in relation to the rotor speed ω. r The active power reference value is calculated in a cubic proportional form, which can more effectively prevent OD phenomenon.

[0107] In other words, the combined inertia of a wind turbine releases the kinetic energy stored in the rotating body, thereby increasing the minimum frequency. However, since the kinetic energy stored in the rotating body is finite, excessive release of kinetic energy can induce an over-the-top (OD) phenomenon, where the rotor speed reaches the minimum rotor speed. At low wind speeds, to prevent OD, the increase in output must be reduced, thus the effect of reducing the rise in the minimum frequency, i.e., the maximum decrease in the system frequency, is relatively small.

[0108] However, as shown in mathematical formula 1 of this invention, if k is set to... g ω r 3 During the execution of the synthetic inertial function, this component decreases along with the rotor speed. Therefore, compared with the case where it is set to a constant as in Non-Patent Document 0001 and Non-Patent Document 0002, the effect of preventing OD is greater.

[0109] In one or more other embodiments, k in mathematical formula 1 g ω r 3 It can be set to a constant with a specific value, or it can be set to a value equal to ω. r The relevant non-cubic function kω r 、kω r 2 、kω r 4 、kω r nThe form of the function (here, k is an arbitrary constant) or based on the rotor speed (ω) r Other function forms that change.

[0110] On the other hand, when the second term in mathematical expression 1 is set to α(ω) r When the value is Δf, the active power output can increase proportionally to the magnitude of the interference (i.e., the deviation from the reference frequency due to the change in system frequency caused by the interference). As shown in Non-Patent Documents 0001 and 0002, regardless of the magnitude of the interference, with only a certain increase in output (ΔP), when the interference is small, excessive energy may be released into the system, leading to frequency fluctuations. Furthermore, even when the interference is large, the rise in the lowest frequency is limited because only a certain amount of energy is always released.

[0111] Conversely, according to an embodiment of the invention, since the second term is set to be proportional to Δf, the increase in output is proportionally smaller when the interference is small, thereby preventing frequency fluctuations, and the increase in output is larger when the interference is large, thereby also increasing the effect of the minimum frequency rise accordingly.

[0112] The control gain (α(ω) of the present invention is proportional to the rotational speed r ) is not a constant, but rather has a rotor speed (ω) r The control gain (α(ω)) is a function whose shape allows for a large output to be provided to the system initially during interference, followed by a smaller output later. In other words, because the frequency deviation Δf multiplied by the control gain is small initially during interference, a large output can only be provided to the system when multiplied by a large control gain. Therefore, the control gain (α(ω)) is... r As shown in the following mathematical formula 2, when the rotor speed is high, there is a larger control gain, and when the rotor speed is low, there is a smaller control gain.

[0113] [Mathematical Expression 2]

[0114]

[0115] Here, ω max ω represents the maximum rotor speed of the wind turbine. min G represents the minimum rotor speed. max Represents ω max The control gain. In one or more embodiments, G max It can be set to 80, but is not limited to this, and of course, different values ​​can be set according to system conditions.

[0116] Figure 6 This shows the rotor speed ω in mathematical formula 2. r and control gain α(ω)r A graph showing the relationship between the maximum rotor speed ω and the maximum rotor speed ω. max Set to 1.0, minimum rotor speed ω min The control gain is set to 0.4. In typical frequency-based synthesized inertia methods, the control gain is set to around 20, but the control gain of this invention is at ω. r It has values ​​greater than 20 in the range >0.45, and at the maximum rotor speed ω max The value is set to 80, so the minimum frequency rise effect is better.

[0117] Furthermore, since the control gain of a wind turbine is not constant during the performance of its combined inertia and decreases along with the rotor speed, the control gain will also decrease over time, thus preventing over-the-air (OD) defects.

[0118] In one or more other embodiments, regarding the control gain α(ω) r The mathematical expression 2 can also be realized in various forms that increase along with the rotor speed, rather than in the form of a root function.

[0119] Based on the active power reference value calculated as described above, the control unit 150 performs a certain first time (T) set During this period, the output of the wind turbine is controlled. Here, the first time T... set This can be set to the time until the system frequency recovers and converges to a certain level after passing the lowest frequency. In other words, it can be set to the time until the frequency deviation decreases to within the reference value (|Δf|≤ reference value) or the rate of frequency change decreases to within the reference value. The time.

[0120] For example, the first time T set It can be set to the time until a change in system frequency within 0.1% is detected.

[0121] In non-patent literature 0002, in order to release as little kinetic energy as possible, the active power P is maintained. ref The time is set to the lowest frequency time (t). FN The first time T in this invention is the time required for the system frequency to reach its lowest point after interference occurs. set The time until the system frequency rises back to a certain level after passing the lowest frequency is set, and is therefore set to a value relatively larger than that in Non-Patent Document 0002. Nevertheless, the present invention, due to the previously described control gain α(ω) r (e.g., can maintain the effect of preventing OD.)

[0122] Refer again Figure 4 After the first step of control, after the first time (T) setAfter that, by continuously reducing the active power reference value, the step of converging the rotor speed (second step) is executed. This is equivalent to... Figure 5 The active power reference value P is located between BC and BC. ref Along the connection first time T set One point in (ω) Tset P ref (T set The point of minimum rotor speed (ω) min The linear relationship between , 0) decreases as shown in the following mathematical formula 3.

[0123] [Mathematical Expression 3]

[0124]

[0125] When the active power P ref When following mathematical formula 3, the rotor speed converges to point C, i.e. (ω c P ref (ω c Point C is the point where the active power output of the wind turbine and the mechanical input of the wind turbine become the same, equivalent to... Figure 5 The green curve representing the mechanical input of the wind turbine is shown in Figure 3, and the point where it intersects with the straight line shown in Equation 3.

[0126] On the other hand, if the active power baseline value of mathematical formula 3 continues to decrease in the BC interval, it can also be realized in the form of a parabola or a polynomial function, rather than just having a one-dimensional straight line slope.

[0127] In addition, Figure 5 In order to make the rotor speed converge to a point on the green curve (Pm curve), a path was used along the connection point B and the point (ω). min The linear decrease in active power reference value is 0, but here it is specified as point (ω). min A point that is 0 is not necessarily (ω) min For any point (0), as long as it is below the Pm curve and is ω r <ω Tset Only one point in the region is needed. Therefore, it can be achieved by connecting point B and Pm below the curve where ω r <ω Tset A function that sets the active power baseline value for a point in the region using various functions.

[0128] The rotor speed convergence condition for terminating the second step can be set to ensure that the rotor speed change is within a specified value (e.g., |Δω|≤10) over a specified time interval (e.g., the wind turbine output control time interval of 260 μsec). -4 ).

[0129] Through the control in the second step, when the rotor speed converges to point C, the reduced rotor speed control is restored. To bring the wind turbine's rotor speed to the level on the MPPT control curve, the third step (reducing the active power reference value during the second time period) is equivalent to... Figure 5 The CD interval, at this time the active power reference value P ref It can be calculated using the following mathematical formula 4.

[0130] [Mathematical Expression 4]

[0131]

[0132] Here, k g This refers to the constant used in MPPT operations, ΔP c The active power at point C and k g ω c 3 The difference between them, t c ΔT refers to the time at point C, and ΔT refers to the second time set at point C to reach the MPPT curve.

[0133] Equation 4 shows the P value of the rotor speed reaching the MPPT curve after a time interval ΔT. ref .

[0134] In non-patent document 0002, ΔT is set to 15 seconds in order to quickly restore the rotor speed. In this case, the rotor speed recovers quickly, but a large frequency drop may occur in the CD range. In severe cases, the frequency may drop below 59.8Hz, the AGC stops working, and the frequency may not be able to recover to 60Hz.

[0135] Therefore, in this invention, ΔT is set to ≥ 45s in order to minimize the magnitude of the frequency drop that may occur during the third step of control. In this case, the rotor speed recovery may be slower than in Non-Patent Literature 0002, but it prevents the AGC from stopping due to the frequency drop that occurs during the rotor speed recovery process, thus avoiding slowing down the frequency recovery to 60Hz.

[0136] Although the second term of mathematical expression 4 has ΔP C The form that linearly decreases to 0 over time, but the present invention is not limited to this; for example, ΔP C This can be achieved using various functions, including polynomial functions that allow ΔT to subsequently become 0dl.

[0137] When the second time (ΔT) controlled by the third step is reached, P ref Upon reaching point D on the MPPT curve, the TFS control switches back to Maximum Power Point Tracking (MPPT) control. Afterwards, P... refMove along the MPPT curve to point A, thus restoring the operating point before the disturbance.

[0138] exist Figure 5 The related description describes setting an active power reference value for power control of a wind turbine generator on the active power-rotor speed plane. However, since torque can be obtained by dividing active power by rotor speed, the active power reference value P proposed in this invention... ref The same method can be implemented even on the torque-rotor speed plane.

[0139] The following describes the verification test results that compare the synthetic inertial control results according to the embodiments of the present invention with those of conventional control methods.

[0140] To verify the performance of the synthetic inertial control method and system according to the present invention, as shown in the example... Figure 7 The test system shown. Figure 7 This is a modified IEEE 14 bus system. The original IEEE 14 bus system included five synchronous generators, loads, and a transmission system (including a distribution system), with a total load of approximately 300MW. SG4, with a rated capacity of 60MVA, which was connected to bus 8 of the IEEE 14 bus system, was disconnected from the system, and the PMSG wind power generation park with a capacity of 66MVA was connected to bus 9. As interference, SG2 was disconnected from the system within 10 seconds. The performance of this invention was compared and verified using different wind speeds and interference magnitudes.

[0141] The verification test results applicable to the above test systems are illustrated with reference to Figures 8 to 10.

[0142] [Verification Experiment Example 1]

[0143] Verification test example 1 was conducted under the conditions of wind speed 9 m / s and interference magnitude 36 MW. The system frequency was illustrated in graphs for MPPT operation, application of the method in non-patent literature 0001 (2011), application of the method in non-patent literature 0002 (2018), application of the embodiment of this invention (Proposed), and application of only a synchronous generator (No WPP). Figure 8a Wind farm output Figure 8b and rotor speed ( Figure 8c The result of ).

[0144] The lowest frequency during MPPT operation is 59.499 Hz, which is 0.501 Hz lower than the rated frequency (reference frequency) and 0.015 Hz lower than the case consisting only of a synchronous generator. Non-Patent Document 0001 shows 59.676 Hz, and Non-Patent Document 0002 shows 59.728 Hz, but the case constructed according to the embodiment of the present invention shows 59.732 Hz, exhibiting the highest improvement in the lowest frequency.

[0145] Looking at the output of the wind farm after the interference, the output of the method in Non-Patent Document 0001 increased by 10%, remained for 6 seconds, and then decreased; the output of the method in Non-Patent Document 0002 increased by 15.46%, remained for 3 seconds, and then decreased. With the configuration according to the embodiment of the present invention, it can be observed that the output increases in a manner proportional to the frequency deviation after the interference, and the output increases by more than 10% compared to the method in Non-Patent Document 0002 during a longer 6-second period. Figure 8a As explained, this resulted in an improvement in the lowest frequency, and no frequency fluctuations were observed.

[0146] Regarding rotor speed, the method according to the embodiment of the present invention releases more kinetic energy than the method in non-patent document 0002, which may result in an increase in the minimum frequency. Furthermore, in the case of the present invention, although rotor speed recovery is slower than the method in non-patent document 0002, a more favorable magnitude of frequency drop and change can be observed during rotor speed recovery.

[0147] [Verification Experiment Example 2]

[0148] Verification test example 2 had a wind speed of 9 m / s and an interference magnitude of 54 MW, approximately 1.4 times that of the first example, with the same wind speed. The system frequency is shown in graphs for MPPT operation, the application of the method in non-patent literature 0001 (2011), the application of the method in non-patent literature 0002 (2018), the application of the embodiment of this invention (Proposed), and the case consisting only of a synchronous generator (No WPP). Figure 9a ), wind power park output ( Figure 9b and rotor speed ( Figure 9c The result of ).

[0149] The lowest frequency during MPPT operation is 58.678 Hz, which is 1.313 Hz lower than the rated frequency (reference frequency) and 0.112 Hz lower than the case consisting only of a synchronous generator. Non-Patent Document 0001 shows 59.003 Hz, and Non-Patent Document 0002 shows 59.146 Hz, but the configuration according to the embodiment of the present invention shows 59.396 Hz, representing an improvement of 54.0% in the lowest frequency, which is 19% higher than the method in Non-Patent Document 0002.

[0150] Looking at the output of the wind farm after the interference, the output of the method in Non-Patent Document 0001 increased by 10%, remained for 6 seconds, and then decreased. The output of the method in Non-Patent Document 0002 increased by 15.46%, remained for 3 seconds, and then decreased. Even with an increase in the magnitude of the interference, the same output was provided. Conversely, in the configuration according to the embodiment of the present invention, the output is increased in a manner proportional to the frequency deviation after the interference, and the increased output is delivered over a longer period of 6 seconds compared to the method in Non-Patent Document 0002. Furthermore, in the step of shifting the active power to the MPPT curve, the output decrease is smaller than that in the method in Non-Patent Document 0002, and the frequency decrease is also smaller.

[0151] Regarding the rotor speed, it can be observed that the method according to the embodiment of the present invention releases more kinetic energy than the method of non-patent document 0002, and also releases more kinetic energy than verification test example 1. Furthermore, in the case of the present invention, although the rotor speed recovery is slower than the method of non-patent document 0002, it can be observed that the magnitude of the system frequency drop and change during the rotor speed recovery process is superior.

[0152] [Verification Experiment Example 3]

[0153] Verification Test Example 3, with a wind speed of 5 m / s and an interference magnitude of 54 MW, has the same interference magnitude as Verification Test Example 2, but due to the low wind speed, very little kinetic energy can be released. The system frequency is shown in graphs for MPPT operation, the application of the method in Non-Patent Document 0001 (2011), the application of the method in Non-Patent Document 0002 (2018), the application of the embodiment of this invention (Proposed), and the case consisting only of a synchronous generator (No WPP). Figure 10a ), wind power park output ( Figure 10b and rotor speed ( Figure 10c The result of ).

[0154] The lowest operating frequency of the MPPT is 58.723 Hz, which is 0.076 Hz lower than when it consists of only a synchronous generator.

[0155] From the perspective of the wind farm output after the interference, as shown in verification test examples 1 and 2 of non-patent literature 0001, the aim is to increase the output by 10% and maintain it for 6 seconds, but the amount of kinetic energy that can be released is small. After 3 seconds, the minimum rotor speed is reached, and OD (refer to) is generated. Figure 10c Therefore, as the synthesis inertia is interrupted and returns to MPPT, the output drops rapidly (see reference). Figure 10b The lowest frequency is 58.982 Hz.

[0156] The method in non-patent literature 0002 also releases less kinetic energy, thus far less than in verification test examples 1 and 2. After increasing by 1.09%, it was maintained for 3 seconds and then decreased again (see reference). Figure 10b In this case, although no OD occurred, the lowest frequency was 58.758 Hz, which was 0.388 Hz lower than that of verification test example 2, so it was difficult to expect an increase in the lowest frequency.

[0157] Conversely, in the configuration according to the embodiment of the present invention, during the step of increasing active power proportional to the frequency deviation after interference, the increased output is delivered over a longer period of 6 seconds compared to the method of Non-Patent Document 0002. Furthermore, although there is a range with a larger increase in output than the method of Non-Patent Document 0001, the control gain decreases as the rotor speed decreases, thus preventing over-displacement (OD). The lowest frequency is 58.972 Hz, which is 0.214 Hz higher than the method of Non-Patent Document 0002.

[0158] On the other hand, the steps of the control method according to the present invention can be implemented in the form of program instructions executed by a processor of a computing device and can be recorded in a computer-readable medium. Examples of computer-readable recording media include, but are not limited to, hard disks, ROMs, RAMs, CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, etc.

[0159] Although the invention has been described above, those skilled in the art will recognize that it may be implemented in other forms while maintaining the technical concept and essential features of the invention.

[0160] Although the scope of the invention is essentially defined by the patent claims, it should be interpreted that all modifications or variations derived directly from the contents of the patent claims, as well as from equivalent contents, are included within the scope of the invention.

Claims

1. A synthetic inertia control method of a wind power generator, as a synthetic inertia control method according to a control system of a wind power generator, characterized by, comprises the following steps: performing maximum power point tracking (MPPT) control; detecting a frequency deviation of the power system; when the frequency deviation is greater than a prescribed value, switching the maximum power point tracking (MPPT) control to temporary frequency support (TFS) control, the temporary frequency support (TFS) control comprises a first step, for a prescribed first time period from a time point (switching time point) of switching from the maximum power point tracking (MPPT) control to the temporary frequency support (TFS) control, performing calculation and control based on an active power reference value that is increased from a reference value of the maximum power point tracking (MPPT) control at the switching time point, the active power reference value according to the temporary frequency support (TFS) control is calculated as a function of the frequency deviation and the rotor speed of the wind power generator.

2. The synthetic inertia control method of a wind power generator according to claim 1, characterized by, Further comprising: a second step of converging the rotor speed by continuously decreasing the active power reference value; a third step of decreasing the active power reference value for a second time period so that the rotor speed reaches a rotor speed on the MPPT control curve; when the rotor speed reaches the rotor speed on the MPPT control curve, terminating the temporary frequency support (TFS) control and resuming the step of the MPPT control, the active power reference value in the second step is calculated as a function of the rotor speed, the active power reference value in the third step is calculated as a function of the rotor speed and time.

3. The synthetic inertia control method for a wind power generator according to claim 1, wherein the expression for calculating the active power reference value in the first step comprises a control gain that varies according to the rotor speed multiplied by a value obtained by the frequency deviation.

4. The synthetic inertia control method for a wind power generator according to claim 3, wherein the active power reference value in the first step is calculated by the following expression: P ref (ω r ,Δf)=k*F(ω r )+a(ω r )*Δf, for t0<t≤t0+T set (k g for MPPT operation), Here, k is an arbitrary constant, ω r is the speed of the rotor, F(ω r ) is a function of ω r that varies according to the speed of the rotor, a(ω r ) is a control gain that varies according to the speed of the rotor, Af is the deviation of the reference frequency and the measured system frequency, and T set is the first time.

5. The synthetic inertia control method for a wind power generator according to claim 4, wherein F(ωr) = ω r n (n is 0 or a natural number).

6. The synthetic inertia control method for a wind power generator according to claim 4, wherein The control gain a(ω) that varies in accordance with the rotor speed is expressed by the following equation: r ) is expressed by the following equation: Here, ω max is the maximum rotor speed of the wind turbine, ω min is the minimum rotor speed, G max is the control gain of ω max .

7. The synthetic inertia control method for a wind power generator according to claim 2, wherein In the second step, in the active power - rotor speed plane, the reference value of the active power is reduced along the line connecting a point in the first time and a point in the area under the Pm curve and ω r <ω Tset in the first time and a point in the area under the Pm curve and ω 8. The synthetic inertia control method for a wind power generator according to claim 2, wherein the active power reference value in the second step is calculated by the following expression: Here, P ref (T set ) and ω Tset are the active power reference value and the rotor speed at the time point after the first time, ω r is the speed of the rotor, and ω min is the minimum rotor speed.

9. The synthetic inertia control method for a wind power generator according to claim 2, wherein the active power reference value in the third step is calculated by the following expression: Here, ω r is the speed of the rotor, k g is a constant for MPPT operation, ΔP c is the active power at the point of convergence of the rotor speed in the second step (point C of Fig. 5) and k g ω c 3 is the difference, t c is the time at point C, and ΔT is the second time set at point C in order to reach the rotor speed on the MPPT control curve.

10. The synthetic inertia control method for a wind power generator according to claim 1, wherein the first time is a time when the system frequency deviation is within a prescribed reference value after the system frequency has risen past a minimum frequency.

11. A synthetic inertia control system for a wind power generator, as a synthetic inertia control system for a wind power generator, characterized by, comprises: a frequency deviation detection unit that detects a frequency deviation of the power system from a reference frequency and a measured system frequency; a rotor speed detection unit that detects the rotor speed of the wind power generator; a switching unit that switches between the maximum power point tracking (MPPT) control and the temporary frequency support (TFS) control; an active power reference value calculating section that calculates an active power reference value for output control of the wind power generator using the frequency deviation and the rotor speed; and a control section that controls the wind power generator in accordance with the calculated active power reference value, when the conversion section is converted to temporary frequency support (TFS) control, the active power reference value calculating section calculates an active power reference value that is increased from the original reference value in accordance with maximum power point tracking (MPPT) control at the point in time (conversion point in time) at which the conversion to temporary frequency support (TFS) control is made, the increased active power reference value is calculated as a function of the frequency deviation and the rotor speed, the control section performs the first step of control in accordance with the active power reference value calculated as a function of the frequency deviation and the rotor speed for a prescribed first time period from the conversion point in time.

12. The synthetic inertia control system for a wind power generator according to claim 11, characterized in that the active power reference value calculating section calculates the active power reference value of the second step that is continuously decreased as a function of the rotor speed, and calculates the active power reference value of the third step as a function of the rotor speed and time, the control section performs the second step of control in which the active power reference value of the second step is used to continuously decrease the active power so as to converge the speed of the rotor, and performs the third step of control in which the active power reference value of the third step is used to control the speed of the rotor so as to reach the rotor speed on the MPPT control curve for a second time period, when the speed of the rotor reaches the rotor speed on the MPPT control curve, the conversion section terminates the temporary frequency support (TFS) control and again converts to MPPT control.

13. The synthetic inertia control system for a wind power generator according to claim 11, characterized in that the expression used to calculate the active power reference value of the first step includes a control gain that varies in accordance with the speed of the rotor multiplied by a value obtained from the frequency deviation.

14. The synthetic inertia control system for a wind power generator according to claim 13, characterized in that the active power reference value used to control the first step is calculated by the following expression: P ref (ω r ,Δf) = k * F(ω r ) + a(ω r ) * Δf, for t0< t < t0+ T set (kg is a constant for MPPT operation), Here, k is an arbitrary constant, ω r is the speed of the rotor, F(ω r ) is a function of ω r that varies according to the speed of the rotor, a(ω r ) is a control gain that varies according to the speed of the rotor, Af is the deviation of the reference frequency and the measured system frequency, and T set is the first time.

15. The synthetic inertia control system for a wind power generator according to claim 14, characterized in that F(ω r ) = ω r n (n is 0 or a natural number).

16. The synthetic inertia control system for a wind power generator according to claim 14, characterized in that The control gain a(ω) that varies in accordance with the rotor speed is expressed by the following equation: r ) is expressed by the following equation: Here, ω max is the maximum rotor speed of the wind turbine, ω min is the minimum rotor speed, G max is the control gain of ω max .

17. The synthetic inertia control system for a wind power generator according to claim 12, characterized in that The second step control is a control to reduce the reference value of the active power along a line connecting a point in the first time and a point in the region under the Pm curve and ω r <ω Tset in the active power-rotor speed plane.

18. The synthetic inertia control system for a wind power generator according to claim 12, characterized in that the active power reference value used for the second step of control is calculated by the following expression: Here, P ref (T set ) and ω Tset are the active power reference value and the rotor speed at the time point after the first time, ω r is the speed of the rotor, and ω min is the minimum rotor speed.

19. The synthetic inertia control system for a wind power generator according to claim 12, characterized in that the active power reference value used for the third step of control is calculated by the following expression: Here, ω r is the speed of the rotor, k g is a constant for MPPT operation, ΔP c is the active power at the point of convergence of the rotor speed in the second step (point C of Fig. 5) and k g ω c 3 is the difference value, t c is the time at point C, and ΔT is the second time set at point C in order to reach the rotor speed on the MPPT control curve.

20. The synthetic inertia control system for a wind power generator according to claim 11, characterized in that the first time period is a time period in which the system frequency deviation is within a prescribed reference value after the system frequency has risen past the minimum frequency.

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