Frequency control method and device based on overspeed load shedding and direct current cooperation of doubly-fed wind turbine generator and medium

Abstract

The invention discloses a frequency control method and device based on overspeed load shedding and direct current cooperation of a doubly-fed wind turbine generator and a medium, and belongs to the technical field of wind power integration. The method comprises the steps that when a sending end power grid system is disturbed, the initial frequency change rate X0 under disturbance power Pd is obtained; according to the initial frequency change rate X0, judging whether the sending-end power grid system is in an abnormal operation state or not; when the system is in an abnormal operation state, a conventional unit of a sending-end power grid system and a wind turbine generator jointly participate in frequency modulation, in the frequency modulation process, the wind turbine generator adopts overspeed load shedding control frequency modulation, whether the initial frequency change rate X0 is larger than the limit frequency change rate X2 of the overspeed load shedding control frequency modulation or not is judged, if yes, a direct-current frequency limiter participates in frequency modulation, and if not, the direct-current frequency limiter does not participate in frequency modulation. Searching an optimal parameter set of the direct-current frequency limiter and overspeed load shedding cooperative control; and if not, keeping the current overspeed load shedding control frequency modulation. The system frequency modulation requirement can be met under the working condition of large disturbance, and the frequency modulation capacity of the wind turbine generator is effectively utilized.

Description

Technical Field

[0001] The present invention belongs to the technical field of wind power grid connection, and in particular relates to a frequency control method, device and medium based on overspeed load reduction and direct current coordination of a doubly-fed wind turbine set. Background Art

[0002] Wind energy has become one of the most promising new energy sources due to its renewable, pollution-free and economical nature. Wind power is random and intermittent. As the penetration rate of wind power continues to increase, the problems of low inertia and weak frequency regulation capabilities of the power grid at the sending end will become more prominent, and the frequency stability of the power system will become increasingly severe. With the large-scale grid connection of wind turbines, the system inertia and frequency control capabilities have significantly decreased. In order to ensure the safe and stable operation of the system, wind turbines need to have active power control and frequency regulation capabilities similar to synchronous units.

[0003] At present, the strategies for wind turbines to participate in system frequency regulation are mainly divided into frequency regulation using rotor kinetic energy and power reserve frequency regulation. Although rotor kinetic energy frequency regulation can suppress the high frequency of the system by gradually absorbing the rotor kinetic energy of the wind turbine, it is economical, but it cannot absorb the rotor kinetic energy for a long time and is only suitable for short-term frequency regulation. Power reserve frequency regulation mainly provides continuous power support for the system by reserving some active reserve. However, the current power reserve frequency regulation of wind turbines mainly focuses on the strategy research of increasing the reserve power to a greater extent, and less consideration is given to the effective use of reserve power by wind turbines in the stage of participating in the grid frequency regulation. In addition, since the sending-end grid is affected by the upper limit of the rotor speed of the wind turbine, if the power reserve provided is small, it may not meet the system frequency regulation requirements under large disturbance conditions. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a frequency control method, device and medium based on overspeed load reduction and DC coordination of a doubly-fed wind turbine set, which can meet the system frequency regulation requirements under large disturbance conditions and effectively utilize the frequency regulation capability of the wind turbine set.

[0005] The present invention provides the following technical solutions:

[0006] In a first aspect, a frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine generator system is provided, comprising:

[0007] When the sending-end power grid system is disturbed, according to the disturbance power P d , get the disturbance power P d The initial frequency change rate X0 under

[0008] According to the disturbance power P d The initial frequency change rate X0 under the condition is used to judge whether the power grid system at the sending end is in an abnormal operating state;

[0009] When the system is in an abnormal operating state, the conventional units and wind turbines of the sending-end power grid system jointly participate in frequency modulation. During the frequency modulation process, the wind turbines use overspeed load reduction control frequency modulation and judge the disturbance power P d Whether the initial frequency change rate X0 under overspeed load shedding control is greater than the limit frequency change rate X2 of overspeed load shedding control frequency modulation, if so, the DC frequency limiter participates in the frequency modulation, and finds the optimal set of parameters for the DC frequency limiter and overspeed load shedding coordinated control to control the frequency of the sending-end power grid system; if not, maintain the current overspeed load shedding control frequency modulation, and control the frequency of the sending-end power grid system.

[0010] Optionally, the specific process of determining whether the power grid system at the sending end is in an abnormal operating state is as follows: determining the disturbance power P d Whether the initial frequency change rate X0 under the condition exceeds the initial frequency change rate X1 corresponding to the system when it runs continuously at the frequency upper limit, if so, the system is in an abnormal operating state, otherwise, it is in a normal operating state.

[0011] Optionally, the initial frequency change rate X1 corresponding to the upper frequency limit during continuous operation and the disturbance power P are obtained. d The initial frequency change rate X0 under the condition is as follows:

[0012] Construct the first frequency response model of the sending-end power grid system when overspeed load shedding and DC frequency regulation are not required;

[0013] The expression of the first frequency response model is:

[0014]

[0015] Among them, Δω1(t) is the system frequency deviation value when there is no need for overspeed load reduction and DC frequency modulation at time t, is any disturbance power when overspeed load shedding and DC frequency modulation are not required; α, l', ω n1 and φ are parameters used to simplify the formula, R is the speed regulator adjustment coefficient, D is the damping coefficient, ω r is the wind turbine rotor speed, K m is the mechanical power gain coefficient, T R is the turbine reheat time constant, H is the conventional unit inertia time constant, F H is the turbine reheat constant;

[0016] According to the first frequency response model, the disturbance power P is obtained. d The initial frequency change rate X0 under

[0017]

[0018] Among them, φ1 is a parameter used to simplify the formula;

[0019] According to the first frequency response model, an initial frequency change rate X1 corresponding to the upper frequency limit during continuous operation is obtained;

[0020]

[0021] Among them, ΔP1 is the disturbance power corresponding to the system when the upper frequency limit is continuously running, t'0 is the time when the system reaches the frequency deviation peak when the upper frequency limit is continuously running, It is the peak value of system frequency deviation when the system runs continuously at the upper frequency limit.

[0022] Optionally, the determination of disturbance power P step Whether the initial frequency change rate X0 under the overspeed load shedding control frequency modulation is greater than the limit frequency change rate X2 of the overspeed load shedding control frequency modulation, including: obtaining the limit frequency change rate X2 of the overspeed load shedding control frequency modulation;

[0023] The specific process of obtaining the limit frequency change rate X2 of overspeed load reduction control frequency modulation is:

[0024] According to the maximum operating power tracking curve equation and the load reduction power tracking curve equation of the wind turbine generator set, the relationship between the speed at the load reduction point and the speed at the maximum operating power tracking point is obtained;

[0025] According to the relationship between the speed at the load reduction point and the speed at the maximum operating power tracking point, the limit frequency modulation power ΔP of the wind turbine is obtained. emax ;

[0026] Construct the second frequency response model of the sending-end power grid system during overspeed load shedding and frequency regulation;

[0027]

[0028] According to the limit frequency modulation power ΔP of the wind turbine emax and the second frequency response model, to obtain the limiting frequency change rate X2 of the overspeed load reduction control frequency modulation;

[0029]

[0030] Among them, Δω2(t) is the system frequency deviation value when overspeed load reduction frequency regulation at time t, is any disturbance power during overspeed load shedding frequency modulation; α, l, ω n , φ and φ1 are parameters used to simplify the formula, R is the speed regulator adjustment coefficient, D is the damping coefficient, ω r is the wind turbine rotor speed, K m is the mechanical power gain coefficient, T R is the turbine reheat time constant, H is the conventional unit inertia time constant, F His the turbine reheat constant; ΔP1 is the disturbance power corresponding to the continuous operation of the system at the upper frequency limit; ΔP2 is the disturbance power of the system at the overspeed load reduction frequency regulation limit; t0 is the time when the system reaches the frequency deviation peak when the system is at the overspeed load reduction frequency regulation limit. K is the peak value of system frequency deviation when the system is at the overspeed load reduction frequency regulation limit. d is the droop control coefficient.

[0031] Optionally, the maximum operating power tracking curve equation of the wind turbine generator set is:

[0032]

[0033] The load shedding power tracking curve equation is:

[0034]

[0035] The speed at the load reduction point ω opt and the maximum operating power tracking point speed ω de0 The relationship between them is:

[0036]

[0037] The limit frequency modulation power ΔP of the wind turbine emax for:

[0038]

[0039] Among them, k de0 is the load shedding power tracking factor, P opt is the active power at the maximum operating power tracking operating point, P de0 is the active power at the load reduction point, d is the load reduction rate of the wind turbine, ρ is the air density, C p is the wind energy utilization coefficient, λ opt is the tip speed ratio of the wind turbine; R0 is the blade radius of the wind turbine.

[0040] Optionally, the DC frequency limiter participates in frequency modulation, and an optimal set of parameters for coordinated control of the DC frequency limiter and overspeed load reduction is found to control the frequency of the sending-end power grid system. The specific process is as follows:

[0041] Obtain the DC power modulation amount when the system frequency deviation exceeds the DC frequency limiter dead zone;

[0042] Construct the third frequency response model of the sending-end power grid system during overspeed load shedding and DC coordinated frequency regulation;

[0043] According to the third frequency response model and the DC power adjustment amount, a first objective function and a first constraint condition of the droop control coefficient of the wind turbine set, a second objective function and a second constraint condition of the inertia coefficient of the wind turbine set, a third objective function and a third constraint condition of the DC frequency limiter control parameter, and a fourth objective function and a fourth constraint condition of the frequency regulation cost are designed;

[0044] According to all the objective functions and corresponding constraints, the optimal set of wind turbine droop control coefficient, wind turbine inertia coefficient, DC frequency limiter control parameters and frequency regulation cost is found to control the frequency of the sending-end power grid system so that the sending-end power grid system can be restored to stability.

[0045] Optionally, the DC power modulation amount ΔP FLC :

[0046] ΔP FLC =K F Δω

[0047] Among them, K F is the DC frequency limiter control parameter, Δω is the system frequency change;

[0048] The expression of the third frequency response model is:

[0049]

[0050] Where Δω(t) is the system frequency deviation value when overspeed load reduction and DC frequency limiter coordinate frequency regulation at time t, P step is any disturbance power during overspeed load shedding and DC frequency limiter coordinated frequency modulation; α, l, ω n , φ and φ1 are parameters used to simplify the formula, R is the speed regulator adjustment coefficient, D is the damping coefficient, ω r is the wind turbine rotor speed, K m is the mechanical power gain coefficient, T R is the turbine reheat time constant, H is the conventional unit inertia time constant, F H is the turbine reheat constant, K d is the droop control coefficient.

[0051] Optionally, the first objective function F1 is:

[0052] F1=λ1f1+λ2f2

[0053] f1=minΔf max

[0054] f2=min{P opt -P st}

[0055] Where f1 is the maximum system frequency deviation Δf max The objective function is as small as possible, f2 is the objective function of the difference between the system MPPT point power and the steady-state operation point power; P opt is the system MPPT point power, P st is the power at the steady-state operating point, λ1 and λ2 are the weights of f1 and f2 respectively;

[0056] The first constraint condition is:

[0057] ω de0 <ω st <1.3pu

[0058] Among them, ω de0 is the maximum operating power tracking point speed, ω st is the speed at the steady-state operating point, pu is the per-unit value of the rated speed relative to the set reference value;

[0059] The second objective function F2 is:

[0060]

[0061] in, is the initial frequency change rate when the DC frequency limiter and overspeed load reduction coordinated control are adopted;

[0062] The second constraint is:

[0063]

[0064] Among them, K p is the virtual inertia coefficient, P de0 is the active power at the load reduction point, P ref,min and P ref,max They are the upper and lower limits of wind turbine converter power respectively;

[0065] The third objective function F3 is:

[0066] F3=λ3f3+λ4f4

[0067] f3=min(Δω)

[0068] f4=min(ΔP FLC )

[0069] Among them, λ3 and λ4 are the weights of f3 and f4 respectively, Δω is the system frequency deviation, ΔP FLC is the DC power modulation amount;

[0070] The third constraint condition is:

[0071] 0<P FLC<1.2P den

[0072] Among them, P FLC is the DC frequency limiter output power, P den is the DC rated power;

[0073] The fourth objective function F4 is:

[0074] F4=max(ΔE1-ΔE2)

[0075]

[0076] ΔE2=(P opt -P de0 )t s

[0077] The fourth constraint condition is:

[0078] 0≤d≤0.15pu

[0079] Among them, ω de0 is the maximum operating power tracking point speed, ω opt is the speed at the load reduction point, H s is the moment of inertia of the fan, t s is the sampling interval, and d is the load reduction rate of the wind turbine.

[0080] In a second aspect, a computer device is provided, comprising a processor and a memory; wherein, when the processor executes a computer program stored in the memory, the steps of the frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine set as described in any one of the first aspects are implemented.

[0081] In a third aspect, a computer-readable storage medium is provided for storing a computer program; when the computer program is executed by a processor, the steps of the frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine set as described in any one of the first aspects are implemented.

[0082] Compared with the prior art, the present invention has the following beneficial effects:

[0083] The present invention adopts the system frequency change rate as the frequency regulation index, which can not only complete the frequency regulation more quickly and shorten the time when the system is in an abnormal operating state, but also reduce the system frequency deviation and make the sending-end power grid system more stable; in addition, the present invention can judge whether the current system adopts overspeed load reduction frequency regulation or overspeed load reduction and DC frequency limiter coordinated frequency regulation control strategy according to the value of the system frequency change rate, which can give full play to the frequency regulation potential of the wind turbine set and meet the system frequency regulation requirements under large disturbance conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Figure 1It is an overall flow chart of the frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine generator set of the present invention;

[0085] Figure 2 It is a schematic diagram of the relationship between the output power and the rotation speed of the wind turbine generator set when the load suddenly decreases according to the present invention;

[0086] Figure 3 It is a control principle diagram of the DC frequency limiting controller of the present invention;

[0087] Figure 4 It is a schematic diagram of a third frequency response model including a wind turbine generator set and a DC frequency limit controller of the present invention;

[0088] Figure 5 It is a schematic diagram of the optimal load reduction rate corresponding to different wind speeds considering the constraint conditions of the present invention. DETAILED DESCRIPTION

[0089] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0090] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the term "comprising" and any variation thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0091] Example 1

[0092] like Figure 1 As shown, a frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine generator set is provided, comprising:

[0093] Step S1: When the power grid system at the sending end is disturbed, according to the disturbance power P of the power grid system at the sending end d , get the disturbance power P d The initial frequency change rate X0 under.

[0094] Step S2: According to the disturbance power P d The initial frequency change rate X0 under the condition is used to determine whether the sending-end power grid system is in an abnormal operating state.

[0095] The method for judging whether the power grid system at the sending end is in an abnormal operating state is as follows: d Whether the initial frequency change rate X0 under the condition exceeds the initial frequency change rate X1 corresponding to the system when it runs continuously at the frequency upper limit, if so, the system is in an abnormal operating state, otherwise, it is in a normal operating state.

[0096] Obtain the initial frequency change rate X1 corresponding to the upper limit of the frequency during continuous operation and the obtained disturbance power P d The initial frequency change rate X0 under the condition is as follows:

[0097] Step a: construct the first frequency response model of the sending-end power grid system when overspeed load shedding and DC frequency regulation are not required;

[0098] The expression of the first frequency response model is:

[0099]

[0100]

[0101] Among them, Δω1(t) is the system frequency deviation value when there is no need for overspeed load reduction and DC frequency modulation at time t, is any disturbance power when overspeed load shedding and DC frequency modulation are not required; α, l', ω n1 and φ are parameters used to simplify the formula, R is the speed regulator adjustment coefficient, D is the damping coefficient, ω r is the wind turbine rotor speed, K m is the mechanical power gain coefficient, T R is the turbine reheat time constant, H is the conventional unit inertia time constant, F H is the turbine reheat constant;

[0102] Step b: According to the first frequency response model, obtain the disturbance power P d The initial frequency change rate X0 under

[0103]

[0104] Among them, φ1 is a parameter used to simplify the formula;

[0105] Step c: according to the first frequency response model, obtaining the initial frequency change rate X1 corresponding to the upper frequency limit during continuous operation;

[0106]

[0107] Among them, ΔP1 is the disturbance power corresponding to the system when the upper frequency limit is continuously running, t'0 is the time when the system reaches the frequency deviation peak when the upper frequency limit is continuously running, It is the peak value of system frequency deviation when the system runs continuously at the upper frequency limit.

[0108] Step S3: When the system is in an abnormal operating state, the conventional units and wind turbines of the sending-end power grid system jointly participate in frequency modulation. During the frequency modulation process, the wind turbines use overspeed load reduction control frequency modulation and determine the disturbance power P d Whether the initial frequency change rate X0 under overspeed load shedding control is greater than the limit frequency change rate X2 of overspeed load shedding control frequency modulation, if so, the DC frequency limiter participates in the frequency modulation, and finds the optimal set of parameters for the DC frequency limiter and overspeed load shedding coordinated control to control the frequency of the sending-end power grid system; if not, maintain the current overspeed load shedding control frequency modulation, and control the frequency of the sending-end power grid system.

[0109] Determine the disturbance power P step Whether the initial frequency change rate X0 under the overspeed load shedding control frequency modulation is greater than the limit frequency change rate X2 of the overspeed load shedding control frequency modulation, comprising: step S31: obtaining the limit frequency change rate X2 of the overspeed load shedding control frequency modulation;

[0110] The specific process of obtaining the limit frequency change rate X2 of overspeed load reduction control frequency modulation is:

[0111] Step S311: according to the maximum operating power tracking curve equation and the load shedding power tracking curve equation of the wind turbine generator set, the relationship between the speed at the load shedding point and the speed at the maximum operating power tracking point is obtained.

[0112] Specifically, the maximum mechanical power captured by the wind turbine can be expressed as:

[0113]

[0114] Where ρ is the air density; A is the wind swept area of ​​the wind wheel; U w is the wind speed; C p (λ opt ,β) is the wind energy utilization coefficient, λ opt is the tip speed ratio of the wind turbine; β is the pitch angle of the wind turbine; λ i is the intermediate variable; R0 is the blade radius of the wind turbine; ω r is the wind turbine rotor speed.

[0115] From the above formula, the maximum operating power tracking curve equation of the wind turbine is:

[0116]

[0117] The load shedding power tracking curve equation is:

[0118]

[0119] Among them, kde0 is the load shedding power tracking factor, P opt is the active power at the maximum operating power tracking operating point, P de0 is the active power at the load reduction operation point, d is the load reduction rate of the wind turbine;

[0120] The active power and standby power of wind turbines are:

[0121] P sc =P opt -P de0 =dP opt

[0122] like Figure 2 As shown, the reserved power P of the wind turbine before frequency regulation sc , causing the wind turbine to deviate from the MPPT point. In the initial stage of frequency regulation, the wind turbine runs at the overspeed load reduction point B. When the load suddenly decreases in the initial stage of frequency regulation, the electromagnetic power ΔP output by the wind turbine e From point B to point C, the electromagnetic power is less than the mechanical power captured by the wind turbine. The wind turbine speed increases to absorb the rotor kinetic energy. After a transient process, the wind turbine ΔP e =ΔP m When , the wind turbine reaches a new steady-state operating point D, and the overspeed load reduction control ends.

[0123] Speed ​​at load reduction pointω opt and the maximum operating power tracking point speed ω de0 The relationship between them is:

[0124]

[0125] Step S312: Obtain the limit frequency modulation power ΔP of the wind turbine generator set according to the relationship between the speed at the load reduction point and the speed at the maximum operating power tracking point emax ;

[0126]

[0127] Among them, P opt is the active power at the maximum operating power tracking operating point, P de0 is the active power at the load reduction operation point, and d is the load reduction rate of the wind turbine.

[0128] Step S313: constructing a second frequency response model of the sending-end power grid system during overspeed load shedding and frequency modulation;

[0129]

[0130] Step S314: According to the limit frequency modulation power ΔP of the wind turbine emaxand the second frequency response model, to obtain the limiting frequency change rate X2 of the overspeed load reduction control frequency modulation;

[0131]

[0132] Among them, Δω2(t) is the system frequency deviation value when overspeed load reduction frequency regulation at time t, is any disturbance power during overspeed load shedding frequency modulation; α, l, ω n , φ and φ1 are parameters used to simplify the formula, R is the speed regulator adjustment coefficient, D is the damping coefficient, ω r is the wind turbine rotor speed, K m is the mechanical power gain coefficient, T R is the turbine reheating time constant, H is the conventional unit inertia time constant, F H is the turbine reheat constant; ΔP1 is the disturbance power corresponding to the continuous operation of the system at the upper frequency limit; ΔP2 is the disturbance power of the system at the overspeed load reduction frequency regulation limit; t0 is the time when the system reaches the frequency deviation peak when the system is at the overspeed load reduction frequency regulation limit. K is the peak value of system frequency deviation when the system is at the overspeed load reduction frequency regulation limit. d is the droop control coefficient.

[0133] When a sudden disturbance occurs during the actual operation of the system, when the system initial frequency change rate X0 is in [0, X1], it is determined that the system frequency deviation will not exceed 50.5Hz at this time, that is, the system is in normal operation, and there is no need for overspeed and DC to participate in frequency modulation; when the system initial frequency change rate X0 is in [X1, X2], it is determined that the single frequency modulation can be independently adjusted at this time to meet the frequency requirements of continuous operation of the system, and there is no need for DC to participate in frequency modulation; when the system initial frequency change rate X0 is greater than X2, it is determined that the single frequency modulation cannot meet the frequency requirements of continuous operation of the system, and it is necessary to adopt a frequency modulation strategy that coordinates overspeed load reduction control and DC control; using the system frequency change rate as a frequency modulation indicator can not only complete the frequency modulation more quickly and shorten the time the system is in an abnormal operating state, but also reduce the system frequency deviation and make the system more stable.

[0134] Step S32: When the disturbance power P d The initial frequency change rate X0 under overspeed load shedding control is greater than the limit frequency change rate X2 of overspeed load shedding control frequency modulation, the DC frequency limiter participates in frequency modulation, and the optimal set of parameters for the DC frequency limiter and overspeed load shedding coordinated control is found to control the frequency of the sending-end power grid system. The specific process is as follows:

[0135] S321: Obtain the DC power modulation amount when the system frequency deviation exceeds the DC frequency limiter dead zone.

[0136] like Figure 3As shown in the figure, when the system frequency regulation cannot meet the system continuous operation requirements, the DC frequency limit controller begins to participate in the frequency regulation. The DC frequency limit controller reduces the power imbalance of the system after the disturbance by increasing the active power. The input quantity is the system frequency, and the output quantity is the active power. The long-term operation of the DC line in the overload state is not conducive to the safe and stable operation of the system, so the limiting link is added; when the system frequency deviation exceeds the dead zone of the DC frequency limiter, taking high frequency as an example, the DC power modulation amount is:

[0137] ΔP FLC =K F Δω

[0138] Among them, K F is the DC frequency limiter control parameter, and Δω is the system frequency change.

[0139] S322: Construct the third frequency response model of the sending-end power grid system during overspeed load reduction and DC coordinated frequency regulation.

[0140] When the system load suddenly decreases, the conventional units and wind turbines in the system detect the system abnormality and jointly participate in the frequency regulation. At this time, the following rotor motion equation is established for the system:

[0141]

[0142] For conventional units, the power change is as follows:

[0143]

[0144] Among them, T G K is the speed regulator action time constant, G Adjust power for unit;

[0145] The conventional unit may optionally be a thermal power unit.

[0146] For wind turbines that use overspeed load reduction control, the power variation is related to the system frequency deviation and the frequency change rate. The electromagnetic power variation of the wind turbine ΔP e The specific formula is as follows:

[0147]

[0148] like Figure 4 As shown in the figure, the primary frequency regulation link and DC control link of the wind turbine are introduced into the power system frequency response model, and the expression of the third frequency response model is:

[0149]

[0150] Where Δω(t) is the system frequency deviation value when overspeed load shedding and DC frequency limiter coordinate frequency regulation at time t, P step is any disturbance power during overspeed load shedding and DC frequency limiter coordinated frequency regulation; α, l, ω n , φ and φ1 are parameters used to simplify the formula, R is the speed regulator adjustment coefficient, D is the damping coefficient, ω r is the wind turbine rotor speed, K m is the mechanical power gain coefficient, T R is the turbine reheating time constant, H is the conventional unit inertia time constant, F H is the turbine reheat constant, K d is the droop control coefficient.

[0151] In the coordinated control process of DC frequency limiter and overspeed load reduction: at the initial stage of disturbance, the frequency deviation can be regarded as 0, and only the virtual inertia coefficient responds to the system frequency change. Therefore, from the expression of the third frequency response model, the initial frequency change rate of the current system is:

[0152]

[0153] Derivative the expression of the third frequency response model, and when the derivative is 0, the time when the system reaches the frequency deviation peak is:

[0154]

[0155] The steady-state frequency change of the system is:

[0156]

[0157] S323: According to the third frequency response model and the DC power adjustment amount, design the first objective function and the first constraint of the wind turbine droop control coefficient, the second objective function and the second constraint of the wind turbine inertia coefficient, the third objective function and the third constraint of the DC frequency limiter control parameter, and the fourth objective function and the fourth constraint of the frequency regulation cost.

[0158] The droop control coefficient of a wind turbine is the ratio of the power change to the frequency change. In overspeed load reduction control, the power change is the reserve power participating in the primary frequency regulation. Therefore, the droop control coefficient can be written as follows:

[0159]

[0160] Considering that the control goal of the system inertial response link is to improve the frequency stability of the power grid, the maximum deviation of the system frequency can be reduced as much as possible as the objective function:

[0161] f1=minΔf max

[0162] Where Δf max is the maximum deviation of the system frequency.

[0163] Considering the control goal of the primary frequency regulation of the system, it is necessary to make full use of the load reduction power to make the steady-state operation point of the wind turbine as close to the MPPT point as possible. Therefore, the minimum difference between the system MPPT point power and the steady-state operation point power can be used as the objective function.

[0164] f2=min{P opt -P st}

[0165] Taking into account the control objectives of the primary frequency regulation stage of the system, the first objective function F1 is designed. Since the minimum frequency deviation peak value and the wind turbine steady-state operation point as close to the MPPT point as possible are contradictory, a weight coefficient is added to select different proportions according to different working conditions. The expression is:

[0166] F1=λ1f1+λ2f2

[0167] In order to avoid instability caused by excessively high speed of wind turbines, the speed of wind turbines should meet the first constraint condition:

[0168] ω de0 <ω st <1.3pu

[0169] Among them, ω de0 is the maximum operating power tracking point speed, ω st is the speed at the steady-state operating point, pu is the per-unit value of the rated speed relative to the set reference value;

[0170] At the beginning of system disturbance, the wind turbine quickly absorbs the rotor kinetic energy to slow down the frequency surge, thereby reducing the system initial frequency change rate to buy time for subsequent frequency regulation. The virtual inertia coefficient of the wind turbine can be adjusted by minimizing the initial frequency change rate as the second objective function F2:

[0171]

[0172] in, is the initial frequency change rate when the DC frequency limiter and overspeed load reduction coordinated control are adopted;

[0173] In order to avoid the rotor kinetic energy increasing too fast and adjusting the power too large, the wind turbine should meet the second constraint:

[0174]

[0175] Among them, K p is the virtual inertia coefficient, P ref,min and Pref,max They are the upper and lower limits of wind turbine converter power respectively.

[0176] The control principle of the DC frequency limiter is similar to the principle of primary frequency regulation of synchronous machines. The DC frequency limiter reduces the unbalanced power of the sending-end power grid through proportional control, thereby suppressing the frequency deviation of the sending-end power grid. The DC frequency limiter should participate in frequency regulation to ensure effective suppression of the frequency change of the sending-end power grid, so the system frequency deviation is as low as possible as the optimization objective function f3:

[0177] f3=min(Δω)

[0178] In order to ensure the stability of the power grid at the sending end, the power regulation of the DC frequency limiter should be reduced as much as possible to reduce the impact on the grid frequency. Therefore, the modulation power of the DC frequency limiter is considered to be as small as possible while meeting the system frequency regulation requirements as the objective function f4:

[0179] f4=min(ΔP FLC )

[0180] Where Δω is the system frequency deviation, ΔP FLC is the DC power modulation amount;

[0181] Taking the above optimization objectives into consideration, the third objective function F3 is established. Since the steady-state frequency is as small as possible and the DC power modulation is as small as possible, it is contradictory to add a weight coefficient to select different proportions according to different working conditions. The expression is:

[0182] F3=λ3f3+λ4f4

[0183] Since the DC frequency limiter increases the DC power modulation value under the action of the droop control link, if the DC power is too large, it will cause the DC line to operate in an overload state. Therefore, the additional power modulation value is generally taken as 1.2 times the DC rated power, that is, the third constraint condition is:

[0184] 0<P FLC <1.2P den

[0185] Among them, P FLC is the DC frequency limiter output power, P den is the DC rated power;

[0186] Wind turbines can improve the system's frequency regulation capability to a certain extent by participating in system frequency regulation through primary frequency regulation. However, fixed load reduction control cannot change according to changes in operating conditions in actual operating conditions, and the frequency regulation efficiency is low. Therefore, the selection of load reduction points should change according to changes in actual operating conditions.

[0187] In overspeed load reduction control, when the system operates at the overspeed load reduction point, the wind turbine rotor kinetic energy variable ΔE1 is:

[0188]

[0189] The power generation loss ΔE2 caused by overspeed load reduction control during this period is:

[0190] ΔE2=(P opt -P de0 )t s

[0191] Among them, ω de0 is the maximum operating power tracking point speed, ω opt is the speed at the load reduction point, H s is the moment of inertia of the fan, t s is the sampling interval;

[0192] The change in the rotor kinetic energy of the wind turbine is regarded as the frequency regulation benefit, and the power generation loss caused by overspeed load reduction control is regarded as the frequency regulation cost. The fourth objective function F4 is established, and its expression is:

[0193] F4=max(ΔE1-ΔE2)

[0194] By optimizing the fourth objective function F4, the optimal load reduction point under different wind speeds can be obtained, which is more efficient and flexible than fixed load reduction control.

[0195] The rotor speed of the wind turbine must be guaranteed to be within a safe and reliable range. In the sending-end power grid, when disturbance occurs, the rotor speed of the wind turbine must accelerate to absorb the unbalanced power, so the load reduction rate should not be too high to avoid being too close to the upper limit of the rotor speed, resulting in too little reserve power for the wind turbine. Therefore, the selection of the load reduction point must meet the fourth constraint:

[0196] 0≤d≤0.15pu

[0197] Wherein, d is the load reduction rate of the wind turbine.

[0198] The fminimax optimization algorithm is used for the fourth objective function F4 to obtain the optimal load reduction rate of the wind turbine after overspeed load reduction, and the optimal load reduction rate of the wind turbine under different wind speeds is obtained by changing the wind speed, such as Figure 5 shown.

[0199] S324: According to all objective functions and corresponding constraints, find the optimal set of wind turbine droop control coefficient, wind turbine inertia coefficient, DC frequency limiter control parameter and frequency regulation cost, and perform frequency control on the sending-end power grid system to restore the stability of the sending-end power grid system.

[0200] The specific method of overspeed load reduction control frequency regulation can refer to the existing technology, or it can be solved according to the first objective function, the second objective function, the third objective function and the corresponding constraints of the present application to solve the optimal set of wind turbine droop control coefficient, wind turbine inertia coefficient and frequency regulation cost, so as to control the frequency of the sending-end power grid system and restore the stability of the sending-end power grid system.

[0201] Example 2

[0202] The present invention provides a computer device, comprising a processor and a memory; wherein, when the processor executes a computer program stored in the memory, the steps of the frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine are implemented.

[0203] For more specific processes of the above method, please refer to the corresponding contents disclosed in the aforementioned embodiments, which will not be repeated here.

[0204] Example 3

[0205] In another embodiment, the present invention provides a computer-readable storage medium for storing a computer program; when the computer program is executed by a processor, the steps of the above-mentioned frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine are implemented.

[0206] For more specific processes of the above method, please refer to the corresponding contents disclosed in the aforementioned embodiments, which will not be repeated here.

[0207] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device and storage medium disclosed in the embodiment, since they correspond to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0208] Those skilled in the art can clearly understand that the technology in the embodiments of the present invention can be implemented by means of software plus a necessary general hardware platform. Based on this understanding, the technical solution in the embodiments of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which can be stored in a storage medium such as ROM / RAM, a disk, an optical disk, etc., and includes a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment of the present invention or some parts of the embodiments.

[0209] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine generator set, characterized in that: include: When the sending-end power grid system is disturbed, according to the disturbance power P d , get the disturbance power P d The initial frequency change rate X0 under According to the disturbance power P d The initial frequency change rate X0 under the condition is used to judge whether the power grid system at the sending end is in an abnormal operating state; When the system is in an abnormal operating state, the conventional units and wind turbines of the sending-end power grid system jointly participate in frequency modulation. During the frequency modulation process, the wind turbines use overspeed load reduction control frequency modulation and judge the disturbance power P d Whether the initial frequency change rate X0 under overspeed load shedding control is greater than the limit frequency change rate X2 of overspeed load shedding control frequency modulation, if so, the DC frequency limiter participates in the frequency modulation, and finds the optimal set of parameters for the DC frequency limiter and overspeed load shedding coordinated control to control the frequency of the sending-end power grid system; if not, maintain the current overspeed load shedding control frequency modulation, and control the frequency of the sending-end power grid system.

2. The frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine generator set according to claim 1 is characterized in that: The specific process of judging whether the power grid system at the sending end is in an abnormal operating state is as follows: judging the disturbance power P d Whether the initial frequency change rate X0 under the condition exceeds the initial frequency change rate X1 corresponding to the system when it runs continuously at the frequency upper limit, if so, the system is in an abnormal operating state, otherwise, it is in a normal operating state.

3. The frequency control method based on overspeed load shedding and DC coordination of a doubly-fed wind turbine generator set according to claim 2 is characterized in that: Obtain the initial frequency change rate X1 corresponding to the upper limit of the frequency during continuous operation and the obtained disturbance power P d The initial frequency change rate X0 under the condition is as follows: Construct the first frequency response model of the sending-end power grid system when overspeed load shedding and DC frequency regulation are not required; The expression of the first frequency response model is: Among them, Δω1(t) is the system frequency deviation value when there is no need for overspeed load reduction and DC frequency modulation at time t, is any disturbance power when overspeed load shedding and DC frequency modulation are not required; α, l', ω n1 and φ are parameters used to simplify the formula, R is the speed regulator adjustment coefficient, D is the damping coefficient, ω r is the wind turbine rotor speed, K m is the mechanical power gain coefficient, T R is the turbine reheat time constant, H is the conventional unit inertia time constant, F H is the turbine reheat constant; According to the first frequency response model, the disturbance power P is obtained. d The initial frequency change rate X0 under Among them, φ1 is a parameter used to simplify the formula; According to the first frequency response model, an initial frequency change rate X1 corresponding to the upper frequency limit during continuous operation is obtained; Among them, ΔP1 is the disturbance power corresponding to the system when the upper frequency limit is continuously running, t'0 is the time when the system reaches the frequency deviation peak when the upper frequency limit is continuously running, It is the peak value of system frequency deviation when the system runs continuously at the upper frequency limit.

4. The frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine generator set according to claim 1 is characterized in that: The determination of disturbance power P step Whether the initial frequency change rate X0 under the overspeed load shedding control frequency modulation is greater than the limit frequency change rate X2 of the overspeed load shedding control frequency modulation, including: obtaining the limit frequency change rate X2 of the overspeed load shedding control frequency modulation; The specific process of obtaining the limit frequency change rate X2 of overspeed load reduction control frequency modulation is: According to the maximum operating power tracking curve equation and the load reduction power tracking curve equation of the wind turbine generator set, the relationship between the speed at the load reduction point and the speed at the maximum operating power tracking point is obtained; According to the relationship between the speed at the load reduction point and the speed at the maximum operating power tracking point, the limit frequency modulation power ΔP of the wind turbine is obtained. emax ; Construct the second frequency response model of the sending-end power grid system during overspeed load shedding and frequency regulation; According to the limit frequency modulation power ΔP of the wind turbine emax and the second frequency response model, to obtain the limiting frequency change rate X2 of the overspeed load reduction control frequency modulation; Among them, Δω2(t) is the system frequency deviation value when overspeed load reduction frequency regulation at time t, is any disturbance power during overspeed load shedding frequency modulation; α, l, ω n , φ and φ1 are parameters used to simplify the formula, R is the speed regulator adjustment coefficient, D is the damping coefficient, ω r is the wind turbine rotor speed, K m is the mechanical power gain coefficient, T R is the turbine reheat time constant, H is the conventional unit inertia time constant, F H is the turbine reheat constant; ΔP1 is the disturbance power corresponding to the continuous operation of the system at the upper frequency limit; ΔP2 is the disturbance power of the system at the overspeed load reduction frequency regulation limit; t0 is the time when the system reaches the frequency deviation peak when the system is at the overspeed load reduction frequency regulation limit. K is the peak value of system frequency deviation when the system is at the overspeed load reduction frequency regulation limit. d is the droop control coefficient.

5. The frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine generator set according to claim 4 is characterized in that: The maximum operating power tracking curve equation of the wind turbine is: The load shedding power tracking curve equation is: The speed at the load reduction point ω opt and the maximum operating power tracking point speed ω de0 The relationship between them is: The limit frequency modulation power ΔP of the wind turbine emax for: Among them, k de0 is the load shedding power tracking factor, P opt is the active power at the maximum operating power tracking operating point, P de0 is the active power at the load reduction point, d is the load reduction rate of the wind turbine, ρ is the air density, C p is the wind energy utilization coefficient, λ opt is the tip speed ratio of the wind turbine; R0 is the blade radius of the wind turbine.

6. The frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine generator set according to claim 1 is characterized in that: The DC frequency limiter participates in frequency modulation, and finds the optimal set of parameters for the DC frequency limiter and overspeed load reduction coordinated control to control the frequency of the sending-end power grid system. The specific process is as follows: Obtain the DC power modulation amount when the system frequency deviation exceeds the DC frequency limiter dead zone; Construct the third frequency response model of the sending-end power grid system during overspeed load shedding and DC coordinated frequency regulation; According to the third frequency response model and the DC power adjustment amount, a first objective function and a first constraint condition of the droop control coefficient of the wind turbine set, a second objective function and a second constraint condition of the inertia coefficient of the wind turbine set, a third objective function and a third constraint condition of the DC frequency limiter control parameter, and a fourth objective function and a fourth constraint condition of the frequency regulation cost are designed; According to all the objective functions and corresponding constraints, the optimal set of wind turbine droop control coefficient, wind turbine inertia coefficient, DC frequency limiter control parameters and frequency regulation cost is found to control the frequency of the sending-end power grid system so that the sending-end power grid system can be restored to stability.

7. The frequency control method based on overspeed load shedding and DC coordination of a doubly-fed wind turbine generator set according to claim 6 is characterized in that: The DC power modulation amount ΔP FLC : ΔP FLC =K F Give Among them, K F is the DC frequency limiter control parameter, Δω is the system frequency change; The expression of the third frequency response model is: Where Δω(t) is the system frequency deviation value when overspeed load reduction and DC frequency limiter coordinate frequency regulation at time t, P step is any disturbance power during overspeed load shedding and DC frequency limiter coordinated frequency modulation; α, l, ω n , φ and φ1 are parameters used to simplify the formula, R is the speed regulator adjustment coefficient, D is the damping coefficient, ω r is the wind turbine rotor speed, K m is the mechanical power gain coefficient, T R is the turbine reheat time constant, H is the conventional unit inertia time constant, F H is the turbine reheat constant, K d is the droop control coefficient.

8. The frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine generator set according to claim 6 is characterized in that: The first objective function F1 is: F1=λ1f1+λ2f2 f1=minΔf max f2=min{P opt -P st } Where f1 is the maximum system frequency deviation Δf max The objective function is as small as possible, f2 is the objective function of the difference between the system MPPT point power and the steady-state operation point power; P opt is the system MPPT point power, P st is the power at the steady-state operating point, λ1 and λ2 are the weights of f1 and f2 respectively; The first constraint condition is: ω de0 <ω st <1.3pu Among them, ω de0 is the maximum operating power tracking point speed, ω st is the speed at the steady-state operating point, pu is the per-unit value of the rated speed relative to the set reference value; The second objective function F2 is: in, is the initial frequency change rate when the DC frequency limiter and overspeed load reduction coordinated control are adopted; The second constraint is: Among them, K p is the virtual inertia coefficient, P de0 is the active power at the load reduction point, P ref,min and P ref,max They are the upper and lower limits of wind turbine converter power respectively; The third objective function F3 is: F3=λ3f3+λ4f4 f3=min(Δω) f4=min(ΔP FLC ) Among them, λ3 and λ4 are the weights of f3 and f4 respectively, Δω is the system frequency deviation, ΔP FLC is the DC power modulation amount; The third constraint condition is: 0<P FLC <1.2P den Among them, P FLC is the DC frequency limiter output power, P den is the DC rated power; The fourth objective function F4 is: F4=max(ΔE1-ΔE2) ΔE2=(P opt -P de0 )t s The fourth constraint condition is: 0≤d≤0.15pu Among them, ω de0 is the maximum operating power tracking point speed, ω opt is the speed at the load reduction point, H s is the moment of inertia of the fan, t s is the sampling interval, and d is the load reduction rate of the wind turbine.

9. A computer device, characterized in that: It comprises a processor and a memory; wherein, when the processor executes the computer program stored in the memory, the steps of the frequency control method based on overspeed load reduction and DC coordination of a doubly-fed wind turbine set as described in any one of claims 1 to 8 are implemented.

10. A computer-readable storage medium, characterized in that: Used to store computer programs; when the computer programs are executed by the processor, the steps of the frequency control method based on overspeed load reduction and DC coordination of a doubly fed wind turbine set as described in any one of claims 1 to 8 are implemented.

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