CN116345478A - System and method for enhancing grid support capability of wind farm during critical events - Google Patents
System and method for enhancing grid support capability of wind farm during critical events Download PDFInfo
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Abstract
The invention relates to a system and a method for enhancing the supporting capacity of a wind power plant to a power grid during a key event, which take wake effects of fans into consideration, so that part of the wind power plant is integrally operated in a maximum power mode or is operated in an unloading mode according to load requirements, and the active output of the wind power plant is optimized while a certain active reserve margin is reserved. And in the unloading mode, the nonfunctional capacity of the wind power plant is maximized, and the voltage supporting capacity of the wind power plant on the power grid voltage is improved. And a reference value is distributed to the controller, so that the abrasion of the variable pitch adjustment on the fan mechanical device in the fan mode switching process is reduced while the maximum reactive power of the wind power plant is met. And generating a controller parameter lookup table of the maximum active power support based on the power grid guide rule and the system constraint, and improving the support capacity of the wind power plant on the power grid frequency during the voltage crossing. The method is realized based on the controller parameter lookup table, so that the controller parameter lookup table is generated only by one-time calculation for a specific wind power plant.
Description
Technical Field
The invention belongs to the technical field of active output control of wind power generation, relates to an active supporting method of a wind power plant on power grid voltage and frequency during faults, and particularly relates to a system and a method for enhancing the supporting capability of the wind power plant on the power grid during key events.
Background
With the continuous increase of the permeability of wind power generation in a power grid, the capacity of the power grid for receiving wind power is improved, on one hand, the regulation capacity of the power grid is required to be improved, and on the other hand, the regulation capacity of the wind power is required to be improved. The wind farm itself has frequency and voltage supporting capability, which is one of the important features of "grid friendly" wind farms.
In order to improve the output efficiency of a wind power plant, a single-machine maximum wind energy capturing scheme is generally adopted at present, and the optimal wind energy utilization coefficient is obtained by adjusting the pitch angle and the rotating speed of a wind turbine generator, so that a single turbine generator can capture wind energy to the maximum extent. However, due to the influence of wake effects, the input wind speed of the downwind unit is reduced after the upwind unit in the wind farm acquires wind energy. If all wind turbines of the wind power plant run in the mode of maximum wind energy capture, the wind energy captured by the upwind turbine can be excessively large, the wind speed decreases along with the wake flow propagation direction, the loss of the wind speed input by the downwind turbine is large, and the maximization of the output efficiency of the wind power plant is difficult to realize. Therefore, it is necessary to coordinate wind energy captured by each unit, so as to adjust wake flow distribution in the wind power plant, improve aerodynamic coupling between units, and improve wind energy utilization rate from the wind power plant level.
As a variable speed wind turbine generator of a main flow machine type of a grid-connected wind power plant, the active power and the reactive power output by the wind power plant can be regulated through an inverter, the track of the maximum power point is tracked, and the wind energy utilization rate is improved. For wind farms to participate in system frequency adjustment, many countries are researching off-load operation of some wind turbines, for example spanish is well defined in the grid code, which must have a frequency reserve margin of 1.5%. The load shedding has the advantages that: under the condition of no cutting machine, a part of spare parts are reserved for the system, so that the investment cost of conventional equipment is saved; the system frequency real-time response can be realized, and the power grid frequency stability is ensured.
In a high-proportion new energy power system, the capability of a wind turbine generator to keep running and provide support for the system when a power grid fails is increasingly important. The current research method mainly aims at how a wind turbine generator provides reactive power to support the voltage of a power grid during low-voltage ride through. And as reactive power priority control is generally adopted during the low voltage ride through period of the wind turbine, the active power output is limited. Meanwhile, the active power of the power unit is recovered at a given slower speed after the fault is removed, so that the sudden and large increase of the load of the unit is avoided. It can be seen that the system will be affected by a continuous and non-stepped active absence in this process, and that the problem of frequency stability during voltage ride-through is more severe the higher the permeability of wind turbines that do not participate in the system frequency modulation.
In summary, a new coordination control method is needed to be provided, on one hand, the wind energy utilization rate is optimized from the wind power plant level, and on the other hand, the frequency supporting capacity of the wind turbine generator to the power grid during the voltage crossing period is improved.
Disclosure of Invention
The invention aims to solve the defects of the prior art and provides a system and a method for enhancing the supporting capability of a wind farm to a power grid during a key event.
The invention solves the technical problems by the following technical proposal:
a system for enhancing the support capacity of a wind farm to a grid during a critical event, characterized by: comprises a wind power plant layer optimization module and a power grid support module,
the wind power plant layer optimization module determines that the wind power plant operates in a maximum power mode or a load shedding mode according to the steady-state active demand of the wind power plant, and distributes an optimal controller reference value for a fan controller;
under the maximum power mode, the wind power plant layer optimization module considers wake flow effects among fans, and generates controller parameters of each fan so that the overall active output value of the wind power plant reaches a peak value;
in the load shedding mode, the wind power plant layer optimization module also considers wake flow effects among fans, so that the wind power plant power output meets load requirements, and simultaneously maximizes the reactive power of the wind power plant, maximizes the kinetic energy stored in a rotor and minimizes the change quantity of the pitch angle during mode switching;
the wind power plant layer optimization module is mainly used for optimizing the running condition of the wind power plant in a non-fault period, so that the wind power plant has active and reactive reserves, and whether the wind power plant can provide safe and compliant voltage and frequency support in a grid fault period depends on the constraint of the grid support module on a fan power reference value in the fault period;
the grid support module generates a set of grid support constraints according to a reactive capacity curve of the wind farm, the constraints being active power support limits for the wind farm providing a primary frequency response during high/low voltage crossings; during the fault period, the frequency of the power grid is supported through droop control, and the power reference value of the droop control is required to be within the limit value range, so that the voltage supporting capacity of the wind power plant and the operation limit of the power grid cannot be affected, and the final source of the energy supported by the frequency in the power grid supporting module is the kinetic energy stored in the rotor in the optimizing module.
A method of enhancing the grid support capacity of a wind farm during a critical event, characterized by: the method comprises the following steps:
Step 2, solving an optimization objective function of the wind power plant in a maximum power operation mode according to the fan output power calculated in the step 1 and the wake effect, and optimizing different wind speeds to obtain a wind energy utilization coefficient of each fan in the maximum power mode
Step 3, solving an optimization objective function of the wind power plant in an unloading mode according to the fan output power calculated in the step 1 and the wake effect, and carrying out combined repeated optimization on different wind speeds and electric field load rates to obtain a wind energy utilization coefficient of each fan in the unloading mode
Step 4, converting the wind energy utilization coefficient in the maximum power mode in step 2 and the wind energy utilization coefficient in the unloading mode in step 3 into optimal controller reference values, thereby generating pitch angle reference values
And rotor speed->
A controller parameter lookup table of reference values;
step 5, generating a group of maximum active support limit values of the power grid according to the reactive capacity curve of the wind field;
and 6, the fan is controlled to provide primary frequency modulation during voltage crossing for the power grid through sagging within the range of the active support limit value in the step 5, and meanwhile, the fan does not influence the nonfunctional capacity of the wind field.
Moreover, according to the Jensen model, when considering the wake effects of fans, the cut-in wind speed for each fan can be expressed as:
wherein v is wind,i Wind speed v accepted by fan i j For the non-shielding wind speed, alpha is the axial interference coefficient, D j For the rotor diameter of fan j, A ji X is the ratio of the shielding area of fan i on fan j to the sweeping area of fan j ji The diameter distance between the fans j and i is the attenuation constant, and n is the number of fans;
then in step 1, the output power of each fan taking into account wake effects can be expressed as:
λ＝K b ω/v wind
wherein ρ is ar Is the fan power constant, C p Is wind energy utilization coefficient, beta is pitch angle, lambda is tip speed ratio, v wind To cut in wind speed, K b Being constant, ω is the rotor speed.
Moreover, the optimal objective function of the wind farm with wake effect in the step 2 in the maximum power operation mode is as follows:
wherein P is i For the output power of each fan at different wind speeds,
converting the output power of the fan in the maximum power mode into the wind energy utilization coefficient of the fan according to the following formula:
wherein ρ is ar Fan power constant, v wind For the cut-in wind speed,
the wind energy utilization coefficient of the fan in the maximum power mode is obtained.
Moreover, the optimal objective function of the wind farm with wake effect in step 3 in the unloading mode is:
1)
2)min||[L ΔC pi L]||
wherein, the liquid crystal display device comprises a liquid crystal display device,
for maximum reactive power of fan i, V pcc Delta C is the grid-connected point voltage of the wind power plant pi The variation of the wind energy utilization coefficient of the ith fan,
converting the output power of the fan in the unloading mode into the wind energy utilization coefficient of the fan according to the following formula
Wherein ρ is ar Fan power constant, v wind For the cut-in wind speed,
the wind energy utilization coefficient of the fan in the unloading mode is obtained.
Moreover, in both the maximum power mode and the unloading mode of step 2 and step 3, the operating point of the wind farm satisfies the following constraints:
v wind,i ≥v min
λ min,i ≤λ i ≤λ max,i
0≤C pi ≤C p,i,max
P i,min ≤P i ≤P i,max
wherein v is min To minimum cut-in wind speed lambda min,i And lambda (lambda) max,i Respectively minimum value and maximum value of tip speed ratio, C pi C is the wind energy utilization coefficient of the ith fan in two modes p,i,max The maximum value of the wind energy utilization coefficient of the ith fan, P i,min And P i,max For the minimum value and the maximum value of the output power of the fan, Q i Is the reactive power output of the fan,
and->
Is the minimum value and the maximum value of the nonfunctional force of the fan.
And, step 4 converts the wind energy utilization coefficient in the maximum power mode in step 2 and the wind energy utilization coefficient in the unloading mode in step 3 into optimal controller reference values, and a secondary optimization objective function between the wind energy utilization coefficient and the pitch angle reference values and the angular velocity reference values needs to be established, so that the kinetic energy stored in the fan rotor is maximum, and the change amount of the pitch angle of the fan when the wind field is switched from the maximum power mode to the unloading is minimum.
And the establishing a secondary optimization objective function between the wind energy utilization coefficient and the pitch angle reference value and the angular speed reference value is as follows:
λ min,i ≤λ i ≤λ max,i
0≤C pi ≤C p,max,i
β min ≤β i ≤β max
wherein lambda is i Is the tip speed ratio of the fan,
k is the rotor rotation speed reference value b Is constant, v wind To cut in wind speed, C pi For the wind energy utilization coefficient in two modes, < >>
Load as pitch angle reference cmd The load factor of the wind power plant is obtained.
Furthermore, in step 5 a set of grid maximum active support limit values is generated from the reactive capacity curve of the wind farm, which during grid low voltage ride through is expressed as:
wherein P is i Is the active power output by the fan,
is the maximum value of the nonfunctional force of the fan, V pcc Grid-connected point voltage of the wind power plant;
the high voltage ride through period of the grid is expressed as:
wherein P is i Is the active power output by the fan,
is the minimum value of the nonfunctional force of the fan, V pcc And (5) connecting the grid to the grid for the wind power plant.
The invention has the advantages and beneficial effects that:
according to the wind power generation system, the wake flow effect of the fan is considered, the wind energy utilization efficiency is optimized from the wind power plant level, and the wind power plant is integrally operated in a maximum power mode or operated in an unloading mode according to the system load requirement. And the wind farm has voltage supporting capability and primary frequency modulation capability. The invention minimizes the pitch angle variation during mode switching while maximizing the wind farm non-functionality and kinetic energy stored in the rotor to reduce the loss of mechanical devices from wind farm operating mode switching. The invention is based on the controller parameter lookup table, and for a specific wind power plant, the controller reference value lookup table is generated by only one calculation.
Drawings
FIG. 1 is pitch angle control and inverter control of a wind turbine;
FIG. 2 is a flow chart of a general implementation of the controller parameter lookup table based grid support scheme of the present invention;
in fig. 1: v w For the real-time wind speed of the wind farm, load is the load rate of the wind farm, omega ref And beta ref Fan angular frequency and pitch angle reference value, beta, generated for controller parameter lookup table ω Is a pitch angle correction value, P, generated from rotor frequency fluctuations ref For the active reference value, f means And omega means Respectively, system frequency and angular frequency measurements, K f As a droop coefficient of primary frequency response, ΔP PFR P is the power increment in the frequency response process ord V for the active control signal of the final input side converter rot,dq The port voltage output by the side converter.
In fig. 2: beta ref,min,max (v wind Load) is the pitch angle reference value, maximum, minimum controller parameter lookup table, ω ref,min,max (v wind Load) is a controller parameter lookup table of angular frequency reference, maximum, minimum. Q (Q) cap,max (P,V pcc (II) and Q) cap,min (P,V pcc (ii) are controller parameter lookup tables of reactive reference values of the wind farm during low voltage ride through and high voltage ride through, respectively.
Detailed Description
The invention is further illustrated by the following examples, which are intended to be illustrative only and not limiting in any way.
The control loop of the scheme is shown in figure 1. And generating a controller parameter lookup table of the power grid under steady state and transient state by optimizing an objective function, and updating a pitch angle reference value and a fan angular frequency reference value of the controller by the fan controller according to different wind speeds and load rates when the power grid is in the steady state or transient state. The control loop comprises two parts of pitch angle control and machine side converter control. Pitch angle control controls the amount of electricity extracted from incident wind by adjusting the angle of the turbine blades, and meanwhile, the PI controller senses rotor rotation speed deviation through a speed sensor to balance load fluctuation, so that a pitch angle reference value is corrected, and the correction value is beta in FIG. 1 ω . The servo link simulates the dynamic response process of the pitch system and limits the rate and range of change of pitch angle. The machine side converter adopts active powerDroop control, namely controlling active power P output by a fan by sensing rotor rotating speed deviation through a PI controller ref ，P ref Adding the power increment ΔP in the frequency response PFR And obtains the final control signal P of the input side converter through the rate limiter ord . The port voltage output by the machine side converter under the rotating coordinate system is v through the double-ring control inside the converter rot,dq 。
The specific implementation flow of the scheme is shown in fig. 2. Firstly, the data of the wind farm are read, whether the topological structure of the wind farm changes is judged, and if the topological structure of the wind farm changes, a controller parameter lookup table is regenerated according to an optimization algorithm. When the topological structure of the wind power plant is unchanged, the operating point of the wind power plant can be set directly according to the controller parameter lookup table. When the wind power plant operating point is set, whether the wind power plant is in a steady state is firstly judged, and if the wind power plant is in the steady state, the wind power plant is operated in a maximum power mode or a load shedding mode according to the load demand in the system. When the power grid is only subjected to load disturbance, the wind farm provides a frequency response for the power grid through droop control. When a voltage crossing event occurs to the power grid, the wind power plant provides corresponding voltage support and primary frequency response for the power grid according to different voltage crossing types.
A system to enhance the grid support capacity of a wind farm during a critical event consists of two modules: the wind power plant layer optimization (Farm-Level Optimization, FLO) module determines that the wind power plant operates in a maximum power mode or a load shedding mode according to the steady-state active demand of the wind power plant, and distributes an optimal controller reference value for a fan controller so as to maximize the reactive power of the wind power plant and the kinetic energy stored in a rotor and reduce the mechanical loss generated in the mode switching process;
under the maximum power mode, the wind power plant layer optimization module considers wake flow effects among fans, and generates controller parameters of each fan so that the overall active output value of the wind power plant reaches a peak value;
in the load shedding mode, the wind power plant layer optimization module also considers wake flow effects among fans, so that the wind power plant power output meets load requirements, the reactive power of the wind power plant is maximized, the kinetic energy stored in the rotor is maximized, and the change quantity of the pitch angle during mode switching is minimized.
The wind power plant layer optimization module is mainly used for optimizing the operation of the wind power plant in a non-fault period, so that the wind power plant has active and reactive reserves, and whether the wind power plant can provide safe and compliant voltage and frequency support in a grid fault period depends on the constraint of the grid support module on a fan power reference value in the fault period;
the Grid support module generates a set of Grid support constraints (GS-L) according to a reactive capacity curve of the wind farm, the constraints providing active power support limits for the wind farm for a frequency response during high/low voltage crossings; during the fault period, the frequency of the power grid is supported through the droop control, the power reference value of the droop control is required to be within the limit value range, so that the voltage supporting capacity of the wind power plant and the operation limit of the power grid can not be influenced, and the final source of the energy supported by the frequency in the power grid supporting module is the kinetic energy stored in the rotor in the optimizing module
The innovation point of the invention is that: and considering the wake effect of the fan, enabling part of the wind power plant to integrally operate in a maximum power mode or operate in an unloading mode according to load requirements, optimizing the active output of the wind power plant and leaving a certain active reserve margin. And in the unloading mode, the nonfunctional capacity of the wind power plant is maximized, and the voltage supporting capacity of the wind power plant on the power grid voltage is improved. And a reference value is distributed to the controller, so that the abrasion of the variable pitch adjustment on the fan mechanical device in the fan mode switching process is reduced while the maximum reactive power of the wind power plant is met. And generating a controller parameter lookup table of the maximum active power support based on the power grid guide rule and the system constraint, and improving the support capacity of the wind power plant on the power grid frequency during the voltage crossing. The method is realized based on the controller parameter lookup table, so that the controller parameter lookup table is generated only by one-time calculation for a specific wind power plant.
A method of enhancing the grid support capability of a wind farm during a critical event, comprising the steps of:
Step 2, solving an optimization objective function of the wind power plant in a maximum power operation mode according to the fan output power calculated in the step 1 and the wake effect, and optimizing different wind speeds to obtain a wind energy utilization coefficient of each fan in the maximum power mode
Step 3, solving an optimization objective function of the wind power plant in an unloading mode according to the fan output power calculated in the step 1 and the wake effect, and carrying out combined repeated optimization on different wind speeds and electric field load rates to obtain a wind energy utilization coefficient of each fan in the unloading mode
Step 4, converting the wind energy utilization coefficient in the maximum power mode in step 2 and the wind energy utilization coefficient in the unloading mode in step 3 into optimal controller reference values, thereby generating pitch angle reference values
And rotor speed->
A controller parameter lookup table of reference values;
step 5, generating a group of maximum active support limit values of the power grid according to the reactive capacity curve of the wind field;
and 6, the fan is controlled to provide primary frequency modulation during voltage crossing for the power grid through sagging within the range of the active support limit value in the step 5, and meanwhile, the fan does not influence the nonfunctional capacity of the wind field.
According to the Jensen model, when considering the wake effects of fans, the cut-in wind speed for each fan can be expressed as:
wherein v is wind,i Wind speed v accepted by fan i j For the non-shielding wind speed, alpha is the axial interference coefficient, D j For the rotor diameter of fan j, A ji X is the ratio of the shielding area of fan i on fan j to the sweeping area of fan j ji The diameter distance between fans j and i is k, the attenuation constant, and n, the number of fans.
Then in step 1, the output power of each fan taking into account wake effects can be expressed as:
λ＝K b ω/v wind
wherein ρ is ar Is the fan power constant, C p Is wind energy utilization coefficient, beta is pitch angle, lambda is tip speed ratio, v wind To cut in wind speed, K b Being constant, ω is the rotor speed.
And (3) the optimal objective function of the wind farm with the wake effect in the step (2) in the maximum power operation mode is as follows:
wherein P is i For the output power of each fan at different wind speeds
Converting the output power of the fan in the maximum power mode into the wind energy utilization coefficient of the fan according to the following formula:
wherein ρ is ar Fan power constant, v wind For the cut-in wind speed,
the wind energy utilization coefficient of the fan in the maximum power mode is obtained.
The optimal objective function of the wind power plant with wake effect in the step 3 in the unloading mode is as follows:
1)
2)min||[L ΔC pi L]||
wherein, the liquid crystal display device comprises a liquid crystal display device,
for maximum reactive power of fan i, V pcc Delta C is the grid-connected point voltage of the wind power plant pi The variable quantity of the wind energy utilization coefficient of the ith fan.
Converting the output power of the fan in the unloading mode into the wind energy utilization coefficient of the fan according to the following formula
Wherein ρ is ar Fan power constant, v wind For the cut-in wind speed,
the wind energy utilization coefficient of the fan in the unloading mode is obtained.
In the maximum power mode and the unloading mode of the step 2 and the step 3, the operation points of the wind farm meet the following constraint conditions:
v wind,i ≥v min
λ min,i ≤λ i ≤λ max,i
0≤C pi ≤C p,i,max
P i,min ≤P i ≤P i,max
wherein v is min To minimum cut-in wind speed lambda min,i And lambda (lambda) max,i Respectively minimum value and maximum value of tip speed ratio, C pi C is the wind energy utilization coefficient of the ith fan in two modes p,i,max The maximum value of the wind energy utilization coefficient of the ith fan, P i,min And P i,max For the minimum value and the maximum value of the output power of the fan, Q i Is the reactive power output of the fan,
and->
Is the minimum value and the maximum value of the nonfunctional force of the fan.
And 4, converting the wind energy utilization coefficient in the maximum power mode in the step 2 and the wind energy utilization coefficient in the unloading mode in the step 3 into optimal controller reference values, and establishing a secondary optimization objective function between the wind energy utilization coefficient and the pitch angle reference values and between the wind energy utilization coefficient and the angular speed reference values so as to maximize the kinetic energy stored in the fan rotor, wherein the change amount of the pitch angle of the fan is minimum when the wind field is switched from the maximum power mode to the unloading mode.
The establishing a secondary optimization objective function between the wind energy utilization coefficient and the pitch angle reference value and the angular speed reference value is as follows:
λ min,i ≤λ i ≤λ max,i
0≤C pi ≤C p,max,i
β min ≤β i ≤β max
wherein lambda is i Is the tip speed ratio of the fan,
k is the rotor rotation speed reference value b Is constant, v wind To cut in wind speed, C pi For the wind energy utilization coefficient in two modes, < >>
Load as pitch angle reference cmd The load factor of the wind power plant is obtained.
In step 5, a set of grid maximum active support limit values is generated from the reactive capacity curve of the wind farm, which is expressed as during grid low voltage ride through:
wherein P is i Is the active power output by the fan,
is the maximum value of the nonfunctional force of the fan, V pcc And (5) connecting the grid to the grid for the wind power plant.
The high voltage ride through period of the grid is expressed as:
wherein P is i Is the active power output by the fan,
is the minimum value of the nonfunctional force of the fan, V pcc And (5) connecting the grid to the grid for the wind power plant.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: modifications and equivalents may be made to the specific embodiments of the invention without departing from the spirit and scope of the invention, which is intended to be covered by the claims.
Claims (9)
1. A system for enhancing the support capacity of a wind farm to a grid during a critical event, characterized by: comprises a wind power plant layer optimization module and a power grid support module,
the wind power plant layer optimization module is used for optimizing the running condition of the wind power plant in a non-fault period so as to enable the wind power plant to have active and reactive reserves, and whether the wind power plant can provide safe and compliant voltage and frequency support in a grid fault period depends on the constraint of the grid support module on a fan power reference value in the fault period;
the grid support module generates a set of grid support constraints according to a reactive capacity curve of the wind farm, the constraints being active power support limits for the wind farm providing a primary frequency response during high/low voltage crossings; during the fault period, the frequency of the power grid is supported through droop control, and the power reference value of the droop control is required to be within the limit value range, so that the voltage supporting capacity of the wind power plant and the operation limit of the power grid cannot be affected, and the final source of the energy supported by the frequency in the power grid supporting module is the kinetic energy stored in the rotor in the optimizing module.
2. A method of enhancing the grid support capacity of a wind farm during a critical event, characterized by: the method comprises the following steps:
step 1, obtaining the output power of the fan considering the wake effect of the fan according to a Jensen modelP i ；
Step 2, solving an optimization objective function of the wind power plant in a maximum power operation mode according to the fan output power calculated in the step 1 and the wake effect, and optimizing different wind speeds to obtain a wind energy utilization coefficient of each fan in the maximum power mode
Step 3, solving an optimization objective function of the wind power plant in an unloading mode according to the fan output power calculated in the step 1 and the wake effect, and carrying out combined repeated optimization on different wind speeds and electric field load rates to obtain a wind energy utilization coefficient of each fan in the unloading mode
Step 4, converting the wind energy utilization coefficient in the maximum power mode in step 2 and the wind energy utilization coefficient in the unloading mode in step 3 into optimal controller reference values, thereby generating pitch angle reference values
And rotor speed->
A controller parameter lookup table of reference values;
step 5, generating a group of maximum active support limit values of the power grid according to the reactive capacity curve of the wind field;
and 6, the fan is controlled to provide primary frequency modulation during voltage crossing for the power grid through sagging within the range of the active support limit value in the step 5, and meanwhile, the fan does not influence the nonfunctional capacity of the wind field.
3. A method of enhancing the grid support capability of a wind farm during a critical event according to claim 2, wherein: according to the Jensen model, when considering the wake effects of fans, the cut-in wind speed for each fan can be expressed as:
wherein v is wind,i Wind speed v accepted by fan i j For the non-shielding wind speed, alpha is the axial interference coefficient, D j For the rotor diameter of fan j, A ji X is the ratio of the shielding area of fan i on fan j to the sweeping area of fan j ji The diameter distance between the fans j and i is the attenuation constant, and n is the number of fans;
then in step 1, the output power of each fan taking into account wake effects can be expressed as:
λ＝K b ω/v wind
wherein ρ is ar Is the fan power constant, C p Is wind energy utilization coefficient, beta is pitch angle, lambda is tip speed ratio, v wind To cut in wind speed, K b Being constant, ω is the rotor speed.
4. A method of enhancing the grid support capability of a wind farm during a critical event according to claim 2, wherein: and (3) the optimal objective function of the wind farm with the wake effect in the step (2) in the maximum power operation mode is as follows:
wherein P is i For the output power of each fan at different wind speeds,
converting the output power of the fan in the maximum power mode into the wind energy utilization coefficient of the fan according to the following formula:
wherein ρ is ar Fan power constant, v wind For the cut-in wind speed,
the wind energy utilization coefficient of the fan in the maximum power mode is obtained.
5. A method of enhancing the grid support capability of a wind farm during a critical event according to claim 2, wherein: the optimal objective function of the wind power plant with wake effect in the step 3 in the unloading mode is as follows:
1)
2)min||[L ΔC pi L]||
wherein, the liquid crystal display device comprises a liquid crystal display device,
for maximum reactive power of fan i, V pcc Delta C is the grid-connected point voltage of the wind power plant pi The variation of the wind energy utilization coefficient of the ith fan,
converting the output power of the fan in the unloading mode into the wind energy utilization coefficient of the fan according to the following formula
Wherein ρ is ar Fan power constant, v wind For the cut-in wind speed,
the wind energy utilization coefficient of the fan in the unloading mode is obtained.
6. A method of enhancing the grid support capability of a wind farm during a critical event according to claim 2, wherein: in the maximum power mode and the unloading mode of the step 2 and the step 3, the operation points of the wind farm meet the following constraint conditions:
v wind,i ≥v min
λ min,i ≤λ i ≤λ max,i
0≤C pi ≤C p,i,max
P i,min ≤P i ≤P i,max
wherein v is min To minimum cut-in wind speed lambda min,i And lambda (lambda) max,i Respectively minimum value and maximum value of tip speed ratio, C pi C is the wind energy utilization coefficient of the ith fan in two modes p,i,max The maximum value of the wind energy utilization coefficient of the ith fan, P i,min And P i,max For the minimum value and the maximum value of the output power of the fan, Q i Is the reactive power output of the fan,
and->
Is the minimum value and the maximum value of the nonfunctional force of the fan.
7. A method of enhancing the grid support capability of a wind farm during a critical event according to claim 2, wherein: and 4, converting the wind energy utilization coefficient in the maximum power mode in the step 2 and the wind energy utilization coefficient in the unloading mode in the step 3 into optimal controller reference values, and establishing a secondary optimization objective function between the wind energy utilization coefficient and the pitch angle reference values and between the wind energy utilization coefficient and the angular speed reference values so as to maximize the kinetic energy stored in the fan rotor, wherein the change amount of the pitch angle of the fan is minimum when the wind field is switched from the maximum power mode to the unloading mode.
8. The method of enhancing grid support capability of a wind farm during a critical event of claim 7, wherein: the establishing a secondary optimization objective function between the wind energy utilization coefficient and the pitch angle reference value and the angular speed reference value is as follows:
λ min,i ≤λ i ≤λ max,i
0≤C pi ≤C p,max,i
β min ≤β i ≤β max
wherein lambda is i Is the tip speed ratio of the fan,
k is the rotor rotation speed reference value b Is constant, v wind To cut in wind speed, C pi For the wind energy utilization coefficient in two modes, < >>
Load as pitch angle reference cmd The load factor of the wind power plant is obtained.
9. A method of enhancing the grid support capability of a wind farm during a critical event according to claim 2, wherein: in step 5, a set of grid maximum active support limit values is generated from the reactive capacity curve of the wind farm, which is expressed as during grid low voltage ride through:
wherein P is i Is the active power output by the fan,
is the maximum value of the nonfunctional force of the fan, V pcc Grid-connected point voltage of the wind power plant;
the high voltage ride through period of the grid is expressed as:
wherein P is i Is the active power output by the fan,
is the minimum value of the nonfunctional force of the fan, V pcc And (5) connecting the grid to the grid for the wind power plant.
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