CN115995825A - Wind-storage combined frequency control method considering frequency modulation dead zone - Google Patents
Wind-storage combined frequency control method considering frequency modulation dead zone Download PDFInfo
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Abstract
The invention relates to a wind-storage combined frequency modulation method for a frequency modulation dead zone, which comprises the following steps: setting a frequency modulation dead zone of a fan and an energy storage system, generating fluctuation of the frequency of a power grid, judging whether the frequency deviation detected by the fan exceeds the frequency modulation dead zone of the fan, enabling the system to enter a fan frequency modulation response zone, judging whether the frequency deviation detected by the energy storage exceeds the frequency modulation dead zone, enabling the system to enter a wind storage transition zone, enabling the system to enter the energy storage frequency modulation response zone, judging whether the frequency deviation detected by the energy storage is recovered to the fan frequency modulation zone, and enabling the frequency of the power grid to be recovered stably; the method can determine the output frequency modulation power of the fan and the energy storage, and after the wind storage combined frequency modulation is started, the frequency modulation power calculation result of the fan and the energy storage is acted on the fan and the energy storage active power instruction value. According to the method, the self characteristics of the fan and the energy storage and the relevance between the fan and the energy storage are comprehensively considered, so that the control process and the control parameters are simplified, from the aspect of frequency modulation dead zone, the system frequency fluctuation can be effectively restrained, the problem of fan stall can be solved, and the service life of the energy storage device is prolonged.
Description
Technical Field
The invention relates to the field of frequency control of power systems, in particular to a control method for a fan and an energy storage system to jointly participate in system frequency modulation, and specifically relates to a wind-storage joint frequency control method considering a frequency modulation dead zone.
Background
With the generation and grid connection of large-scale new energy, the problems are also revealed. The random fluctuation and intermittence of the new energy source bring trouble to the operation scheduling of the power grid, meanwhile, the synchronous generator with large inertia and strong damping is gradually replaced, new energy sources such as wind power, photoelectricity and the like are connected by adopting power electronics, the inherent inertia damping effect of the system is gradually weakened, the frequency index of the system is gradually deteriorated, and the problem of short-term frequency stability is easily caused. Therefore, wind power and photoelectricity are required to be gradually responsible for maintaining safe and stable operation of a power grid, the advantage of flexibility and controllability of a converter system is exerted, and the insufficient inertia damping effect in the system is equivalently compensated, so that the stability of the system frequency is ensured.
The kinetic energy of the doubly-fed wind generator (DFIG) rotor can be used as an energy source for frequency support. The fan participation system frequency modulation method is characterized in that the rotor kinetic energy is utilized to increase or decrease the output power of the fan through virtual inertia control, sagging control and a control method combining the virtual inertia and sagging control, so that the purpose of fan frequency modulation is realized. The virtual inertia control (D control) takes the frequency change rate as input, and aims to quickly inhibit the falling/sudden increase rate of the power grid and shorten the fluctuation time of the system frequency; the droop control (P control) takes frequency deviation as input, so that the maximum value and recovery speed of the system frequency response are correspondingly improved; the virtual inertia control combines the virtual inertia and the sagging control, and by setting reasonable proportional coefficients and differential coefficients, the wind turbine generator can quickly respond to the system frequency change, the descending/ascending speed of the system frequency is reduced, the maximum deviation of the system frequency is reduced, and the frequency response characteristic of the system is improved.
The energy storage system (Energy Storage System, ESS) is used as a high-quality frequency modulation power supply, the advantages of rapid action and flexible frequency modulation mode can be fully exerted when different disturbance is faced, active power on two sides of a source load is balanced through rapid throughput power, the stable frequency of a power grid is maintained, and the energy storage system has faster response speed and higher response precision than those of a traditional unit in the aspect of frequency modulation. At present, an energy storage system is connected with an external power grid through a power conversion system, and the output power of the energy storage system is controlled by an inverter, wherein main control modes of the inverter comprise PQ control, VF control, droop control and virtual synchronous generator control, and the four control modes have advantages and disadvantages and need specific analysis in specific situations.
The wind turbine utilizes the kinetic energy of the rotor of the wind turbine to adjust the frequency of the system, and reduces the frequency modulation pressure of the synchronous generator when the load is disturbed by changing the grid-connected power, but the mechanical output of the wind turbine is not increased, but the wind turbine is reduced because the rotating speed of the wind turbine deviates from the optimal value, so that the wind energy utilization rate is reduced. The throughput kinetic energy in the fan rotor is limited due to the influence of the safe operation constraint of the fan, the kinetic energy is released too deeply/absorbed energy, the rotating speed is too small/too large, and even the phenomenon of unstable rotating speed is caused. In addition, the fan suddenly increases/absorbs power, so that the mechanical stress of a fan transmission system is increased, and the mechanical fatigue of the fan is increased.
The energy storage system has better response speed and precision in the aspect of frequency modulation by virtue of the advantages of accurate tracking, quick response, bidirectional regulation and the like, but frequent charge and discharge of the energy storage system accelerates electrical aging, reduces the service life of a battery, even causes the risks of severe fluctuation of bus voltage, quick reduction of capacitance value, swelling or slurry explosion, electrical insulation damage and the like, and simultaneously considers the higher manufacturing cost of the energy storage system, takes the problems of self battery capacity, charge state and the like into consideration in the participation of the energy storage system in frequency modulation, avoids irreversible influence on the service life of the energy storage system, and improves the frequency modulation economy of the energy storage system.
At present, the primary frequency modulation of a power system is limited by a fan and energy storage independently, but the existing wind storage frequency modulation method is difficult to set parameters only from the aspect of a wind storage self-control method, and the control process is complex, so that the coordination between the characteristics of the wind storage self-control method and the control method is mostly ignored. Therefore, when the system is disturbed, how to make the fan and the energy storage system cooperate with each other to inhibit the power grid frequency fluctuation has become a technical problem to be solved in the art.
Disclosure of Invention
The wind-storage combined frequency control method aims to solve the technical problems that the limitation that a fan, energy storage and wind storage are combined to participate in primary frequency modulation of a power system is overcome, the characteristics of the fan and the energy storage are comprehensively considered, a control method between the fan and the energy storage is jointly considered, a control process and control parameters are simplified, from the aspect of a frequency modulation dead zone, the problem of system frequency fluctuation can be effectively restrained, the problem of fan stall can be solved, the service life of an energy storage device is further prolonged, and the wind-storage combined frequency control method is scientific, reasonable, high in applicability and good in effect and takes the frequency modulation dead zone into account.
The wind-storage combined frequency modulation method for solving the technical problems adopts the technical scheme that the wind-storage combined frequency modulation method for measuring a frequency modulation dead zone is characterized by comprising the following steps of:
1) Frequency modulation dead zone of fan and energy storage system
Referring to the idea of setting a dead zone of a synchronous generator set, wherein the synchronous generator set adopts a small frequency modulation dead zone to participate in primary frequency modulation, uses a large frequency modulation dead zone and only responds to the change of the frequency of a power grid with large disturbance, and sets the frequency modulation dead zone of a fan to be smaller than an energy storage frequency modulation dead zone, wherein the frequency modulation dead zone of the fan is respectively [0,0.01] and [0,0.2];
2) Fluctuation of power grid frequency
The system detects that the frequency of the power grid fluctuates;
3) Fan detection frequency deviation exceeds frequency modulation dead zone of fan
If the fan detection frequency deviation exceeds the fan frequency modulation dead zone, executing the step 4); otherwise, executing the step 9);
4) The system enters into a fan frequency modulation response area
The system frequency deviation exceeds the fan frequency modulation dead zone, and the energy storage frequency modulation dead zone is not exceeded. And calculating the system frequency deviation delta f according to the detected power grid frequency, and taking the absolute value of the system frequency deviation delta f. The frequency modulation power calculation mode of the fan output is specifically as follows:
(1) Collecting the rotor rotating speed of the current fan, and analyzing the rotational kinetic energy capacity stored in the fan rotor according to the current running state of the fan;
(2) Calculating a fan frequency modulation coefficient:
in order to ensure that the fan can fully exert the frequency modulation potential of the fan under the premise of ensuring the stability of the fan, the DFIG frequency modulation coefficient and the effective rotational kinetic energy of the rotor are established in a coupling relation, and the expression is as follows:
wherein: k (K) WC 、K WD Frequency modulation coefficients of the fan at the high frequency stage and the low frequency stage are respectively obtained; omega r The DFIG rotation speed; omega min 、ω max The minimum and maximum rotational speeds of the DFIG; alpha is a grid frequency performance adjustment factor.
(3) Calculating the frequency modulation and transmission increasing power output by the fan:
in order to avoid noise caused by frequency differentiation, droop control is used, the frequency deviation of a power grid is in direct proportion to the output frequency modulation power, and the expression is as follows:
wherein: ΔP WC (t)、ΔP WD (t) increasing the power of the fan at the high frequency and the low frequency respectively; Δf is the system frequency deviation;
5) Energy storage detection frequency deviation exceeds frequency modulation dead zone
If the energy storage detects that the frequency deviation exceeds the self frequency modulation dead zone, executing the step 6); otherwise, executing the step 3);
6) The system enters a wind storage transition zone
The system frequency deviation reaches the energy storage frequency modulation dead zone boundary, and the fan exits frequency modulation to cause frequency modulation active mutation in consideration of the switching stage of the fan and the energy storage frequency modulation, so that the problem of mechanical fatigue of the fan is caused at the fan level; at the system level, the power shortage of the system is increased, so that the mechanical fatigue and the frequency drop are caused, therefore, the fan is arranged to smoothly reduce the frequency modulation power, and the calculation is carried out as follows:
i. recording the time t when the system frequency reaches the boundary of the energy storage dead zone 0 ；
ii, determining and inputting the exiting frequency modulation time delta t of the fan;
meter (III)Calculating the frequency modulation and transmission increasing power delta P output when the fan exits frequency modulation W (t) is formula (3):
wherein: ΔP W0 At t for the fan 0 Outputting frequency modulation and transmission increasing power at moment;
7) The system enters an energy storage frequency modulation response area
The system frequency deviation exceeds an energy storage frequency modulation dead zone, an energy storage frequency modulation control system is started, frequency modulation output is increased by energy storage according to the current State of Charge (SOC), and frequency modulation power calculation of the energy storage output is carried out as follows:
a. determining the current energy storage running state and SOC, and analyzing the potential of energy release/absorption of the energy storage during frequency modulation;
b. calculating the frequency modulation power of the energy storage output
Considering that the service life of the ESS is closely related to the charge and discharge depth, the cycle times and the operating temperature factors, in the frequency modulation stage, if the output power of the energy storage device is still forced when the energy storage SOC value is small, the service life of the energy storage system is irreversibly damaged, so that the coupling relation between the energy storage frequency modulation output power and the energy storage SOC is established, and the calculation expression is as follows:
wherein: ΔP BC (t) and ΔP BD (t) increasing the power of the energy storage system in the high-frequency and low-frequency stages respectively; k (k) B Is a proportionality coefficient and is used for adjusting the frequency modulation performance of energy storage; SOC (State of Charge) 0 The initial value of the SOC of the energy storage device; SOC (State of Charge) min 、SOC ma x is the minimum and maximum value of the energy storage device SOC respectively;
8) Energy storage detection whether frequency deviation is restored to fan frequency modulation area
If the frequency deviation is detected to be restored to the fan frequency modulation area, executing the step 4): otherwise, continuing to execute the step 7);
9) Grid frequency recovery stabilization
And (3) determining the output frequency modulation power of the fan and the energy storage through the steps 1) -8), and applying the frequency modulation power calculation result of the fan and the energy storage to the fan and the energy storage active power instruction value after the wind storage combined frequency modulation is started, so that the system frequency is recovered and stabilized.
Compared with the prior art, the wind-storage combined frequency modulation method considering the frequency modulation dead zone has the following technical effects:
(1) The method is different from the existing wind-storage combined frequency modulation, and proposes a time sequence frequency modulation control technical scheme of firstly carrying out fan and then storing energy, and stall phenomenon caused by excessive frequency modulation of the fan can be effectively avoided by reasonably setting a frequency modulation dead zone of the fan and an energy storage system, the charge and discharge times of the energy storage system are reduced, the cycle efficiency of the energy storage system is improved, and the maintenance cost is reduced;
(2) According to the frequency change times, the method divides the disturbed power grid frequency response into four stages: namely, a no-response area, a fan response area, a wind storage transition area and an energy storage response area, and is designed according to each section of frequency modulation process, and the fan response area is: the DFIG frequency modulation coefficient and the effective rotational kinetic energy of the rotor are established in a coupling relation, so that the rotational kinetic energy of the fan is more sufficient on the premise of ensuring the stability of the fan, and the system frequency fluctuation is restrained; for wind reservoir transition zone: the fan is smoothly withdrawn from frequency modulation, so that mechanical fatigue of a fan rotor is relieved, power shortage of a system is effectively reduced, and the possibility of secondary drop of the system frequency is avoided; for the energy storage response region: by establishing a coupling relation between the SOC of the energy storage system and the frequency modulation output power, the phenomenon of overcharge or overdischarge of the energy storage system is effectively avoided, and the service life of the energy storage system is prolonged.
(3) The method utilizes the primary function to construct the frequency modulation parameters of the wind-stored energy storage system, is simple in construction and easy to realize on hardware, and can realize frequency modulation increment with different variation degrees by adjusting the control parameters in the face of different engineering demands, thereby providing technical support for engineering application of the later energy storage system.
(4) The method is scientific and reasonable, and has strong applicability and good effect.
Drawings
FIG. 1 is a schematic block diagram of a wind reservoir model according to an embodiment of the present invention;
FIG. 2 is a flowchart illustrating steps for responding to a wind-powered system in accordance with an embodiment of the present invention;
FIG. 3 is a simulation system model of FIG. 1;
FIG. 4 is a graph of a random wind speed image of FIG. 1;
FIG. 5 (a) is a graph of grid frequency at 24% wind power permeability and 50MW active loss for example 1 of the present invention;
FIG. 5 (b) is a graph of wind reservoir frequency modulation output at 24% wind power permeability and 50MW active loss for example 1 of the present invention;
FIG. 5 (c) is a graph of fan speed at 24% wind power permeability and 50MW active loss for example 1 of the present invention;
FIG. 5 (d) is a plot of fan torque angle for example 1 of the present invention at 24% wind power permeability and 50MW active loss;
FIG. 5 (e) is a graph showing the change of the energy storage SOC at the time of active loss of 50MW at the wind power permeability of 24% in example 1 of the present invention;
FIG. 6 (a) is a graph of grid frequency at 24% wind power permeability and 80MW active loss for example 2 of the present invention;
FIG. 6 (b) is a graph of wind reservoir frequency modulation output at 24% wind power permeability and 80MW active loss for example 2 of the present invention;
FIG. 6 (c) is a plot of fan speed at 24% wind power permeability and 80MW active loss for example 2 of the present invention;
FIG. 6 (d) is a plot of fan torque angle for example 2 of the present invention at 24% wind power permeability and 80MW active loss;
FIG. 6 (e) is a graph showing the change of the energy storage SOC at the time of active loss of 80MW at 24% of wind power permeability in example 2 of the present invention;
FIG. 7 (a) is a graph of grid frequency at 40% wind power permeability and 80MW active loss for example 3 of the present invention;
FIG. 7 (b) is a graph of wind reservoir frequency modulation output at 40% wind power permeability and 80MW active loss for example 3 of the present invention;
FIG. 7 (c) is a plot of fan speed at 40% wind power permeability and 80MW active loss for example 3 of the present invention;
FIG. 7 (d) is a plot of fan torque angle for example 3 of the present invention at 40% wind power permeability and 80MW active loss;
fig. 7 (e) is a graph showing the change of the energy storage SOC at a wind power permeability of 40% and an active loss of 80MW in example 3 of the present invention.
Detailed Description
The invention is described in further detail below in connection with fig. 1 and the specific embodiment.
The present embodiment provides a wind storage model, and in a specific embodiment, the wind turbine generator model is a simplified model of a doubly-fed wind turbine generator. The whole principle block diagram of the invention is shown in figure 1, U ra 、U rb 、U rc U and U ga 、U gb 、U gc ABC three-phase voltages of a rotor side and a stator side of a doubly-fed wind generator (DFIG); the specific flow chart is shown in fig. 2, and specifically includes:
1) Frequency modulation dead zone of fan and energy storage system
Referring to the idea of setting a dead zone of a synchronous generator set, wherein the synchronous generator set adopts a small frequency modulation dead zone to participate in primary frequency modulation, uses a large frequency modulation dead zone and only responds to the change of the frequency of a power grid with large disturbance, and sets the frequency modulation dead zone of a fan to be smaller than an energy storage frequency modulation dead zone, wherein the frequency modulation dead zone of the fan is respectively [0,0.01] and [0,0.2];
2) Fluctuation of power grid frequency
The system detects that the frequency of the power grid fluctuates;
3) Fan detection frequency deviation exceeds frequency modulation dead zone of fan
If the fan detection frequency deviation exceeds the fan frequency modulation dead zone, executing the step 4); otherwise, executing the step 9);
4) The system enters into a fan frequency modulation response area
The system frequency deviation exceeds the fan frequency modulation dead zone, and the energy storage frequency modulation dead zone is not exceeded. And calculating the system frequency deviation delta f according to the detected power grid frequency, and taking the absolute value of the system frequency deviation delta f. The frequency modulation power calculation mode of the fan output is specifically as follows:
(1) Collecting the rotor rotating speed of the current fan, and analyzing the rotational kinetic energy capacity stored in the fan rotor according to the current running state of the fan;
(2) Calculating a fan frequency modulation coefficient:
in order to ensure that the fan can fully exert the frequency modulation potential of the fan under the premise of ensuring the stability of the fan, the DFIG frequency modulation coefficient and the effective rotational kinetic energy of the rotor are established in a coupling relation, and the expression is as follows:
wherein: k (K) WC 、K WD Frequency modulation coefficients of the fan at the high frequency stage and the low frequency stage are respectively obtained; omega r The DFIG rotation speed; omega min 、ω max The minimum and maximum rotational speeds of the DFIG; alpha is a grid frequency performance adjustment factor.
(3) Calculating the frequency modulation and transmission increasing power output by the fan:
in order to avoid noise caused by frequency differentiation, droop control is used, the frequency deviation of a power grid is in direct proportion to the output frequency modulation power, and the expression is as follows:
wherein: ΔP WC (t)、ΔP WD (t) increasing the power of the fan at the high frequency and the low frequency respectively; Δf is the system frequency deviation;
5) Energy storage detection frequency deviation exceeds frequency modulation dead zone
If the energy storage detects that the frequency deviation exceeds the self frequency modulation dead zone, executing the step 6); otherwise, executing the step 3);
6) The system enters a wind storage transition zone
The system frequency deviation reaches the energy storage frequency modulation dead zone boundary, and the fan exits frequency modulation to cause frequency modulation active mutation in consideration of the switching stage of the fan and the energy storage frequency modulation, so that the problem of mechanical fatigue of the fan is caused at the fan level; at the system level, the power shortage of the system is increased, so that the mechanical fatigue and the frequency drop are caused, therefore, the fan is arranged to smoothly reduce the frequency modulation power, and the calculation is carried out as follows:
i. recording the time t when the system frequency reaches the boundary of the energy storage dead zone 0 ；
ii, determining and inputting the exiting frequency modulation time delta t of the fan;
calculating the frequency modulation and transmission increasing power delta P output when the fan exits frequency modulation W (t) is formula (3):
wherein: ΔP W0 At t for the fan 0 Outputting frequency modulation and transmission increasing power at moment;
7) The system enters an energy storage frequency modulation response area
The system frequency deviation exceeds an energy storage frequency modulation dead zone, an energy storage frequency modulation control system is started, frequency modulation output is increased by energy storage according to the current State of Charge (SOC), and frequency modulation power calculation of the energy storage output is carried out as follows:
a. determining the current energy storage running state and SOC, and analyzing the potential of energy release/absorption of the energy storage during frequency modulation;
b. calculating the frequency modulation power of the energy storage output
Considering that the service life of the ESS is closely related to the charge and discharge depth, the cycle times and the operating temperature factors, in the frequency modulation stage, if the output power of the energy storage device is still forced when the energy storage SOC value is small, the service life of the energy storage system is irreversibly damaged, so that the coupling relation between the energy storage frequency modulation output power and the energy storage SOC is established, and the calculation expression is as follows:
wherein: ΔP BC (t) and ΔP BD (t) respectivelyIncreasing the power of the energy storage system in the high-frequency and low-frequency stages; k (k) B Is a proportionality coefficient and is used for adjusting the frequency modulation performance of energy storage; SOC (State of Charge) 0 The initial value of the SOC of the energy storage device; SOC (State of Charge) min 、SOC ma x is the minimum and maximum value of the energy storage device SOC respectively;
8) Energy storage detection whether frequency deviation is restored to fan frequency modulation area
If the frequency deviation is detected to be restored to the fan frequency modulation area, executing the step 4): otherwise, continuing to execute the step 7);
9) Grid frequency recovery stabilization
And (3) determining the output frequency modulation power of the fan and the energy storage through the steps 1) -8), and applying the frequency modulation power calculation result of the fan and the energy storage to the fan and the energy storage active power instruction value after the wind storage combined frequency modulation is started, so that the system frequency is recovered and stabilized.
The technical effects of the present invention will be described in detail with reference to simulation examples.
The invention establishes an IEEE14 node simulation system with different wind power permeabilities based on an EMTP-RV simulation platform for verification, wherein the simulation system comprises a DFIG aggregate wind power plant with energy storage power/capacity of 40MW/6 MW.h, 5 synchronous generator sets and static load with capacity of 600MW, as shown in figure 3.
In order to alleviate the problems of service life reduction and mechanical fatigue caused by frequent frequency modulation of the wind storage system, the frequency modulation dead zone of the synchronous machine is set, and the frequency modulation dead zones of the fan and the ESS are respectively set to be 0.01Hz<Δf<0.2Hz and Δf>0.2Hz. Alpha is set to 46.6, delta t is set to 5 seconds, k B Set to 300.
In actual operation, wind speed fluctuation is a main disturbance factor causing frequency fluctuation, the fluctuation wind speed penetrates through the wind speed fluctuation simulation device in the whole simulation, a wind speed image is shown in fig. 4, and the synchronous machine SG2 is cut off as high-power disturbance excitation in the simulation process 130 s. The effectiveness of the proposed method was verified under fan only, energy storage only and wind storage frequency modulation methods, respectively, with specific example settings as shown in tables 1 and 2, respectively.
Table 1 example settings
Table 2 frequency modulation method settings
Example 1: wind power permeability 24%, active loss 50MW
FIG. 5 shows that the maximum positive and negative frequency deviations for the non-FM control method are 0.21Hz and 0.19Hz, respectively, during 60s to 130s, subject to wind speed variations; 130s is affected by the off-line of the synchronous machine, and the lowest point of the power grid frequency drops to 59.40Hz.
During the period of only wind speed variation, the method 2 can effectively inhibit frequency fluctuation, wherein the positive and negative maximum frequency deviation is respectively reduced to 0.15Hz and 0.15Hz, mainly because the fan participates in frequency modulation through rotor throughput kinetic energy; after the synchronous machine is offline, the lowest frequency point is lifted to 59.54Hz, the reason is that the depth of invoking the kinetic energy of the rotor is increased by the fan, the maximum frequency modulation and power increase reaches 24.62MW, the torque angle of the transmission system is increased to 0.44deg., the mechanical stress is increased, and meanwhile, the minimum rotating speed reaches 0.79p.u., so that the risk of stalling of the fan exists.
In the wind speed variation stage and the synchronous machine set offline scene, the method 3 realizes almost the same frequency modulation performance as the method 2 through the charge and discharge of the stored energy. However, when the frequency is small and fluctuated due to wind speed variation, the ESS is shallow charged and discharged for 6 times to participate in frequency modulation, and long-time accumulation of frequent charging and discharging phenomena tends to reduce the service life of the energy storage device.
When the wind storage system adopts the method 4, when the wind speed only changes, the frequency does not exceed the energy storage frequency modulation dead zone under the frequency modulation of the fan, so that the frequent participation of energy storage in frequency modulation can be avoided, and the circulating service life of the wind storage system is prolonged; after the synchronous machine is offline, the frequency drops out of an energy storage frequency modulation dead zone, a wind storage transition zone is established, the fan smoothly exits frequency modulation and is restored to an MPPT operation mode, in addition, the lowest point of the power grid frequency is 0.02Hz higher than that of the method 3, because the wind storage temporarily participates in frequency modulation at the same time, and the maximum frequency modulation power is 6.41MW higher than that of the method 3; the ESS then solely assumes the frequency modulation task, maintaining the superior frequency modulation characteristics of method 3, while avoiding the risk of stall of the fan due to too low rotational speed. Although method 4 stored SOC was 0.12% lower than method 3 SOC, there was little impact on ESS.
If the wind storage system participates in frequency modulation at the same time when the wind speed changes, the frequency fluctuation can be effectively stabilized, however, the frequent charge and discharge of the energy storage seriously affects the service life.
Example 2: wind power permeability 24%, active loss 80MW
In the wind speed variation interval, the wind storage frequency modulation system has similar frequency modulation effect by adopting the method 2, the method 3 and the method 4, however, the frequent charge and discharge phenomena of the energy storage system in the method 3 are not beneficial to the service life of the wind storage frequency modulation system.
The frequency minimum points of the synchronous machine set offline interval, method 2, method 3 and method 4 are respectively as follows: 59.30, 59.35 and 59.36Hz, the maximum amplified frequency modulation output of method 2, method 3 and method 4 is increased by 9.4, 9.97 and 12.36MW respectively, compared with that of example 1, so that the frequency modulation effect is improved to different degrees, as shown in figure 6. The method 2 is disturbed and increased, more rotor kinetic energy is released to participate in frequency modulation, so that the lowest point of the rotating speed reaches 0.77p.u., and the risk of stall of the fan is increased; method 4 maintains the good frequency modulation capability at example 1.
Example 3: wind power permeability 40%, active loss 80MW
While the system inertia and frequency modulation decrease with increasing wind-electricity permeability, the problems of the method 2 of fan stall risk and the method 3 of energy storage life decrease are not improved, and the method 4 can still realize advantage complementation through time sequence control of the wind-storage system, and maintain high-quality frequency modulation capability, as shown in fig. 7, although the frequency modulation capability under low permeability is maintained by each method.
From the simulation results, the frequency modulation characteristics of the fan and the energy storage can be effectively utilized, from the perspective of the fan and the energy storage, the stall phenomenon caused by the excessive release of the rotor kinetic energy of the fan is avoided, meanwhile, the charge and discharge times of the energy storage system are reduced, and the cycle efficiency is improved; from the aspect of a power system, the stability of the system frequency under the high wind power grid-connected background is improved. The feasibility and effectiveness of the wind-storage combined frequency modulation method considering the frequency modulation dead zone are proved.
The specific embodiments of the invention are not intended to be exhaustive, and modifications and variations that do not require inventive faculty are intended to be within the scope of the invention as defined by the claims.
Claims (1)
1. The wind-storage combined frequency modulation control method for the frequency modulation dead zone is characterized by comprising the following steps of:
1) Frequency modulation dead zone of fan and energy storage system
Referring to the idea of setting a dead zone of a synchronous generator set, wherein the synchronous generator set adopts a small frequency modulation dead zone to participate in primary frequency modulation, uses a large frequency modulation dead zone and only responds to the change of the frequency of a power grid with large disturbance, and sets the frequency modulation dead zone of a fan to be smaller than an energy storage frequency modulation dead zone, wherein the frequency modulation dead zone of the fan is respectively [0,0.01] and [0,0.2];
2) Fluctuation of power grid frequency
The system detects that the frequency of the power grid fluctuates;
3) Fan detection frequency deviation exceeds frequency modulation dead zone of fan
If the fan detection frequency deviation exceeds the fan frequency modulation dead zone, executing the step 4); otherwise, executing the step 9);
4) The system enters into a fan frequency modulation response area
The system frequency deviation exceeds the fan frequency modulation dead zone, but does not exceed the energy storage frequency modulation dead zone, the system frequency deviation deltaf is calculated according to the detected power grid frequency, and the absolute value is taken, and the frequency modulation power output by the fan is calculated in the following specific mode:
(1) Collecting the rotor rotating speed of the current fan, and analyzing the rotational kinetic energy capacity stored in the fan rotor according to the current running state of the fan;
(2) Calculating a fan frequency modulation coefficient:
in order to ensure that the fan can fully exert the frequency modulation potential of the fan under the premise of ensuring the stability of the fan, the DFIG frequency modulation coefficient and the effective rotational kinetic energy of the rotor are established in a coupling relation, and the expression is as follows:
wherein: k (K) WC 、K WD Frequency modulation coefficients of the fan at the high frequency stage and the low frequency stage are respectively obtained; omega r The DFIG rotation speed; omega min 、ω max The minimum and maximum rotational speeds of the DFIG; alpha is a power grid frequency performance adjusting factor;
(3) Calculating the frequency modulation and transmission increasing power output by the fan:
in order to avoid noise caused by frequency differentiation, droop control is used, and the power grid frequency deviation is directly proportional to the output frequency modulation power, and the expression is as follows:
wherein: ΔP WC (t)、ΔP WD (t) increasing the power of the fan at the high frequency and the low frequency respectively; Δf is the system frequency deviation;
5) Energy storage detection frequency deviation exceeds frequency modulation dead zone
If the energy storage detects that the frequency deviation exceeds the self frequency modulation dead zone, executing the step 6); otherwise, executing the step 3);
6) The system enters a wind storage transition zone
The system frequency deviation reaches the energy storage frequency modulation dead zone boundary, and the fan exits frequency modulation to cause frequency modulation active mutation in consideration of the switching stage of the fan and the energy storage frequency modulation, so that the problem of mechanical fatigue of the fan is caused at the fan level; at the system level, the power shortage of the system is increased, so that the mechanical fatigue and the frequency drop are caused, therefore, the fan is arranged to smoothly reduce the frequency modulation power, and the calculation is carried out as follows:
i. recording the time t when the system frequency reaches the boundary of the energy storage dead zone 0 ；
ii, determining and inputting the exiting frequency modulation time delta t of the fan;
calculating the frequency modulation and transmission increasing power delta P output when the fan exits frequency modulation W (t) is formula (3):
wherein: ΔP W0 At t for the fan 0 Outputting frequency modulation and transmission increasing power at moment;
7) The system enters an energy storage frequency modulation response area
The system frequency deviation exceeds an energy storage frequency modulation dead zone, an energy storage frequency modulation control system is started, frequency modulation output is increased by energy storage according to the current State of Charge (SOC), and frequency modulation power calculation of the energy storage output is carried out as follows:
a. determining the current energy storage running state and SOC, and analyzing the potential of energy release/absorption of the energy storage during frequency modulation;
b. calculating the frequency modulation power of the energy storage output
Considering that the service life of the ESS is closely related to the charge and discharge depth, the cycle times and the operating temperature factors, in the frequency modulation stage, if the output power of the energy storage device is still forced when the energy storage SOC value is small, the service life of the energy storage system is irreversibly damaged, so that the coupling relation between the energy storage frequency modulation output power and the energy storage SOC is established, and the calculation expression is as follows:
wherein: ΔP BC (t) and ΔP BD (t) increasing the power of the energy storage system in the high-frequency and low-frequency stages respectively; k (k) B Is a proportionality coefficient and is used for adjusting the frequency modulation performance of energy storage; SOC (State of Charge) 0 The initial value of the SOC of the energy storage device; SOC (State of Charge) min 、SOC ma x is the minimum and maximum value of the energy storage device SOC respectively;
8) Energy storage detection whether frequency deviation is restored to fan frequency modulation area
If the frequency deviation is detected to be restored to the fan frequency modulation area, executing the step 4): otherwise, continuing to execute the step 7);
9) Grid frequency recovery stabilization
And (3) determining the output frequency modulation power of the fan and the energy storage through the steps 1) -8), and applying the frequency modulation power calculation result of the fan and the energy storage to the fan and the energy storage active power instruction value after the wind storage combined frequency modulation is started, so that the system frequency is recovered and stabilized.
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| CN116742699A (en) * | 2023-05-19 | 2023-09-12 | 国网湖北省电力有限公司随州供电公司 | Wind-solar energy storage station centralized frequency modulation control method and system considering power grid frequency characteristics |
| CN117375027A (en) * | 2023-12-08 | 2024-01-09 | 华控泰思(北京)储能技术有限公司 | Wind-storage combined frequency modulation frequency control method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116742699A (en) * | 2023-05-19 | 2023-09-12 | 国网湖北省电力有限公司随州供电公司 | Wind-solar energy storage station centralized frequency modulation control method and system considering power grid frequency characteristics |
| CN117375027A (en) * | 2023-12-08 | 2024-01-09 | 华控泰思(北京)储能技术有限公司 | Wind-storage combined frequency modulation frequency control method |
| CN117375027B (en) * | 2023-12-08 | 2024-02-27 | 华控泰思(北京)储能技术有限公司 | Wind-storage combined frequency modulation frequency control method |
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