Wind farm and energy storage quasi-synchronous machine grid frequency coordination support control method and system

Abstract

The application provides a wind farm and energy storage quasi-synchronous machine grid frequency cooperative support control method and system, comprising: based on the grid frequency response process of the traditional synchronous generator, the response of the wind farm-wind farm-flexible-wind energy storage system to the load change of the grid is remodeled to obtain the ΔP in the response process; based on the size relationship between the ΔP and the active output of the energy storage system, the frequency response control of the wind turbine and the energy storage system is cooperated. The application decomposes the grid frequency response process of the traditional synchronous generator, and cooperates the frequency response control of the wind turbine and the energy storage system respectively, so that the response of the wind power and the energy storage is integrated, the similar characteristics of the traditional synchronous generator power are embodied, the frequency stability of the grid is enhanced, and the work of the grid dispatchers is facilitated.

Description

Technical Field

[0001] This invention relates to the field of power grid technology, and more specifically, to a method and system for frequency coordination support control of a quasi-synchronous power grid for wind farms and energy storage. Background Technology

[0002] As my country's power system gradually shifts from being dominated by traditional fossil fuels to clean and renewable energy, the characteristics of the power grid are also changing. Specifically, this manifests as increased power supply volatility, reduced power system inertia, and weakened equivalent grid strength. Against this backdrop, the ever-growing capacity of wind power (hundreds of MW to GW levels) is replacing fossil fuels while also bringing corresponding challenges. The replacement of synchronous generators by wind power, with its inertia-free operation, reduces the overall inertia of the power grid, severely impacting the frequency stability of grid operation. To build a new energy system with wind and solar power as the primary power source, wind farms need to transform from follower-type power sources to dominant-type power sources, acting to some extent as analogous to synchronous generators, undertaking the responsibility of establishing power system voltage and maintaining real-time energy balance, thus supporting grid frequency stability. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for coordinated grid frequency support control of wind farms and energy storage.

[0004] According to one aspect of the present invention, a method for coordinated grid frequency support control of a quasi-synchronous machine for wind farms and energy storage is provided, comprising:

[0005] Based on the grid frequency response process of synchronous generators, the response reshaping of wind farm-flexible DC-energy storage system to grid load changes is performed to obtain the actual additional power ΔP required by the system during the response reshaping process;

[0006] Based on the relationship between the actual power increase ΔP required by the system and the active power output of the energy storage system, the frequency response of the wind turbine and the energy storage system are controlled in a coordinated manner.

[0007] Preferably, the grid frequency response process of the synchronous generator includes:

[0008] At time t1, the synchronous generator has two initial operating points, namely the initial active power P0 and the initial frequency f0.

[0009] At time t1, a load surge occurs, and the active power changes abruptly from P0 to P1. At this time, the synchronous generator, based on its electrical distance to the load surge point, undertakes the increased power from P1 to P0; simultaneously, the output frequency begins to decrease from f0.

[0010] During the time period t1-t2, the load power is redistributed among multiple synchronous generators according to the magnitude of their inertia, and power angle oscillation occurs. After time point P2, the oscillation ends, the load power borne by each synchronous generator tends to stabilize, and finally transitions to P3. P3 is determined by the frequency regulation coefficient of the load and the primary frequency regulation coefficient of the generator itself.

[0011] Time t3 is the time corresponding to P3. At this time, the output frequency is also stable at f3.

[0012] Preferably, the process of reshaping the wind farm-flexible DC-energy storage system's response to grid load changes to obtain the actual additional power ΔP required by the system during the response reshaping process includes:

[0013] Detect the rate of frequency change when the power grid frequency change exceeds the dead zone;

[0014] Based on the frequency change rate, and according to the virtual inertia of the wind farm-flexible DC-energy storage system, the power required to be generated when the grid frequency change exceeds the dead zone is calculated.

[0015] By incorporating a delay factor, the actual power required to be increased is obtained based on the calculated power increase.

[0016] The actual power required to be increased decreases as the frequency decreases until the final actual power required to be increased is obtained;

[0017] Entering the first frequency modulation phase.

[0018] Preferably, the additional power required when the grid frequency change exceeds the dead zone is specifically as follows:

[0019]

[0020] ΔP0 represents the additional power required calculated from the virtual inertia; H v The virtual inertia coefficient, representing the effect of frequency changes on power changes, is related to the number of submodules and the size of the submodule capacitors; ω g Represents the power grid frequency, dω g / dt represents the change in grid frequency.

[0021] Preferably, the actual power increase required is specifically as follows:

[0022]

[0023] ΔP represents the actual additional power required by the system; ΔP0 represents the additional power required calculated by virtual inertia, that is, the theoretical additional power required when the grid frequency change exceeds the dead zone. Let K represent a first-order inertial element, and let K represent the delay caused by the control, detection, and filtering components.PF The proportionality coefficient between the frequency change and the active power change, also known as the primary frequency regulation coefficient; Δω g It represents the change in frequency.

[0024] Preferably, the final actual required additional power is specifically as follows:

[0025] ΔP=-K PF Δω g .

[0026] Preferably, the step of coordinating the frequency response of the wind turbine and the energy storage system based on the relationship between the actual power increase ΔP required by the system and the active power output of the energy storage system includes:

[0027] If the active power output capacity of the energy storage system is greater than the actual additional power ΔP required by the system, then all the power will be provided by the energy storage system.

[0028] Preferably, the step of coordinating the frequency response of the wind turbine and the energy storage system based on the relationship between ΔP and the active power output of the energy storage system includes:

[0029] If the active power output of the energy storage system is less than ΔP, the inertial response is provided by the wind turbine, and the remaining power is supplemented by the energy storage system.

[0030] Preferably, if the energy storage system is still unable to replenish the active power output to ΔP after the wind turbine provides inertial response, the energy storage system outputs at maximum power.

[0031] According to a second aspect of the present invention, a quasi-synchronous grid frequency coordination support control system for wind farms and energy storage is provided, comprising:

[0032] Response reshaping module: Based on the grid frequency response process of synchronous generators, the response reshaping of wind farm-flexible DC-energy storage system to grid load changes is performed to obtain the actual additional power ΔP required by the system during the response reshaping process;

[0033] System response module: Based on the relationship between the actual power increase ΔP required by the system and the active power output of the energy storage system, it coordinates the frequency response of the wind turbine and the energy storage system.

[0034] Compared with the prior art, the embodiments of the present invention have at least one of the following beneficial effects:

[0035] The wind farm and energy storage quasi-synchronous generator grid frequency coordinated support control method and system in this embodiment of the invention decomposes the grid frequency response process of traditional synchronous generators and coordinates the frequency response control of wind turbines and energy storage systems respectively, so that the response of wind power and energy storage is integrated, exhibiting characteristics similar to traditional synchronous generator power supply, thereby enhancing the frequency stability of the grid and facilitating the work of grid dispatchers. Attached Figure Description

[0036] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0037] Figure 1 This is a flowchart of a quasi-synchronous grid frequency coordinated support control method for wind farms and energy storage in one embodiment of the present invention.

[0038] Figure 2 This is a schematic diagram of the response process of a synchronous generator to changes in grid load in a preferred embodiment of the present invention; wherein, (a) represents active power and (b) represents frequency;

[0039] Figure 3 This is a schematic diagram of the response reshaping process of the wind farm-flexible DC-energy storage system to changes in grid load in a preferred embodiment of the present invention, wherein (a) represents active power and (b) represents frequency;

[0040] Figure 4 This is a single-line diagram of the simulation system in a specific embodiment of the present invention;

[0041] Figure 5 This is a schematic diagram of the grid frequency response results of the simulation system connected to the synchronous grid in a specific embodiment of the present invention; wherein (a) represents the synchronous machine speed (grid frequency); (b) represents the bipolar DC voltage difference; (c) represents the wind farm frequency; (d) represents the output active power of wind farm 1; (e) represents the output active power of the energy storage of wind farm 1; (f) represents the output active power of wind farm 2; (g) represents the output active power of the energy storage of wind farm 2; (h) represents the active power of wind farm-side converter 1; (i) represents the active power of wind farm-side converter 2; (j) represents the active power of grid-side converter 1; and (k) represents the active power of grid-side converter 2. Detailed Implementation

[0042] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0043] In one embodiment of the present invention, a method for coordinated grid frequency support control of a quasi-synchronous machine for wind farms and energy storage is provided, such as... Figure 1 As shown, it includes the following steps:

[0044] Step 1: Based on the grid frequency response process of the synchronous generator, reshape the response of the wind farm-flexible DC-energy storage system to grid load changes, and obtain the actual additional power ΔP required by the system during the response reshaping process;

[0045] Step 2: Based on the relationship between the power ΔP that the system actually needs to generate and the active power output of the energy storage system, coordinate the frequency response of the wind turbine and the energy storage system.

[0046] The above embodiments can solve the problem that the coordination between wind farms and energy storage in the current frequency response of the power grid is not good, and it is impossible to simulate the response characteristics of real synchronous generators.

[0047] In a preferred embodiment of the present invention, the grid frequency response process of a conventional synchronous generator is decomposed. For example... Figure 2 Figures (a) and (b) show the active power and frequency response curves of a typical synchronous generator during a sudden increase in grid load, respectively. P0 and f0 are the initial operating points of the synchronous generator. At time t1, a sudden load change occurs. At this time, the synchronous generator takes on the load increase power of (P1-P0) according to the electrical distance to the load change point, and the output frequency begins to decrease. During the time period t1-t2, the load power is redistributed among multiple synchronous generators according to the magnitude of inertia, and a small power angle oscillation occurs. After time point P2, the oscillation ends, the load power undertaken by each unit tends to stabilize, and finally transitions to P3. P3 is determined by the frequency regulation coefficient of the load and the primary frequency regulation coefficient of the unit itself.

[0048] Based on the grid frequency response process of the traditional synchronous generator in the above embodiments, another preferred embodiment reshapes the response of the wind farm-flexible DC-energy storage system to grid load changes. For the wind farm-flexible DC-energy storage system, it is not necessary to simulate the output power fluctuation caused by the power angle oscillation during the period P1-P2; instead, the response characteristics shown in Figures (a) and (b) of 3 can be used. Specifically:

[0049] After the grid frequency change exceeds the dead zone, the frequency change rate df / dt is detected, and the additional power required at this time is calculated based on the virtual inertia of the wind farm-flexible DC-energy storage system.

[0050]

[0051] Where ΔP0 represents the additional power required calculated from the virtual inertia; H v The virtual inertia coefficient, representing the effect of frequency changes on power changes, is related to the number of submodules and the size of the submodule capacitors; ω g Represents the power grid frequency, dω g / dt represents the change in grid frequency. Since ω=2πf, this formula can be expressed as: This establishes the relationship between the rate of change of power grid frequency and the change of active power. Since 2π is a constant, ω is commonly used. g Replace f g Indicates the power grid frequency.

[0052] Ideally, the increased power should be instantaneous, but in reality, due to delays in control, detection, and filtering, the actual power response will have a delay of about 100ms. Then, the settings are:

[0053]

[0054] In the formula, ΔP represents the actual additional power required by the system; ΔP0 represents the additional power required calculated by the virtual inertia, that is, the theoretical additional power required when the grid frequency change exceeds the dead zone. Let K represent a first-order inertial element, and let K represent the delay caused by control, detection, and filtering processes. PF The proportionality coefficient between the frequency change and the active power change can also be expressed as the primary frequency regulation coefficient; Δω g It represents the change in frequency.

[0055] At this point, ΔP will continue to decrease as the frequency decreases, until finally:

[0056] ΔP=-K PF Δω g

[0057] Primary frequency regulation refers to the system adjusting its active power to adapt to changes in system frequency. The required additional power calculated using virtual inertia deviates from the actual required additional power due to physical factors (delays in control, detection, and filtering processes). Therefore, after completely filtering out this deviation, the system enters the primary frequency regulation stage. That is, when ΔP = -K... PF Δω g It then enters a frequency modulation phase.

[0058] Through the reshaping process described in the above embodiments, ΔP is obtained for the entire response process. In some preferred embodiments, if the active power output capability of the energy storage is greater than ΔP, then all power can be provided by the energy storage. In other embodiments, if the active power output capability of the energy storage is less than ΔP, then the wind turbine needs to provide the inertial response, and the energy storage can then make up the remainder. Furthermore, if the energy storage still cannot make up the active power output to ΔP after the wind turbine provides the inertial response, then the energy storage can output at its maximum power.

[0059] Based on the same inventive concept, other embodiments of the present invention provide a quasi-synchronous grid frequency coordination support control system for wind farms and energy storage, comprising:

[0060] Response reshaping module: Based on the grid frequency response process of synchronous generators, the response reshaping of wind farm-flexible DC-energy storage system to grid load changes is performed to obtain the actual additional power ΔP required by the system during the response reshaping process;

[0061] System response module: Based on the relationship between the actual power increase ΔP required by the system and the active power output of the energy storage system, it coordinates the frequency response of the wind turbine and the energy storage system.

[0062] The specific implementation techniques of each module / unit in the above examples of the present invention can be referred to the steps of the pseudo-synchronous machine grid frequency coordinated support control method for wind farms and energy storage in the above embodiments, which will not be repeated here.

[0063] To verify the feasibility and effectiveness of the quasi-synchronous machine-grid frequency coordinated support control method for wind farms and energy storage proposed in the above embodiments, a specific embodiment of the present invention establishes a simulation model of a large-scale wind farm connected to the grid via a multi-terminal flexible DC transmission system in PSCAD / EMTDC based on the simulation system shown in Figure 4. In this model, the capacity of wind farm 1, wind farm-side converter 1, and grid-side converter 1 is 750MW each, and the capacity of wind farm 2, wind farm-side converter 2, and grid-side converter 12 is 1500MW each. The specific parameters of the system are shown in the table below:

[0064] Table 1 Parameters of Wind Farm-Side Converter Station 1 and Grid-Side Converter Station 1

[0065]

[0066] Table 2 Parameters of Wind Farm Side Converter Station 2 and Grid Side Converter Station 2

[0067]

[0068] Table 3 Line Parameters

[0069]

[0070]

[0071] Table 4 Aggregate parameters of full-power wind turbine generators

[0072]

[0073] Both grid-side converter 1 and grid-side converter 2 are connected to the same power grid, which consists of a 20GW synchronous generator and a 5GW load equivalent. The K-axis of grid-side converter 1... P Set to 1, K dc Set to 5, K W Set to 125, H v Set to 0.1s, active power setpoint is 375MW. K of grid-side converter 2. P Set to 1, K dc Set to 10, K W Set to 250, H v The simulation was set to 0.1s, with an active power setpoint of 750MW. Energy storage systems with 15% of the rated capacity were connected to the AC side of the sending-end converter. At 15s, the grid load suddenly increased by 1GW. The simulation results are as follows: Figure 5 As shown in Figures (a)-(k), it can be observed that when the grid frequency changes, the frequency change is accurately mapped onto the frequencies of the two wind farms via the DC grid and the bipolar DC voltage difference. After the wind turbines detect the frequency change, both wind farms can provide inertial response in real time. The supporting power provided by the wind farms can be proportionally distributed between the converters on the two grid sides and flows into the grid, damping the grid frequency change. After the inertial response ends, the energy storage system can also compensate for the reduced power of the wind turbines, avoiding secondary power drops. Furthermore, through the reshaping of the energy storage system, the grid frequency response characteristics of the wind farm-flexible DC grid connection system can be made close to the response characteristics of a synchronous generator.

[0074] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.

Claims

1. A method for coordinated grid frequency support control of a quasi-synchronous machine for wind farms and energy storage, characterized in that, include: Based on the grid frequency response process of synchronous generators, the response reshaping of the wind farm-flexible DC-energy storage system to grid load changes is performed to obtain the actual additional power ΔP required by the system during the response reshaping process, including: Detect the rate of frequency change when the power grid frequency change exceeds the dead zone; Based on the frequency change rate, and according to the virtual inertia of the wind farm-flexible DC-energy storage system, the power required to be generated when the grid frequency change exceeds the dead zone is calculated. By incorporating a delay factor, the actual power increase required is obtained from the calculated required additional power, specifically: ； ΔP represents the actual additional power required by the system; This represents the additional power required calculated from the virtual inertia, which is the theoretically required additional power when the grid frequency change exceeds the dead zone. This represents a first-order inertial element, indicating the delay caused by the control, detection, and filtering components. It represents the proportionality coefficient between the frequency change and the active power change, and is also called the primary frequency regulation coefficient; Represents the change in frequency; The actual power required to be increased decreases as the frequency decreases until the final actual power required to be increased is obtained; Entering the first frequency modulation phase; Based on the relationship between the actual power increase ΔP required by the system and the active power output of the energy storage system, the frequency response of the wind turbine and the energy storage system are controlled in a coordinated manner.

2. The method for coordinated grid frequency support control of a quasi-synchronous machine for wind farms and energy storage according to claim 1, characterized in that, The grid frequency response process of the synchronous generator includes: time t 1. A synchronous generator has two initial operating points, namely the initial active power. P 0 and initial frequency f 0; time t 1. A sudden load change occurs, and the active power is changed from... P 0 mutation to P 1. At this time, the synchronous generator undertakes the load based on the electrical distance to the point of sudden load change. P 1- P 0 load surge power; simultaneously, the output frequency changes from f It started to decline from 0; Time period t 1- t 2. Multiple synchronous generators redistribute load power based on their inertia, resulting in power angle oscillations. P After point 2, the oscillation ended, the load power borne by each synchronous generator tended to stabilize, and eventually... P 3. Transition; among which, P 3. It is determined by both the load frequency regulation coefficient and the unit's primary frequency regulation coefficient; Time t3 is P At the time corresponding to 3, the output frequency also stabilizes at... f 3 .

3. The method for coordinated grid frequency support control of a quasi-synchronous machine for wind farms and energy storage according to claim 1, characterized in that, The additional power required when the grid frequency change exceeds the dead zone is specifically as follows: ； This represents the additional power required calculated from the virtual inertia. The virtual inertia coefficient is used to characterize the effect of frequency changes on power changes, and is related to the number of sub-modules and the size of the sub-module capacitors. Represents the power grid frequency. This represents changes in the power grid frequency.

4. The method for coordinated grid frequency support control of a quasi-synchronous machine for wind farms and energy storage according to claim 1, characterized in that, The final actual required additional power is as follows: 。 5. The method for coordinated grid frequency support control of a quasi-synchronous machine for wind farms and energy storage according to claim 1, characterized in that, The method of coordinating the frequency response of the wind turbine and the energy storage system based on the relationship between the actual power increase ΔP required by the system and the active power output of the energy storage system includes: If the active power output capacity of the energy storage system is greater than the actual additional power ΔP required by the system, then all the power will be provided by the energy storage system.

6. The method for coordinated grid frequency support control of a quasi-synchronous machine for wind farms and energy storage according to claim 1, characterized in that, The method of coordinating the frequency response of the wind turbine and the energy storage system based on the relationship between ΔP and the active power output of the energy storage system includes: If the active power output capacity of the energy storage system is less than Δ P In this case, the inertial response is provided by the wind turbine, and the remaining power is supplemented by the energy storage system.

7. The method for coordinated grid frequency support control of a quasi-synchronous machine for wind farms and energy storage according to claim 6, characterized in that, If the wind turbine provides inertial response, the energy storage system is still unable to compensate for the active power output to Δ. P If so, the energy storage system will output at maximum power.

8. A quasi-synchronous grid frequency coordinated support control system for wind farms and energy storage, characterized in that, include: Response reshaping module: Based on the grid frequency response process of synchronous generators, the response reshaping of the wind farm-flexible DC-energy storage system to grid load changes is performed to obtain the actual additional power ΔP required by the system during the response reshaping process, including: Detect the rate of frequency change when the power grid frequency change exceeds the dead zone; Based on the frequency change rate, and according to the virtual inertia of the wind farm-flexible DC-energy storage system, the power required to be generated when the grid frequency change exceeds the dead zone is calculated. By incorporating a delay factor, the actual power increase required is obtained from the calculated required additional power, specifically: ； This indicates the actual additional power required by the system. This represents the additional power required calculated from the virtual inertia, which is the theoretically required additional power when the grid frequency change exceeds the dead zone. This represents a first-order inertial element, indicating the delay caused by the control, detection, and filtering components. It represents the proportionality coefficient between the frequency change and the active power change, and is also called the primary frequency regulation coefficient; Represents the change in frequency; The actual power required to be increased decreases as the frequency decreases until the final actual power required to be increased is obtained; Entering the first frequency modulation phase; System response module: Based on the relationship between the actual power increase ΔP required by the system and the active power output of the energy storage system, it coordinates the frequency response of the wind turbine and the energy storage system.

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