A control method for hybrid energy storage-assisted photovoltaic power station participating in primary frequency regulation

Abstract

The present invention discloses a control method for a hybrid energy storage-assisted photovoltaic power station to participate in primary frequency regulation. The hybrid energy storage system composed of a flywheel and a lithium battery is used to combine the advantages of the two energy storages, and the economic efficiency of the energy storage-assisted photovoltaic power station to participate in the primary frequency regulation of the power grid is improved while ensuring the primary frequency regulation effect. When the power system experiences a long period of continuous random load fluctuation, the power grid frequency deviation is decomposed into two parts through a frequency divider, the high-frequency part of the frequency deviation is adjusted by the flywheel energy storage in the hybrid energy storage system, and the low-frequency part of the frequency deviation is adjusted by the lithium battery energy storage in the hybrid energy storage system, thereby reducing the number of charge and discharge times of the lithium battery energy storage and extending its service life.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a control method for a hybrid energy storage-assisted photovoltaic power station to participate in primary frequency modulation. Background Art

[0002] With the proposal of the "dual carbon" goal, the penetration rate of photovoltaic power generation in the power system has increased significantly. However, the access of a large number of photovoltaic and wind power to the power system has had a great impact on the safe and stable operation of the power grid. On the one hand, the intermittent and random nature of photovoltaic power generation poses a serious threat to the frequency stability of the power grid; on the other hand, in order to improve the utilization rate of photovoltaic power, photovoltaic power generation generally works in the maximum power tracking operation state, does not provide inertia support, does not reserve spare capacity, and photovoltaic power generation is connected to the grid through the power electronics interface, which has a very limited frequency support effect on the power grid. Energy storage has the advantages of bidirectional regulation, fast charging and discharging speed and high regulation accuracy. Installing an energy storage system in a photovoltaic power station can assist the photovoltaic power station in participating in primary frequency regulation and improve the active support role of the photovoltaic power station for the power grid frequency. Power-type energy storage, such as flywheel energy storage, has the advantages of high cycle number, high short-time charging and discharging power and fast response speed, but the unit capacity cost is high; energy-type energy storage, such as lithium batteries, has a low cost, but the low cycle number, slow response speed and frequent charging and discharging will seriously reduce its life. When the power system experiences continuous random load fluctuations for a long period of time, a single power-type energy storage is difficult to participate in a frequency modulation for a long time due to its limited capacity; although a single energy-type energy storage has a large capacity and can participate in a frequency modulation for a long time, frequent charging and discharging will seriously shorten its life and increase the number of times it needs to be replaced. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the above technical defects and provide a control method for a hybrid energy storage-assisted photovoltaic power station to participate in primary frequency regulation. The hybrid energy storage system composed of a flywheel and a lithium battery is used to combine the respective advantages of the two energy storages. While ensuring the primary frequency regulation effect, the economy of the energy storage-assisted photovoltaic power station participating in the primary frequency regulation of the power grid is improved.

[0004] In order to solve the above technical problems, the technical solution provided by the present invention is: a control method for a hybrid energy storage-assisted photovoltaic power station to participate in primary frequency modulation, comprising the following steps:

[0005] 1) When the grid in the area where the photovoltaic power station is located experiences a long period of continuous random load fluctuation, the grid frequency f of the photovoltaic storage system grid connection point is collected, and the frequency deviation Δf between the grid frequency f of the grid connection point and the grid reference frequency f0 is calculated, where f0 is 50Hz;

[0006] 2) Design a first-order low-pass filter link, and filter the frequency deviation Δf through the first-order low-pass filter link to obtain the low-frequency part Δf of Δf L , then subtract Δf from ΔfL Get the high frequency part of Δf H ;

[0007] 3) The low frequency part Δf L Transmit to the lithium battery energy storage system; the high frequency part Δf H Delivered to the flywheel energy storage system;

[0008] 4) In order to avoid unnecessary frequent charging and discharging actions that may cause loss of energy storage life due to small frequency fluctuations, both the lithium battery energy storage system and the flywheel energy storage system are set with a frequency modulation dead zone. When -0.033Hz<Δf L <0.033Hz, lithium battery energy storage does not participate in primary frequency modulation. L <-0.033Hz or Δf L >0.033Hz, the lithium battery energy storage system starts the frequency modulation function; when -0.033Hz<Δf H When <0.033Hz, the flywheel energy storage does not participate in the primary frequency modulation, Δf H <-0.033Hz or Δf L When >0.033Hz, the flywheel energy storage system starts the frequency modulation function once;

[0009] 5) Considering that virtual inertia control will inhibit frequency recovery, energy storage uses virtual droop control to participate in primary frequency modulation, Δf L The power reference value ΔP of lithium battery energy storage participating in primary frequency modulation is calculated through the droop control link B ; Δf H The power reference value ΔP of the flywheel energy storage participating in the primary frequency regulation is calculated through the droop control link F ;

[0010] 6) In order to reduce the number of overcharge and overdischarge of energy storage, an adaptive output control module is introduced to control the actual output of energy storage. The lithium battery energy storage adaptive output control module is based on the state of charge SOC of the lithium battery and the primary frequency modulation power reference value ΔP B Comprehensive judgment determines the actual output of the primary frequency modulation of the lithium battery energy storage; the flywheel energy storage adaptive output control module comprehensively calculates ΔP based on the flywheel SOC and the primary frequency modulation power reference value F Determine the actual output of the flywheel energy storage primary frequency regulation.

[0011] The method proposed in this patent decomposes the frequency deviation Δf into high and low frequency components through a first-order low-pass filter and then inputs them into different energy storage systems respectively, making full use of the frequency modulation advantages of lithium battery and flywheel energy storage. The actual output of the primary frequency modulation of lithium battery energy storage and flywheel energy storage is shown in the attached manual. Figure 1 As shown;

[0012] When the frequency deviation Δf is not processed by the patented method (no high and low frequency decomposition), the actual output of the primary frequency modulation of the lithium battery energy storage and the flywheel energy storage is as shown in the attached manual. Figure 2 As shown;

[0013] contrast Figure 1 and Figure 2 It can be seen that when the lithium battery and flywheel hybrid energy storage adopts the method proposed in this patent to participate in the primary frequency modulation of the photovoltaic power station, the number of charge and discharge times of the lithium battery energy storage is greatly reduced, which is beneficial to extend the service life of the lithium battery energy storage; the number of charge and discharge times of the flywheel battery is slightly increased, but considering the advantage of the high number of flywheel energy storage cycles, the impact on its operating life is not significant;

[0014] Compared with the prior art, the advantages of the present invention are: using a hybrid energy storage system composed of a flywheel and a lithium battery, combining the advantages of the two energy storages, while ensuring the primary frequency regulation effect, improving the economic efficiency of the energy storage-assisted photovoltaic power station participating in the primary frequency regulation of the power grid. When the power system experiences a long period of continuous random load fluctuations, the power grid frequency deviation is decomposed into two parts through a frequency divider. The high-frequency part of the frequency deviation is adjusted by the flywheel energy storage in the hybrid energy storage system, and the low-frequency part of the frequency deviation is adjusted by the lithium battery energy storage in the hybrid energy storage system, reducing the number of charge and discharge times of the lithium battery energy storage and extending its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention discloses a control method for a hybrid energy storage-assisted photovoltaic power station to participate in primary frequency modulation, and a schematic diagram of the actual output structure of the hybrid energy storage primary frequency modulation using the method.

[0016] Figure 2 The present invention discloses a control method for a hybrid energy storage-assisted photovoltaic power station to participate in primary frequency regulation, and the actual output of the hybrid energy storage primary frequency regulation when the method is not adopted.

[0017] Figure 3 The present invention provides a control method for a hybrid energy storage-assisted photovoltaic power station participating in primary frequency modulation, assuming that a random load fluctuation of one hour occurs in a regional power grid.

[0018] Figure 4 The frequency deviation low frequency part Δf of the control method of the hybrid energy storage auxiliary photovoltaic power station participating in the primary frequency modulation of the present invention L .

[0019] Figure 5 The frequency deviation high frequency part Δf of the control method of the hybrid energy storage auxiliary photovoltaic power station participating in primary frequency modulation of the present invention H .

[0020] Figure 6 It is a frequency deviation frequency division principle diagram of a control method for a hybrid energy storage-assisted photovoltaic power station participating in primary frequency modulation according to the present invention.

[0021] Figure 7 It is a lithium battery energy storage primary frequency modulation reference power of a control method for a hybrid energy storage-assisted photovoltaic power station participating in primary frequency modulation of the present invention.

[0022] Figure 8 It is a flywheel energy storage primary frequency modulation reference power of a control method for a hybrid energy storage-assisted photovoltaic power station participating in primary frequency modulation of the present invention.

[0023] Fig. 9 The invention discloses a control method for a hybrid energy storage-assisted photovoltaic power station to participate in primary frequency modulation and a relationship between the maximum chargeable and dischargeable power of the energy storage and the SOC.

[0024] Fig.10 The present invention discloses a control method for a hybrid energy storage-assisted photovoltaic power station to participate in primary frequency modulation and actual output of lithium battery energy storage primary frequency modulation.

[0025] Fig.11 The present invention discloses a flywheel energy storage primary frequency regulation actual output of a control method for a hybrid energy storage-assisted photovoltaic power station participating in primary frequency regulation. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0027] A control method for a hybrid energy storage-assisted photovoltaic power station to participate in primary frequency modulation comprises the following steps:

[0028] 1) When the regional power grid where the photovoltaic power station is located experiences a long period of continuous random load fluctuation, it is assumed that the regional power grid experiences a 1-hour random load fluctuation as shown in the attached manual. Figure 3 The grid frequency f of the grid connection point of the photovoltaic energy storage system is collected, and the frequency deviation Δf between the grid frequency f of the grid connection point and the grid reference frequency f0 (50Hz) is calculated;

[0029] 2) Design a first-order low-pass filter link, and filter the frequency deviation Δf through the first-order low-pass filter link to obtain the low-frequency part Δf of Δf L , then subtract Δf from Δf L Get the high frequency part of Δf H Among them, the low-frequency part of the grid frequency deviation Δf L and the high frequency part Δf L As shown in the instruction manual Figure 4 and Figure 5 As shown;

[0030] 3) The low frequency part Δf L Transmitted to the lithium battery energy storage system; the high frequency part Δf H The frequency deviation frequency division principle is as shown in the attached manual. Figure 6As shown;

[0031] 4) In order to avoid unnecessary frequent charging and discharging actions that cause loss of energy storage life due to small frequency fluctuations, both the lithium battery energy storage system and the flywheel energy storage system are set with a frequency modulation dead zone. L <0.033Hz, lithium battery energy storage does not participate in primary frequency modulation. L <-0.033Hz or Δf L >0.033Hz, the lithium battery energy storage system starts the frequency modulation function; when -0.033Hz<Δf H When <0.033Hz, the flywheel energy storage does not participate in the primary frequency modulation, Δf H <-0.033Hz or Δf L When >0.033Hz, the flywheel energy storage system starts the frequency modulation function once;

[0032] 5) Considering that virtual inertia control will inhibit frequency recovery, energy storage uses virtual droop control to participate in primary frequency modulation. The principle of virtual droop control is:

[0033] ΔP=KΔf (1)

[0034] Among them, ΔP is the power of energy storage participating in primary frequency regulation; K is the droop coefficient.

[0035] Δf L The power reference value ΔP of lithium battery energy storage participating in primary frequency modulation is calculated through the droop control link B , as shown in the instruction manual Figure 7 As shown; Δf H The power reference value ΔP of the flywheel energy storage participating in the primary frequency regulation is calculated through the droop control link F , as shown in the instruction manual Figure 8 As shown;

[0036] 6) In order to reduce the number of overcharge and overdischarge of energy storage, an adaptive output control module is introduced to control the actual output of energy storage. The lithium battery energy storage adaptive output control module controls the actual output of energy storage according to the state of charge (SOC) of the lithium battery and the primary frequency modulation power reference value ΔP B The flywheel energy storage adaptive output control module uses the flywheel SOC and the primary frequency modulation power reference value to comprehensively judge the actual output of the lithium battery energy storage primary frequency modulation; the ... F Determine the actual output of the flywheel energy storage primary frequency modulation. The working principle of the energy storage adaptive output control module is:

[0037] First, the Logistic regression function is used to determine the actual maximum charge and discharge power of the energy storage according to the energy storage SOC. The relationship between the two is:

[0038]

[0039] Where: P c , P d The maximum chargeable power and the maximum dischargeable power of energy storage are respectively; P0, r, and b are 0.01, 13, and 0.2 respectively; SOC max , SOC min They are the upper and lower limits of energy storage SOC respectively; SOC H , SOC L They are the upper and lower limits of SOC for normal charging and discharging of energy storage. The relationship between the maximum charge and discharge power of energy storage and SOC is shown in the attached manual. Fig. 9 As shown;

[0040] Secondly, the actual output of the energy storage primary frequency regulation is comprehensively judged based on the frequency deviation, the maximum charge and discharge power of the energy storage, the primary frequency regulation power reference value, and the rated power.

[0041] 1) For lithium battery energy storage:

[0042] (1) When Δf L >0, the lithium battery energy storage is charged, and the actual output of the lithium battery energy storage frequency regulation is:

[0043]

[0044] Among them, P Bmax is the rated power of lithium battery energy storage.

[0045] (2) When Δf L <0, the lithium battery energy storage is discharged, and the actual output of the lithium battery energy storage frequency regulation is:

[0046]

[0047] 2) For flywheel energy storage:

[0048] (1) When Δf H >0, the flywheel energy storage is charged, and the actual output of the flywheel energy storage frequency regulation is:

[0049]

[0050] Among them, P Fmax is the rated power of the flywheel energy storage.

[0051] (2) When Δf H <0, the flywheel energy storage discharges, and the actual output of the flywheel energy storage frequency regulation is:

[0052]

[0053] The actual output of lithium battery energy storage and flywheel energy storage participating in the primary frequency regulation of photovoltaic power station is shown in the attached manual. Fig.10 and Fig.11 shown.

[0054] It can be seen that the number of charge and discharge times for lithium battery energy storage is much less than that for flywheel energy storage, which is beneficial to extend the service life of lithium batteries and give full play to the advantages of the high number of flywheel cycles.

[0055] The present invention and its embodiments are described above, and such description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if ordinary technicians in the field are inspired by it, without departing from the purpose of the invention, they can design a structure and embodiment similar to the technical solution without creativity, which should belong to the protection scope of the present invention.

Claims

1. A control method for a hybrid energy storage-assisted photovoltaic power station to participate in primary frequency modulation, characterized in that: The following steps are involved: 1) When the grid in the area where the photovoltaic power station is located experiences a long period of continuous random load fluctuation, the grid frequency f of the photovoltaic storage system grid connection point is collected, and the frequency deviation Δf between the grid frequency f of the grid connection point and the grid reference frequency f0 is calculated, where f0 is 50Hz; 2) Design a first-order low-pass filter link, and filter the frequency deviation Δf through the first-order low-pass filter link to obtain the low-frequency part Δf of Δf L , then subtract Δf from Δf L Get the high frequency part of Δf H ; 3) The low frequency part Δf L Transmit to the lithium battery energy storage system; the high frequency part Δf H Delivered to the flywheel energy storage system; 4) In order to avoid unnecessary frequent charging and discharging actions that may cause loss of energy storage life due to small frequency fluctuations, both the lithium battery energy storage system and the flywheel energy storage system are set with a frequency modulation dead zone. When -0.033Hz<Δf L <0.033Hz, lithium battery energy storage does not participate in primary frequency modulation. L <-0.033Hz or Δf L >0.033Hz, the lithium battery energy storage system starts the frequency modulation function; when -0.033Hz<Δf H When <0.033Hz, the flywheel energy storage does not participate in the primary frequency modulation, Δf H <-0.033Hz or Δf L When >0.033Hz, the flywheel energy storage system starts the frequency modulation function once; 5) Considering that virtual inertia control will inhibit frequency recovery, energy storage uses virtual droop control to participate in primary frequency modulation, Δf L The power reference value ΔP of lithium battery energy storage participating in primary frequency modulation is calculated through the droop control link B ; Δf H The power reference value ΔP of the flywheel energy storage participating in the primary frequency regulation is calculated through the droop control link F ; 6) In order to reduce the number of overcharge and overdischarge of energy storage, an adaptive output control module is introduced to control the actual output of energy storage. The lithium battery energy storage adaptive output control module is based on the state of charge SOC of the lithium battery and the primary frequency modulation power reference value ΔP B Comprehensive judgment determines the actual output of the primary frequency modulation of the lithium battery energy storage; the flywheel energy storage adaptive output control module comprehensively calculates ΔP based on the flywheel SOC and the primary frequency modulation power reference value F Determine the actual output of the flywheel energy storage primary frequency regulation; For lithium battery energy storage: (1) When Δf L >0, the lithium battery energy storage is charged, and the actual output of the lithium battery energy storage frequency regulation is: Among them, P Bmax Rated power for lithium battery energy storage (2) When Δf L <0, the lithium battery energy storage is discharged, and the actual output of the lithium battery energy storage frequency regulation is: For flywheel energy storage: (1) When Δf H >0, the flywheel energy storage is charged, and the actual output of the flywheel energy storage frequency regulation is: Among them, P Fmax Rated power of flywheel energy storage (2) When Δf H <0, the flywheel energy storage discharges, and the actual output of the flywheel energy storage frequency regulation is:

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