WO2020087576A1 - Energy storage system active frequency modulation closed-loop control method - Google Patents

Abstract

Disclosed in the present disclosure is an energy storage system active frequency modulation closed-loop control method. The method comprises frequency modulation output power control and energy storage battery charge state control, which are correlated and work collaboratively.

Description

Active frequency modulation closed-loop control method of energy storage system

Cross-reference of related applications

This application is based on a Chinese patent application with an application number of 201811281085.X and an application date of October 30, 2018, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby incorporated by reference.

Technical field

The present disclosure relates to energy storage frequency modulation technology but is not limited to energy storage frequency modulation technology, in particular to an active frequency modulation closed loop control method of an energy storage system.

Background technique

The frequency of the power system is an important control parameter for the operation of the power system. It reflects the balance between the active power of the power generation and the load, and is closely related to the safety and efficiency of the vast number of user power equipment and the power generation equipment itself. The primary frequency regulation of the power system is implemented by the speed control system of the thermal power unit. There is a long time lag in response to the frequency change of the system. The ramp rate of the unit is low. It cannot accurately track the automatic power generation control commands. Sometimes it may even cause the reverse adjustment of the regional control error. At the same time, due to the existence of non-linear links such as primary frequency dead zone, traditional thermal power unit frequency modulation can not achieve good dynamic regulation performance.

The battery energy storage system has the characteristics of high control accuracy and fast response speed. It can achieve fast tracking of the system frequency in any case. It is a means to adjust the power system grid frequency.

There are manufacturing differences in thermal power units, and the performance of the units is different. To stabilize the frequency of the power system, it is also undesirable to simply increase the thermal power unit to expand the system adjustment capacity. Taking advantage of the characteristics of large-scale energy storage systems, such as fast response speed, strong short-term power throughput capability, and easy change of adjustment direction, participating in one-time FM control can effectively improve the power system FM capability of thermal power units.

Summary of the invention

The present disclosure provides an active frequency modulation closed-loop control method for an energy storage system.

The technical solutions provided by this disclosure are:

An active frequency modulation closed-loop control method for an energy storage system. The energy storage system includes multiple energy storage subunits and a background control system. The energy storage subunit includes an energy storage bidirectional converter PCS and an energy storage battery. The method includes FM power control and energy storage battery state-of-charge control are interrelated and work together, including the following steps:

1) Monitor the grid frequency in real time, and send the information to the background control system to determine whether the grid frequency is in the FM startup interval; if it is in the FM startup interval, enter the FM interval, and the coordinated controller control function determines the total energy storage system output , For frequency modulation power control;

2) The background control system monitors the SOC of the energy storage battery of each energy storage subunit before issuing the frequency modulation power output command to the energy storage bidirectional converter PCS of each energy storage subunit, if the energy storage of the energy storage subunit If the energy storage battery SOC is in the normal state, select the energy storage subunit and work according to the subunit power correction formula; if the energy storage battery SOC of the subunit is not in the normal state, the energy storage subunit will not be put into frequency modulation and enter Protection recovery state;

3) At the same time as the frequency modulation, the background control system monitors the grid frequency and the SOC of each energy storage subunit battery. When the grid frequency reaches the frequency modulation cut-off interval, the frequency modulation ends, and each PCS cycle waits for the frequency modulation instruction; at the same time, it determines whether each energy storage subunit battery is to be charged Recovery state, recovery state to be discharged or protection recovery state;

4) If the battery of the energy storage subunit enters the state to be recovered from charging or to be recovered from discharge, if the PCS of this subunit receives the FM power output command, it will participate in the FM power output; if the FM power output command is not received, then The background control system charges and discharges the battery at x times the rated power until the energy storage sub-unit battery SOC reaches the charge cut-off value SOC ₅ or the discharge cut-off value SOC ₆ ; if the energy storage sub-unit battery enters the protection recovery state, the The energy storage unit is not put into frequency modulation temporarily, and after controlling the PCS to charge and discharge at x times the rated power to the protection recovery cut-off value SOC ₇ , the energy storage unit returns to normal working state;

Among them, the value range of x is 0 <x <1.

According to the above scheme, in the step 1), enter the frequency modulation interval and perform the frequency modulation power output control as follows;

11) Monitor the grid frequency and send the frequency to the background control system. The background control system determines whether the frequency modulation start interval is reached. If yes, proceed to step 12). If not, proceed to step 19);

12) Enter the FM startup interval and determine whether the high-frequency FM startup interval or the low-frequency FM startup interval is entered. If the high-frequency FM startup interval enters step 13), if the low-frequency FM startup interval enters step 16);

13) Calculate the total output of the energy storage system based on the grid frequency and the output control function, and then allocate and release the charging output value to each subunit energy storage bidirectional converter PCS according to the SOC of each energy storage subunit battery and the adjustment formula , Perform frequency modulation and enter step 14);

14) Cyclically monitor the grid frequency to determine whether the frequency is still in the high-frequency frequency modulation interval, if yes, go to step 13, if not, go to step 15);

15) Determine whether the frequency of the power grid is abnormal, if it is, the energy storage system exits the frequency modulation; otherwise, if the frequency enters the low frequency FM startup interval, enter step 16); if the frequency enters the high frequency FM cutoff interval, enter step 19);

16) Calculate the total output of the energy storage system based on the grid frequency and the output control function, and then assign and release the discharge output value to the PCS of each subunit according to the battery SOC and correction formula of each energy storage subunit, perform frequency modulation and enter the step 17);

17) Cyclically monitor the grid frequency to determine whether the frequency is still in the low-frequency FM interval, if so, go to step 16); if not, go to step 18);

18) Determine whether the frequency is abnormal, if it is, the energy storage system exits FM; if not, determine if the frequency enters the high-frequency FM start interval, enter step 13); if the frequency enters the low-frequency FM cut-off interval, enter step 19);

19) The PCS of each subunit of the energy storage system waits for an action instruction.

According to the above solution, the coordinated controller in step 1) controls the work function as follows:

P _total = K (f ₀ -f)

Among them, f ₀ represents the reference frequency, f represents the real-time frequency of the power grid, and K represents the frequency modulation coefficient.

According to the above scheme, the SOC of the energy storage battery in step 2) is in a normal state means that it has not entered the protection recovery state, and the SOC of the energy storage sub-unit battery is in SOC ₁ <SOC <SOC ₄ , SOC ₁ represents the lower limit of protection, SOC ₄ represents the upper limit of protection, and the relationship between them is 1% <SOC ₁ <SOC ₄ <99%.

According to the above scheme, the work Pn of the _nth energy storage subunit PC2 in step 2) is obtained according to the work unit correction formula of the subunit:

Among them, P _a represents the average work value of each PCS, SOC _a represents the average SOC of the subunit battery, SOC _n represents the SOC of the _nth subunit battery, min () is a small function, P represents the rated power, k represents the overload coefficient, The value range of k is 1 <k≤1.5.

According to the above scheme, in step 3), the start value of the state to be charged and restored is set to SOC ₂ , and the start value of the charge to be discharged and discharged is set to SOC ₃ to be discharged, and the relationship between them is SOC ₁ <SOC ₂ <SOC ₃ < SOC ₄ .

According to the above scheme, in step 3), the startup low value of the protection recovery state is SOC ₁ and the startup high value is SOC ₄ .

According to the above scheme, the value range of x in step 4) is: 0 <x <0.6.

According to the above scheme, x in step 4) is 0.1 or 0.3.

According to the above scheme, in step 4), SOC ₅ is set as the charge recovery cut-off value, SOC ₆ is the discharge recovery cut-off value, and the relationship between them is SOC ₂ <SOC ₅ <SOC ₃ , SOC ₂ <SOC ₆ <SOC ₃ .

According to the above scheme, in step 4), SOC ₇ is set as the protection recovery cut-off value, and the relationship is SOC ₂ <SOC ₇ <SOC ₃ .

In the technical solution of the present disclosure, the frequency response function of the energy storage system that actively responds to the power grid frequency is implemented. The frequency modulation power output is determined according to the power grid frequency, the energy storage battery SOC and the power control function, forming power output frequency modulation-frequency modulation exit and power frequency modulation- Frequency modulation closed-loop control of energy storage battery state adjustment, and the exit cut-off frequency of the control method can be set between the frequency regulation dead zones of the thermal power unit to achieve a smooth exit after the energy storage system completes frequency modulation;

In the technical solution of the present disclosure, the control of the energy storage battery SOC can be achieved when the grid frequency fluctuates in the frequency modulation cut-off interval, and the energy storage battery SOC is used as a factor to determine the work of the energy storage subunit, which helps each energy storage subunit The balance of the SOC of the unit battery reduces the factory difference, protects the energy storage battery, and can avoid the overcharge and overdischarge of the SOC of the energy storage battery when the direction deviation of the daily fluctuation of the grid frequency is unbalanced, further improving the dynamics of the energy storage system Responsiveness and long-term reliability improve the stability of the power grid.

BRIEF DESCRIPTION

The disclosure will be further described below with reference to the drawings and embodiments. In the drawings:

1 is a schematic flowchart of an active frequency modulation control method of an energy storage system according to an embodiment of the present disclosure;

2 is a flow chart of frequency modulation power control according to an embodiment of the present disclosure;

FIG. 3 is a flow chart of SOC control of the state of charge of the energy storage battery in the embodiment of the present disclosure.

detailed description

In order to make the purpose, technical solutions and advantages of the disclosure more clear, the disclosure will be further described in detail in conjunction with the embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present disclosure and are not intended to limit the present disclosure.

The present disclosure provides a closed loop control method for active frequency modulation of an energy storage system, which can improve the reliability of the frequency modulation operation of the energy storage system. The control method of the background control system is used to achieve fine control of the energy storage unit during active frequency modulation of the energy storage system, including Start the energy storage system frequency modulation and the energy storage system frequency modulation ends and exit the frequency modulation to realize the closed-loop control of the state of charge (SOC) of the energy storage battery to ensure that the SOC of the energy storage battery is always in the frequency modulation response range, further improving the dynamic response capacity and long-term of the energy storage system frequency modulation Reliability of operation.

The present disclosure provides a closed-loop control method for the energy storage system to track the grid frequency and actively participate in the primary frequency modulation to solve the problem of when the active frequency modulation of the energy storage system starts, active control, and achieve the problem of long-term closed-loop operation. The dynamic performance of frequency modulation of energy storage power stations, and then make use of the characteristics of battery energy storage systems to quickly respond to grid frequency for frequency modulation, effectively reduce the random switching of large impact loads and the periodic switching of industrial loads. The adverse effect of frequency fluctuation on the reliability of the power grid.

An active frequency modulation closed-loop control method for an energy storage system. The active frequency modulation control method includes energy storage system frequency modulation power control and energy storage battery SOC control. The relationship between the two is shown in FIG. 1, where the two are the energy storage. System frequency modulation power control and energy storage battery SOC control:

1) Cyclically monitor the grid frequency in real time, and send the information to the background control system to determine whether the grid frequency is in the FM startup interval; if not, cyclically monitor the grid frequency and upload it to the background judgment; if in the FM startup interval, enter the FM interval , The total output of the energy storage system is determined by the control function of the coordinated controller;

2) Before the background control system issues the FM power output command to each subunit PCS, monitor the battery SOC of each energy storage subunit of the energy storage system, select the subunit whose energy storage battery SOC is in a normal state, and modify the formula according to the work output of the subunit Work; if not, the battery unit exits frequency modulation and enters the protection recovery state;

3) The energy storage system monitors the power grid frequency and the SOC of each energy storage battery at the same time when the frequency modulation is working. The power grid frequency reaches the corresponding frequency modulation cut-off interval, that is, the frequency modulation ends. Each PCS cycle waits for the frequency modulation instruction; at the same time, it determines whether each energy storage subunit battery is to be charged Recovery state, recovery state to be discharged or protection recovery state;

4) If the battery of the energy storage subunit enters the state to be recovered from charging or to be recovered from discharge, if the PCS of this subunit receives the FM power output command, it will first participate in the FM power output; if the FM power output command is not received, The background control system charges and discharges the battery at x times the rated power until the energy storage subunit battery SOC reaches the charge cutoff value SOC ₅ or the discharge cutoff value SOC ₆ ; if the energy storage subunit battery enters the protection recovery state, then The energy storage unit is not put into frequency modulation temporarily, and after controlling the PCS to charge and discharge at x times the rated power to the protection recovery cut-off value SOC ₇ , the energy storage unit returns to the normal working state.

Among them, in step 1), the flow chart of frequency modulation power output control is shown in FIG. 2, which specifically includes the following steps:

11) Monitor the grid frequency and send the frequency to the background control system, the control system determines whether the frequency modulation start interval is reached, if so, proceed to step 12), if not, proceed to step 19);

12) Enter the FM startup interval, determine whether the high-frequency FM startup interval (f ₁ ≤f≤f ₂ ) or low-frequency FM startup interval (f ₃ ≤f≤f ₄ ), if it is the high-frequency FM startup interval, go to step 13) , If it is low frequency FM start interval, go to step 16);

13) Calculate the total output of the energy storage system based on the grid frequency and the output control function, and then allocate and issue charging to each subunit energy storage bidirectional converter (PCS) according to the SOC of each energy storage subunit battery and the adjustment formula Work value, perform frequency modulation and go to step 14);

14) Cyclically monitor the grid frequency to determine whether the frequency is still in the high-frequency frequency modulation interval (f ₅ ≤ f ≤ f ₂ ), if yes, go to step 13, if not, go to step 15);

15) Determine whether the frequency is abnormal (f ≥ f ₂ or f ≤ f ₃ ), if it is, the energy storage system exits FM; if not, determine if the frequency enters the low frequency FM startup interval (f3 ≤ f ≤ f4), enter step 16); If the frequency enters the high-frequency FM cut-off interval, that is, f ₄ ≤ f ≤ f ₅ , go to step 19);

16) Based on the grid frequency and the power control function frequency modulation, calculate the total power output of the energy storage system, and then assign and release the discharge power value to each subunit PCS according to the battery SOC and adjustment formula of each energy storage subunit, perform frequency modulation and Go to step 17);

17) Cyclically monitor the grid frequency to determine whether the frequency is still in the low-frequency frequency modulation interval (f ₃ ≤ f ≤ f ₆ ), if yes, go to step 16); if not, go to step 18);

18) Determine whether the frequency is abnormal (f ≥ f ₂ or f ≤ f ₃ ), if it is, the energy storage system exits FM; if not, determine if the frequency enters the high-frequency FM startup interval (f ₁ ≤ f ≤ f ₂ ), enter the step 13); If the frequency enters the cut-off interval of low-frequency FM, that is f ₆ <f≤f ₁ , if yes, go to step 19);

19) The PCS of each subunit of the energy storage system waits for an action instruction.

Explanation of the frequency relationship in the above steps: f ₃ ＜ f ₄ ＜ f ₆ ＜ f ₀ ＜ f ₅ ＜ f ₁ ＜ f ₂ , f ₀ is the reference frequency, f is the grid frequency; f ₁ is the high-frequency frequency modulation start threshold, f ₂ Is the high-frequency protection value, f ₃ is the low-frequency protection value, f ₄ is the low-frequency FM start threshold, f ₅ is the high-frequency FM cut-off threshold, and f ₆ is the low-frequency FM cut-off threshold.

The energy storage battery SOC control flow chart is shown in Figure 3, which specifically includes the following steps:

21) Monitor the SOC value of each energy storage sub-unit battery to determine whether the SOC of each energy storage battery is within the normal operating range (SOC ₁ <SOC <SOC ₄ ), if yes, go to step 22); if not, go to step 30);

22) Determine the specific state of the SOC, if it is in the natural working state (SOC ₂ <SOC <SOC ₃ ), go to step 23); if it is in the state to be charged (SOC ₁ <SOC≤SOC ₂ ), go to step 24), if To be discharged (SOC ₃ ≤SOC <SOC ₄ ), go to step 27);

23) Determine whether the PCS has received the FM command from the background control system. If yes, charge and discharge the energy storage battery according to the power output command, go to step 21); if not, wait for the FM command cyclically;

24) Determine whether the PCS receives the FM command of the background control system. If yes, charge the energy storage battery according to the power output command, go to step 25); if not, the energy storage subunit is x times the rated power of a single PCS Charge the battery, go to step 26);

25) Monitor whether the battery SOC status is within the normal operating range, if yes, go to step 26); if not, go to step 30);

26) Determine whether the SOC of the energy storage battery reaches the charge recovery cut-off value (SOC ₅ ), and if so, go to step 23); if not, go to step 24);

27) Determine whether the PCS receives the FM command of the background control system. If yes, discharge the energy storage battery according to the power output command, and then go to step 28); if not, then the energy storage subunit is x times the rated power of a single PCS The battery is discharged, go to step 29);

28) Monitor whether the battery SOC status is within the normal working range, if yes, go to step 29); if not, go to step 30);

29) Determine whether the SOC of the energy storage battery reaches the discharge recovery cut-off value (SOC ₆ ), and if so, proceed to step 23); if not, proceed to step 27);

30) If SOC ≤ SOC ₁ , charge and discharge the energy storage subunit battery at x times the rated power of a single PCS, and cycle to determine whether the protection recovery cutoff value (SOC ₇ ) is reached, if yes, go to step 23), if not, Continue charging; if SOC ≥ SOC ₄ , charge the energy storage subunit battery at x times the rated power of a single PCS, and determine whether the protection recovery cut-off value is reached (SOC ₇ ), if it goes to step 23), if not, continue Discharge

The SOC relationship in the above steps: 1% <SOC ₁ <SOC ₂ <SOC ₃ <SOC ₄ <99%; SOC ₂ <SOC ₅ <SOC ₃ ; SOC ₂ <SOC ₆ <SOC ₃ ; SOC ₂ <SOC ₇ <SOC ₃ .

In this embodiment, a lithium iron phosphate battery is used as an example for the energy storage battery of the energy storage system. The background control parameters set a high-frequency starting frequency f ₁ = 50.03 Hz, a high-frequency protection frequency f ₂ = 53 Hz, and a low-frequency protection frequency f ₃ = 47Hz, low frequency start frequency f ₄ = 49.97Hz, low frequency cut-off frequency f ₆ = 49.99Hz, high frequency cut-off frequency f ₅ = 50.01Hz;

According to the size of the historical load of the power grid, determine the frequency modulation system K, where K = 40000, the work control function is P = 40000 * (50-f), kW;

Set x = 0.1, at this time the SOC recovery speed of the energy storage battery is slow;

Set the battery SOC protection lower limit SOC ₁ = 7%, protection upper limit SOC ₄ = 93%, recovery start low value SOC ₂ = 20%, recovery start high value SOC ₃ = 80%, charge recovery cutoff value SOC ₅ = 45%, discharge The recovery cut-off value SOC ₆ = 55% and the protection recovery cut-off value SOC ₇ = 50%. This symmetrical setting of parameters can be applied to regional grids where the direction of the daily deviation of the grid frequency is relatively balanced.

In this embodiment, the case where the energy storage battery of the energy storage system uses a full vanadium flow battery is taken as an example for illustration. When the direction of the daily deviation of the grid frequency is unbalanced, the parameters can be flexibly set according to the actual situation. The specific background control parameters are set as follows:

For the setting of frequency parameters, if the daily deviation of the grid frequency is more downward, the parameters can be set as follows: high frequency start frequency f ₁ = 50.1 Hz, high frequency protection frequency f ₂ = 54 Hz, low frequency protection frequency f ₃ = 46 Hz, Low-frequency start-up frequency f ₄ = 49.92 Hz, low-frequency cut-off frequency f ₅ = 49.95 Hz, high-frequency cut-off frequency f ₆ = 50.06 Hz;

Here, the frequency modulation coefficient K is set to 50000, and the power control function is P = 50000 * (50-f), kW; set x = 0.3; set the battery SOC protection lower limit SOC ₁ = 20%, and the upper protection limit SOC ₄ = 85%, Recovery start low value SOC ₂ = 30%, recovery start high value SOC ₃ = 75%, charge recovery cut-off value SOC ₅ = 50%, discharge recovery cut-off value SOC ₆ = 55%, protection recovery cut-off value SOC ₇ = 50%. This setting method has a wider start of downward deviation and a frequency modulation interval, and the battery SOC recovers faster, which can effectively play the role of frequency modulation.

This embodiment also provides an active frequency modulation closed-loop control device for an energy storage system. The energy storage system includes multiple energy storage subunits and a background control system. The energy storage subunit includes an energy storage bidirectional converter PCS and energy storage Battery; the method includes frequency modulation power control and energy storage battery state-of-charge control, which are related to each other and work together, including the following steps

The first module is configured to monitor the grid frequency in real time and send the information to the background control system to determine whether the grid frequency is in the FM startup interval; if it is in the FM startup interval, it enters the FM interval and the energy storage is determined by the coordinated controller control function The total power output of the system is used for frequency modulation power output control;

The second module is configured to monitor the state of charge of the energy storage battery SOC of each energy storage subunit of the energy storage system before the background control system issues the frequency modulation power output command to the energy storage bidirectional converter PCS of each subunit. If the energy storage battery SOC of the subunit is in a normal state, select the energy storage subunit and assign and issue a power output instruction to the subunit energy storage bidirectional converter PCS according to the energy storage subunit power correction formula; if the energy storage The SOC of the energy storage battery of the subunit is not in a normal state, and the energy storage subunit is temporarily not put into frequency modulation, and enters the protection recovery state;

The third module is configured to monitor the power grid frequency and the SOC of each energy storage sub-unit battery while the frequency modulation is in progress. When the power grid frequency reaches the frequency modulation cut-off interval, the frequency modulation ends, and each PCS cycle waits for the frequency modulation instruction; at the same time, it judges each energy storage sub-unit battery Whether to enter the recovery state to be charged, the recovery state to be discharged or the protection recovery state;

The fourth module is configured to enter the state where the battery of the energy storage sub-unit enters the state to be charged or discharged to recover, and if the PCS of the sub-unit receives the FM power output command, it will participate in the FM power output; if the FM power output is not received Power command, the background control system charges and discharges the battery at x times the rated power until the energy storage subunit battery SOC reaches the charge cutoff value or discharge cutoff value; if there is an energy storage subunit battery that enters the protection recovery state, the The energy storage unit is not put into frequency modulation temporarily, and after controlling the PCS to charge and discharge at x times the rated power to the protection recovery cut-off value, the energy storage unit returns to normal working state;

Among them, the value range of x is 0 <x <1.

In some embodiments, the first configuration module is configured to perform the following steps

11) Monitor the grid frequency and send the frequency to the background control system. The background control system determines whether the frequency modulation start interval is reached. If yes, proceed to step 12). If not, proceed to step 19);

12) Enter the FM startup interval and determine whether the high-frequency FM startup interval or the low-frequency FM startup interval is entered. If the high-frequency FM startup interval enters step 13), if the low-frequency FM startup interval enters step 16);

13) Calculate the total output of the energy storage system based on the grid frequency and the output control function, and then allocate and deliver the charging output to each subunit energy storage bidirectional converter PCS according to the SOC and adjustment formula of each energy storage subunit battery Value, perform frequency modulation and enter step 14);

14) Cyclically monitor the grid frequency to determine whether the frequency is still in the high-frequency frequency modulation interval, if yes, go to step 13, if not, go to step 15);

15) Determine whether the frequency of the power grid is abnormal, if it is, the energy storage system exits the FM; if not, if the frequency enters the low frequency FM start interval, enter step 16); if the frequency enters the high frequency FM cutoff interval, enter step 19);

16) Calculate the total output of the energy storage system based on the grid frequency and the output control function, and then allocate and release the discharge output value to the PCS of each subunit according to the battery SOC and correction formula of each energy storage subunit, perform frequency modulation and enter Step 17);

17) Cyclically monitor the grid frequency to determine whether the frequency is still in the low-frequency FM interval, if so, go to step 16); if not, go to step 18);

18) Determine whether the frequency is abnormal, if it is, the energy storage system exits FM; if not, determine if the frequency enters the high-frequency FM start interval, enter step 13); if the frequency enters the low-frequency FM cut-off interval, enter step 19);

19) The PCS of each subunit of the energy storage system waits for an action instruction.

In some embodiments, the coordination controller controls the work function as follows:

P _total = K (f ₀ -f)

Among them, f ₀ represents the reference frequency, f represents the real-time frequency of the power grid, and K represents the frequency modulation coefficient.

In some embodiments, the SOC of the energy storage battery is in a normal state means that it does not enter the protection recovery state, and the SOC of the energy storage sub-unit battery is in SOC ₁ <SOC <SOC ₄ , SOC ₁ represents the lower limit of protection, and SOC ₄ represents The upper limit of protection, the relationship between them is 1% <SOC ₁ <SOC ₄ <99%.

In some embodiments, the work of the nth energy storage subunit PCS, P _{n, is obtained} according to the work unit correction formula of the subunit:

Among them, P _a represents the average work value of each PCS, SOC _a represents the average battery SOC of the energy storage subunit, SOC _n represents the nth energy storage subunit battery SOC, min () is a small function, P represents the rated Power, k represents the overload coefficient, and the value range of k is 1 <k≤1.5.

In some embodiments, the start value of the charge recovery state is set to SOC ₂ , and the start value of the discharge recovery charge is set to SOC ₃ to be discharged, and the relationship between them is SOC ₁ <SOC ₂ <SOC ₃ <SOC ₄ .

In some embodiments, the startup low value of the protection recovery state is SOC ₁ and the startup high value is SOC ₄ .

In some embodiments, SOC ₅ is the charge recovery cutoff value, SOC ₆ is the discharge recovery cutoff value, and the relationship between them is SOC ₂ <SOC ₅ <SOC ₃ , SOC ₂ <SOC ₆ <SOC ₃ .

In some embodiments, SOC ₇ is a protection recovery cutoff value, and the relationship is SOC ₂ <SOC ₇ <SOC ₃ .

An embodiment of the present invention also provides a computer storage medium that stores computer-executable instructions. After being executed, the computer-executable instructions can implement the active frequency modulation closed-loop control method of the energy storage system provided by any one of the foregoing technical solutions. The computer storage medium may be a non-transitory storage medium.

It should be understood that those of ordinary skill in the art may make improvements or changes according to the above description, and all such improvements and changes shall fall within the protection scope of the claims appended to this disclosure.

Claims (10)

1. An active frequency modulation closed-loop control method for an energy storage system. The energy storage system includes multiple energy storage subunits and a background control system. The energy storage subunit includes an energy storage bidirectional converter PCS and an energy storage battery. The method includes FM power output control and energy storage battery state-of-charge control are related to each other and work together, including the following steps:

   1) Monitor the grid frequency in real time, and send the information to the background control system to determine whether the grid frequency is in the FM startup interval; if it is in the FM startup interval, enter the FM interval, and the coordinated controller control function determines the total energy storage system output , For frequency modulation power control;

   2) The background control system monitors the state of charge of the energy storage battery of each energy storage subunit of the energy storage system before issuing the frequency modulation power output command to the energy storage bidirectional converter PCS of each subunit, if the energy storage of the energy storage subunit If the energy battery SOC is in a normal state, select the energy storage subunit and assign and issue work instructions to the subunit energy storage bidirectional converter PCS according to the energy storage subunit power correction formula; if the energy storage subunit If the energy battery SOC is not in a normal state, the energy storage subunit does not put into frequency modulation for the time being and enters the protection recovery state;

   3) The background control system monitors the power grid frequency and the SOC of each energy storage sub-unit battery in real time. When the power grid frequency reaches the frequency modulation cut-off interval, the frequency modulation ends, and each PCS cycle waits for the frequency modulation instruction; Recovery state to be discharged or protection recovery state;

   4) If the battery of the energy storage subunit enters the state to be recovered from charging or to be recovered from discharge, if the PCS of this subunit receives the FM power output command, it will participate in the FM power output; if the FM power output command is not received, then The background control system charges and discharges the battery at x times the rated power until the energy storage subunit battery SOC reaches the charge cutoff value or discharge cutoff value; if the energy storage subunit battery enters the protection recovery state, the energy storage unit temporarily Without frequency modulation, control the PCS to charge and discharge at x times the rated power to the protection recovery cut-off value, the energy storage unit returns to normal working state;

   Among them, the value range of x is 0 <x <1.
2. An active frequency modulation closed-loop control method for an energy storage system according to claim 1, wherein in step 1), the frequency modulation interval is entered, and the steps of performing frequency modulation power control are as follows;

   11) Monitor the grid frequency and send the frequency to the background control system. The background control system determines whether the frequency modulation start interval is reached. If yes, proceed to step 12). If not, proceed to step 19);

   12) Enter the FM startup interval and determine whether the high-frequency FM startup interval or the low-frequency FM startup interval is entered. If the high-frequency FM startup interval enters step 13), if the low-frequency FM startup interval enters step 16);

   13) Calculate the total output of the energy storage system based on the grid frequency and the output control function, and then allocate and deliver the charging output to each subunit energy storage bidirectional converter PCS according to the SOC and adjustment formula of each energy storage subunit battery Value, perform frequency modulation and enter step 14);

   14) Cyclically monitor the grid frequency to determine whether the frequency is still in the high-frequency frequency modulation interval, if yes, go to step 13, if not, go to step 15);

   15) Determine whether the frequency of the power grid is abnormal, if it is, the energy storage system exits the FM; if not, if the frequency enters the low frequency FM start interval, enter step 16); if the frequency enters the high frequency FM cutoff interval, enter step 19);

   16) Calculate the total output of the energy storage system based on the grid frequency and the output control function, and then allocate and release the discharge output value to the PCS of each subunit according to the battery SOC and correction formula of each energy storage subunit, perform frequency modulation and enter Step 17);

   17) Cyclically monitor the grid frequency to determine whether the frequency is still in the low-frequency FM interval, if so, go to step 16); if not, go to step 18)

   18) Determine whether the frequency is abnormal, if it is, the energy storage system exits FM; if not, determine if the frequency enters the high-frequency FM start interval, enter step 13); if the frequency enters the low-frequency FM cut-off interval, enter step 19);

   19) The PCS of each subunit of the energy storage system waits for an action instruction.
3. An active frequency modulation closed-loop control method for an energy storage system according to claim 1, wherein in step 1) the coordinated controller controls the work function as follows:

   P _total = K (f ₀ -f)

   Among them, f ₀ represents the reference frequency, f represents the real-time frequency of the power grid, and K represents the frequency modulation coefficient.
4. An active frequency modulation closed-loop control method for an energy storage system according to claim 1, wherein in step 2) the SOC of the energy storage battery is in a normal state means that it has not entered the protection recovery state, and the SOC of the energy storage sub-unit battery is SOC ₁ <SOC <SOC ₄ , SOC ₁ represents the lower limit of protection, SOC ₄ represents the upper limit of protection, and the relationship between them is 1% <SOC ₁ <SOC ₄ <99%.
5. An active frequency modulation closed-loop control method for an energy storage system according to claim 1, wherein the power of the nth energy storage subunit PCS in step 2) P _{n is obtained} according to the subunit power correction formula:

   

   Among them, P _a represents the average work value of each PCS, SOC _a represents the average battery SOC of the energy storage subunit, SOC _n represents the nth energy storage subunit battery SOC, min () is a small function, P represents the rated Power, k represents the overload coefficient, and the value range of k is 1 <k≤1.5.
6. An active frequency modulation closed-loop control method for an energy storage system according to claim 4, wherein in step 3), the startup value of the charge recovery state is set to SOC ₂ and the startup value of the discharge recovery charge is set to SOC ₃ Discharge, the relationship between them is SOC ₁ <SOC ₂ <SOC ₃ <SOC ₄ .
7. An active frequency modulation closed-loop control method for an energy storage system according to claim 4, wherein in step 3), the startup low value of the protection recovery state is SOC ₁ and the startup high value is SOC ₄ .
8. An active frequency modulation closed loop control method for an energy storage system according to claim 1, wherein in step 4), x is 0.1 or 0.3.
9. An active frequency modulation closed-loop control method for an energy storage system according to claim 6, wherein in step 4), SOC ₅ is set as the charge recovery cut-off value, SOC ₆ is the discharge recovery cut-off value, and the relationship between them is SOC ₂ <SOC ₅ <SOC ₃ , SOC ₂ <SOC ₆ <SOC ₃ .
10. An active frequency modulation closed-loop control method for an energy storage system according to claim 6, wherein in step 4), SOC ₇ is set as the protection recovery cut-off value, and the relationship is SOC ₂ <SOC ₇ <SOC ₃ .

Images