Charging and discharging power control method of all-vanadium redox flow battery energy storage system based on S-curve

Abstract

The present invention discloses a charge and discharge power control method for an all-vanadium liquid flow battery energy storage system based on an S-curve, which sets the power required for battery charge and discharge and provides a power smoothing time. The power required for battery charge and discharge is smoothed to output a power reference value; the power reference value is subtracted from the actual value of the battery charge and discharge power to obtain an error, which is input to a power controller for PI adjustment to obtain a charge and discharge current reference value; the obtained current reference value is subtracted from the actual value of the battery charge and discharge current and input to a current controller for PI adjustment to obtain a control voltage, which is used to control a bidirectional DC / DC converter by controlling the voltage, thereby adjusting the battery charge and discharge power. The present invention improves charge and discharge efficiency: by dividing the charge and discharge process into multiple stages, the optimal charging current and voltage can be used for different stages, thereby reducing the inrush current, extending the battery life, and improving the overall charging efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of all-vanadium redox flow batteries, and more particularly to a method for controlling the charge and discharge power of an all-vanadium redox flow battery energy storage system based on an S-curve. The present invention reduces sudden changes in the battery's charge and discharge current by smoothing the battery's charge and discharge power, thereby extending the battery's lifespan. Background Art

[0002] As a highly efficient energy storage system, all-vanadium redox flow batteries are widely used in large-scale energy storage due to their long lifespan, excellent adjustability, and environmental friendliness. During the charge and discharge process of all-vanadium redox flow batteries, the battery current and voltage vary with load, which can cause fluctuations in charge and discharge power, affecting system stability and service life. Therefore, smooth control of charge and discharge power is one of the key technologies to improve battery performance and extend battery life.

[0003] The fundamental goal of smooth control is to reduce the rate of change of charging current by regulating the power during the charge and discharge process. The fundamental principle of constant power charging is to maintain a constant charging power by adjusting the charging current. During the initial charging process of a vanadium redox flow battery (VRB), a sudden current surge—a short-term rapid increase in current—may occur. Because the battery's open-circuit voltage is initially low, the charging current will be higher to maintain constant power or achieve rapid charging, and even a momentary current surge may occur.

[0004] Sudden current changes can cause drastic changes in the flow of electrons and ions, resulting in local overheating in a short period of time, causing local damage to the carbon felt structure, affecting the permeability of the electrolyte in the electrode, reducing the active area of ​​the electrode, and thus affecting battery performance; large current mutations can cause mechanical stripping or electrochemical dissolution of catalysts on the electrode surface, reducing the catalytic effect, and thus affecting the battery's charge and discharge efficiency; sudden current changes can cause rapid changes in the potential near the electrode, which may trigger side reactions; sudden current changes may cause the current density in certain areas of the electrode surface to be much higher than in other areas, making the redox reaction in this area uneven and increasing the risk of local corrosion of the electrode. This local polarization may reduce the concentration gradient of vanadium ions in the electrolyte and accelerate battery capacity decay; sudden current changes can cause drastic changes in the flow of ions inside the ion exchange membrane, causing local membrane expansion or contraction. Long-term high current shocks can destroy the structural integrity of the membrane and reduce its performance. Under high current mutations, the selective permeability of the ion membrane may be reduced, causing the V 2+ or positive V 5+ It is easier to penetrate the membrane, leading to cross-electrolyte contamination and reduced Coulombic efficiency. The sudden change in current will increase the internal loss of the battery, such as ohmic loss and polarization loss, which will reduce the overall energy conversion efficiency of VRB. Summary of the Invention

[0005] The purpose of the present invention is to remedy the shortcomings of the existing technology and provide a method for controlling the charge and discharge power of an all-vanadium liquid flow battery energy storage system based on an S-curve. The charge and discharge characteristics of a VRB determine its charge and discharge mode, which directly affects the battery performance and service life. Therefore, the charge and discharge control of a VRB is of vital importance. Based on the analysis of the current status of VRB charge and discharge control research, the present invention sets the charge and discharge power to different change values ​​for smoothing the current mutation during constant power charging and discharging of a VRB energy storage system to prevent damage to the internal components of the battery caused by current shock.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for controlling the charge and discharge power of an all-vanadium liquid flow battery energy storage system based on an S-shaped curve specifically comprises the following steps:

[0008] (1) Before charging and discharging the energy storage system, set the power P required for battery charging and discharging geiding , and gives the power smoothing time t1, t2, t3;

[0009] (2) According to the given battery charging and discharging power and power smoothing time, the power required for battery charging and discharging is smoothed, and the output power reference value P is obtained. control , as follows:

[0010] 1) When 0≤t<t3, use the S-shaped curve to charge and discharge the battery at increasing power, and the power reference value P control As shown in the following formula:

[0011] ,

[0012] where ΔP max is the maximum value of the power change rate, and t represents the real-time point of the charging and discharging process;

[0013] 2) When t≥t3, the power reference value rises to the given required power P geiding ,Right now:

[0014] P control =P geiding

[0015] Then according to the given required power P geiding Charge and discharge the battery;

[0016] (3) The power reference value P is obtained control The error e is obtained by subtracting the actual value P of the battery charge and discharge power, and the error e is input to the power controller. The power controller performs PI adjustment on the error e to obtain the charge and discharge current reference value. ;

[0017] (4) The current reference value obtained The difference between the actual value of the battery charge and discharge current I is input to the current controller, and the current controller performs PI adjustment on the difference to obtain the control voltage U p , by controlling the voltage U p To control the bidirectional DC / DC converter, and then adjust the battery charging and discharging power.

[0018] After smoothing in steps 1) and 2), the battery charge and discharge process is divided into three stages: the accelerated power increase stage 0 to t1, the uniform power increase stage t1 to t2, and the decelerated power increase stage t2 to t3. The details are as follows:

[0019] The first section 0≤t<t1: the power change rate increases linearly from 0 to ΔP max , the slope is ; The power reference value is the integral of the power change rate, ;

[0020] The second stage t1≤t<t2: the power change rate is constant at ΔP max The power reference value increases linearly from the end point of the first segment. The power reference value is the integral of the power change rate. ;

[0021] The third section t2≤t<t3: the power change rate changes from ΔP max It decreases linearly to 0 with a slope of The power reference value increases linearly from the end point of the second segment. The power value is the integral of the power change rate.

[0022] .

[0023] The maximum value of the power change rate ΔP max There are certain restrictions, namely , set the required power P before charging and discharging geiding When the power smoothing time is t1, t2, and t3, the maximum value of the power change rate ΔP is calculated according to the above formula. max size.

[0024] The power controller and current controller are both PI controllers.

[0025] The bidirectional DC / DC converter performs charge and discharge operations according to the received control voltage signal. The bidirectional DC / DC converter converts the input control voltage into the charge and discharge voltage required by the battery, thereby achieving regulation of battery charge and discharge.

[0026] The bidirectional DC / DC converter operates in the following ways: ① Charging mode: Energy from an external power source is transferred to the battery, and the battery begins charging. The bidirectional DC / DC converter converts the input control voltage into the charge and discharge voltage required by the battery based on the received control voltage signal, thereby achieving battery charge regulation. ② Discharging mode: Energy from the battery is output to the load, and the battery begins discharging. The bidirectional DC / DC converter converts the battery voltage into a voltage suitable for the load based on the control voltage signal, thereby achieving discharge regulation.

[0027] The external power source refers to a large grid power source, a wind power generation power source, a hydropower generation power source or a photovoltaic power generation power source.

[0028] The advantages of the present invention are: 1. The present invention improves the charging and discharging efficiency: by dividing the charging and discharging process into multiple stages, the optimal charging current and voltage can be used for different stages to improve the overall charging efficiency.

[0029] 2. Extend battery life: Staged charging and discharging can effectively control the battery's temperature, voltage, and current, reduce the stress of the battery during the charging and discharging process, and thus extend the battery's cycle life.

[0030] 3. Optimize performance: By optimizing the charging and discharging at different stages, the overall performance of the battery can be improved, including energy density, power density, etc.

[0031] 4. Improve energy utilization: The staged charging and discharging strategy can more effectively utilize the battery's energy storage capacity, reduce energy loss, and thus improve energy utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a structural diagram of the present invention;

[0033] Figure 2 A graph showing the change of the charge and discharge power of the present invention and the conventional constant power charge and discharge power over time;

[0034] Figure 3 It is the power change rate change curve. DETAILED DESCRIPTION

[0035] A method for controlling the charge and discharge power of an all-vanadium liquid flow battery energy storage system based on an S-shaped curve specifically comprises the following steps:

[0036] (1) Before charging and discharging the energy storage system, set the power P required for battery charging and discharging geiding , and gives the power smoothing time t1, t2, t3; the power P required for battery charging and discharging geidingThe setting is determined by the operator based on the rated power of the battery and the actual load requirements. For example, if the load requires the battery to provide 5kW of power, then the charge and discharge power is set to 5kW, and the charge and discharge power setting value should be less than the rated power of the battery. According to the current national standard GB / T 43526-2023, the charge / discharge adjustment time should be no more than 2s. However, the energy storage system requires a certain response time for charging and discharging, so the charge and discharge power rise time is set to t1=t2=t3=0.5 seconds.

[0037] (2) According to the given battery charging and discharging power and power smoothing time, the power required for battery charging and discharging is smoothed, and the output power reference value P is obtained. control ;

[0038] (3) The power reference value P is obtained control The error e is obtained by subtracting the actual value P of the battery charge and discharge power, and the error e is input to the power controller. The power controller performs PI adjustment on the error e to obtain the charge and discharge current reference value. ;

[0039] (4) The current reference value obtained The difference between the actual value of the battery charge and discharge current I is input to the current controller, and the current controller performs PI adjustment on the difference to obtain the control voltage U p , by controlling the voltage U p To control the bidirectional DC / DC converter, and then adjust the battery charging and discharging power.

[0040] like Figure 1 As shown, it is a block diagram of the present invention. geiding P is the power required for battery charging and discharging, which is a parameter given by humans; t is the charging and discharging time, in seconds. control The smoothed battery charge and discharge power reference value is input to the bidirectional DC / DC converter, which then charges and discharges the battery based on this power reference. The current controller and power controller use the common PI controller.

[0041] Figure 2 It is a curve showing the change of the strategy-set charge and discharge power and the traditional constant power charge and discharge power over time.

[0042] (1) When 0≤t<t3, the battery is charged and discharged with an S-shaped curve. The power smoothing value is shown as follows:

[0043] ,

[0044] The power smoothing process is divided into three stages:

[0045] The first section 0≤t<t1: the power change rate increases linearly from 0 to ΔP max , the slope is ; The power value is the integral of the power change rate, which can be obtained ;

[0046] The second stage t1≤t<t2: the power change rate is constant at ΔP max The power value increases linearly from the end of stage 1. The power value is the integral of the power change rate, which can be obtained ;

[0047] The third section t2≤t<t3: the power change rate changes from ΔP max It decreases linearly to 0 with a slope of The power value increases linearly from the end of stage 2. The power value is the integral of the power change rate, which can be obtained

[0048] ;

[0049] (2) When t≥t3, the power rises to the given power, and then the battery is charged according to the given power.

[0050] P control =P geiding

[0051] After the above-mentioned smoothing strategy, the power-up charging and discharging process is divided into three stages: the accelerated power-up stage (0-t1), the uniform power-up stage (t1-t2), and the decelerated power-up stage (t2-t3). max is the maximum value of the power change rate, and the power change rate curve is as follows Figure 3 shown.

[0052] ΔP max There are certain restrictions, namely .

[0053] ΔP max Is the maximum value of the power change rate. At t3, the power reaches the power P required for battery charging and discharging. geiding The integral of the power change rate from time 0 to time t3 is P geiding , so we get .

[0054] Before charging and discharging, set the power setting value P geiding When the smoothing time is t1, t2, and t3, ΔP can be calculated according to the above formula. max size.

[0055] Before the energy storage system is charged and discharged, the power required for battery charging and discharging is set, and the power smoothing time, i.e., the smoothness, is given. The power smoothing controller will geidingAccording to the above strategy, smoothing is performed to output a power reference value that rises slowly and then remains stable. The difference between this power reference value and the actual value of battery charge and discharge power is input to the power controller to obtain the charge and discharge current reference value after PI adjustment. The difference between this current reference value and the actual value of battery charge and discharge current is input to the current controller to obtain the control voltage U after PI adjustment. p , by controlling the voltage U p To control the bidirectional DC / DC converter and thus regulate the battery charging and discharging power.

[0056] The power controller compares the power reference with the actual battery power. A PI controller (proportional-integral controller) is used to control the power output. The PI controller adjusts the output signal using the proportional term (P) and the integral term (I), ensuring that the battery power gradually approaches the target value during the charging or discharging process.

[0057] The current controller further adjusts the current output based on the current reference value. Like the power controller, it uses a PI controller to ensure that the current is accurately regulated to the target value. The current controller's purpose is to minimize the error between the actual battery current and the reference current, thereby improving the stability of the charging and discharging process.

[0058] The PI controller works as follows: ① Proportional term (P): directly determines the size of the control quantity based on the current error value; ② Integral term (I): processes the accumulated error to eliminate long-term system errors.

[0059] The bidirectional DC / DC converter is responsible for matching the battery's DC voltage with the voltages of the rest of the system and performing charging and discharging operations based on power control signals. The DC / DC converter converts the input voltage into the required charging and discharging voltages for the battery, enabling precise regulation of battery charging and discharging. In this system, the DC / DC converter operates in two modes: ① Charging mode: transferring power from the external power source to the battery, and the battery begins charging; ② Discharging mode: delivering the battery's energy to the load, and the battery begins discharging.

[0060] 1. Power smoothing stage

[0061] Accelerated power ramp-up phase (0-t1): When the energy storage system begins charging and discharging, the battery is charged and discharged using an S-shaped curve. The S-shaped curve is a nonlinear function characterized by a slow initial power increase, a rapid increase in the middle, and a gradual slowdown in the final stage. This approach avoids rapid power changes in the initial stages of charge and discharge, minimizing impact on the battery.

[0062] Constant Power Rise Phase (t1-t2): After the accelerated power rise phase, the power reference value reaches a relatively stable level. It then continues to rise at a rate close to the required power until it approaches the required power. The power changes during this phase are relatively stable, helping to further stabilize the battery's charge and discharge processes.

[0063] Deceleration and Power Rise Phase (t2-t3): As the power reference approaches the desired power, the rate of increase gradually decreases. Ultimately, at t ≥ t3, the power reference reaches the desired power and remains constant. This phase ensures a smooth transition to the final charge and discharge power, avoiding sudden power changes.

[0064] 2. PI regulation and current control stage

[0065] The power controller uses PI regulation: The difference between the power reference value and the actual battery charge and discharge power value P is calculated to obtain an error, e, which is then input into the power controller. The power controller uses PI regulation, which combines proportional (P) and integral (I) regulation. The proportional regulation directly adjusts the output based on the magnitude of the error, while the integral regulation adjusts based on the accumulated error to eliminate steady-state errors. Through PI regulation, the power controller obtains a reference value for the charge and discharge current.

[0066] Current controller PI regulation: The difference between the current reference value and the actual battery charge and discharge current, I, is fed into the current controller, which also uses PI regulation. This PI regulation generates a control voltage, which controls the bidirectional DC / DC converter, thereby regulating the battery charge and discharge power.

[0067] 3. Bidirectional DC / DC converter working stage

[0068] Charging mode: When the system is in the charging state, the bidirectional DC / DC converter transfers energy from the external power supply to the battery, starting the battery charging process. Based on the control voltage signal received, the converter converts the input control voltage into the required charge and discharge voltages for the battery, thereby achieving battery charge regulation.

[0069] Discharge mode: When the system is in the discharge state, the bidirectional DC / DC converter outputs the battery energy to the load, causing the battery to begin discharging. Similarly, the converter converts the battery voltage to a voltage suitable for the load based on the control voltage signal to achieve discharge regulation. (For the bidirectional DC-DC charging and discharging process, please refer to the paper: [1] Fan Dongdong. Research on Bidirectional DC / DC Converter for Battery Energy Storage System [D]. Anhui University of Science and Technology, 2017.)

[0070] This invention uses an S-shaped curve to smooth the battery charge and discharge power, avoiding sudden power fluctuations. In the initial stages of charge and discharge, the power increases slowly, reducing impact on the battery and extending battery life. As the power approaches the setpoint, the power increase gradually slows, allowing for a smooth transition to the final charge and discharge power, improving system stability and reliability.

[0071] This invention uses PI regulation of the power controller and current controller to precisely control the battery's charge and discharge power. PI regulation adjusts based on the magnitude and accumulation of errors, rapidly responding to power changes and eliminating steady-state errors, ensuring the stability and accuracy of the battery's charge and discharge power.

[0072] The smooth power variation of the present invention reduces the stress of the battery during the charging and discharging process, reduces the change in the chemical reaction rate inside the battery, thereby slowing down the aging speed of the battery and extending the service life of the battery.

[0073] The precise power control and current control of the present invention can ensure that the battery operates in an optimal working state, reduce energy loss, and improve the overall efficiency of the energy storage system.

[0074] The present invention can flexibly adjust parameters such as the power smoothing time and the maximum value of the power change rate according to different battery types and application scenarios, and has strong adaptability.

Claims

1. A method for controlling charge and discharge power of an all-vanadium redox flow battery energy storage system based on an S-shaped curve, characterized by: The specific steps include: (1) Before charging and discharging the energy storage system, set the power P required for battery charging and discharging geiding , and gives the power smoothing time t1, t2, t3; (2) According to the given battery charging and discharging power and power smoothing time, the power required for battery charging and discharging is smoothed, and the output power reference value P is obtained. control , as follows: 1) When 0≤t<t3, use the S-shaped curve to charge and discharge the battery at increasing power, and the power reference value P control As shown in the following formula: ， where ΔP max is the maximum value of the power change rate, and t represents the real-time point of the charging and discharging process; 2) When t≥t3, the power reference value rises to the given required power P geiding ,Right now: P control =P geiding Then according to the given required power P geiding Charge and discharge the battery; (3) The power reference value P is obtained control The error e is obtained by subtracting the actual value P of the battery charge and discharge power, and the error e is input to the power controller. The power controller performs PI adjustment on the error e to obtain the charge and discharge current reference value. ; (4) The current reference value obtained The difference between the actual value of the battery charge and discharge current I is input to the current controller, and the current controller performs PI adjustment on the difference to obtain the control voltage U p , by controlling the voltage U p To control the bidirectional DC / DC converter, and then adjust the battery charging and discharging power.

2. The method for controlling charge and discharge power of an all-vanadium redox flow battery energy storage system based on an S-shaped curve according to claim 1, characterized in that: After smoothing in steps 1) and 2), the battery charging and discharging process is divided into three stages: the accelerated power increase stage from 0 to t1, the uniform power increase stage from t1 to t2, and the decelerated power increase stage from t2 to t3.

3. The method for controlling charge and discharge power of an all-vanadium redox flow battery energy storage system based on an S-shaped curve according to claim 2, characterized in that: The first stage of accelerated power increase 0≤t<t1: the power change rate increases linearly from 0 to ΔP max , the slope is ; The power reference value is the integral of the power change rate, .

4. The method for controlling charge and discharge power of an all-vanadium redox flow battery energy storage system based on an S-shaped curve according to claim 3, characterized in that: The second stage of uniform power increase: t1≤t<t2: the power change rate is constant at ΔP max The power reference value increases linearly from the end point of the first segment. The power reference value is the integral of the power change rate. .

5. The method for controlling charge and discharge power of an all-vanadium redox flow battery energy storage system based on an S-shaped curve according to claim 4, characterized in that: The third stage of deceleration and power increase t2≤t<t3: the power change rate changes from ΔP max It decreases linearly to 0 with a slope of The power reference value increases linearly from the end point of the second segment. The power value is the integral of the power change rate. 。 6. The method for controlling charge and discharge power of an all-vanadium redox flow battery energy storage system based on an S-shaped curve according to claim 1, characterized in that: The maximum value of the power change rate ΔP max There are certain restrictions, namely , set the required power P before charging and discharging geiding When the power smoothing time is t1, t2, and t3, the maximum value of the power change rate ΔP is calculated according to the above formula. max size.

7. The method for controlling charge and discharge power of an all-vanadium redox flow battery energy storage system based on an S-shaped curve according to claim 1, characterized in that: The power controller and current controller are both PI controllers.

8. The method for controlling charge and discharge power of an all-vanadium redox flow battery energy storage system based on an S-shaped curve according to claim 1, characterized in that: The bidirectional DC / DC converter performs charge and discharge operations according to the received control voltage signal. The bidirectional DC / DC converter converts the input control voltage into the charge and discharge voltage required by the battery, thereby achieving regulation of battery charge and discharge.

9. The method for controlling charge and discharge power of an all-vanadium redox flow battery energy storage system based on an S-shaped curve according to claim 8, characterized in that: The bidirectional DC / DC converter operates in the following ways: ① Charging mode: Energy from an external power source is transferred to the battery, and the battery begins charging. The bidirectional DC / DC converter converts the input control voltage into the charge and discharge voltage required by the battery based on the received control voltage signal, thereby achieving battery charge regulation. ② Discharging mode: Energy from the battery is output to the load, and the battery begins discharging. The bidirectional DC / DC converter converts the battery voltage into a voltage suitable for the load based on the control voltage signal, thereby achieving discharge regulation.

10. The method for controlling charge and discharge power of an all-vanadium redox flow battery energy storage system based on an S-shaped curve according to claim 9, characterized in that: The external power source refers to a large grid power source, a wind power generation power source, a hydropower generation power source or a photovoltaic power generation power source.

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