Three closed loop charging and discharging control method based on all-vanadium redox flow battery core voltage estimation

Abstract

The application discloses a three-closed-loop charging and discharging control method based on a full-vanadium redox battery core voltage estimation, which comprises first, second and third closed-loop control links; in the first closed-loop control link, whether a charging process or a discharging process is judged based on SOC; when the charging process is adopted, a reference current and a core voltage setting value are output to the second closed-loop control link; in the second closed-loop control link, the reference current and the core voltage setting value are obtained, and the charging and discharging current of the full-vanadium redox battery and the core voltage of the full-vanadium redox battery are obtained, and then the adjusted reference current is obtained through voltage proportional integral adjustment and output to the third closed-loop control link; in the third closed-loop control link, the sum is calculated by combining the components of the alternating current on the d-axis and the q-axis and the components of the three-phase power grid voltage on the d-axis and the q-axis; the control voltage of the thyristor is obtained by the PQ control module based on the sum, and then the space vector modulation is performed.

Description

Technical Field

[0001] The present invention relates to the field of all-vanadium redox flow battery charge and discharge control methods, in particular to a three-closed-loop charge and discharge control method based on all-vanadium redox flow battery core voltage estimation. Background Art

[0002] The service life of all-vanadium liquid flow batteries is closely related to the quality of their charge and discharge control strategy. Among traditional charge and discharge control strategies, dual closed-loop control has a relatively good control effect. The outer loop of the dual closed-loop control uses a voltage outer loop to give the set voltage value to the voltage outer loop, and accurately tracks the voltage through the internal proportional-integral controller, so that the DC side voltage value can reach the set value. The strategy of the inner loop to control the current includes the following steps: first compare the deviation between the reference value and the feedback value of the d-axis and q-axis currents, and then adjust them through the PI controller. This process uses the proportional-integral regulation mechanism to accurately track the target values ​​of the d-axis and q-axis currents, thereby achieving fine control of the current and zero-static error regulation, ensuring high control accuracy.

[0003] While dual closed-loop PI control can quickly follow the target setpoint through adjustments to the inner and outer loops, the effects on different energy storage devices still vary. For example, when controlling the all-vanadium redox flow battery used in this article, during constant-voltage charging, the target feedback value is the battery's terminal voltage, but the core voltage is the most reasonable and clearest indicator of battery status. This is a shortcoming of all-vanadium redox flow batteries. A second shortcoming is the lack of accurate implementation for determining the battery's charge and discharge status and taking corresponding actions.

[0004] The document "Flexible Charge and Discharge Control of All-Vanadium Liquid Flow Batteries" proposes a three-loop control strategy using SOC loop, voltage loop, and current loop, and uses terminal voltage, charge and discharge current, and internal resistance to estimate the core voltage. However, this strategy does not consider how to control the all-vanadium liquid flow battery when connected to the power grid, and does not consider that the battery's internal resistance changes during actual operation, resulting in inaccurate estimated core voltage. Summary of the Invention

[0005] The present invention provides a three-closed-loop charge and discharge control method based on the core voltage estimation of an all-vanadium liquid flow battery, so as to solve the problem in the prior art double-closed-loop control process that when constant voltage charging is performed, the target feedback value is the terminal voltage of the battery, but the most reasonable and clear expression of the battery status is the core voltage of the battery, and there is a lack of accurate implementation links.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A three-closed-loop charge and discharge control method based on core voltage estimation of an all-vanadium redox flow battery, wherein the all-vanadium redox flow battery is connected to a three-phase AC grid via a two-level three-phase half-bridge circuit and an inverter, and the all-vanadium redox flow battery implements inverter control via a PQ control module, includes a first closed-loop control link, a second closed-loop control link, a third closed-loop control link, and a core voltage estimation module, wherein:

[0008] The first closed-loop control link includes an SOC selector and an SOC controller. The SOC controller is connected to the second closed-loop control link via two outputs. Each output is connected to a switch. The SOC selector controls the on / off of the switch in each output. The charging and discharging process is as follows:

[0009] S1. Calculate the SOC of the all-vanadium liquid flow battery;

[0010] S2, based on the SOC setting value SOC* and the SOC of the all-vanadium redox flow battery in step 1, subtract ΔSOC, ΔSOC = SOC* - SOC;

[0011] S3, if ΔSOC>0, start the charging process, if SOC≤SOC H The SOC selector controls the switch of the first output to be closed and the switch of the second output to be open. The SOC controller outputs the reference current i to the second closed-loop control link. * d , the all-vanadium flow battery is charged in a constant current mode; if SOC H <SOC<SOC*时,SOC选择器控制第一路输出的开关断开、第二路输出的开关闭合,SOC控制器向第二闭环控制环节输出全钒液流电池的内核电压设定值u * s , the all-vanadium redox flow battery is charged at a constant voltage; if SOC = SOC*, that is, ΔSOC = 0, the charging process is stopped;

[0012] If ΔSOC<0, the discharge process is started. If SOC≥SOC L The SOC selector controls the switch of the first output to be closed and the switch of the second output to be open. The SOC controller outputs the reference current i to the second closed-loop control link. * d , the all-vanadium flow battery is discharged at a constant current; if SOC* <SOC<SOC L When the SOC selector controls the switch of the first output to be disconnected and the switch of the second output to be closed, the SOC controller outputs the core voltage setting value u of the all-vanadium liquid flow battery to the second closed-loop control link in a constant voltage manner. * s, the all-vanadium redox flow battery discharges at a constant voltage; if SOC = SOC*, that is, ΔSOC = 0, the discharge process stops;

[0013] The second closed-loop control link obtains the reference current i output by the first closed-loop control link * d 、The core voltage setting value u of the all-vanadium redox flow battery * s The core voltage estimation module obtains the actual current i of the all-vanadium liquid flow battery d1 、Vanadium redox flow battery terminal voltage U d1 And the SOC of the all-vanadium redox flow battery is obtained by random forest algorithm and the core voltage u of the all-vanadium redox flow battery is obtained s ; When the second closed-loop control link obtains the reference current i * d When the reference current i * d and the actual current i d1 The adjusted reference current i is obtained by performing current proportional integral adjustment on the difference between * dadj1 And output to the third closed-loop control link; when the second closed-loop control link obtains the core voltage setting value u * s When the core voltage is set to u * s and core voltage u s The difference between the voltage proportional integral is adjusted to obtain the adjusted reference current i * dadj2 And output to the third closed-loop control link.

[0014] Furthermore, the second closed-loop control link includes two groups of PI regulators, one of which is a PI regulator that serves as a voltage controller and receives the core voltage setting value u output by the first closed-loop control link. * s , another set of PI regulator current controller receives the reference current i output by the first closed-loop control link * d .

[0015] Furthermore, the third closed-loop control link includes two groups of PI regulators and two groups of inductive reactances, wherein the first group of PI regulators receives the adjusted reference current i output by the current proportional integral and voltage proportional integral in the second closed-loop control link. * dadj , the first group of inductive reactance input component i q , combined with the output of the first group of PI regulators and the component i passing through the first group of inductive reactances q And the component e of the three-phase grid voltage on the d axis dThe reference voltage is calculated on the d-axis component v d ;

[0016] The second set of PI regulators receives i * q -i q , where i * q Equal to 0, the second group of inductive reactance input component i d , combined with the output of the second set of PI regulators and the component i passing through the second set of inductive reactance d And the component e of the three-phase grid voltage on the q axis q Calculate v q .

[0017] Furthermore, the PQ control module is used to adjust the reference voltage in the q-axis component v q , the reference voltage is in the d-axis component v d Transform from the two-phase rotating coordinate system to the three-phase stationary coordinate system, thereby obtaining the value v of the reference voltage in the three-phase stationary coordinate system abc .

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] Based on the traditional dual closed-loop control, this invention introduces the core voltage of the battery and predicts it through the random forest algorithm, which more accurately controls the battery's charge and discharge status. At the same time, the SOC loop is introduced above the dual closed-loop current loop and voltage loop. After adding the SOC loop, the battery's charge and discharge status is accurately judged, forming a three-closed-loop charging control strategy based on the voltage core for all-vanadium liquid flow batteries. This method increases the control accuracy of the corresponding all-vanadium liquid flow batteries. At the same time, a PQ control based on load tracking is designed for discharge. By adding current sensors and voltage sensors on the grid side to calculate the load size, the battery discharge has good tracking performance. The implementation function of the phase-locked loop is designed. The accuracy of the phase-locked loop implementation determines the quality of subsequent power conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a principle diagram of the method of an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the accompanying drawings and examples.

[0022] like Figure 1 As shown, this embodiment discloses a three-closed-loop charge and discharge control method based on core voltage estimation of an all-vanadium redox flow battery. The all-vanadium redox flow battery is connected to a three-phase AC grid through a two-level three-phase half-bridge circuit and an inverter, and the all-vanadium redox flow battery realizes inverter control through a PQ control module.

[0023] During traditional charging and discharging processes, the battery's terminal voltage is used as a standard indicator of the battery's charge and discharge status. However, using the battery's core voltage as a more accurate indicator of battery status is more accurate. However, due to structural issues, the core voltage of some batteries cannot or is difficult to measure, so terminal voltage is used as a fallback. However, the structural properties of all-vanadium redox flow batteries dictate that the core voltage can be well measured. Therefore, this embodiment proposes a three-closed-loop charge and discharge control method based on core voltage estimation for all-vanadium redox flow batteries.

[0024] In this embodiment, the core voltage of the all-vanadium redox flow battery is set to u s , according to the formula Calculated, where E0 represents the potential difference between the two electrodes of the battery under standard conditions; R represents the gas constant, usually R = 8.314 J / (mol·K); T is generally taken as the standard temperature 0°C; F is the Ferrari constant 96485C / mol. SOC is the state of charge (State of Charge) of the all-vanadium redox flow battery. The SOC calculation formula at chemical concentration is C2, C3, C4, and C5 represent the V content of the electrolyte in the all-vanadium redox flow battery. 2+ , V 3+ , VO 2+ , ion concentration.

[0025] This embodiment provides a three-closed-loop charge and discharge control method based on core voltage estimation of an all-vanadium redox flow battery, including a first closed-loop control link, a second closed-loop control link, a third closed-loop control link, and a core voltage estimation module, wherein:

[0026] The first closed-loop control link of this embodiment includes an SOC selector and an SOC controller. The SOC controller is connected to the second closed-loop control link via two outputs. Each output is connected to a switch, and the SOC selector controls the on and off of the switch in each output.

[0027] The SOC selector and the SOC controller respectively obtain the SOC of the all-vanadium redox flow battery and compare the obtained SOC of the all-vanadium redox flow battery with the SOC setting value SOC. * , the specific calculation formula is as follows:

[0028] ΔSOC=SOC * -SOC

[0029] The SOC selector and SOC controller determine whether the all-vanadium redox flow battery is in the charging process or the discharging process according to the positive or negative value of ΔSOC. When ΔSOC>0, it is determined to be the charging process, and the SOC selector controls the switch 1 of the first output of the SOC controller to close and the switch 2 of the second output to open, and the SOC controller outputs the reference current i to the second closed-loop control link through the first output in a constant current manner. * d Until the SOC of the all-vanadium flow battery is close to the SOC set value SOC * After that, the SOC selector controls the switch 1 of the first output of the SOC controller to be disconnected and the switch 2 of the second output to be closed, and the SOC controller outputs the core voltage setting value u of the all-vanadium redox flow battery to the second closed-loop control link through the second output in a constant voltage manner. * s , and when the SOC of the all-vanadium flow battery reaches the SOC setting value SOC * , the switch 1 of the first output and the switch 2 of the second output of the SOC controller controlled by the SOC selector are both disconnected, thereby stopping charging.

[0030] When ΔSOC<0, it is judged as a discharge process. When it is a discharge process, the SOC selector discharges according to a manually set discharge method and outputs a reference current i to the second closed-loop control link in a constant current manner. * d1 , or output the core voltage setting value u of the all-vanadium redox flow battery to the second closed-loop control link in a constant voltage manner * s .

[0031] The second closed-loop control link of this embodiment includes two groups of PI regulators, one of which is a PI regulator that serves as a voltage controller and receives the core voltage setting value u output by the first closed-loop control link. * s , another set of PI regulator current controller receives the reference current i output by the first closed-loop control link * d In addition, the second closed-loop control link also obtains the actual current i of the all-vanadium redox flow battery d 、The core voltage u of the all-vanadium redox flow battery s .

[0032] When the current controller of the second closed-loop control link obtains the reference current i * d When the current controller is used to control the reference current i * d and the actual current i d1 The difference (i * d -i d1) After current proportional integral adjustment, the adjusted reference current i is obtained * dadj And output to the third closed-loop control link, the calculation formula is as follows:

[0033]

[0034] Among them, K p2 is the proportional coefficient of the current controller, K i2 is the integral coefficient of the current controller.

[0035] When the voltage controller of the second closed-loop control link obtains the core voltage setting value u * s When the voltage controller sets the core voltage to u * s and core voltage u s The difference (u * s -u s ) After voltage proportional integral adjustment, the adjusted reference current i is obtained * dadj And output to the third closed-loop control link, the calculation formula is as follows:

[0036]

[0037] Among them, K p1 is the proportional coefficient of the voltage controller, K i1 is the integral coefficient of the voltage controller.

[0038] The core voltage u s The core voltage estimation module obtains the actual current i of the all-vanadium liquid flow battery by d1 、Vanadium redox flow battery terminal voltage U d1 The SOC of the all-vanadium flow battery and the random forest algorithm are obtained. The specific steps are as follows:

[0039] Step A: Initialize model parameters. Set the number of decision trees to n t and the maximum depth d max .

[0040] Step B: Randomly extract samples. The training set D contains the terminal voltage U of the all-vanadium redox flow battery. d1 Dataset, charge and discharge current i of all-vanadium redox flow battery d1 Dataset, all-vanadium redox flow battery SOC data set and corresponding all-vanadium redox flow battery core voltage u s Dataset. From the training data set D, use the Bootstrap sampling method to randomly select n sample subsets D with replacement. i ={D1,D2,…D n}, to create a training set for each decision tree.

[0041] Step C: Randomly select features. At each node split, randomly select features.

[0042] Step D: Split the node. The training data set contains m features, and then randomly select features are split until the maximum depth d is reached max Repeat steps 3 and 4 to build multiple decision trees until the preset number of trees n is reached. t .

[0043] Step E: Regression prediction. Based on the terminal voltage u of the all-vanadium redox flow battery collected on site d1 、Charge and discharge current i of all-vanadium redox flow battery d1 The calculated SOC of the vanadium redox flow battery is used to aggregate the prediction results of multiple decision trees and output the core voltage u of the vanadium redox flow battery. s .

[0044] The third closed-loop control link of this embodiment obtains the adjusted reference current i output by the current proportional integral and voltage proportional integral in the second closed-loop control link. * dadj , and obtain the inverter AC side current component i on the d axis from the PQ control module d , the component i of the inverter AC side current on the q axis q , the component e of the three-phase grid voltage on the d axis d , the component e of the three-phase grid voltage on the q axis q .

[0045] Specifically, the third closed-loop control link includes two groups of PI regulators (proportional integral regulators) and two groups of inductive reactance ωL, wherein the first group of PI regulators receives the adjusted reference current i output by the current proportional integral and voltage proportional integral in the second closed-loop control link. * dadj 、-i d , the first group of inductive reactance input component i q The second set of PI regulators receives i * q -i q , the second group of inductive reactance input component i d .

[0046] In the PQ control module, the d-axis component i of the inverter AC side current is d , the component i of the inverter AC side current on the q axis q , the component e of the three-phase grid voltage on the d axis d , the component e of the three-phase grid voltage on the q axis q, the process of obtaining these parameters is as follows:

[0047] Let L be the inductance of the filter reactor; R be the equivalent resistance of the filter reactor; C1 and C2 be the DC side capacitors of the inverter, e abc Indicates the three-phase grid voltage, i abc represents the three-phase grid current, and PLL represents the phase-locked loop. The grid voltage phase θ is given by the formula Calculate, where ω represents the angular frequency of three-phase alternating current; t represents time; V m Indicates that the voltage amplitude of the three-phase grid is 311, k p represents the proportionality coefficient, k i is the integration coefficient.

[0048] The component e of the three-phase grid voltage on the d-axis d , the component e of the three-phase grid voltage on the q axis q , is obtained by the following formula through equal amplitude transformation:

[0049]

[0050] where e a Indicates the voltage of phase A, e b Indicates the B phase voltage, e c Indicates the C-phase voltage.

[0051] Then by Find the reference current and The value of the third closed loop Take 0, Represent the specified active and reactive power targets respectively; the obtained Provided to the first closed loop.

[0052] The component i of the inverter AC side current on the d axis d , the component i of the inverter AC side current on the q axis q , obtained by the following formula:

[0053]

[0054] Among them, i a is the phase A current, i b is the B phase current, i c is the C phase current.

[0055] In the third closed-loop control link, the output of the first group of PI regulators and the component i passing through the first group of inductive reactances are combined. q And the component e of the three-phase grid voltage on the d axis d The reference voltage is calculated in the q-axis component v q, the calculation formula is as follows:

[0056] v q =K P3 (-i q )+K i3 ∫(-i q )dt-i d *ωL+e q

[0057] Among them, K p3 K is the proportional coefficient of the first group of PI regulators in the third closed-loop control link, i3 It is the integral coefficient of the first group of PI regulators in the third closed-loop control link.

[0058] In the third closed-loop control link, the output of the second group of PI regulators and the component i passing through the second group of inductive reactance are combined. d And the component e of the three-phase grid voltage on the q axis q The reference voltage is calculated on the d-axis component v d , the calculation formula is as follows:

[0059]

[0060] Among them, K p4 K is the proportional coefficient of the second group of PI regulators in the third closed-loop control link. i4 It is the integral coefficient of the second group of PI regulators in the third closed-loop control link.

[0061] The reference voltage calculated in the third closed-loop control link is the q-axis component v q , the reference voltage is in the d-axis component v d They are output to the PQ control module respectively, and in the PQ control module, the v q 、v d Transform from the two-phase rotating coordinate system to the three-phase stationary coordinate system, thereby obtaining the value v of the reference voltage in the three-phase stationary coordinate system abc , the calculation formula is:

[0062]

[0063] Get the three-phase voltage components v a 、v b 、v c After that, we can get v abc .

[0064] Finally, the PQ control module controls v abc After space vector modulation (SVPWM), the control voltage v is obtained to control the thyristor in the two-level three-phase half-bridge circuit. ta 、v tb 、vtc The calculation formula is as follows:

[0065]

[0066] Wherein: T S represents a sampling period; T2=T S v β ;T0=T S -T1-T2;,

[0067] The preferred embodiments of the present application are described in detail in combination with the drawings, and the embodiments described in the present application are only used to describe the preferred embodiments of the present application, and do not limit the concept and scope of the present application. In the above specific embodiments, various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction, and such combination should also be considered as disclosed by the present disclosure as long as it does not deviate from the technical concept of the present application. In order to avoid unnecessary repetition, the present application will not be described again.

[0068] The present application is not limited to the specific details in the above embodiments, and various modifications and improvements of the technical solutions of the present application made by those skilled in the art within the technical concept of the present application and without departing from the design idea of the present application should fall within the protection scope of the present application. The technical content claimed by the present application has been fully recorded in the claims.

Claims

1. A three-closed-loop charge and discharge control method based on core voltage estimation of an all-vanadium redox flow battery, wherein the all-vanadium redox flow battery is connected to a three-phase AC grid via a two-level three-phase half-bridge circuit and an inverter, and the all-vanadium redox flow battery implements inverter control via a PQ control module, characterized in that: It includes a first closed-loop control link, a second closed-loop control link, a third closed-loop control link and a core voltage estimation module, wherein: The first closed-loop control link includes an SOC selector and an SOC controller. The SOC controller is connected to the second closed-loop control link via two outputs. Each output is connected to a switch. The SOC selector controls the on / off of the switch in each output. The charging and discharging process is as follows: S1. Calculate the SOC of the all-vanadium liquid flow battery; S2, based on the SOC setting value SOC* and the SOC of the all-vanadium redox flow battery in step 1, subtract ΔSOC, ΔSOC = SOC* - SOC; S3. If ΔSOC > 0, start the charging process. If SOC ≤ SOC H , the SOC selector controls the closing of the switch of the first output and the opening of the switch of the second output, and the SOC controller outputs a reference current i to the second closed-loop control link * d , the all-vanadium redox flow battery is charged in a constant-current manner; if SOC H < SOC < SOC*, the SOC selector controls the opening of the switch of the first output and the closing of the switch of the second output, and the SOC controller outputs the core voltage setting value u of the all-vanadium redox flow battery to the second closed-loop control link * s , the all-vanadium redox flow battery is charged in a constant-voltage manner; if SOC = SOC* (i.e., ΔSOC = 0), stop the charging process; If ΔSOC<0, the discharge process is started. If SOC≥SOC L The SOC selector controls the switch of the first output to be closed and the switch of the second output to be open. The SOC controller outputs the reference current i to the second closed-loop control link. * d , the all-vanadium flow battery is discharged at a constant current; if SOC* <SOC<SOC L When the SOC selector controls the switch of the first output to be disconnected and the switch of the second output to be closed, the SOC controller outputs the core voltage setting value u of the all-vanadium liquid flow battery to the second closed-loop control link in a constant voltage manner. * s , the all-vanadium redox flow battery discharges at a constant voltage; if SOC = SOC*, that is, ΔSOC = 0, the discharge process stops; The second closed-loop control link obtains the reference current i output by the first closed-loop control link * d 、The core voltage setting value u of the all-vanadium redox flow battery * s The core voltage estimation module obtains the actual current i of the all-vanadium liquid flow battery d1 、Vanadium redox flow battery terminal voltage U d1 And the SOC of the all-vanadium redox flow battery is obtained by random forest algorithm and the core voltage u of the all-vanadium redox flow battery is obtained s ; When the second closed-loop control link obtains the reference current i * d When the reference current i * d and the actual current i d1 The adjusted reference current i is obtained by performing current proportional integral adjustment on the difference between * dadj1 And output to the third closed-loop control link; when the second closed-loop control link obtains the core voltage setting value u * s When the core voltage is set to u * s and core voltage u s The difference between the voltage proportional integral is adjusted to obtain the adjusted reference current i * dadj2 And output to the third closed-loop control link.

2. The three-closed-loop charge and discharge control method based on core voltage estimation of all-vanadium redox flow battery according to claim 1, characterized in that: The second closed-loop control link includes two groups of PI regulators, one of which is a PI regulator that receives the core voltage setting value u output by the first closed-loop control link as a voltage controller. * s , another set of PI regulator current controller receives the reference current i output by the first closed-loop control link * d .

3. The three-closed-loop charge and discharge control method based on core voltage estimation of all-vanadium redox flow battery according to claim 1, characterized in that: The third closed-loop control link includes two groups of PI regulators and two groups of inductive reactances, wherein the first group of PI regulators receives the adjusted reference current i output by the current proportional integral and voltage proportional integral in the second closed-loop control link. * dadj , the first group of inductive reactance input component i q , combined with the output of the first group of PI regulators and the component i passing through the first group of inductive reactances q And the component e of the three-phase grid voltage on the d axis d The reference voltage is calculated on the d-axis component v d ; The second set of PI regulators receives i * q -i q , where i * q Equal to 0, the second group of inductive reactance input component i d , combined with the output of the second set of PI regulators and the component i passing through the second set of inductive reactance d And the component e of the three-phase grid voltage on the q axis q Calculate v q .

4. The three-closed-loop charge and discharge control method based on core voltage estimation of all-vanadium redox flow battery according to claim 1, characterized in that: The PQ control module is used to adjust the reference voltage to the q-axis component v q , the reference voltage is in the d-axis component v d Transform from the two-phase rotating coordinate system to the three-phase stationary coordinate system, thereby obtaining the value v of the reference voltage in the three-phase stationary coordinate system abc .

Images