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

Abstract

The invention discloses a three-closed-loop charge-discharge control method based on all-vanadium redox flow battery core voltage estimation, which comprises a first closed-loop control link, a second closed-loop control link and a third closed-loop control link, and in the first closed-loop control link, whether a charge flow or a discharge flow is determined based on SOC; in the charging process, reference current and a kernel voltage set value are output to a second closed-loop control link; in the second closed-loop control link, reference current and a kernel voltage set value are obtained, charging and discharging current of the all-vanadium redox flow battery and kernel voltage of the all-vanadium redox flow battery are obtained, and adjusted reference current is obtained after voltage proportional-integral adjustment and output to a third closed-loop control link; in the third closed-loop control link, the components of the alternating-current side 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 are combined, and # imgabs0 # and # imgabs1 # are obtained through calculation; and a # imgabs4 # is obtained by the PQ control module based on the # imgabs2 # and the # imgabs3 #, and the control voltage of the thyristor is obtained after space vector modulation.

Description

Technical Field

[0001] The invention relates to the field of all-vanadium liquid flow battery charge and discharge control methods, in particular to a three-closed-loop charge and discharge control method based on all-vanadium liquid 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 the 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 uses the internal proportional integral controller to achieve accurate voltage tracking, so that the DC side voltage value can reach the set value. The strategy of inner loop control 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 chase 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] Although the dual closed-loop PI control can follow the target setting value faster through the adjustment of the inner and outer loops, the effects on different energy storage devices are still different. Taking the all-vanadium liquid flow battery in this article as an example, when charging at a constant voltage, 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, which is the shortcoming of the all-vanadium liquid flow battery; the battery charging and discharging status judgment and corresponding actions lack accurate implementation links, which is the second shortcoming.

[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, it takes into account how to control the all-vanadium liquid flow battery when connected to the power grid, and does not consider that the battery 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 problems existing in the double closed-loop control process of the prior art that during constant voltage charging, 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] Three - closed - loop charge - discharge control method based on the core voltage estimation of a vanadium redox flow battery. The vanadium redox flow battery is connected to a three - phase AC power grid through a two - level three - phase half - bridge circuit and an inverter, and the vanadium redox flow battery realizes the control of the inverter through a PQ control module, 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, where:

[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 through two outputs, and each output is connected with a switch. The SOC selector controls the on - off of the switches in each output. Its charge - discharge process is as follows:

[0009] S1. Calculate the SOC of the vanadium redox flow battery;

[0010] S2. Subtract the SOC of the vanadium redox flow battery obtained in step 1 from the SOC set value SOC* to get 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 close and the switch of the second output to open. The SOC controller outputs a reference current i * d to the second closed - loop control link, and the vanadium redox flow battery charges in a constant - current manner. If SOC H <SOC<SOC*, the SOC selector controls the switch of the first output to open and the switch of the second output to close. The SOC controller outputs the core voltage set value u * s of the vanadium redox flow battery to the second closed - loop control link, and the vanadium redox flow battery charges in a constant - voltage manner. If SOC = SOC*, that is, ΔSOC = 0, stop the charging process;

[0012] If ΔSOC<0, start the discharging process. If SOC≥SOC L , the SOC selector controls the switch of the first output to close and the switch of the second output to open. The SOC controller outputs a reference current i * d to the second closed - loop control link, and the vanadium redox flow battery discharges in a constant - current manner. If SOC*<SOC<SOC L , the SOC selector controls the switch of the first output to open and the switch of the second output to close. The SOC controller outputs the core voltage set value u * s, the all-vanadium liquid 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 liquid flow battery * s The core voltage estimation module obtains the actual current i of the all-vanadium liquid flow battery d1 、Vanadium liquid flow battery terminal voltage U d1 And the SOC of the all-vanadium liquid flow battery and the core voltage u of the all-vanadium liquid flow battery are obtained through the random forest algorithm 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 difference between the current proportional integral is adjusted to obtain the adjusted reference current i * 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 is adjusted by voltage proportional integral 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 to receive 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 PI regulator receives i * q -i q , where i * q = 0, the second group of inductive reactance input component i d , combined with the output of the second PI regulator and the component i passing through the second group 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 control 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] On the basis of traditional double closed-loop control, the present 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 state. At the same time, the SOC loop is introduced on the current loop and voltage loop of the double closed loop. After adding the SOC loop, the battery's charge and discharge state 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 in terms of discharge. By adding current sensors and voltage sensors on the grid side to calculate the load size, the battery discharge has a good follow-up performance. The implementation function of the phase-locked loop is designed, and the accuracy of the phase-locked loop implementation determines the quality of future power conversion. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0021] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

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

[0023] In the traditional charging and discharging process, the terminal voltage of the battery is used as the standard display of the battery charging and discharging state, while the core voltage of the battery is more accurate as the standard for judging the battery state. Due to structural problems, the core voltage of some batteries cannot be measured or is difficult to measure, so the terminal voltage is used for measurement. However, the structural properties of the all-vanadium liquid flow battery determine that the core voltage can be well measured, so this embodiment proposes a three-closed-loop charging and discharging control method based on the core voltage estimation of the all-vanadium liquid flow battery.

[0024] In this embodiment, the core voltage of the all-vanadium liquid 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 liquid 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 liquid flow battery. 2+ , V 3+ , VO 2+ , ion concentration.

[0025] The present embodiment provides a three-closed-loop charge and discharge control method based on the core voltage estimation of an all-vanadium liquid flow battery, comprising 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 liquid flow battery, and respectively compare the obtained SOC of the all-vanadium liquid 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 liquid 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 judged as 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 liquid flow battery approaches the SOC setting value SOC * After that, the SOC selector controls the switch 1 of the first output of the SOC controller to be opened 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 liquid 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 liquid 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 liquid 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 voltage controller that 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 liquid flow battery d 、Core voltage u of all-vanadium liquid 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 regulation, 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 regulation, 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 liquid flow battery terminal voltage U d1 And the SOC of the all-vanadium liquid flow battery is obtained by using the random forest algorithm. 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 liquid flow battery. d1 Dataset, charging and discharging current i of all-vanadium redox flow battery d1 Dataset, all-vanadium redox flow battery SOC data set and the 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 nodes. The training data set contains m features, so 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. According to the terminal voltage u of the all-vanadium liquid flow battery collected on site d1 、Charge and discharge current i of all-vanadium redox flow battery d1 The SOC of the all-vanadium liquid flow battery calculated by the calculation is averaged to summarize the prediction results of multiple decision trees and output the core voltage u of the all-vanadium liquid 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 reactances 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 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] Assume that L represents the inductance of the filter reactor; R represents the equivalent resistance of the filter reactor; C1 and C2 represent the DC side capacitors of the inverter, e abc Represents 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 power 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 , obtained by equal amplitude transformation using the following formula:

[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 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 is the proportional coefficient of the first group of PI regulators in the third closed-loop control link, K 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 is the proportional coefficient of the second group of PI regulators in the third closed-loop control link, K 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, 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 component 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 used to control the thyristor in the two-level three-phase half-bridge circuit is obtained. ta 、v tb 、vtc , the calculation formula is as follows:

[0065]

[0066] Where: T S Indicates the sampling period; T2=T S v β ; T0 = T S -T1-T2;

[0067] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. The embodiments described in the present invention are merely descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. The various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction, and such combinations should also be regarded as the contents disclosed in the present disclosure as long as they do not violate the concept of the present invention. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0068] The present invention is not limited to the specific details of the above-mentioned embodiments. Within the technical concept of the present invention and without departing from the design concept of the present invention, various modifications and improvements made to the technical solution of the present invention by technical personnel in this field should fall within the protection scope of the present invention. The technical contents for which protection is sought in the present invention have 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 liquid flow battery, wherein the all-vanadium liquid 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 liquid flow battery realizes inverter control through 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 liquid 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. The SOC controller outputs a reference current i to the second closed-loop control link * d , and the all-vanadium redox flow battery is charged in a constant current mode. 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. 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 , and the all-vanadium redox flow battery is charged in a constant voltage mode. If SOC = SOC*, that is, 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 close and the switch of the second output to open, and the SOC controller outputs the reference current i to the second closed-loop control link. * d , the all-vanadium liquid 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 liquid 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 liquid flow battery * s The core voltage estimation module obtains the actual current i of the all-vanadium liquid flow battery d1 、Vanadium liquid flow battery terminal voltage U d1 And the SOC of the all-vanadium liquid flow battery and the core voltage u of the all-vanadium liquid flow battery are obtained through the random forest algorithm 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 difference between the current proportional integral is adjusted to obtain the adjusted reference current i * 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 is adjusted by voltage proportional integral 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 is characterized in that: 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 to receive 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 .

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 is 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 PI regulator receives i * q -i q , where i * q = 0, the second group of inductive reactance input component i d , combined with the output of the second PI regulator and the component i passing through the second group 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 control 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 .

Images