A method and system for balancing control of parallel battery clusters

Abstract

The present invention relates to a method and system for balancing control of parallel battery clusters, and relates to the field of battery energy storage systems. The actual current value and state of charge value of the battery cluster are obtained through a central controller, and the current average value and the state of charge average value are determined. The working state of the battery cluster is determined according to the current average value, and the control target of the battery cluster is determined according to the working state of the battery cluster and the state of charge average value. The output voltage expected value of multiple cascade converters is determined according to the battery cluster control target, and the multiple cascade converters are adjusted according to the output voltage expected value. Compared with the prior art, the present invention adopts a staged control method that combines the state of charge and the highest and lowest voltages of the battery cell, and independently controls the charge and discharge current of each battery cluster, which solves the problem that the existing parallel battery cluster cannot be filled and discharged at the same time, and the available capacity of the energy storage unit is low. It can also reduce the degree of dependence on the accuracy of the state of charge and improve the balancing effect.

Description

Technical Field

[0001] The present invention relates to the field of battery energy storage systems, and in particular to a method and system for balancing control of parallel battery clusters. Background Art

[0002] The smallest basic unit of the electrochemical energy storage system is the battery cell. The system architecture is that several battery cells are connected in series to form a battery module, several battery modules are connected in series to form a battery cluster, and several battery clusters are connected in parallel to form an energy storage unit. The energy storage unit is connected to the power grid through an energy storage inverter and a step-up transformer.

[0003] Due to the inconsistency of the production, working environment, and aging of the battery cells, the open circuit voltage and equivalent series impedance of each battery cell are inconsistent. During the charge and discharge cycle of the energy storage system, the state of charge and port voltage of different batteries are different. Since the battery module is composed of several battery cells connected in series, the state of charge and port voltage of different battery modules are different. Since the battery cluster is composed of several battery modules connected in series, the state of charge and port voltage of different battery clusters are different.

[0004] In the energy storage unit of the electrochemical energy storage system, several battery clusters with different states of charge and port voltages are connected in parallel. The difference in state of charge and port voltage between the battery clusters causes the battery cluster with a high state of charge to be fully charged first during charging. In order to prevent overcharging of the battery cluster, the system will stop charging, while the other battery clusters are not fully charged at this time. Similarly, during discharge, the battery cluster with a low state of charge is emptied first. In order to prevent overdischarge of the battery cluster, the system will stop discharging, while the other battery clusters are not completely emptied at this time. This reduces the overall capacity utilization of the energy storage system.

[0005] Therefore, how to achieve capacity state balance among parallel battery clusters and improve the capacity utilization of energy storage systems is an urgent need at present. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the prior art and provide a method and system for balancing control of parallel battery clusters.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A method for balancing and controlling a parallel battery cluster, the method comprising:

[0009] The central controller obtains the actual current value, the state of charge value, the minimum voltage value of the battery cell and the maximum voltage value of the battery cell of each of the multiple battery clusters;

[0010] The central controller determines the current average value and the state of charge average value of the plurality of battery clusters according to the actual current value and the state of charge value;

[0011] The central controller determines the current working state of the battery cluster according to the average current value, and the working state of the battery cluster includes the charging state and the discharging state;

[0012] The central controller determines the control target of the battery cluster according to the working status and the average value of the state of charge of the battery cluster. The control target of the battery cluster includes controlling the state of charge, controlling the minimum voltage of the battery cell, and controlling the maximum voltage of the battery cell.

[0013] The central controller determines the expected output voltage values ​​corresponding to each of the plurality of cascade converters according to the control target of the battery cluster;

[0014] The plurality of cascade converters are adjusted according to their respective corresponding output voltage expected values ​​so that the output voltage approaches the output voltage expected value.

[0015] Preferably, the central controller determines the current working state of the battery cluster according to the current average value, including:

[0016] When the current average value is positive, the central controller determines the current working state of the battery cluster as a discharge state;

[0017] When the current average value is negative, the central controller determines the current working state of the battery cluster as a charging state.

[0018] Preferably, the central controller determines the control target of the battery cluster according to the working state and the average value of the state of charge of the battery cluster, including:

[0019] When the working state of the battery cluster is a discharge state and the average state of charge is greater than a first state of charge threshold, the central controller determines the control target of the battery cluster to control the state of charge;

[0020] When the working state of the battery cluster is a discharge state and the average state of charge is less than or equal to a first state of charge threshold, the central controller determines the control target of the battery cluster as controlling the minimum voltage of the battery cell;

[0021] When the working state of the battery cluster is a charging state and the average state of charge is greater than or equal to a second state of charge threshold, the central controller determines the control target of the battery cluster to control the maximum voltage of the battery cell;

[0022] When the working state of the battery cluster is the charging state and the state of charge average value is less than the second state of charge threshold, the central controller determines the battery cluster control target as controlling the state of charge.

[0023] Preferably, the first state of charge threshold is 20%, and the second state of charge threshold is 80%.

[0024] Preferably, the central controller determines the expected output voltage values ​​corresponding to each of the plurality of cascade converters according to the battery cluster control target, including:

[0025] The central controller determines the current expected values ​​corresponding to each of the plurality of battery clusters according to the control target of the battery cluster;

[0026] The central controller determines the expected output voltage values ​​corresponding to the multiple cascade converters according to the expected current value and the actual current values ​​of the multiple battery clusters.

[0027] Preferably, the central controller determines the current expected values ​​corresponding to each of the plurality of battery clusters according to the battery cluster control target, including:

[0028] When the control target of the battery cluster is to control the state of charge, the central controller calculates the difference between the state of charge value of each of the multiple battery clusters and the average state of charge value, and then proportionally integrates the difference to obtain the current expected value corresponding to each of the multiple battery clusters;

[0029] When the control target of the battery cluster is to control the minimum voltage of the battery cell, the central controller calculates the average value of the minimum voltages of the battery cells of the multiple battery clusters according to the minimum voltage values ​​of the battery cells of the multiple battery clusters, and then calculates the difference between the minimum voltage values ​​of the battery cells of the multiple battery clusters and the average value of the minimum voltage of the battery cells, and then proportionally integrates the difference to obtain the current expected value corresponding to each of the multiple battery clusters;

[0030] When the control target of the battery cluster is to control the maximum voltage of the battery cell, the central controller calculates the average value of the maximum voltages of the battery cells of the multiple battery clusters based on the maximum voltage values ​​of the battery cells of the multiple battery clusters, and then calculates the difference between the maximum voltage values ​​of the battery cells of the multiple battery clusters and the average value of the maximum voltage of the battery cells, and then proportionally integrates the difference to obtain the expected current value corresponding to each of the multiple battery clusters.

[0031] Preferably, the central controller determines the expected output voltage values ​​corresponding to the multiple cascade converters according to the expected current value and the actual current values ​​of the multiple battery clusters, including:

[0032] The central controller calculates the difference between the expected current value and the actual current value of each of the multiple battery clusters, and then performs proportional integration on the difference to obtain the expected output voltage value corresponding to each of the multiple cascade converters.

[0033] Preferably, the plurality of cascaded converters are adjusted according to their respective corresponding expected output voltage values ​​so that the output voltage approaches the expected output voltage value, including:

[0034] The plurality of cascaded converters determine the expected duty cycle values ​​corresponding to the plurality of internal switches according to the expected output voltage values ​​corresponding to the plurality of cascaded converters;

[0035] The plurality of cascade converters each loads a corresponding desired duty cycle value to the plurality of switches, so that the output voltages of the plurality of cascade converters tend to the desired output voltage value.

[0036] A system for balancing control of a parallel battery cluster, the system comprising:

[0037] The central controller is connected to the multiple cascade converters and the multiple battery clusters for communication, and is used to: obtain the actual current value, state of charge value, minimum cell voltage value and maximum cell voltage value of each of the multiple battery clusters; determine the average current value and the average state of charge value of the multiple battery clusters according to the actual current value and the state of charge value; determine the current working state of the battery cluster according to the average current value, and the working state of the battery cluster includes the charging state and the discharging state; determine the control target of the battery cluster according to the working state and the average state of charge value of the battery cluster, and the control target of the battery cluster includes controlling the state of charge, controlling the minimum cell voltage and controlling the maximum cell voltage; determine the expected output voltage value corresponding to each of the multiple cascade converters according to the control target of the battery cluster;

[0038] Multiple cascade converters, the negative end of each cascade converter output voltage is connected to the positive end of each battery cluster, the positive ends of the multiple cascade converter output voltages are connected as the positive electrode of the battery cluster, the multiple cascade converters are connected in series to the battery cluster and draw power from the battery cluster, and the charging current and discharging current of the parallel battery cluster are controlled by changing the output voltage of the cascade converters. They are also used to: adjust according to the corresponding expected output voltage values ​​so that the output voltage tends to the expected output voltage value.

[0039] Preferably, the cascade converter includes a multi-stage cascaded DC converter capable of bidirectional power flow, wherein the first stage is an isolated DC converter and the remaining stages are non-isolated DC converters, the isolated DC converter includes one or two sub-power conversion circuits, and the non-isolated DC converter includes one or more parallel sub-non-isolated power conversion circuits.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] 1. The present invention independently controls the charge and discharge current of each battery cluster according to the state of charge of each battery cluster and the maximum and minimum voltages of the battery cells, and solves the problem that the existing parallel battery clusters cannot be fully charged or discharged at the same time, and the system has low available capacity.

[0042] 2. In the early stage of charging and discharging of the battery cluster, the state of charge (SOC) is used as the balancing control target, and in the late stage of charging and discharging, the highest and lowest voltages of the battery cells are used as the control targets. This staged control method that combines the state of charge and the highest and lowest voltages of the battery cells reduces the dependence on the accuracy of the state of charge and improves the balancing effect compared to the traditional method of balancing control based only on the state of charge. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A flow chart of a method for balancing control of parallel battery clusters according to the present invention;

[0044] Figure 2 A flow chart of obtaining an expected value of an output voltage of a cascade converter when the control target of an embodiment of the present invention is to control the state of charge;

[0045] Figure 3 A flow chart of obtaining an expected value of an output voltage of a cascade converter when the control target of an embodiment of the present invention is to control the minimum voltage of a battery cell;

[0046] Figure 4 This is a flow chart of obtaining an expected value of the output voltage of a cascade converter when the control target of an embodiment of the present invention is to control the maximum voltage of a battery cell;

[0047] Figure 5 A connection diagram of a system for balancing control of parallel battery clusters according to the present invention;

[0048] Figure 6 It is a topological cascade structure diagram of the cascade converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0049] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0050] The method and system for balancing control of a parallel battery cluster of the present invention are suitable for use in scenarios where energy storage units using parallel battery clusters are charged and discharged.

[0051] In this scenario, several battery clusters with different states of charge and port voltages are connected in parallel in the energy storage unit. The differences in state of charge and port voltage between the battery clusters result in the battery cluster with a high state of charge being fully charged first during charging. To prevent overcharging of the battery cluster, the energy storage unit will stop charging while the other battery clusters are not fully charged. Similarly, during discharge, the battery cluster with a low state of charge is emptied first. To prevent overdischarging of the battery cluster, the energy storage unit will stop discharging while the other battery clusters are not completely emptied, thereby reducing the overall capacity utilization of the energy storage unit.

[0052] The method and system for parallel battery cluster balancing control provided by the present invention obtains the actual current value, state of charge value, minimum voltage value and maximum voltage value of each battery cluster through a central controller, and determines the current average value and state of charge average value of the battery cluster, determines the working state of the battery cluster according to the current average value, and then determines the battery cluster control target according to the working state of the battery cluster and the state of charge average value, determines the output voltage expected value corresponding to each of the multiple cascade converters according to the battery cluster control target, and adjusts the multiple cascade converters according to the corresponding output voltage expected value, so that the output voltage tends to the output voltage expected value. Compared with the prior art, the present invention adopts a staged control method that combines the state of charge and the maximum and minimum voltages of the battery cell, and independently controls the charge and discharge current of each battery cluster, which solves the problem that the existing parallel battery cluster cannot be filled and discharged at the same time, and the energy storage unit has low available capacity, and can also reduce the degree of dependence on the accuracy of the state of charge and improve the balancing effect.

[0053] In view of the problems existing in the prior art, the present invention provides a method for balancing control of parallel battery clusters, such as Figure 1 As shown, the method may include the following steps:

[0054] In step S101 , the central controller obtains actual current values, state of charge values, minimum cell voltage values, and maximum cell voltage values ​​of each of a plurality of battery clusters.

[0055] The central controller is connected to multiple battery clusters and multiple cascade converters. The central controller obtains the current state of charge value, the minimum voltage value of the battery cell, and the maximum voltage value of the battery cell of each battery cluster by communicating with the multiple battery clusters respectively; and obtains the current actual value of the current of each battery cluster by communicating with the multiple cascade converters respectively.

[0056] Step S102 : The central controller determines the current average value and the state of charge average value of the plurality of battery clusters according to the actual current value and the state of charge value.

[0057] The central controller calculates the current average value of the energy storage unit composed of multiple battery clusters based on the actual current value of each battery cluster. The calculation formula for the current average value is as follows:

[0058]

[0059] in I Bat_average represents the average current of the battery cluster, I Batk represents the current of each battery cluster, k=1, 2,…, n represents the kth battery cluster.

[0060] The central controller calculates the average state of charge of the energy storage unit composed of multiple battery clusters based on the current state of charge value of each battery cluster. The calculation formula for the average state of charge is as follows:

[0061]

[0062] in SOC average Represents the average state of charge of the battery cluster, SOC k represents the state of charge of each battery cluster, k=1, 2,…, n represents the kth battery cluster.

[0063] Step S103: the central controller determines the current working state of the battery cluster according to the current average value.

[0064] The current working state of the battery cluster includes a charging state and a discharging state.

[0065] The central controller determines whether the current working state of the battery cluster is a discharge state or a charge state according to the positive or negative value of the current average value. In some embodiments, when the current average value is positive, the central controller determines the current working state of the battery cluster as a discharge state; when the current average value is negative, the central controller determines the current working state of the battery cluster as a charge state.

[0066] Step S104 : the central controller determines a control target of the battery cluster according to the working state and the average state of charge of the battery cluster.

[0067] The battery cluster control targets include controlling the state of charge, controlling the minimum voltage of the battery cell, and controlling the maximum voltage of the battery cell. Controlling the state of charge means controlling the state of charge of the battery cluster, controlling the minimum voltage of the battery cell means controlling the minimum voltage of the battery cluster, and controlling the maximum voltage of the battery cell means controlling the maximum voltage of the battery cluster.

[0068] In some embodiments, the central controller may determine the battery cluster control target in the following four cases:

[0069] 1) When the working state of the battery cluster is a discharge state and the average state of charge is greater than a first state of charge threshold, the central controller determines the control target of the battery cluster to control the state of charge;

[0070] 2) When the working state of the battery cluster is a discharge state and the average state of charge is less than or equal to a first state of charge threshold, the central controller determines the control target of the battery cluster to be a minimum voltage of the control cell;

[0071] 3) When the working state of the battery cluster is the charging state and the average state of charge is greater than or equal to the second state of charge threshold, the central controller determines the control target of the battery cluster to control the maximum voltage of the battery cell;

[0072] 4) When the working state of the battery cluster is the charging state and the average state of charge value is less than the second state of charge threshold value, the central controller determines the control target of the battery cluster to control the state of charge.

[0073] The first state of charge threshold and the second state of charge threshold may be set according to actual needs or engineering experience. For example, the first state of charge threshold may be set to 20%, and the second state of charge threshold may be set to 80%.

[0074] Step S105 : the central controller determines the expected output voltage values ​​corresponding to each of the plurality of cascade converters according to the control target of the battery cluster.

[0075] In some embodiments, the central controller determines the current expected values ​​corresponding to each of the multiple battery clusters according to the battery cluster control target, and then determines the output voltage expected values ​​corresponding to each of the multiple cascade converters according to the current expected values ​​and the actual current values ​​of the multiple battery clusters.

[0076] In some embodiments, the central controller determines the current expected values ​​corresponding to the multiple battery clusters according to the battery cluster control target, which may include the following three situations:

[0077] 1) When the control target of the battery cluster is to control the state of charge, the central controller calculates the difference between the state of charge value of each of the multiple battery clusters and the average state of charge value, and then proportionally integrates the difference to obtain the current expected value corresponding to each of the multiple battery clusters;

[0078] 2) When the control target of the battery cluster is to control the minimum voltage of the battery cell, the central controller calculates the average value of the minimum voltages of the battery cells of the multiple battery clusters according to the minimum voltage values ​​of the battery cells of the multiple battery clusters, and then calculates the difference between the minimum voltage values ​​of the battery cells of the multiple battery clusters and the average value of the minimum voltage of the battery cells, and then proportionally integrates the difference to obtain the current expected value corresponding to each of the multiple battery clusters;

[0079] The calculation formula for the average value of the minimum cell voltage is as follows:

[0080]

[0081] in Ucellmin average Indicates the average value of the lowest cell voltage of the battery cluster. Ucellmin k Indicates the lowest voltage of the cells in each battery cluster, k=1, 2,…, n, indicates the kth battery cluster.

[0082] 3) When the control target of the battery cluster is to control the maximum voltage of the battery cell, the central controller calculates the average value of the maximum voltage of the battery cells of the multiple battery clusters according to the maximum voltage values ​​of the battery cells of the multiple battery clusters, and then calculates the difference between the maximum voltage values ​​of the battery cells of the multiple battery clusters and the average value of the maximum voltage of the battery cells, and then proportionally integrates the difference to obtain the current expected value corresponding to each of the multiple battery clusters;

[0083] The calculation formula for the average value of the maximum cell voltage is as follows:

[0084]

[0085] in Ucellmax average Indicates the average value of the maximum voltage of the battery cells in the battery cluster. Ucellmax k represents the maximum voltage of the cells in each battery cluster, k=1, 2,…, n, represents the kth battery cluster.

[0086] In some embodiments, the central controller calculates the difference between the expected current value and the actual current value of each of the multiple battery clusters, and then performs proportional integration on the difference to obtain the expected output voltage value corresponding to each of the multiple cascade converters.

[0087] Figure 2 1 is a flow chart of obtaining the expected value of the output voltage of the cascade converter when the control target is to control the state of charge in this embodiment. Figure 2 As shown, when the control target is to control the state of charge, the state of charge value of the battery cluster is calculated. SOC sample The average state of charge of the battery cluster SOC average The difference between the two is proportionally integrated (PI) to obtain the expected current value of the battery cluster. I outref ， Then calculate the expected current value of the battery cluster I outref The actual current value of the battery cluster I out_sample The difference between the two is proportionally integrated (PI) to obtain the expected output voltage of the cascade converter. U ref .

[0088] Figure 3 1 is a flow chart of obtaining the expected output voltage value of the cascade converter when the control target in this embodiment is to control the minimum voltage of the battery cell. Figure 3 As shown, when the control target is to control the minimum voltage of the battery cell, calculate the minimum voltage value of the battery cell of the battery cluster Ucellmin sample The average value of the lowest voltage of the battery cell in the battery cluster Ucellmin average The difference between the two is proportionally integrated (PI) to obtain the expected current value of the battery cluster. I out_ref , and then calculate the expected current value of the battery cluster I out_ref The actual current value of the battery cluster I out_sample The difference between the two is proportionally integrated (PI) to obtain the expected output voltage of the cascade converter. U ref .

[0089] Figure 4 1 is a flow chart of obtaining the expected output voltage value of the cascade converter when the control target in this embodiment is to control the maximum voltage of the battery cell. Figure 4 As shown, when the control target is to control the maximum voltage of the battery cell, calculate the maximum voltage value of the battery cell of the battery cluster Ucellmax sample The average value of the maximum voltage of the battery cells in the battery cluster Ucellmax average The difference between the two is proportionally integrated (PI) to obtain the expected current value of the battery cluster. I out_ref , and then calculate the expected current value of the battery cluster I out_ref The actual current value of the battery cluster I out_sample The difference between the two is proportionally integrated (PI) to obtain the expected output voltage of the cascade converter. U ref .

[0090] In step S106 , the plurality of cascaded converters are adjusted according to their corresponding expected output voltage values ​​so that the output voltage approaches the expected output voltage value.

[0091] In some embodiments, multiple cascaded converters determine the expected duty cycle values ​​corresponding to multiple internal switches based on their respective corresponding expected output voltage values; and then each loads the corresponding expected duty cycle value to the multiple switches, so that the output voltages of the multiple cascaded converters tend to the expected output voltage values.

[0092] Specifically, multiple cascade converters receive the expected output voltage value sent from the central controller, and each calculates the difference between the expected output voltage value and the actual output voltage value, and then proportionally integrates the difference to obtain the expected duty cycle value corresponding to the multiple internal switches. After the expected duty cycle value is loaded to each switch, the output voltage of the multiple cascade converters tends to the expected output voltage value.

[0093] For example, when the energy storage unit is in a charging state and the state of charge (SOC) of the first battery cluster is higher than the state of charge of other battery clusters, the output voltage of the cascade converter 1 is controlled so that the output voltage of the cascade converter 1 increases, thereby reducing the charging current of the first battery cluster, that is, the increase of the state of charge of the first battery cluster slows down, and finally the state of charge of each battery cluster is consistent; when the energy storage unit is in a discharging state and the state of charge of the first battery cluster is higher than the state of charge of other battery clusters, the output voltage of the cascade converter 1 is controlled so that the output voltage of the cascade converter 1 increases, thereby increasing the discharge current of the first battery cluster, that is, the decrease of the state of charge of the first battery cluster is accelerated, and finally the state of charge of each battery cluster is consistent.

[0094] The present invention also provides a system for balancing control of a parallel battery cluster, which includes a central controller and a plurality of cascade converters.

[0095] The central controller is connected to the multiple cascade converters and the multiple battery clusters for communication, and is used to: obtain the actual current value, state of charge value, minimum cell voltage value and maximum cell voltage value of each of the multiple battery clusters; determine the average current value and the average state of charge value of the multiple battery clusters according to the actual current value and the state of charge value; determine the current working state of the battery cluster according to the average current value, and the working state of the battery cluster includes the charging state and the discharging state; determine the control target of the battery cluster according to the working state of the battery cluster and the average state of charge value, and the control target of the battery cluster includes controlling the state of charge, controlling the minimum cell voltage and controlling the maximum cell voltage; determine the expected output voltage value corresponding to each of the multiple cascade converters according to the battery cluster control target;

[0096] Multiple cascade converters, the negative end of each cascade converter output voltage is connected to the positive end of each battery cluster, the positive ends of the multiple cascade converter output voltages are connected as the positive electrode of the battery cluster, and the multiple cascade converters are connected in series to the battery cluster and draw power from the battery cluster. By changing the output voltage of the cascade converter, the charging current and discharging current of the parallel battery cluster can be controlled. It is also used to: adjust according to the corresponding output voltage expected value so that the output voltage tends to the output voltage expected value.

[0097] Figure 5 FIG. 1 is a connection diagram of a system for parallel battery cluster balancing control according to the present invention. Figure 5 As shown, the system includes a plurality of cascade converters and a central controller, a plurality of battery clusters including a first battery cluster Bat1 , Second battery cluster Bat2 , ..., nth battery cluster Batn , and their currents are I Bat1 、I Bat2 、……、IBatn , and their charge states are SOC 1 、 SOC 2 ,……,SOC n , and their minimum single cell voltages are Ucellmin 1 、Ucellmin 2 、……、Ucellmin n , and their maximum single cell voltages are Ucellmax 1 , Ucellmax 2 ,……, Ucellmax n The expected output voltages of multiple cascade converters are U ref1 、U ref2 、……、U refn . Each battery cluster is connected in series with a cascade converter, and the negative end of the cascade converter output voltage is connected to the positive end of the battery cluster. The positive ends of all cascade converter output voltages are connected and serve as the positive pole of the battery cluster. The central controller is connected to multiple battery clusters and multiple cascade converters for communication, receives the current, state of charge, maximum cell voltage, and minimum cell voltage of multiple battery clusters, and sends the expected output voltage value to each cascade converter after calculation. Multiple cascade converters are connected in series to multiple battery clusters and draw power from the battery clusters. By changing the series compensation voltage, the charging current and discharging current of the parallel battery clusters can be controlled.

[0098] In some embodiments, the cascade converter includes multiple stages of cascaded DC converters with bidirectional power flow, wherein the first stage is an isolated DC converter and the remaining stages are non-isolated DC converters, the isolated DC converter includes one or two sub-power conversion circuits, and the non-isolated DC converter includes one or more parallel sub-non-isolated power conversion circuits.

[0099] Figure 6 FIG. 1 is a topological cascade structure diagram of the cascade converter of the present invention. Figure 6 As shown, it includes a multi-stage cascaded DC converter capable of bidirectional power flow, wherein the first stage is an isolated DC converter and the remaining stages are non-isolated DC converters.

[0100] The first-stage isolated DC converter provides isolation, the ability to stabilize the input voltage of the subsequent non-isolated DC converter when the load changes rapidly, and the fixed high-gain conversion capability. The subsequent non-isolated DC converter of the cascade converter provides wide-range voltage regulation capability and stable compensation voltage capability for rapid changes in large current loads.

[0101] The isolated DC converter includes one or two sub-power conversion circuits, and the non-isolated DC converter includes one or more parallel-connected sub-non-isolated power conversion circuits.

[0102] The first influencing factor for the selection of the number of sub-power conversion circuits in the isolated DC converter is the battery cluster voltage. U Bat The second influencing factor is the primary switch voltage stress specification. The selection method includes: when the primary switch voltage stress specification of the sub-power conversion circuit meets the use stress, one sub-power conversion circuit is used, otherwise two sub-power conversion circuits are used, so that the cost, efficiency and power density are comprehensively optimized.

[0103] Figure 6 middle n In this embodiment, the first influencing factor for selecting the number of non-isolated DC converter cascades is the compensation voltage. U C The second influencing factor is the range of the voltage at the output end of the first-stage isolated DC converter, and the third influencing factor is the processing capability of the digital signal processor for the gain range. The method for selecting the number of cascaded non-isolated DC converters includes: determining the gain range that a single-stage non-isolated DC converter can handle according to the processing capability of the digital signal processor for the gain range, and then determining its own input voltage and output voltage range according to the compensation voltage range and the voltage range at the output end of the first-stage isolated DC converter, and finally determining the number of cascades with the best combination of cost, efficiency and power density.

[0104] In summary, the solution provided by the present application can obtain the actual current value, state of charge value, minimum cell voltage value and maximum cell voltage value of each of the multiple battery clusters through the central controller, and determine the average current value and the average state of charge value of the battery cluster, determine the working state of the battery cluster according to the average current value, and then determine the control target of the battery cluster according to the working state of the battery cluster and the average state of charge value, determine the output voltage expected value corresponding to each of the multiple cascade converters according to the battery cluster control target, and adjust the multiple cascade converters according to their corresponding output voltage expected values ​​so that the output voltage tends to the output voltage expected value. Compared with the prior art, the present invention adopts a staged control method that combines the state of charge and the maximum and minimum cell voltages to independently control the charge and discharge current of each battery cluster, solving the problem that the existing parallel battery cluster cannot be fully charged and discharged at the same time, and the energy storage unit has low available capacity, and can also reduce the degree of dependence on the accuracy of the state of charge and improve the balancing effect.

[0105] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0106] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0107] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for balancing control of parallel battery clusters, characterized in that: The method includes: The central controller obtains the actual current value, the state of charge value, the minimum voltage value of the battery cell and the maximum voltage value of the battery cell of each of the multiple battery clusters; The central controller determines the current average value and the state of charge average value of the plurality of battery clusters according to the current actual value and the state of charge value; The central controller determines the current working state of the battery cluster according to the current average value, wherein the working state of the battery cluster includes a charging state and a discharging state; The central controller determines the control target of the battery cluster according to the working state of the battery cluster and the average state of charge, including: when the working state of the battery cluster is a discharge state and the average state of charge is greater than a first state of charge threshold, the central controller determines the control target of the battery cluster as controlling the state of charge; when the working state of the battery cluster is a discharge state and the average state of charge is less than or equal to the first state of charge threshold, the central controller determines the control target of the battery cluster as controlling the minimum voltage of the battery cell; when the working state of the battery cluster is a charging state and the average state of charge is greater than or equal to a second state of charge threshold, the central controller determines the control target of the battery cluster as controlling the maximum voltage of the battery cell; when the working state of the battery cluster is a charging state and the average state of charge is less than the second state of charge threshold, the central controller determines the control target of the battery cluster as controlling the state of charge; wherein the control target of the battery cluster includes controlling the state of charge, controlling the minimum voltage of the battery cell, and controlling the maximum voltage of the battery cell; The central controller determines the expected output voltage values ​​corresponding to each of the plurality of cascade converters according to the battery cluster control target, including: the central controller determines the expected current values ​​corresponding to each of the plurality of battery clusters according to the battery cluster control target, including: when the battery cluster control target is to control the state of charge, the central controller calculates the difference between the state of charge value of each of the plurality of battery clusters and the average state of charge value, and then proportionally integrates the difference to obtain the expected current values ​​corresponding to each of the plurality of battery clusters; when the battery cluster control target is to control the minimum voltage of the battery cell, the central controller calculates the average value of the minimum voltages of the plurality of battery cells of the plurality of battery clusters according to the minimum voltage values ​​of the plurality of battery clusters, and then calculates the difference between the minimum voltage values ​​of the plurality of battery cells of the plurality of battery clusters and the average value of the minimum voltage of the battery cell, and then proportionally integrates the difference to obtain the expected current values ​​corresponding to each of the plurality of battery clusters; when the battery cluster control target is to control the maximum voltage of the battery cell, the central controller calculates the average value of the minimum voltages of the plurality of battery cells of the plurality of battery clusters according to the minimum voltage values ​​of the plurality of battery clusters The maximum voltage value of the battery cell is used to calculate the average value of the maximum voltage of the battery cells of the plurality of battery clusters, and then the difference between the maximum voltage value of each battery cell of the plurality of battery clusters and the average value of the maximum voltage of the battery cell is calculated, and then the difference is proportionally integrated to obtain the expected current value corresponding to each of the plurality of battery clusters; the central controller determines the expected output voltage value corresponding to each of the plurality of cascade converters according to the expected current value and the actual current value of each of the plurality of battery clusters, including: the central controller calculates the difference between the expected current value and the actual current value of each of the plurality of battery clusters, and then proportionally integrates the difference to obtain the expected output voltage value corresponding to each of the plurality of cascade converters; wherein the negative end of the output voltage of each cascade converter is connected to the positive end of each battery cluster, and the positive ends of the output voltages of the plurality of cascade converters are connected as the positive electrode of the battery cluster, and the plurality of cascade converters are connected in series to the battery cluster and draw power from the battery cluster, and the charging current and discharging current of the parallel battery clusters are controlled by changing the output voltage of the cascade converter; The plurality of cascade converters are adjusted according to the corresponding expected output voltage values ​​so that the output voltage approaches the expected output voltage value.

2. The method according to claim 1, characterized in that The central controller determines the current working state of the battery cluster according to the current average value, including: When the current average value is positive, the central controller determines the current working state of the battery cluster as a discharging state; When the current average value is negative, the central controller determines the current operating state of the battery cluster as a charging state.

3. The method according to claim 1, characterized in that The first state of charge threshold is 20%, and the second state of charge threshold is 80%.

4. The method according to claim 1, characterized in that: The plurality of cascaded converters are adjusted according to the respective corresponding expected output voltage values ​​so that the output voltage approaches the expected output voltage value, including: The plurality of cascaded converters determine the expected duty cycle values ​​corresponding to the plurality of internal switches according to the respective corresponding expected output voltage values; Each of the plurality of cascade-type converters loads the corresponding desired duty cycle value to the plurality of switches, so that the output voltages of the plurality of cascade-type converters tend to the desired output voltage value.

5. A system for balancing control of parallel battery clusters, characterized in that: The system includes: The central controller is connected to multiple cascade converters and multiple battery clusters for: obtaining actual current values, state of charge values, minimum cell voltage values, and maximum cell voltage values ​​of each of the multiple battery clusters; determining the current average value and the state of charge average value of the multiple battery clusters according to the actual current values ​​and the state of charge values; determining the current working state of the battery cluster according to the current average value, wherein the working state of the battery cluster includes a charging state and a discharging state; determining the control target of the battery cluster according to the working state of the battery cluster and the state of charge average value, including: when the working state of the battery cluster is a discharging state and the state of charge average value is greater than a first state of charge threshold value, the central The controller determines the battery cluster control target as controlling the state of charge; when the working state of the battery cluster is a discharge state and the average state of charge is less than or equal to a first state of charge threshold, the central controller determines the battery cluster control target as controlling the minimum voltage of the battery cell; when the working state of the battery cluster is a charging state and the average state of charge is greater than or equal to a second state of charge threshold, the central controller determines the battery cluster control target as controlling the maximum voltage of the battery cell; when the working state of the battery cluster is a charging state and the average state of charge is less than the second state of charge threshold, the central controller determines the battery cluster control target as controlling the state of charge; wherein the battery cluster control target includes controlling Controlling the state of charge, controlling the minimum voltage of the battery cell, and controlling the maximum voltage of the battery cell; determining the expected output voltage values ​​corresponding to each of the multiple cascade converters according to the battery cluster control target, including: determining the expected current values ​​corresponding to each of the multiple battery clusters according to the battery cluster control target, including: when the battery cluster control target is to control the state of charge, the central controller calculates the difference between the state of charge value of each of the multiple battery clusters and the average value of the state of charge, and then proportionally integrates the difference to obtain the expected current value corresponding to each of the multiple battery clusters; when the battery cluster control target is to control the minimum voltage of the battery cell, the central controller calculates the expected current value corresponding to each of the multiple battery clusters according to the average value of the state of charge of the multiple battery clusters The minimum voltage value calculates the average value of the minimum voltages of the cells of the multiple battery clusters, and then calculates the difference between the minimum voltage values ​​of the cells of the multiple battery clusters and the average value of the minimum voltages of the cells, and then proportionally integrates the difference to obtain the expected current value corresponding to each of the multiple battery clusters; when the control target of the battery cluster is to control the maximum voltage of the cells, the central controller calculates the average value of the maximum voltages of the cells of the multiple battery clusters according to the maximum voltage values ​​of the cells of the multiple battery clusters, and then calculates the difference between the maximum voltage values ​​of the cells of the multiple battery clusters and the average value of the maximum voltages of the cells, and then proportionally integrates the difference to obtain the expected current value corresponding to each of the multiple battery clusters;Determining the expected output voltage values ​​corresponding to each of the plurality of cascaded converters according to the expected current value and the actual current values ​​of each of the plurality of battery clusters, including: calculating the difference between the expected current value and the actual current values ​​of each of the plurality of battery clusters, and then performing proportional integration on the difference to obtain the expected output voltage values ​​corresponding to each of the plurality of cascaded converters; A plurality of cascade converters, each of which has a negative end connected to the positive end of each battery cluster, and a plurality of positive ends connected to the positive end of the output voltage of the cascade converters as the positive electrode of the battery cluster. The plurality of cascade converters are connected in series to the battery cluster and draw power from the battery cluster. The charging current and the discharging current of the parallel battery cluster are controlled by changing the output voltage of the cascade converters. The cascade converters are also used to: adjust according to the respective corresponding expected output voltage values ​​so that the output voltage approaches the expected output voltage value.

6. The system according to claim 5, characterized in that The cascade converter includes a multi-stage cascaded DC converter capable of bidirectional power flow, wherein the first stage is an isolated DC converter and the remaining stages are non-isolated DC converters. The isolated DC converter includes one or two sub-power conversion circuits, and the non-isolated DC converter includes one or more parallel sub-non-isolated power conversion circuits.

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