Active battery charge level compensation

Abstract

A rechargeable energy storage system includes a direct current (DC / DC) converter capable of: receiving battery discharge power at two first local nodes; and converting the battery discharge power to pack discharge power at two first inter-assembly nodes while in a discharge mode in response to a control signal. The DC / DC converter is further capable of: receiving pack charge power at the two first inter-assembly nodes; and converting the pack charge power to battery charge power at the two first local nodes while in a charge mode. A first battery assembly has a first state of charge. A second battery assembly has a second state of charge and operates in series with the first battery assembly. The controller generates the control signal that varies the DC / DC converter to balance the first state of charge with the second state of charge in the discharge mode.

Description

[0001] The present disclosure relates to a system and method for active state of charge balancing.

[0002] US 2008 / 0 042 493 A1 discloses a battery control unit for charging and discharging a plurality of batteries. The battery control unit has a plurality of direct current-to-direct current (DC-to-DC) converters connected in series. Each of a plurality of batteries is electrically connectable to a corresponding DC-to-DC converter. A coordinator connected to each of the plurality of DC-to-DC converters controls the charging and discharging of the battery electrically connected to the respective converter. The coordinator can also control the charging and discharging of one of the batteries to ensure that the battery maintains sufficient electrical capacity and to increase the longevity of the respective batteries.Because each battery is electrically connected to a corresponding DC-DC converter, the energy from one battery can be used to charge another battery, allowing for monitoring battery characteristics, including the energy capacity of each battery. Each of the DC-DC converters is selected to operate preferably below 30 volts, while the total voltage of the entire battery system can be well above 30 volts, depending on the number of DC-DC converters connected in series.

[0003] US 2014 / 0 145 681 A1 discloses that the state of charge of a lithium-ion cell module comprising multiple cells is managed by observing changes in the differential capacity curve of a cell that exceed or fall below a predetermined threshold during a discharge or charge process of the cell. Each of the changes is a change specific to that particular cell and corresponds to a particular state of charge of the cell, wherein the atomic number of a differential capacity curve change is used as the basis for determining a state of charge of the cell that corresponds to the change or a difference in the states of charge between two or more cells. The state of charge differences thus determined between the cells are then to be compensated by a compensation system suitable for balancing a charge.

[0004] US 2014 / 0 035 532 A1 discloses a cell balancing module for voltage balancing of a battery stack. The cell balancing module comprises an interface for inputting a coded reference voltage and input nodes for connecting a stack of energy storage cells. A switching unit is connected to each of the input nodes, and a local balancing unit is coupled to the switching unit and the interface. The local balancing unit is designed to compare the coded reference voltage with cell voltages of the energy storage cell stack to be connected and to balance the energy storage cell stack to be connected depending on the comparison of the coded reference voltage and the cell voltages. The invention further relates to a voltage balancing device and a method for cell balancing, in particular for voltage balancing of a stack of batteries.

[0005] US 2014 / 0 292 259 A1 discloses a DC microgrid charging / discharging system provided with an algorithm. Compared with a single battery, a charging / discharging voltage during charging and discharging is significantly increased by connecting a plurality of secondary batteries in series. The power conversion efficiency of a DC / DC converter is increased for charging / discharging power control by setting an appropriate voltage of a DC microgrid to be approximately twice the maximum voltage of a battery group. By adding a linear constant current source, stable charging and discharging is enabled regardless of battery group changes.The power conversion efficiency of the DC microgrid charging / discharging system is increased by configuring a DC energy storage system (ESS) used for both charging and discharging with a combination of a typical electrolytic capacitor and a supercapacitor or a group of secondary batteries.

[0006] DE 10 2019 121 918 A1 discloses DC power conversion for electrified vehicles with battery state balancing. A high-voltage battery pack comprises series-connected battery units, each of which separately supplies power to a respective DC / DC converter. The converter outputs are connected in parallel to supply a low-voltage DC bus. A central module includes an external controller that generates a target current to regulate the bus voltage and an allocator that distributes the target current via commands regarding the allocated current for respective converters. Local controllers each regulate an output current of a respective converter.The allocator identifies battery units with a specified deviation from a reference metric that characterizes the battery pack, assigns return currents to respective converters for the identified battery units, and increases the target current commanded for the DC / DC converters that have not been assigned return current by the assigned return currents.

[0007] Battery packs in consumer vehicles contain battery modules connected in series. As the battery modules discharge, some battery modules may reach a state of discharge that prevents the electrical power of the undischarged battery modules from being fully utilized. The varying states of charge of the battery modules are typically due to the different storage capacities of the battery modules. The different storage capacities are due to different sizes, ages, and / or different chemical compositions.

[0008] Accordingly, experts continue their research and development work in the field of battery state of charge balancing to increase the utility of battery packs.

[0009] A rechargeable energy storage system is provided herein. The rechargeable energy storage system includes a first DC-DC converter, a first battery assembly, a second battery assembly, and a first controller. The first DC-DC converter has two first local nodes and two first inter-assembly nodes. The first DC-DC converter is capable of: receiving a first battery discharge power at the two first local nodes; converting the first battery discharge power into a pack discharge power provided to the two first inter-assembly nodes in a discharge mode. The conversion of the first battery discharge power to the pack discharge power varies depending on a first control signal.The first DC-DC converter is further capable of receiving pack charging power at the first two inter-assembly nodes and converting the pack charging power into a first battery charging power provided by the first two local nodes in a charging mode. The first battery assembly has a first state of charge and is directly wired to the first two local nodes. The second battery assembly has a second state of charge, is in communication with one of the first two inter-assembly nodes, and operates in series with the first battery assembly. The first controller is in communication with the first DC-DC converter and is capable of generating the first control signal that varies the first DC-DC converter to balance the first state of charge with the second state of charge while in the discharging mode.

[0010] In one or more embodiments, the rechargeable energy storage system includes a second DC-DC converter, a third battery assembly, and a second controller. The second DC-DC converter has two second local nodes and two second inter-assembly nodes. The second DC-DC converter is capable of receiving a second battery discharge power at the two second local nodes. The second battery assembly is directly wired to the two second local nodes. The second DC-DC converter is further operable to convert the second battery discharge power to the pack discharge power applied to the two second inter-assembly nodes in the discharge mode. The conversion of the second battery discharge power to the pack discharge power varies depending on a second control signal.The second DC-DC converter is further operable to receive the pack charging power at the two second inter-assembly nodes and to convert the pack charging power into a second battery charging power supplied by the two second local nodes in charge mode. The third battery assembly has a third state of charge, is in communication with one of the two second inter-assembly nodes, and operates in series with the second battery assembly. The second controller is in communication with the second DC-DC converter and is capable of generating the second control signal that varies the second DC-DC converter to balance the second state of charge with the third state of charge in discharge mode.

[0011] In one or more embodiments, the rechargeable energy storage system includes a first adjustment module that communicates with the first battery assembly, the second battery assembly, and the first DC-DC converter. The first adjustment module is operable to: measure the first state of charge of the first battery assembly; measure the second state of charge of the second battery assembly; and generate a first target parameter based on the first state of charge and the second state of charge. The first controller is further operable to vary the first DC-DC converter depending on the first target parameter.

[0012] In one or more embodiments of the rechargeable energy storage system, the first controller is further capable of measuring a feedback voltage at one of the two first inter-assembly nodes and varying the first DC-DC converter in further dependence on the feedback voltage. The first target parameter is a voltage.

[0013] In one or more embodiments of the rechargeable energy storage system, the first controller is further capable of measuring a feedback current flowing from the first battery assembly to the first DC-DC converter and varying the first DC-DC converter in further dependence on the feedback current. The first target parameter is a current.

[0014] In one or more embodiments of the rechargeable energy storage system, the first adjustment module is further capable of generating the first target parameter using a model predictive control technique based on the first state of charge and the second state of charge.

[0015] In one or more embodiments of the rechargeable energy storage system, the first battery assembly has a different storage capacity than the second battery assembly.

[0016] In one or more embodiments of the rechargeable energy storage system, the first battery assembly has a different chemistry than the second battery assembly.

[0017] In one or more embodiments of the rechargeable energy storage system, the first battery assembly and the second battery assembly are part of a vehicle.

[0018] A method for actively balancing the battery state of charge is provided herein. The method includes receiving a first battery discharge power from a first battery assembly at two first local nodes of a first DC-DC converter. The first battery assembly has a first state of charge and is directly wired to the two first local nodes. The method includes converting the first battery discharge power to a stack discharge power provided to two first inter-assembly nodes of the first DC-DC converter in a discharge mode. One of the two first inter-assembly nodes is in communication with a second battery assembly. The second battery assembly has a second state of charge. The second battery assembly operates in series with the first battery assembly. The conversion of the first battery discharge power to the stack discharge power varies depending on a first control signal.The method further comprises receiving a pack charging power at the two first inter-assembly nodes; converting the pack charging power into a first battery charging power provided by the two first local nodes during a charging mode; and generating the first control signal with a first controller that varies the first DC-DC converter to balance the first state of charge with the second state of charge during the discharging mode.

[0019] In one or more embodiments, the method comprises receiving a second battery discharge power at two second local nodes of a second DC-DC converter. The second battery assembly is directly wired to the two second local nodes. The method comprises converting the second battery discharge power to the stack discharge power, which is present in the discharge mode at two second intermediate nodes of the second DC-DC converter. One of the two second intermediate nodes is in communication with a third battery assembly. The third battery assembly has a third state of charge. The third battery assembly operates in series with the second battery assembly. The conversion of the second battery discharge power to the stack discharge power varies depending on a second control signal.The method further comprises receiving the pack charging power at the two second inter-assembly nodes; converting the pack charging power into a second battery charging power provided by the two second local nodes during the charging mode; and generating the second control signal with a second controller that varies the second DC-DC converter to balance the second state of charge with the third state of charge during the discharging mode.

[0020] In one or more embodiments, the method includes measuring the first state of charge of the first battery assembly with a first adjustment module, measuring the second state of charge of the second battery assembly, and generating a first target parameter based on the first state of charge and the second state of charge. Varying the first DC-DC converter further occurs in response to the first target parameter.

[0021] In one or more embodiments, the method comprises measuring a feedback voltage at one of the two first intermediate assembly nodes. Varying the first DC-DC converter is performed as a function of the feedback voltage. The first target parameter is a voltage.

[0022] In one or more embodiments, the method includes measuring a feedback current flowing from the first battery assembly to the first DC-DC converter. Varying the first DC-DC converter occurs in response to the feedback current. The first target parameter is a current.

[0023] In one or more embodiments of the method, generating the first target parameter comprises a model predictive control technique based on the first state of charge and the second state of charge.

[0024] In one or more embodiments of the method, the first battery assembly has a different storage capacity than the second battery assembly.

[0025] In one or more embodiments of the method, the first battery assembly has a different chemical composition than the second battery assembly.

[0026] A vehicle is provided herein. The vehicle includes a battery pack and a first controller. The battery pack has a first battery assembly, a second battery assembly, and a first DC-DC converter. The first DC-DC converter has two first local nodes and two first inter-assembly nodes. The first DC-DC converter is capable of: receiving a first battery discharge power at the two first local nodes; and converting the first battery discharge power into a pack discharge power provided to the two first inter-assembly nodes in a discharge mode. The conversion of the first battery discharge power to the pack discharge power varies depending on a first control signal.The first DC-DC converter is further capable of receiving pack charging power at the first two inter-assembly nodes and converting the pack charging power into a first battery charging power provided by the first two local nodes in a charging mode. The first battery assembly has a first state of charge and is directly wired to the first two local nodes. The second battery assembly has a second state of charge, is in communication with one of the first two inter-assembly nodes, and operates in series with the first battery assembly. The first controller is in communication with the first DC-DC converter and is capable of generating the first control signal that varies the first DC-DC converter to balance the first state of charge with the second state of charge in the discharging mode.

[0027] In one or more embodiments, the vehicle includes a first adjustment module that communicates with the first battery assembly, the second battery assembly, and the first DC-DC converter. The first adjustment module is capable of: measuring the first state of charge of the first battery assembly; measuring the second state of charge of the second battery assembly; and generating a first target parameter based on the first state of charge and the second state of charge. The first controller is further capable of modifying the first DC-DC converter depending on the first target parameter.

[0028] In one or more embodiments of the vehicle, the first adaptation module is further capable of generating the first target parameter using a model predictive control technique based on the first state of charge and the second state of charge. Fig. 1 is a schematic diagram showing the context of a system according to one or more example embodiments. Fig. 2 is a schematic diagram of a state of charge map in accordance with one or more example embodiments. Fig. 3 is a schematic block diagram of a first mixed chemical balance according to one or more example embodiments. Fig. 4 is a schematic block diagram of a second mixed chemical balance in accordance with one or more example embodiments. Fig. 5 is a schematic block diagram of a first setpoint charge / discharge controller according to one or more exemplary embodiments Fig. 6 is a schematic block diagram of a second forward setpoint charge / discharge controller in accordance with one or more example embodiments. Fig. 7 is a schematic block diagram of an adaptive forward charge / discharge controller in accordance with one or more example embodiments. Fig. 8 is a schematic block diagram of a DC-DC setpoint control for packet balancing using feedback and model predictive control in accordance with one or more example embodiments. Fig. 9 is a schematic block diagram of an enhanced rechargeable energy storage system according to one or more example embodiments.

[0029] Mixed-chemistry battery packs often contain multiple battery assemblies of different chemistries connected in series. The different chemistries result in different battery storage capacities. Embodiments of the disclosure provide one or more variable bidirectional DC-DC converters and one or more corresponding controllers coupled to the battery assemblies. The controllers adjust power conversion by the DC-DC converters to enable balancing of states of charge between the different battery assemblies during charging and discharging. The balancing enables independent use of the available energy in each battery assembly to maximize vehicle range. In various embodiments, adjustment modules measure the states of charge of the battery assemblies and generate target parameters for the controllers based on the measurements.The controllers then adjust the power throughput of the DC-DC converters to balance the adjacent battery assemblies. In some designs, the battery assemblies may be battery cells. In other designs, the battery assemblies may be battery modules, each containing multiple battery cells.

[0030] With reference to Fig. 1, a schematic floor plan is shown illustrating the context of a system according to one or more example embodiments. The system may include a vehicle 80. The vehicle 80 generally includes an engine 90, a power controller 92, and a rechargeable energy storage system 100. The rechargeable energy storage system 100 includes one or more controllers 110 (one shown), one or more matching modules 120 (one shown), and a battery pack 130. The battery pack 130 includes one or more DC-DC converters 140 (one shown) and a plurality of battery assemblies 150a-150b (two shown).

[0031] The vehicle 80 may include, but is not limited to, mobile objects such as cars, trucks, motorcycles, boats, trains, and / or aircraft. In various embodiments, the vehicle 80 may be an electric vehicle, a truck, a motorcycle, and the like. In other embodiments, the vehicle 80 may be a hybrid vehicle, a truck, a motorcycle, or the like. In some embodiments, the vehicle 80 may include stationary objects such as billboards, kiosks, emergency power systems (e.g., uninterruptible power supplies), and / or marquees. Other types of vehicles 80 may be implemented to meet the design criteria of a particular application.

[0032] The engine 90 (or individual ones of a plurality of engines 90) is an electric motor or a hybrid gas / electric motor. The engine 90 generally serves to rotate the drive wheels of the vehicle 80 and generate torque to propel the vehicle 80 along the ground and / or road. The electrical energy consumed by the engine 90 may be provided by the rechargeable energy storage system 100 and / or an alternator of the vehicle 80 under the control of the power controller 92.

[0033] The power regulator 92 is an electrical power device that exchanges electrical energy between the rechargeable energy storage system 100 and the engine 90. The power regulator 92 is generally capable of transferring electrical power from an alternator to the rechargeable energy storage system 100 in charge mode to charge the battery assemblies 150a-150b when the engine 90 includes an internal combustion engine to power the alternator. The power regulator 92 may extract electrical energy from the rechargeable energy storage system 100 in discharge mode. The electrical power received from the rechargeable energy storage system 100 may be used to drive the engine 90 and / or other loads in the vehicle 80.

[0034] The rechargeable energy storage system 100 consists of a high-voltage battery used to store electrical energy. In various embodiments, the rechargeable energy storage system 100 is a mixed-chemistry battery pack. The rechargeable energy storage system 100 is electrically connected to the power controller 92. In a discharge mode, the rechargeable energy storage system 100 is generally operable to discharge by supplying electrical energy to the motor 90 to move the vehicle 80. In a charge mode, the rechargeable energy storage system 100 is generally capable of recharging by receiving electrical energy from the power controller 92 and storing the electrical energy for later use.

[0035] The rechargeable energy storage system 100 includes a plurality of battery assemblies 150a-150b electrically connected at least in series between a positive power system terminal 102 and a negative power system terminal 104. In various embodiments, the rechargeable energy storage system 100 can provide an electrical potential of approximately 200 to 1,000 volts DC (direct current) between the positive power system terminal 102 and the negative power system terminal 104. Other power system voltages can be implemented to meet the design criteria of a particular application.

[0036] The controller 110 is a power conversion regulator. The controller 110 is electrically connected to the DC-DC converter 140 and the adjustment module 120. A target parameter signal 122 is received by the adjustment module 120. A control signal 112 is generated by the controller 110 and provided to the DC-DC converter 140. The control signal 112 conveys information based on the target parameter signal 122. The control signal 112 determines the extent to which the DC-DC converter 140 converts battery discharge power received from the corresponding battery assembly 150a into pack discharge power supplied to the power regulator 92. The control signal 112 may also determine the extent to which the DC-DC converter 140 converts pack charge power received from the power regulator 92 into battery charge power.

[0037] Each adjustment module 120 implements a state of charge sensing system with feedback to the controller 110 via the target parameter signals 122. Each adjustment module 120 is in communication with a corresponding DC-DC converter 140 and two adjacent battery assemblies 150a-150b. Each adjustment module 120 is capable of measuring battery parameters such as voltage, current, and temperature and converting the parameters into a first state of charge of a first battery assembly (e.g., 150a), measuring a second state of charge of a second battery assembly (e.g., 150b), and generating a target parameter in the target parameter signal 122 based on the first state of charge and the second state of charge.

[0038] The battery pack 130 is a high-voltage battery pack configured to store electrical energy. The battery pack 130 is generally operable to receive electrical energy from the power regulator 92 in a charge mode and to supply electrical energy to the power regulator 92 in a discharge mode. The battery pack 130 includes at least one DC-DC converter 140 and at least two battery assemblies 150a-150b electrically connected in series and / or parallel between a positive battery pack terminal 132 and a negative battery pack terminal 134. In various embodiments, the battery pack 130 can provide an electrical potential of approximately 200 to 1,000 volts DC (direct current) between the positive battery pack terminal 132 and the negative battery pack terminal 134. Other battery voltages can be implemented to meet the design criteria of a particular application.The positive battery pack terminal 132 may be electrically connected directly to the positive power system terminal 102. The negative battery pack terminal 134 may be electrically connected directly to the negative power system terminal 104.

[0039] Each DC / DC converter 140 is a bidirectional, variable-power, variable-boost / boost voltage converter. The direction of conversion is controlled by a corresponding controller 110. The electrical power conversion during the discharge mode is adjustable via the control signal 112 received by the controller 110. The control signal 112 can convey information that configures the DC / DC converter 140 during the discharge mode to vary the rate at which electrical energy is drawn from a corresponding battery assembly (e.g., 150a, as shown). The discharge rate can be changed by varying an electrical voltage or current that the DC / DC converter 140 contributes to an output voltage of the battery pack 130.

[0040] During a charging mode, control signal 112 conveys information that configures DC-DC converter 140 to vary the rate at which electrical energy charges the corresponding battery assembly 150a. The charging rate can be changed by changing an electrical voltage that DC-DC converter 140 contributes to an output voltage of battery pack 130. The charging rate can be changed by varying an electrical voltage or current that DC-DC converter 140 draws from an input voltage received from battery pack 130.

[0041] Each battery assembly 150a-150b consists of one or more battery modules and / or multiple battery cells. Each battery module generally includes multiple battery cells. Each battery assembly 150a-150b has a corresponding battery assembly type. In various embodiments, the battery assembly type generally includes lithium iron phosphate batteries, lithium iron manganese phosphate batteries, and / or sodium ion batteries. The battery assembly types may have corresponding battery assembly chemistries, including lithium iron phosphate chemistry, lithium iron manganese phosphate chemistry, and / or sodium ion chemistry. Other battery types and / or battery chemistries may be implemented to meet the design criteria of a particular application. In various embodiments, the first battery assembly 150a may have a different battery chemistry than the second battery assembly 150b.In some embodiments, the first battery assembly 150a may have a different storage capacity than the second battery assembly 150b.

[0042] With reference to Fig. 2, a schematic diagram of an exemplary state of charge map 152 is shown in accordance with one or more exemplary embodiments. The state of charge map 152 illustrates a first state of charge 154 (SOC A ) of the first battery assembly 150a in relation to a second state of charge 156 (SOC B ) a second battery assembly 150b having a different battery chemistry and / or a different storage capacity than the first battery assembly 150a. For example, the first battery assembly 150a may have a nickel-cobalt-manganese (NCM) chemistry and a first storage capacity CAP A The second battery assembly 150b may have a lithium iron phosphate (LFP) chemistry and a second storage capacity CAP BThe first storage capacity CAP A is with the second storage capacity CAP B connected by equation 1 as follows: CAPA=(100% / S%)×CAPB

[0043] Where S% is a percentage of the first storage capacity CAP A , which extends over the entire second storage capacity CAP B (e.g. from 0% charge level to 100% charge level).

[0044] The first battery assembly 150a has the first state of charge 154 at a measurement (or observation) time k, 154 = SOC A (k). The second battery assembly 150b has the second state of charge 156 at the measurement (or observation) time k, 156 = SOC B (k). The first SOC A is with the second SOC B connected by equation 2 as follows: SOCA(k)=((CAPB / CAPA)×SOCB(k))+d%

[0045] Where d% is a percentage of the first storage capacity CAP Awhich has a zero value of the first state of charge SOC A up to a zero value of the second state of charge SOC B overstretched.

[0046] By setting a discharge current / charge current from / to the first battery assembly 150a and the second battery assembly 150b based on the ratio of the second storage capacity CAP B to the first storage capacity CAP A the first state of charge SOC A (k) at any time k approximately in equilibrium with the second state of charge SOC B(k). Thus, the first battery assembly 150a and the second battery assembly 150b can jointly approach the 100% state of charge during a charging process and the 0% state of charge during a discharging process. Simultaneously approaching the 0% state of charge increases the range of the vehicle 80 compared to one battery assembly reaching the 0% state of charge while the other battery assembly still has a usable charge.

[0047] The controller 110 generally balances the states of charge so that SOC A = SOC B . The equilibrium can be achieved according to equation 3 and equation 4 as follows: ∫ia_idtCAPa=∫IdtCAPb ia_i=CAPa.ICAPb

[0048] With reference to Fig. 3 and back to Fig. 1 shows a schematic block diagram of an example of a first mixed-chemistry balancer 200 according to one or more example embodiments. Example implementations of the DC / DC converter 140 are also illustrated. In the first mixed-chemistry balancer 200, the first battery assembly 150a has a lower storage capacity than the second battery assembly 150b. The DC / DC converter 140 includes two first local nodes 210a-210b directly connected to the first battery assembly 150a. The DC / DC converter 140 includes two first inter-assembly nodes 212a-212b, with one inter-assembly node (e.g., 212b) connected in series to the second battery assembly 150b.

[0049] During the discharge mode, the DC-DC converter 140 may be configured to discharge the first battery assembly 150a with lower storage capacity (e.g., LFP chemistry) more slowly than the second battery assembly 150b with higher storage capacity (e.g., NCM chemistry). The discharge creates a pack voltage 202 measured from the positive battery pack terminal 132 to the negative battery pack terminal 134. A first discharge current 204 from the first battery assembly 150a is generally less than a second discharge current 206 from the second battery assembly 150b. During the charge mode, the DC-DC converter 140 may be configured to charge the first battery assembly 150a with lower storage capacity more slowly than the second battery assembly 150b with higher storage capacity.

[0050] With reference to Fig. 4 and back to Fig. 1 shows a schematic block diagram of an example of a second mixed-chemistry equalization 220 in accordance with one or more example embodiments. In the second mixed-chemistry equalization 220, the first battery assembly 150a has a higher storage capacity (e.g., NCM chemistry) than the second battery assembly 150b (e.g., LFP chemistry). The two local nodes 210a-210b of the DC / DC converter 140 are directly connected to the first battery assembly 150a. One of the two inter-assembly nodes 212a-212b is connected in series with the second battery assembly 150b.

[0051] During the discharge mode, the DC-DC converter 140 may be configured to discharge the first battery assembly 150a with higher storage capacity more quickly than the second battery assembly 150b with lower storage capacity. The discharge produces a pack voltage 222, measured from the positive battery pack terminal 132 to the negative battery pack terminal 134. A third discharge current 224 from the first battery assembly 150a is generally greater than a fourth discharge current 226 from the second battery assembly 150b. During the charge mode, the DC-DC converter 140 may be configured to charge the first battery assembly 150a with higher storage capacity more quickly than the second battery assembly 150b with lower storage capacity.

[0052] With reference to Fig. 5 and back to the Fig. 1 and Fig. 3, a schematic block diagram of an exemplary first feedforward setpoint charge / discharge controller 240 is shown in accordance with one or more example embodiments. The first feedforward setpoint charge / discharge controller 240 provides a first feedforward target current signal 242 to a first controller 110a. The first controller 110a is a variant of the controller 110. A first feedback signal 244 communicates a current value of a feedback current 246 between the first battery assembly 150a and the DC-DC converter 140. The first feedback signal 244 is received by the first controller 110a.

[0053] The first controller 110a generates the control signal 112 based on the first forward target current signal 242 and the current value in the first feedback signal 244. The first forward target current signal 242 contains the target parameter, which is the ratio of the two storage capacities CAP A and CAP B defined for the first controller 110a.

[0054] With reference to Fig. 6 and back to the Fig. 1 and Fig. 3, a schematic block diagram of an exemplary second feedforward setpoint charge / discharge controller 260 is shown in accordance with one or more example embodiments. The second feedforward setpoint charge / discharge controller 260 provides a second feedforward target voltage signal 262 to a second controller 110b. The second controller 110b is a variant of the controller 110. A second feedback signal 264 carries a voltage value of a feedback voltage 266 at an inter-assembly node of the DC-DC converter 140. The second feedback signal 264 is received by the second controller 110b.

[0055] The second controller 110b generates the control signal 112 based on the second forward target voltage signal 262 and the voltage value in the second feedback signal 264. The second forward target voltage signal 262 contains the target parameter that defines the ratio of the two storage capacities CAP A and CAP B defined for the second controller 110b.

[0056] With reference to Fig. 7 and back to the Fig. 1 and Fig. 6, a schematic block diagram of an exemplary adaptive forward charge / discharge controller 280 is shown in accordance with one or more example embodiments. The adaptive forward charge / discharge controller 280 includes the second controller 110b, the DC-DC converter 140, the first battery assembly 150a, the second battery assembly 150b, and a first adjustment module 160a. The modules described herein may be implemented in hardware and / or software executed by hardware. The second forward target voltage signal 262 is transmitted to the second controller 110b. The second feedback signal 264 carries the voltage value of the feedback voltage 266 at the inter-assembly node of the DC-DC converter 140. The second feedback signal 264 is received by the second controller 110b.

[0057] The power controller 92 may include a three-phase DC-to-AC converter circuit 93, a linear parameter-variable model predictive control (LPV / MPC) or linear time-varying model predictive control (LTV / MPC) circuit 94, multiple AC feedback sensors 95 for the three-phase currents driving the motor 90, and motor speed and position sensors 96. Model predictive control technique is a control technique in which a computed control action minimizes a cost function for a constrained dynamic system.

[0058] The first adjustment module 160a includes a comparator 162, a register 166, a gamma adjustment module 170, and a first ratio adjustment module 174. The first adjustment module 160a receives a first state of charge signal 282a from the first battery assembly 150a and a second state of charge signal 282b from the second battery assembly 150b. A filter voltage signal 176 is received from the first ratio adjustment module 174. The second forward target voltage signal 262 is generated by the first ratio adjustment module 174.

[0059] The comparator 162 compares a first SOC A in the first state of charge signal 282a with a second SOC Bin the second state of charge signal 282b to produce a logical one value (or high value) or a logical zero value (or low value) in a comparison signal 164, whichever is greater. The efficiency of the adjustment can be effective in a quasi-stable state. Therefore, the logical one value / logical zero value is periodically stored in register 166.

[0060] The gamma adjustment module 170 generates a gamma value in a gamma signal 172 based on the logical value (read from the register 166 in a read signal 168) of the first SOC A and the second SOC B . The gamma value (γ) is generated by equation 5 as follows: γ=SOCA / SOCB

[0061] The first ratio adjustment module 174 generates the second forward target voltage signal 262 based on the first storage capacity CAP A , the second storage capacity CAP B, the gamma value γ and a filter constant voltage V F . The filter constant voltage V F can be calibrated based on a DC-DC response time constant of the system. The second forward target voltage signal 262 can be calculated according to Equation 6 as follows: Target voltage = γ × (CAPA / CAPB) × VF

[0062] With reference to Fig. 8 and back to the Fig. 1 and Fig. 5 shows a schematic block diagram of an exemplary DC-DC setpoint controller for packet balancing using feedback and model predictive control 300 in accordance with one or more example embodiments. The DC-DC setpoint controller for packet balancing using feedback and model predictive control 300 includes the first controller 110a, the DC-DC converter 140, the first battery assembly 150a, the second battery assembly 150b, and a second adjustment module 160b.

[0063] The first forward target current signal 242 is transmitted to the first controller 110a. The second feedback signal 264 carries the voltage value of the feedback voltage 266 at the intermediate node of the DC-DC converter 140. The second feedback signal 264 is received by the first controller 110a.

[0064] The power control 92 may include the three-phase DC-AC converter circuit 93, the linear parameterizable model prediction control (LPV / MPC) or linear time-varying model prediction control (LTV / MPC) circuit 94, a plurality of AC sensors 95 for the three-phase currents driving the motor 90, and the motor speed and position sensors 96.

[0065] A second adaptation module 160b includes the comparator 162, a gain scheduling or model predictive control (MPC) module 180, a subtraction module 184, and a second ratio adaptation module 188. The comparator 162 compares the first SOC A in a third charge state signal 286a with the second SOC B in a fourth charge state signal 286b. The gain scheduling or model predictive control module 180 generates a feedback signal 182 based on the comparison signal 164.

[0066] The second ratio adjustment module 188 generates a ratio signal 186 based on a filter current signal 190. The feedback signal 182 is subtracted from the ratio signal 186 by the subtraction module 184 to generate the first feedforward target current signal 242. The second ratio adjustment module 188 generates the ratio signal 186 based on a filter constant current V I . The filter constant current V I can be calibrated based on a DC-DC response time constant.

[0067] A cost function of the model predictive control module 180 is given in Equation 7 as follows: J=∑k=1N(SOCB(k)−SOCB(k))2+cΔiA_i2

[0068] Changes in the state of charge of the first battery assembly 150a from a time k to a time k+1 can be modeled by equation 8 as follows: SOCA(k+1)=SOCA(k)+ΔiA_iCAPA where Δmin<ΔiA_i<Δmax

[0069] With reference to Fig. 9 and back to Fig. 1 shows a schematic block diagram of an exemplary enhanced rechargeable energy storage system 100a according to one or more exemplary embodiments. The enhanced rechargeable energy storage system 100a is a variation of the rechargeable energy storage system 100 with a plurality of controllers 110a-110d, a plurality of battery assemblies 150a-150d, and a plurality of DC-DC converters 140a-140d connected in series between the positive power system terminal 102 and the negative power system terminal 104.

[0070] The active battery state of charge balancing method can be extended to accommodate multiple common chemistry or mixed chemistry battery assemblies 150a-150d with different storage capacities. For example, a first controller 110a can control a first DC-DC converter 140a with a first control signal 112a to balance the states of charge between a first battery assembly 150a and a second battery assembly 150b. A second controller 110b can control a second DC-DC converter 140b with a second control signal 112b to balance the states of charge between the second battery assembly 150b and a third battery assembly 150c. A third controller 110c can control a third DC-DC converter 140c with a third control signal 112c to balance the states of charge between the third battery assembly 150c and a fourth battery assembly 150d.A fourth controller 110d may control a fourth DC-DC converter 140d with a fourth control signal 112d to balance the charge states between the fourth battery assembly 150d and a fifth battery assembly, and so on.

[0071] A dominant battery assembly 150a-150d can be selected to establish a reference setpoint controller 302 with a target parameter (e.g., a target voltage or a target current). The dominant battery assembly 150a-150d can be either the smallest or the largest storage capacity among the battery assemblies 150a-150d. The equalization process is performed at selected SOC intervals and targets a final minimum SOC point, [SOC_min(i), SOC_max(i)], i=1 to n battery assemblies.

[0072] Embodiments of the rechargeable energy storage system use buck / boost DC / DC converters to balance the states of charge in mixed-chemistry battery assemblies to maximize the drivable range of a vehicle. In various embodiments, the DC / DC converters may be integrated with feedforward current / voltage controls to balance the battery assembly states of charge. Some embodiments may include feedforward control and adaptive control of the DC / DC currents / voltages to balance the battery assembly states of charge. In still other embodiments, feedforward control and modular predictive control of the DC / DC converters is used to balance the battery assembly states of charge.

[0073] Embodiments of the rechargeable energy storage system enable cost-effective design and high energy density to maximize vehicle range through intelligent battery management.

Claims

[1] Rechargeable energy storage system (100), comprising: a first DC-DC converter (140a), having two first local nodes (210a, 210b) and two first intermediate assembly nodes (212a, 212b), and the first DC-DC converter (140a) is ready for operation: to receive a first battery discharge power at the first two local nodes (210a, 210b); converting the first battery discharge power into a pack discharge power applied to the two first intermediate assembly nodes (212a, 212b) in a discharge mode, wherein the conversion of the first battery discharge power into the pack discharge power varies in response to a first control signal (112); to receive a packet loading power at the first two intermediate assembly nodes (212a, 212b); and converting the packet charging power into a first battery charging power provided by the first two local nodes (210a, 210b) in a charging mode; a first battery assembly (150a) having a first state of charge, directly connected to the first two local nodes (210a, 210b); a second battery assembly (150b) having a second state of charge, connected to one of the two first intermediate assembly nodes (212a, 212b) and operating in series with the first battery assembly (150a); and a first controller (110) in communication with the first DC-DC converter (140a) and operable to generate the first control signal (112) that varies the first DC-DC converter (140a) to, in the discharge mode, balance the first state of charge with the second state of charge. [2] The rechargeable energy storage system (100) of claim 1, further comprising: a second DC-DC converter (140b) having two second local nodes (210a, 210b) and two second intermediate assembly nodes (212a, 212b), and the second DC-DC converter (140b) is operational: to receive a second battery discharge power at the two second local nodes (210a, 210b), wherein the second battery assembly (150b) is directly wired to the two second local nodes (210a, 210b); converting the second battery discharge power into the pack discharge power applied to the two second interposer nodes (212a, 212b) during the discharge mode, wherein the conversion of the second battery discharge power into the pack discharge power varies in response to a second control signal (112); to receive the packet charging power at the two second intermediate assembly nodes (212a, 212b); and converting the pack charging power into a second battery charging power supplied by the two second local nodes (210a, 210b) in charging mode; a third battery assembly (150c) having a third state of charge, connected to one of the two second intermediate assembly nodes (212a, 212b) and operating in series with the second battery assembly (150b); and a second controller (110) in communication with the second DC-DC converter (140b) and operable to generate the second control signal (112) that varies the second DC-DC converter (140b) to, in the discharge mode, balance the second state of charge with the third state of charge. [3] The rechargeable energy storage system (100) of claim 1, further comprising: a first matching module (120) in communication with the first battery assembly (150a), the second battery assembly (150b) and the first DC-DC converter (140a), the first matching module (120) being operable to: to measure the first state of charge of the first battery assembly (150a); to measure the second state of charge of the second battery assembly (150b); and to generate a first target parameter based on the first state of charge and the second state of charge, wherein the first controller (110) is further operable to vary the first DC-DC converter (140a) in response to the first target parameter. [4] Rechargeable energy storage system (100) according to claim 3, wherein: the first controller (110) is further ready for operation: to measure a feedback voltage at one of the first two intermediate assembly nodes (212a, 212b); and varying the first DC-DC converter (140a) in further response to the feedback voltage; and the first target parameter is a voltage. [5] Rechargeable energy storage system (100) according to claim 3, wherein: the first controller (110) is further operable to: measure a feedback current supplied from the first battery assembly (150a) to the first DC-DC converter (140a); and the first DC-DC converter (140a) as a further reaction to the feedback current; and the first target parameter is a current. [6] The rechargeable energy storage system (100) of claim 3, wherein the first adjustment module (120) is further operable to generate the first target parameter with a model predictive control technique based on the first state of charge and the second state of charge. [7] The rechargeable energy storage system (100) of claim 1, wherein the first battery assembly (150a) has a different storage capacity than the second battery assembly (150b). [8] The rechargeable energy storage system (100) of claim 1, wherein the first battery assembly (150a) has a different chemistry than the second battery assembly (150b). [9] The rechargeable energy storage system (100) of claim 1, wherein the first battery assembly (150a) and the second battery assembly (150b) are part of a vehicle (80). [10] A method for actively balancing the state of charge of a battery, comprising: Receiving a first battery discharge power from a first battery assembly (150a) at two first local nodes (210a, 210b) of a first DC-DC converter (140a), the first battery assembly (150a) having a first state of charge and being directly wired to the two first local nodes (210a, 210b); Converting the first battery discharge power into a pack discharge power applied to two first inter-assembly nodes (212a, 212b) of the first DC-DC converter (140a) during a discharge mode, wherein: one of the two first intermediate assembly nodes (212a, 212b) is connected to a second battery assembly (150b); the second battery assembly (150b) has a second state of charge; the second battery assembly (150b) operates in series with the first battery assembly (150a); and the conversion of the discharge power of the first battery assembly (150a) into the pack discharge power varies in dependence on a first control signal (112); Receiving a charging power at the first two intermediate assembly nodes (212a, 212b); Converting the package charging power into a first battery charging power provided by the two first local nodes (210a, 210b) in a charging mode; and Generating the first control signal (112) with a first controller (110) which, in the discharge mode, varies the first DC-DC converter (140a) to balance the first state of charge with the second state of charge.

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