Energy storage circuit

Abstract

The present disclosure relates to energy storage circuits. An energy storage circuit includes a battery module formed of a plurality of battery cells, a current sense resistor, and a controller. Each battery cell is coupled to a corresponding cell resistor via a switch. The controller is operable to arrange the switches in a first configuration to perform an impedance measurement of one or more battery cells in the battery module. In the first configuration, the cell resistors are coupled in series with one another and in series with the current sense resistor.

Description

Technical Field

[0001] This disclosure relates to energy storage circuits, and more particularly to battery-based energy storage circuits. More specifically, this disclosure relates to energy storage circuits comprising a battery module and a controller configured to perform impedance measurements of one or more battery cells in the battery module. Background Technology

[0002] Impedance measurements, such as electrochemical impedance spectroscopy (EIS), can be used to examine the state of a battery cell, including its state of charge (SoC) and state of health (SoH). Impedance measurements can also be used to determine the core temperature of a battery cell that differs significantly from the surface temperature measured using a temperature sensor.

[0003] In energy storage systems such as battery packs formed by several battery modules connected in series, the properties of battery cells can be evaluated at the individual battery cell level, or at the module level, or at the battery pack level.

[0004] Module-level methods do not involve the complexities of group-level techniques, such as the integration of excitation circuitry and the stringent time synchronization requirements between current and voltage measurements from different sensors. Compared to cell-level methods, module-level methods are more cost-effective because no additional wiring is required between the battery cell and the excitation signal source. However, current systems for module-level EIS measurements require dedicated EIS excitation circuitry. Furthermore, the excitation current required for measuring battery impedance is very high.

[0005] The purpose of this disclosure is to address one or more of the limitations mentioned above. Summary of the Invention

[0006] According to a first aspect of the present disclosure, an energy storage circuit is provided, comprising: a battery module formed of a plurality of battery cells, wherein each battery cell is coupled to a corresponding cell resistor via a switch; a current sensing resistor; and a controller configured to control the switch; wherein the controller is operable to arrange the switch in a first configuration to perform impedance measurements on one or more battery cells in the battery module; wherein in the first configuration, the cell resistors are coupled in series with each other and in series with the current sensing resistor.

[0007] For example, in a first configuration, the controller may be operable to perform impedance measurements on each individual battery cell in the battery module. The cell resistor may be a bleed resistor or a discharge resistor.

[0008] Optionally, the controller can operate to arrange switches in a second configuration to balance the charge of individual battery cells.

[0009] Optionally, the battery cells are connected in series along a first conductive channel, and the cell resistors are connected in series along a second conductive channel; and a switch is provided for each battery cell along a third conductive channel that intersects the first and second conductive channels.

[0010] Optionally, the energy storage circuit includes an additional switch provided along an additional conductive channel that intersects both the first and second conductive channels.

[0011] Optionally, each battery cell has a first terminal and a second terminal, wherein the first terminal is coupled to a cell resistor via a switch, and the second terminal is coupled to a cell resistor via another switch from the next battery cell.

[0012] For example, the first terminal can be the negative terminal and the second terminal can be the positive terminal, or vice versa.

[0013] Optionally, the controller is configured to provide a switching control signal for generating an excitation signal, and to measure a response signal in response to the excitation signal.

[0014] For example, the excitation signal can be current and the response signal can be voltage. Alternatively, the excitation signal can be voltage and the response signal can be current.

[0015] Optionally, in the first configuration, the switch control signal is used to control one of the multiple switches, and the other switches are turned off except for the additional switch that is turned on.

[0016] Optionally, in the first configuration, the excitation signal is the current flowing through the unit resistor and the current sensing resistor.

[0017] Optionally, the controller is configured to measure the voltage across the current sensing resistor to derive the current, and to measure the set of voltages across individual battery cells.

[0018] Optionally, the controller is configured to calculate the impedance of each battery cell in the module based on the current and the set of voltages across individual battery cells.

[0019] Optionally, the switch control signal is a sinusoidal signal.

[0020] Optionally, in the second configuration, at least one battery cell in the module is discharged independently via a cell resistor.

[0021] Optionally, impedance measurements for each battery cell are performed in parallel and / or simultaneously for all battery cells in the module.

[0022] Optionally, the controller is configured to perform electrochemical impedance spectroscopy (EIS).

[0023] Optionally, the battery cell is a lithium-ion cell.

[0024] According to a second aspect of this disclosure, an energy storage system is provided, including a plurality of energy storage circuits according to the first aspect.

[0025] Optionally, multiple energy storage circuits are coupled to the main controller via a communication interface.

[0026] For example, the main controller can be a microcontroller (MCU).

[0027] Optionally, the energy storage circuits are connected in series to form a battery pack.

[0028] According to a third aspect of this disclosure, a method is provided for performing impedance measurements of one or more battery cells in a battery module, wherein each battery cell is coupled to a corresponding cell resistor via a switch; the method includes:

[0029] Provide a current sensing resistor;

[0030] Provides a controller configured to control switches; and

[0031] An operating controller is used to arrange switches in a first configuration to perform impedance measurements of one or more battery cells; wherein, in the first configuration, cell resistors are coupled in series with each other and in series with a current sensing resistor.

[0032] Optionally, the method includes providing a switching control signal for generating an excitation signal, and measuring a response signal. Attached Figure Description

[0033] This disclosure is further described in detail by way of example and with reference to the accompanying drawings, wherein:

[0034] Figure 1 This is a schematic diagram of the battery pack;

[0035] Figure 2 This is a diagram of a high-voltage lithium-ion battery pack.

[0036] Figure 3 This is a diagram of a traditional passive unit balanced circuit architecture;

[0037] Figure 4 This is a flowchart of a method for performing impedance measurement of a battery module according to this disclosure; and

[0038] Figure 5 It is an energy storage circuit according to this disclosure. Detailed Implementation

[0039] Figure 1This is a schematic diagram of a battery pack, such as a lithium-ion battery pack. Battery pack 100 includes multiple lithium-ion cells connected in series, creating several modules. These modules are then coupled in series to create a pack.

[0040] The impedance of a battery cell can be measured using a technique called electrochemical impedance spectroscopy (EIS). Here, the battery cell is excited with a time-varying current or voltage signal, and the corresponding time-varying voltage or current response is measured, respectively. The ratio of the time-varying voltage to the time-varying current is the complex impedance of the battery cell. Typically, the excitation signal is a time-varying current signal, and the corresponding time-varying voltage response of the cell is measured to calculate the complex AC impedance.

[0041] Impedance measurements can be used to assess the state or condition of individual cells in a battery pack. The excitation signal used for EIS measurements can be at different levels: i) pack level, ii) cell level, and iii) module level.

[0042] In group-level EIS, a single AC excitation signal is applied in series to all cells in the group, and the response of all cells to this excitation signal is measured.

[0043] The excitation signal source can be a separate signal source or it can be integrated with other systems in the application. In the case of electric vehicle (EV) applications, the group-level excitation signal can be integrated into the on-board charger (OBC), DC / DC converter, or inverter, or into the pre-charge circuit.

[0044] This method offers the following advantages: the excitation signal is applied to the cell only once, and the impedance of all cells in the battery pack can be measured simultaneously. The disadvantages of this method are the high complexity involved in integrating the excitation signal with other systems in the application. Furthermore, the measurements of the excitation current and voltage responses from the cells must be strictly time-synchronized, which further increases the complexity of the group-level EIS method, as current measurements and cell voltage measurements are performed by different modules in the system.

[0045] In contrast to the group-level EIS method, the group-level EIS method applies the excitation signal directly to each cell in a series-connected lithium-ion battery pack. Here, an existing passive cell balancing network consisting of discharge resistors and switches is used to generate the excitation signal. The low cost and low complexity resulting from the use of existing components for EIS measurements are advantages of this method.

[0046] One of the biggest drawbacks of the cell-level approach is that the impedance of the cable connecting the battery cell and the passive balancing network is significantly greater than the impedance of the battery cell itself, leading to errors in the impedance measurement of the battery cell. To overcome this problem, additional low-impedance connection cables are required to connect the battery cell and the passive balancing network, thus increasing the overall cost of the approach. Furthermore, the impedance of all cells cannot be measured simultaneously, resulting in an increased overall system impedance acquisition time. Additionally, the excitation current is not actively measured and is only programmed by the battery management system (BMS) controller. Parasitic circuit components in the current flow path are different for each cell and therefore may not produce the same current as set by the BMS controller. This will lead to errors in the measured impedance of the cell.

[0047] Compared to cell-level EIS, the module-level EIS method simplifies the integration of excitation sources and enables simultaneous measurement of excitation current and cell voltage response without increasing complexity. The module-level method is also more cost-effective than cell-level EIS because no additional wiring is required between the cell and the excitation signal source.

[0048] However, current systems for module-level EIS measurements require dedicated EIS excitation circuitry.

[0049] Figure 2 This diagram illustrates the structure of a high-voltage lithium-ion battery pack typically used in EV applications or stationary energy storage systems (ESS). Multiple lithium-ion cells are connected in series and grouped to form modules, which are then connected in series to form a battery pack that achieves the required operating voltage. Lithium-ion cells need to be maintained within a safe operating range determined by voltage, temperature, pressure, and current. Violating safe operating conditions will reduce cell life and may lead to thermal runaway, which could result in fire or explosion. A battery management system (BMS) monitors several parameters, including voltage, temperature, and pressure for each cell in the battery pack, and ensures safe operating conditions. Furthermore, the BMS calculates the battery pack's state parameters, namely the state of charge (SoC) and state of health (SoH), and isolates the battery pack in case of a fault.

[0050] like Figure 2 As shown, the BMS consists of multiple Battery Monitoring Integrated Circuits (BMICs) that measure and monitor parameters of the cells within the module. The BMICs monitor the voltage, temperature, and pressure of the cells within the module. The BMICs communicate with each other and with the BMS master controller via a daisy-chain communication link to exchange measured voltages and temperatures of the cells, which the master controller uses to calculate the System-on-Chips (SoC) and SoH (Solar Hourly Rate). Furthermore, the BMICs rapidly report any faults in any cell within the module to the master controller, allowing the battery pack to be safely shut down.

[0051] Figure 3 This is a diagram of a conventional passive unit balanced circuit architecture.

[0052] The passive cell balancing circuit consists of a high-power resistor (also known as a bleed resistor) connected to the battery cell using a switching element. For example, for cell B1, the bleed resistor R1 is coupled to B1 via switch S1.

[0053] When the SoC of any cell in a series-connected battery pack is higher than that of the other cells, the excess energy is released via a bleed resistor by turning on the switching element.

[0054] The bleed resistor can only be connected to a single unit. As a result, Figure 3 The passive balanced architecture can only be used for execution unit level EIS.

[0055] Figure 4 This is a flowchart of a method for performing impedance measurements of one or more battery cells in a battery module, according to this disclosure. The battery module (also referred to as a battery assembly) is formed by multiple battery cells connected in series. Each battery cell is coupled to a corresponding cell resistor via a switch. The battery resistor may be a bleed resistor or a discharge resistor.

[0056] In step 410, a sensing resistor, also known as a current-sensing resistor or a shunt resistor, is provided. In step 420, a controller configured to control a switch is provided. In step 430, the controller is operated to arrange the switch in a first configuration to perform impedance measurements of one or more battery cells. In the first configuration, the cell resistors are coupled in series with each other and in series with the sensing resistor.

[0057] For example, in a first configuration, the controller could be operable to perform impedance measurements on each individual battery cell in the battery module. This can be performed in parallel or sequentially.

[0058] Impedance measurement can be obtained by generating an excitation signal and measuring the response signal in response to the excitation signal.

[0059] For example, the excitation signal can be current, and the response signal can be voltage. For instance, various sinusoidal currents of different frequencies can be used to excite the battery cell. Alternatively, the excitation signal can be voltage, and the response signal can be current.

[0060] Figure 5 This is an energy storage circuit according to the present disclosure. The energy storage circuit 500 includes a plurality of battery cells B1-B1 connected in series, numbering N. N The resulting battery module 510. The battery cells can be implemented in different ways; for example, the battery cells can be lithium-ion cells. Each battery cell B1-B NCoupled to the corresponding unit resistor R1-R via two switching elements N Resistors R1-R N These can also be referred to as bleed resistors because they are used to discharge the cell. For example, bleed resistor R1 is connected to cell B1 via switches S0 and S1, and resistor R2 is connected to cell B2 via S1 and S2. Circuit 500 also includes a sensing resistor R sense And a controller 520 configured to control the switch of each battery cell.

[0061] Controller 520 is capable of operating to arrange switches S0-S in a first configuration. N To perform impedance measurements of the battery cells. In the first configuration, the cell resistors R1-R... N They are coupled in series with each other and with the sensing resistor R sense Series coupling. Impedance measurement can be performed using electrochemical impedance spectroscopy (EIS).

[0062] Controller 520 has features for generating control switches S0-S N-1 Control signal C0-C N-1 The controller 520 includes a control signal generator 521 and a control signal C_eis for generating an excitation signal (in this case, a current I_eis). The control signal C_eis can be a sinusoidal signal. The controller 520 also includes multiple voltage sensors 523_1-523_N for sensing the voltage of individual units. For example, the voltage sensors can be implemented as ADC sensors. Another voltage sensor 524 is provided to measure voltages across R. sense Voltage V across the terminals sns The controller 520 also includes an impedance calculator 525. The impedance calculator can be configured to perform various types of impedance measurements, such as various types of EIS techniques.

[0063] The controller 520 can be a BMIC. Typically, a BMIC already includes an EIS excitation circuit system; therefore, there is no need for an additional dedicated EIS excitation circuit system.

[0064] Battery cell B1-B N They are connected in series along the first conductive channel 531. Similarly, the unit resistors R1-R N Connected in series along the second conductive channel 532. For each battery cell B1-B N A switch S is provided along a third conductive channel 533 that intersects with both the first conductive channel 531 and the second conductive channel 532.

[0065] For example, for cell B1, a switch S1 is provided along the third conductive channel 533_1 between nodes 01 and 01'.

[0066] Similarly, for unit B N Along node 0 N and 0 N The third conductive channel 533_N between the switches provides the switch S. N .

[0067] Optionally, the energy storage circuit may include an additional switch S0 provided along an additional third conductive channel.

[0068] By adding switch S0 to cell B1, this topology allows for both passive cell balancing and module-level impedance measurement.

[0069] In this case, each battery cell has a first terminal (e.g., positive terminal) coupled to the cell resistor R via a switch S, and a second terminal (e.g., negative terminal) coupled to the cell resistor R via another switch S or S0 from the next battery cell.

[0070] For example, battery B N With via from battery cell B N-1 Switch S N-1 Coupled to unit resistor R N The positive terminal and via switch S N Coupled to unit resistor R N The negative terminal (negative terminal).

[0071] Unit B1 has a positive terminal coupled to unit resistor R1 via an additional switch S0 and a negative terminal coupled to unit resistor R1 via switch S1.

[0072] exist Figure 5 In the middle, the sensing resistor R sense Just in R N Previously provided on the second conductive channel 532, however R sense It can be provided anywhere on the second conductive channel 532. For example, it can be exactly at R. N R will be provided afterward. sense In this case, R sense The terminal with the most negative potential coupled to the module and coupled to R N The other terminal makes current measurement easier.

[0073] Current sensing resistor R sense It can be an external resistor that is separate from the unit and different from the bleed resistor. R sense The purpose is to measure current, and it is connected to the bleed resistor R1-R. N They have different values ​​compared to each other.

[0074] During operation, the controller can be operated to perform impedance measurement (first configuration) or to perform unit balancing (second configuration).

[0075] In the first configuration, controller 520 generates a control signal C_eis to perform impedance measurement. Signal C_eis is used to control one of a plurality of switches, such as switch S. N Controller 520 disconnects (opens) all switches except for the connected (closed) auxiliary switch S0. Therefore, resistors R1-R... N They are coupled in series to form a single module-level resistor connected in series with the sensing resistor.

[0076] The control signal C_eis can be a sinusoidal signal generated by circuit 521 within controller 520. This causes a sinusoidal excitation current I_eis to be drawn from all units in the module. The excitation current I_eis flows through unit resistors R1-R N and sensing resistor R sense Various sinusoidal currents of different frequencies can be used to excite the battery cells.

[0077] Coupled to R sense The voltage sensor 524 measures the voltage across R sense Voltage V across the terminals sns Then, the voltage V sns Used to derive the value of the excitation current I_eis. The impedance calculator 525 receives the set of cell voltages measured across the individual cell terminals, as well as the voltage V. sns It calculates the impedance of all units in the module. In other words, the impedance calculator 525 calculates the impedance of each individual unit.

[0078] Impedance measurements of each individual cell can be performed in parallel and / or simultaneously across all cells in the module. Each cell has a dedicated voltage sensor (an ADC sensor in this example). This allows for simultaneous measurement of the voltage (voltage response) of all cells in the module.

[0079] The battery cell can be excited using various sinusoidal currents of different frequencies. The impedance at these different frequencies can then be used to understand the properties of the battery cell.

[0080] Complex AC impedance can be used to calculate the additional state properties of a battery cell (each individually), namely the state of charge (SoC) and state of health (SoH). Furthermore, the impedance of a battery cell is also related to the cell's internal temperature, and by accurately measuring the impedance, the core temperature of the battery cell (each individually) can be determined, which differs significantly from the surface temperature measured using a temperature sensor.

[0081] In the second configuration, the controller arranges switches to balance the charge of individual battery cells. In this case, the cell is connected to its corresponding bleed resistor to dissipate excess charge as heat.

[0082] For example, by closing switches S0 and S1, unit B1 can be balanced separately from other units. To balance unit B2, switch S0 is open and switches S1 and S2 are closed. Similar switching schemes allow for the balancing of individual units within a module.

[0083] Therefore, resistor R1-R N It can be used to achieve passive balancing of units in a module, and also to perform impedance measurements.

[0084] Circuit 500 enables module-level impedance measurements such as EIS. This is achieved by rearranging the connections of the bleed resistors used for passive unit balancing. Figure 5 The circuit also offers significant cost savings and reduced footprint.

[0085] Energy storage systems can be used in conjunction with Figure 2 The same method shown is used to connect multiple energy storage circuits 500 together in series. In this case, a main controller, such as a microcontroller, is connected to multiple modules via a communication interface.

[0086] Energy storage systems can be used in various applications. For example, energy storage systems can be implemented to form battery packs.

[0087] Those skilled in the art will appreciate that variations of the disclosed arrangement are possible without departing from this disclosure. Therefore, the above description of specific embodiments is by way of example only and is not intended to be limiting. Those skilled in the art will understand that minor modifications can be made without significantly altering the operation.

Claims

1. An energy storage circuit, comprising: A battery module is formed by multiple battery cells, wherein each battery cell is coupled to a corresponding cell resistor via a switch; Current sensing resistor; as well as The controller is configured to control the switch. The controller is operable to arrange the switches in a first configuration to perform impedance measurements on one or more battery cells in the battery module. as well as In the first configuration, the unit resistors are coupled in series with each other and in series with the current sensing resistor.

2. The energy storage circuit of claim 1, wherein the controller is operable to arrange the switches in a second configuration to balance the charge of individual battery cells.

3. The energy storage circuit according to claim 1, wherein: The battery cells are connected in series along the first conductive channel, and the cell resistors are connected in series along the second conductive channel. as well as For each battery cell, the switch is provided along a third conductive channel that intersects both the first and second conductive channels.

4. The energy storage circuit of claim 3 further includes an additional switch provided along an additional conductive channel intersecting both the first conductive channel and the second conductive channel.

5. The energy storage circuit of claim 3, wherein each battery cell has a first terminal and a second terminal, wherein the first terminal is coupled to the cell resistor via the switch, and the second terminal is coupled to the cell resistor via another switch from the next battery cell.

6. The energy storage circuit of claim 4, wherein the controller is configured to provide a switching control signal for generating an excitation signal, and to measure a response signal in response to the excitation signal.

7. The energy storage circuit of claim 6, wherein in the first configuration, the switch control signal is used to control one of the plurality of switches, and wherein, except for the additional switch that is turned on, the other switches are turned off.

8. The energy storage circuit of claim 7, wherein in the first configuration, the excitation signal is the current flowing through the unit resistor and the current sensing resistor.

9. The energy storage circuit of claim 8, wherein the controller is configured to measure the voltage across the current sensing resistor to derive the current, and to measure the voltage set across individual battery cells.

10. The energy storage circuit of claim 9, wherein the controller is configured to calculate the impedance of each battery cell in the module based on the current and the set of voltages across individual battery cells.

11. The energy storage circuit according to claim 6, wherein the switching control signal is a sinusoidal signal.

12. The energy storage circuit of claim 2, wherein in the second configuration, at least one battery cell in the module discharges independently via the cell resistor.

13. The energy storage circuit of claim 1, wherein impedance measurements for each battery cell are performed in parallel and / or simultaneously for all of the battery cells in the module.

14. The energy storage circuit of claim 1, wherein the controller is configured to perform electrochemical impedance spectroscopy (EIS).

15. The energy storage circuit according to claim 1, wherein the battery cell is a lithium-ion cell.

16. An energy storage system comprising a plurality of energy storage circuits according to claim 1.

17. The energy storage system of claim 16, wherein the plurality of energy storage circuits are coupled to the main controller via a communication interface.

18. The energy storage system of claim 16, wherein the energy storage circuits are connected in series to form a battery pack.

19. A method for performing impedance measurement on one or more battery cells in a battery module, wherein each battery cell is coupled to a corresponding cell resistor via a switch, the method comprising: Provide a current sensing resistor; A controller is provided, the controller being configured to control the switch; as well as The controller is operated to arrange the switches in a first configuration to perform the impedance measurement of the one or more battery cells; In the first configuration, the unit resistors are coupled in series with each other and in series with the current sensing resistor.

20. The method of claim 19, further comprising: Provides a switch control signal for generating the excitation signal, and Measure the response signal.

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