Method for determining a cooling power of a cooling system of a battery pack

Abstract

The invention relates to a method for determining a cooling power of a cooling system (4) of a battery pack (2), comprising the following steps: - determining a predefined calibration profile (10); - applying the calibration profile (10) to the battery pack (2); - determining a reference temperature of the battery pack (2); - activating the cooling system (4); - determining a cooling saturation temperature of the battery pack (2); - comparing the cooling saturation temperature and the reference temperature in order to determine the cooling power. The invention also relates to a cooling system (4) of a battery pack (2), comprising a control unit (6) which is designed to carry out the method according to the invention and which controls at least one pump unit (8) in order to deliver coolant within the cooling system (4).

Description

[0001] Method for determining the cooling capacity of a cooling system for a battery storage system

[0002] Description

[0003] The disclosure relates to a method for determining the cooling capacity of a cooling system of a battery storage system, in particular a high-voltage storage system.

[0004] Background of the Revelation

[0005] A high-voltage storage system in a hybrid or electric vehicle is an energy storage system that stores electrical energy in the form of direct current at high voltage. This stored energy is typically used to power at least one of the vehicle's electric motors. These high-voltage storage systems are typically composed of individual battery cells, such as lithium-ion cells, or modules configured in a battery pack.

[0006] Battery cells exist in various designs and dimensions for this purpose. Circular cylindrical cells (round cells) or flat cells, such as prismatic cells or so-called pouch cells, are used. Flat cells, such as pouch cells or prismatic cells, are particularly preferred with regard to better heat dissipation and stackability.

[0007] When cycling such battery cells, mechanical deformation can be observed during the charging and discharging phases. This means that within a charge-discharge cycle, a battery cell undergoes a volume increase. The volume of a battery cell also increases over its lifetime. This phenomenon is referred to as "swelling." In cylindrical battery cells, this growth acts inwards, particularly due to the high mechanical integrity of the casing. In pouch and prismatic battery cells, however, the forces caused by the volume growth, which can deform the casing or encapsulation, act outwards.

[0008] During operation, high-voltage storage systems typically require temperature control (i.e., cooling and / or heating) to ensure battery performance and lifespan. In high-voltage storage systems for electric vehicles, battery cells are cooled and / or heated, for example, by means of cooling coils or cooling modules containing coolant / cooling fluid / temperature control fluid located between or on the battery cells. The coolant usually flows through the cooling coils or modules to exchange heat energy with the battery cells, thus maintaining their temperature—that is, heating or cooling them to a predetermined operating temperature.

[0009] It is known from the prior art to use such cooling concepts or cooling or temperature control modules to compensate for volume growth. For example, WO 2020 / 221 856 A1 discloses a pressure module for a battery cell, wherein the pressure module is an elastomeric component for swelling compensation with simultaneous cooling or heating function for rechargeable batteries.

[0010] The cooling capacity of the cooling system is typically controlled by adjusting the coolant supply temperature and / or the flow rate. However, this presents the problem that such a known control system cannot be adapted to changing boundary conditions, particularly reduced flow cross-sections, as there is no way to determine the currently available cooling capacity. Prior art includes concepts for determining the available cooling capacity or diagnosing the cooling circuit using additional sensors, for example, for pressure or flow rate measurement.

[0011] However, in prior art concepts, compensating for volume growth always involves compression of a cooling channel through which the coolant flows. This means that as the battery cells expand due to swelling, the components responsible for temperature control and cooling are deformed, reducing the cross-section of the cooling channels inside these components. Consequently, the flow rate through the cooling channels decreases, which in turn reduces the cooling capacity and ultimately the performance of the high-voltage storage system. In other words, the cooling capacity changes over the battery's lifetime, particularly due to a decrease in flow rate or increased back pressure in the cooling system. Therefore, adequate temperature control of the high-voltage storage system can no longer be guaranteed. This is, among other things,This can be explained by the fact that the implemented control of the cooling capacity, which is usually set via the coolant supply temperature and / or the volume flow, cannot compensate for the changed boundary conditions.

[0012] Summary of Revelation

[0013] The tasks and objectives of this disclosure are to eliminate or at least mitigate the disadvantages of the prior art. In particular, a cost-effective method is to be provided that enables a quantitative assessment of the cooling system's performance or available cooling capacity at any point during the battery storage system's life cycle.

[0014] The tasks and objectives are solved, as disclosed, by the subject matter of claim 1 with respect to a generic method. The disclosure is thus based on the realization that it is possible to measure / detect the available cooling capacity throughout the entire life cycle of the battery storage system without using additional sensors.

[0015] The procedure is accordingly configured as disclosed by the following steps:

[0016] - Determining a predefined calibration profile (current profile);

[0017] - Applying the calibration profile to the battery storage;

[0018] - Determining a reference temperature for the battery storage; - Activating the cooling system;

[0019] - Determining a cooling saturation temperature of the battery storage;

[0020] -Comparing the cooling saturation temperature and the reference temperature to determine the cooling capacity.

[0021] To determine the cooling capacity, a calibration profile is predefined / predetermined, as disclosed. This calibration profile represents a defined thermal load for the battery storage system. In other words, the battery storage system is subjected to a current profile defined by the calibration profile to induce a thermal response, i.e., heating of the battery storage system. Subsequently, a reference temperature is determined as a reference value. The activated cooling system causes the battery storage system to cool down to a cooling saturation temperature. A comparison of the determined cooling saturation temperature with the reference temperature allows, as disclosed, the determination of the cooling capacity.

[0022] In other words, the battery storage system is heated according to the defined calibration profile. Activating the cooling system cools the battery storage system again. During the entire heating and cooling process, temperatures are recorded at defined points in order to obtain a temperature difference between the heated and cooled states of the battery storage system as a measure of the cooling performance.

[0023] If this temperature difference is small, the cooling system can only provide limited cooling capacity. Conversely, if the temperature difference is larger, the cooling system exhibits high cooling performance. Therefore, if the cooling capacity is low, the cooling system can be readjusted, for example, by increasing the flow rate to compensate for the reduced flow cross-section. This ensures adequate temperature control of the battery storage system, even under changing conditions. Damage due to insufficient cooling can thus be effectively prevented. Advantageous embodiments are claimed in the dependent claims and are explained below.

[0024] In a preferred embodiment, the cooling system can be activated simultaneously with the determination of the predefined calibration profile. This means the cooling saturation temperature can be determined with the calibration profile specified and the cooling system activated at the same time. A predetermined temperature can be used as a reference temperature for comparison. Preferably, this predetermined temperature is the temperature to which the cooling system can cool the battery storage at the beginning of its life cycle, i.e., with undeformed flow cross-sections. This allows for an inference to be made about the currently available cooling capacity.

[0025] According to an alternative embodiment, the cooling system can be activated after the reference temperature has been detected. The battery storage can then be heated by applying the calibration profile to establish a saturation temperature as the reference temperature. The cooling system can then be activated, resulting in a difference between the cooling saturation temperature and the saturation temperature, which serves as a measure of the current cooling capacity. It can be particularly advantageous if the reference temperature is determined using at least one of the following temperatures: the battery storage temperature, the coolant supply temperature, and the coolant return temperature. That is, the reference temperature can preferably be a function of at least one of the aforementioned temperatures. These temperatures can be detected using appropriate sensors.In particular, to determine the reference temperature, a component temperature of the battery storage system and / or a fluid temperature in the supply line of the cooling system and / or a fluid temperature in the return line of the cooling system can preferably be used.

[0026] In a particularly advantageous further development, the cooling saturation temperature can be determined using at least one of the battery storage temperature, the coolant supply temperature, and the coolant return temperature. It can be particularly advantageous if the reference temperature and the cooling saturation temperature can be determined analogously. This avoids the need for additional, costly sensors.

[0027] Preferably, the calibration profile can be a pulse-duration modulated profile. That is, the calibration profile can be a profile that alternates between two values ​​in the form of a rectangular pulse. It can be advantageous if the rectangular pulse is essentially defined by its amplitude.

[0028] According to an advantageous embodiment, the battery storage system can be connected to, or connectable to, an electrical power source, in particular a charging station, for carrying out the method. The electrical power for heating the battery storage system can therefore be provided via the electrical power source. It can also be advantageous if the battery storage system is configured for bidirectional charging (so-called Vehicle-to-Grid or V2G application), since the calibration profile can then be designed to be virtually state-of-charge (SOC) neutral. This means that by drawing and supplying electrical power to and from the electrical power source, the disclosed method can be carried out without changing the state of charge (SOC) of the battery storage system.

[0029] In other words, the disclosure described here essentially provides for the specification of a predefined calibration profile, with cooling being activated either concurrently or subsequently. Analyzing the temperature profile during the application of the current profile or during the subsequent cooling process allows conclusions to be drawn about the available cooling capacity. In the V2G application, the current profile can be a state-of-the-occupy (SOC) neutral pulse pattern. Comparing the temperatures at different points in the lifecycle enables the detection of any decrease in available cooling performance.

[0030] Furthermore, the present disclosure relates to a cooling system for a battery storage device with a control unit configured to execute the disclosed method and which controls at least one pump unit to circulate coolant within the cooling system. Preferably, the control unit can regulate the coolant flow rate circulated by the at least one pump unit as a function of the specified cooling capacity. That is, the control unit can regulate the at least one pump unit as a function of a temperature difference representing the cooling capacity. It may be advantageous to increase the coolant flow rate at low cooling capacities to compensate for the reduced flow cross-section. Thus, adequate temperature control of the battery storage device can be ensured, even under changing boundary conditions. Damage due to insufficient cooling can therefore be effectively avoided.

[0031] Brief description of the characters

[0032] The disclosure is explained in more detail below with reference to a preferred embodiment and the figures. These show:

[0033] Fig. 1 shows a schematic view of a vehicle with a battery storage system;

[0034] Fig. 2 shows a flowchart of a method according to a disclosed method in a preferred embodiment; and

[0035] Fig. 3 shows an example of a calibration profile of the method according to the preferred embodiment.

[0036] The figures are schematic in nature and serve only to aid in understanding the revelation.

[0037] Detailed description of a preferred embodiment

[0038] Fig. 1 shows a schematic side view of a vehicle 1 with a battery storage system 2. The vehicle 1 is designed as an electric vehicle and the battery storage system 2 therefore supplies electrical power to drive the vehicle 1. For this purpose, a large number of battery cells are arranged in the battery storage system 2.

[0039] As shown in Fig. 1, the battery storage system 2 also has a cooling system 4. The cooling system 4 has a control unit 6, which is configured to control a pump unit 8 to pump coolant through corresponding cooling channels for cooling the battery storage system 2. For this purpose, the control unit 6 can control the coolant flow rate delivered by the pump unit 8.

[0040] During a battery storage system's life cycle, the volume of the battery cells increases, causing them to press against the cooling channels between them and deform them. This reduces the flow cross-section of the cooling channels and consequently the cooling capacity of the cooling system.

[0041] Fig. 2 shows a method for determining the currently available cooling capacity. This method enables the determination of the cooling capacity throughout the entire life cycle of the battery storage system 2. Based on the determined current cooling capacity, the control unit 6 can then increase the flow rate of the pump unit 8 to compensate for the reduction in the flow cross-section and to provide sufficient cooling capacity throughout the entire life cycle.

[0042] In step S1, the control unit 6 first determines a predefined calibration profile 10. As can be seen in Fig. 3, the calibration profile 10 is a pulse-width modulated current profile, which is applied to the battery storage unit 2 to heat it up (step S2). For this purpose, the vehicle 1 is connected to an electrical power source, for example, a charging station, so that the vehicle 1 or the battery storage unit 2 can exchange electrical power with the power source according to the calibration profile 10. That is, current flows both from the power source into the battery storage unit 2 and from the battery storage unit 2 back to the power source. Thus, it is possible to heat up the battery storage unit 2 without changing its state of charge. As soon as the battery storage unit 2 has heated up sufficiently, i.e.,As soon as the temperature of the battery storage unit 2 no longer changes, the control unit 6 determines the saturation temperature of the battery storage unit 2 as a reference temperature (step S3). In the preferred embodiment, the saturation temperature of the battery storage unit 2 is used as the reference temperature. Alternatively, a coolant supply temperature or a coolant return temperature can also be used as the reference temperature. Furthermore, the reference temperature can also be determined as a function of several of these temperatures.

[0043] In step S4, the control unit 6 activates the cooling system 4 or the pump unit 8 of the cooling system 4, so that it circulates the coolant to cool the battery storage unit 2. During the cooling process, the control unit 6 monitors the temperature of the battery storage unit 2. As soon as this temperature no longer changes, the control unit 6 records the stable temperature as the cooling saturation temperature of the battery storage unit 2 (step S5).

[0044] In step S6, the control unit 6 compares the cooling saturation temperature of the battery storage unit 2 with the reference temperature. That is, the control unit 6 determines a temperature difference between the cooling saturation temperature of the battery storage unit 2 and the reference temperature. The magnitude of this temperature difference represents a measure of the currently available cooling capacity. Based on this temperature difference, the control unit 6 can then control the pump unit 8 to provide the necessary coolant flow rate for adequate cooling. (Reference numeral list)

[0045] 1 vehicle

[0046] 2 battery storage units, 4 cooling systems

[0047] 6 Control unit 8 Pump unit 10 Calibration profile

Claims

Claims 1. Method for determining the cooling capacity of a cooling system (4) of a battery storage system (2), comprising the following steps: - Determining a predefined calibration profile (10); - Applying the calibration profile (10) to the battery storage (2); - Determining a reference temperature of the battery storage (2); -Activating the cooling system (4); - Determining a cooling saturation temperature of the battery storage (2); -Comparing the cooling saturation temperature and the reference temperature to determine the cooling capacity.

2. Method according to claim 1, characterized in that the cooling system (4) is activated simultaneously with the determination of the predefined calibration profile (10).

3. Method according to claim 1, characterized in that the cooling system (4) is activated after the reference temperature has been detected.

4. Method according to claim 3, characterized in that the reference temperature is determined by means of at least one of a battery storage temperature, a coolant supply temperature and a coolant return temperature.

5. Method according to any one of the preceding claims 1 to 4, characterized in that the cooling saturation temperature is determined by means of at least one of the battery storage temperature, the coolant supply temperature and the coolant return temperature.

6. Method according to any one of the preceding claims 1 to 5, characterized in that the calibration profile (10) is a pulse duration modulated profile.

7. Method according to one of the preceding claims 1 to 6, characterized in that the battery storage (2) can be connected to an electrical power source, in particular a charging station, for carrying out the method.

8. Cooling system (4) of a battery storage device (2) with a control unit (6) which is configured to carry out the method according to any one of the preceding claims 1 to 7 and controls at least one pump unit (8) to circulate coolant within the cooling system (4).

9. Cooling system (4) according to claim 8, characterized in that the control unit (6) controls a coolant volume flow supplied by the at least one pump unit (8) depending on the determined cooling capacity.

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