Sodium batteries

Abstract

The invention relates to a sodium battery comprising at least one battery module (10) comprising: - sodium battery cells (11); - a DC-DC converter (16) connected to a supply bus (Vbus); and - a battery management system (BMS) for putting the battery cells (11) in a formation context, in which the DC-DC converter (16) receives a first voltage level, and in a usage context, in which the DC-DC converter (16) receives a second voltage level higher than the first voltage level; the battery comprising at least two series-connected battery modules (10); and the DC-DC converter (16) comprising: - a first converter (40) configured to lower the input voltage; - a second converter (50) configured to boost the input voltage; and - a third galvanic isolation converter (60).

Description

[0001] SODIUM BATTERIES

[0002] TECHNICAL FIELD

[0003] The invention relates to an electric battery for UPS systems, or Uninterruptible Power Supply systems. The invention finds a particularly advantageous application in providing sodium-metal chloride batteries for high-voltage UPS systems operating autonomously in training and operational contexts.

[0004] Industrial applications of UPS systems include data centers, where they ensure business continuity and prevent data loss. Another area of ​​application is the automation of floating liquefied natural gas (FLNG) vessels, where UPS systems provide backup power to critical automation systems. UPS systems are also used in the telecommunications sector to maintain communication services even during power outages.

[0005] In the transportation sector, UPS systems are used to ensure the continuity of transport services. Finally, UPS systems are used more generally for energy storage. These applications may require high operating power, and UPS systems containing batteries with a capacity of several hundred volts may be necessary.

[0006] STATE OF THE ART

[0007] In industry, batteries have numerous applications, one of which is their placement between a power-generating electrical grid and a critical electrical grid to create a backup power supply. Positioned in this way, and connected to a charger and an inverter, these batteries act as uninterruptible power supply (UPS) systems. These devices are essential for ensuring a continuous and stable power supply, even in the event of a main power outage. UPS systems are crucial in various industrial sectors to protect sensitive equipment and critical processes, guaranteeing the safety and reliability of industrial operations. There are two main types of UPS systems: direct current (DC) and alternating current (AC).UPS systems containing batteries of several hundred volts can be used.

[0008] The main battery technologies used for these applications are valve-regulated lead-acid batteries, also known as "VRLA" for "Valve Regulated Lead Acid" in the English-language literature, nickel-cadmium batteries, also known as "NiCd", lithium-ion batteries, also known as "Li-ion", and sodium-metal chloride batteries, also known as "SMC" for "Sodium-Metal Chloride" in the English-language literature.

[0009] Among these technologies, valve-regulated lead-acid batteries have the advantages of low initial cost and low maintenance requirements. However, valve-regulated lead-acid batteries have the disadvantages of a shorter lifespan than other battery technologies, the risk of production losses associated with their open failure mode, and a high lifecycle cost for shipping, storage, recharging during long-term storage, handling, and periodic cell replacement.

[0010] The second nickel-cadmium battery technology has the advantages of withstanding high ambient temperatures well and having a more robust technology; it is the battery technology traditionally used in industrial applications where strong environmental constraints such as high ambient temperature are required.

[0011] These nickel-cadmium batteries also require periodic maintenance and have a high lifecycle cost, although lower than for lead-acid batteries.

[0012] The third battery technology includes lithium-ion batteries, whose advantages are high power density, small size, and integrated battery monitoring. This technology is perfectly suited for short runtimes (less than one hour). This battery technology is less suitable for the long runtimes required in industrial applications. This battery technology also carries a risk of thermal runaway. Finally, the fourth battery technology, sodium-metal chloride, overcomes the drawbacks of the other battery technologies, enabling the creation of high-energy-density UPS and battery systems. These batteries require little to no maintenance. These batteries are also the safest due to the stable chemical reaction that occurs after the formation of the battery elements, also called battery cells.After this formation process, these batteries do not release any gases, particularly hydrogen, during charging and discharging. These batteries can be stored virtually indefinitely without loss of lifespan and without requiring charging during extended storage. Finally, these batteries exhibit an extremely long lifespan, even at ambient temperatures exceeding 40°C.

[0013] However, sodium batteries require a high operating temperature in order to keep their battery cells within their operating temperature range, even during standby phases in a usage context.

[0014] To achieve this, sodium batteries use a specific battery management system (BMS). This BMS, coupled with a DC-DC converter, ensures that a power cell maintains its temperature, even during standby phases.

[0015] As an example, Figure 1 illustrates the configuration of a 100 sodium battery according to the prior art. The 100 sodium battery is powered by a Vbus, Vbus+, Vbus- power supply bus connected to the 400 DC-DC converter.

[0016] In the operation of a single-unit battery, the Vbus, Vbus+, Vbus- power supply bus of the 100 sodium battery is conventionally connected to the String+, String- output connectors.

[0017] Battery 100 is used in two different contexts: the training context and the usage context.

[0018] Indeed, the battery cell manufacturing process requires the formation of these cells. The formation process, inherent to all sodium-ion batteries, precedes the operating process. This formation process consists of a heating phase followed by one or more initial charge and discharge phases of the battery cells. This step is essential to activate the battery cells and give them their nominal capacity. During this formation process, sodium ions intercalate into the cathode and anode materials, thus enabling the battery to efficiently store and release energy.

[0019] In a training context, the converter's input range is supplied by the mains to which the battery is connected and is typically 250V. This voltage passes through the DC-DC converter before being supplied to the rest of the battery.

[0020] Once the training context is complete, the 100 battery can be used in the usage context including standby, warm-up, charging and discharging phases.

[0021] The charging and discharging phases of the operating context are similar to the partial charging and partial discharging phases of the training context, but have a Vbus input range that can exceed the 250V training voltage. Typically, Vbus can vary from 250V to 650V depending on the load variations of the charger and inverter connected to the Vbus supply.

[0022] During these phases, a microcontroller 25 controls the DC-DC converter 400 over time to provide the desired voltage and current on internal outputs D+, D-, so as to power sodium technology battery elements 11, in the charging phases, as well as a heating device 12, in all phases of use.

[0023] More specifically, the power supplied to the heating device 12 is modulated by a transistor 26 controlled by the microcontroller 25, which detects the temperature of the battery cells 11 by thermocouples 17a, 17b, 17c. The thermocouples 17a, 17b, 17c are typically located inside the housing 13, 14 which integrates the battery cells 11.

[0024] Battery management systems (BMS) used for sodium-ion batteries allow not only the control of the voltage applied to the battery cells (11) in the different phases, but also the control and maintenance of the temperature of the battery cells (11) within their operating temperature range. These battery management systems may also include a relay system (18, 19, 20) that enables the connection or disconnection of the B+ and B- electrodes of the battery cells (11) to the D+ and D- outputs of the DC-DC converter (400) and to the String+ and String- output connectors of the battery (100). This relay system (18, 19, 20) allows, in the context of use, the control of the charge, discharge, and standby modes of the battery (100). Similarly, in the context of training, the relays (18-20) allow the control of the charge and discharge phases.

[0025] More specifically, to control the transition between these phases, the microcontroller 25 controls the relays 18, 19, 20 according to the current captured by a Hall effect current sensor 24 as well as the various other signals.

[0026] In the operating context, battery 100 first enters a warm-up phase in which relays 18, 19, and 20 are open, disconnecting the battery cells 11 from the DC-DC converter 400 and the String power output. During this warm-up phase, relay 26 is periodically closed by the microcontroller, which receives temperature information from the battery cells 11 via thermocouples 17a, 17b, and 17c.

[0027] Once the battery cells 11 have reached their operating temperature, the microcontroller 25 closes relay 20 and puts battery 100 into charging mode by closing relay 19 until the battery cells 11 are charged. Then, battery 100 is put into standby mode by opening relay 19, while relay 20 remains closed.

[0028] The standby phase is the primary phase for the batteries. From the standby phase, the charge and discharge phases can be accessed, corresponding conventionally to the phases during which the battery cells 11 are charged or discharged. Typically, the battery cells 11 are discharged when the UPS system is used to maintain power to a load, and they are charged after the discharge phases. The standby phases are implemented when the sodium battery is not in use, while maintaining power to the heating device 12.

[0029] The transition from standby to discharge mode occurs during a current surge resulting from a power supply maintenance need. In this event, the current reverses and flows from the positive terminal (String+) to the negative terminal (String-). Diode 22 conducts in this direction, instantly allowing the discharge current to flow. To minimize losses, diode 22 is quickly short-circuited by power relay 18, and battery 100 enters the discharge phase. Once the discharge current detected by Hall effect sensor 24 falls below a certain threshold, the microcontroller switches the battery to charging mode, once the main voltage (from the UPS charger) is restored.

[0030] To switch from the standby or discharge phase to the charging phase, the microcontroller 25 checks for the absence of discharge current through the hall effect sensor 24 and then opens the relay 18 if it is not already open, then closes the relay 19 in order to connect the battery elements 11 to the output of the DC-DC converter 400.

[0031] Furthermore, this 100 mAh sodium battery features several protection modes against overload and short circuits; these protections are electronic systems integrated into the BMS. A fuse 23, located at the negative String- connector of the 100 mAh battery, provides ultimate protection in case of failure of the BMS's electronic protections.

[0032] To increase the voltage and power output of UPS systems for applications with the highest power and UPS autonomy requirements, it could be considered to power several 100 battery modules in series.

[0033] However, when connected in series, since the Vbus power supply is common to the 100 battery modules connected in series, a short circuit would occur between the two groups of battery elements through the non-isolated "buck" type converters commonly used.

[0034] Furthermore, connecting multiple 100 battery modules in series would increase the voltage difference on the Vbus power supply between the training context and the usage context.

[0035] In use context, as the supply voltage Vbus can vary, typically from 250V to 650V, the DC-DC 400 converter lowers the supply voltage Vbus to a normalised voltage identical to the voltage used in the training context, typically 250V, in order to provide the charging voltage of the battery elements 11. However, in the training context, a normalised supply voltage Vbus around 250V is imposed by the equipment and the DC-DC converter is classically sized so that the internal voltage VDCDC is also close to 250V in the use context.

[0036] Therefore, the Vbus supply voltage, connected to the load, cannot be too different from the voltage of the training environment without degrading the efficiency of the DC-DC converter. Although the prior art offers a step-down DC-DC converter for UPS systems with supply voltages typically up to 350V, a wider supply voltage range makes isolation between the 100 battery modules more difficult, necessitating the use of wide-range DC-DC converters with lower energy efficiency.

[0037] For these reasons, sodium batteries are not connected in series and there is currently a limitation to the use of this technology for high voltage UPS systems.

[0038] There is therefore a need for a sodium-metal chloride battery for UPS systems that is compatible with high voltages and operates autonomously in training and usage contexts.

[0039] DESCRIPTION OF THE INVENTION

[0040] The invention proposes to solve this technical problem by connecting several battery modules in series, incorporating a specific DC-DC converter.

[0041] For this purpose, this DC-DC converter includes a converter that provides galvanic isolation.

[0042] This galvanic isolation converter has an input voltage, known as the internal voltage of the DC-DC converter, that is higher than the externally imposed supply voltage in the training context. This internal voltage is chosen to guarantee a high level of efficiency around this high internal voltage, even when the battery is in use. In order to increase the external supply voltage, particularly in the training context, and possibly during operation when the Vbus voltage is low, the DC-DC converter incorporates a voltage booster to ensure the minimum range of the input voltage of the galvanic isolation converter.

[0043] Finally, the DC-DC converter incorporates a step-down converter, known as a "buck," used in the context of use to guarantee the maximum input voltage range of the other converters.

[0044] The invention therefore relates to a sodium battery comprising at least one battery module including a power bus and a power output.

[0045] The battery module includes:

[0046] sodium battery elements comprising a positive electrode and a negative electrode;

[0047] a DC-DC converter connected to the power bus and comprising a positive output and a negative output; and

[0048] A battery management system incorporating relays allows the battery elements to be placed in a training context, in which the DC-DC converter receives a first voltage level, and in a usage context, in which the DC-DC converter receives a second voltage level higher than the first. The invention is characterized in that the battery comprises at least two battery modules connected in series.

[0049] In addition, the DC-DC converter in each battery module includes:

[0050] a first converter connected at the input to the terminals of the power bus and configured to lower the voltage of the power bus to a second voltage in said context of use;

[0051] a second converter connected to the output of the first converter and configured to boost said second voltage to a third voltage in said training context; and

[0052] A third galvanic isolation converter is connected to the output of the second converter and configured to lower said third voltage to a voltage controlled by a microcontroller in training and operating contexts. The use of three converters within the DC-DC converter allows the series connection of several battery modules while maintaining autonomous battery operation thanks to regulation of the voltage applied to the battery cells as well as the associated battery module management system in training and operating contexts.

[0053] The use of the third galvanic isolation converter prevents short circuits between two battery modules connected in series. This galvanic isolation is essential for connecting multiple battery modules in series because without it, the common power supply to the series-connected battery modules would induce a short circuit between two groups of battery cells through the unisolated converters.

[0054] To improve the efficiency of the third galvanic isolation converter, the external supply voltage to the DC-DC converter is boosted upstream of the third converter by a second converter, referred to as a "boost" converter in English-language literature. This second converter increases the external supply voltage of the DC-DC converter, particularly during training and, potentially, during operation when the external supply voltage is low. The use of this second converter ensures the minimum input voltage range of the third galvanic isolation converter.Therefore, this second converter makes it possible to overcome the upper limitation of the external supply voltage in a training context when choosing the internal input voltage of the galvanic isolation converter, a voltage around which the efficiency of said galvanic isolation converter is optimal.

[0055] To ensure that the second converter works even in the event of very high external supply voltage, particularly when using the battery, a first converter lowering the external supply voltage, called a "buck" in Anglo-Saxon literature, is used.

[0056] According to one embodiment of the invention, the training context includes:

[0057] a warm-up phase in which the battery elements are disconnected from the DC-DC converter and the power output;

[0058] a charging phase in which the battery elements are connected to the DC-DC converter and to the power output via a diode; and a discharging phase in which the battery elements are disconnected from the DC-DC converter and connected directly to the power output.

[0059] Similarly, the context of use includes:

[0060] a standby phase in which the battery elements are disconnected from the DC-DC converter and are connected to the power output via said diode;

[0061] a warm-up phase in which the battery elements are disconnected from the DC-DC converter and the power output;

[0062] a charging phase in which the battery elements are connected to the DC-DC converter and to the power output via said diode; and

[0063] a discharge phase in which the battery elements are disconnected from the DC-DC converter and connected directly to the power output.

[0064] Indeed, the battery cell manufacturing process requires a cell formation phase. This formation process consists of a heating phase followed by one or more initial charge and discharge phases. This step is essential to activate the battery cells and give them their nominal capacity.

[0065] During the heating phase, according to one embodiment of the invention, the battery cells are disconnected from the DC-DC converter and the battery power output to prevent voltage from being induced across the battery cells before they reach their operating temperature. During this heating phase, the DC-DC converter can optionally power a heating device for the battery cells.

[0066] During the charging phase, according to one embodiment of the invention, the battery elements are connected to the DC-DC converter and to the power output via said diode in order to allow the charging of each of the groups of power elements without short circuits with the groups of power elements of the series battery modules that could interfere with their charging.

[0067] During the discharge phase, according to one embodiment of the invention, the battery cells are disconnected from the DC-DC converter and connected directly to the power output to allow each group of battery cells to be discharged without short circuits with the DC-DC converter. After the manufacturing process, according to one embodiment of the invention, the batteries are placed in the operating context in which the supply voltage of the DC-DC converter may be higher than in the manufacturing context.

[0068] The heating, charging and discharging phases of the usage context are preferably carried out in a similar way to those of the training context.

[0069] The standby phase described in this embodiment of the invention is a transition phase occurring at the end of a charging phase in order to place the battery in standby mode for a current demand resulting from a need to maintain the power supply, at the end of which a transition to the discharge phase is initiated.

[0070] According to one embodiment of the invention, the power output comprises a positive connector and a negative connector, and the diode described above is mounted in direct direction between the negative connector and the negative electrode of the battery elements.

[0071] Positioning the diode in forward direction between the negative connector and the negative electrode allows current to flow in the direction of discharge, but blocks current backflow from one battery module to another when charging battery modules in series.

[0072] According to one embodiment of the invention, the power bus comprises a negative power terminal and a positive power terminal, and the series connection of at least two battery modules is achieved by connecting the positive connector of the first battery module to the negative connector of the second battery module, connecting the negative connector of the first battery module to the negative power terminal of the battery modules, and connecting the positive connector of the second battery module to the positive power terminal of the battery modules.

[0073] Connecting several battery modules in series in this configuration allows the voltage of the two batteries to be added between the negative connector of the first battery module and the positive connector of the second battery module, thus providing a load with a higher voltage than that of a single battery module. Of course, more than two modules can be connected in series depending on the desired discharge voltage and, therefore, the desired battery life. This allows for a high-voltage, high-capacity battery system, particularly desirable for industrial battery applications, such as UPS systems.

[0074] In addition, the DC-DC converter may also include a fourth galvanic isolation converter connected in parallel with the third converter, i.e. connected at the input to the output of the second converter and at the output terminals of the DC-DC converter.

[0075] The use of a fourth galvanically isolated converter distributes heat losses across the entire printed circuit board, resulting in a larger heat dissipation surface area. This optimizes the dissipation of heat generated by the DC-DC converter, particularly during charging phases. When using this invention in a BMS enclosure with an IP55 protection rating and where no ventilation is permitted, the efficiency of heat dissipation from the DC-DC converter is indeed crucial.

[0076] In addition, the fourth converter connected in parallel with the third converter is activated via the microcontroller.

[0077] The microcontroller activates the two galvanic isolation converters when the current through the DC-DC converter exceeds a current threshold, indicating a significant charging phase of the battery cells and increased thermal heating. In this configuration, the microcontroller inhibits the operation of this fourth converter when the current through the DC-DC converter falls below the current threshold, indicating that the battery cells are nearly charged and the DC-DC converter is dissipating less heat.

[0078] Disabling the fourth converter during phases of lower heat dissipation allows for improved efficiency in power conversion within the DC-DC converter. This deactivation of the fourth converter enables charging with better thermal efficiency when the battery cells are near their maximum charge and during maintenance phases at operating temperature. Furthermore, the battery module includes a heating device powered by the DC-DC converter. This voltage is required to power the heating device and can be modulated by a power transistor placed in series between the positive terminal and the positive supply input of the heating device to maintain the battery cells within a predefined operating temperature range during training and use.

[0079] The heating device's temperature setpoint is preferably obtained by modulating the duty cycle via a transistor. This technique allows for precise temperature control of the heating device and maintains the operating temperature of sodium-metal battery cells throughout all phases of battery formation and use.

[0080] According to one embodiment, the battery management system of each module is configured to power the DC-DC converter and the heating system associated with said module, according to at least two contexts comprising a total of four battery operating phases obtained by the opening and closing of three relays controlled by the microcontroller:

[0081] a first relay placed in series between the positive electrode and the positive connector, open during the heating phase and closed during the charging, discharging and standby phases; a second relay placed between the negative electrode and the negative connector, open during the heating, standby and charging phases, and closed during the discharging phases; and a third relay placed between the positive electrode and the positive output of the DC-DC converter, open during the heating, standby and discharging phases, and closed during the charging phases.

[0082] This relay system allows the four operating phases occurring in the two battery contexts to be addressed autonomously by the commands of the microcontroller included in the battery management system.

[0083] According to one embodiment of the invention, the battery module's microcontroller receives a measurement from a current sensor connected in series across the negative electrode of the battery cells, and from at least one thermocouple located near the battery cells. Communication between the microcontroller and the current sensor connected in series across the negative electrode of the battery cells allows the microcontroller to determine the phase changes between the standby, charging, and discharging phases of the battery cells. This enables the microcontroller to modulate, via a voltage, the current-mode control of the galvanic isolation converter as well as the control of the relays. The relay control results in a phase change at the end of a charging or discharging phase, or a current surge during a standby phase.

[0084] Furthermore, connecting the microcontroller with at least one thermocouple placed near the battery elements allows it to determine whether the output voltage of the DC-DC converter should be applied to the heating device or not, via a transistor.

[0085] These sensors thus allow greater autonomy in the battery management system for monitoring battery usage modes by the microcontroller.

[0086] According to one embodiment, the battery module comprises at least two battery elements or cells composed of sodium chloride and a metal, for example nickel or iron, connected in series, forming the battery elements of the battery module.

[0087] This embodiment makes it possible to obtain a higher or lower battery voltage depending on the intended application by modulating the number of elements composing the battery cells.

[0088] According to one embodiment of the invention, the DC-DC converter and the BMS battery management system are mounted on the same printed circuit board having a part comprising the BMS battery management system and a part containing the DC-DC converter.

[0089] SUMMARY DESCRIPTION OF THE FIGURES

[0090] The manner of carrying out the invention and the advantages which result therefrom will be clearly shown in the following embodiments, given by way of indication but not limitation, in support of the figures in which: Figure 1 is a schematic representation of a sodium battery of the prior art;

[0091] Figure 2 is a schematic representation of a sodium battery module in a training context according to a first embodiment of the invention;

[0092] Figure 3 is a schematic representation of a sodium battery module in use context, during heating phase, according to a first embodiment of the invention;

[0093] Figure 4 is a schematic representation of a sodium battery module in use context, in charging phase, according to the first embodiment of the invention;

[0094] Figure 5 is a schematic representation of a sodium battery module in use context, in standby phase, according to the first embodiment of the invention;

[0095] Figure 6 is a schematic representation of a sodium battery module in use context, in discharge phase, according to the first embodiment of the invention;

[0096] Figure 7 is a schematic representation of a sodium battery composed of two battery modules, in a context of use, of which a first module is placed in the heating phase, and a second module is placed in the standby phase, according to an embodiment of the invention;

[0097] Figure 8 is a schematic representation of a sodium battery composed of two battery modules, in a context of use, where both modules are placed in the charging phase, according to an embodiment of the invention; and

[0098] Figure 9 is a representation of the electrical diagram of a DC-DC converter of a sodium battery according to another embodiment of the invention.

[0099] DETAILED DESCRIPTION OF THE INVENTION

[0100] According to an embodiment of the invention visible in Figures 2 to 8, a sodium-metal battery 30 comprises at least two battery modules 10 having a power bus Vbus consisting of a positive power terminal Vbus+ and a negative power terminal Vbus-. Each battery module also has a String power output consisting of a positive String+ connector and a negative String- connector. The battery module 10 includes in particular a casing whose internal walls 13 and external walls 14 provide thermal insulation of the inside of the casing from the other components of the battery module 10. This casing integrates sodium battery cells 11 whose negative electrode B- is connected outside the casing to the negative String- connector of the battery module 10 and whose positive electrode B+ is connected outside the casing to the positive String+ connector of the battery module 10.These battery elements 11 allow energy to be stored during charging, and this energy to be released during discharge.

[0101] A heating device 12, powered by a DC-DC converter 16 located outside the battery module 10, is also housed within this enclosure. The heating device 12 maintains the battery cells 11 at their operating temperature. This heating device 12 is essential for sodium batteries because their operating temperature is typically much higher than ambient temperature. Typically, this heating device 12 is powered during the heating phase, as illustrated in Figure 2, and during the operation of the battery module 10, as illustrated in Figure 3. Preferably, this heating device 12 is also intermittently powered during other operating phases of the battery module 10 to maintain the temperature of the battery cells 11 within their operating range.

[0102] In addition, the DC-DC converter 16 is also used for managing the charging and discharging of the battery elements 11. In the battery module 10, the DC-DC converter 16 is placed at the input on the Vbus voltage supply.

[0103] This DC-DC converter has a positive output D+ connected to the positive electrode B+ of said power element 11, and a negative output D- placed between the negative electrode B- of said power element 11 and the negative String- connector of the battery module 10. The negative output D- is also connected to ground. According to the embodiment of the invention illustrated in Figures 2 to 5, this DC-DC converter 16 comprises a first buck converter 40, a second boost converter 50, and a third voltage-controlled galvanic isolation converter 60, placed in series in that order between the Vbus supply and the two output terminals D+, D- of the converter.

[0104] Preferably, the invention includes at least two operating contexts. The first training context, illustrated in Figure 2, is carried out during the manufacturing process of the battery elements 11 of the battery module 10. During the training context, the battery modules 10 are preferably not placed in series.

[0105] In a training context, the Vbus supply to the DC-DC converter 16 is provided by the UPS charger to which the battery module 10 is connected and is typically 250V. In this context, the Vbus supply voltage passes through the step-down converter 40 to form a second voltage V2 identical to the Vbus voltage. This second voltage V2 is then boosted to a third voltage V3 by the step-up converter 50, typically around 405V. Finally, this third voltage V3 feeds the galvanic isolation converter 60, which transforms this third voltage V3 into the DC-DC output voltage VDCDC of the DC-DC converter 16, lower than V3 and galvanically isolated, typically 250V.

[0106] In the operating context (Cu), shown in Figures 3 to 8, the Vbus supply of the DC-DC converter 16 is provided by the load backed up by the battery 30. This Vbus supply voltage can typically vary from 250V to 700V and is preferably close to the voltage of the battery 30 in which one or more battery modules 10 are connected in series. In this context, the Vbus supply voltage passes through the step-down converter 40 to form a second voltage V2 less than or equal to the Vbus voltage, typically less than 425V. Then, this second voltage V2 is boosted, if necessary, to a third voltage V3 by the step-up converter 50, depending on the desired input voltage for the galvanic isolation converter, typically close to 405V.Finally, this third voltage V3 powers the galvanic isolation converter 60, which transforms this third voltage V3 into a VDCDC output voltage of the DC-DC converter 16, lower than V3 and galvanically isolated, typically 250V. In addition to the DC-DC converter, for managing the charging and discharging phases of the battery cells 11, the battery module 10 also includes a battery management system (BMS) powered by the Vbus power supply.

[0107] The battery management system (BMS) preferably has a current sensor 24 configured to follow the current to the negative electrode B- of the battery cells 11. This current can come from the negative String- connector of the battery module 10 and / or the negative output terminal D- of the DC-DC converter 16. This current is an indicator of the charging or discharging rate of the battery cells 11 and can be measured by a sensor, for example by a Hall effect current sensor 24, and retrieved by a microcontroller 25 for analysis.

[0108] In addition, the BMS battery management system incorporates an on / off transistor 26 placed between the heating device 12 and one of the output terminals D+ or D- of the DC-DC converter 25, giving a modulating duty cycle of the heating current.

[0109] Thermocouples 17a, 17b, 17c can then be added near the battery cells 11 to create a feedback loop between the temperature obtained for the battery cells and the duty cycle of the heating current. These thermocouples 17a, 17b, 17c can be placed inside the housing 13, 14 as close as possible to the battery cells 11.

[0110] To control this operating temperature, the use of a microprocessor or microcontroller 25 can prove essential. Indeed, the microcontroller can then control both the output voltage of the DC-DC converter 16, and the duty cycle of the transistor 26, based on the temperature data of the power elements 11 obtained by the thermocouples 17a, 17b, 17c.

[0111] This BMS battery management system preferentially allows the battery module 10 to be placed in at least four operating phases occurring during the at least two training (Cf) and usage (Cu) contexts of the battery elements 11.

[0112] During the heating phase, illustrated in Figure 3, the battery cells 11 are disconnected from the DC-DC converter 16 and the String power output. In this phase, the microcontroller 25 controls the heating of the battery cells 11 via the heating device 12.

[0113] The standby phase, illustrated in Figure 5, occurs during operation and corresponds to the discharge waiting phase of the battery module 10. During the standby phase, the battery cells 11 are disconnected from the DC-DC converter 16 but remain connected to the String power output via the closed relay 20 between the positive electrode B+ and the positive String power output on one side, and a diode 22 connected in forward bias between the negative String power output and the negative electrode B- on the other. This ensures that the battery is always available when a discharge is requested.

[0114] The charging phase, illustrated in Figure 4, allows the battery elements 11 to be charged. During the charging mode, the battery elements 11 are connected to the DC-DC converter 16 and connected to the String power output via the blocking diode 22 in the outward direction to the negative connector of the battery module 10.

[0115] The discharge phase, illustrated in Figure 6, discharges the battery cells 11 and powers an electronic device (for example, the UPS inverter) connected to the String power output of the battery module. During the discharge mode, the battery cells 11 are connected to the String power output and are disconnected from the DC-DC converter 16.

[0116] In order to place the battery module in these different operating phases, the BMS battery management system preferably includes three relays 18, 19, 20 whose opening and closing can be controlled by the microcontroller 25 according to the phases of use of the battery module.

[0117] For the purposes of the invention, two directly connected elements means elements connected via a closed relay, amounting to a series connection of said two elements.

[0118] The first relay 20 is placed in series between the positive electrode B+ and the positive connector String+a, String+b. This first relay 20 is only open during the heating phase in order to disconnect the battery cells 11 from the positive connector String+ and prevent discharge of the battery cells 11 into the power output String. This first relay 20 is closed during the charging, discharging, and standby phases.

[0119] During the first heating of the battery elements, figure 3, relay 20 is open and therefore prevents battery discharge until the battery elements are at their operating temperature, relays 18 and 19 are also open.

[0120] The second relay 18 is placed between the negative electrode B- and the negative connector String-a, String-b. This second relay 18 is closed during the discharge and test phases, thus directly connecting the negative electrode B- to the negative connector String-a. When the relay 18 is open, during the heating, standby, and charging phases, the negative electrode B- is connected to the negative connector String-a via diode 22.

[0121] During standby and charging phases, this second relay is open to connect the battery cells 11 to the negative String- connector via diode 22, which is connected in direct current from the negative String- connector to the negative electrode B-. The use of this diode allows discharge when required by the application.

[0122] The third relay 19 is placed between the positive electrode B+ and the positive output D+ of the DC-DC converter 16. This third relay 19 is open during the heating, standby, and discharge phases to disconnect the battery cells 11 from the positive output D+ of the DC-DC converter 25, thus preventing any current flow back into the DC-DC converter during discharge and inactivity phases. This third relay 19 is closed during the charging phases.

[0123] The transitions between phases initiated by the microcontroller are described below.

[0124] In the context of use, the microcontroller 25 first places the battery module 10 into the heating phase, illustrated in Figure 3, by opening the 3 relays 18, 19 and 20, and modulating the transistor 26 in order to power the heating device 12.

[0125] Once the operating temperature of the battery elements 11 has been reached, the microcontroller successively closes the first relay 20 and then the third relay 19 in order to place the battery in the charging phase, illustrated in Figure 4.

[0126] During the charging phase, the current flowing in the battery element 11 can be monitored by a current sensor 24 which can be in communication with the microcontroller 25.

[0127] When the charge reaches a certain level, the DC-DC converter has reached its maximum applicable voltage to the battery cells; the current then gradually decreases until it becomes almost zero. When the cells are fully charged, the microcontroller cuts off the charging and opens relay 19.

[0128] The battery module 10 then enters the standby phase, as shown in Figure 5. When a discharge request is made, the current passes through diode 22, and instantly the microcontroller 25 closes relay 18 to put the battery module 10 into the discharge phase, illustrated in Figure 6.

[0129] The battery elements 11 are then connected to the String power output and can discharge through any electronic device connected to this String power output.

[0130] When the discharge current decreases until it becomes almost zero, the battery module 10 is put back into charging mode when the UPS charger power is restored, by opening relay 18 and then closing relay 19.

[0131] As illustrated in Figures 7 and 8, connecting two 10a, 10b battery modules according to the invention in series is achieved by connecting the positive String+a connector of the first 10a battery module to the negative String-b connector of the second 10b battery module, connecting the negative String-a connector of the first 10a battery module to the negative Vbus- supply terminal, and connecting the positive String+b connector of the second 10b battery module to the positive Vbus+ supply terminal. Of course, more than two 10a, 10b modules can be connected in series depending on the battery voltage required for the application.

[0132] During this series connection, the operation and modes of use of modules 10a, 10b remain the same as those described for a module 10 and presented in figures 2 to 4.

[0133] Although the battery modules 10 are galvanically isolated by the DC-DC converter, a fuse 23 can also be added in series with the negative connector String-a, String-b of each associated module 10a, 10b to provide protection of the battery module circuit against possible external short circuits.

[0134] Figure 7 illustrates an embodiment of the invention in which module 10a is in the heating phase, following a module replacement for example, and in which module 10b is in the standby phase. In this configuration, module 10b does not interfere with the operation of module 10a, and the heating phase and then the charging phase can thus be carried out on module 10b independently of module 10a.

[0135] Furthermore, the charging of several 10a, 10b battery modules, as illustrated in Figure 8, can be carried out simultaneously by the same Vbus power supply.

[0136] The heating, charging and discharging of modules 10a and 10b can therefore be carried out independently of the other modules and a replacement of module 10a, 10b can therefore be performed.

[0137] As illustrated in Figure 9, a fourth galvanic isolation converter 60' can also be connected in parallel with the third galvanic isolation converter 60, i.e. connected in input to the output of the second converter and in output to the output terminals of the DC-DC converter.

[0138] The use of a fourth 60' galvanically isolated converter distributes heat losses across the entire printed circuit board, resulting in a larger heat dissipation surface. This optimizes the dissipation of heat generated by the 16 DC-DC converter, particularly during charging phases.

[0139] When using the invention in an IP55 enclosure without ventilation, the efficiency of heat dissipation of the DC-DC converter is indeed a crucial point.

[0140] The fourth galvanic isolation converter 60' can be activated by the microcontroller 25 to be dependent on the current flowing through the DC-DC converter 16, particularly when this current exceeds a threshold indicating a significant charging phase of the battery cells 11 and increased thermal heating. In this configuration, the microcontroller disables converter 60' when the current through the DC-DC converter 16 falls below this current threshold, indicating that the battery cells 11 are nearly charged and the DC-DC converter 25 is dissipating less heat. Disabling the fourth converter during phases of lower heat dissipation allows for improved power conversion efficiency of the DC-DC converter 16.

[0141] Thus, the use of three converters within the DC-DC converter allows the battery modules to be connected in series while maintaining an autonomous battery regardless of the desired mode of use.

[0142] Indeed, in the context of use, high supply voltage phases, such as the load phases, can reach up to approximately 700V. The first converter 40 then reduces the input voltage to a maximum of approximately 425V.

[0143] During phases with low supply voltage, such as those in the training context, which can reach a minimum of approximately 250V, the first converter 40 will only have an output voltage of around 250V, and it will be the second converter 50 which will raise, if necessary, the input voltage to its output to a voltage V3 of around 405V in order to power the galvanic isolation converter 60. When using the DC-DC converter 16, isolating the Vbus supply, whose voltage can vary, from the components located at the output of the DC-DC converter 16, is necessary in order to avoid potentially very high short-circuit currents.The galvanic isolation converters 60, 60' allow the isolation of battery modules 10 placed in series, while having a correct efficiency over a supply voltage range on Vbus higher than the supply voltage in training context thanks to a boost converter 40 and a step converter 50 allowing a higher optimal operating voltage for the galvanic isolation converters 60 and 60'.

[0144] In addition, the galvanic isolators allow the output voltage V3 of the second converter 50 to be lowered to a voltage controlled by the microcontroller 25 according to the number of battery cells, for example close to 250V and isolated from the voltage V3.

[0145] In conclusion, the invention makes it possible to provide a sodium-metal chloride battery for UPS systems that is compatible with high voltage and operates autonomously in training and usage contexts.

Claims

DEMANDS 1. Sodium battery (30) comprising at least one battery module (10, 10a, 10b) comprising a power bus (Vbus) and a power output (String); said battery module (10, 10a, 10b) comprising: sodium battery elements (11) comprising a positive electrode (B+) and a negative electrode (B-); a DC-DC converter (16) connected to the power supply bus (Vbus) and comprising a positive output (D+) and a negative output (D-); and a battery management system (BMS, BMS1, BMS2) incorporating relays (18-20) allowing the said battery elements (11) to be placed in a training context in which said DC-DC converter (16) receives a first voltage level and in a usage context in which said DC-DC converter (16) receives a second voltage level higher than the first voltage level; characterized in that said battery comprises at least two battery modules (10, 10a, 10b) connected in series; and in that said DC-DC converter (16) of each battery module (10, 10a, 10b) comprises: a first converter (40) connected at input to the terminals of the power supply bus (Vbus) and configured to lower the voltage of the power supply bus (Vbus) to a second voltage (V2) in said context of use; a second converter (50) connected to the output of the first converter (40) and configured to boost said second voltage (V2) to a third voltage (V3) in said training context; and a third galvanic isolation converter (60) connected at the output of the second converter (50) and configured to lower said third voltage (V3) to a voltage (VDC-DC) whose current destination is controlled by a microcontroller (25) in training and use contexts.

2. Sodium battery according to claim 1, wherein the formation context comprises: a heating phase in which the battery elements (11) are disconnected from the DC-DC converter (16) and the power output (String); a charging phase in which the battery elements (11) are connected to the DC-DC converter (16) and the power output (String) via a diode (22); and a discharging phase in which the battery elements (11) are disconnected from the DC-DC converter (16) and connected directly to the power output (String); and where said context of use includes: a standby phase in which the battery elements (11) are disconnected from the DC-DC converter (16) and are connected to the power output (String) via said diode (22); a heating phase in which the battery elements (11) are disconnected from the DC-DC converter (16) and the power output (String); a charging phase in which the battery elements (11) are connected to the DC-DC converter (16) and to the power output (String) via said diode (22); and a discharge phase in which the battery elements (11) are disconnected from the DC-DC converter (16) and connected directly to the power output (String).

3. Sodium battery according to claim 2, wherein the power output (String) has a positive connector (String+a, String+b) and a negative connector (String-a, String-b); and wherein the diode (22) is mounted in forward direction between the negative connector (String-a, String-b) and the negative electrode (B-).

4. Sodium battery according to claim 1 to 3, wherein the power bus (Vbus) has a negative power terminal (Vbus-) and a positive power terminal (Vbus+); and wherein the series connection of at least two battery modules (10, 10a, 10b) is achieved by connecting the positive connector (String+a) of the first battery module (10a) to the negative connector (String-b) of the second battery module (10b), connecting the negative connector (String-a) of the first battery module (10a) to the negative power terminal (Vbus-), and connecting the positive connector (String+b) of the second battery module (10b) to the positive power terminal (Vbus+).

5. Sodium battery according to claims 1 to 4, wherein a fourth galvanic isolation converter (60') is connected in parallel with the third converter (60), i.e., connected at the input to the output of the second converter (50) and at the output to the output terminals (D-, D+) of the DC-DC converter (16).

6. Sodium battery according to claim 5, wherein the fourth converter (60') is connected in parallel with the third converter (60); said fourth converter (60') being able to be activated by the microcontroller (25) to be in operation when the current through the DC-DC converter (16) exceeds a current threshold, and deactivated when the current through the DC-DC converter (16) falls below this current threshold.

7. Sodium battery according to any one of claims 1 to 6, wherein the battery module (10, 10a, 10b) comprises a heating device (12) supplied with voltage by the DC-DC converter (16), said voltage being configured to supply the heating device (12) and modulated by a power transistor (26) placed in series between the positive terminal (D+) and the positive supply input of the heating device (12) in order to maintain the battery cells (11) within a predefined operating temperature range in the training and use contexts.

8. Sodium battery according to any one of claims 1 to 7, wherein the battery management system (BMS, BMS1, BMS2) of each module (10, 10a, 10b) is configured to power the DC-DC converter (16) and the heating system (12) associated with said module (10, 10a, 10b), according to at least two contexts comprising in total at least four battery operating phases (30) obtained by the opening and closing of three relays (18, 19, 20) controlled by the microcontroller (25): a first relay (20) placed in series between the positive electrode (B+) and the positive connector (String+a, String+b), open during the heating phase and closed during the charging, discharging and standby phases; a second relay (18) placed between the negative electrode (B-) and the negative connector (String-a, String-b), open during the heating, standby and charging phases, and closed during the discharging phases; and a third relay (19) placed between the positive electrode (B+) and the positive output (D+) of the DC-DC converter (16), open during the heating, standby and discharge phases, and closed during the charging phases.

9. Sodium battery according to any one of claims 1 to 8, wherein the microcontroller (25) of the battery module (10, 10a, 10b) is, among other things, in communication with a current sensor placed in series on the negative electrode B- of the battery cells (11); and at least one thermocouple placed near the battery cells (11).

10. Sodium battery according to any one of claims 1 to 9, wherein said battery module (10, 10a, 10b) comprises at least two elements connected in series so as to form the battery elements (11) of said battery module (10, 10a, 10b).

11. Sodium battery according to any one of claims 1 to 10, wherein the DC-DC converter (16) and the battery management system (BMS, BMS1, BMS2) are mounted on the same printed circuit board having a part comprising the battery management system (BMS, BMS1, BMS2) and a part containing the DC-DC converter (16).

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