RECHARGEABLE BATTERY

Description

[0001] The present invention relates to a battery of the type comprising: a set of cells connected in series, each cell comprising an energy storage element connected in series with a controllable isolation switch and a controllable shunt switch connected in parallel with the energy storage element and the controllable isolation switch, a control unit for the isolation and shunt switches of each cell, the controllable switches of the same cell being in opposite states, a coil connected in series with the set of cells connected in series between two supply terminals; and a current measurement sensor flowing between the supply terminals.

[0002] Batteries are made up of a set of cells, each containing at least one electrical energy storage element. These cells are connected in series to allow the battery to provide a high output voltage that can reach the sum of the individual voltages of the storage elements in the cells.

[0003] Each energy storage element has a maximum permissible charging current and care must be taken to ensure that this current is not exceeded during charging phases.

[0004] In order to ensure charging from several sources of electrical energy, such as the mains, often 220 or 110 volts alternating current, a solar panel providing direct current, or an electric vehicle charging station also providing direct current, it is known to provide between the battery charging terminals and all the energy storage cells, a charger capable of injecting an electric current opposite to that supplied during the discharge of the cells.

[0005] Chargers are generally composed of a mains regulation circuit consisting of a transformer followed by a diode rectifier, then smoothing using a capacitor, and finally a regulation circuit.

[0006] This charger is relatively bulky and causes losses during the electrical current processing phases.

[0007] The invention aims to provide a battery with a limited size that can be charged from different sources of electrical energy while exhibiting reduced losses during charging.

[0008] To this end, the invention relates to a battery of the aforementioned type, characterized in that the control unit is suitable for measuring the voltage from the sensor and for controlling the switches at a frequency greater than 1 kHz as a function of the measured intensity; and the control unit includes means for, at each cycle, adding a series energy storage element to the set of series-connected energy storage elements if the measured intensity is greater than a maximum intensity and shunting a series energy storage element to the set of series-connected energy storage elements if the measured intensity is less than a minimum intensity.

[0009] Depending on the specific embodiment, the battery includes one or more of the following characteristics: It includes a disconnecting relay connected for its control to the control unit, designed to interrupt the flow of current between the two terminals and the control unit, and is designed to: while the relay is open, connect in series a number of storage cells such that the voltage across the terminals of the storage cells connected in series is between the supply voltage and the supply voltage reduced by a predetermined load voltage; close the relay, then the voltage across the terminals of the storage cells connected in series is between the supply voltage and the supply voltage reduced by a predetermined load voltage; it includes a rectifier whose input is connected to the two supply terminals through the coil, the set of cells connected in series being connected to the output of the rectifier; the rectifier includes a diode bridge;the battery has no charger between the power supply terminals and the series-connected cell assembly; the charging voltage is less than or equal to the maximum charging voltage of one of the energy storage elements; the battery includes means for measuring the voltage of each energy storage element connected to the control unit, and the control unit is capable of controlling the cell switches according to the voltage measured across the terminals of each storage element; the coil inductance is greater than; R L fln 1 − R L I max U L , where RL is the resistance of the coil, f is the measurement and control frequency, I max is the maximum charging current of a cell, UL is the maximum charging voltage of a cell and In is the natural logarithm; and the inductance of the coil is between 1 µH and 1 mH.

[0010] The invention will be better understood upon reading the following description, given solely by way of example and made with reference to the drawings in which: there figure 1 is a schematic view of a battery according to the invention; The figure 2 is a flowchart illustrating the choice of cells whose energy storage elements should be connected first; and the figure 3 is a flowchart illustrating the battery control during charging.

[0011] Battery 10 shown on the figure 1 It comprises a set of 12 identical cells connected in series for electrical energy storage. On the figure 1 Only three cells are shown. In practice, the number of cells is much higher and, for example, equal to 128.

[0012] Each cell 12 includes an energy storage element 14 schematically represented by a battery 16 mounted in series with a resistor 18. In practice, the resistor 18 is the resistance of the battery 16.

[0013] Each energy storage element 14, for example, has a maximum charging current of three Amperes and is capable of producing a maximum voltage of 4.2 Volts across its terminals when charged. The voltage across its terminals varies from 2.8 V to 4.2 V depending on its state of charge.

[0014] In each cell, the energy storage element 14 is connected in series with a controllable switch 20 for isolating the energy storage element 14. In addition, the cell includes a controllable shunt switch 22 connected in parallel with the assembly formed by the storage element 14 and the isolation switch 20.

[0015] The switches 20 and 22 of each cell are controlled independently from one cell to another by being connected to a control unit 25.

[0016] The isolation switches 20 and shunt switches 22 of each cell are linked and / or controlled so that they are systematically in opposite states, i.e. that when the shunt switch 22 is closed, the isolation switch 20 is open and vice versa.

[0017] The 12 cells are connected in series to form the cell set.

[0018] The battery has a battery charging input 30 to which the cell assembly is connected via a relay 31, a coil 32 and a rectifier 34.

[0019] More specifically, input 30 has two terminals, 30A and 30B, designed to receive a voltage denoted Vin. Relay 31, coil 32, and the input of rectifier 34 are connected in series between terminals 30A and 30B. Coil 32 has an inductance between 1 µH and 1 mH.

[0020] Relay 31 is connected to control unit 25 for its control between its open and closed state.

[0021] As previously stated, the rectifier has two branches, 42 and 44, connected in parallel at its inputs. Each branch has two controlled switches, 42A, 42B, 44A, and 44B. The entire set of cells is connected to the midpoints 42C and 44C of each branch, which are formed by the connection points between the two controlled switches of the same branch. These midpoints constitute the outputs of the rectifier.

[0022] The four switches of the rectifier 34 are connected for their control to the control unit 25 according to a control law known in itself.

[0023] Alternatively, the rectifier 24 is formed by a diode bridge, the structure of which corresponds to that previously described by replacing the switches controlled by diodes.

[0024] In addition, a current sensor 50 is positioned between relay 31 and coil 32 to measure the load current ICh. A voltage sensor 51 is provided between terminals 30A and 30B to measure the input voltage Vin. These sensors are connected to the control unit 25.

[0025] Each cell 12 also includes a sensor 52 for measuring the voltage across the cell's energy storage element 14 and a sensor 53 for measuring the cell's temperature. These sensors are connected to the control unit 25.

[0026] For battery charging, inputs 30A and 30B are connected to a power supply such as the collective power grid under 110 volts or 230 volts AC, a solar panel or another battery.

[0027] The algorithm implemented by the control unit 25 continuously sorts the cells 12 to classify in order of preference the cells whose energy storage elements should be connected or disconnected from the set of connected storage elements according to the input current I ch induced by the input voltage V in.

[0028] To that end, and as illustrated on the figure 2 Voltage and temperature measurements are taken on each cell, and these cells are sorted cyclically. The control unit performs this measurement and sorting at a reduced frequency, for example, 1 Hz. In step 80, a voltage measurement across each cell is taken from sensors 52, and a temperature measurement of each cell is taken from sensors 53. Similarly, a measurement of the current Ich applied to the cells is taken from sensor 50.

[0029] At stage 82, the cells are sorted according to the measurements taken to maintain a balance in tension, temperature and state of health (commonly referred to as SOH, an acronym for State of Health).

[0030] From the sorting performed in step 82, a list of sorted cells noted 84 is updated at each cycle, for example every second when the processing frequency is 1 Hz.

[0031] For battery recharging, and simultaneously with the implementation of the algorithm of the figure 2 , the algorithm of the figure 3 is implemented by control unit 25 to ensure the recharging of the cells.

[0032] Initially, relay 31 is open at step 100 before charging begins.

[0033] At step 102, the control unit 25 performs a measurement of the voltage V in at the input 30 using the sensor 51. Similarly, at step 104, it performs a measurement of the voltage U celli of each cell 12, the index i being representative of the cell considered.

[0034] At step 106, the control unit 25 selects, based on the voltage Vin and a predetermined charging voltage Vload, the storage elements of the cells to be connected in series. The selected cells are such that the sum of the voltages across these cells is between the measured voltage Vin minus a predetermined charging voltage Vload and the voltage Vin.

[0035] The selected cells thus satisfy the relation V in - V load < Σ U celli < V in , where ΣU celli represents the sum of the voltages across the terminals of only the cells selected so that the storage elements are connected in series.

[0036] Advantageously, the voltage V load is chosen, i.e. 4.2V in the example considered of the set of energy storage elements 14.

[0037] The selected cells are chosen primarily in the order of Table 84, which lists the sorted cells. According to a particular embodiment, they are chosen in the reverse order of the cells' state of charge, that is, in the reverse order of the voltage measured across their terminals.

[0038] At step 108, the isolation switches 20 of the selected cells are closed, while the shunt switches 22 of the selected cells are open. Conversely, for the unselected cells, the states of the controlled switches are opposite: the isolation switches 20 are open and the shunt switches 22 are closed. Thus, only the storage elements of the selected cells are connected in series.

[0039] Relay 31 is then closed at stage 108.

[0040] The control unit 25 is suitable for ensuring measurements and cyclic control of cell connection and disconnection at a frequency greater than 1 kiloHertz and preferably substantially equal to 20 kiloHertz.

[0041] For each cycle, the control unit 25 implements the following steps from the flowchart illustrated on the figure 3 .

[0042] At step 110, the charging current I ch is measured by the intensity sensor 31.

[0043] In step 112, the measured current is compared to a defined permissible load current range [I ch_min ; I ch_max ] where I ch_min is a minimum load value and I ch_max is a maximum load value. If each cell accepts a maximum load current of three amperes by design, the maximum load current I ch_max is taken to be 2.4 amperes and the minimum load current I ch_min is taken to be 1.5 amperes.

[0044] If the charging current measured in step 112 is within the charging current range, step 110 is implemented again.

[0045] On the other hand, if the current is outside the acceptable range, the charging current 114 is compared to the minimum charging current I ch_min.

[0046] If the charging current Ich is lower, a storage element in a cell is removed from the series-connected storage elements. To achieve this, the storage element is shunted by controlling the cell's shunt switch, and the cell's isolation switch is opened.

[0047] The cell whose storage state is subtracted is chosen first according to the order of the list contained in table 84.

[0048] Conversely, if at step 114 the charging current I ch is greater than the maximum charging current I ch_max, the storage element of a cell is added at step 118 to the set of storage elements connected in series.

[0049] The cell whose storage element is added serially is chosen from the list of sorted cells in table 84.

[0050] To add the storage element, the shunt switch of the retained cell is opened while the isolation switch of the cell is closed.

[0051] The loop started in step 110 is implemented at a high frequency, for example equal to 20 kilohertz.

[0052] It is thus understood that, regardless of the supply voltage, the cell charging current is kept within the permissible current range, even if the supply voltage is sinusoidal or of any other shape.

[0053] Since the regulation frequency for steps 110 and following is high, and the coil 32 reduces the rate of change of intensity, during a regulation cycle the intensity cannot increase too rapidly and exceed the acceptable intensity for the cells constituting the battery during a cycle.

[0054] Steps 110 and following are implemented again during the next cycle.

[0055] It is understood that initially, during the first charging cycle, the voltage applied to all the selected cells whose storage elements are connected in series during charging is between 0 and Vload, where Vload is equal to the maximum charging voltage of a cell. By implementing the algorithm, the voltage applied to all the cells is lower than the voltage of the most heavily charged cell.

[0056] Furthermore, since each cell has an intrinsic resistance 18 of value R, the maximum current flowing through the cells is equal to V in − Σ U celli Σ R and this current is less than V load Σ R where the ∑ U celli and ∑ U are respectively the sum of the voltages and the sum of the resistances of the selected cells actually connected in series.

[0057] By constructing a cell and as V load is equal to the maximum voltage across the terminals of a cell, V load R is less than the maximum charging current intensity, considered here to be equal to 3A and therefore V load Σ R It is too.

[0058] In addition, coil 32 provides a delay of the current transmitted to all the cells, allowing the frequency of the control unit 25 to ensure a connection of a sufficient number of cells to prevent the current flowing through all the cells from exceeding the maximum intensity taken here as 3 Amperes for the entire duration of the cycle.

[0059] For this purpose, coil 32 is sized so that over a period of one cycle, the current flowing through all the cells cannot exceed 3 Amperes.

[0060] For this purpose, advantageously coil 32 has an inductance greater than R L fln 1 − R L I max U L , where RL is the resistance of coil 32, f is the measurement and control frequency, I max is the maximum load current of a cell, UL is the maximum load voltage of a cell and In is the natural logarithm.

Claims

1. A battery comprising: - a set of cells (12) connected in series, each cell (12) comprising an energy storage element (14) connected in series with a controllable isolation switch (20) and a controllable shunt switch (22) connected in parallel with the energy storage element (14) and the controllable isolation switch (20), - a unit (25) for controlling the isolation (20) and shunt (22) switches of each cell, the controllable switches (20, 22) of the same cell being in opposite states, - a coil (32) connected in series with the set of cells (12) connected in series between two power supply terminals (30A, 30B), - a rectifier (34) whose input is connected to the two power supply terminals (30A, 30B) through the coil (32), the set of cells (12) connected in series being connected to the output of the rectifier (34), and - a sensor (51) for measuring intensity (Ich) of the load current flowing across the power supply terminals (30A, 30B), characterised in that the control unit (25) is capable of measuring the voltage from the sensor (51) and controlling the switches (20, 22) at a frequency greater than 1 kHz according to the intensity measured, and the control unit (25) comprises means for, at each cycle, adding an energy storage element (14) in series to the set of energy storage elements (14) connected in series if the intensity (Ich) measured is greater than a maximum intensity (Ich_max), and shunting an energy storage element (14) in series in the set of energy storage elements (14) connected in series if the intensity measured is less than a minimum intensity (Ich_min).

2. The battery according to claim 1, characterised in that it comprises a sectioning relay (31) connected for being controlled by the control unit (25), capable of interrupting flow of a current between the two terminals (30A, 30B) and in that the control unit (25) is capable of: - while the relay (31) is open, connecting in series storage elements (14) of the cells in such a number that the voltage across the terminals of the storage elements (14) connected in series is between the power supply voltage (Vin) and the power supply voltage (Vin) reduced by a predetermined load voltage (Vload); - closing the relay (31), then the voltage across the terminals of the storage elements (14) connected in series is between the power supply voltage (Vin) and the power supply voltage (Vin) reduced by a predetermined load voltage (Vload).

3. The battery according to claim 1 or 2, characterised in that the rectifier (34) comprises a diode bridge.

4. The battery according to any one of the preceding claims, characterised in that it is without a charger between the power supply terminals (30A, 30B) and the set of cells (12) connected in series.

5. The battery according to any one of the preceding claims, characterised in that the load voltage (Vload) is less than or equal to the maximum load voltage of one of the energy storage elements (14).

6. The battery according to any one of the preceding claims, characterised in that it comprises means (52) for measuring voltage of each energy storage element (14) connected to the control unit (25) and the control unit (25) is capable of controlling the switches (20, 22) of the cells according to the voltage measured across the terminals of each storage element (14).

7. The battery according to any one of the preceding claims, characterised in that the inductance of the coil (32) is greater than R L fln 1 − R L I max U L , where RL is the resistance of the coil (32), f is the measurement and control frequency, Imax is the maximum load intensity of a cell, UL is the maximum load voltage of a cell, and In is the natural logarithm.

8. The battery according to any one of the preceding claims, characterised in that the inductance of the coil (32) is between 1 µH and 1 mH.