Pulsed fast-charging method with regulated-amplitude voltage increments

Abstract

The present invention relates to a method for carrying out pulsed charging of an energy storage element (4) comprising, in a first phase of a charging cycle (E1), commanding a voltage profile (VC) having voltage regulation-driven increments (S1, S2, S3, S4, S5) defining a current profile (IC) in a charging cycle of a predetermined duration, and wherein a voltage increment (S1, S2, S3, S4, S5) is computed at a voltage amplitude at the time of a calculation step i according to a function depending on an estimate of the no-load voltage and on an estimate of the internal resistance at said time, on a coefficient n defining the charging duration and on the nominal capacity of the storage element. The invention is applicable to the fast-charging protocol, in particular for electromobility applications.

Description

[0001] DESCRIPTION

[0002] TITLE: RAPID IMPULSE CHARGING METHOD WITH REGULATED AMPLITUDE VOLTAGE STEPS

[0003]

[0001] The present invention claims priority from French application No. 2301779 filed on 02 / 27 / 2023, the content of which (text, drawings and claims) is incorporated herein by reference.

[0004]

[0002] The field of the invention relates to a method for pulse charging an electrochemical cell energy storage system.

[0005]

[0003] In the high-power energy storage systems industry, manufacturers are seeking to develop fast charging protocols that are optimal in charging speed and avoid cell aging.

[0006]

[0004] Known charging protocols are executed in two successive phases designated by the English acronym CC-CV for "Constant Current" and "Constant Voltage". Figure 1 shows an example of a conventional CC-CV charging protocol where the state of charge SOC ("State of Charge" in English) is represented by the dotted curve. The first phase, referenced PH1, consists of controlling a constant charging current (represented by the CC curve) until the cell voltage (represented by the U curve) reaches a maximum voltage recommended by the manufacturer. Then, these protocols provide a second phase PH2 at constant voltage equal to the maximum voltage. The maximum voltage has the function of avoiding the undesirable chemical phenomenon of lithium deposition, commonly referred to by the English term "lithium plating".This type of charging protocol requires finding a compromise between charging speed and temperature rise to limit cell aging. Indeed, the first conventional charging stage PH1 in CC-CV protocol operates at constant current, which contributes to increasing the cell temperature. The potentiostatic stage of the second phase PH2 significantly increases the overall charging time.

[0007]

[0005] Furthermore, the maximum charging current in CC-CV mode indicated by the cell manufacturer is also determined so as not to generate parasitic reactions which could lead to the degradation of the electrolyte and the deposition of lithium on the negative electrode which could lead to the formation of dendrites and therefore to the observation of a short circuit. Beyond the safety aspects, this phenomenon causes a reduction in the capacity of the element, a degradation of the elements of the battery, in particular the electrolyte, as well as an increase in its internal resistance. This phenomenon therefore accelerates the aging of the cell and consequently its performance decreases.

[0008]

[0006] Due to these constraints, it is therefore difficult to increase the charging speed of a cell in CC-CV protocol and generally leads to significant heating of the cells. For example, for devices conventionally used for electric traction of motor vehicles, by implementing this protocol, it is difficult to achieve charging speeds greater than 2 C-Rate (Charging current value for a complete charge in half an hour).

[0009]

[0007] To overcome this drawback, it is possible to opt either for electrode weights which accept higher cycling currents, to the detriment of the element's capacity, or to use other chemistries, but also offering less energy density.

[0010]

[0008] Furthermore, to avoid the phenomena of "Lithium Plating" it is known to use alternative charging protocols with pulse control. A pulse control alternates a charging pulse and a relaxation phase at zero current, or a polarity inversion phase. These last two phases do not allow sufficient time for the Lithium to be deposited in metallic form at the electrode. This protocol therefore makes it possible to increase the lifespan of the cell even if the maximum voltage limit of 4.2V is exceeded. The following documents describing pulse control protocols are known from the state of the art.

[0011]

[0009] The applicant filed document WO-A1-2021156553 describing a pulsed charging method with voltage regulation with a variable amplitude step depending on the variation in the internal resistance of the cell. This method is advantageous in that it provides a charging technique improving the thermal control of the cells.

[0012]

[0010] Furthermore, the following state of the art has been identified in this document. Document US-B1-6707272 describes a protocol where the pulses are limited by a voltage which depends on the current state of charge of the cell. When the voltage reaches the voltage limit, the protocol controls a relaxation phase. Document EP-A2-1396061 describes a protocol controlling pulses in current regulation. The protocol alternates pulses, chopped at the resonant frequency of the battery, of the order of 100 to 10000 Hz, and having a duration of between 200 and 1500 milliseconds, and relaxation and discharge phases of 1500 milliseconds maximum and 50 milliseconds maximum respectively. Document US-A1-20150028819 is also known, describing in Figure 4 of this same document a four-stage charging protocol.A constant current pre-charge (CC mode), a constant current main charge (CC mode), a pulse charge in current regulation at the constant Isup value (pulse mode) and a constant voltage phase (CV mode). Document US-A1 -20170005497 describes a pulse charge protocol by controlling constant amplitude voltage pulses followed by a relaxation phase to limit the aging effect. According to this protocol, the duration and amplitude of the charge, discharge and relaxation phases are controlled randomly and makes it possible to increase the charge current without damaging the cell. Document WO-A1-2019111226A1 describes a pulse charge protocol controlled by non-linear voltage regulation aimed at reducing the charging time, where the charging voltage is controlled by keeping constant the product, of the derivative with respect to time, of the intensity by that of the voltage.Note that recharging is complete when the cell voltage reaches a maximum value.

[0013]

[0011] The results of the known state of the art reveal that there is no universal solution to reduce the charging time without increasing the aging of the cells. The algorithms generally proposed for batteries are complex and involve developing a control technique specific to each battery system due to the diversity of chemistries and their design.

[0014]

[0012] The object of the present invention is to overcome the aforementioned problems and to propose a rapid charge control of electrochemical cells. In particular, an objective of the invention is to propose a technique for controlling pulsed charging by voltage profile controlled by voltage regulation making it possible to recharge the battery within a given time limit while preserving the life of its operational cycle.

[0015]

[0013] More specifically, the invention relates to a method for pulse charging an energy storage element comprising, during a first phase of a charging cycle, the control of a voltage profile with controlled voltage regulation steps determining a current profile in a charging cycle of a predetermined duration, and in which a voltage step is calculated according to the following relationship [Math 1]:

[0016]

[0015] Where, V(SOCi) is the voltage amplitude of a step calculated at the instant of a calculation step i, Vocv (SOCi) is the estimate of the no-load voltage as a function of the state of charge of the storage element at step i expressed in Volts, Ri is the estimate of the internal resistance of the storage element at step i expressed in milliohms, n is the coefficient determining the predetermined charging duration in hours, Qnominal is the nominal capacity of the storage element in mAh.

[0017]

[0016] The method according to the invention may include the following additional characteristics, alone or in combination:

[0018]

[0017] - the duration of a voltage profile step is limited by the value of the charging current of the current profile relative to a first minimum current threshold, a new voltage profile step value being recalculated at the times when the charging current reaches the first minimum current threshold;

[0019]

[0018] - the value of the first minimum current threshold is variable and is specific to each level of the voltage profile;

[0020]

[0019] - the value of the first minimum current threshold varies in a decreasing manner during the charging cycle between a first current value and a second current value;

[0021]

[0020] - the duration of a voltage profile step is limited to a predetermined duration, a new voltage profile step value being recalculated as soon as the duration of the step reaches the predetermined duration;

[0022]

[0021] - the first phase of the charging cycle ends when the amplitude value of a step reaches a second voltage threshold, then the method comprises a second phase of the charging cycle with voltage pulses, the second phase alternating voltage pulses and relaxation phases, the amplitude of the voltage pulses being calculated according to the relation Math 1;

[0023]

[0022] - the value of the second voltage threshold is equal to the maximum authorized voltage of the energy storage element in nominal operation;

[0023] - the second phase ends when the voltage of the storage element reaches a third predetermined voltage threshold corresponding to a maximum authorized state of charge of the storage element;

[0024]

[0024] - the voltage pulses and the relaxation phases of the second phase form a periodic voltage profile of rectangular, triangular, trapezoidal or sinusoidal shape;

[0025]

[0025] According to the invention, a device for charging an energy storage element is envisaged, comprising a control unit configured to implement the charging method according to any one of the preceding embodiments.

[0026]

[0026] Further contemplated is an assembly comprising the device for charging an energy storage element, the energy storage element and a control unit configured to implement the charging method according to any one of the preceding embodiments.

[0027]

[0027] The invention further relates to an electrified motor vehicle comprising the device for charging an energy storage element, the energy storage element and a control unit configured for implementing the charging method according to any one of the preceding embodiments.

[0028]

[0028] The invention provides a computer program comprising instructions which, when the program is executed by a control unit of a charging device, cause the latter to implement any one of the embodiments of the pulse charging method according to the invention.

[0029]

[0029] The method according to the invention improves performance in terms of charging speed, thermal control and limitation of cell aging.

[0030]

[0030] Other characteristics and advantages of the present invention will appear more clearly on reading the detailed description which follows, comprising embodiments of the invention given as non-limiting examples and illustrated by the appended drawings, in which:

[0031]

[0031] [Fig. 1] is a graph representing a known charge control technique of the direct current control type and described in the preamble to this description.

[0032] [Fig.2] represents a functional block diagram of a charging system of an energy storage system intended to implement the charging method according to the invention.

[0032]

[0033] [Fig. 3] is a graph illustrating a first embodiment of the time-limited voltage step charging method according to the invention during a complete charging cycle of an energy storage system.

[0033]

[0034] [Fig. 4] is a graph illustrating a second embodiment of the current-limited voltage step charging method according to the invention during a complete charging cycle of an energy storage system.

[0034]

[0035] [Fig.5] is a graph describing an alternative embodiment of the voltage profile controlled in the first phase in accordance with the invention.

[0035]

[0036] [Fig.6A] is a graph showing an alternative embodiment of a triangular-shaped voltage profile controlled in the second phase in accordance with the invention.

[0036]

[0037] [Fig.6B] is a graph showing another alternative embodiment of the controlled trapezoidal-shaped voltage profile in the second phase in accordance with the invention.

[0037]

[0038] [Fig7A] shows a test scenario of the charging process according to the invention for an NMC / graphite type electrochemical cell.

[0038]

[0039] [Fig.7B] shows the evolution of the state of charge and temperature during the test execution.

[0039]

[0040] The invention relates to a technique for controlling pulsed charging with a controlled voltage profile. It is particularly applicable to energy storage systems for electromobility applications, in particular electrified motor vehicles, as well as to stationary energy storage systems, in particular for renewable energy installations and grid regulation. These high-power storage systems are composed of an energy storage element composed of individual sub-elements, called electrochemical cells, electrically interconnected in a particular configuration aimed at meeting the electrical specifications of the system. Typically, the cells are electrically connected in series and / or parallel so as to have an electrical capacity and an operating voltage meeting these specifications.The invention applies to the charging of high-power energy storage systems having at their terminals a voltage of several hundred volts, for example 350 Volts or 1000 Volts, or even a maximum voltage of 1500 Volts or more, in particular for stationary storage systems. However, it is envisaged that the charging method applies to the charging of an individual cell or to low-power systems, for example of the order of a few volts or tens of volts, in particular for portable electronic devices. An energy storage element can therefore be an individual cell or a group of cells.

[0040]

[0041] It is recalled that an electrochemical cell is an electrical energy accumulator having two terminals, a positive electrode and a negative electrode, and presenting a voltage of a few volts, most often between 2.3V and 4.2V, approximately. The cells can be of the Lithium-ion type (for example a lithium Nickel Manganese Cobalt oxide NMC), Nickel Cadmium (Ni-cd), Nickel-Metal-Hydride (Ni-MH) for example. More precisely, a Lithium-ion cell is composed mainly of a porous positive electrode, a porous negative electrode, a separator and an electrolyte. The operating principle of a Lithium-ion cell is based on the reversible exchange of lithium ions between the two porous electrodes. The cells can for example be of the Lithium iron phosphate, Lithium polymer or solid electrolyte type.

[0041]

[0042] Furthermore, the charging method according to the invention can be applied to electrochemical battery systems known as multi-level inverter structures. This type of system comprises elementary cell modules interconnected so as to form a multi-level inverter structure distributed in the battery making it possible to connect the battery to an electrical system operating in direct voltage and also in alternating voltage without the intermediary of an inverter. Thus, it can be connected directly to an extended electrical power supply network operating in alternating voltage and to an electrical motor machine. Examples include documents WO-A1-2017 / 153366, WO-A1-2021 / 048477 and FR-A1-3121797 which describe this type of architecture.

[0042]

[0043] Figure 2 schematically represents functional blocks of a charging assembly 1 comprising an energy storage system 4 with electrochemical cells. This assembly comprises an energy source 2, which may be an extended electrical supply network operating at alternating voltage, a charging device 3 provided with an alternating-direct voltage converter making it possible to control the voltage profile in steps and pulses in accordance with the charging method according to the invention. The storage system 4 is for example an electrified motor vehicle battery or a stationary battery. The charging device 3 may be the on-board charger of a vehicle or the charger of a so-called fast charging station directly delivering a direct voltage adapted to the energy storage system 4.Furthermore, the energy storage system 4 is controlled by a control unit 5 for its operation, designated by the term BMS (“Battery Management System”) or BCU (for “Battery Control Unit” in English).

[0043]

[0044] More specifically, in accordance with the invention, the charging device 3 comprises power electronic means capable of controlling a step charging voltage profile or voltage pulse determining a charging current profile of the energy storage system 4. The voltage converter comprises a unit provided with several MOSFET transistors controlled by its computer. These transistors are arranged and controlled by an opening and closing state scheduling program to convert the input alternating voltage (single-phase or three-phase) into a charging voltage according to the voltage profile.

[0044]

[0045] More specifically, the control unit 5 is equipped with an integrated circuit computer and electronic memories, as well as means for acquiring operating parameters of the storage system 4, such as the temperature, the voltage, the value of the charge / discharge current passing through the cells, the state of charge (SOC) and the internal resistance of a cell, in particular. The control unit 5 further comprises models or maps recorded in memory for characterizing the cells obtained experimentally, in particular maps of the open-circuit voltage as a function of an estimate of the state of charge and the internal resistance of the cells. Data communication means are provided between the storage system 4 and the charging device 3 allowing the exchange of information concerning the electrical parameters of the storage system 4 and the charging device 3 for implementing the charging method according to the invention.

[0045]

[0046] The state of charge refers to the level of charge of the battery expressed by a ratio between the quantity of energy stored at a given time and the maximum quantity of energy storable at a given time, generally expressed in percent. The state of charge can be estimated at any time from a known initial state of charge and by coulometric measurement between two times of measurement of the charging current according to the following relationship:

[0046]

[0047] [Math 2]:

[0047]

[0049] Where, 7] is the average current at measurement step i, Ât[ is the estimated average time between the two measurement steps i and i+1 and So is the estimated state of charge at measurement step i.

[0048]

[0050] Open circuit voltage (OCV) is a measure of the cell's electromotive force. This measurement depends on the cell's state of charge. OCV is the voltage difference across a cell's terminals when the circuit is open, i.e., in a no-charge condition.

[0049]

[0051] Internal resistance is defined as the opposition to the current flow through the cell. The basic parameters that affect internal resistance are ohmic resistance and ionic resistance which are temperature dependent. Ohmic resistance includes the resistance of cell components like positive electrode, negative electrode and current collector. Whereas ionic resistance is the resistance shown mainly by the electrolyte to the flow of ions. It is assumed that ionic resistance is negligible compared to ohmic resistance because the polarization effect is slow compared to ohmic resistance.

[0050]

[0052] The charge rate ratio or C-rate in English is defined as a charge or discharge current value defining a speed at which a battery or cell is fully charged or discharged. For example, 1 C-rate corresponds to a current value allowing full charge or discharge in 1 hour, 3 C-rate corresponds to a current value allowing charge or discharge in 20 minutes and 0.5 C-rate in 2 hours.

[0051]

[0053] A charging cycle is understood to mean a charging sequence, i.e. from 0% to 100% SOC, or more generally in the case of electrified vehicles from 10% to 90% SOC. A charging cycle can also be defined by the instant from which a charge is triggered until the energy source is stopped and disconnected.

[0052]

[0054] The characterization of the cells consists of determining, by experimental techniques known to those skilled in the art in the field of electrochemical cells, the characteristic parameters of the cells in operation, such as the internal resistance and the OCV. For example, the internal resistance can be mapped using the so-called current interrupt technique (CIT) present in the EC-lab software from Biologie ®. The OCV can be mapped by measuring the voltage at different states of charge under given temperature conditions. The characterization parameters are recorded in the memory of the battery control unit and can be determined at any time.

[0053]

[0055] For example, the OCV can be determined at each instant from a map taking as input an estimate of the state of charge and the internal resistance from a map taking as input a measurement of the temperature and an estimate of the state of charge.

[0054]

[0056] The control functions of the control unit 5 and the charging device 3 can be implemented in the form of software modules (or computer modules (or even “software”)), or electronic circuits (or “hardware”), or a combination of electronic circuits and software modules such as for example circuits of the ASIC (“Application Specific Integrated Circuit” type in English), or DSP (“Digital Signal Processor” in English).

[0055]

[0057] The charging device 3 is configured for implementing the pulse charging method according to the invention comprising two phases making it possible to ensure a complete charging cycle within a predetermined duration while limiting the effects of aging of the cells.

[0056]

[0058] Figures 3 and 4 describe two embodiments of the charging method for a charging cycle between 10% of the SOC and 90% of the SOC. The first phase E1 with voltage steps and the second phase E2 with voltage pulses consist of controlling a voltage profile with voltage steps or voltage pulses of controlled amplitude according to the following relationship:

[0057]

[0059] [Math 3]:

[0058]

[0061] Where, V(soci) is the voltage amplitude of a step calculated at the instant of a calculation step i, Vocv (SOCi) is the estimate of the no-load voltage as a function of the state of charge of the storage element at step i expressed in Volts, Ri is the estimate of the internal resistance of the storage element at step i expressed in milliohms, n is the coefficient determining the predetermined charging duration in hours, Qnominai is the nominal capacity of the storage element in mAh.

[0059]

[0062] For example, the coefficient n has a value of 1 / 3 for a desired charging time of 20 minutes for a complete charging cycle of an energy storage element.

[0060]

[0063] The value of the voltage amplitude is judiciously controlled over the course of the charging cycle as a function of a first component dependent on the monitoring of the no-load voltage OCV and the second component aiming on the one hand to compensate for the ohmic losses linked to the variation in the state of charge of a cell and on the other hand to limit the duration of the charging cycle. This voltage control makes it possible to control the charging current profile so that the complete charging cycle takes place in the desired time.

[0061]

[0064] More precisely, the first phase is initiated from the beginning of the charging cycle. The initial state of charge for triggering the first phase may be between 0% and 70% of the SOC of the energy storage element, preferably the first phase is triggered when the SOC is at least equal to or greater than 10%. Generally, in automotive applications, discharging the battery below an SOC of 10% is prohibited. Consequently, the first phase with a voltage profile controlled according to the amplitude defined by the Math 3 relationship is therefore applied from the triggering of a charging cycle. However, below 10% of SOC, direct current charging control may be provided due to the high internal resistance in this operating zone of a cell, for example at a charging speed ratio of 0.5 C-rate.

[0062]

[0065] With reference to Figures 3 and 4, in this example of the protocol, the first phase E1 comprises 5 calculation steps or levels, referenced S1, S2, S3, S4 and S5, and the second phase E2 comprises two calculation steps or levels referenced S6 and S7. Other quantities of steps are conceivable for a load cycle, which may be between 5 and 100 for example.

[0066] In the first phase E1, the voltage levels evolve in an increasing manner and these levels preferably follow one another without incorporating relaxation phases, thus presenting a staircase-shaped voltage profile. However, it is envisaged that the first phase E1 may further comprise relaxation phases between each level, as shown in Figure 5.

[0063]

[0067] The voltage of the first stage S1 can be between 3.7 Volts and 3.9 Volts. The first phase E1 is completed when the amplitude of a voltage stage controlled by the charging device 3 and calculated according to the relation Math 3 becomes equal to or greater than the maximum voltage threshold Smax. Smax corresponds to the maximum authorized voltage value of the cell or battery, designated by the English term “upper cut-off voltage”. This threshold Smax is determined by the manufacturer of the charged energy cell and depends mainly on the chemistry. For an individual cell of the NMC type, this threshold Smax is generally close to 4.2 volts.

[0064]

[0068] In the second phase E2, the voltage pulses alternate with relaxation phases. The voltage pulses have constant voltage values ​​calculated according to the relation Math 3 at each calculation step S6 and S7 of a predetermined duration. During the second phase with voltage pulses, the charge cycle ratio can be configured for example according to a pulse duration of 0.8s and 0.2s then constituting a charge duration factor ("duty cycle") of 80%. The amplitude values ​​of the pulses during the second phase E2 are higher than the threshold Smax, for example between 4.2 volts and 4.65 volts. This high voltage makes it possible to reduce the charging time in the last phase between 80% and 90% of SOC. The relaxations, which are obligatory unlike the first E1, make it possible to avoid undesirable chemical reactions of lithium deposition and heating of the cells. Therefore, the aging effect is reduced.Relaxations allow time for lithium ions to properly deposit at the receiving site and provide fluidity to the system.

[0065]

[0069] Two embodiments of the charging protocol are now described. Figure 3 shows a first embodiment where the levels S1, S2, S3, S4 and S5 of the voltage profile are limited by a predetermined duration during the first phase E1. To simplify the graphical representation, in this example the charging cycle ranging from 10% to 90% of SOC is carried out by controlling 7 voltage amplitude levels in accordance with the relation Math 3. Each level has an equal duration predetermined by the number of levels sought and the desired charging duration. According to this first embodiment, as soon as the level duration reaches the predetermined duration, a new level value is controlled at a higher value to compensate for the ohmic losses.It is observed that at the start time of each step, the current profile IC starts at a first maximum value and then decreases exponentially due to the progressive increase in internal resistance. When a new step is controlled at a higher value, the charging current is increased. Phase E1 is controlled until the value of the voltage step reaches the threshold Smax. At the end of S5, the second phase E2 is triggered and the voltage profile is regulated according to a pulse cycle of 80% charge ratio. The relaxation is chosen at a voltage value determining a zero charging current IC during the relaxation. It is observed that the current profile IC resulting from the voltage pulses starts at a maximum value and then decreases exponentially.

[0066]

[0070] The step durations t1, t2, t3, t4, t5 are of equal value, for example within a range from 5s to 90s. The durations t6 and t7 of the calculation steps of the second phase E2 are in this example of greater value. The number of steps, depending on the chosen duration and the duration of the load cycle, can be within a range from 6 to 90 steps.

[0067]

[0071] A variant of this first embodiment provides that the successive durations t1, t2, t3, t4, t5 are set to values ​​that are distinct from each other and evolve in a decreasing manner. Another variant of this first embodiment provides that the parameterized durations are chosen randomly or chosen so as to favor the duration of one level over the other levels. For example, an intermediate level in a SOC zone of the cell where it has been observed that the internal resistance increases less quickly can be maintained for a longer duration.

[0068]

[0072] Figure 4 shows a second embodiment of the charging method where the voltage levels are limited by the charging current value IC relative to a current threshold l_lim nspecific to each step Sn. In this example, 7 voltage steps S1, S2, S3, S4, S5, S6 and S7 are calculated according to the relation math 3. A new voltage amplitude value is calculated as soon as the current reaches or crosses the minimum limit l_lim n associated with the Sn level. The values ​​of the current limits I _lim n evolve in a decreasing manner as the recharge progresses. For example, depending on the value of n which is set these values ​​can vary in a speed ratio range from 4 C-Rate to 2 C-Rate allowing a recharge up to 80% of the SOC in 20 minutes.

[0069]

[0073] With reference to Figure 4, for the sake of clarity only the limits IJ im 1 , IJim3 and IJim5 are shown, for the voltage steps S1 , S3 and S5 respectively. The current limits IJim2 and IJim4 are not indicated but are intended to trigger the calculation of a new step value of the voltage profile. As can be seen, at the first voltage step S1 , the current profile IC decreases exponentially. As soon as the current IC reaches the threshold IJiml , the method calculates a new step value S2, likewise for step S2, as soon as the current IC reaches the limit IJim2, a new step value S3 is calculated, and so on until the step amplitude reaches the maximum permitted voltage threshold Smax.

[0070]

[0074] At the end of S5, the second phase E2 is triggered and the voltage profile VC is regulated according to a cycle of voltage pulses of 80% load ratio where the duration of each step of calculation of the voltage amplitudes is predetermined. The relaxation is chosen at a voltage value determining a zero load current IC during the relaxation. It is observed that the current profile IC resulting from the voltage pulses starts at a maximum value then decreases exponentially. During the second phase E2, the voltage profile is a periodic profile of rectangular shape.

[0071]

[0075] In Figure 5, a graph is shown describing an alternative embodiment of the first phase E1 where the charging device controls the voltage profile regulated in voltage according to voltage steps Sn calculated in accordance with the relation Math 3 and in which relaxation phases are provided between each step.

[0072]

[0076] In a variant, it is provided that during phase E1, the voltage levels calculated in accordance with relation Math 3 and relaxation phases alternate over a predetermined SOC range and that over another SOC range the charging method controls only the voltage levels.

[0073]

[0077] In another variation, it is provided that during phase E1 in the same charging cycle, the voltage steps can be limited by a predetermined duration over a first SOC range and that the voltage steps are limited by a current limit over a second SOC range.

[0078] Figures 6A and 6B show two other variants of the voltage profile for the second phase E2. The duration in seconds is shown on the abscissa and the voltage value of the charging voltage profile VC on the ordinate. Instead of being rectangular in shape, the voltage profile controlled by the charging device can be triangular in shape, as can be seen in Figure 6A. A voltage pulse then corresponds to the part having a positive slope, the duration t1, and the relaxation phase then corresponds to the part having a negative slope, the duration t2. The voltage peak of the triangular shape is calculated according to the relation Math 3.

[0074]

[0079] In Figure 6B, the voltage profile controlled by the charging device is trapezoidal in shape. A voltage pulse then corresponds to the part having a positive slope, duration t1, and the relaxation phase then corresponds to the part having a negative slope, duration t3. Duration t2 corresponds to the voltage plateau or step of the pulse. The value of the voltage plateau is calculated according to the relation Math 3.

[0075]

[0080] The negative slope phases of the voltage profile make it possible to limit the lithium deposition effect and to limit aging. It makes it possible to periodically slow down the lithium ion flow. These profiles are particularly interesting for quickly finalizing the recharge in the 80% to 90% SOC range. Other shapes are possible, such as a sinusoidal shape.

[0076]

[0081] Figure 7A shows a test scenario for an NMC / graphite cell with the following specifications: 3.6 volts and 200mAh. The graphs in the upper part show the voltage profile controlled in accordance with the invention and below the current profile resulting from the controlled voltage profile. On the abscissa is the duration of the charging cycle, which is completed in less than 12 minutes. In this scenario, the cell is charged from 0% to 80% of the SOC. The table in the lower part shows the parameters of the voltage profile and the resulting current profile, including the voltage amplitude and duration of each step, the average charging current, and the pulse and relaxation duration during the second pulse phase.

[0077]

[0082] In Figure 7B, two graphs show the evolution of the SOC expressed between 0 and 1 and the temperature in degrees Celsius of the cell during the execution of the test scenario.

[0078]

[0083] The charging method has the advantage of reducing the battery recharge time, resulting in a better suitability of the electric vehicle compared to the market. In addition, it makes it possible to limit the increase in temperature of the battery during recharging, with the consequence that the thermal power to be evacuated by the cooling system is greatly reduced, implying a reduction in the cost of the architecture of the battery cooling system. The method also allows the battery life to be increased, which makes it possible to guarantee the customer a duration equivalent to the vehicle life. In addition, due to the improved thermal control, it is possible to achieve rapid recharging of the car even in hot climates. More generally, this charging solution contributes to lowering the selling price of electric vehicles.

[0079]

[0084] The invention advantageously relates to rechargeable electrified, electric or hybrid vehicles known as “Plug-in” comprising a charging device according to the invention and a battery capable of being charged according to a rapid charging protocol. The improvement in performance in terms of charging speed and temperature control makes it possible to consequently increase the number of rapid charges accepted by the vehicles in a vehicle life cycle.

[0085] The invention is described in the above by way of example. It is understood that the person skilled in the art is able to produce different variant embodiments of the invention by associating, for example, the different characteristics above taken alone or in combination, without departing from the scope of the invention.

Claims

CLAIMS 1. Method for pulse charging an energy storage element (4) characterized in that it comprises, during a first phase of a charging cycle (E1), the control of a voltage profile (VC) with steps (S1, S2, S3, S4, S5) controlled by voltage regulation determining a current profile (IC) in a charging cycle of a predetermined duration, and in which a voltage step (S1, S2, S3, S4, S5) is calculated according to the following relation [Math 4]: (soct) where, V(SOCi) is the voltage amplitude of a step calculated at the instant of a calculation step i, Vocv (SOCi) is the estimate of the no-load voltage as a function of the state of charge of the storage element (4) at step i expressed in Volts, Ri is the estimate of the internal resistance of the storage element (4) at step i expressed in milliohms, n is the coefficient determining the predetermined charging duration in hours, Qnominal is the nominal capacity of the storage element (4) in mAh.

2. Charging method according to claim 1 wherein the duration of a level of the voltage profile (VC) is limited by the value of the charging current of the current profile relative to a first minimum current threshold (I _lim n ), a new voltage profile step value (VC) being recalculated at the times when the load current (IC) reaches the first minimum current threshold (l_l im n ).

3. Charging method according to claim 2 wherein the value of the first minimum current threshold (l_lim n ) is variable and is specific to each level (Sn) of the voltage profile.

4. Charging method according to claim 3, wherein the value of the first minimum current threshold (l_lim n ) varies in a decreasing manner during the charge cycle between a first current value and a second current value.

5. Charging method according to any one of claims 1 to 4 wherein the duration of a step of the voltage profile (VC) is limited to a predetermined duration (t1, t2, t3, t4, t5), a new step value of the voltage profile (VC) being recalculated as soon as the duration of the step reaches the predetermined duration (t1, t2, t3, t4, t5).

6. Charging method according to any one of claims 1 to 5 in which the first phase (E1) of the charging cycle ends when the amplitude value V(SOCi) of a level reaches a second voltage threshold (Smax), then the method comprises a second phase (E2) of the charging cycle with voltage pulses, the second phase alternating voltage pulses and relaxation phases, the amplitude of the voltage pulses being calculated according to the relation Math 4.

7. Method according to claim 6, in which the value of the second voltage threshold (Smax) is equal to the maximum permitted voltage of the energy storage element (4) in nominal operation.

8. Method according to claim 6 or 7 in which the second phase (E2) ends when the voltage of the storage element (4) reaches a third predetermined voltage threshold corresponding to a maximum authorized charge state of the storage element (4).

9. Charging method according to any one of claims 6 to 8 wherein the voltage pulses and the relaxation phases of the second phase (E2) form a periodic voltage profile of rectangular, triangular, trapezoidal or sinusoidal shape.

10. Charging device (3) of an energy storage element (4) comprising a control unit configured for implementing the charging method according to any one of claims 1 to 9.

11. Assembly comprising the charging device (3) of an energy storage element (4), the energy storage element (4) and a control unit configured for implementing the charging method according to any one of claims 1 to 9.

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