Patent Application
20160064964
The present document relates to the charging of rechargeable batteries. In particular, the present document relates to the charging of battery stacks comprising a plurality of battery cells.
Many electrical applications require the transfer of energy from a power supply or electric energy supply (e.g. a mains power supply) to an electronic device comprising a battery. In particular, the electric energy may be transferred from a charging unit (receiving power from the mains power supply) and the electronic device comprising the battery. The battery (or battery stack) may comprise a plurality of battery cells which are arranged in series, thereby increasing the energy storage capacity of the rechargeable battery. The battery cells may e.g. be lithium-ion based battery cells.
a shows an example battery 100 (also referred to as battery stack or a storage) comprising three battery cells 101, 102, 103 which are arranged in series. The battery cells may also be referred to as storage cells. The battery cells 101, 102, 103 are represented by capacitors. The plurality of different battery cells 101, 102, 103 may have different respective voltage requirements with regards to the voltage required in order to store electric energy within the respective battery cell, i.e. in order to charge the respective battery cell. A conventional charging unit is typically only configured to provide an overall voltage drop across the entire battery 100. The individual voltage drop at the individual battery cells 101, 102, 103 cannot typically be controlled. This may lead to different charging levels within the different battery cells 101, 102, 103.
The present document addresses the above mentioned technical problem. In particular, the present document describes a charging system and a corresponding method (as well as a corresponding discharging system and method) which are configured to provide a consistent charging/discharging of the plurality of battery cells 101, 102, 103 of a rechargeable battery 100. The systems and methods may be used to balance the charging levels of the different battery cells 101, 102, 103 of a battery stack 100. According to an aspect, a system configured to charge a first subset of storage cells from a storage (e.g. a storage for electric energy) comprising a serial arrangement of storage cells is described. The system may be implemented as an electronic circuit. The system may be implemented in conjunction with a charger for an electronic device comprising the storage for electric energy. The storage may also be referred to as a storage stack. The storage may comprise (or may be) a battery and the storage cells may comprise (or may be) battery cells. The storage of energy may be performed in a chemical manner (as is typically the case for battery cells) and/or in a capacitive manner (as is typically the case of capacitors and super capacitors). A storage cell may comprise one or more battery cells and/or one or more capacitors in parallel and/or in series. The first subset (or any other subset) may comprise one or more directly adjacent storage cells from the serial arrangement of storage cells.
The system may comprise a driver circuit configured to generate an AC voltage at an AC frequency from a power source at a DC voltage. In other words, the driver circuit may be configured to generate AC (alternating current) electrical power (also referred to as electrical energy) from DC (direct current) electrical power provided by a power source. In yet other words, the driver circuit may be configured to generate an AC voltage comprising a frequency component at or with an AC frequency. The frequency component may be or may comprise a sinusoidal frequency component at the AC frequency. The power source may comprise a charger configured to provide a (DC) charge current to the storage at the DC voltage. As such, the system may be configured to individually control the amount of electrical power which is provided to the first set of storage cells. Alternatively or in addition, the power source (also referred to as the electrical energy source) may comprise another subset of storage cells from the storage. The first subset may be different from the another subset of storage cells. As such, the system may be configured to redistribute electrical energy from the another subset of storage cells to the first subset of storage cells.
The driver circuit may comprise a half-bridge comprising a high-side switch and a low side switch which are opened and/or closed in accordance to the AC frequency. The high-side switch and the low-side switch may be opened and/or closed such that at a particular time instant at the most only one of the high-side switch and the low side switch is closed. The AC voltage may be provided at a midpoint of the half-bridge.
The system may comprise a first resonance circuit configured to amplify and/or attenuate the AC voltage as a function of the AC frequency, to yield a modified AC voltage. In particular, an amplitude of the AC voltage may be amplified and/or attenuated. The resonance circuit may exhibit a resonance frequency, such that the first resonance circuit provides a (at least locally) maximum gain for the resonance frequency. On the other hand, the gain may be lower (compared to the gain at the resonance frequency) for AC frequencies which are higher or lower than the resonance frequency. By way of example, the first resonance circuit may comprise a LC and/or a LLC circuit.
Furthermore, the system may comprise a first rectifying unit configured to generate a modified DC voltage from the modified AC voltage. The first rectifying unit may be configured to provide power at the modified DC voltage to the first subset of storage cells. As such, the first rectifying unit may be configured to be or to act as a DC power source, which is configured to provide electrical energy at the modified DC voltage. The rectifying unit may comprise one or more diodes and/or switches. The switches referred to in the present document may comprise transistors, such as metal oxide semiconductor field effect transistors. In particular, the rectifying unit may be configured to perform half-wave or full-wave rectification of the modified AC voltage.
Overall, the driver circuit, the first resonance circuit and the first rectifying unit may form a DC-to-DC power converter which is configured to convert electrical energy at the DC voltage into electrical energy at the modified DC voltage. As such, the system may comprise a DC-to-DC power converter which is configured to convert electrical energy at the DC voltage into electrical energy at the modified DC voltage.
The system may comprise a controller configured to control the driver circuit to generate the AC voltage at the AC frequency. In other words, the controller may be configured to control the switches of the driver circuit to generate the AC voltage with the AC frequency. Furthermore, the controller may be configured to determine the AC frequency in dependence on charging voltage requirements of the first subset of storage cells. By way of example, the charging voltage requirements may be indicative of a minimum voltage drop at the first subset of storage cells, which is required for charging the subset of storage cells.
The controller may be configured to control the amount of electric energy which is provided to the first subset of storage cells. The amount of electric energy which is provided to the first subset of storage cells may be controlled by adjusting the AC frequency. The controller may be configured to control the charging current towards the first subset of storage cells by adjusting the AC frequency.
The system may comprise a first set of switches configured to couple or decouple the rectifying unit to or from the first subset of storage cells. In particular, the system may comprise switch pairs for each storage cell of the storage, thereby allowing the rectifying unit to be coupled to and/or decoupled from each one of the storage cells of the storage. As such, a single resonance circuit may be used to charge (and/or discharge) various storage cells or subsets of storage cells.
The controller may be configured to control the first set of switches to couple the rectifying unit to the first subset of storage cells during a first pre-determined isolated time slot assigned to the charging of the first subset of storage cells. Different (disjoint) time slots may be assigned to different subsets of storage cells, thereby enabling a time multiplexing of the different subsets of storage cells. Within a given time slot, the set of switches may be controlled to couple the rectifying unit to the particular subset of storage cells, to which the given time slots is assigned to. On the other hand, the controller may be configured to control the first set of switches to decouple the rectifying unit) from the first subset of storage cells (and/or to anther subset of storage cells) during a second pre-determined isolated time slot which is not assigned to the charging of the first subset of storage cells (and/or of the another subset of storage cells).
The controller may be configured to receive an indication of the DC voltage. In particular, the controller may be configured to determine variations of the DC voltage. Furthermore, the controller may be configured to determine the AC frequency in dependence on the DC voltage, such that relative absolute variations of the modified DC voltage are at or below a pre-determined variation threshold. As such, the controller may be used to stabilize the modified DC voltage, subject to variations of the DC voltage.
The resonance frequency of the first resonance circuit may be adapted based on the charging voltage requirements of the first subset of storage cells. In particular, the resonance frequency of the first resonance circuit may be adapted to the minimum voltage drop at the first subset of storage cells, which is required to charge the first subset of storage cells.
As indicated above, the system may comprise an LLC circuit. In particular, the system may comprise a transformer comprising a primary inductor and a first and a second secondary inductor which are magnetically coupled to the primary inductor. The first resonance circuit may comprise the first secondary inductor. Furthermore, the system may comprise a second resonance circuit comprising the second secondary inductor. The second resonance circuit may be used (e.g. in conjunction with a further rectifying unit) to charge a second subset of storage cells from the storage. As such, a plurality of resonance circuits may be provided for a corresponding plurality of subsets of storage cells, using a plurality of secondary inductors of the transformer. The plurality of resonance circuits (notably the first and second resonance circuits) may have different resonance frequencies. As indicated above, the different resonance frequencies may be adapted to the voltage requirements (for charging/discharging) of the corresponding plurality of subsets of storage cells.
According to a further aspect, a system configured to discharge a subset of storage cells from a storage comprising a serial arrangement of storage cells is described. The system may comprise similar components and features as the system configured to charge the subset of storage cells. In particular, the system may comprise a driver circuit configured to generate an AC voltage at an AC frequency from power at a DC voltage, wherein the power is taken from (or drawn from) the subset of storage cells. Furthermore, the system may comprise a resonance circuit configured to amplify and/or attenuate the AC voltage as a function of the AC frequency, to yield a modified AC voltage. In addition, the system may comprise a rectifying unit configured to generate a modified DC voltage from the modified AC voltage, and to provide power at the modified DC voltage.
An output of the rectifying unit may be coupled to an input of the serial arrangement of storage cells. The input of the serial arrangement of storage cells may e.g. correspond to a high voltage pin of the storage, wherein the storage typically comprises a high voltage pin and an opposed low voltage pin (which may be coupled to ground). The system may be configured to provide the power at the modified DC voltage to one or more storage cells of the storage.
According to a further aspect, a method for charging a first subset of storage cells from a storage comprising a serial arrangement of storage cells is described. The method comprises generating an AC voltage at an AC frequency from a power source at a DC voltage. The method proceeds in amplifying and/or attenuating the AC voltage as a function of the AC frequency, to yield a modified AC voltage. Furthermore, the method comprises generating a modified DC voltage from the modified AC voltage. In addition, the method may comprise providing power at the modified DC voltage to the first subset of storage cells.
According to another aspect, a method for discharging a subset of storage cells from a storage comprising a serial arrangement of storage cells is described. The method comprises generating an AC voltage at an AC frequency from power at a DC voltage taken from the subset of storage cells. Furthermore, the method comprises amplifying and/or attenuating the AC voltage as a function of the AC frequency, to yield a modified AC voltage. In addition, the method comprises generating a modified DC voltage from the modified AC voltage.
According to a further aspect, a software program is described. The software program may be adapted for execution on a processor and for performing the method steps outlined in the present document when carried out on the processor.
According to another aspect, a storage medium is described. The storage medium may comprise a software program adapted for execution on a processor and for performing the method steps outlined in the present document when carried out on the processor.
According to a further aspect, a computer program product is described. The computer program may comprise executable instructions for performing the method steps outlined in the present document when executed on a computer.
It should be noted that the methods and systems including its preferred embodiments as outlined in the present document may be used stand-alone or in combination with the other methods and systems disclosed in this document. In addition, the features outlined in the context of a system are also applicable to a corresponding method. Furthermore, all aspects of the methods and systems outlined in the present document may be arbitrarily combined. In particular, the features of the claims may be combined with one another in an arbitrary manner.
In the present document, the term “couple” or “coupled” refers to elements being in electrical communication with each other, whether directly connected e.g., via wires, or in some other manner.
The invention is explained below in an exemplary manner with reference to the accompanying drawings, wherein
a illustrates an example rechargeable battery comprising a plurality of battery cells;
b shows an example charging system configured to adjust the charging level of a particular one of the plurality of battery cells;
a and 2b show an example charging system and a corresponding discharging system configured to control the energy level of a particular one of the plurality of battery cells;
a, 3b, 3c and 3d show block diagrams of example charging systems configured to control the charging level of a plurality of battery cells;
As indicated in the background section, the present document addresses the technical problem of a consistent charging of a rechargeable battery 100 comprising a plurality of battery cells 101, 102, 103. A problem in this context is that one or more of the plurality of battery cells 101, 102, 103 may receive a reduced current during charging or that the charge can only be added to one or more of the plurality of battery cells 101, 102, 103, while no charge is added to the other battery cells. This technical problem may be caused to the fact that converters (or charging units) are not flexible with respect to different voltage requirements of the different battery cells 101, 102, 103 of a battery 100. In other words, charging units may not be configured to control the individual voltage drop at the individual battery cells, in order to ensure that the individual voltage drop exceeds a minimum, battery cell dependent, voltage level.
It is therefore desirable to provide a system which allows for a flexible balancing of the plurality of different battery cells 101, 102, 103 during charging and/or discharging. In particular, the system may be configured to provide flexible input/output voltages for the charging/discharging of one or more of the plurality of battery cells 101, 102, 103.
b shows a block diagram of an example system 120 for charging the second battery cell 102 of a battery 100 comprising the plurality of battery cells 101, 102, 103. The system 120 comprises a charger 110 configured to provide electrical energy to be stored within the battery 100. The charger 110 may induce an overall voltage drop at the serial arrangement of battery cells 101, 102, 103, wherein the overall voltage drop is divided into individual voltage drops across the battery cells 101, 102, 103 respectively. The individual voltage drops across the battery cells 101, 102, 103 typically depends on pre-determined characteristics of the battery cells (e.g. the capacitance of the battery cells).
As indicated above, the individual voltage requirements for charging the different battery cells 101, 102, 103 may differ for the different battery cells 101, 102, 103. The charger 110 is typically only configured to control the overall voltage drop, without being able to adjust the individual voltage drops with respect to one another. As a result of this, the charging level of the different battery cells 101, 102, 103 may differ.
The charging system 120 of
As such, it is proposed to make use of a resonant converter (comprising e.g. a LRC, inductance resistance capacitance, circuit). By changing the frequency of the alternating voltage (using the driver circuit 124), the resonant converter may be operated as a buck or a boost converter (i.e. as a step-down converter or as a step-up converter).
By doing this, the individual voltage drop at the battery cell 102 may be increased or lowered. In particular, by changing the frequency of the alternating voltage (also referred to as the AC frequency), the individual voltage drop across the battery cell 102 may be adjusted (e.g. in accordance to the minimum voltage drop required for charging the battery cell 102).
The charging system 120 further comprises a rectifying unit 121 configured to convert the alternating voltage at the output of the LC circuit 125, i.e. at the output of the resonance circuit, into a DC voltage. In the illustrated example, the rectifying unit 121 comprises two diodes configured to rectify the positive half wave and the negative half wave of the alternating voltage at the output of the LC circuit 125. As such, the illustrated rectifying unit 121 comprises a full wave rectifier. Alternatively, the rectifying unit 121 may comprise a half wave rectifier (e.g. using only a single diode configured to let pass only one of the two half waves of the alternating voltage).
In the illustrated example of
a and 2b illustrate the operation of the charging system of
When operated in the buck function (
In the boost function (
As such, the charging levels of the plurality of cells 101, 102, 103 may be balanced. The balancing may be performed at any time, even at small load conditions. It may be possible to redistribute the electrical energy among any of the plurality of cells 101, 102, 103 only using the buck function (shown in
A benefit of the described charging/balancing scheme is the low power dissipation. This means that a controlled charging/discharging of the battery cells of a battery stack 100 may be performed in a power efficient manner.
Time multiplexing schemes may be used to charge/discharge individual battery cells. In particular, different time slots may be assigned to different battery cells. The charging/discharging of a battery cell may be performed within the assigned time slot of the battery cell. By doing this, a single resonant converter may be used for the charging/discharging of a plurality of individual battery cells. As such, in the different time slots the cells may be balanced individually. Alternatively or in addition, two or more cells in series may be balanced at the same time (using an appropriate switch matrix).
The switch pairs may be used to couple one of the plurality of battery cells 101, 102, 103 to the output of the rectifying unit 121, thereby allowing the selected one of the plurality of battery cells 101, 102, 103 to be charged. If one of the switch pairs is closed, the other switch pairs may be open, thereby decoupling the respective others of the plurality of battery cells 101, 102, 103 from the output of the rectifying unit 121.
Furthermore, the switches (e.g. the transistors) 601, 602, 603, 604, 605, 606 may be controlled to couple a subset (e.g. a subseries) of the serial arrangement of battery cells 101, 102, 103 to the single resonance circuit 625. By way of example, the switches 601 and 605 may be closed, while keeping the other switches open, thereby coupling the subset (i.e. the sub serial arrangement) of cells 101, 102 to the resonance circuit 615. By doing this, the subset of cells may be charged (or discharged) jointly.
a to 3d illustrate the use of LLC converters as resonant converters for the charging/discharging of the cells 101, 102, 103 of a battery stack 100. The LLC converter of
Furthermore, the converter comprises a primary capacitor 302, as well as resonance capacitors 323, 123. The resonance capacitors 323, 123 may be different, in order to provide different resonance frequencies for the different cells 101, 102. In particular, the different resonance capacitors 323, 123 may be adjusted individually to the respective different cells 101, 102. In addition, the converter comprises rectifying units 321, 121 configured to provide a DC voltage to the respective cells 101, 102. In the illustrated example, a half-wave rectifier (comprising a single diode) is used.
The LLC converters of
In a similar manner, the resonance circuits 325, 125 of
The system of
The supply variations of the driver can be compensated with the frequency. This means that the AC frequency 402 of the alternating voltage may be adapted (e.g. regulated) to provide a constant output voltage at a respective battery cell 101, 102, 103, even subject to variations of the power supply of the driver 124. The benefit of using an LLC converter comprising a transformer is that no selecting switches are required to couple the resonant converter to a particular one or more of the battery cells 101, 102, 103. This may be beneficial for high voltage applications, where the voltage may exceed the operating voltages of the switching technology.
c shows an example of a system comprising an LLC converter, where the rectifying units are implemented as switches 351, 352, 353 (e.g. transistors such as metal oxide semiconductor field effect transistors, MOSFET), providing a half wave rectifier.
The configuration of
It should be noted that the charging/discharging systems described in the present document may comprise a controller (not shown) configured to control the driver circuits to modify the AC frequency 402. The controller may be aware of the voltage requirements of the different battery cells of the battery 100. Furthermore, the controller may be aware of or may be configured to determine the AC frequencies 402 which adapt the output voltage of the resonance circuit(s) in accordance to the voltage requirements of the different battery cells. In addition, the controller may be configured to control the switches of the charging/discharging system (e.g. in order to implement a time multiplexing of the different battery cells). Furthermore, the controller may be configured to adjust the AC frequency 402 in dependence of a sensed variation of a DC voltage of a power source (e.g. of the charger 110 or of another battery cell of the battery 100).
As outlined above, the charging/discharging system comprises a resonance circuit which forms a DC/DC converter in conjunction with the driver circuit and the rectifying unit. This DC/DC converter may be used for the charge balancing of battery or storage cells (as outlined in the present document). Furthermore, the same DC/DC converter may be used for power conversion purposes within the device or system comprising the storage cells. In particular, the DC/DC converter may be used for charge balancing, when the storage cells are being charged. On the other hand, when the storage cells are not being charged, the DC/DC converter may be used to convert the electric energy provided by the battery into electric energy at the voltage level of some or all of the components of the device or system which comprises the battery (e.g. the electric vehicle or the electronic device).
In the present document, a system for charging/discharging one or more cells of a battery has been described. The system allows for a flexible balancing of the plurality of cells of a battery. Furthermore, the system allows for the provision of flexible input/output voltages for charging/discharging of one or more cells of the battery. In addition, for isolation no transformer is required by using a PRC (LC resonant converter). Furthermore, the input and output can be exchanged, meaning that the charging/discharging concept is a bidirectional concept. In addition, the described charging/discharging concept allows for energy transfer from cell to cell and from the stacked cells. In particular, the concept (buck/ boost) can be used in several configurations and is flexible without a DC path (capacitor or transformer decoupling).
In other words, the described charging/discharging system may work in an isolated manner from cell to cell of the battery stack without transformer (e.g. using time multiplexing). The charging/discharging voltage may be flexibly adjusted over a large voltage range. The described system may be implemented at low cost and with low sized external components. Furthermore, the described system provides a high efficiency over the complete voltage range (a high Q factor is not required, e.g. a factor 3 may be sufficient, thereby reducing the requirements with regards to the characteristics of the one or more capacitors and the one or more inductors).
It should be noted that the description and drawings merely illustrate the principles of the proposed methods and systems. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and embodiment outlined in the present document are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the proposed methods and systems. Furthermore, all statements herein providing principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
Particular aspects of the present document are:
| Number | Date | Country | Kind |
|---|---|---|---|
| 13170270 | Jun 2013 | EP | regional |
This application is a Continuation of: PCT application number PCT/EP2014/061126, filed May 28, 2014, which claims priority to European application number EP13170270.6, filed Jun. 3, 2013, both of which are owned by a common assignee and are herein incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2014/061126 | May 2014 | US |
| Child | 14936066 | US |
