RU2799767C1 - Active battery cell balancing system - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: systems for active balancing of battery cells. The system contains individual modules for measuring cell state parameters, electrically interconnected through the secondary windings of induction power converters, individual power exchange modules, each of which is made in the form of an inverter on a planar transformer with control keys and a block for generating and issuing control signals in the form of a low-voltage differential bus. At the same time, the system is equipped with inverter control key drivers communicated with the differential bus, and individual modules for measuring cell parameters and individual power exchange modules are connected in parallel to the bus through galvanic isolation.

EFFECT: reduction of the mutual influence of the magnetic fields of transformers with the elimination or significant reduction in the probability of occurrence and magnitude of induced EMF in planar coils.

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Description

The invention relates to electrical engineering, namely to systems for monitoring, operating and charging batteries.

Currently, the most popular are lithium-ion batteries, which, due to their advantages, are widely used in electrical engineering. Their main advantages are high specific capacity and durability, and they can withstand a large number of charge-discharge cycles without a significant decrease in performance. However, the operation of a battery consisting of cells-elements connected in series and/or in parallel has a number of features, the main of which is the possibility of overheating during operation. When assembling rechargeable batteries, cells are selected with the closest possible characteristics, in particular, the rate of degradation of electrode materials, self-discharge current during storage, cell capacity, internal resistance during charging and discharging. Accordingly, the voltage values on the battery cells should be as close as possible to each other. For example, the voltage below which it is unacceptable to discharge a cell in a battery is in the range of 2.4-2.8 V, and the voltage above which it is impossible to charge the cell lies in the range of 4.1-4.3 V. The operation of the cell within the specified voltage limits guarantees long and safe operation of the batteries. Minimization of the scatter in the values of the characteristics of lithium-ion cells that change during operation requires the introduction of devices for monitoring parameters and controlling the charge-discharge mode into the composition of batteries consisting of such cells. During the operation of the battery, these factors of parameter scatter lead to a voltage difference between the most charged and the most discharged battery cells. With an increase in this difference, the battery capacity will decrease, since the maximum and minimum allowable voltages on any cell will be reached before the full charge or discharge of the entire battery. As a result of this process, the overall capacity of the battery decreases. To prevent such processes, an electronic unit with a circuit for monitoring battery parameters and controlling the charge-discharge mode is introduced into the batteries, which ensures the balancing of the charge-discharge of the battery cells. The most promising are active balancing systems. The advantages of such systems include high efficiency, a significant extension of battery life, the use of a recharge device, which is especially important for uninterruptible power supplies based on lithium-ion batteries.

Known active balancing system based on DC/DC converter, made for two batteries. The secondary windings of the converter are wound on one core. The energy is redistributed in the core, and the most discharged battery in the chain will receive more energy than the most charged one (A. Rykovanov. “Li-ion battery balance systems”. Power Electronics, No. 1’2009, pp. 52-55). The disadvantage of such a system is the limited use of balancing by the number of batteries.

A battery cell balance system based on the LTC3300-1 chip from Linear Technology is known. One such microcircuit is capable of redistributing energy in a battery containing up to six Li-ion batteries connected in series. At the same time, it is possible to build a balance system for high-voltage batteries (with voltage up to 1000 V) based on the required number of LTC3300-1 microcircuits, each of which will serve its own group of batteries. The use of this microcircuit is possible both in tandem with the LTC6803-1 Li-ion battery control microcircuit of the same manufacturer, and with other control devices. This is due to the presence of a digital control interface and a simple protocol for the exchange of control and monitoring information (A. Rykovanov, S. Belyaev. "Active and passive balance systems for Li-ion batteries." COMPONENTS AND TECHNOLOGIES. No. 3'2014, pp. 121-124).

The disadvantages of this solution are the need to use powerful MOSFET transistors and insufficiently high overflow currents, not exceeding 10 A, which reduces the ability to recharge batteries.

A device for balancing energy storage devices is known, which contains n storage devices and a switchable capacitor that performs sequential switching of elements through the storage devices. It additionally includes n-1 balancing circuits, each of which contains a pulse shaper, a resistor, a switchable capacitor and 4 keys, while the pulse shaper is connected to the keys so that alternate pairwise closing of 2-(n-1) circuits with a protective pause, including adjacent cells, is provided. Balanced energy accumulators are located in adjacent cells; both supercapacitors and rechargeable batteries of any type (lithium-ion, alkaline, polymer, etc.) can be used as accumulators. The pulse shaper provides pairwise alternating switching of circuits with a protective pause by applying a signal to field-effect transistors that act as keys, thus it becomes possible to balance adjacent energy storage cells without introducing additional elements (RU 201266).

The disadvantage of the design is the possibility of balancing only adjacent cells, as well as a high probability of breakdown of the capacitor in case of possible failures in the synchronization of the supply of control signals.

A device for balancing a lithium-ion battery is known for leveling the voltage difference across the batteries that make up the battery and consisting of: series-connected battery modules (hereinafter referred to as the Module), each of which contains a given number of batteries; Block of the system for monitoring, charge and discharge control (SCZR) of the Module, each Block of the SCZR Module contains DC/AC converters for each battery of the Module and a DC/AC converter for the Module as a whole, monitoring and charge control units for each battery of the Module and a charge monitoring and control unit for the Module as a whole, as well as blocks for switching modes for each battery of the Module and a block for switching the mode of the Module as a whole; a Module transformer containing a primary winding connected to the module mode switching unit as a whole, secondary windings according to the number of batteries in the Module connected to the mode switching unit of each module battery and an additional module transformer winding, while additional transformer windings of all Modules are in-phase combined for energy exchange between the Modules; battery management controller (RU 2722619).

The disadvantages of the device are the high complexity and bulkiness of the design, the overloading of transformers, which leads to their mutual influence and the induction of intense parasitic EMF in the transformer windings, leading to disruptions in the operation of the system as a whole.

The closest technical solution to the proposed one is the balancing device control system, which contains a general control unit and control units for each of the plurality of battery cells. Moreover, each cell of the set is controlled by its own unit, which may contain a microcontroller configured to receive data on the state of the cell, transfer the received information to the general control unit and balance the cell voltage with high currents (when receiving a control command from the general control unit). The balancing mode can work when charging, when the battery is discharged, and also at rest. It is assumed that the battery converters can be synchronized by a common control signal from the general control unit or, depending on the state of the cell, perform a synchronous conversion of direct current to alternating current and back from alternating current to direct current (RU 2546978) according to the control system signal.

The disadvantages of this balancing system are high weight and size characteristics, due to the presence of many metal-intensive transformer inverters and a complex general control system. The disadvantages include a significant increase in the level of noise and interference during the operation of the DC / AC converter. An increase in interference requires a more complex system for measuring battery voltages, shielding, filtering, and increased control currents, which also leads to an increase in the cost of the entire battery power supply system and high energy costs for control and balancing. The need for a dense and compact arrangement of the elements of the balancing system leads to a close arrangement of transformers to each other. In turn, this leads to the mutual influence of electromagnetic fields, the induction of parasitic EMF in the windings of neighboring transformers, which not only disrupts the operation of measuring and control modules, but can also lead to failure of both parts of the balancing system and the battery cells themselves, and the general control system. In addition, a system with a common control unit, in which the keys of the battery converters are synchronized with a common control signal from such a common control unit, can lead to false, uncontrolled, opening of power switches, moreover, simultaneously in both arms of the converters, while the so-called "through current" develops and the transistor keys fail.

The technical results achieved by the present invention are a decrease in the level of influence of magnetic fields of inverters on the operation of the balancing system, an increase in the reliability of the system, the prevention of through currents in the control keys of inverters, an increase in the number of serviced cells while reducing specific energy consumption for control and balancing.

The technical result is achieved by the fact that the system for active balancing of battery cells, containing individual modules for measuring cell state parameters, electrically interconnected through the secondary windings of induction energy converters, individual energy exchange modules, each of which is made in the form of an inverter on a transformer with control keys and a unit for generating and issuing control signals, is equipped with drivers of inverter control keys communicated with the unit for generating and issuing control signals, and the unit for generating and issuing control signals is made in the form of a low-voltage differential bus, to which in parallel individual modules for measuring cell parameters and individual modules for energy exchange are connected via galvanic isolation, while the inverter transformers are made planar.

The specified set of signs is essential. Replacing conventional inverter transformers with planar ones showed an unexpected effect - a significant reduction in the mutual influence of the magnetic fields of transformers with the elimination of the effect of the occurrence of induced EMF in planar coils, or at least such a decrease in the level of interference that does not affect the operation of the system as a whole. Perhaps this is due both to a significant reduction in the dimensions of transformers and an increase in the corresponding distances between them, and to the very design of planar inductors, where the core almost completely covers the windings on the boards and shields electromagnetic fields. Perhaps the change in the nature of eddy currents in planar windings with the elimination of skin effects, etc., also played a role. A significant reduction or elimination of interference with the elimination of parasitic EMF in the windings, in turn, made it possible to simplify the design of the balance system and increase its reliability by eliminating the common control unit when dividing its functions between the differential bus introduced into the design and the special drivers used to control the power transistors-keys. They not only improved the time parameters for opening and closing transistors, but also, due to cross-control, completely eliminated the simultaneous opening of transistors and the occurrence of through currents. But, since they do not have the function of galvanic isolation, it was necessary to use a digital isolator in the form of galvanic isolation connecting the low-voltage differential bus with individual modules for measuring cell state parameters and the specified key control drivers.

The figure shows a schematic diagram of the claimed system for active balancing of battery cells.

The system includes individual modules 1 for measuring the parameters of the state of series-connected cells 2 of batteries 3. In parallel with the cells 2, individual energy exchange modules 4 are connected, each of which is made in the form of an inverter 5 on a transformer 6 with control keys 7 and 8, electrically interconnected through the secondary windings 9 of transformers 6. The transformation ratio of the latter is 15. Keys 7 and 8 are connected to key drivers 10 and 11, which are connected to the block for generating and issuing control 12. Block 12 is made in the form of a low-voltage differential bus 13 with a bus driver 16, to which individual modules 1 for measuring cell parameters and individual energy exchange modules 4 are connected in parallel through a galvanic isolation 14. As part of the galvanic isolation 14, there is a separate connection in the form of an optocoupler 15 for turning the module 1 on and off. The transformers 6 of the inverters 5 are made planar. To measure the flow current in module 4 there is a sensor 17 on the Hall effect.

The system works as follows.

Module 1 monitors the state of the cell, its voltage, temperature and current flow. Information is collected by module 1 and transmitted via galvanic isolation 14 to differential bus 13 upon request. Block 12 receives control signals (lines A and B) and outputs them through galvanic isolation 14 to drivers 10 and 11. Optocoupler 15 is used to detect the presence or absence of the supply voltage of the interface, if there is power, then module 1 goes into operating mode, otherwise it "falls asleep", consuming a current of 2-6 μA from the cell. When the supply voltage appears on the differential bus (+V and -V lines), optocoupler 15 opens and gives module 1 a turn-on signal, which activates the internal power supply and all elements of module 1 start working. The optocoupler also ensures that the modules 1 are turned off. As soon as the differential bus 13 is disconnected from power, the optocoupler 15 closes and gives the module 1 a signal to enter the power-saving mode. Power is supplied to the bus driver 16 and decoupling 14 through the LED of the optocoupler 15, which made it possible to reduce the total current consumption from bus 13. As a result, the level of current consumption by each module 1 from bus 13 remains at the level of 6-10 mA, depending on the activity of the components of the circuit. Low power consumption currents allow up to 25 modules 1 and corresponding cells 2 to be connected by one bus 13. Differential bus 13 can receive a differential signal (lines H and L)) and convert it to an RxD signal, as well as receive a TxD signal and convert it to a differential signal. To monitor the temperature, an internal temperature-sensitive element is used inside module 1 (not shown), which makes it possible to estimate the temperature of the immediate environment, primarily power transistors - switches 7 and 8 and transformer 6 of module 4. The flow current is measured by a Hall effect sensor 17. In the absence of current, half of the supply voltage (2.5 V) is present at the output of sensor 17. The appearance of a positive or negative current raises or lowers this voltage. Module 1 measures this voltage and calculates the magnitude of the current and its direction. Cell 2 voltage is also measured by module 1. Control signals A and B are out of phase with each other and are connected each to both drivers 10 and 11, but to different inputs, direct or inverse. Such a connection ensures that only one power transistor will be open at any given time, or both will be closed. This is an additional protection against through current in case of possible synchronization failures. Power transistors - keys 7 and 8, alternately turning on and off, create alternating voltages at the output of the secondary windings of transformers 6, which will differ depending on the voltage of the cell to which the inverter 5 is connected. And, accordingly, the balancing currents will flow from those transformers 6, the voltage on the secondary windings of which is higher, and flow into those whose voltages on the secondary windings are lower, due to which the balancing of the battery cells 2 of the battery 3 is carried out.

The claimed invention ensures the absence (or significant reduction) of the mutual influence of magnetic fields and the corresponding interference, which eliminates errors in measuring the true parameters of the state of cells and prevents erroneous decisions of the system when balancing for charging or discharging cells, and also ensures the reliability and operability of the system, preventing cell failures and reducing the life and capacity of cells and batteries as a whole. At the same time, the elimination or significant reduction in the level of interference makes it possible to reduce the control currents, which, in turn, makes it possible to increase the number of batteries served by one balancing system.

Claims (1)

The system for active balancing of battery cells, containing individual modules for measuring cell state parameters, electrically interconnected through the secondary windings of induction energy converters, individual energy exchange modules, each of which is made in the form of an inverter on a transformer with control keys, and a block for generating and issuing control signals, characterized in that it is equipped with drivers of inverter control keys communicated with the block for generating and issuing control signals and galvanic isolation through which the block for generating and issuing control signals is connected to individual modules for measuring parameters cells and individual energy exchange modules, while the inverter transformers are made planar, and the block for generating and issuing control signals is made in the form of a low-voltage differential bus.

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