WO1997004513A1

WO1997004513A1 - Device for equalizing the charges in a multiplicity of accumulators or power converters

Info

Publication number: WO1997004513A1
Application number: PCT/EP1996/003193
Authority: WO
Inventors: Heribert Schmidt
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 1995-07-22
Filing date: 1996-07-19
Publication date: 1997-02-06
Also published as: DE19526836C2; DE19526836A1

Abstract

The invention concerns a device (10) for equalizing the charge in two accumulators or power converters (1, 11) connected in series to form a power-storage unit. The device has an inductive element (23) which can be connected in parallel to the accumulators by means of switches (2, 12) controlled by a time-signal generator (4, 14), the inductive element (23) being connected at one of its terminals (22) between the two accumulators or power converters (1, 11) while the other terminal can be connected, by means of two switches (2, 12) associated one with each of the accumulators or power converters (1 and 11, respectively), in parallel to the respective accumulator or power converter (1 or 11). The device also includes a comparator circuit (27) by means of which the voltages of the two accumulators or power converters can be compared with each other or with a reference value. The comparator circuit (27) is connected by control lines to the time-signal generator (4, 14). During a cut-in phase initiated by the comparator circuit (27), only the switch (2 or 12) associated with the accumulator or power converter (1 or 11) with the higher voltage is closed by the time-signal generator (4 or 14) so that, in a cut-out phase also initiated by the comparator circuit (27), the power stored in the inductive element (23) is delivered through the other switch (12 or 2), which is closed during this phase, or through one of two diodes (13 and 3) connected in parallel to the switches (12 and 2, respectively) into the lower-voltage accumulator or power converter (11 or 1). When a circuit of this kind (10) is used with a multiplicity of accumulators (1, 11), the accumulators (1, 11; 1a, 11a; 1b, 11b) whose charge is equalized by one particular charge-equalization device (10) are also each associated with another charge-equalization device (10).

Description

DESCRIPTION

Charge balancing device between a plurality of energy stores or converters

The invention relates to a device for charge balancing between a plurality of energy stores or energy converters, in which an inductive element can be connected in parallel to the energy stores or energy converters with the aid of switches which can be controlled by a clock generator.

Such a device is known from the applicant's DE 39 40 928, in which a charge equalization between a plurality of battery cells connected in series is created with the aid of centrally arranged or a plurality of decentralized flyback converters.

In the circuit described there, the emphasis is placed on charge equalization between a large number of energy stores, the flyback converters permitting galvanic isolation between the individual battery blocks.

This has the advantage that individual battery blocks from the entire battery can be specifically supported and that any battery blocks can deliver energy to the overall battery. This advantage is offset by the disadvantage of a relatively high circuit complexity of the transformers.

DE 39 40 929 from the applicant discloses a monitoring device for rechargeable batteries in which charge equalization is achieved with the aid of capacitors which are connected in parallel to selected rechargeable batteries. A circuit complexity similar to that of DE 39 40 928 is necessary here. Finally, from the subsequently published DE 44 22 409 by the applicant, a device for charge exchange between a multiplicity of energy stores or converters connected in series is known, in which the charge exchange is achieved via transformer windings, which are connected to the energy stores with alternating polarity. The common core of the windings requires a certain amount of circuitry.

On the basis of this prior art, the object of the invention is to create a device of the type mentioned at the outset, in which the charge equalization can be achieved with a lower amount of circuitry compared to the prior art.

This object is achieved according to the invention for a device according to the preamble of claim 1 in that the inductive element is connected with its one connection between the two energy stores or energy converters and in parallel at its other connection via two switches each associated with an energy store or energy converter the respective energy store or energy converter can be switched, that a comparator circuit is provided, with which the voltages of the two energy stores or energy converters can be compared with one another or with a setpoint value, that the comparator circuit is connected to the clock generators via control lines and that in one of the comparator circuits Predeterminable switch-on phase, only one switch can be closed by the clock generator, the associated energy store or energy converter of which has the greater voltage value, so that in a switch-off phase predefinable by the comparator circuit the energy stored in the inductive element can be emitted into the lower-voltage energy store or energy converter via the other switch closed in the switch-off phase or via diodes connected in parallel with the switches.

This results in a virtual parallel connection of the memories, cells or accumulators actually connected in series, so that when voltage differences occur between the two accumulators, a compensating current flows between the cells. In the case of a device for charge equalization between a plurality of energy stores or energy converters connected in series and forming a total energy store, a large number of devices for charge equalization with the above-mentioned features are used, the energy stores, each of which can be compensated by a single device for charge equalization, also each have a different device for Charge balancing are assigned.

This means that the voltage of a large number of energy stores can be compensated for in a simple manner, the different voltages that may occur being only compensated for in pairs, but all the individual voltages in the total energy store are adjusted overall by a nested arrangement of the individual devices for charge compensation.

Further refinements of the invention are characterized in the subclaims.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawing, in which:

1 shows a basic circuit diagram of a device for charge equalization for two accumulators according to a first exemplary embodiment,

2 shows a schematic representation of a section of a circuit diagram of a further device for charge equalization for four accumulators shown in this section according to a second exemplary embodiment,

3 shows a schematic representation of a section of a circuit diagram of a further device for charge equalization for four accumulators shown in this section according to a third exemplary embodiment,

4 shows a basic circuit diagram of a window comparator for comparing the cell voltages of a device for charge equalization, and Fig. 5 is a circuit diagram of an analog controller with pulse width modulation for a device for charge compensation.

FIG. 1 shows a basic circuit diagram of a device for charge equalization 10 for two accumulators 1 according to a first exemplary embodiment. The device for charge equalization 10 is provided for two accumulators connected in series and forming a total energy store as energy stores 1 and 11. There is a center tap 22 between the two energy stores 1 and 11. An inductive element 23 is connected to this center tap 22, a resistor 24 serving for current monitoring being connected upstream in the exemplary embodiment shown. The inductive element 23 can be connected in parallel with the energy stores 1 and 1 1 by means of switches 2 and 1 2 which can be controlled by clock generators 4 and 14, respectively.

Instead of the energy stores 1 and 11, energy converters can also be compensated in each case. This includes in particular all energy converting systems that consist of a series connection, such as electrolysis units and fuel cells.

Diodes 3 and 13 are arranged in parallel to switches 2 and 12, these diodes being connected as freewheeling diodes. These diodes can also be formed by the parasitic diodes which are present within MOS-FET switches with which the switches 2 and 1 2 can be implemented.

Switches 2 and 1 2 can be supplied with a clock signal by said clock generators 4 and 14, provided that there is a control command from a comparator circuit 27 which uses tapping lines 5, 15 and 25 to measure the voltages of the two energy stores 1 and 1 1 determined.

Finally, the voltage drop across the resistor 24 is made available to the clock generators 4 and 14, which advantageously have a current monitor. The function of the circuit is based on the fact that, with the aid of the comparator circuit 27, the actual voltages of the two energy stores, also called actual values, are compared with an average battery voltage, the target value, and with the corresponding deviation in the voltage value only the clock generator 4 or 14 is acted upon by a control signal which is assigned to the higher-voltage energy store. The clock generator 4 or 14 generates a high-frequency clock signal, preferably with a frequency of more than 20 kHz, with which the switch 2 or 12 is acted upon. During this switch-on phase, a current that increases in value flows from the higher-voltage energy store through the inductive element or also storage choke 23. In a switch-off phase, the current flows through the diode 13 or 3 into the lower-voltage energy store. Both switches 2 and 1 2 are then open. In an alternative embodiment, the switch 1 2 or 2 can be provided instead of the diode 13 or 3 in such a way that it then closes in the switch-off phase. The two switches 2 and 1 2 are switched on in a complementary manner, ie when switch 2 closes, switch 12 is open and vice versa. In this case, the switch 2 or 1 2 assigned to the accumulator with the higher voltage is first actuated with a pulse duty factor of greater than 50 percent, the current limitation contained in the clock generators 4 or 14 in the steady state reducing the duty cycle to a value in the Limited way that a predetermined maximum equalizing current flows.

If the two energy stores 1 and 11 have different nominal operating voltages, the clock steps are replaced by correspondingly different clock lengths.

According to the device shown in the drawing, the switches 2 and 1 2 and the clock generators 4 and 14 can also be implemented as integrated circuits which already contain the switches, a clock generator, an overcurrent protection device, an overtemperature protection device and also a soft start circuit. As shown in FIG. 1, the measuring lines 5, 15 and 25 are routed separately from the lines 6, 16 and 26 of the power unit in order to prevent the measured values from being falsified by voltage drops on the current-carrying lines.

FIG. 2 shows a schematic representation of a device for charge equalization for a number of four accumulators shown in this example by means of several of the devices for charge equalization described in FIG. 1 according to a second exemplary embodiment. In principle, however, the number of accumulators 1 or 11 connected in series is not limited.

In FIG. 2, the same features are identified with the same reference symbols with respect to FIG. 1. To simplify the illustration and for better clarity, the tap lines 5, 15 and 25 shown in FIG. 1 for exact measurement of the accumulator voltages and the lines 6, 16 and 26 carrying the equalizing currents are each combined to form a line sums up. The individual accumulators 1 and 11 as well as the devices for charge equalization 10 are further provided with additional indices a, b and c for better allocation. The comparator circuit 27 and the clock generators and further elements have likewise been omitted (as in FIG. 3).

For each N accumulator, N-1 devices for charge equalization 10 are necessary which, as shown in FIG. 2, overlap by one accumulator. Since each of the N-1 devices for charge equalization 10 independently compensates for voltage differences between its two accumulators 1 and 11, an energy transfer between all cells is ultimately possible.

The switches present in the respective charge equalization devices 10 and designated by reference numerals 2 and 12 in FIG. 1 can be controlled both by a central clock generator and can run freely independently of one another, it then being possible to use circuits corresponding to FIG. 1. The use of a central clock generator has the advantage of greater electromagnetic compatibility, since beat states between individual devices for charge balancing 10 can be avoided, which inevitably occur with independently operating clock generators.

The wiring of the devices for charge equalization 10 with a central clock generator can be further improved in that neighboring devices for charge equalization 10 are operated with a phase-shifted clock generator signal in order to avoid that large charging currents occur periodically on a weak accumulator when from A charge current flows into the weak accumulator on both sides of the chain of accumulators and the devices for charge equalization 10.

FIG. 3 shows a further possibility of arranging individual devices for charge equalization 10 according to FIG. 1 for several accumulators. 3 shows a section of a circuit diagram for four accumulators shown in this section according to a third exemplary embodiment.

The two circuits for charge equalization 10a and 10b arranged on the left side of the drawing sheet, as described above, each compensate between the associated accumulators 1 a and 1 1 a or 1 b and 1 1 b. The arranged on the right side of the drawing sheet further circuit for charge equalization 10c creates a balance between those from the two batteries 1 a and 1 1 a btw. 1 b and 1 1 b formed subgroups.

In contrast to the embodiment of the device according to FIG. 2, in which neighboring accumulators were each assigned to neighboring devices for charge equalization 10, there is another nesting in such a way that the accumulators 1 a and 1 1 a or 1 b and 1 1 b are considered as a unit for the device for charge equalization 10c and each further device for charge equalization 10a or 10b compensate for the smallest accumulator groups 1 a, 1 1 a or 1 b and 1 1 b. Of course, further step sizes are also conceivable and in particular actual and target voltages of different accumulator groups can be determined and processed, which is only reflected in a different length of the clock steps, provided that it is guaranteed that every smallest indivisible accumulator group or energy cell at least is present twice in order to be able to balance the at least one further charge and that each larger indivisible accumulator group or energy cell is in direct charge compensation with a corresponding multiple of smaller accumulator groups or energy cells.

With such an arrangement, a faster charge equalization between larger blocks of accumulators or energy converters is possible. in FIG. 3 a faster energy transfer between the two halves of groups of accumulators is achieved.

Each device for charge equalization 10 requires the comparator circuit provided with the reference number 27 in FIG. A possible embodiment of such a comparator circuit is shown in FIG. 4, which shows a basic circuit diagram of a window comparator 27 for comparing the cell voltages of a device for charge equalization 10.

The measuring lines 5 and 15 are led to the comparators 33 and 34 via the resistors 31 and 32. The actual battery voltages are thus present at the corresponding inputs of the comparators 33 and 34. The other input of the comparators 33 and 34 is to be connected to the measuring line 25. In order to prevent the influence of a voltage drop on the line 35 between the two accumulators 1 and 11 when charging or discharging currents occur, which is caused by the resistance 36 formed by the connection of the individual accumulators , The target voltage is determined via two high-resistance resistors 37 connected in series between the accumulators 1 and 11, the center tap between the two resistors 37 corresponding to the measuring line 25. A control signal is thus present at each of the outputs 38 and 39 if there is a deviation of the battery voltages from the respective target value. The comparators preferably have a specific one Hysteresis, which enable a control signal 38 or 39 to occur only when a minimum deviation of the battery voltages from the target value is exceeded. Furthermore, the comparators 33 and 34 are preferably locked against one another in a time-dependent manner, so that an energy supply in one direction in a predetermined time of, for example, one second is not canceled by an energy transfer in the other direction. This prevents the circuit from vibrating.

The switches can also be actuated with a clock signal whose duty cycle in relation to the total period, ie the so-called pulse width, is dependent on the difference between the target battery voltage and the actual battery voltages. A closed control loop is thus formed, which can be configured by a P, a PI, a PID controller or a controller with unsharp logic (fuzzy logic). FIG. 5 shows such a circuit diagram of an analog controller with pulse width modulation for a device for charge equalization 10.

An advantage of this analogous approach is that compensation currents can be set as a function of the control deviations, and thus a gentle operation of the charge compensation can be carried out.

The actual value of the average battery voltage is tapped in the same way as in the device according to FIG. 4. Likewise, the setpoint value is determined with the aid of high-resistance resistors 37, regardless of possible battery currents, and both values are fed to a PI controller 40, which, with the help of the resistors 41 and 42, amplifies a possible difference and this difference thanks to the capacitor 43 also integrated. In the case of non-ideal accumulators, there is a shift in the potential of the center tap 25 with respect to the mean battery voltage, so that a signed output signal is present at the output 44 of the PI controller. As already stated above, instead of the PI controller shown, both a P controller and a PID controller or other controller structures can be used. This output signal is rectified in a rectifier 45 and fed to a pulse width modulator 46, which creates a proportional pulse width ratio of the clock signal to the absolute value of the control deviation. At the same time, the sign of the control deviation is determined for this output signal in a comparator 47 and the clock signal generated by the pulse width modulator 46 is fed via a corresponding logic circuit 48 to the corresponding switch connection 38 or 39, which is connected to the switch 2 or 12. The comparator 47 can also work as a window comparator, which prevents the clock signal from being output if the control deviation is too small.

Claims

claims

Device for charge equalization (10) between two energy stores or energy converters (1, 1 1) connected in series and forming a total energy store, in which an inductive element (23) can be controlled by switches (2, 14) controlled by a clock generator (4, 14) , 12) can be connected in parallel to the energy stores or energy converters (1, 1 1),

characterized ,

that the inductive element (23) is connected with its one connection (22) between the two energy stores or energy converters (1, 1 1) and at its other connection via two each associated with an energy store or energy converter (1 or 1 1) Switches (2 or 12) can be connected in parallel to the respective energy store or energy converter (1 or 11) in such a way that a comparator circuit (27) is provided with which the voltages of the two energy stores or energy converters can be compared with one another or with a setpoint are that the comparator circuit (27) is connected to the clock generators (4, 14) via control lines and that in a switch-on phase which can be predetermined by the comparator circuit (27) only the one switch (2 or 12) from the clock generator ( 4 or 14) can be closed, its associated energy store or energy converter (1 or 11) has the greater voltage value, so that in a cutout which can be predetermined by the comparator circuit (27) hold phase, the energy stored in the inductive element (23) via the other switch (12 or 2) closed in the switch-off phase or via diodes (13 or 3) connected in parallel to the switches (12 or 2) in the lower-voltage energy store or energy converter (11 or 1) can be emitted.

2. Device according to claim 1,

characterized,

that a current monitoring device (24) is provided, by means of which the current flowing through the inductive element (23) can be detected, and that the current monitoring device (24), when a threshold value for the named current is reached, the clock generator (4, 14) of the Switched on phase in the switch-off phase.

3. Device for charge equalization between a plurality of energy stores or energy converters (1, 11) connected in series and forming an overall energy store,

characterized,

that they have a multiplicity of devices for charge balancing (10) according to one of claims 1 or 2 and that the energy storage devices or energy converters (1, 11; 1a, 11a, 1b, 11b), each of which can be compensated for by a single device for charge balancing (10) are also assigned to another device for charge equalization (10).

4. The device according to claim 3,

characterized,

that the two energy storage devices or energy converters (1, 11), each of which can be compensated by a single charge equalization device (10), are each exactly assigned to another charge equalization device (10).

5. The device according to claim 3,

characterized,

that the two energy stores or energy converters (1, 11), which can be equalized by a single charge equalization device (10), are subdivided into smaller energy stores or energy converters (1a, 11a, 1b, 11b), each of which also has another device for Charge balancing (10) are assigned.