WO2007025692A1

WO2007025692A1 - Method and device for measuring differential voltages at the terminals of elements of a battery with transformation into periodic signal

Info

Publication number: WO2007025692A1
Application number: PCT/EP2006/008396
Authority: WO
Inventors: Nicolas Michel
Original assignee: Johnson Controls Technology Company
Priority date: 2005-08-30
Filing date: 2006-08-28
Publication date: 2007-03-08
Also published as: FR2890175B1; FR2890175A1

Abstract

The invention concerns a device for measuring differential voltages sensed at the terminals of multiple sets (2) of battery elements mounted in series, each set having a reference voltage, an output voltage and a differential voltage equal to the difference between the reference and output voltages while wishing to provide its differential voltage relative to a reference potential different from its reference voltage, the differential voltage of a set is transformed into a stream of signals capable of being directly processed as a logic signals by centralized processing means (5), the stream of signals, prior to processing, being sent on a galvanic insulation means (4). The invention is suitable for vehicle batteries.

Description

Method and device for measuring differential voltages at the terminals of the elements of a battery with transformation into a periodic signal

The invention relates to voltage measurements of the elements or groups of elements of the batteries during operation.

The measurement of the voltages at the terminals of the elements or groups of elements, that is to say the voltages supplied by each of the groups, of a battery during its operation, is necessary to ensure proper management and monitoring of the electrical energy available at the output of the battery of motor vehicles as well as their capacity to respond to significant loading or unloading demands, particularly in the case of hybrid or fully electric vehicles, since in this case the battery is a primary source of locomotion, if not the only source.

As the measurements of the voltages provided by the groups must be made during operation, it is not possible to isolate the groups and therefore each measurement must be performed on each group relative to a reference voltage which is the voltage of the group. output of the preceding group, different for each group, so that in the extreme, the voltage supplied by the last group is measured relative to a reference voltage equal approximately, for an electric vehicle, to fifteen to twenty-five times its value.

For a given group, the measurement is performed by an operational amplifier mounted to subtract its reference voltage from its output voltage and thereby obtain the voltage it provides.

To process all the measurements and for example perform calculations to give the state of charge, or health, of the battery (forecast availability) by jointly using other parameters (current, temperature, ...), in a word to manage the battery, it is necessary to report by adaptation circuits all measurements to a common reference. But as the quality, therefore the cost, of an amplifier depends on all its errors, one of which is a function of the common mode voltage, that is to say of the half sum of SQS inputs, it is important to minimize other errors, especially those that would lead to complex adaptation circuits and, above all, to be able to overcome this common mode error.

US 6,313,637 proposes a solution consisting of digitizing the measurements immediately at the output of the amplifiers, limiting the errors of the amplifiers, then transmitting the digital data by photo-coupling to a microprocessor for processing. But this process remains expensive because it requires as many analog digital converters (ADC) as groups of elements.

US 6 184 656 proposes a system in which the measurements are transmitted to a central organ by radio, which imposes a radio transmitter on each group. This solution is also very expensive.

The applicant proposes a much lighter solution that does not require CAN or radio means.

Thus, the invention firstly relates to a method for measuring differential voltages sensed at the terminals of a plurality of groups of battery elements connected in series, each group having a reference voltage, an output voltage and a voltage differential equal to the difference between the reference and output voltages, characterized in that, since it wishes to have its differential voltage with respect to a reference potential different from its reference voltage, the differential voltage of a group is transformed in a periodic signal, of frequency proportional to the measured voltage, which can be directly processed by central processing means, the signal, before processing, being sent on a galvanic isolation means.

Advantageously, the differential voltage of a group is transformed into a signal train that can be directly processed as a logical signal stream.

Preferably, the signals are processed cyclically in time, each cycle corresponding to the transmission of at least one measurement.

More preferably, according to a first mode of operation, the signals are comparable to binary pulses whose frequency is representative of the measurement.

In this case, it is sufficient to count the pulses for a predetermined time in the cycle.

According to a second mode of operation, the signals can be assimilated to pulse modulated in width, the modulation determining a duty cycle representative of the measurement.

In this case, it suffices to count the tops of a clock intervening during a pulse or, which amounts to the same, during a cycle.

Advantageously always, it is possible to multiplex the signal streams according to the groups monitored on the same counter and the same clock.

The embodiment of the device implementing the method of the invention is then particularly economical.

Thus, the invention also relates to a device for measuring differential voltages across a plurality of groups of battery cells in series, having at the terminals of each group, a voltage-frequency conversion assembly delivering a periodic signal, under binary pulse form whose frequency f is representative of the differential voltage measurement, and which is transmitted to means for centralized processing of measurements through galvanic isolation means. The invention will be better understood with the aid of the following description of the method and device for measuring differential voltages according to the invention, with reference to the appended drawing in which:

FIG. 1 represents an electrical diagram implementing the first mode of operation of the method for measuring and transmitting a differential voltage measurement according to the invention;

FIG. 2 represents an electrical diagram implementing the second mode of operation of the method for measuring and transmitting a differential voltage measurement according to the invention; and FIG. 3 is a timing diagram of the main signal trains corresponding to the operations of the first and second modes of operation according to the invention.

Referring to Figure 1, a battery 1 of a motor vehicle has a plurality of groups 2 in series having a number of battery elements of about 1.25 volts. In Figure 1, there has been only a group 2 having a single element 2 for the sake of clarity.

Each group 2 delivers a differential voltage DV sensed by an operational amplifier 1 1 whose output controls a voltage-frequency conversion means 12. The assembly 3, comprising the amplifier 1 1 and the converter 12, can be replaced by a circuit VCXO voltage controlled crystal oscillator 3 ("Voltage Controlled Crystal Oscillator") well known.

The assembly 3 delivers, with reference to FIG. 3, an uninterrupted train of signals F3 in the form of binary pulses whose frequency f is representative of the measurement DV.

This signal stream F3 is transmitted to means 5 for centralized processing of the differential voltage measurements of the groups 2 through means 4 of galvanic isolation, photocoupler or other inductive means, whose bandwidth must be sufficient to pass the signal. to the processing means 5, and a multiplexing switch 6. There are as many assemblies 3, isolation means 4 and switches 6 as groups 2. Thus, by multiplexing, the processing means 5 cyclically scan all the groups 2 by cyclically controlling the switches 6.

Here, the centralized processing means 5 comprise a microprocessor 8, a clock 9 and a counter 10.

Clocked by the clock 9, the microprocessor 8 controls the switch 6 during the cycle F6 of duration to and, in this cycle F6 of the scan, the clock 9 determines a phase F9 of duration t during which it must receive a train of signals representative of the DV measurement corresponding to group 2.

During this phase F9, the counter 10 counts the number n of pulses F3 and transmits the result to the microprocessor 8, which deduces the frequency f, equal to n / t, thus the measurement DV, which is a predetermined function of f which is implemented in the microprocessor 8.

The duration t of phase F9 must be less than half the duration to cycles F6, so that multiplexing and counting can be asynchronous. The beginning of the count FlO is then synchronized on the first rising edge of the phase F9 present in the cycle F6.

In this first mode of operation, it will be noted that the signals F3 representative of the measurement DV are at their frequency f.

In Figure 2, there is the same structure of the device described above and shown in Figure 1, the same references corresponding to the same means or elements.

The assembly 3 is replaced by the assembly 13 comprising an operational amplifier 20 mounted as an integrator, a threshold latch 18, a resistor 16, and a clock 17. The assembly carries out pulse modulation in FIG. MIL width, better known as PWM ("Pulse Width Modulation") as explained below.

The integrator 20 is connected to the terminals of the group 2 at the beginning of a cycle for a time t1 during which it is charged. Then it is connected to the resistor 16 and the input of the latch 18 for a time t2, resistance in which it discharges. This process of duration t1 + t2 is cyclically repeated uninterruptedly and is clocked by the clock 1 7.

At the output of the flip-flop 18, a signal train F13 is obtained which is a pulse width modulation t3 whose duty cycle t3 / t2 is representative of the measurement DV. The times t1 and t2 being predetermined in the clock 17, t3 is representative of DV, which is a predetermined function of t3 implemented in the microprocessor 8.

The total duration tl + t2 must be less than half the duration to cycle F 6 so that there is at least one phase Fl 3 completely in the cycle F6.

In this second mode of operation the roles of the clock 19 and the transmitted signals F13 are opposite to those filled by the clock 9 and the signals F3 of the first mode of operation. Here the clock 19 delivers clock ticks Fl 9 intended to be counted by the counter 14 and the pulses F 13 define the corresponding counting times t3.

For this, the counter 14 differs from the counter 10 in that it comprises at the input an AND gate (not shown) for chopping the pulses Fl 3 by the tops Fl 9 and counting these tops only during the durations t3 of the phase of count F14 of duration t1 + t2, phase F14 which is synchronized by the first rising edge of the signal stream Fl 3 present in the cycle F6. As a result, the counter 14 measures the duration t3.

In this second mode of operation, it will be noted that the signals Fl 3 representative of the measurement DV are by their duration t3.

Claims

1. - Method for measuring differential voltages sensed at the terminals of a plurality of groups (2) of battery cells connected in series, each group having a reference voltage, an output voltage and a differential voltage equal to the difference between the reference and output voltages, characterized in that, in order to have its reference voltage, the differential voltage of a group is converted into a periodic signal, of frequency proportional to the measured voltage, which can be directly processed by central processing means (5; 15), the signal, before processing, being sent on a galvanic isolation means (4).

2. - Measuring method according to claim 1, wherein the differential voltage of a group is transformed into a signal train that can be directly processed.

3. - Method according to one of claims 1 and 2, wherein the signals are processed cyclically (F6) in time, each cycle (F6) corresponding to the transmission of at least one measurement (DV).

4. - Method according to one of claims 1 to 3, wherein the signals (F3) are comparable to binary pulses whose frequency (f) is representative of the measurement (DV).

5. - The method of claim 4, wherein there is (10) the pulses for a predetermined time (t) in the cycle (F6).

6. - Method according to one of claims 1 to 3, wherein the signals (F 13) are comparable to pulse modulated width.

7. - Method according to claim 6 wherein there are (14) the tops of a clock (19) involved during a pulse.

8. - Method according to one of claims 1 to 7, wherein one multiplexes the signal trains (F3, F13) according to groups (2).

9. - Device for measuring differential voltages at the terminals of a plurality of groups (2) of battery cells in series, comprising, at the terminals of each group, a set (3) of voltage-frequency conversion delivering a periodic signal , in the form of binary pulses whose frequency f is representative of the differential voltage measurement, and which is transmitted to means (5) for centralized processing of measurements through galvanic isolation means (4).

10. - Device according to claim 9, wherein the voltage-frequency conversion assembly (3) comprises an operational amplifier (1 1).

1. - Device according to claim 9, wherein the voltage-frequency conversion assembly comprises a voltage-controlled crystal oscillator (3).

12. - Device for measuring differential voltages at the terminals of a plurality of groups (2) of battery cells in series, comprising, at the terminals of each group, a set (13) for converting the voltage into form signals. of width-modulated pulses, whose duty cycle is representative of the differential voltage measurement, and which are transmitted to means (15) for centralized processing of measurements through galvanic isolation means (4).

13. - Device according to one of claims 9 to 12, wherein the central processing means (5; 15) control a plurality of multiplexing switches (6) for the cyclic scanning groups of elements (2).