Patent Application
20190277918
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2018-039654, filed on Mar. 6, 2018; the entire contents of which are incorporated herein by reference.
An embodiment of the present invention relates to a battery monitoring device and a battery monitoring system.
A battery monitoring system is known, which individually monitors voltages of a plurality of battery cells connected in series. Such a battery monitoring system is provided with a filter circuit to remove noise unnecessary for voltage measurement.
In certain applications, such as an automotive application, redundancy in a voltage measurement path is required in preparation for an unexpected situation such as failure. However, it is difficult to form a redundant voltage measurement path having filter characteristics equivalent to a voltage measurement path in a normal state in a filter circuit. Therefore, when measuring voltage of a battery cell on a redundant voltage measurement path, noise may not be satisfactorily attenuated, for example.
An embodiment of the present invention provides a battery monitoring device and a battery monitoring system that are capable of combining redundancy in a voltage measurement path and noise attenuation characteristics.
Embodiments will now be explained with reference to the accompanying drawings. The present invention is not limited to the embodiments.
The battery monitoring system 1 includes a first filter circuit 10, a second filter circuit 20, and a battery monitoring device 30. The battery monitoring device 30 has a multiplexer 31 and a voltage measurement unit 32.
The first filter circuit 10 has a plurality of resistors R10 (first resistors) and a plurality of capacitors C10 (first capacitors). One end of each resistors R10 is connected to both ends (positive and negative poles) of each battery cell, whereas the other end of each resistors R10 is connected to the second filter circuit 20. Each capacitor C10 is connected between the other ends of the resistors R10 or between the other end of the corresponding resistor R10 and ground wiring of the battery monitoring device 30. The resistors R10 and the capacitors C10 constitute a so-called n-type filter circuit. The first filter circuit 10 removes a common mode noise with respect to the ground.
The second filter circuit 20 is located in a subsequent stage of the first filter circuit 10. This second filter circuit 20 has a plurality of resistors R21a to R23b (second resistors) and a plurality of capacitors C20 (second capacitors).
One ends of a resistor R2na and a resistor R2nb are commonly connected to the other end of a corresponding one of the resistors R10. Here, “n” is an integer. In addition, each capacitor C20 is connected between other ends of the resistor R2nb and a resistor R2(n+1)a. The resistor R2nb is connected to a lower potential side of the corresponding capacitor C10, and the resistor R(n+1) is connected to a higher potential side of the capacitor C10.
The voltage of the battery cell 40a corresponds to the voltage across the capacitor C20 connected between the resistor R23a and the resistor R22b. Moreover, the voltage of the battery cell 40b corresponds to the voltage across the capacitor C20 connected between the resistor R22a and the resistor R21b.
On the input side of the multiplexer 31, provided is a plurality of terminals 31a to 31f connected to the other ends of the respective resistors R21a to R23b. In the multiplexer 31, a plurality of switches (not shown) connected to the respective terminals are provided. A voltage measurement path of the voltage across each capacitor C20, i.e., the voltage of each battery cell, is selectively switched by switching on and off of the switches in a predetermined order.
For example, the switch connected to the terminal 31d and the switch connected to the terminal 31e are turned on, a voltage measurement path 20a shown in
In addition, when it is not possible to select the voltage measurement path 20a due to failure or the like of the resistor R23a, the switch connected to the terminal 31c and the switch connected to the terminal 31f are turned on. In this case, a redundant voltage measurement path 20b is selected to measure the voltage of the battery cell 40a. If the redundant voltage measurement path 20b is selected, filter effect of the second filter circuit 20 may be lost.
The voltage measurement unit 32 has an AD converter 33 and a digital filter circuit 34. Now, configuration of the AD converter 33 is described with reference to
The subtraction circuit 35 subtracts a fixed value set by the switch circuit 38 from a value of an analog signal transmitted on the voltage measurement path selected by the multiplexer 31. The subtraction circuit 35 outputs a result of the calculation to the adder circuit 36.
The adder circuit 36 sequentially adds the result of the calculation by the subtraction circuit 35. Also, the adder circuit 36 outputs a result of the calculation to the quantization circuit 37.
The quantization circuit 37 compares the result of the calculation by the adder circuit 36 with a reference value at a predetermined sampling frequency. In accordance with a result of the comparison, “1” or “0” is output. As a result, the analog signal is quantized and converted into a digital signal.
The switch circuit 38 sets the fixed value in accordance with the result of the comparison in the quantization circuit 37. Specifically, the switch circuit 38 outputs to the subtraction circuit 35, the positive or negative fixed value in accordance with the output of “1, or “0”.
The AD converter 33 of this embodiment is capable of reducing quantization noise. Note that, the configuration of the AD converter 33 is not limited to the circuit diagram shown in
The digital filter circuit 34 performs filtering that removes a frequency component higher than a predetermined frequency (e.g., 1 kHz), on the digital signal input from the quantization circuit 37. In this embodiment, the digital filter circuit 34 performs the filtering by performing moving average processing on the digital signal.
The digital signal filtered by the digital filter circuit 34 is input to a CPU (Central Processing Unit) 50. The CPU 50 outputs a command to a charge control circuit 60 in accordance with a digital signal value. The charge control circuit 60 controls charge of the assembled battery 40 on the basis of the command from the CPU 50.
According to this embodiment described above, the AD converter 33 performs an analog-to-digital conversion before the digital filter circuit 34 performs filtering. Thus, even though the multiplexer 31 selects the redundant voltage measurement path, a noise component contained in a signal indicating the voltage of each battery cell can be satisfactorily attenuated. Consequently, it is possible to combine redundancy in the voltage measurement path and noise attenuation characteristics.
The noise processing is performed on the digital signal entirely by the digital filter circuit 34, and thus, filtering can be uniformly performed on each battery cell.
(Modification)
As with the first filter circuit 10, the first filter circuit 10a also constitutes a n-type filter circuit and therefore can remove the common mode noise with respect to the ground.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-039654 | Mar 2018 | JP | national |
