JP2004245743A - Flying capacitor type voltage detection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flying capacitor type voltage detection circuit for detecting, by a simple method, a failure in the reading of voltage into a flying capacitor. <P>SOLUTION: In the flying capacitor type voltage detection circuit, turned-on periods are altered of input-side sampling switches SW1 and SW2 or output-side sampling switches SW3 and SW4. When the change rate is large in output voltage of a voltage amplifying circuit 9 in consequence of the alteration, it is determined that an operation failure has occurred. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flying capacitor type voltage detection circuit.
[0002]
[Prior art]
Conventionally, a flying capacitor type voltage detection circuit has been described in, for example, the following Patent Documents 1 and 2 in high voltage battery voltage detection and the like.
[0003]
[Patent Document 1] JP-A-11-248755 [Patent Document 2] JP-A-11-248756
[Problems to be solved by the invention]
However, in the above-described conventional flying capacitor type voltage detection circuit, there is a possibility that the voltage of the voltage source to be measured (voltage to be measured) may be erroneously detected due to a circuit element defect or an external wiring defect. For example, in a flying capacitor type voltage detection circuit, after the voltage source to be measured is transferred to the flying capacitor through the input side sampling switch, the input side sampling switch is shut off and the flying capacitor is connected to the input terminal of the measuring circuit through the output side sampling switch. Therefore, if the wiring resistance value between the voltage source to be measured and the input side sampling switch increases due to a defect in the external wiring, the voltage to be measured will fall within the specified ON period of the input side sampling switch. The flying capacitor cannot be read sufficiently, and the output voltage of the measurement circuit is smaller than the actual measured voltage. Furthermore, the same problem may occur when the stored voltage of the flying capacitor is read out to the voltage source to be measured.
[0005]
As described above, when such a false detection occurs when the secondary battery voltage is detected by the flying capacitor type voltage detection circuit, it may cause a serious battery failure such as overcharge or overdischarge of the secondary battery. . The same type of problem also occurs due to an increase in the on-resistance of the input side sampling switch and a defect in the wiring connecting the input side sampling switch and the flying capacitor. Further, in the method of resetting the stored voltage of the flying capacitor after voltage detection, it may be caused by a failure of the discharge circuit that performs this reset.
[0006]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a flying capacitor type voltage detection circuit capable of detecting a voltage reading failure to a flying capacitor by a simple method.
[0007]
[Means for Solving the Problems]
The flying capacitor type voltage detection circuit according to claim 1, a flying capacitor;
A pair of input-side sampling switches that individually connect both ends of the voltage source to be measured to both ends of the flying capacitor, a voltage measurement circuit, and a pair of input terminals of the voltage measurement circuit are individually connected to both ends of the flying capacitor. In a flying capacitor type voltage detection circuit comprising a pair of output side sampling switches and a control circuit for controlling the sampling switches,
The control circuit changes an ON time of the input side sampling switch or the output side sampling switch.
[0008]
Preferably, the control circuit determines whether or not a change rate of the output voltage of the voltage measurement circuit before and after the change exceeds a predetermined value, and if it exceeds, an operation test for determining that a malfunction has occurred. To implement.
[0009]
According to the flying capacitor type voltage detection circuit of the present invention, it is possible to detect and determine a voltage reading failure to the flying capacitor by a simple method, and to cause a bad effect caused by operating an erroneous measured voltage, for example, a measured voltage source As a result, it is possible to prevent overcharge, overdischarge, capacity misjudgment, and the like of the secondary battery.
[0010]
The operation of reading the measured voltage to the flying capacitor will be briefly described as an example. As is well known, the stored voltage of the flying capacitor after reading is the input impedance (input) between the measured voltage source and the flying capacitor. This is a voltage value obtained by multiplying the voltage to be measured by an exponential function value having R, the capacitance C of the flying capacitor, and the reading time t as variables. Therefore, when a connection failure between the voltage source to be measured and the flying capacitor occurs, the input resistance R increases and the reading voltage (accumulated voltage) Vc of the flying capacitor decreases. This decrease in the read voltage (storage voltage) Vc itself is unavoidable in principle, but in normal read operation, the input resistance R is sufficiently increased to suppress the error within the practical range. If the input resistance R increases greatly due to some kind of accident, the read voltage (storage voltage) Vc decreases significantly.
[0011]
Therefore, if the measured voltage is considered to be constant, the reading time t is changed and reading is performed a plurality of times (for example, the on-time is extended several times longer than the on-time of the input sampling switch during normal reading) At this time, if the change in the output voltage of the flying capacitor type voltage detection circuit is below the allowable level, the circuit is normal, and if it exceeds the allowable level, the circuit is determined to be defective. be able to. Although the above description has explained the abnormal increase of the input resistance R, essentially the same is true for the abnormal increase of the output resistance connecting the flying capacitor and the voltage measuring circuit.
[0012]
As a result, it is possible to determine the malfunction of the flying capacitor type voltage detection circuit without complicating the circuit configuration, and it is possible to perform voltage detection with excellent reliability. Although the idea that the input side sampling switch should be turned on for a long time from the beginning when reading the voltage to be measured is derived, it is natural that the on time of the input side sampling switch should be extended due to voltage fluctuations of the voltage source to be measured. It is obvious that there is a limit.
[0013]
Thereby, for example, when detecting the voltage of a secondary battery such as a vehicle battery, it is possible to prevent a serious battery failure such as overcharge or overdischarge of the secondary battery due to erroneous detection of the voltage.
[0014]
In this invention, the on-time of the sampling switch is changed. However, as a modification, instead of changing the on-time of the sampling switch, the capacitance of the flying capacitor is changed by, for example, switching a plurality of capacitors in series and parallel, etc. A similar test can be performed according to the change rate of the stored voltage before and after. Therefore, the technical concept of changing the on-time of the flying capacitor in the present invention includes the technical concept of changing the capacitance of the flying capacitor.
[0015]
Similarly, as a modification, for example, by short-circuiting or not connecting a resistance element connected in series to the input side sampling switch, the input resistance from the voltage source to be measured to the flying capacitor is artificially changed, A similar test can be performed according to the change rate of the stored voltage of the flying capacitor before and after this change. Therefore, the technical concept of changing the on-time of the flying capacitor in the present invention includes the technical concept of changing the input resistance of the flying capacitor.
[0016]
However, changing the on-time of the sampling switch does not require any circuit change, so the test can be performed most simply.
[0017]
In a preferred aspect, the control circuit does not perform the operation test when the change in the output voltage of the voltage measurement circuit exceeds a predetermined value, or discards the test result. Thereby, it is possible to prevent the voltage change of the voltage source to be measured from being mixed into the operation test, and to improve the reliability of the operation test.
[0018]
In a preferred aspect, the control circuit commands regulation of fluctuation of the potential of the voltage source to be measured when the operation test is performed. Thereby, it is possible to prevent the voltage change of the voltage source to be measured from being mixed into the operation test, and to improve the reliability of the operation test.
[0019]
In a preferred aspect, when the result of the operation test is not good, the control circuit narrows the capacity range in charge / discharge control of the secondary battery that is the voltage source to be measured around the intermediate capacity value. Thereby, the danger of the overcharge of a secondary battery resulting from the false detection of a secondary battery voltage and an overdischarge can be reduced.
[0020]
In a preferred aspect, when the operation test result is not good, the control circuit extends the on time of the input side sampling switch or the output side sampling switch more than usual. Thereby, although the number of times of sampling of the voltage to be measured is reduced, the degree of erroneous detection can be suppressed.
[0021]
In a preferred aspect, when the operation test result is not good, the control circuit determines the voltage measurement circuit based on a degree of increase of the charging resistance value or discharging resistance value of the flying capacitor estimated based on the test result. Correct the output voltage.
[0022]
For example, consider the case where the on-time of the input side sampling switch is changed for operation.
[0023]
In one measurement, the input resistance R connecting the voltage source to be measured and the flying capacitor, the voltage to be measured V, the on-time t of the input side sampling switch, the capacitance C of the flying capacitor, and the storage voltage Vc of the flying capacitor If C is known, t and Vc can be obtained, R and V become unknown, and the relationship between these variables is related as a simple exponential function as described above. If the measurement is performed twice, one of the variables R and V can be deleted.
[0024]
Therefore, if the measured voltage V is eliminated and the exponential function is arranged, the value of R can be estimated. Next, the voltage to be measured V can be calculated from the storage voltage Vc of the flying capacitor obtained in normal measurement, the R, the on-time t, and the capacitance C of the flying capacitor. In this way, the measured voltage can be detected normally even if the input resistance R is somewhat degraded.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the flying capacitor type voltage detection circuit of the present invention will be described in detail with reference to the following examples.
(Example 1)
(Overall explanation)
A battery pack voltage detection apparatus to which the present invention is applied will be described with reference to a circuit diagram shown in FIG.
[0026]
V1 is one of many secondary batteries constituting the high-voltage assembled battery. The voltage source to be measured in the present invention, SW1 and SW2 are input side sampling switches, C1 is a flying capacitor, and SW3 and SW4 are output side sampling switches. , R1 and R2 are current limiting resistor elements, 9 is a differential amplifier circuit (voltage measuring circuit) having a high input resistance, ADC is an A / D converter, 10 is input side sampling switches SW1 and SW2, and output side sampling switch SW3 , SW4. R3 and R4 are input resistance elements of the voltage measurement circuit 9, R5 is a feedback resistance element of the voltage measurement circuit 9, AMP is an operational amplifier of the voltage measurement circuit 9, and R6 is an output load resistance element of the voltage measurement circuit 9.
[0027]
One end of the secondary battery V1 is connected to one end of the flying capacitor C1 through the resistance element R1 and the input side sampling switch SW1, and the other end of the secondary battery V1 is connected to the other end of the flying capacitor C1 through the resistance element R2 and the input side sampling switch SW2. It is connected to the. Both ends of the flying capacitor C1 are individually connected to a pair of input terminals of the differential amplifier circuit 9 through output side sampling switches SW3 and SW4, respectively. The output voltage of the differential amplifier circuit 9 is predetermined by an A / D converter ADC. Converted to a bit digital signal.
[0028]
To explain the operation, the output side sampling switches SW3 and SW4 are turned off during the reading period, the input side sampling switches SW1 and SW2 are kept on and the flying capacitor C1 is charged by the secondary battery V1, and the next reading period is reached. 2, the input side sampling switches SW 1 and SW 2 are turned off, and the output side sampling switches SW 3 and SW 4 are kept on, and the stored voltage of the flying capacitor C 1 is read to the differential amplifier circuit 9. More specifically, the control circuit 10 adopts a microcomputer configuration, and normally, a reading period in which the input side sampling switches SW1 and SW2 are turned on and a reading period in which the output side sampling switches SW3 and SW4 are turned on are alternately alternated. The output voltage of the A / D converter ADC is captured during the reading period.
[0029]
In order to detect the voltage of each secondary battery constituting the assembled battery, each of the secondary batteries may be read into the flying capacitor C1 in time order by using the input side sampling switches SW1 and SW2 as a multiplexer circuit. A flying capacitor type voltage detection circuit similar to the above may be provided for each secondary battery.
[0030]
(Failure diagnosis)
Next, the operation for detecting a reading abnormality of the flying capacitor type voltage detection circuit will be described with reference to the flowchart shown in FIG. In addition, this flowchart is implemented for every fixed period.
[0031]
First, it is checked whether or not the change in the detection voltage (or change in the charge / discharge current) in the immediately preceding predetermined period is below an allowable constant level (S100). If so, the process proceeds to step S106 to start the test operation. If not, it is checked whether or not an operation test has been performed for a long time (S102), and if not, the process returns to step S100. In step S102, if the operation test has not been performed for a long period of time, the flowchart of FIG. 2 may be terminated this time and the next test may be awaited.
[0032]
If it is determined in step S102 that the operation test has not been performed for a long time, the process proceeds to step S104 to prohibit charging / discharging of the assembled battery in the battery controller (not shown), or the charging / discharging current becomes zero. It requests to perform such power generation control or load control, waits for a predetermined time, and proceeds to step S106. If it is determined in step S102 that the operation test has not been performed for a long time, the battery controller (not shown) prohibits charging / discharging of the assembled battery, or the charging / discharging current is zero. Alternatively, instead of performing the load control, the process may proceed to step S100 and wait for the voltage change (or change in charge / discharge current thereof) of the assembled battery to be a predetermined value or less.
[0033]
In step S106, the operation abnormality of the flying capacitor type voltage detection circuit described in FIG. 1 is tested. As will be described below, this test includes a measurement voltage reading test and a storage voltage reading test, which are sequentially performed.
(Measurement voltage reading test)
First, the on-time period (reading time) of the input side sampling switches SW1 and SW2 is set to several times the normal value, and a long-term reading operation for reading the measured voltage into the flying capacitor C1 is performed, and then the output side sampling switch SW3. The storage voltage of the flying capacitor C1 is read as current voltage data through the differential amplifier circuit 9 and the A / D converter ADC while the on period (reading period) of SW4 is kept normal.
[0034]
Next, a change rate (may be a difference) between the previous voltage data read and stored by the read operation and read operation performed immediately before this long-term read operation (immediately before this test) and the current voltage data is predetermined. Determine if it is below the acceptable level. If the change in the input resistance, which is the electrical resistance value between the voltage source to be measured and the flying capacitor, is within a predetermined tolerance, the rate of change between the previous voltage data and the current voltage data is predetermined. If the change in the input resistance deviates from the predetermined allowable range, the rate of change between the previous voltage data and the current voltage data deviates from the predetermined allowable range. Therefore, it is determined whether or not the input resistance is normal. For the sake of accuracy, an average value of voltage data detected a plurality of times in succession may be employed as the previous voltage data and the current voltage data. Of course, as the previous voltage data, for example, an on-time shorter than the normal on-time of the input-side sampling switches SW1 and SW2 may be adopted in the current test period. (Reading test of stored voltage)
First, the on period (reading period) of the input side sampling switches SW1 and SW2 remains normal, and after performing the normal reading operation of reading the measured voltage into the flying capacitor C1, the on period of the output side sampling switches SW3 and SW4 (Reading time) is set to several times the normal value, and the long-term reading operation of reading the storage voltage of the flying capacitor C1 into the differential amplifier circuit 9 is performed, and the output voltage of the differential amplifier circuit 9 is converted to the A / D converter ADC. To read out the current voltage data.
[0035]
Next, the change rate (which may be a difference) between the previous voltage data read and stored by the read operation and read operation performed immediately before the measurement voltage read test and the current voltage data is a predetermined allowable level. It is determined whether or not: If the change in the output resistance, which is the electrical resistance value between the flying capacitor C1 and the differential amplifier circuit 9, is within a predetermined allowable range, the rate of change between the previous voltage data and the current voltage data described above Is within a predetermined allowable range, and if the change in the output resistance deviates from the predetermined allowable range, the rate of change between the previous voltage data and the current voltage data is within the predetermined allowable range. Thus, it is determined whether or not the output resistance is normal. For the sake of accuracy, an average value of voltage data detected a plurality of times in succession may be employed as the previous voltage data and the current voltage data. Of course, as the previous voltage data, for example, an on-time shorter than the normal on-time of the output side sampling switches SW3 and SW4 may be adopted in the current test period.
[0036]
Next, proceeding to step S108, it is determined whether the result of the test performed at step S106 is good or bad. If it is good, this test routine is terminated. If the test result is poor, the battery controller that controls the charging current and the discharging current to control the capacity of the assembled battery to a predetermined target capacity range is instructed to reduce the target capacity range (S110). More specifically, when the target capacity range is normally controlled to 40 to 60% SOC, this battery controller changes this to 45 to 55%. As a result, when the capacity value is estimated based on the battery voltage detected by the battery controller, overcharge and overdischarge of the battery are less likely to occur even if the capacity is calculated based on an incorrect battery voltage. Of course, although it is necessary to quickly replace or repair the flying capacitor type voltage detection circuit, this countermeasure is effective in the case where the flying capacitor type voltage detection circuit must be used until it is done.
[0037]
Next, the process proceeds to step S112, and when it is determined that the input resistance is abnormally large, the ON period of the input side sampling switches SW1 and SW2 in the subsequent measurement voltage reading operation is set to several times the normal value. When it is determined that the output resistance is abnormally large, the ON period of the output side sampling switches SW3 and SW4 in the subsequent operation of reading the measured voltage is set to a multiple of the normal value. Thereby, the detection error based on such resistance abnormality can be reduced. As a matter of course, such an extension of the ON period leads to a decrease in the number of times of battery voltage sampling within a certain period. However, even if the number of times is small, the error is small compared to frequently detecting a voltage with a large error. The detection of the voltage is naturally preferable in, for example, battery capacity estimation.
[0038]
Next, proceeding to step S114, the voltage data output from the A / D converter ADC is corrected. As described above, by acquiring a plurality of voltage data, the value of the input resistance or output resistance can be estimated. It is used to calculate the voltage to be measured. As a result, although there are more errors than actually measured, it is possible to acquire voltage data with practically sufficient accuracy in spite of abnormal changes in input resistance or output resistance.
[0039]
Next, it progresses to step S116, alert | reports the abnormality of a flying capacitor type voltage detection circuit, and complete | finishes this test.
[Brief description of the drawings]
FIG. 1 is a circuit diagram illustrating a flying capacitor type voltage detection circuit according to a first embodiment.
FIG. 2 is a flowchart illustrating a test operation of the circuit according to the first exemplary embodiment.
[Explanation of symbols]
V1 Voltage source SW1 and SW2 to be measured Input side sampling switch C1 Flying capacitors SW3 and SW4 Output side sampling switch 9 Differential amplifier circuit (voltage measuring circuit)
ADC A / D converter 10 control circuit

Claims (7)

A flying capacitor,
An input side sampling switch for connecting both ends of the voltage source to be measured to both ends of the flying capacitor;
A voltage measurement circuit;
An output-side sampling switch that reads the storage voltage of the flying capacitor into the voltage measurement circuit;
A control circuit for controlling the sampling switch;
In a flying capacitor type voltage detection circuit comprising:
The control circuit includes:
A flying capacitor type voltage detection circuit, wherein an on-time of the input side sampling switch or the output side sampling switch is changed. In the flying capacitor type voltage detection circuit with read failure determination function according to claim 1,
The control circuit includes:
A flying capacitor type characterized in that it is determined whether or not the change rate of the output voltage of the voltage measurement circuit before and after the change exceeds a predetermined value, and an operation test is performed to determine that an operation failure has occurred when the change rate exceeds the change rate. Voltage detection circuit. In the flying capacitor type voltage detection circuit with read failure determination function according to claim 2,
The control circuit includes:
The flying capacitor type voltage detection circuit characterized in that the operation test is not performed or the test result is discarded when the change rate of the output voltage of the voltage measurement circuit exceeds a predetermined value. In the flying capacitor type voltage detection circuit according to claim 2,
The control circuit includes:
A flying-capacitor-type voltage detection circuit that commands regulation of fluctuations in potential of the voltage source to be measured when the operation test is performed. In the flying capacitor type voltage detection circuit according to claim 2,
The control circuit includes:
A flying capacitor type voltage detection circuit characterized in that, when the operation test result is not good, a capacity range in charge / discharge control of a secondary battery as the voltage source to be measured is narrowed around an intermediate capacity value. In the flying capacitor type voltage detection circuit according to claim 2,
The control circuit includes:
A flying-capacitor-type voltage detection circuit characterized by extending the on-time of the input-side sampling switch or the output-side sampling switch from a normal time when the operation test result is not good. In the flying capacitor type voltage detection circuit according to claim 2,
The control circuit includes:
When the operation test result is not good, the output voltage of the voltage measuring circuit is corrected based on the degree of increase in the charging resistance value or discharging resistance value of the flying capacitor estimated based on the test result. Flying capacitor type voltage detection circuit.

Images