JP4928854B2 - Battery internal resistance measuring device - Google Patents

Description

  The present invention relates to a battery internal resistance measuring apparatus, and more particularly to a technique for eliminating measurement errors due to ringing that occurs when a current is interrupted when measuring the internal resistance of a fuel cell by a current interrupting method.

  A fuel cell is known as a power generation device that converts a chemical energy of a fuel into electric energy by electrochemically reacting a fuel such as hydrogen with an oxidant such as air. As shown in the circuit diagram, an ohmic resistance Rsol and a reaction resistance Rct exist inside the fuel cell FC.

  The ohmic resistance Rsol is mainly a membrane resistance of the fuel cell FC or a pure resistance due to an electrolyte. Usually, a capacitor component Cdl is present in parallel with the reaction resistance Rct, and the reaction state of the electrode can be known by the reaction resistance Rct. Therefore, when evaluating the performance of the fuel cell FC, it is necessary to simultaneously measure the ohmic resistance Rsol and the reaction resistance Rct, which are internal resistances.

  As one of the measuring methods, there is a current interruption method described in Patent Document 1. In the measurement by the current interruption method, as shown in FIG. 3, a load L is connected to the fuel cell FC via the switch SW. Although not shown, an ammeter that measures the load current I supplied from the fuel cell FC to the load L and a voltmeter that measures the voltage across the terminals of the fuel cell FC are used as measuring instruments.

  First, the switch SW is turned on, and the load current I supplied from the fuel cell FC to the load L is measured. As shown in FIG. 4A, the load current I is substantially constant as a steady-state current. At this time, the voltmeter has a voltage drop VL at the load L as shown in FIG. 4B. Measured.

  Next, the switch SW is instantaneously turned off to interrupt the load current, and the voltage across the terminals of the fuel cell FC is measured with a voltmeter. As the load current I becomes 0 [A], the voltage drop Vsol at the ohmic resistance Rsol becomes 0, so that the voltage across the terminals of the fuel cell FC increases from VL to VL + Vsol. The time during this period is about 1-2 μs in a very short time. By measuring this voltage Vsol, the ohmic resistance Rsol can be obtained by the equation Vsol / I.

  On the other hand, the voltage drop Vct at the reaction resistance Rct does not rapidly decrease but gradually decreases due to the CR time constant with the capacitor component Cdl. Therefore, the terminal voltage of the fuel cell FC finally becomes VL + Vsol + Vct (= Edc), and the reaction resistance Rct is obtained from Vct / I. It should be noted that since the rate of voltage increase of the voltage drop Vct at the reaction resistance Rct is gradual, detection takes several s (seconds).

JP 2005-166601 A

  The problem with the current interruption method described above is that there is a reactance component in the wiring of the measurement system, so that ringing occurs in the voltage waveform of FIG. 4B when the current is interrupted, and depending on the magnitude, ohmic resistance Rsol In some cases, it is impossible to accurately measure the voltage drop Vsol.

  Therefore, in the invention described in Patent Document 1, paying attention to the fact that the relationship between voltage and time can be regarded as a linear relationship within a time range of about several hundred μs from the time of current interruption, the current is obtained by linear regression analysis. Although the voltage at the time of interruption is calculated, this requires a high-capacity memory and a high-performance arithmetic processing means capable of performing arithmetic processing on data at high speed, which is not preferable in terms of cost.

  Therefore, an object of the present invention is to eliminate a measurement error due to ringing that occurs at the time of current interruption with a simpler configuration when measuring the internal resistance of a battery (particularly a fuel cell) by the current interruption method.

  In order to solve the above problems, the present invention provides, as described in claim 1, current measuring means for measuring a load current supplied from a battery to a load, switch means for controlling on / off of the load current, Voltage measuring means for measuring the voltage between the terminals of the battery, and control means for calculating the internal resistance of the battery from the measured value of each measuring means and controlling the switch means, and the battery to the load is constant. The load current is rapidly reduced to 0 [A] by the switch means while the load current is being supplied, and the internal resistance of the battery is measured based on the voltage response waveform measured by the voltage measurement means at that time. In the battery internal resistance measuring device, a variable current cutoff speed switch is used as the switch means, and a filter circuit is connected to the input side of the voltage measuring means. An FFT (Fast Fourier Transform means) for analyzing the voltage response waveform is provided, and the control means converts the fall time Tf of the load current due to the current cutoff speed of the variable current cutoff speed type switch into a frequency f2, It is determined whether the single frequency component f1 included in the voltage response waveform obtained by FFT is f1> f2, and based on the determination result that f1> f2, the frequency f2 is passed through the filter circuit, A low-pass filter capable of removing the frequency component f1 is used.

  In the present invention, as described in claim 2, the control means supplies the voltage measurement value by the voltage measurement means at the time when the load current becomes 0A to the load from Vsol, the battery. Assuming that a constant current value is I, an ohmic resistance value included in the internal resistance of the battery is measured from Vsol / I.

  In the present invention, as described in claim 3, the current interruption speed of the variable current interruption speed switch is set faster than the time constant of the reaction resistance included in the internal resistance of the battery. .

  According to the present invention, on the input side of the voltage measuring unit, the frequency f2 that is a frequency converted value of the current interruption speed (current interruption time) is passed, and the frequency component f1 obtained by the FFT calculation of the voltage response waveform is removed. By providing the low-pass filter to be obtained, the ringing waveform is not included in the voltage waveform, so that the ohmic resistance of the internal resistance of the battery can be measured more accurately. In addition, since there is no need for a high-performance arithmetic processing means capable of performing arithmetic processing on a large capacity memory or data at high speed, the cost can be reduced accordingly.

  Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2, but the present invention is not limited to this. FIG. 1 is a schematic circuit diagram showing a battery internal resistance measuring apparatus according to the present invention, and FIGS. 2A and 2B are waveform diagrams showing current waveforms and voltage response waveforms when current is interrupted. Note that the measurement object in this embodiment is the fuel cell FC as described in FIG. 3, but may be a secondary battery or the like.

  As shown in FIG. 1, this internal resistance measuring device has, as a basic configuration, switch means 11 for turning on / off a load current I supplied from a fuel cell FC to a load L, and current measuring means for measuring the load current I. 12. A voltage measuring means 13, a control means 14 and a display 15 for measuring the voltage across the terminals of the fuel cell FC are provided.

  In the present invention, the switch means 11 is a variable current interrupt speed switch that can arbitrarily adjust the current interrupt speed, and the current interrupt speed is controlled by the control means 14. The current measuring means 12 may be an ammeter that is normally used, and the current measurement value is given to the control means 14 via the A / D converter 12a.

  The voltage measuring means 13 may also be a voltmeter that is usually used, and the voltage measurement value is given to the control means 14 via the A / D converter 13a. In the present invention, the A / D converter 13a An FFT 16 that performs fast Fourier transform on the converted digital voltage data is provided. Further, a filter circuit 17 having a cutoff frequency described later is connected to the input side of the voltage measuring means 13.

  A central processing unit (CPU) or a microcomputer may be used for the control means 14. A liquid crystal panel, a plasma display, or the like is used for the display 15, but a printer may be used depending on the case.

  The method for measuring the internal resistance is a current interruption method. That is, in a state where the switch means 11 is turned on and a constant load current I flows from the fuel cell FC to the load L, the switch means 11 is turned off rapidly, and the load current I is reduced to 0 as shown in FIG. [A], the voltage response waveform (FIG. 2B) of the fuel cell FC measured by the voltage measuring means 13 at that time is observed, and the voltage value Vsol by the ohmic resistance Rsol is read.

  However, since there is a reactance component in the measurement system wiring shown in FIG. 1, ringing occurs in the voltage response waveform at the time of current interruption as shown exaggeratedly in FIG. Depending on the magnitude of the ringing, an error may be included when the voltage value Vsol is read from the voltage response waveform. In order to remove the error caused by the ringing, the present invention takes the following measures.

  First, the frequency component f1 included in the voltage response waveform measured by the voltage measuring means 13 is obtained by the FFT 16. Generally, the frequency component f1 is a single frequency because it is a frequency due to resonance of the measurement system.

Next, the falling time of the load current I (time until the load current I becomes 0 [A]) Tf is obtained from the current interruption waveform of FIG. 2A and converted to the frequency f2. For this frequency conversion, an ELMORE relational expression obtained by Laplace transforming Gaussian response characteristics (y ′ = exp (−af ² )) is applied, and f2 = 0.35 / Tf [Hz].

  If it is confirmed by the control means 14 that f1> f2, a low-pass filter that passes the frequency f2 and removes the frequency f1 is applied to the filter circuit 17.

  Note that if the cutoff frequency of the low-pass filter is close to f2, the f2 component of the voltage response waveform is slightly attenuated and an error may occur in the measurement of the voltage value Vsol. X10 [Hz] is preferable.

  Next, the current interruption speed will be described. In order to perform accurate measurement, it is necessary to make the current interruption rate sufficiently faster than the CR time constant of the reaction resistance Rct. As shown in FIG. 2 (c), when the current interruption rate (time Tf until the load current I becomes 0 [A]) is made slower than the CR time constant of the reaction resistance Rct, ringing disappears, but FIG. ), The voltage response waveform is distorted and an error may occur in reading the voltage value Vsol.

  Therefore, several types of current interruption speed patterns are set in the control means 14, and the voltage response signal is measured for each pattern to measure the ringing level and the voltage value Vsol. It is better to determine the optimum current interruption rate.

  As described above, according to the present invention, on the input side of the voltage measuring means 13, the frequency f2, which is the frequency converted value of the current interruption speed (current interruption time), is passed and obtained by the FFT calculation of the voltage response waveform. By connecting a low-pass filter that can remove the frequency component f1 and making the current interruption speed slower than the conventional instantaneous interruption, the voltage response waveform does not include a ringing waveform, so the voltage value Vsol by the ohmic resistance Rsol is accurately Can be measured.

The schematic circuit diagram which shows the internal resistance measuring apparatus of the battery by this invention. The wave form diagram which shows the electric current waveform at the time of the current interruption used by operation | movement description of this invention, and a voltage response waveform. The schematic diagram for demonstrating the internal resistance measurement method of the fuel cell by an electric current interruption method. A basic waveform diagram showing a current waveform and a voltage response waveform when current is interrupted.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Switch means 12 Current measuring means 13 Voltage measuring means 14 Control means 15 Display means 16 FFT
17 Filter circuit FC Fuel cell Rsol Ohmic resistance Rct Reaction resistance Cdl Capacitor component

Claims (3)

From the current measurement means for measuring the load current supplied from the battery to the load, the switch means for controlling the load current on / off, the voltage measurement means for measuring the voltage between the terminals of the battery, and the measurement values of the measurement means Control means for calculating the internal resistance of the battery and controlling the switch means, and the switch means rapidly reduces the load current to 0 [0] while supplying a constant load current from the battery to the load. A], and in the battery internal resistance measuring device for measuring the internal resistance of the battery based on the voltage response waveform measured by the voltage measuring means at that time,
A variable current cutoff speed switch is used as the switch means, a filter circuit is connected to the input side of the voltage measuring means, and an FFT (Fast Fourier Transform means) for analyzing the voltage response waveform is provided.
The control means converts the fall time Tf of the load current due to the current interruption speed of the variable current interruption speed switch into a frequency f2, and a single frequency component f1 included in the voltage response waveform obtained by the FFT. Determine whether f1> f2,
A battery internal resistance measuring apparatus using a low-pass filter capable of passing the frequency f2 and removing the frequency component f1 in the filter circuit based on a determination result that f1> f2.   The control means sets Vsol as the voltage measurement value by the voltage measurement means when the load current reaches 0 A, and I as a constant current value supplied from the battery to the load. The battery internal resistance measuring device according to claim 1, wherein an ohmic resistance value included in the internal resistance is measured. The battery internal resistance measurement according to claim 1 or 2, wherein the current interruption speed of the variable current interruption speed type switch is set to be faster than a time constant of a reaction resistance included in the internal resistance of the battery. apparatus.

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