KR-102960314-B1 - APPARATUS AND METHOD FOR PRECISE MEASUREMENT OF BATTERY SELF-DISCHARGE CURRENT USING ZRA CIRCUIT

KR102960314B1KR 102960314 B1KR102960314 B1KR 102960314B1KR-102960314-B1

Abstract

The battery self-discharge current measuring device based on the ZRA circuit of the present invention includes an operational amplifier in which the open-circuit voltage of the battery is applied to the non-inverting input terminal and the inverting input terminal is connected to the negative terminal of the battery, a feedback resistor connected between the inverting input terminal and the output terminal of the operational amplifier, and a current measuring unit connected to the output terminal to measure the feedback current flowing through the feedback resistor. The operational amplifier is configured to maintain the potential difference between the non-inverting input terminal and the inverting input terminal at zero so that a feedback current of the same magnitude as the current flowing from the battery to the inverting input terminal flows through the feedback resistor, and the current measuring unit can measure the feedback current to calculate the self-discharge current of the battery.

Inventors

홍영진
이영재
최소일
구관모
김영욱
김종현

Assignees

주식회사 민테크

Dates

Publication Date: 20260508
Application Date: 20250909

Claims (20)

An operational amplifier in which the open-circuit voltage of a battery is applied to the non-inverting input terminal and the inverting input terminal is connected to the negative terminal of the battery; A feedback resistor connected between the inverting input terminal and the output terminal of the operational amplifier; and A current measuring unit connected to the output terminal above and measuring the feedback current flowing through the feedback resistor; Includes, The above operational amplifier is configured to maintain the potential difference between the non-inverting input terminal and the inverting input terminal at zero, so that a feedback current of the same magnitude as the current flowing from the battery to the inverting input terminal flows through the feedback resistor, and A ZRA circuit-based battery self-discharge current measuring device, wherein the current measuring unit measures the feedback current to calculate the self-discharge current of the battery.
In paragraph 1, the operational amplifier is, A battery self-discharge current measuring device based on a ZRA circuit, characterized by an input offset voltage of 10μV or less and an input bias current of 100fA or less.
In paragraph 1, A battery self-discharge current measuring device based on a ZRA circuit, characterized by having a current resolution of 10 pA based on the connection characteristics of the operational amplifier and the feedback resistor.
In paragraph 1, the current measuring unit is, A battery self-discharge current measuring device based on a ZRA circuit, characterized by continuously sampling the output voltage of the operational amplifier, applying a noise reduction filter to the sampled output voltage, and then calculating and determining the feedback current by dividing the filtered output voltage by the feedback resistance value.
A first ZRA comprising a first non-inverting input terminal to which the open-circuit voltage of the battery is applied, a first inverting input terminal, and a first output terminal; A first feedback resistor connected between the first inverting input terminal and the first output terminal; A first voltage measuring unit connected to the first output terminal and measuring the first output voltage; A second ZRA comprising a second non-inverting input terminal to which a reference voltage is applied, a second inverting input terminal, and a second output terminal; A second feedback resistor connected between the second inverting input terminal and the second output terminal; A second voltage measuring unit connected to the second output terminal above and measuring the second output voltage; A voltage control loop that controls the reference voltage so that the output voltage of the second ZRA becomes 0; and A calculation unit that calculates the self-discharge current of the battery by dividing the difference between the first output voltage and the second output voltage by the feedback resistance value; A battery self-discharge current measuring device based on a ZRA circuit, characterized by including
In paragraph 5, the voltage control loop is, A battery self-discharge current measuring device based on a ZRA circuit, comprising a DAC and an operational amplifier for voltage matching in the μV unit, and characterized by adjusting the reference voltage to match the open-circuit voltage of the battery in real time.
In paragraph 5, the first feedback resistor and the second feedback resistor are, A battery self-discharge current measuring device based on a ZRA circuit, characterized by having the same feedback resistance value and the same temperature characteristics, and being placed adjacently in the same thermal environment to offset relative errors between circuits due to differences in temperature coefficients.
In paragraph 5, the above first ZRA and the above second ZRA are, A battery self-discharge current measuring device based on a ZRA circuit, characterized by being implemented in a dual operational amplifier chip of the same specifications.
In paragraph 5, the above-mentioned operation unit is, The self-discharge current (I sd ) is calculated by the following mathematical formula 8, and [Mathematical Formula 8] A battery self-discharge current measuring device based on a ZRA circuit, characterized in that, where V1 represents a first output voltage, V2 represents a second output voltage, and Rf represents a feedback resistance value.
In paragraph 5, the voltage control loop is, A feedback control loop including a reference voltage regulating DAC, an output detection high-gain amplifier, and a voltage comparator for matching the open-circuit voltage of the battery in the µV range; A battery self-discharge current measuring device based on a ZRA circuit, characterized by including
A self-discharge current measurement circuit comprising an operational amplifier connected to a battery, a feedback resistor, and a current measuring section; A voltage stimulus generating unit connected to the non-inverting input terminal of the above operational amplifier and applying a voltage stimulus of a predetermined range to the open-circuit voltage of the battery; A high-resolution analog-to-digital converter that samples the time response of the output voltage of the operational amplifier after the voltage stimulus is applied at the voltage stimulus generator; and A response analysis unit that derives the internal RC response characteristics of the battery by analyzing the time response of the sampled output voltage; Includes, and the response analysis unit, A battery dynamic characteristic analysis device based on battery self-discharge current, characterized by analyzing the Distribution of Relaxation Times (DRT) or Relaxation characteristics of the battery from the above time response.
In Clause 11, the voltage stimulation generating unit is, A voltage buffer for buffering the open-circuit voltage of the above battery; and An adder circuit that adds a step voltage to the output of the above voltage buffer; A battery dynamic characteristic analysis device based on battery self-discharge current, characterized by including
In Paragraph 11, The above voltage stimulus is a step voltage selected within the range of 1mV to 50mV, and A battery dynamic characteristic analysis device based on battery self-discharge current, characterized in that the sampling rate of the above-described high-resolution analog-to-digital converter is 1 kHz to 100 kHz.
In Clause 11, the above response analysis unit, A preprocessing unit that converts the above time response data into log time axis data; A DRT analysis unit that derives a relaxation time distribution by applying a Regularized Inversion algorithm to the above logarithmic time axis data; and A diagnostic unit that evaluates the internal state of the battery from the above relaxation time distribution; A battery dynamic characteristic analysis device based on battery self-discharge current, characterized by including
In paragraph 11, the self-discharge current measuring circuit is, A first ZRA comprising a first non-inverting input terminal to which the open-circuit voltage of the battery is applied, a first inverting input terminal, and a first output terminal; A first feedback resistor connected between the first inverting input terminal and the first output terminal; A first voltage measuring unit connected to the first output terminal and measuring the first output voltage; A second ZRA comprising a second non-inverting input terminal to which a reference voltage is applied, a second inverting input terminal, and a second output terminal; A second feedback resistor connected between the second inverting input terminal and the second output terminal; A second voltage measuring unit connected to the second output terminal above and measuring the second output voltage; A voltage control loop that controls the reference voltage so that the output voltage of the second ZRA becomes 0; and A calculation unit that calculates the self-discharge current of the battery by dividing the difference between the first output voltage and the second output voltage by the feedback resistance value; Includes, The above self-discharge current measurement circuit is, A battery dynamic characteristic analysis device based on battery self-discharge current, characterized by analyzing the dynamic response of the self-discharge current in which temperature change and circuit error are removed from the time response of the output voltage according to the above voltage stimulation.
In Clause 11, the above response analysis unit, In the above relaxation time distribution, conforming cells and nonconforming cells are distinguished based on a predetermined threshold value, and A battery dynamic characteristic analysis device based on battery self-discharge current, characterized in that the suitable cell has a longer time constant than the unsuitable cell.
In a method for measuring the self-discharge current of a battery, A stabilization step of maintaining the above battery in an electrically open state for a predetermined time to stabilize it; A circuit configuration step of applying the open-circuit voltage of the battery to the non-inverting input terminal of the operational amplifier, connecting the inverting input terminal to the negative terminal of the battery, and connecting a feedback resistor between the inverting input terminal and the output terminal to form a ZRA (Zero Resistance Ammeter) circuit; A current induction step in which the operational amplifier operates to maintain a potential difference between input terminals at zero, thereby inducing a feedback current of the same magnitude as the self-discharge current flowing from the battery to flow through the feedback resistor; A voltage measurement step for measuring the output voltage of the above operational amplifier; A current calculation step for calculating a feedback current by dividing the output voltage by the feedback resistance value; and A self-discharge current determination step for determining the above feedback current as the self-discharge current of the battery; A battery self-discharge current measurement method based on a ZRA circuit including
In Paragraph 17, In the above stabilization step, the above predetermined time is 10 to 60 minutes, and A ZRA circuit-based battery self-discharge current measurement method characterized by performing continuous measurement for at least 1 minute in the above voltage measurement step to obtain the self-discharge current value in a stable state of the output voltage.
In Clause 17, the above circuit configuration step is, A reference circuit configuration step for configuring a second ZRA circuit based on a reference voltage; A reference current measurement step for measuring the second feedback current in the second ZRA circuit; and A difference calculation step for deriving a self-discharge current with common temperature change and circuit error removed by calculating the difference between the first feedback current measured in the first ZRA circuit and the second feedback current; A battery self-discharge current measurement method based on a ZRA circuit, characterized by further including
In Clause 17, the current induction step is, A stimulus application step of applying a step voltage of a predetermined magnitude to the non-inverting input terminal of the above ZRA circuit; A response measurement step for high-speed sampling of the output voltage change of the operational amplifier after applying the above step voltage; and A dynamic characteristic analysis step for deriving the distribution of relaxation times of the battery by analyzing the high-speed sampled response data; A battery self-discharge current measurement method based on a ZRA circuit, characterized by further including

Description

Apparatus and Method for Precise Measurement of Battery Self-Discharge Current Using ZRA Circuit The present invention relates to a battery self-discharge current measurement device and method based on a ZRA circuit, and more specifically, to a method and device for precisely measuring the self-discharge current of a secondary battery through a ZRA (Zero Resistance Ammeter) circuit and analyzing the dynamic characteristics of the secondary battery based on the characteristics of the measured current. Rechargeable batteries possess a self-discharge characteristic in which they lose charge over time, serving as a key indicator for determining storage stability, reliability, and quality. In particular, subtle abnormalities such as internal cell soft short circuits, lithium plating, and electrolyte decomposition manifest as an abnormal increase in self-discharge current; consequently, there is a growing demand for technologies capable of precisely detecting and quantitatively analyzing these factors. Currently, the general method used in rechargeable battery production processes involves measuring the cell's Open Circuit Voltage (OCV) at regular intervals and determining suitability based on the amount of change. However, this method has the drawback of reducing process efficiency because it requires a stabilization time of several hours or more before voltage changes are detected. Consequently, there have recently been attempts to transition to technologies that can determine suitability early without waiting for changes in OCV by directly measuring the self-discharge current more quickly and precisely. Figure 1(a) is a diagram visually showing the general trend of self-discharge current increasing over time, demonstrating that conforming cells and nonconforming cells can be distinguished based on the magnitude of the current after a certain period of measurement. As shown in the figure, if the self-discharge current exceeds a preset threshold for classification at the end of the measurement, the cell can be determined to have abnormal leakage characteristics. In addition, FIG. 1(b) is an equivalent circuit model of a battery to explain this self-discharge phenomenon, showing a mathematical relationship indicating that the self-discharge current changes exponentially according to the time constant (τ) determined by the self-discharge resistance (R sd ) and the effective capacitance (C eff ). As such, direct measurement of the self-discharge current can function as a highly reliable means for distinguishing between suitable and unsuitable cells. However, in order to directly measure the self-discharge current, there is a technical challenge in measuring the battery's open-circuit voltage (OCV) with precision at the microvolt (μV) level and accurately applying it as a reference voltage. Currently, commercially available potentiometers provide voltage resolution in the mV range, so applying a precise voltage at the μV level is structurally impossible, and DAC-based digital control methods also cannot guarantee long-term stable voltage maintenance at the μV level due to quantization noise and temperature drift. Reflecting this, various self-discharge diagnostic technologies have been developed. For example, Patent Document 1 in the prior art proposes a method to minimize temperature drift at a specific SOC (State of Charge), but it has limitations in that high costs are required for high-precision voltage control and hardware matching. Patent Document 2 describes a method of detecting the inflection point of the current by applying a constant voltage lower than the OCV and determining the severity of self-discharge through this, but it has the problem that it is difficult to secure a stable reference point and requires long-term measurement. Patent Document 3 presents a method of indirectly inducing and analyzing current flow through ADC-DAC conversion, but the complexity of the circuit and high dependence on high-precision conversion devices are pointed out as problems, and Patent Document 4 introduces a model-based approach that estimates self-discharge based on the zero-crossing point of the current after voltage application, but it has the disadvantage of being sensitive to noise and environmental changes. As such, conventional technology has limitations in terms of cost and reliability because the current sensing method for self-discharge diagnosis is indirect, or it requires high-precision ADCs and complex auxiliary circuits for thermal noise (Johnson-Nyquist noise) correction. To overcome the limitations of such conventional technology, there has been a need for a method that can improve the reliability of precise measurement and suitability determination of self-discharge current without relying on high-precision voltage control and complex auxiliary circuits. Conventional technology refers to technical information that the inventor possessed for the derivation of the present invention or acquired during t