Current detection system

Abstract

To more precisely detect current in a power line of a power transmission system of an electric vehicle or the like by excluding an influence of a skin effect.SOLUTION: A system 11 for detecting current circulated through a power line extracts an AC component from detection values of first and second current sensors 10 in which detection gains of AC components in the current mutually differs, converts the ratio of the AC components to gain, determines a frequency giving a difference that matches the gain value of the ratio of AC components from the difference in detection gain that changes depending on the frequency of respective AC components of the first and second previously examined current sensors, calculates actual values of AC components by multiplying AC components extracted from detection values of the first and second current sensors by input / output ratios in the first and second current sensors calculated from the detection gains of the first and second current sensors at that frequency, and adds DC components extracted from detection values of the first and second current sensors to calculate an actual value of current.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a current detection system, and more particularly to a system for detecting the value of DC current in input / output lines of batteries or the like in power transmission systems for machinery and equipment such as electric vehicles and stationary power sources. [Background technology]

[0002] In power transmission systems for machinery and equipment (electric vehicles, etc.) such as electric vehicles and stationary power sources, various configurations have been proposed for monitoring ripples or AC components so as to suppress excessive ripples or AC components when they flow in power lines through which DC current flows, such as input / output lines for batteries, etc. For example, Patent Document 1 proposes a configuration that determines that a ripple is occurring in the input / output current when the integrated value, over a first predetermined time period, of the difference between the output value of a current sensor that detects the input / output current of a power storage device and the output value of a low-pass filter that attenuates and cuts off the high-frequency components is equal to or greater than a first threshold value, or when the difference between the maximum and minimum output values ​​of the current sensor over a second predetermined time period is equal to or greater than a second threshold value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-52163 Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable to be able to detect not only the presence or absence of ripple or AC components in power lines (buzz-buzz) through which DC current flows in power transmission systems for electric vehicles and other devices, but also their amplitude. Current sensors typically detect AC components in power lines using magnetic fields or voltage drops due to the current flowing through them. However, the skin effect occurs for AC components in power lines, causing impedance to vary with the frequency of the AC component. This causes the detection gain (output / input ratio) for AC components to vary depending on the shape of the power line and the sensor's detection method, resulting in the amplitude of the AC component being overestimated or underestimated. Therefore, when AC components are present in the current flowing through the power line, the current sensor's detection value cannot be used as an actual or true current value. It is also difficult to directly use the current sensor's detection value to detect ripple or AC component amplitude. Furthermore, attempts to reduce the skin effect, such as by modifying the power line to a more complex shape or adding filters to the sensor or ECU, can result in issues such as increased hardware costs, heat generation in the power line, and poor installation and manufacturability.

[0005] Power transmission systems, such as those for electric vehicles, often incorporate multiple current sensors of different types to ensure reliable current detection. In such a configuration, the influence of the skin effect on each current sensor varies depending on the configuration of each current sensor. Therefore, when an AC component is superimposed on the power line, the amplitude of the AC component detected by each current sensor varies depending on the frequency of the AC component. In this case, as will be described in detail later, the inventors of the present invention have discovered that by utilizing the difference in the AC component detected by each current sensor, it is possible to determine the detection gain for the AC component of each current sensor. Using this detection gain, it is possible to calculate the true value of the AC component superimposed on the power line from the AC component detected by each current sensor, eliminating the influence of the skin effect. This makes it possible to more accurately detect the magnitude of the current, even when an AC component is superimposed on the power line. This finding is utilized in the present invention.

[0006] Thus, a main object of the present invention is to enable more accurate detection of current in a power line of a power transmission system for an electric vehicle or the like by eliminating the influence of the skin effect. [Means for solving the problem]

[0007] According to the present invention, the above problem is solved by a system for detecting a current flowing through a power line, comprising: a first current sensor and a second current sensor for detecting the current, the first current sensor and the second current sensor having different detection gains for AC components in the current; means for extracting AC components from the detected values ​​of the first and second current sensors; means for calculating a ratio of the AC components extracted from the detection values ​​of the first and second current sensors; means for converting the ratio of the AC components into a gain; a means for determining, from among differences in detection gains of the first and second current sensors that change depending on the frequency of the AC components examined in advance, a frequency that gives a difference that coincides with the gain value converted from the ratio of the AC components; means for multiplying the AC components extracted from the detection values ​​of the first and second current sensors by an input / output ratio in the first and second current sensors, the ratio being calculated from the detection gains of the first and second current sensors at the frequency, to calculate actual values ​​of the AC components; a means for calculating an actual value of the current flowing through the power line by adding an actual value of the AC component to a DC component extracted from the detection values ​​of the first and second current sensors; This is achieved by a system including:

[0008] In the above configuration of the present invention, the "power line" may be a power line through which current flows at any location in a power transmission system for an electric vehicle or the like, such as an input / output line of a battery. The "first and second current sensors" may be any current sensors having different detection gains for AC components, as described above. The first and second current sensors detect current on the same power line and are connected in series on the power line. For example, when detecting current flowing into or out of a battery, the first and second current sensors may be connected to either the positive or negative terminal of the battery. Each of the above means may be realized by a computer device operating in accordance with a program using the detection values ​​of the first and second current sensors. In the operation of the above system of the present invention, each means sequentially processes the detection values ​​of the first and second current sensors to calculate the actual value of the current flowing through the power line, as described below.

[0009] Specifically, in the system of the present invention, the current I(t) to be detected can usually be expressed as a DC component Id superimposed with an AC component A·sin(ωt) as follows (the AC component to be detected in the system of the present invention is, for example, a ripple superimposed on a power line, and it is assumed that there is only one oscillation frequency): I(t)=Id+A·sin(ωt) …(1) Here, t is time, A is the amplitude of the AC component, and ω is the angular frequency of the AC component. As described above, the first and second current sensors have different detection gains for the AC component, and if the ratios of the output to the input of the AC component are F1(ω) and F2(ω), respectively, the detected current values ​​I1 and I2 are expressed as follows: I1(t)=Id+F1(ω)A·sin(ωt) …(2a) I2(t)=Id+F2(ω)A·sin(ωt) …(2b) As already mentioned, F1(ω) and F2(ω) are determined by the skin effect of the respective sensors, and are therefore functions of the angular frequency ω (=2πf [f is frequency]) of the AC component. Thus, in the above configuration, the "means for extracting AC components from the detection values ​​of the first and second current sensors" is configured to extract the AC components F1(ω)A·sin(ωt) and F2(ω)A·sin(ωt) in equations (2a) and (2b), respectively, by any method (the extraction period may be set appropriately).

[0010] In the above configuration, when the current sensor outputs F(ωt)·A·sin(ωt) in response to an input of AC component A·sin(ωt), the detection gain G of the AC component of the current sensor is expressed as follows: G=X Log 10 (F(ω)·A·sin(ωt) / A·sin(ωt)) =X·Log 10 (F(ω)) …(3) (X is a coefficient, for example, X=20). Therefore, the ratio F1(ω)A·sin(ωt) / F2(ω)A·sin(ωt)=F1(ω) / F2(ω) of the AC components extracted from the detection values ​​of the first and second current sensors is given as the gain G R Converting to G R =X·Log 10 (F1(ω) / F2(ω)) …(4) The gain G of this AC component ratio is obtained. R teeth, G R =X·Log 10 (F1(ω))-X Log 10 (F2(ω)) …(4a) This value is the difference between the detection gains of the AC components of the first and second current sensors, which changes depending on the frequency of the AC components. Note that at this stage, the angular frequency ω of the AC component is unknown.

[0011] The detection gains of the first and second current sensors, which vary depending on the frequency of the AC components, can be determined in advance, and the difference between the detection gains of the first and second current sensors for each frequency can be determined in advance. That is, once the detection gain difference is known, the frequency of the AC component that provides it can be determined. Thus, from the previously determined detection gain differences of the first and second current sensors, which vary depending on the frequency of the AC components, as described above, a frequency that provides a difference that matches the gain value converted from the ratio of the AC components can be determined, and the determined frequency corresponds to the frequency of the AC components superimposed on the detection values ​​of the first and second current sensors.

[0012] As described above, once the frequency of the AC component superimposed on the detection values ​​of the first and second current sensors can be determined, the magnitude of the detection gain of each AC component of the first and second current sensors can be known. Therefore, in the device of the present invention, the actual value of the AC component is calculated by multiplying the AC component extracted from the detection values ​​of each of the first and second current sensors by the input / output ratio of the first and second current sensors, which is calculated from the detection gains of the first and second current sensors, and the actual value of the AC component is calculated by adding the actual value of the AC component to the DC component extracted from the detection values ​​of each of the first and second current sensors.

[0013] In the system of the present invention, the first and second current sensors may be either of a type that uses a magnetic field generated by a current for detection or a type that uses a voltage drop for detection. Furthermore, the "means for determining, from differences in detection gains of the AC components of the first and second current sensors that vary depending on the frequency thereof, which have been previously determined, a frequency that provides a difference that coincides with the gain value converted from the ratio of the AC components" may include a map of differences in detection gains of the AC components of the first and second current sensors that vary depending on the frequency thereof, a search for a difference in detection gains of the AC components of the first and second current sensors that is equal to the gain of the ratio of the AC components extracted from the detection values ​​of the first and second current sensors by referring to the map, and a frequency that provides the searched difference in detection gain may be determined.

[0014] The extraction of the AC component and the DC component from the detection values ​​of the first and second current sensors may be achieved using any type of amplitude detection technique, high-pass filter, or low-pass filter. Note that the detection values ​​of the first and second current sensors may be filtered to remove noise prior to the extraction of the AC component and the DC component. [Effects of the Invention]

[0015] Thus, in the system for detecting current flowing in a power line according to the present invention, the detection values ​​of two current sensors with different detection gains for the AC component of the current are used to eliminate the influence of the skin effect of the AC component in the detection values, thereby enabling more accurate detection of the current magnitude. The configuration of the present invention can accurately detect the magnitude of ripples and surges occurring in power lines, and is therefore advantageously used in current control to suppress such ripples and surges. Furthermore, as already mentioned, power transmission systems for electric vehicles and the like may already employ a configuration using two current sensors to detect current flowing in power lines. In such cases, the configuration of the present invention is advantageous in that it utilizes the existing configuration to eliminate the influence of the skin effect and more accurately detect the current magnitude.

[0016] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1(A) is a schematic diagram of a power transmission system of an electric vehicle to which the current detection system of this embodiment is applied, and FIG. 1(B) is a schematic diagram of the current detection system of this embodiment provided in the power line of the power transmission system of FIG. 1(A). [Figure 2] FIG. 2 is a block diagram showing the configuration of the current detection system of this embodiment. [Figure 3] FIG. 3(A) is a schematic diagram of the current I(t) to be detected in the current detection system of this embodiment, and the currents I1(t) and I2(t) detected by the two current sensors, respectively. FIGS. 3(B) and 3(C) are graphs schematically illustrating the changes in detection gains G1(ω) and G2(ω) of the first and second current sensors in the current detection system of this embodiment versus the frequency of the AC component. FIG. 3(D) is a graph superimposed on the changes in detection gain of the first and second current sensors in the current detection system of this embodiment, illustrating that the difference Δ between the detection gains of the first and second current sensors depends on frequency. FIG. 3(E) is a graph schematically illustrating the correction values ​​of the AC components of the detected values ​​of the first and second current sensors calculated according to the teachings of this embodiment. [Explanation of symbols]

[0018] 1...vehicle, 2...battery pack, 3...battery cell, 4...power line, 5...inverter, 6...motor, 7...charger, 8...inlet, 9...power line, 10...current sensor, 10_1 ...First sensor 10s_1...detection element, 10f_1...noise filter, 10_2...second sensor 10s_2...detection element, 10f_2...noise filter, 11...arithmetic and control device BEST MODE FOR CARRYING OUT THE INVENTION

[0019] Schematic configuration of the power transmission system The current detection system according to this embodiment may be applied to, for example, detection of a current on a power line 4 in a power transmission system in an electric vehicle 1 as shown in FIG. 1A . More specifically, the power transmission system in the electric vehicle 1 may be configured such that power is transmitted from the battery cells 3 of a battery pack 2 through a power line 4 and an inverter 5 to a drive motor 6, and a power line 9 is connected to the power line 4 from an external charger 7 via an inlet 8 so that the battery cells 3 can be charged from the charger 7. In a power transmission system configured as described above, during power transmission to the drive motor 6, a ripple r may be superimposed on the current on the power line connected to the battery cells due to switching of switching elements in the inverter and motor rotation. Furthermore, during charging of the battery cells 3 from the charger 7, a ripple r may be superimposed on the current due to switching of switching elements in the charger and the main power grid. If such a ripple r, i.e., the amplitude of the AC component, is excessive, it may damage the battery cells 3 or other components. The current detection system is configured to monitor the magnitude of the current flowing through the power line 4 using a current sensor 10 appropriately installed on the power line 4, without ignoring fluctuations due to the AC component, so that such excessively large amplitude ripples or AC components do not occur, or if they do occur, can be quickly suppressed.

[0020] Current detection system configuration As described in the Summary of the Invention section, in the current detection system of this embodiment, as shown in FIG. 1B, two types of current sensors 10_1 and 10_2 with different detection gains for AC components (which vary depending on the frequency) are connected in series on a power line 4 through which the current to be detected flows. For example, one of the current sensors 10_1 and 10_2 may be a shunt resistor type, and the other may be a magnetic type (e.g., a TMR type). As shown in the figure, each sensor includes a detection element 10s_1 or 10s_2 for detecting the magnitude of the current and a filter 10f_1 or 10f_2 for removing noise from the detection value obtained therefrom. The noise-removed detection value is input to an arithmetic and control device 11. In the arithmetic and control device 11, the actual value of the current flowing on the power line 4, from which the effects of the skin effect have been removed, is calculated using the detection values ​​of the two current sensors, which are affected by the skin effect, as described below. The operation of the arithmetic and control device 11 may be realized by the operation of a computer device in accordance with a program.

[0021] Operation of the current detection system As explained in the Summary of the Invention section, when a current sensor detects a current on a power line, the AC component of the detected current is generally affected by the skin effect, causing the detection gain of the current sensor to vary depending on the frequency of the AC component, resulting in the detection value of the current sensor deviating from the actual current value on the power line. Therefore, in this embodiment, a configuration is provided in which the detection values ​​of two current sensors with different detection gain frequency characteristics are used to eliminate the influence of the skin effect when detecting a current with a current sensor, thereby obtaining an actual current value.

[0022] Specifically, first, the first and second current sensors each detect the current on the power line. Here, the detected values ​​I1(t) and I2(t) of the first and second current sensors deviate from each other and from the true current value I(t), as shown in Figure 3(A). This is because the detection gains G1(ω) and G2(ω) of the AC components of the first and second current sensors increase or decrease from 0 as the frequency of the AC component increases due to the skin effect, as shown in Figures 3(B) and 3(C). This causes the amplitude of the AC component superimposed on the DC component in the detected current value to increase or decrease. Therefore, if the detection gains G1(ω) and G2(ω) of the first and second current sensors for the AC component in the detected current value are obtained, the true amplitude can be determined by correcting for changes due to the detection gains G1(ω) and G2(ω) in the amplitude of the AC component in the detected values ​​I1(t) and I2(t), and thereby the true current value I(t) can be obtained.

[0023] Thus, in the calculation and control device 11 of this embodiment, as shown on the left side of Figure 2, the detection values ​​I1(t) and I2(t) are input to the amplitude detector, and AC components F1(ω)A·sin(ωt) and F2(ω)A·sin(ωt) of I1(t) and I2(t) are extracted (see equations (2a) and (2b) above). The ratio F1(ω) / F2(ω) is calculated by a divider, and this AC component ratio is further converted into gain units using equation (4) by a gain converter. Here, the gain value of equation (4) is equal to the difference G1(ω)-G2(ω) between the detection gains of the first and second current sensors, as shown in equation (4a) (see Figure 3(D)). As already mentioned, the detection gains G1(ω) and G2(ω) for each frequency of the first and second current sensors can be found in advance, and the difference Δ between the detection gains for each frequency, Δ=G1(ω)-G2(ω), can also be found in advance. Thus, in this embodiment, a map of the difference Δ between the detection gains for each frequency that has been prepared in advance is prepared in the difference map calculator, and in this map, the gain conversion value G of the ratio F1(ω) / F2(ω) of the AC components obtained from the detection values ​​I1(t) and I2(t) of the first and second current sensors is calculated. RA detection gain difference Δ that matches the difference G1(ω)−G2(ω) is searched for, and the frequency that gives the searched difference Δ=G1(ω)−G2(ω) can be determined to be the frequency ωx of the AC component in the detection values ​​I1(t) and I2(t), as shown in FIG. 3(D).

[0024] As described above, once the frequency ωx of the AC component in the detected values ​​I1(t) and I2(t) is determined, the detection gains G1(ωx) and G2(ωx) of the frequency ωx in the first and second current sensors are determined from the maps of each sensor (which may be as shown in Figures 3(B) and 3(C)). Next, a gain inverse converter converts the determined detection gains G1(ωx) and G2(ωx) into the output-to-input ratios F1(ωx) and F2(ωx) of each sensor using the following equations: F(ωx)=10 G(ωx) / X …(5) Then, by dividing the AC components F1(ω)A·sin(ωt) and F2(ω)A·sin(ωt) of the detected values ​​I1(t) and I2(t) by the obtained input-output ratios F1(ωx) and F2(ωx), respectively, the true amplitude A·sin(ωt) of the AC components is calculated. By adding this to the AC components of the detected values ​​I1(t) and I2(t), the true current value Id+A·sin(ωt) is obtained, as shown in Figure 3(E).

[0025] Thus, according to the current detection system of the present embodiment, the actual or true value of the current in the power line, from which the influence of the skin effect has been removed, can be obtained.

[0026] The above description has been made in relation to the embodiments of the present invention, but it will be apparent that many modifications and changes will be readily apparent to those skilled in the art, and the present invention is not limited to the above-described exemplary embodiments, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] A system for detecting a current flowing through a power line, comprising: a first current sensor and a second current sensor for detecting the current, the first current sensor and the second current sensor having different detection gains for AC components in the current; means for extracting AC components from the detected values ​​of the first and second current sensors; means for calculating a ratio of the AC components extracted from the detection values ​​of the first and second current sensors; means for converting the ratio of the AC components into a gain; a means for determining, from among differences in detection gains of the first and second current sensors that change depending on the frequency of the AC components examined in advance, a frequency that gives a difference that coincides with the gain value converted from the ratio of the AC components; means for multiplying the AC components extracted from the detection values ​​of the first and second current sensors by an input / output ratio in the first and second current sensors calculated from the detection gains of the first and second current sensors at the frequency, to calculate actual values ​​of the AC components; a means for calculating an actual value of the current flowing through the power line by adding an actual value of the AC component to a DC component extracted from the detection values ​​of the first and second current sensors; A system including:

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