Current / voltage detecting device and current / voltage detecting method

Abstract

A current / voltage detecting device (1) comprises: a switch (31) which, in accordance with a timing signal, selects and switches an input path to be electrically connected to an output side, from among an input path from a current input terminal (11) and an input path from a voltage input terminal (12); a switch (21) which, in accordance with a selection signal, selects and switches a resistance, from among shunt resistors (22a, 22b, 22c), to be electrically connected to the input path from the current input terminal (11); a timing generating unit (54) which outputs the timing signal to the switch (31); and a current range determining unit (55) which determines, from among the shunt resistors (22a, 22b, 22c), a shunt resistor which reduces the value of a difference between a current conversion value and an input voltage value, and which outputs, to the switch (21), the selection signal for selecting the determined shunt resistor.

Description

Current / voltage detection device and current / voltage detection method

[0001] The present disclosure relates to a current / voltage detection device and a current / voltage detection method.

[0002] In power measurement, because power is calculated as the product of current and voltage, it is necessary to simultaneously or quickly switch between current detection and voltage detection. For example, if a power measurement device has a circuit for current detection and a circuit for voltage detection, it can detect current and voltage values ​​almost simultaneously, enabling instantaneous power measurement.

[0003] However, in a device that has both circuits for current detection and voltage detection in one device, if two systems of circuits are provided, one for current detection and one for voltage detection, from the analog signal input to the part that performs digital signal processing via AD conversion, the circuit size will increase.

[0004] In contrast, for example, in the power control device described in Patent Document 1, the circuits provided after the current detection unit and the voltage detection unit are shared, and the shared circuit is switched between the current detection unit and the voltage detection unit using a switch, which makes it possible to suppress an increase in the circuit size of the device.

[0005] In current detection, the current from the input terminal is passed through a shunt resistor, and the amount of current (hereinafter referred to as the current conversion value) is measured by converting it into a voltage, which is the product of the shunt resistance and the input current, i.e., the potential difference generated across the shunt resistor.

[0006] Japanese Patent Application Laid-Open No. 2020-160245

[0007] The conventional technology described in Patent Document 1 has a problem in that when switching from current detection to voltage detection, if a large level difference occurs between the current conversion value and the input voltage value, large ringing occurs in the voltage waveform. For example, since ringing occurs in the initial stage of switching, if switching is performed in a short time, a voltage signal including the ringing waveform will be AD converted in a subsequent stage, causing an error in the input data (current value or voltage value).

[0008] The present disclosure is intended to solve the above-mentioned problems, and has an object to provide a current / voltage detection device that can suppress ringing that occurs when switching between current detection and voltage detection.

[0009] The current-voltage detection device according to the present disclosure includes an input changeover switch that selects and switches an input path to be connected to the output side from among the input path from the current input terminal and the input path from the voltage input terminal in accordance with a timing signal; a plurality of shunt resistors having different resistance values; a resistance changeover switch that selects and switches a resistor from the plurality of shunt resistors to be connected to the input path from the current input terminal in accordance with a selection signal; a timing generation unit that outputs a timing signal to the input changeover switch; and a determination unit that determines, from the plurality of shunt resistors, a shunt resistor that minimizes the difference between a current-equivalent value converted to voltage by multiplying the input current value input from the current input terminal and the value of the shunt resistor, and the input voltage value input from the voltage input terminal, and outputs a selection signal to the resistance changeover switch to select the determined shunt resistor.

[0010] According to the present disclosure, a shunt resistor that minimizes the difference between a current equivalent value and an input voltage value is selected from among a plurality of shunt resistors having different resistance values, and the selected shunt resistor is connected to an input path from a current input terminal. Since the magnitude of ringing decreases as the difference between the current equivalent value and the input voltage value decreases, the current-voltage detection device according to the present disclosure can suppress ringing that occurs when switching between current detection and voltage detection.

[0011] Fig. 1 is a circuit diagram showing a configuration example of a current-voltage detection device according to a first embodiment; Fig. 2 is a waveform diagram showing a voltage waveform, a timing signal waveform, and a ringing waveform in the first embodiment; Fig. 3 is a flowchart showing a current-voltage detection method according to the first embodiment; Fig. 4 is a circuit diagram showing a configuration example of a current-voltage detection device according to a second embodiment; Fig. 5 is a waveform diagram showing a voltage waveform, a ringing waveform, a first timing signal waveform, and a second timing signal waveform in the second embodiment;

[0012] 1 is a circuit diagram showing an example of the configuration of a current / voltage detection device 1 according to a first embodiment. In FIG. 1, the current / voltage detection device 1 detects, for example, the voltage value of an AC voltage and the current value of an AC current applied to a load from a commercial power source. The current / voltage detection device 1 includes a current input terminal 11, a voltage input terminal 12, and an input return terminal 13. The current input terminal 11 receives an input current signal I ｉｎ The voltage input terminal 12 is a terminal to which an input voltage signal V ｉｎ The input return terminal 13 is a terminal connected to the ground. A return signal Rtn flowing between the current / voltage detection device 1 and the power supply is returned to the ground through the input return terminal 13.

[0013] A current detection unit (not shown in Fig. 1) is connected to the current input terminal 11. The current detection unit detects an analog input current signal I ｉｎ For example, the current detection unit converts the current so that the voltage value falls within the input range of the AD conversion unit 52 to generate an input current signal I ｉｎ To the voltage input terminal 12, for example, a voltage detection unit (not shown in FIG. 1) is connected. The voltage detection unit converts the voltage value of the AC power supplied from the power supply and generates an analog input voltage signal V ｉｎ For example, the voltage detection unit converts the voltage at a rate that the peak value of the AC voltage from the power supply falls within the input range of the AD conversion unit 52, thereby generating the input voltage signal V ｉｎ Generate.

[0014] The switch 21 is a resistor selector switch that selects one of the shunt resistors 22a, 22b, and 22c to be connected to the input path from the current input terminal 11 in response to a selection signal. The shunt resistors 22a, 22b, and 22c have different resistance values. For example, the resistance values ​​are 100 times different from each other. Specifically, the resistance value Rsa of the shunt resistor 22a is 0.1 mΩ, the resistance value Rsb of the shunt resistor 22b is 10 mΩ, and the resistance value Rsc of the shunt resistor 22c is 1000 mΩ. By having such significantly different resistance values, it is possible to select from these shunt resistors the shunt resistor that minimizes the difference between the current equivalent value and the input voltage value, as described below. The shunt resistors 22a, 22b, and 22c are collectively referred to as shunt resistor 22.

[0015] The switch 31 is an input changeover switch that selects and switches the input path to be connected to the output side from the input path from the current input terminal 11 and the input path from the voltage input terminal 12 in accordance with a timing signal. An amplifier 41 is connected to the output side of the switch 31. When the switch 31 connects the input path from the current input terminal 11 to the output side, the input current signal I ｉｎ is output to the amplifier 41, and when the input path from the voltage input terminal 12 is made conductive to the output side, the input voltage signal V ｉｎ is output to the amplifier 41.

[0016] The amplifier 41 receives the analog input signal output from the switch 31 and amplifies the strength of the analog input signal. The analog input signal amplified by the amplifier 41 is output to a sample-and-hold circuit 42. The analog input signal is converted into an input current signal I ｉｎ or the input voltage signal V ｉｎ is.

[0017] The sample-and-hold circuit 42 is a circuit that holds an analog signal that is input from the current input terminal 11 or the voltage input terminal 12 and output through the switch 31. For example, the sample-and-hold circuit 42 is a circuit made up of a resistor and a capacitor. One end of the resistor is connected to the output terminal of the amplifier 41, and the other end is connected to one end of the capacitor. The other end of the capacitor is grounded. Furthermore, the connection point between the other end of the resistor and the other end of the capacitor is connected to the AD conversion unit 52 in the subsequent stage.

[0018] In the sample-and-hold circuit 42, the analog input signal output from the amplifier 41 is connected to a capacitor via a resistor. When the switch 31 is switched, the charge of the analog input signal is accumulated in the capacitor, and when the switch 31 is switched again, the charge accumulated in the capacitor is discharged. In other words, the sample-and-hold circuit 42 is a circuit that holds the analog input signal for a certain period of time by accumulating charge in the capacitor. By using the sample-and-hold circuit 42 and the AD conversion unit 52, it is possible to hold the analog input signal for a certain period of time and then convert it into a digital signal.

[0019] The control unit 51 controls the overall operation of the current / voltage detection device 1. The control unit 51 includes an AD conversion unit 52, a data processing unit 53, a timing generation unit 54, and a current range determination unit 55. For example, the control unit 51 executes a current / voltage detection application, whereby the control unit 51 realizes the functions of the AD conversion unit 52, the data processing unit 53, the timing generation unit 54, and the current range determination unit 55.

[0020] The AD conversion unit 52 converts into a digital input signal the analog input signal output from the sample-and-hold circuit 42. For example, the AD conversion unit 52 samples data from the analog input signal within the input range at a constant sampling period, thereby generating a digital input signal made up of the sampled digital data.

[0021] The data processing unit 53 receives the input current signal I ｉｎThe current value is detected using the ｉｎ For example, the data processing unit 53 detects the voltage value using the input current signal I ｉｎ The current value is calculated from the input voltage signal V ｉｎ The data processing unit 53 may calculate the effective value of the AC voltage based on the change in the detected voltage value.

[0022] The timing generation unit 54 generates a timing signal and outputs the generated timing signal to the switch 31. For example, the timing generation unit 54 generates a square wave signal that alternates between high and low levels at a regular interval as the timing signal. When this square wave timing signal is at a high level, the input path is switched to that from the voltage input terminal 12 to perform a voltage detection sequence, and when it is at a low level, the input path is switched to that from the current input terminal 11 to perform a current detection sequence.

[0023] The current range determination unit 55 is a determination unit that determines, from among the shunt resistors 22a, 22b, and 22c, the shunt resistor that minimizes the difference between the current-converted value and the input voltage value input from the voltage input terminal, and outputs a selection signal to the switch 21 to select the determined shunt resistor. The current-converted value is the voltage converted from the product of the input current value input from the current input terminal 11 and the value of the shunt resistance.

[0024] For example, based on the result of comparing the digital input signal output from the AD conversion unit 52 with the timing signal output from the timing generation unit 54, the current range determination unit 55 determines from among the shunt resistors 22a, 22b, and 22c which shunt resistor results in the smallest difference between the input voltage value detected in the voltage detection sequence and the current equivalent value.

[0025] In the current detection sequence, an input current is passed through one of shunt resistors 22 a, 22 b, and 22 c, and the current range determination unit 55 detects the input current value (A). The current range determination unit 55 then calculates a current equivalent value (V) converted into voltage by multiplying the input current value (A) by the known resistance value (Ω) of the currently selected shunt resistor. In this way, the input current value can be uniquely determined by knowing the voltage value input to the AD conversion unit 52 and the resistance value of the selected and used shunt resistor.

[0026] The current range determination unit 55 detects the input current signal I output from the AD conversion unit 52 to the data processing unit 53 in the current detection sequence. ｉｎ and obtains the input current signal I ｉｎ The current range determination unit 55 calculates a current equivalent value converted into voltage by multiplying the current value of the input voltage signal V output from the AD conversion unit 52 to the data processing unit 53 in the voltage detection sequence. ｉｎ and obtains the input voltage signal V ｉｎ Then, the current range determination unit 55 detects the voltage value of the input voltage signal V ｉｎ The shunt resistor to be switched next is selected so that the level difference between the voltage value and the current equivalent value becomes small.

[0027] The current range determination unit 55 determines whether the digital signal output from the AD conversion unit 52 is equal to or smaller than the input current signal I based on the timing signal obtained from the timing generation unit 54. ｉｎ or the input voltage signal V ｉｎ For example, assume that the timing signal is a square wave signal that alternates between high and low levels at a regular interval, and that a voltage detection sequence is performed when the timing signal is high and a current detection sequence is performed when the timing signal is low. In this case, the current range determination unit 55 determines the shunt resistance that reduces the difference between the input voltage value and the equivalent current value detected in the voltage detection sequence performed when the timing signal is high.

[0028] Furthermore, the current-voltage detection device 1 may repeat the voltage detection sequence and the current detection sequence until the difference between the input voltage value and the converted current value becomes equal to or less than a reference value, and during the repetition of these sequences, the current range determination unit 55 may determine a shunt resistor that causes the difference between the input voltage value and the converted current value to become equal to or less than the reference value. This allows switching to a shunt resistor that suppresses ringing caused by switching between current detection and voltage detection.

[0029] 2 is a waveform diagram showing a voltage waveform, timing signal waveform A, and ringing waveform B in embodiment 1. In Fig. 2, the waveform at the top is a voltage waveform switched by switch 31, and shows the signal waveform output from AD conversion unit 52 to data processing unit 53. When timing signal waveform A is at a high level, a voltage detection sequence is performed, and when it is at a low level, a current detection sequence is performed.

[0030] In the voltage waveform at the top, the portion corresponding to the high level section of the timing signal waveform A is the input voltage signal V obtained in the voltage detection sequence. ｉｎ The portion corresponding to the low level section of the timing signal waveform A is the current equivalent value I obtained in the current detection sequence. ｉｎａ , I ｉｎｂ and I ｉｎｃ This shows:

[0031] For example, assume that the resistance value Rsa of the shunt resistor 22a is 0.1 mΩ, the resistance value Rsb of the shunt resistor 22b is 10 mΩ, and the resistance value Rsc of the shunt resistor 22c is 1000 mΩ. When the shunt resistor 22a is selected by the switch 21, a current equivalent value I of several mV is generated as shown in FIG. ｉｎａ is obtained.

[0032] Input voltage signal V ｉｎ When the voltage value is several volts, the current equivalent value I ｉｎａ and the input voltage signal V ｉｎ As shown by the double arrow, there is a large level difference between the voltage value of the input voltage signal V ｉｎ Voltage value and current equivalent value I ｉｎａIf the difference is large, a large ringing waveform B occurs in the voltage waveform input to the amplifier 41 due to a sudden change in potential when the input path is switched by the switch 31.

[0033] When the potential difference is large, not only does the ringing amplitude increase, but the convergence time for the amplitude to converge also increases. When an analog input signal containing a ringing component is input to the AD conversion unit 52, a difference corresponding to the ringing component occurs in the current value or current value converted into a digital signal by the AD conversion unit 52. This ultimately becomes a cause of error in the input data input to the data processing unit 53.

[0034] When the shunt resistor 22b is selected by the switch 21, the current equivalent value I ｉｎｂ The input voltage signal V ｉｎ If the voltage value is several volts, the current equivalent value I ｉｎｂ and the input voltage signal V ｉｎ In this case, a level difference occurs between the voltage value of ｉｎａ Although it is smaller than that in the case of (1), a ringing waveform B of a medium magnitude occurs.

[0035] When the shunt resistor 22c is selected by the switch 21, the current equivalent value I ｉｎｃ The input voltage signal V ｉｎ When the voltage value is several volts, the current equivalent value I ｉｎｃ and the input voltage signal V ｉｎ As indicated by the double-headed arrow, the smallest level difference occurs between the voltage value of 1 and 2. In this case, the smallest ringing waveform B occurs in the voltage waveform. Therefore, the current range determination unit 55 selects the shunt resistor 22c as the shunt resistor 22 to be used for current detection and voltage detection of the AC power supplied from the power supply.

[0036] Next, a current / voltage detection method according to the first embodiment will be described. Fig. 3 is a flowchart showing the current / voltage detection method according to the first embodiment, illustrating current / voltage detection by the current / voltage detection device 1. In accordance with the timing signal input from the timing generation unit 54, the switch 31 switches the input path to be conducted to the output side to the input path from the voltage input terminal 12 (step ST1). For example, when the timing signal waveform A is at a high level, the switch 31 switches to the voltage detection sequence.

[0037] The control unit 51 receives the input voltage signal V ｉｎ For example, the voltage value of the input voltage signal V output from the switch 31 is detected (step ST2). ｉｎ is input to the amplifier 41, and the amplifier 41 outputs an input voltage signal V ｉｎ The amplifier 41 amplifies the intensity of the amplified input voltage signal V ｉｎ is output to the sample-and-hold circuit 42. The sample-and-hold circuit 42 outputs the temporarily held input voltage signal V ｉｎ to the AD conversion unit 52. The AD conversion unit 52 converts the input voltage signal V ｉｎ is converted into a digital signal, the input voltage signal V ｉｎ The voltage value is detected.

[0038] In accordance with the timing signal input from the timing generation unit 54, the switch 31 switches the input path to be connected to the output side to the input path from the current input terminal 11 (step ST3). For example, when the timing signal waveform A is at a low level, the switch 31 switches to the current detection sequence.

[0039] The current range determination unit 55 calculates a current conversion value converted into a voltage by multiplying the input current value output from the AD conversion unit 52 by the resistance value of the shunt resistor 22 (step ST4). Here, the input current value output from the AD conversion unit 52 is calculated based on the input current signal I input from the current input terminal 11. ｉｎ is the current value.

[0040] Next, the current range determination unit 55 determines the current conversion value and the input voltage signal V ｉｎThe difference between the voltage value of the shunt resistor 22a and the current value of the shunt resistor 22c is calculated (step ST5). After the voltage detection sequence is performed in this manner, when the switch 31 is switched to perform the current detection sequence, the voltage value is known but the current value is unknown. Therefore, the shunt resistor to be initially selected is the shunt resistor with the smallest resistance value among the shunt resistors 22a, 22b, and 22c.

[0041] The current range determination unit 55 determines whether or not there is an unselected shunt resistor among the shunt resistors 22a, 22b, and 22c (step ST6). If it is determined that there is an unselected shunt resistor and that a shunt resistor can be reselected (step ST6; YES), the current range determination unit 55 selects the unselected shunt resistor among the shunt resistors 22a, 22b, and 22c and outputs a selection signal indicating the selected shunt resistor to the switch 21. This executes a series of processes from step ST1.

[0042] If it is determined that there are no unselected shunt resistors and that a shunt resistor cannot be reselected (step ST6; NO), the current range determination unit 55 selects a shunt resistor from among the shunt resistors 22a, 22b, and 22c that minimizes the difference calculated in step ST5, and outputs a selection signal indicating the selected shunt resistor to the switch 21. This allows the current-voltage detection device 1 to suppress ringing that occurs when switching between current detection and voltage detection. Note that the reselection of the shunt resistor may be terminated when the difference between the current conversion value and the input voltage value becomes equal to or less than the allowable value.

[0043] When the first current detection sequence is completed, as described above, the current conversion value and the input voltage signal V ｉｎ The difference between the voltage value of the input voltage signal V and the shunt resistor V is calculated. Then, the flow chart can be completed or the process can be returned to voltage detection. When the second voltage detection sequence is completed, the shunt resistor to be used in the second current detection sequence is already known from the first current detection sequence. Therefore, the current conversion value is calculated based on the input voltage signal V. ｉｎThe shunt resistor 22 is selected so that the voltage value is closest to the input voltage value. This makes it possible to reduce the difference between the input voltage value and the current equivalent value when switching between current detection and voltage detection, thereby suppressing the magnitude and duration of ringing and enabling high-speed switching between current detection and voltage detection.

[0044] Although the shunt resistors 22a, 22b, and 22c having three different resistance values ​​have been described above as examples, the shunt resistor 22 may be a shunt resistor having two or more different resistance values. For example, if the resistance value Rsa of the shunt resistor 22a is 0.1 mΩ, the resistance value Rsb of the shunt resistor 22b is 10 mΩ, and the resistance value Rsc of the shunt resistor 22c is 1000 mΩ, only the shunt resistors 22b and 22c may be provided. Furthermore, the shunt resistor 22 may be a shunt resistor having four or more different resistance values. These resistance values ​​are determined in advance, for example, through experiments for the power supply expected to be detected.

[0045] As described above, the current-voltage detection device 1 according to the first embodiment includes a switch 31 that selects and switches the input path to be connected to the output side from the input path from the current input terminal 11 and the input path from the voltage input terminal 12 in accordance with a timing signal, shunt resistors 22 a, 22 b, and 22 c, a switch 21 that selects and switches the resistor to be connected to the input path from the current input terminal 11 from shunt resistors 22 a, 22 b, and 22 c in accordance with a selection signal, a timing generator 54 that outputs a timing signal to switch 31, and a current range determiner 55 that determines a shunt resistor from shunt resistors 22 a, 22 b, and 22 c that reduces the difference between the current equivalent value and the input voltage value and outputs a selection signal to switch 21 to select the determined shunt resistor. Since the magnitude of ringing decreases as the difference between the current equivalent value and the input voltage value decreases, the current-voltage detection device 1 can suppress ringing that occurs when switching between current detection and voltage detection. Furthermore, although ringing occurs in the initial stage of switching, in the current / voltage detection device 1, the magnitude of the ringing itself is small, so switching between current detection and voltage detection can be performed in a short time, i.e., high-speed switching is possible.

[0046] In the first embodiment, the current-voltage detection device 1 includes a sample-and-hold circuit 42 that holds an analog signal input from the current input terminal 11 or the voltage input terminal 12 and output via the switch 31, and an AD conversion unit 52 that converts the analog signal output from the sample-and-hold circuit 42 into a digital signal. Based on the result of comparing the digital signal output from the AD conversion unit 52 with the timing signal output from the timing generation unit 54, a current range determination unit 55 determines from among the shunt resistors 22a, 22b, and 22c a shunt resistor that minimizes the difference between the input voltage value detected in the voltage detection sequence and its equivalent current value. This enables the current-voltage detection device 1 to switch to a shunt resistor that suppresses ringing caused by switching between current detection and voltage detection.

[0047] In the first embodiment, the current-voltage detecting device 1 repeatedly performs a voltage detection sequence and a current detection sequence until the difference between the input voltage value and the converted current value becomes equal to or less than a reference value. The current range determining unit 55 determines a shunt resistor that makes the difference between the input voltage value and the converted current value equal to or less than the reference value. This allows the current-voltage detecting device 1 to switch to a shunt resistor that suppresses ringing caused by switching between current detection and voltage detection.

[0048] The current-voltage detection method according to the first embodiment includes the steps of: switching the input path connected to the output side of switch 31 to the input path from voltage input terminal 12; detecting the input voltage value input from voltage input terminal 12; switching the input path connected to the output side of switch 31 to the input path from current input terminal 11; calculating a current-equivalent value converted into voltage by multiplying the input current value input from current input terminal 11 by the value of a shunt resistor; calculating a difference between the current-equivalent value and the input voltage value; and determining whether a shunt resistor that reduces the calculated difference can be selected from shunt resistors 22 a, 22 b, and 22 c. By performing this method, current-voltage detection device 1 can suppress ringing that occurs when switching between current detection and voltage detection.

[0049] Embodiment 2. Figure 4 is a circuit diagram showing an example configuration of a current-voltage detection device 1A according to embodiment 2. In Figure 4, the same components as those in Figure 1 are designated by the same reference numerals, and redundant description will be omitted. The current-voltage detection device 1A detects, for example, the voltage value of an AC voltage and the current value of an AC current applied to a load from a commercial power source. The current-voltage detection device 1A includes a current input terminal 11, a voltage input terminal 12, an input return terminal 13, a switch 21, a shunt resistor 22, a switch 31, an amplifier 41, a sample-and-hold circuit 43, and a control unit 51A.

[0050] The sample-and-hold circuit 43 is a circuit that holds an analog signal input from the current input terminal 11 or the voltage input terminal 12 and output via the switch 31. The sample-and-hold circuit 43 is a circuit consisting of a switch 43a, a resistor, and a capacitor. The switch 43a is an input adjustment switch that interrupts or connects the signal path from the sample-and-hold circuit 43 to the AD conversion unit 52 in accordance with a timing signal. The input side of the switch 43a is connected to the amplifier 41. One end of the resistor is connected to the output side of the switch 43a, and the other end is connected to one end of the capacitor. The other end of the capacitor is grounded. Furthermore, the connection point between the other end of the resistor and the other end of the capacitor is connected to the downstream AD conversion unit 52.

[0051] In the sample-and-hold circuit 43, the analog input signal output from the amplifier 41 is interrupted or conducted by the switch 43a. The analog input signal that is conducted by the switch 43a is connected to a capacitor via a resistor. When the switch 31 is switched, the charge of the analog input signal is accumulated in the capacitor, and when the switch 31 is switched again, the charge accumulated in the capacitor is discharged. In other words, the sample-and-hold circuit 42 is a circuit that holds the analog input signal for a certain period of time by accumulating charge in the capacitor. By using the sample-and-hold circuit 42 and the AD conversion unit 52, it is possible to hold the analog input signal for a certain period of time and then convert it into a digital signal.

[0052] The control unit 51A controls the overall operation of the current / voltage detection device 1. The control unit 51A includes an AD conversion unit 52, a data processing unit 53, a timing generation unit 54A, and a current range determination unit 55. For example, the control unit 51A executes a current / voltage detection application, whereby the control unit 51A realizes the functions of the AD conversion unit 52, the data processing unit 53, the timing generation unit 54A, and the current range determination unit 55.

[0053] The timing generation unit 54A generates a timing signal for the switch 31 and outputs the generated timing signal to the switch 31, and also generates a timing signal for the switch 43a and outputs the generated timing signal to the switch 43a. For example, the timing generation unit 54A generates an on / off timing signal that indicates the timing at which a ringing component included in the analog signal held in the sample and hold circuit 43 is not input to the AD conversion unit 52, and outputs the generated on / off timing signal as a timing signal to the switch 43a. This makes it possible to control the timing at which the analog signal is taken in from the sample and hold circuit 43 to the AD conversion unit 52.

[0054] For example, the timing generation unit 54A generates a timing signal having a rectangular wave whose high level and low level alternate at a constant cycle, as in the first embodiment. When this rectangular wave timing signal is at a high level, it switches the input path to the voltage input terminal 12 in order to perform the voltage detection sequence, and when it is at a low level, it switches the input path to the current input terminal 11 in order to perform the current detection sequence.

[0055] 5 is a waveform diagram showing a voltage waveform, a ringing waveform, a first timing signal waveform A, and a second timing signal waveform C in the second embodiment. In FIG. 5, the waveform at the top is a voltage waveform switched by the switch 31, as in FIG. 2, and shows the signal waveform output from the AD conversion unit 52 to the data processing unit 53. When the first timing signal waveform A is at a high level, a voltage detection sequence is performed, and when it is at a low level, a current detection sequence is performed. When the second timing signal waveform C is at a high level, the switch 43a is turned on, and when it is at a low level, the switch 43a is turned off.

[0056] In the voltage waveform at the top, the portion corresponding to the high level section of the first timing signal waveform A is the input voltage signal V obtained in the voltage detection sequence. ｉｎ The portion corresponding to the low level section of the first timing signal waveform A is the voltage value of the current equivalent value I obtained in the current detection sequence. ｉｎａ , Iｉｎｂ and I ｉｎｃ In addition, the portion of the voltage waveform at the top corresponding to the high level section of the second timing signal waveform C is the input voltage signal V ｉｎ The range D is:

[0057] For example, assume that the resistance value Rsa of the shunt resistor 22a is 0.1 mΩ, the resistance value Rsb of the shunt resistor 22b is 10 mΩ, and the resistance value Rsc of the shunt resistor 22c is 1000 mΩ. When the shunt resistor 22a is selected by the switch 21, a current equivalent value I of several mV is generated as shown in FIG. ｉｎａ is obtained.

[0058] Input voltage signal V ｉｎ When the voltage value is several volts, the current equivalent value I ｉｎａ and the input voltage signal V ｉｎ As shown by the double arrow, there is a large level difference between the voltage value of the input voltage signal V ｉｎ Voltage value and current equivalent value I ｉｎａ If the difference is large, a large ringing waveform occurs in the voltage waveform input to the amplifier 41 due to a sudden change in potential when the input path is switched by the switch 31.

[0059] When the potential difference is large, not only does the ringing amplitude increase, but the convergence time for that amplitude also increases. When an analog input signal containing a ringing component is input to the AD conversion unit 52, a difference corresponding to the ringing component is generated in the current value or current value converted into a digital signal by the AD conversion unit 52. This ultimately becomes a cause of error in the input data input to the data processing unit 53. In response to this, by controlling the switching of the switch 43a, the AD conversion unit 52 can acquire only the analog input signal corresponding to range D after the ringing has converged.

[0060] When the shunt resistor 22b is selected by the switch 21, the current equivalent value I ｉｎｂ The input voltage signal V ｉｎ If the voltage value is several volts, the current equivalent value Iｉｎｂ and the input voltage signal V ｉｎ In this case, a level difference occurs between the voltage value of ｉｎａ Although smaller than in the case of (1), a ringing waveform B of a medium magnitude occurs. Even in this case, by controlling the switching of the switch 43 a, the AD conversion unit 52 can acquire only the analog input signal corresponding to the range D after the ringing has converged.

[0061] When the shunt resistor 22c is selected by the switch 21, the current equivalent value I ｉｎｃ The input voltage signal V ｉｎ When the voltage value is several volts, the current equivalent value I ｉｎｃ and the input voltage signal V ｉｎ As indicated by the double-headed arrow, the smallest level difference occurs between the voltage value of 1 and 2. In this case, the smallest ringing waveform B occurs in the voltage waveform, but by controlling the switching of switch 43a, the AD conversion unit 52 can acquire only the analog input signal corresponding to range D after the ringing has converged. This allows the current range determination unit 55 to select shunt resistor 22c as the shunt resistor 22 to be used for current detection and voltage detection of AC power supplied from the power supply, and the control unit 51A can acquire the analog input signal in range D after the ringing has converged.

[0062] In the second embodiment, the current-voltage detecting device 1A includes a switch 43a for interrupting or connecting the signal path from the sample-and-hold circuit 43 to the AD conversion unit 52 in accordance with a timing signal. The timing generating unit 54A generates a timing signal indicating the timing at which a ringing component included in the analog signal held in the sample-and-hold circuit 43 is not input to the AD conversion unit 52, and outputs the timing signal to the switch 43a, thereby controlling the timing at which the analog signal is taken in from the sample-and-hold circuit 43 to the AD conversion unit 52. Because the switch 43a is switched at a timing at which the ringing component is not input to the AD conversion unit 52, the current-voltage detecting device 1A can suppress ringing that occurs when switching between current detection and voltage detection.

[0063] It is possible to combine the embodiments, modify any of the components of the embodiments, or omit any of the components of the embodiments.

[0064] The current / voltage detection device according to the present disclosure can be used, for example, to detect current / voltage in a power control device.

[0065] 1, 1A Current / voltage detection device, 11 Current input terminal, 12 Voltage input terminal, 13 Input return terminal, 21, 31, 43a Switch, 22, 22a, 22b, 22c Shunt resistor, 41 Amplifier, 42, 43 Sample / hold circuit, 51, 51A Control unit, 52 AD conversion unit, 53 Data processing unit, 54, 54A Timing generation unit, 55 Current range determination unit.

Claims

1. A current / voltage detection device comprising: an input changeover switch which selects and switches an input path to be connected to an output side from among an input path from a current input terminal and an input path from a voltage input terminal in accordance with a timing signal; a plurality of shunt resistors having different resistance values; a resistance changeover switch which selects and switches a resistor to be connected to the input path from the current input terminal from among the plurality of shunt resistors in accordance with a selection signal; a timing generation unit which outputs the timing signal to the input changeover switch; and a determination unit which determines from among the plurality of shunt resistors a shunt resistor which provides the smallest difference between a current equivalent value converted into a voltage by multiplying an input current value of a current signal input from the current input terminal and the value of the shunt resistor, and outputs the selection signal to the resistance changeover switch to select the determined shunt resistor.

2. The current / voltage detection device according to claim 1, further comprising: a sample-and-hold circuit that holds an analog signal input from the current input terminal or the voltage input terminal and output through the input selector switch; and an AD conversion unit that converts the analog signal output from the sample-and-hold circuit into a digital signal, wherein the determination unit determines, from among a plurality of shunt resistors, the shunt resistor that provides the smallest difference between the input voltage value detected in a voltage detection sequence and the current conversion value based on a result of comparing the digital signal output from the AD conversion unit with the timing signal output from the timing generation unit.

3. The current / voltage detection device according to claim 1, characterized in that a voltage detection sequence and a current detection sequence are repeated until a difference between the input voltage value and the current conversion value becomes equal to or less than a reference value, and the determination unit determines the shunt resistor for which the difference between the input voltage value and the current conversion value becomes equal to or less than the reference value.

4. The current / voltage detection device according to claim 2, further comprising an input adjustment switch that cuts off or connects the signal path from the sample-and-hold circuit to the AD conversion unit in accordance with an on / off timing signal, wherein the timing generation unit generates the on / off timing signal that indicates the timing at which a ringing component contained in the analog signal held in the sample-and-hold circuit is not input to the AD conversion unit, and outputs the generated on / off timing signal to the input adjustment switch, thereby controlling the timing at which the analog signal is taken in from the sample-and-hold circuit to the AD conversion unit.

5. A current / voltage detection method for a current / voltage detection device as defined in any one of claims 1 to 4, characterized in that the current / voltage detection device comprises the steps of: switching the input path to be conducted to the output side of the input changeover switch to the input path from the voltage input terminal; detecting the input voltage value input from the voltage input terminal; switching the input path to be conducted to the output side of the input changeover switch to the input path from the current input terminal; calculating the current equivalent value converted into voltage by multiplying the input current value input from the current input terminal and the value of the shunt resistor; calculating the difference between the current equivalent value and the input voltage value; and selecting, from a plurality of the shunt resistors, the shunt resistor that provides the smallest calculated difference value.

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