JP2015118006A - Current value detection device and current value detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a current value while removing noise of a current waveform detected by using one shunt resistance and suppressing the degradation of accuracy due to an influence of noise removal.SOLUTION: A power supply device 12 includes: a motor current detection unit 20 which detects a current by one shunt resistance; and a filter unit 22 which has filters with different time constants τand τconnected in parallel, allows the current detected by the motor current detection unit 20 to pass the plurality of filters and outputs a current waveform for each of the plurality of filters. The power supply device 12 determines a current value from a current waveform selected on the basis of pulse widths and the time contacts τand τ, out of the plurality of current waveforms outputted from the filter unit 22.

Description

  The present invention relates to a current value detection device and a current value detection method.

In a motor control device that controls a motor by a converter circuit and an inverter circuit, current detection is performed by inserting one shunt resistor in the DC part of the inverter circuit (Patent Document 1).
In such current detection, a filter circuit may be provided to remove noise from the detected current waveform. The filter circuit is formed of a resistor and a capacitor, and the effect of noise removal can be enhanced by increasing the time constant of these.

JP 2013-663340 A

  However, if the time constant is long, the current waveform may be affected by the time constant even at the timing of current detection, and the current waveform may be distorted. In particular, the accuracy of the detected current value may be lowered in a current waveform with a narrow pulse width. As a result, the current value may be erroneously determined, and current oscillation may occur in the apparatus or overcurrent may occur. In such a state, a control target such as a motor may be stopped.

  The present invention has been made in view of such circumstances, and removes noise of a current waveform detected using a single shunt resistor and suppresses a decrease in accuracy due to the effect of noise removal. An object is to provide a current value detection device and a current value detection method capable of detecting a value.

  In order to solve the above problems, the current value detection apparatus and current value detection method of the present invention employ the following means.

  In the current value detection device according to the first aspect of the present invention, a current detection means for detecting a current by one shunt resistor and a plurality of filters each having a different time constant are connected in parallel, and the current detection means detects the current detection means. And a filter means for outputting a current waveform for each of the plurality of filters, and among the plurality of current waveforms output from the filter means, the width of the current waveform and the time Current value determination means for determining a current value from the current waveform selected based on a constant.

  According to this configuration, the current detection means detects the current with one shunt resistor. The current detection means is provided in, for example, a motor control device including a converter and an inverter, and detects a current flowing through the motor.

The filter means is formed by connecting a plurality of filters each having a different time constant in parallel. The filter is provided to remove noise in the current waveform. The current detected by the current detection means passes through a plurality of filters, and a current waveform is output for each of the plurality of filters. The longer the time constant, the easier it is to remove noise from the current waveform. However, the accuracy of the current value obtained from the current waveform that has passed through the filter having a long time constant may not be good.
Therefore, the current value determining means determines the current value from the current waveform selected based on the width and time constant of the current waveform among the plurality of currents output from the filter means. That is, the current waveform from which noise is removed and suitable for detection of the current value is selected from the relationship between the width of the current waveform and the time constant of the filter.

  Therefore, this configuration can remove the noise of the current waveform detected using one shunt resistor, and can detect the current value while suppressing the decrease in accuracy due to the effect of noise removal.

  In the first aspect, it is preferable that the current value determination unit determines a current value from the current waveform selected based on a current value detection timing corresponding to a width of the current waveform and the time constant.

The current value is desirably detected from the current waveform at a timing at which noise is removed and there is no influence of the filter. As an example, the detection timing of the current value is around the center of the width of the current waveform. In this configuration, the current waveform is selected based on the current value detection timing and the time constant corresponding to the width of the current waveform. That is, a current waveform that has passed through a filter having a time constant that hardly affects the detection of the current value is selected.
Therefore, this configuration can detect the current value with higher accuracy.

  In the first aspect, it is preferable that the current value determination unit determines a current value from the current waveform that has passed through the filter having the longest time constant when the detection timing is longer than the longest time constant. .

The current waveform that has passed through the filter with the longest time constant has a high noise removal effect. For this reason, according to this configuration, when the detection timing of the current value is longer than the longest time constant, the influence of the distortion of the current waveform due to noise removal at the detection timing is small. Therefore, the current value is determined from the current waveform that has passed through the filter with the longest time constant.
Therefore, this configuration can detect the current value with higher accuracy.

  In the first aspect, when the current value determination means has the time constant longer than the detection timing, the current value of the current waveform that has passed through the filter having the time constant longer than the detection timing; and When the difference between the current value of the current waveform that has passed through the filter and the time constant shorter than the detection timing is calculated, and the difference is smaller than a predetermined value indicating the occurrence of noise, the time shorter than the detection timing A current value is determined from the current waveform that has passed through the constant filter, and if the difference is greater than the predetermined value, a current value is determined from the current waveform that has passed through the filter with the time constant longer than the detection timing. It is preferable to determine.

The current waveform that has passed through the filter with a short time constant may not have sufficient noise removed.
Therefore, according to this configuration, the difference between the current value of the current waveform that has passed through the filter having a time constant longer than the detection timing and the current value of the current waveform that has passed through the filter having a time constant shorter than the detection timing is calculated. The

When the difference is smaller than a predetermined value indicating the occurrence of noise, the current value is determined from the current waveform that has passed through the filter having a time constant shorter than the detection timing of the current value. The case where the difference is smaller than a predetermined value is a case where noise is removed from the current waveform. In this case, the current waveform that has passed through the filter with a long time constant may have low accuracy in current detection, and therefore the current value is determined from the current waveform that has passed through the filter with a short time constant.
On the other hand, when the difference is larger than the predetermined value, the current waveform that has passed through the filter having a time constant longer than the detection timing of the current value is selected. The case where the difference is larger than the predetermined value is a case where the noise of the current waveform that has passed through the filter having a short time constant is not removed. Therefore, the current value is determined from the current waveform that has passed through the filter having a long time constant.

  Therefore, this configuration can detect the current value with higher accuracy.

  In the current value detection method according to the second aspect of the present invention, a current detection unit that detects a current with one shunt resistor and a plurality of filters each having a different time constant are connected in parallel, and the current detection unit detects the current value. A current value detection method for a current value detection device comprising: filter means for passing a plurality of currents that pass through the plurality of filters, wherein the current is detected by the current detection means; A current waveform is output, and a current value is determined from the current waveform selected based on the width of the current waveform and the time constant among the plurality of output current waveforms.

  According to the present invention, there is an excellent effect that noise of a current waveform detected using one shunt resistor can be removed, and a current value can be detected while suppressing a decrease in accuracy due to the effect of noise removal.

1 is a configuration diagram of a power supply device according to a first embodiment of the present invention. It is a block diagram which shows the structure of the filter part which concerns on 1st Embodiment of this invention. It is the schematic diagram which showed the pulse width of the PWM waveform which concerns on 1st Embodiment of this invention. It is a flowchart which shows the flow of the electric current value determination process which concerns on 1st Embodiment of this invention. It is the schematic diagram which showed the electric current waveform which passed the electric current detection timing and filter in the real electric current waveform which concerns on 1st Embodiment of this invention. It is the schematic diagram which showed the electric current waveform which passed the electric current detection timing and filter in the real electric current waveform which concerns on 1st Embodiment of this invention. It is the schematic diagram which showed the electric current waveform which passed the electric current detection timing and filter in the real electric current waveform which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structure of the filter part which concerns on 2nd Embodiment of this invention. It is a flowchart which shows the flow of the electric current value determination process which concerns on 2nd Embodiment of this invention. It is the schematic diagram which showed the electric current waveform which passed the electric current detection timing and filter in the real electric current waveform which concerns on 2nd Embodiment of this invention. It is the schematic diagram which showed the electric current waveform which passed the electric current detection timing and filter in the real electric current waveform which concerns on 2nd Embodiment of this invention. It is the schematic diagram which showed the electric current waveform which passed the electric current detection timing and filter in the real electric current waveform which concerns on 2nd Embodiment of this invention.

  Hereinafter, an embodiment of a current value detection device and a current value detection method according to the present invention will be described with reference to the drawings.

With reference to FIG. 1, the power supply device 12 for supplying electric power to the motor 10 will be described.
The motor 10 is, for example, a permanent magnet type synchronous motor used as a drive source for a compressor of an air conditioner.

  The power supply device 12 includes a converter 14, an inverter 16, an inverter control device 18, a motor current detection unit 20, and a filter unit 22.

  Converter 14 has one end connected to AC power supply 24 and the other end connected to inverter 16. Then, converter 14 converts AC power (three-phase AC power) supplied from AC power supply 24 into DC power and sends it to inverter 16.

  The inverter 16 has one end connected to the converter 14 and the other end connected to the motor 10. The inverter 16 converts the DC power output from the converter 14 into three-phase AC power and supplies it to the motor 10. To do. A capacitor 30 that smoothes the DC voltage is provided between the inverter 16 and the converter 14.

The inverter 16 includes switching elements 32A to 32F.
The switching elements 32A and 32B are connected in series, the emitter of the switching element 32A and the collector of the switching element 32B are connected to the motor 10, and a motor current Iu flows through the motor 10. The switching elements 32C and 32D are connected in series, the emitter of the switching element 32C and the collector of the switching element 32D are connected to the motor 10, and a motor current Iv flows through the motor 10. The switching elements 32E and 32F are connected in series, the emitter of the switching element 32E and the collector of the switching element 32F are connected to the motor 10, and a motor current Iw flows through the motor 10. Further, the capacitor 30, the switching elements 32A and 32B connected in series, the switching elements 32C and 32D connected in series, and the switching elements 32E and 32F connected in series are connected in parallel.

  The inverter control device 18 is a microcomputer (hereinafter also referred to as a “microcomputer”), and includes a computer-readable recording medium such as a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory). Composed. A series of processes for realizing various functions is recorded on a recording medium or the like in the form of a program as an example, and the CPU reads the program into a RAM or the like to execute information processing / arithmetic processing. As a result, various functions are realized. The program is preinstalled in a ROM or other storage medium, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. Etc. may be applied. The computer-readable recording medium is a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like.

  The inverter control device 18 generates a gate drive signal (PWM signal) for each phase so as to make the rotation speed of the motor 10 coincide with a motor rotation speed command given from a host control device (not shown). The gate drive signal is applied to the switching elements 32 </ b> A to 32 </ b> F corresponding to each phase of the inverter 16, whereby the inverter 16 is controlled and a desired three-phase AC voltage is supplied to the motor 10.

Specifically, the inverter control device 18 performs A / D conversion on the detected three-phase (u, v, w) motor currents Iu, Iv, Iw, and converts the three-phase motor current into the two-phase current, that is, the q axis. Convert to current and d-axis current. Then, the inverter control device 18 generates a q-axis voltage command and a d-axis voltage command based on the motor rotation speed command and the two-phase current, converts them into three-phase voltage commands vu, vv, vw, and PWM Used for control.
The PWM control generates a triangular wave with a predetermined carrier frequency, compares the triangular wave with the three-phase voltage commands vu, vv, and vw, and further corrects the duty width of the PWM pulse by using the input DC voltage Vdc. Thus, a gate drive signal corresponding to each phase is generated and output to the inverter 16.

The motor current detection unit 20 includes one shunt resistor 36 and a non-inverting amplifier circuit 38 in order to detect motor currents Iu, Iv, and Iw.
The shunt resistor 36 is connected between the switching element 32B and the capacitor 30.
The non-inverting amplifier circuit 38 amplifies the voltage that appears as a voltage drop in the shunt resistor 36 and outputs the amplified voltage to the filter unit 22.

The filter unit 22 is provided to remove noise of the current waveform detected by the motor current detection unit 20.
FIG. 2 is a configuration diagram of the filter unit 22.
In the filter unit 22 according to the first embodiment, filters 40A and 40B having different time constants τ _A and τ _B are connected in parallel. The filters 40A and 40B have time constants τ _A and τ _B determined by a resistor 42 and a capacitor 44. The time constant τ _A of the filter 40A is longer than the time constant τ _B of the filter 40B.
The filter unit 22 outputs a current waveform for each of the filters 40A and 40B to the current value determination unit 50 provided in the inverter control device 18. The current waveform that has passed through the filters 40A and 40B is input to the inverter control device 18 after A / D conversion.

  The current value determination unit 50 determines the current value from the current waveform selected from the current waveform width and the time constants of the filters 40A and 40B among the plurality of current waveforms output from the filter unit 22.

FIG. 3 is a schematic diagram showing the pulse widths of the three phases (u, v, w) of the PWM waveform.
As shown in FIG. 3, in the triangular wave of the carrier frequency, the range where the triangular wave and the timer value tu intersect is the U-phase pulse width pu. The range where the triangular wave and the timer value tv intersect is the v-phase pulse width pv. The range where the triangular wave and the timer value tw intersect is the w-phase pulse width pw.
The magnitude relationship between timer values is tu>tv> tw, and the pulse width magnitude relationship is pw>pv> pu. Thus, the motor currents Iu, Iv, and Iw have different pulse widths.

表１に示される関係から、モータ電流Ｉｕ及びモータ電流−Ｉｗを検出可能なパルス幅は、図３に示されるパルス幅ｐｕ’，ｐｖ’となる。本第１実施形態では、一例として、パルス幅ｐｕ’，ｐｖ’の略中央近辺でモータ電流Ｉｕ及びモータ電流−Ｉｗが検出される。 The motor currents that can be detected by the motor current detection unit 20 are the motor current Iu and the motor current −Iw in the case of the above-described relationship between the timer value and the pulse width. The motor current Iv is calculated from the motor current Iu and the motor current Iw.
Then, the mode is assigned based on the magnitude relation of the timer value, and as shown in Table 1, the motor current is detected according to the assigned mode.

From the relationship shown in Table 1, the pulse widths capable of detecting the motor current Iu and the motor current −Iw are the pulse widths pu ′ and pv ′ shown in FIG. In the first embodiment, as an example, the motor current Iu and the motor current −Iw are detected around the approximate center of the pulse widths pu ′ and pv ′.

The pulse widths pu ′ and pv ′ that can detect the motor currents Iu and −Iw are different from each other. The filters 40A and 40B are provided to remove current waveform noise. Noise is likely to occur as the switching element 32 is turned on and off, and the filter 40 having a longer time constant is more likely to remove noise from the current waveform. However, the power waveform is more distorted as it passes through the filter 40 having a longer time constant. For this reason, the accuracy of the current value obtained from the current waveform that has passed through the filter 40 having a long time constant may not be good. In particular, the current waveform having a short pulse width pu ′, pv ′ may be distorted at the current value detection timing.
Therefore, in the current value determination process executed by the current value determination unit 50, noise is removed and a current waveform suitable for detection of the current value is selected from the relationship between the width of the current waveform and the time constant of the filter 40, The current value is determined (detected) from the selected current waveform.

  FIG. 4 is a flowchart showing a flow of current value determination processing executed by the current value determination unit 50. A program relating to the current value determination processing is stored in advance in a predetermined area of the inverter control device 18. The current value determination process is executed every time the inverter control device 18 generates a gate drive signal.

First, in step 100, it is determined whether or not the current value detection timing (hereinafter referred to as “current detection timing T”) is longer than the time constant τ _{A of the} filter 40A. If the determination is affirmative, the process proceeds to step 102. If the determination is negative, the process proceeds to step 104.

  In step 102, a current waveform that has passed through the filter 40A having a long time constant is selected, and a current value is determined (detected) from the current waveform.

  In step 104, it is determined whether or not there is noise in the current waveform. If the determination is affirmative, the process proceeds to step 102. If the determination is negative, the process proceeds to step 106.

  In step 106, the current waveform that has passed through the filter 40B having a short time constant is selected, and the current value is determined (detected) from the current waveform.

  The current value determination process will be described with reference to FIGS.

5-7, the actual current waveform (hereinafter referred to as "actual current waveform.") Current waveform that has passed through the filter 40A of the current detection timing T and the time constant tau _A in, when passed through the filter 40B of constant tau _B current It is the schematic diagram which showed the waveform. The actual current waveform is a square as an example. The current detection timing T in FIGS. 5 to 7 is, for example, near the center of the width of the current waveform.

FIG. 5 shows a case where the pulse width of the actual current waveform is long. FIG. 6 shows a case where the pulse width of the actual current waveform is short. The current waveforms that have passed through the filters 40A and 40B rise with response times corresponding to the time constants τ _A and τ _B in order to eliminate noise.

The current value is desirably detected from the current waveform at a timing at which noise is removed and there is no influence of the filters 40A and 40B.
Therefore, in the current value determination process, one current waveform is selected based on the current detection timing T corresponding to the width of the current waveform and the time constants τ _A and τ _B. That is, the current waveform that has passed through the filter 40 having a time constant that hardly affects the detection of the current value is selected.
The current waveform may be selected based on the value obtained by multiplying the time constants τ _A and τ _B by a predetermined constant β and the current detection timing T. Further, the constant β may be set to different constants β _A and β _B depending on the time constants τ _A and τ _B.

As shown in FIG. 5, when the current detection timing T is longer than the time constant τ _A , the influence of the distortion of the current waveform due to noise removal is small at the current detection timing T. For this reason, a current waveform that has passed through the filter 40A having a time constant τ _{A that} has a higher noise removal effect is selected in step 100, and a current value is detected from this current waveform in step 102.

If the current detection timing T shorter than the time constant tau _A as shown in FIG. 6, the current value detected by the current detection timing T is affected by the constant tau _A time. For this reason, the current value determination process proceeds to step 104 when there is a time constant τ _A longer than the current detection timing T.

Here, the current waveform that has passed through the filter 40A having the time constant τ _A longer than the current detection timing T may be distorted and the current detection accuracy may be lowered. On the other hand, noise may not be sufficiently removed from the current waveform that has passed through the filter 40B having the short time constant τ _B.
FIG. 7 shows a state in which noise cannot be removed at the current detection timing T in the filter 40B having a short time constant τ _B.

Therefore, in step 104, the difference between the current value of the current waveform that has passed through the filter 40A with the time constant τ _A and the current value of the current waveform that has passed through the filter 40B with the time constant τ _B (hereinafter referred to as “current difference”). Is calculated.
Then, a predetermined value (hereinafter referred to as “noise value”) α indicating the occurrence of noise is compared with the current difference d. The noise value is a predetermined value.
When the current difference d is smaller than the noise value α, the current value is determined from the current waveform that has passed through the filter 40B having a time constant τ _B shorter than the current detection timing T. The case where the current difference d is smaller than the noise value α is a case where noise is removed from the current waveform.
On the other hand, the current waveform that has passed through the filter 40A of the time constant tau _A, distorted current waveform in the current detection timing T, there is a less accurate probability of current detection.

When the current difference d is larger than the noise value α, a current waveform that has passed through the filter 40A having a time constant τ _A longer than the current detection timing T is selected. The case where the difference is larger than the noise value α is a case where noise is not removed from the current waveform that has passed through the filter 40B having a short time constant τ _B. Therefore, the current value is determined from the current waveform that has passed through the filter 40A having the long time constant τ _A.

  By such a current value determination process, the current value is detected with higher accuracy.

  The current values determined (detected) by the current value determination processing according to the first embodiment are three-phase motor currents Iu and -Iw, which are input to the inverter control device 18 and used for PWM control.

As described above, the power supply device 12 according to the first embodiment includes the motor current detection unit 20 that detects a current by using one shunt resistor 36, and the filters 40A that have different time constants τ _A and τ _B , respectively. 40B is connected in parallel, and the current detected by the motor current detection unit 20 passes through the plurality of filters 40A and 40B, and the filter unit 22 outputs a current waveform for each of the plurality of filters 40A and 40B. Then, the power supply device 12 calculates a current value from the current waveform selected based on the pulse widths pu ′ and pv ′ of the current waveform and the time constants τ _A and τ _B among the plurality of current waveforms output from the filter unit 22. judge.
Therefore, the power supply device 12 according to the first embodiment removes noise of the current waveform detected using one shunt resistor 36 and detects a current value while suppressing a decrease in accuracy due to the effect of noise removal. it can.

[Second Embodiment]
Hereinafter, a second embodiment of the present invention will be described.

  The configuration of the power supply device 12 according to the second embodiment is the same as the configuration of the power supply device 12 according to the first embodiment shown in FIG.

FIG. 8 shows a configuration of the filter unit 22 according to the second embodiment. 8 that are the same as those in FIG. 2 are assigned the same reference numerals as in FIG. 8, and descriptions thereof are omitted.
Filter unit 22 according to the second embodiment includes the filter 40A of the time constant tau _A, the time constant tau _B filter 40B, a filter 40C time constant tau _C.
The time relationship of the time constants of the respective filters 40 is as follows: time constant τ _A > time constant τ _B > time constant τ _C.

  FIG. 9 is a flowchart showing a flow of current value determination processing according to the second embodiment.

First, in step 200, the length of the pulse width is determined. In other words, the current detection timing T determines the time constant tau _A filter 40A, constant tau _B filter time 40B, and whether the time is longer than the constant tau _C of the filter 40C. When the current detection timing T is longer than the time constant τ _A (T> τ _A ), the process proceeds to step 202. If the current detection timing T is longer than the time constant τ _{B and not} more than the time constant τ _A (τ _B <T ≦ τ _A ), the process proceeds to step 204. When the current detection timing T is equal to or less than the time constant τ _B (T ≦ τ _B ), the process proceeds to step 208.

  In step 202, the current waveform that has passed through the filter 40A having the longest time constant is selected, and the current value is determined (detected) from the current waveform.

  In step 204, it is determined whether or not there is noise in the current waveform. If the determination is affirmative, the process proceeds to step 202. If the determination is negative, the process proceeds to step 206.

  In step 206, the current waveform that has passed through the filter 40B is selected, and the current value is determined (detected) from the current waveform.

  In step 208, it is determined whether or not there is noise in the current waveform. If the determination is affirmative, the process proceeds to step 206. If the determination is negative, the process proceeds to step 210.

  In step 210, the current waveform that has passed through the filter 40C with the shortest time constant is selected, and the current value is determined (detected) from the current waveform.

  The current value determination process will be described with reference to FIGS.

10 to 12 show the current waveform that has passed through the filter 40A having the current detection timing T and the time constant τ _{A in} the actual current waveform (hereinafter referred to as “real current waveform”), the current waveform that has passed through the filter 40B having τ _B , It is the schematic diagram which showed the electric current waveform which passed the filter 40C of time constant (tau) _c . The actual current waveform is a square as an example. The current detection timing T in FIGS. 10 to 12 is, for example, near the center of the width of the current waveform.

FIG. 10 shows a case where the pulse width of the actual current waveform is long and the current detection timing T is longer than the time constant τ _A (T> τ _A ). In the case shown in FIG. 10, the process proceeds from step 200 to step 202.
FIG. 11 shows a case where the current detection timing T is longer than the time constant τ _{B and} equal to or less than the time constant τ _A (τ _B <T ≦ τ _A ). In the case shown in FIG. 11, the process proceeds from step 200 to step 204.
FIG. 12 shows the case where the current detection timing T is equal to or less than the time constant τ _B (T ≦ τ _B ). In the case shown in FIG. 11, the process proceeds from step 200 to step 208.

Note that the current waveform may be selected based on a value obtained by multiplying the time constants τ _A , τ _B , and τ _C by a predetermined constant β and the current detection timing T. The constant β may be a constant β _A , β _B , β _C that is different for each time constant τ _A , τ _B , τ _C.

As shown in FIG. 10, when the current detection timing T is longer than the time constant τ _A , the influence of current waveform distortion due to noise removal at the current detection timing T is small. Therefore, the selected current waveform that has passed through the filter 40A constant tau _A at high effect of more noise reduction, the current value from the current waveform in step 102 is detected.

If the current detection timing T is a constant tau _A less time longer than the time constant tau _B as shown in FIG. 11, a current value detected by the current detection timing T is affected by the constant tau _A time. For this reason, the current value determination process proceeds to step 204.

As shown in FIG. 12, when the current detection timing T is equal to or less than the time constant τ _{B, the} current value detected at the current detection timing T is affected by the time constants τ _A and τ _B. For this reason, the current value determination process proceeds to step 208.

In step 204, the current waveform passing through the filter 40A having the time constant τ _A , the current waveform passing through the filter 40B having the time constant τ _B , and the current difference d _AB are calculated. Then, the current difference d _AB and the noise value α _AB are compared.
If the current difference d _AB is equal to or greater than the noise value α _AB (d _AB ≧ α _AB ), the current value is determined from the current waveform that has passed through the filter 40A having the time constant τ _A in step 202.
On the other hand, when the current difference d _AB is smaller than the noise value α _AB (d _AB <α _AB ), the current value is determined from the current waveform that has passed through the filter 40B having the time constant τ _B in step 206.

In step 208, the current waveform passing through the filter 40B having the time constant τ _B , the current waveform passing through the filter 40C having the time constant τ _C , and the current difference d _BC are calculated. Then, the current difference d _BC and the noise value α _BC are compared. Note that the noise value α _AB and the noise value α _BC may be the same value or different values.
If the current difference d _BC is greater than or equal to the noise value α _BC (d _BC ≧ α _BC ), the current value is determined from the current waveform that has passed through the filter 40B having the time constant τ _B in step 206.
On the other hand, when the current difference d _BC is smaller than the noise value α _BC (d _BC <α _BC ), in step 210, the current value is determined from the current waveform that has passed through the filter 40C with the time constant τ _C.

  As mentioned above, although this invention was demonstrated using said each embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above-described embodiments without departing from the gist of the invention, and embodiments to which the changes or improvements are added are also included in the technical scope of the present invention. Moreover, you may combine said each embodiment suitably.

  For example, in each of the above-described embodiments, the form in which the filter unit 22 includes two or three filters 40 has been described. However, the present invention is not limited to this, and the filter unit 22 includes four filters 40. It is good also as a form.

  The flow of the current value determination process described in each of the above embodiments is also an example, and unnecessary steps are deleted, new steps are added, or the processing order is changed within a range not departing from the gist of the present invention. Or you may.

12 power supply device 18 inverter control device 20 motor current detection unit 36 shunt resistor 40 filter 50 current value determination unit

Claims (5)

Current detecting means for detecting current by one shunt resistor;
A plurality of filters each having a different time constant are connected in parallel, the current detected by the current detection means passes through the plurality of filters, and the filter means outputs a current waveform for each of the plurality of filters,
Among the plurality of current waveforms output from the filter means, current value determination means for determining a current value from the current waveform selected based on the width of the current waveform and the time constant;
A current value detection device.   The current value detection device according to claim 1, wherein the current value determination unit determines a current value from the current waveform selected based on a current value detection timing corresponding to a width of the current waveform and the time constant.   3. The current value detection device according to claim 2, wherein, when the detection timing is longer than the longest time constant, the current value determination unit determines a current value from the current waveform that has passed through the filter having the longest time constant. . The current value determining means includes
When there is the time constant longer than the detection timing, the current value of the current waveform that has passed through the filter with the time constant longer than the detection timing and the filter with the time constant shorter than the detection timing Calculate the difference between the current value of the current waveform and
If the difference is smaller than a predetermined value indicating the occurrence of noise, determine the current value from the current waveform that has passed through the filter of the time constant shorter than the detection timing,
4. The current value detection device according to claim 2, wherein when the difference is larger than the predetermined value, a current value is determined from the current waveform that has passed through the filter having the time constant longer than the detection timing. Current detecting means for detecting current by one shunt resistor, and filter means for connecting a plurality of filters each having a different time constant in parallel, and the current detected by the current detecting means passes through the plurality of filters; A current value detection method for a current value detection device comprising:
A current is detected by the current detection means;
Outputting a current waveform for each of the plurality of filters from the filter means;
A current value detection method for determining a current value from the current waveform selected based on a width of the current waveform and the time constant among the plurality of output current waveforms.

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