JP2025028509A - AC motor drives and transmission systems - Google Patents

Abstract

To provide a motor drive system that can detect current with high accuracy and can bring out original efficiency characteristics and response characteristics of a motor relative to an AC motor with a rate of iron loss increasing due to higher speed and multipolarity or a drive system in which a switching frequency is high and a large ringing phenomenon is caused by switching.SOLUTION: A drive device of an AC motor includes: a DC power supply 2; an inverter 3 for converting the DC power supply 2 into AC; an AC motor 1 connected to the inverter 3; current detection means 33 connected to a switching element that is a component of the inverter 3; and controllers 84a to 84b for controlling the AC motor 1 based on current detected by the current detection means 33. Current information detected by the current detection means 33 is subjected to detection filter processing having low pass characteristics. A signal after the filtering is subjected to sampling processing and being read into the controllers 84a to 84b. Correction is performed based on a control signal of the AC motor 1 in the controllers 84a to 84b, and current information of the AC motor 1 is obtained.SELECTED DRAWING: Figure 5

Description

The present invention relates to variable speed drive of AC motors, and in particular to high-precision, high-efficiency drive of AC motors driven at high frequencies.

Variable speed drive systems for AC motors are becoming more widely used in industrial applications such as electric vehicles and drones as a small, clean power source. To improve the power density of a motor, it is desirable to increase the rotation speed, and the rotation speed of motors is on the rise. In addition, the multi-polarization of motors is also effective in miniaturization, and motors with about 40 poles and specifications of 3,000 revolutions per minute have been commercialized. In this way, the drive frequency of motors tends to become higher, and as a result, the proportion of iron loss in losses tends to increase. In recent years, power elements using wide band gap (WBG) semiconductors capable of high-speed switching have begun to spread in order to match this increase in frequency, and drive systems with significantly different loss and noise characteristics compared to conventional motor drive systems are becoming more common.

When motors are driven at high frequencies, the number of turns in the stator winding is reduced, which reduces copper loss and results in low inductance. However, high frequency drive tends to increase iron loss. The increase in iron loss changes the impedance characteristics of the motor, and as a result, conventional current detection methods are accompanied by detection errors. The motor is driven based on low-precision current detection values, which causes a shift in the operating point and prevents the motor from achieving its full potential.

In addition, the use of WBG semiconductor power elements enables steep pulse on/off operation, which intensifies the oscillation phenomenon (ringing phenomenon) that accompanies switching, raising concerns about malfunctions due to noise and current detection errors.

For a long time, the method of detecting current in inverter-driven AC motors has been based on the technique described in Patent Document 1. When driving an inverter with pulse width modulation (PWM) control, highly accurate current detection can be achieved by sampling the motor current at the peak of the carrier wave in synchronization with the triangular wave carrier used in the PWM and importing the sample into the controller through AD conversion. The principle behind this is that the vicinity of the peak of the triangular wave carrier is the timing when the pulsating component contained in the current becomes zero, so that only the value of the fundamental wave component required for motor control can be read without being affected by current ripple.

In addition, in Patent Document 2, in order to avoid the effects of the ringing phenomenon that accompanies the switching operation of the inverter, the inverter pulse generation method itself is corrected to avoid the ringing phenomenon period.

Japanese Patent Application Laid-open No. 58-198165 JP 2014-11944 A

In the method of Patent Document 1, the current can be detected only once in the carrier cycle used for PWM, so if noise such as ringing is present at this point, it will result in a current detection error. In addition, this sampling method is based on the premise that the impedance of an AC motor can be considered to be only inductive (only inductance components) at the switching frequency, so if the proportion of resistive components such as iron loss increases, the current detection error will increase. This means that this conventional current detection method is not suitable for motors that are becoming faster and more multi-polar, which is also the trend for AC motors.

In addition, in Patent Document 2, there is a limit to the amount of correction that can be made when generating pulses, and it is highly likely that it will be impossible to avoid the ringing phenomenon, especially when driving at a high switching frequency. In particular, in the case of WBG semiconductor power elements, the switching frequency becomes high and the ringing phenomenon becomes severe, making it difficult to support such devices.

The present invention was made in consideration of these problems, and provides a motor drive system that enables highly accurate current detection for AC motors in which the proportion of iron loss increases as the motor speed increases and the number of poles increases, or for drive systems in which the switching frequency is high and a large amount of ringing occurs due to switching, making it possible to bring out the inherent efficiency and response characteristics of the motor.

The present invention relates to an AC motor drive device that includes a DC power source, an inverter that converts the DC power source into AC, an AC motor connected to the inverter, current detection means connected to a switching element that is a component of the inverter, and a controller that controls the AC motor based on the current detected by the current detection means, and is characterized in that the current information detected by the current detection means is subjected to detection filtering with low-pass characteristics, the filtered signal is sampled and read into the controller, and correction is performed within the controller based on the control signal for the AC motor to obtain current information for the AC motor.

The present invention also relates to a transportation system for goods or people that uses the above-mentioned AC motor drive device as its power source.

The present invention provides a motor drive system that enables highly accurate current detection for AC motors in which the proportion of iron loss increases as the motor speed increases and the number of poles increases, or for drive systems in which the switching frequency is high and a large amount of ringing occurs due to switching, making it possible to bring out the inherent efficiency and response characteristics of the motor.

1 is a configuration diagram of a drive device for an AC motor in a first embodiment. 4 is an example of waveforms when controlling an AC motor according to a conventional method. 1 is a waveform example showing a triangular wave carrier and current sampling timing according to a conventional method. 1A and 1B are diagrams illustrating a ringing phenomenon that becomes a problem during current detection and a change in waveform due to iron loss, which are common to the conventional method and the first embodiment. FIG. 4 is a diagram showing a current detection waveform according to the first embodiment. 1 is a waveform showing how the filtered current waveform in the first embodiment is sampled and held at high speed. FIG. 2 is a configuration diagram of a duty ratio calculator and a current compensator in the first embodiment. 4 shows example waveforms of a triangular wave carrier, an AC voltage command, a duty ratio, and a current flowing through a shunt resistor according to the first embodiment. FIG. 11 is a configuration diagram of a controller for a driving device for an AC motor in a second embodiment. FIG. 11 is a diagram showing contact selection conditions of three switches in the second embodiment. FIG. 11 is a configuration diagram of a drone using a driving device for an AC motor in Example 3.

The following describes an embodiment of the present invention with reference to the attached drawings. The present invention detects current via shunt resistors attached to each arm of the main circuit of an inverter that drives an AC motor, and includes a filter with low-pass characteristics to avoid the influence of ringing. The output of this filter is sampled multiple times at a frequency higher than the switching frequency of the inverter and loaded into a controller to calculate an average value, and the phase current value of the motor is calculated by performing correction using the conduction rate during inverter switching. As a result, the influence of ringing is eliminated, and a more accurate current value can be detected by multiple sampling, thereby realizing a highly accurate and efficient AC motor drive system.

Figure 1 is a configuration diagram of an AC motor drive device in this embodiment. In Figure 1, the AC motor drive device is intended to drive a three-phase AC motor 1 (hereinafter abbreviated as motor 1), and is broadly composed of a DC power source 2, an inverter 3, a filter 4, and a controller 5. Note that in Figure 1, some component names are written in abbreviated form, and the component names of the corresponding symbols for each component described below are the official names.

In FIG. 1, inverter 3 uses DC power supply 2 as its power source, performs switching operations based on a PWM (pulse width modulation) signal output from controller 5, and applies a pulse width modulated voltage to motor 1. Inverter 3 detects the current flowing through motor 1, which is input to controller 5 via filter 4 to control the rotation speed or torque of motor 1.

The inverter 3 is composed of an inverter main circuit 31 made up of power semiconductors, a smoothing capacitor 32, a current detector 33 made up of shunt resistors, and a gate driver 34 that controls the on/off of each power semiconductor based on the PWM signal sent from the controller 5. The current detector 33 is connected in series to the lower element of the power semiconductor element of each phase, and when the lower element is turned on, a current flows, and the phase current is detected as the value of the voltage drop of the shunt resistor. In this method, the current flowing through the shunt resistor of each phase is an intermittent current, but in the present invention, the current waveform is made into a smooth signal by passing it through a filter 4.

Current detectors using shunt resistors like this are widely used, mainly in small-capacity inverters. Compared to current sensors using Hall elements, they have the advantage of being low-cost and compact, and in recent years have also been used in applications such as electric motorcycles and drones.

The controller 5 is intended to vector control the electric motor 1 and consists of the following components: current compensators 6a-c which perform compensation processing on the output of the filter 4; a dq coordinate converter 7 which converts the compensated phase current values iuc, ivc, iwc into currents on the rotating coordinate system; a vector controller 8 which calculates the applied voltages Vd*, Vq* for controlling the electric motor 1 based on the dq coordinate converted current values IdFB, IqFB; a dq inverse converter 9 which converts the applied voltages Vd*, Vq* into three-phase AC voltage commands Vu*, Vv*, Vw*; a duty ratio calculator 10 which converts the three-phase AC voltage command into a duty ratio for pulse width modulation; and a PWM signal generator 11 which performs pulse width modulation based on the duty ratio command. The vector controller 8 is a typical one that performs current control on the dq coordinate axes, and is composed of a current command generator 81 that outputs an excitation current command Idr and a torque current command Iqr, a phase generator 82 that calculates the rotation coordinate axis θd, adder-subtractors 83a-b that add or subtract two input signals, and current controllers (ACR) 84a-b that match the current detection values IdFB, IqFB to the current commands Idr, Iqr.

Before explaining the current compensators 6a-c, which are a characteristic feature of this embodiment, we will use the waveforms in Figures 2-4 to explain the overall operation of a system that uses a shunt resistor as a current detector.

Figure 2 (a) shows the waveforms of the triangular carrier signal Tri and the U-phase duty ratio command Ku* in the PWM signal generator 11. The magnitudes of Tri and Ku* are compared to generate the pulse waveform Pup (Figure 2 (b)). The pulse waveform Pup is the drive signal for UP in the inverter main circuit 31, and when this signal is "1", UP is turned on, and when it is "0", UP is turned off. The PWM signal generator 11 generates pulse waveforms for all six elements in the inverter main circuit 31. The upper and lower elements of each phase perform complementary operations (when UP is on, UN is off, and conversely, when UP is off, UN is on).

Figure 2 (c) shows the waveform of the U-phase current iu of the motor 1, which is a sinusoidal current that includes pulsation. This pulsation component is generated by the switching operation of the inverter 3. Current flows through each shunt resistor that makes up the current detector 33 when the lower power element is turned on, so the current detection waveform is as shown in Figure 2 (d). In this way, the detectable current waveform is a chopped up version of the original phase current iu, but by taking the current detection timing into account, it is possible to detect the phase current as shown in Figure 2 (e).

Figure 3 is a waveform diagram showing a conventional current detection method. The timing of the upper peak of the triangular wave carrier in the PWM signal generator 11 (Figure 3(a)) is used to sample and hold the current flowing through the shunt resistor (Figure 3(c)). At the upper peak of the triangular wave carrier, the lower power element is always on, so the current flowing through the shunt resistor can be reliably captured. Conversely, if sampling is performed at any other timing, there is a possibility that nothing will be detected (a "zero" will be detected), so setting the detection timing is extremely important in the conventional method.

Figure 4 shows the problems with actual shunt current detection. When controlling the on/off of a power semiconductor element, a slight parasitic capacitance on the circuit causes ringing (Figure 4(a)). This ringing varies depending on various factors, such as the parasitic capacitance of the main circuit, the installation status of the electric motor 1, and the length of the wiring cable. If the current is sampled and held during the period when ringing occurs, the value will differ from the actual required current value, resulting in a detection error. As shown in Figure 4(b), if the flow time is short, the current will be detected before the ringing has subsided, which is problematic as it contains a large error. In addition, power elements using recent WBG semiconductors tend to be more susceptible to ringing due to their short switching on/off times.

In addition, when the motor 1 becomes faster and more multi-polar, the inductance of the motor 1 tends to decrease, and at the same time, the drive frequency tends to become higher. As a result, the current ripple increases, and the proportion of iron loss in the total loss increases. As a result, the waveform of the current ripple changes as shown by the dotted line in Figure 4 (c). The waveform of the current ripple becomes rounded, and even if the current is sampled at the timing of the upper peak of the triangular wave carrier, the fundamental wave portion cannot be captured, and a waveform with an offset is detected. This is because the current ripple contains a large amount of leading components due to the influence of iron loss, and it can be said that this phenomenon is unlikely to occur with conventional motors. In any case, it can be said that there is a limit to using the upper peak of the triangular wave carrier as the timing for current detection.

Next, the characteristics of the present invention will be explained using Figures 1 and 5 to 8.

In the present invention, in order to eliminate the effects of the ringing phenomenon, filter 4 shown in Figure 1 is inserted after current detection. The outputs iunf, ivnf, and isnf of this filter 4 have continuous, smooth waveforms as shown in Figure 5 (b). The cutoff frequency of filter 4 should be set to a value that is sufficiently low relative to the frequency of the ringing waveform. However, if it is set too low, it will cause a phase delay in the fundamental current, so a cutoff frequency that makes the detection waveform continuous as shown in Figure 5 (b) is selected.

In the current compensators 6a-c of the controller 5, the filter outputs iunf, ivnf, and isnf are sampled and held in the sample-and-hold circuits 61a-c. In this case, the sample-and-hold is performed at a period shorter than the period Tc of the triangular wave carrier. This is shown in Figure 6. In Figure 6, the waveform of the output iunf of the filter 4 is sampled and held eight times within the period Tc of the triangular wave carrier. This operation requires a high-speed AD converter and high-speed calculation processing capabilities in the controller 5, but this can be realized with the capabilities of recent control microcomputers.

These sampled and held values iunfs, ivnfs, iwnfs are converted to digital values by AD converters 62a-c, and the average value is calculated by moving average processors 63a-c. The moving average is calculated every Ts period, which is half the triangular wave carrier period Tc (in FIG. 6, there are four detection values in the Ts period, and their average value is calculated). The reason for performing the moving average every Ts period rather than Tc is that the processing of the controller 5 itself is generally performed with Ts as the processing period. Of course, it is possible to perform the processing every Tc period, but in terms of making the resolution of the three-phase voltage waveform as fine as possible, it is more advantageous in terms of voltage resolution to perform the processing every Ts period.

As a result of performing the moving average, the current waveform iunfsm becomes a waveform as shown in Figure 5 (c). This waveform is based on the U-phase current waveform iu of the motor 1, but as shown in the figure, it becomes a distorted waveform with asymmetric positive and negative sides. This is because it is affected by the conduction rate of the power semiconductor elements, and cannot be used as is as a current detection value. After this, correction is performed by the conduction rate correctors 64a-c in Figure 1, and the waveform is modified to one with less distortion as shown in Figure 5 (d).

The operation of the conductance correction is explained using Figure 7.

Figure 7 shows the details of the duty ratio calculator 10 and the duty ratio corrector 64a in the current corrector 6a. In the figure, the duty ratio calculator 10 is composed of dividers 101a-c that divide signals, adders/subtractors 83c-e that add/subtract signals, a DC voltage setter 102, and a gain element 103. Here, the three-phase AC voltage commands Vu*, Vv*, and Vw* are converted into duty ratio commands Ku*, Kv*, and Kw* required for PWM control. In the DC voltage setter 102, the value of the DC power source 2 (Figure 1) is set in advance, and multiplied by a gain of 1/2 using the gain element 103, and the value of EDC/2 is added as an offset to all phase voltage commands. After that, the ratio of the AC voltage command to the EDC (i.e., the duty ratio) is calculated by dividing by the value of EDC. It is to be noted that the EDC used in the calculation may be detected as the actual power source voltage 2 and used without any problem.

Figure 8 (a) shows the operating waveforms of these processes. The AC voltage command Vu* is an AC waveform that swings between positive and negative around zero, and EDC/2 is added to it to provide an offset. The PWM signal generator 11 generates a pulse by comparing the magnitude relationship between the triangular wave carrier and the conduction rate (originally the voltage command). The pulse waveforms are as shown in Figures 8 (b) and (c). Here, the conduction rate of the upper element is Tp/Ts, and the conduction rate of the lower element is Tn/Ts. In addition, the current flowing through the shunt resistor occurs during the conduction period of the lower element, so it has a waveform as shown in Figure 8 (d). In other words, the average value of the detected waveform is the average value of the current flowing through the lower element, not the average value of the actual phase current. Therefore, if a correction is made using the conduction rate, the original phase current can be calculated. This process is performed by the conduction rate correctors 64a to 64c in Figures 1 and 7.

In FIG. 7, the conduction ratio corrector 64a is composed of adder-subtractors 83f-g that add and subtract signals, a divider 101d that divides signals, a constant setter 104 that sets a constant "1", a gain element 105, and signal delayers 106a-c that delay the signal by one sample period. The conduction ratio calculated by the conduction ratio calculator 10 is a conduction ratio command for the upper element of the power element, so in order to convert this to a conduction ratio for the lower element, the conduction ratio command Ku* is subtracted from the value of the constant setter, "1", to calculate the conduction ratio Kun* for the lower element. The switching operation of the inverter 3 based on this conduction ratio is executed with a delay of one sample for the sake of calculation processing, so a delay of one sample period is applied by the signal delayer 106a. Furthermore, since a delay of one sample is involved in the moving average processing, another delay of one sample period is applied by the signal delayer 106b. These two delays result in the conduction ratio of the current obtained as the moving average value. The current detection value can be corrected by dividing the moving average value by this conduction rate. Furthermore, since this process is executed every half cycle Ts of the triangular wave carrier period, the average of the previous correction value is calculated to obtain the average value of the triangular wave carrier period Tc. This process is realized by the signal delay device 106c, the lower limit z period 83g, and the gain element 105.

As a result, the phase current waveforms are accurately calculated, and the waveform shown in Figure 5(d) is obtained. The phase current detection values iuc, ivc, and iwc obtained in this way can detect current values with high accuracy without being affected by ringing due to inverter switching or current ripple due to iron loss.

The cutoff frequency of the filter 4 in the present invention is set to a value at which the filtered current waveform of the current detection means 33 switches from intermittent to continuous without being intermittent. In an intermittent state, the sampled value will contain "zero", which may degrade the linearity of the moving average value. In addition, if the cutoff frequency is lowered too much, the waveform will become smoother, but there is a concern that the phase delay of the fundamental wave component itself may occur, so it is preferable to set the cutoff frequency to the minimum necessary value and make the waveform continuous.

In addition, when sampling and holding the current waveform after filter 4, unless the frequency is at least twice the carrier frequency, there is no point in applying this invention. To increase the accuracy of the moving average, it is desirable to perform sampling at an even higher frequency. However, since synchronization with the carrier frequency is necessary, it is desirable to sample at a frequency that is an integer multiple of the carrier frequency, as shown in the example. If this is not synchronized, it can cause beat phenomena and detection errors.

As described above, according to the first embodiment of the present invention, it is possible to detect the motor current with high accuracy even in an environment where the ringing phenomenon is severe or for a high-speed, multi-pole motor, and a highly accurate and efficient AC motor drive system can be realized.

Figure 9 is a configuration diagram of a controller 5B in a second embodiment of the present invention. By using this controller 5B instead of the controller 5 in Figure 1, a second embodiment of the AC motor drive device can be realized.

The parts in Figure 9 that have the same part numbers as in Figure 1 are the same. The newly added component in Figure 9 is a current selector 12 that selects the current value to be used preferentially for iuc, ivc, and iwc, which are the calculation results of the phase currents. In the current selector 12, the state selector 121 determines which two of the three-phase currents to use based on the magnitude relationship of the conduction rates Ku*, Kv*, and Kw*, and switches the contacts of the switches 121a to c arranged for each phase.

In the case of a three-phase AC motor, it is not necessary to use all currents as the phase current values; if information on at least two phases is obtained, the remaining phase can be found by calculation. This is because the sum of the three-phase currents (iu + iv + iw) is always zero. Therefore, two phases with high current detection accuracy are selected with priority, and the remaining phase can be found by calculation from the selected two phases.

In the present invention, the current flowing through the lower power element of the inverter main circuit 33 is detected and a correction is made to the conduction rate, but if the conduction rate of the lower power element is low, there is a possibility that calculation errors will increase. For example, the lower the conduction width, the more susceptible it is to the effects of the on and off times of the pulse, the dead time, and the amount of dead time compensation, so there is a high possibility that errors will increase. Conversely, the longer the conduction time of the lower power element, the smaller the amount of conduction rate correction, and the more accurately the current value can be obtained. Therefore, based on the conduction rate of each phase, two phases are determined to be used with priority, and the remaining phase is calculated.

Figure 10 shows the conditions for selecting one of the contacts a, b, and c of the switches 121a-c in the state selector 121. The contacts of the switches 121a-c are determined according to the phase that is the maximum among Ku*, Kv*, and Kw*. For example, if Ku* is maximum, contact "c" is selected and ivc and iwc are used preferentially. Since Ku* is maximum, Kun* (the conduction rate of the lower power element) is minimum, and the iuc value is likely to contain a large error, it is not used and is calculated from the other two phases as "-ivc-iwc". In the current selector 12 in Figure 9, the current value of the non-selected condition is calculated from the two selected current values using the adder-subtracters 83h-j. With these configurations, the current selection according to the table in Figure 10 is performed.

As described above, according to the second embodiment of the present invention, it is possible to detect current by prioritizing the two phases with high current detection accuracy, and a more accurate current value can be obtained, thereby providing a motor drive system that can contribute to high accuracy and high efficiency.

Figure 11 shows a third embodiment of the present invention, in which the AC motor drive system in embodiments 1 and 2 is applied to a drone levitation motor.

Figure 11 shows the drone body 200 and the propulsion devices for lifting 201a-f attached to the drone body, with part numbers 1-5 being the same as those in the first embodiment shown in Figure 1. The DC power supply 2 is built into the drone body 200 as a battery. The electric motor 1 drives the propeller 202, and the inverter 3, filter 4, and controller 5 are integrated and built into the propulsion devices for lifting 201a-f. In the AC motor drive system according to the present invention, a shunt resistor is used in the current detector, which allows for a small and lightweight implementation, and also allows for high current detection accuracy, which contributes to extending the life of the battery.

Examples similar to this embodiment include electric kick scooters, electric bikes, and electric cars. It can also be used to power self-propelled robots that are driven by wheels. The same effects can be expected when the present invention is applied to these power sources.

As described above, according to the third embodiment of the present invention, it is possible to realize a mobile system that can be implemented in a compact size and has excellent current detection accuracy.

As described above, in the present invention, a shunt resistor is attached to each arm of the inverter main circuit that drives the AC motor, and the detected value of this shunt current is read into the controller via a filter with low-pass characteristics. In this case, the current value is sampled multiple times at a frequency higher than the switching frequency of the inverter, and the average value is calculated and corrected using the conduction rate during inverter switching to calculate the phase current value of the motor. By controlling the AC motor using this phase current value, a highly accurate and efficient AC motor drive system can be realized.

The present invention makes it possible to provide a drive unit for an AC motor that can detect current with high accuracy and bring out the inherent efficiency and response characteristics of the motor, and a transportation system (motor drive system) that uses this as its power source, for AC motors in which the proportion of iron loss increases as the motor speed increases and the number of poles increases, or for drive systems in which the switching frequency is high and significant ringing occurs due to switching.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

REFERENCE SIGNS LIST 1 electric motor 2 DC power supply 3 inverter 4 filter 5 controller 6a-c current compensator 7 dq coordinate converter 8 vector controller 9 dq inverse converter 10 duty ratio calculator 11 PWM signal generator 31 inverter main circuit 32 smoothing capacitor 33 current detector 34 gate driver 61a-c sample-and-hold circuit 62a-c AD converter 63a-c moving average processor 64a-c duty ratio corrector 81 current command generator 82 phase generator 83a-b adder-subtractor 84a-b current controller (ACR)

Claims (8)

A drive device for an AC motor including a DC power source, an inverter for converting the DC power source into AC, an AC motor connected to the inverter, current detection means connected to a switching element that is a component of the inverter, and a controller for controlling the AC motor based on a current detected by the current detection means,
a detection filter having low-pass characteristics is applied to current information detected by the current detection means, the filtered signal is sampled and read into the controller, and correction is performed within the controller based on a control signal for the AC motor, thereby obtaining current information for the AC motor. 2. The AC motor drive device according to claim 1,
In the detection filter processing of the current information, a cutoff frequency is set so that the intermittent current waveform obtained by the current detection means becomes a continuous waveform. 2. The AC motor drive device according to claim 1,
A driving device for an AC motor, characterized in that in the sampling process after the detection filter process, sampling is performed at a switching frequency that is at least twice as high as an average switching frequency for the switching operation of the inverter. 2. The AC motor drive device according to claim 1,
A driving device for an AC motor, characterized in that in the sampling process after the detection filter process, sampling is performed at a switching frequency that is at least twice as high as an average switching frequency of the inverter and is also an integer multiple of the average switching frequency. 2. The AC motor drive device according to claim 1,
a switching frequency of at least twice as high as an average switching frequency of the inverter in the sampling process after the detection filter process, and a moving average process is performed on the sampled values. 2. The AC motor drive device according to claim 1,
a correction process performed within the controller after the sampling process is based on a voltage applied to the AC motor and a duty ratio calculated from a voltage value of the DC power supply. 2. The AC motor drive device according to claim 1,
a current detection means for detecting a current flow of the AC motor from the AC power source and detecting a current flow of the DC power source based on the current flow rate of the AC motor and a current detection signal for detecting a current flow of the DC power source; A transportation system for goods or people powered by the AC motor drive device according to any one of claims 1 to 7.

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