Drive device of ac motor and transportation system

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

[Technical field]

[0001] The present invention relates to a variable speed drive for an AC motor, and more particularly to a highly accurate and efficient drive for an AC motor driven at high frequency. [Background technology]

[0002] Variable speed drive systems for AC motors are expanding their application from industrial fields to electric vehicles, drones, etc. as a small and clean power source. To improve the power density of an electric motor, it is desirable to increase the rotation speed, and the rotation speed of electric motors is on the rise. In addition, the multi-polarization of electric motors is also effective in miniaturization, and electric motors with about 40 poles and specifications of 3,000 revolutions per minute are being commercialized. In this way, the driving frequency of motors tends to become higher, and as a result, the proportion of iron loss in losses tends to increase. In addition, 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 available.

[0003] By driving electric motors 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 driving 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 original performance.

[0004] In addition, the use of WBG semiconductor power elements makes it possible to perform steep pulse on / off operation, which intensifies the vibration phenomenon (ringing phenomenon) associated with switching, raising concerns about malfunctions due to noise and current detection errors.

[0005] For a long time, the method of detecting current in an inverter-driven AC motor has been based on the technique described in Patent Document 1. When driving an inverter by 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 sampled current into a controller through AD conversion. The principle of 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.

[0006] Furthermore, in Patent Document 2, in order to avoid the influence of the ringing phenomenon that accompanies the switching operation of the inverter, a correction is made to the inverter pulse generation method itself to avoid the ringing phenomenon period. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 58-198165 [Patent Document 2] JP 2014-11944 A Summary of the Invention [Problem to be solved by the invention]

[0008] 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) with respect to the switching frequency, so if the proportion of resistance 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.

[0009] In addition, in Patent Document 2, there is a limit to the amount of correction 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.

[0010] The present invention has been made in consideration of these problems, and provides a motor drive system that enables highly accurate current detection and makes it possible to bring out the inherent efficiency and response characteristics of the motor, for AC motors in which the proportion of iron loss increases as the speed and polarity increase, or for drive systems in which the switching frequency is high and significant ringing occurs due to switching. [Means for solving the problem]

[0011] The present invention relates to a drive device for an AC motor comprising a DC power supply, an inverter for converting the DC power supply into AC, an AC motor connected to the inverter, current detection means connected to a switching element which is a component of the inverter, and a controller for controlling the AC motor based on the current detected by the current detection means, the drive device for an AC motor is characterized in that it performs a detection filter process having a low-pass characteristic on current information detected by the current detection means, samples the filtered signal and reads it into the controller, and performs correction within the controller based on a control signal for the AC motor to obtain current information for the AC motor.

[0012] The present invention also relates to a transportation system for goods or people, powered by the driving device for the AC motor described above. Effect of the Invention

[0013] According to the present invention, it is possible to provide 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 significant ringing occurs due to switching, thereby enabling the provision of a motor drive system that can bring out the inherent efficiency and response characteristics of the motor. [Brief description of the drawings]

[0014] [Figure 1] 1 is a configuration diagram of a driving device for an AC motor in a first embodiment. [Diagram 2] 4 is an example of waveforms when controlling an AC motor according to a conventional method. [Diagram 3] 1 is a waveform example showing a triangular wave carrier and current sampling timing according to a conventional method. [Figure 4] 10 is a diagram showing 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. [Diagram 5] FIG. 4 is a diagram illustrating a current detection waveform according to the first embodiment. [Figure 6] 13 is a waveform showing how the filtered current waveform related to Example 1 is sampled and held at high speed. [Figure 7] FIG. 2 is a configuration diagram of a duty ratio calculator and a current compensator in the first embodiment. [Figure 8] 4 shows examples of 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. [Figure 9] FIG. 11 is a configuration diagram of a controller for a driving device for an AC motor in a second embodiment. [Figure 10] FIG. 11 is a diagram showing contact selection conditions of three switches in the second embodiment. [Figure 11] FIG. 11 is a configuration diagram of a drone using a driving device for an AC motor in a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. The present invention detects current via shunt resistors attached to each arm of an inverter main circuit that drives an AC motor, and includes a filter with low-pass characteristics to avoid the influence of ringing during the detection. Furthermore, 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 duty factor 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. EXAMPLES

[0016] Fig. 1 is a configuration diagram of an AC motor drive device in this embodiment. In Fig. 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 supply 2, an inverter 3, a filter 4, and a controller 5. Note that in Fig. 1, some component names are written in abbreviated form, and the component names with the corresponding symbols of each component described below are the official names.

[0017] 1, inverter 3 uses DC power supply 2 as its power source, performs switching operation based on a PWM (pulse width modulation) signal output from controller 5, and applies a pulse width modulated voltage to electric motor 1. Inverter 3 detects the current flowing through electric motor 1, which is input to controller 5 via filter 4 to control the rotation speed or torque of electric motor 1.

[0018] 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 a shunt resistor, and a gate driver 34 that controls the on / off of each power semiconductor based on a 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.

[0019] Current detectors using shunt resistors are widely used mainly in small-capacity inverters. Compared to current sensors using Hall elements, they have the advantage of being inexpensive and compact, and in recent years have also been used in applications such as electric motorcycles and drones.

[0020] The controller 5 is a controller intended to perform vector control of the electric motor 1, and includes as its components current compensators 6a-c that perform compensation processing on the output of the filter 4, a dq coordinate converter 7 that converts the compensated phase current values ​​iuc, ivc, iwc into currents on the rotating coordinate system, a vector controller 8 that calculates 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 that converts the applied voltages Vd*, Vq* into three-phase AC voltage commands Vu*, Vv*, Vw*, a duty ratio calculator 10 that converts the three-phase AC voltage commands into duty ratios for pulse width modulation, and a PWM signal generator 11 that 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.

[0021] Before describing the current compensators 6a to 6c, which are the characteristic features of this embodiment, the overall operation of the system using a shunt resistor as a current detector will be described with reference to the waveforms in FIGS.

[0022] FIG. 2(a) shows the waveforms of the triangular wave carrier signal Tri and the U-phase duty ratio command Ku* in the PWM signal generator 11, and the magnitudes of Tri and Ku* are compared to generate the pulse waveform Pup (FIG. 2(b)). The pulse waveform Pup is a 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).

[0023] Fig. 2(c) shows the waveform of the U-phase current iu of the motor 1, in which a sinusoidal current including pulsation flows. This pulsation component is generated by the switching operation of the inverter 3. A current flows through each shunt resistor constituting the current detector 33 at the timing when the lower power element is turned on, so the detected current waveform is as shown in Fig. 2(d). In this way, the detectable current waveform is a waveform obtained by chopping up the original phase current iu, but by taking the current detection timing into consideration, it is possible to detect the phase current as shown in Fig. 2(e).

[0024] 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)). Because the lower power element is always on at the upper peak of the triangular wave carrier, it is possible to reliably capture the current flowing through the shunt resistor. Conversely, if sampling is performed at any other timing, there is a possibility that nothing will be detected ("zero" will be detected), so with the conventional method, setting the detection timing is extremely important.

[0025] Figure 4 shows the problems in actual shunt current detection. When controlling the on / off of a power semiconductor element, a slight parasitic capacitance on the circuit causes a ringing phenomenon (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 becomes short, the current will be detected before the ringing has subsided, which causes a large error and is a problem. In addition, power elements using recent WBG semiconductors tend to be more susceptible to ringing because of their short switching on / off times.

[0026] In addition, when the motor 1 becomes faster and more multi-polarized, 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 loss also 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 part cannot be captured, and a waveform with an offset is detected. This is because the current ripple contains many 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.

[0027] Next, the characteristic features of the present invention will be described with reference to FIG. 1 and FIGS.

[0028] In the present invention, in order to eliminate the influence of the ringing phenomenon, the filter 4 shown in Fig. 1 is inserted after current detection. The outputs of this filter 4, iunf, ivnf, isnf, become continuous and smooth waveforms as shown in Fig. 5(b). The cutoff frequency of the filter 4 should be set to a value sufficiently low relative to the frequency of the ringing waveform. However, if it is set too low, it will cause a phase delay of the fundamental wave current, so a cutoff frequency is selected that makes the detection waveform continuous as shown in Fig. 5(b).

[0029] In the current compensators 6a-c of the controller 5, the filter outputs iunf, ivnf, 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 capability in the controller 5, but this can be realized with the capabilities of recent control microcomputers.

[0030] These sample-and-hold values ​​iunfs, ivnfs, and iwnfs are converted to digital values ​​by AD converters 62a-c, and then average values ​​are 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 detected 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, performing the processing every Ts period is advantageous in terms of voltage resolution.

[0031] 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. This is because it is affected by the conduction factor of the power semiconductor elements, and cannot be used as it is as a current detection value. After this, the conduction factor correctors 64a-c in Figure 1 perform correction, and the waveform is modified to one with less distortion as shown in Figure 5(d).

[0032] The operation of the conductance correction will be described with reference to FIG.

[0033] FIG. 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 for dividing signals, adder-subtractors 83c-e for adding and subtracting signals, a DC voltage setting device 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 setting device 102, the value of the DC power source 2 (FIG. 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 actual power source voltage 2 may be detected and used as the EDC used in the calculation.

[0034] FIG. 8(a) shows the operation 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 give an offset. The PWM signal generator 11 generates a pulse by comparing the magnitude relationship between the triangular wave carrier and the duty factor (originally a voltage command). The pulse waveforms are as shown in FIG. 8(b) and (c). Here, the duty factor of the upper element is Tp / Ts, and the duty factor 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 FIG. 8(d). In other words, the average value of the detected waveform is the average value of the current flowing through the lower element, and is not the average value of the actual phase current. Therefore, if a correction is made using the duty factor, the original phase current can be calculated. This process is performed by the duty factor correctors 64a to 64c in FIG. 1 and FIG. 7.

[0035] In FIG. 7, the duty ratio corrector 64a includes adder-subtractors 83f-g for adding and subtracting signals, a divider 101d for dividing signals, a constant setter 104 for setting a constant "1", a gain element 105, and signal delayers 106a-c for delaying signals by one sample period. The duty ratio calculated by the duty ratio calculator 10 is a duty ratio command for the upper element of the power element, so that this is converted to a duty ratio for the lower element by subtracting the duty ratio command Ku* from the value of the constant setter "1" to calculate the duty ratio Kun* for the lower element. The switching operation of the inverter 3 based on this duty ratio is executed with a delay of one sample period for the sake of arithmetic processing, so a delay of one sample period is applied by the signal delayer 106a. Furthermore, since a delay of one sample period is involved in the moving average processing, another delay of one sample period is applied by the signal delayer 106b. These two delays provide the duty ratio of the current obtained as the moving average value. The current detection value can be corrected by dividing the moving average by this conduction ratio. 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.

[0036] As a result, the phase current waveforms are accurately calculated, and the waveforms shown in Fig. 5(d) are obtained. The phase current detection values ​​iuc, ivc, and iwc obtained in this way are not affected by ringing due to inverter switching, current ripples due to iron loss, etc., and can detect current values ​​with high accuracy.

[0037] 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 discontinuous to continuous without being discontinuous. In an intermittent state, the sampled value may contain "zero", which may degrade the linearity of the moving average value. In addition, if the cutoff frequency is lowered too much, the waveform becomes 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.

[0038] Furthermore, when sampling and holding the current waveform after filter 4, there is no point in applying this invention unless the frequency is at least twice the carrier frequency. 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 embodiment. If this is not synchronized, it can cause beat phenomena and detection errors.

[0039] 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. EXAMPLES

[0040] 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 FIG. 1, a second embodiment of the AC motor driving device can be realized.

[0041] Part numbers shown in Fig. 9 that are the same as those in Fig. 1 are the same. A newly added component in Fig. 9 is a current selector 12 that selects a current value to be used preferentially from iuc, ivc, and iwc, which are the calculation results of the phase currents. In the current selector 12, a state selector 121 determines which two phases of the three-phase current should be used based on the magnitude relationship of the conduction rates Ku*, Kv*, and Kw*, and switches the contacts of switches 121a to c arranged for each phase.

[0042] 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.

[0043] In the present invention, the current flowing through the lower power element of the inverter main circuit 33 is detected and the duty factor is corrected. However, if the duty factor of the lower power element is low, there is a possibility that calculation errors will increase. For example, the lower the duty width, the more susceptible it is to the influence of the on-time and off-time of the pulse, the dead time, and the amount of compensation for the dead time, so there is a high possibility that the error will increase. Conversely, the longer the duty time of the lower power element, the smaller the duty factor correction amount will be, and the current value will be obtained with high accuracy. Therefore, based on the duty factor of each phase, two phases to be used with priority are determined, and the remaining one phase is calculated.

[0044] FIG. 10 shows the conditions for selecting one of the contacts a, b, and c of the switches 121a to c in the state selector 121. The contacts of the switches 121a to c are determined according to the phase in which Ku*, Kv*, and Kw* are the maximum. For example, if Ku* is the maximum, the contact "c" is selected, and ivc and iwc are used preferentially. Since Ku* is the maximum, Kun* (the conduction rate of the lower power element) is the minimum, and the value of iuc 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 FIG. 9, the current value of the condition that is not selected is calculated from the two selected current values ​​using the adder-subtracters 83h to j. With these configurations, the selection of the current according to the table in FIG. 10 is performed.

[0045] As described above, according to the second embodiment of the present invention, it is possible to perform current detection by prioritizing the two phases having high current detection accuracy, thereby obtaining a more accurate current value, and it is possible to provide a motor drive system that can contribute to high accuracy and high efficiency. EXAMPLES

[0046] FIG. 11 shows a third embodiment of the present invention, which is an example in which the AC motor drive system in the first and second embodiments is applied to a motor for levitation of a drone.

[0047] FIG. 11 shows a drone body 200 and the propulsion devices for lifting 201a-f attached to the drone body, and part numbers 1-5 are the same as those in the first embodiment shown in FIG. 1. A DC power source 2 is built into the drone body 200 as a battery. An electric motor 1 drives a propeller 202, and an inverter 3, a filter 4, and a 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 for 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.

[0048] Examples of devices similar to this embodiment include electric kick scooters, electric bikes, and electric cars. The present invention can also be used as a power source for self-propelled robots that are driven by wheels. The same effects can be expected when the present invention is applied to these power sources.

[0049] As described above, according to the third embodiment of the present invention, a mobile system that can be implemented in a compact size and has excellent current detection accuracy can be realized.

[0050] As explained 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 through a filter with low-pass characteristics. At this time, 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 duty factor at the time of inverter switching to calculate the phase current value of the motor. By controlling the AC motor using the phase current value, a highly accurate and efficient AC motor drive system can be realized.

[0051] According to the present invention, it is possible to provide a drive unit for an AC motor that enables highly accurate current detection and can 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 speed and polarity increase, or for drive systems in which the switching frequency is high and significant ringing occurs due to switching.

[0052] Incidentally, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0053] 1 electric motor 2 DC power supply 3 Inverter 4. Filters 5. Controller 6a~c Current compensator 7 dq coordinate transformer 8. Vector Controller 9 dq inverse transformer 10 Conductivity 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 Conductivity compensator 81 Current command generator 82 Phase Generator 83a~b Addition / subtraction unit 84a~b Current controller (ACR)

Claims

1. 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. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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 detected by the current detection means;

8. 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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