JP2004096933A - Controller of three-phase ac motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller of a three-phase AC motor which can hold a proper control performance even when the number of A/D converters used as current sensors is limited. <P>SOLUTION: The controller of the three-phase AC motor includes a fault phase specifying means for specifying a fault phase corresponding to a faulted current sensor when the sensor is faulted in such a manner that a third phase current sensor sensed value Iw can be captured by any of the first and second A/D converter circuits 01 and 11, and two phases except the specified faulted phase are synchronized by the first and second A/D converter circuits and captured. Even when any of the three-phase sensors is faulted, residual normal two phase current sensor sensed values are synchronously captured, and hence a current value of the faulted phase is estimated and controlled so that a current control performance equivalent to that at the normal control time can be assured. Even when a low-cost microcomputer having only two A/D converter circuits is used, the above functions can be realized. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for a three-phase AC motor, and relates to a fail-safe technique when a current sensor fails.
[0002]
[Prior art]
In the fail-safe control of a three-phase AC motor (hereinafter abbreviated as a motor) described in the above-mentioned patent document, the sum of detection values by current sensors provided for each phase is described. Is normally 0, it is determined that a failure has occurred in any of the current sensors if the value is equal to or greater than a predetermined value. If it is determined that a fault has occurred in the current sensor, the fault phase is specified based on the deviation between the current command value of each phase and the detection value of the current sensor. A technique is disclosed in which motor control is continued by estimating the current in the failed phase from the detected current values of the remaining two phases.
[0003]
[Problems to be solved by the invention]
However, when the conventional technique as described above is applied to an inexpensive microcomputer, for example, a microcomputer having only two A / D converter circuits for a current sensor, the current of two phases other than the failed phase is reduced. In some cases, it is not possible to capture the detected values in a synchronized manner, and control performance may be degraded. Such a problem occurs not only when an inexpensive computer is used but also when it is desired to reduce the number of A / D converters used for a current sensor.
[0004]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has been made in view of the problem that a three-phase AC motor capable of maintaining good control performance even when the number of A / D converters used for a current sensor is limited. It is an object to provide a control device.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, when a failure occurs in a current sensor, a failure phase identification means for identifying a failure phase corresponding to the failed current sensor is provided, and a third phase current sensor is provided. The detected value is set so that it can be taken in by either the first A / D conversion circuit or the second A / D conversion circuit, and the two phases excluding the fault phase specified by the fault phase specifying means are first and second. The two A / D conversion circuits are configured to synchronize with each other. In other words, the present invention is configured to synchronously capture two-phase current sensor detection values that have not failed in the two A / D conversion circuits by switching the capture destination according to the failed phase. is there.
[0006]
【The invention's effect】
In the present invention, even if a failure occurs in any of the three phase current sensors, the remaining normal two-phase current sensor detection values are taken in synchronously, so that the current value of the failed phase is estimated. Current control performance equivalent to that during normal control, and is used for a current sensor, as in the case of using an inexpensive microcomputer having only two A / D converter circuits. Even when the number of A / D converters is limited, there is an effect that the above excellent functions can be realized.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a block diagram showing an example of a current feedback control device for a three-phase motor to which the present invention is applied.
In FIG. 1, a current command calculator 1 outputs a d-axis current command value Id * and a q-axis current command value Iq * corresponding to a torque command T * commanded from the outside. These current command values are input to the current PI control unit 2.
The current PI control unit 2 performs a proportional integral operation based on the deviation between the d-axis current command value Id * and the d-axis current current value Id, outputs a d-axis voltage command value Vd *, and similarly outputs a q-axis current command value. A q-axis voltage command value Vq * is output based on a deviation between Iq * and the current q-axis current value Iq.
The d-axis voltage command value Vd * and the q-axis voltage command value Vq * are subjected to non-interference calculation processing as necessary, and the two-phase / three-phase converter 3 outputs three-phase voltage command values Vu *, Vv *, After being converted to Vw *, it is provided to the PWM converter 4 and converted to a PWM signal.
The inverter 5 converts the power of a DC power supply (not shown) (not shown) into three-phase AC power according to the PWM signal, and drives the three-phase motor 6.
At this time, the three-phase currents Iu, Iv, and Iw of the three phases are detected by the current sensors 7-1, 7-2, and 7-3, respectively. , Iw ', and converted into a d-axis current current value Id and a q-axis current current value Iq by a three-phase / two-phase converter 10 and fed back to the current PI control unit 2. The rotation angle detector 8 detects a current rotation angle (electric angle θ) of the three-phase motor 6. The electrical angle θ is used for the coordinate conversion calculation in the two-phase to three-phase converter 3 and the three-phase to two-phase converter 10 and the calculation in the current command calculation unit 1.
The current command calculation unit 1, the current PI control unit 2, the two-phase three-phase converter 3, the PWM conversion unit 4, the A / D conversion unit 9, and the three-phase two-phase converter 10 are usually implemented by a microcomputer. The respective phase currents Iu, Iv, Iw of analog values detected by the current sensors 7-1, 7-2, 7-3 are converted into digital signals by the A / D converter 9 and taken in.
[0008]
The present invention is applied to the fail-safe control at the time of failure of the current sensor in the current control of the three-phase motor as described above. Normally, a Kirchhoff relation “Iu + Iv + Iw = 0” is established with a three-phase current value of a three-phase motor, and a current value of two phases (for example, Iu, Iv) is detected using the relation, and the remaining one-phase current value is calculated. It is possible to perform current control by calculating (Iw = −Iu−Iv). Therefore, when a microcomputer incorporating three A / D converter circuits (or sample & hold circuits) is used and simultaneous sampling of three-phase currents is possible, if any one of the current sensors fails, By calculating the current value of the faulty phase from the remaining two phase current detection values by calculation, the same control as in the normal state can be performed.
However, when an inexpensive microcomputer having only two A / D converter circuits (or sample and hold circuits) that can be used for current value conversion is used, the two-phase current values are synchronized. Although it can be captured, the remaining one phase is captured with a delay of one sampling timing. Therefore, even during normal control, control is performed by calculating the current value of the remaining one phase (for example, W phase) from the current values of two phases (for example, U phase and V phase) taken in synchronism, and The taken-in W-phase current value is used for a failure determination as to whether or not a failure determination formula “Iu + Iv + Iw ≧ X” (X: failure determination value) is satisfied.
[0009]
In the above failure determination, if it is determined that the current sensor has failed, a U-phase current command value Iu obtained by converting the d-axis current command value Id ^* and the q-axis current command value Iq ^* in FIG. ^* , V-phase current command value Iv ^* , W-phase current command value Iw ^* (current values corresponding to three-phase voltage command values Vu *, Vv *, Vw *) and detected current sensor outputs Iu, Iv, Iw Fail-safe control by specifying the current sensor failure phase from the magnitude of the deviation from the above and using the detection values of the other two phase current sensors and calculating the current value of the failure phase from the other two phase values. I do. However, as described above, one of the three phases is taken in with a delay of one sampling timing. Therefore, if the current value of the phase taken in late is used for control, the current control performance will deteriorate. For example, if the U-phase and the V-phase are taken in synchronously and the W-phase is taken in late, there is a detection time delay of one sampling timing between Iu and Iw, and between Iv and Iw. When the U-phase or V-phase current sensor fails and the W-phase detection value is used for control, the current control performance deteriorates due to the detection time delay described above.
[0010]
Therefore, in the present invention, the detected value of the current sensor of the third phase (for example, W phase) can be taken in by both the first A / D conversion circuit and the second A / D conversion circuit, Are taken in by the first and second A / D conversion circuits, respectively. In other words, in the present invention, by switching the capture destination according to the failed phase, the two A / D conversion circuits are configured to capture the two-phase current sensor detection values that have not failed in synchronization. .
[0011]
FIG. 2 is a block diagram of one embodiment of the present invention.
2, a control microcomputer 20 includes a current command calculator 1, a current PI controller 2, a two-phase three-phase converter 3, a PWM converter 4, an A / D converter 9, a three-phase two-phase It is equivalent to the converter 10 and includes two A / D conversion sample and hold circuits (01 and 11).
The sample-and-hold circuit 01 and the sample-and-hold circuit 11 have four analog input terminals (channels) AN01 to 04 and AN11 to AN14, respectively, and switch channels for performing sample and hold in accordance with an instruction from the A / D controller 21. . Further, the sample & hold circuit 01 and the sample & hold circuit 11 can simultaneously sample according to a command from the A / D controller 21.
Comparator & A / D converter circuits 01 and 11 convert the data held by sample & hold circuit 01 and sample & hold circuit 11, and store the conversion results in data registers 01 to 14 corresponding to the respective channels.
[0012]
When such a microcomputer 20 is used, in FIG. 2, the U-phase current sensor output value Iu is input to the analog input terminal AN01, and the V-phase current sensor output value Iv is input to the analog input terminal AN11. The W-phase current sensor output value Iw is connected to be input to both the analog input terminal AN02 and the A / D terminal AN12.
[0013]
When the current sensor is under normal control, the sample-and-hold circuit 01 and the sample-and-hold circuit 11 perform simultaneous sampling according to the simultaneous sampling instruction of the channels AN01 (U phase) and AN11 (V phase) by the A / D controller 21. Are converted into digital signals by the comparators & A / D converter circuits 01 and 11, respectively, and the data of the channels AN01 and AN11 are stored in data registers corresponding to the respective channels. In the current control, the data of the simultaneously sampled AN01 and AN11, that is, Iu and Iv are used, and Iw is calculated by calculation (Iw = −Iu−Iv) to perform current control.
[0014]
Further, the W-phase current sensor output value Iw is sampled and input by either AN02 or AN12 with a delay of one sampling timing after the simultaneous sampling of the channels AN01 and AN11 is completed, and this value is determined by the failure determination formula “Iu + Iv + Iw ≧ X (X: failure determination value).
In the above failure determination, when it is determined that the current sensor has failed, a U-phase current command value Iu obtained by performing 2-phase to 3-phase conversion of the d-axis current command value Id ^* and the q-axis current command value Iq ^{*. *} , V-phase current command value Iv ^* , W-phase current command value Iw ^* (current values respectively corresponding to three-phase voltage command values Vu *, Vv *, Vw * in FIG. 1) and detected current sensor outputs Iu, The deviation from Iv and Iw is calculated, and the current sensor failure phase is specified from the magnitude. That is, the phase in which the deviation between the current command value and the actual current detection value is large is specified as the failure phase. Then, the fail-safe control is performed based on the detected values of the two-phase current sensors other than the failed phase. In the present embodiment, each two-phase current used for the current control is controlled by performing the following control according to the failed phase. The configuration is such that simultaneous sampling is always performed to prevent deterioration of the current control performance.
[0015]
(1) When the U-phase current sensor fails When the U-phase is specified as the failed phase, the A / D controller 21 commands simultaneous sampling of the channels AN02 (W-phase) and AN11 (V-phase). As a result, the sample & hold circuit 01 and the sample & hold circuit 11 perform simultaneous sampling, and the comparator & A / D converter circuits 01 and 11 convert the data of the channels AN02 and AN11 into digital signals, and the data registers corresponding to the respective channels. To be stored. In the current control, the data of the simultaneously sampled AN02 and AN11, that is, Iw and Iv are used, and Iu of the failed phase is obtained by calculation (Iu = −Iw−Iv) to perform current control.
[0016]
(2) When the V-phase current sensor fails When the V-phase is specified as the failed phase, the A / D controller 21 commands simultaneous sampling of the channels AN01 (U-phase) and AN12 (W-phase). Accordingly, the sample & hold circuit 01 and the sample & hold circuit 11 perform simultaneous sampling, and the comparator & A / D converter circuits 01 and 11 convert the data of the channels AN01 and AN12 into digital signals, and the data registers corresponding to the respective channels. To be stored. Then, in the current control, the data of the simultaneously sampled AN01 and AN12, that is, Iu and Iw are used, and the Iv of the failed phase is obtained by calculation (Iv = −Iu−Iw) to perform the current control.
[0017]
(3) When the W-phase current sensor fails, when the W-phase is specified as the failed phase, the A / D controller 21 simultaneously operates the channels AN01 (U-phase) and AN11 (V-phase) as in the normal control. Command sampling. Accordingly, the sample & hold circuit 01 and the sample & hold circuit 11 perform simultaneous sampling, and the comparator & A / D converter circuits 01 and 11 convert the data of the channels AN01 and AN11 into digital signals, and store the data in the data registers corresponding to the respective channels. To be stored. In the current control, the simultaneously sampled data of AN01 and AN11, that is, Iu and Iv are used, and Iw of the failed phase is obtained by calculation (Iw = −Iu−Iv) to perform current control.
[0018]
Hereinafter, the contents of the control of the present embodiment will be described based on a flowchart.
FIG. 3 is a flowchart showing the contents of the current sensor failure diagnosis processing.
3, in step S1, the three-phase current detection values Iu, Iv, Iw detected by the current sensors 7-1, 7-2, 7-3 in FIG. 1 are read, and the process proceeds to step S2.
In step S2, it is determined whether or not the current sensor has failed. This failure determination is made using a determination formula shown in the following (Formula 1).
Iu + Iv + Iw ≧ ± X (Equation 1)
However, X: a failure determination value set in consideration of a detection error or the like. In the above determination, if there is a failure in the current sensor, the process proceeds to step S3, and if there is no failure, the failure diagnosis processing ends.
[0019]
In step S3, the following (number) is obtained from the current command values Id ^* and Iq ^{* of the} two axes (d and q axes) input to the current control of FIG. 1 and the motor angle θ (electrical angle) detected by the rotation angle detector 8. 2) A three-phase current command value is calculated by two-phase to three-phase conversion using the equation, and the process proceeds to step S4.
Iu ^* = √ (2/3) × (Id ^* × cos θ−Iq ^* × sin θ)
Iv ^* = √ (1/2) × (Id ^* × sin θ + Iq ^* × cos θ) −Iu ^* / 2
Iw ^* =-Iu ^* -Iv ^* (Equation 2)
In step S4, deviations ErrU, ErrV, and ErrW of each phase between the three-phase current detection values Iu, Iv, Iw read in step S1 and the three-phase current command values Iu ^* , Iv ^* , Iw ^* calculated in step S3. Is calculated, and the routine goes to step S5.
[0020]
In step S5, the phase with the largest deviation calculated in step S4 is specified as the current sensor failure phase, and the phase whose deviation exceeds the preset deviation allowable threshold Y is also specified as the current sensor failure phase, and the process proceeds to step S6. .
In step S6, the number of current sensor failures is determined. If the failure has two or more phases, the process proceeds to step S7, and if only one phase exists, the process proceeds to step S8.
In step S7, if two or more phases fail, normal control cannot be performed, so the motor control is stopped and the process is terminated.
In step S8, a control mode switching signal (a switching command of a phase to be simultaneously sampled by the A / D controller 21) is generated in accordance with the failed phase, and the process ends.
[0021]
Next, FIGS. 4 and 5 are flowcharts for explaining operations from the detection of the three-phase current value to the calculation of the two-phase current values Id and Iq in the current control of FIG. 1 when the control of FIG. 3 is performed. It is. 4 and 5 are connected at points (1), (2) and (3).
First, in FIG. 4, in step S11, the control mode in step S8 in FIG. 4 is determined, and if it is the normal mode or the W-phase failure mode, the process proceeds to step S12; otherwise, the process proceeds to step S13.
In step S13, the control mode is further determined. If the mode is the U-phase failure mode, the process proceeds to step S14. If the mode is the V-phase failure mode, the process proceeds to step S15.
[0022]
In step S12, the channels to be simultaneously sampled are set to AN01 and AN11 (Iu and Iv), and the process proceeds to step S16 in FIG.
In step S16, A / D conversion by simultaneous sampling is started, and the process proceeds to step S17. In step S17, A / D conversion completion wait is performed, and when completed, the process proceeds to step S18.
In step S18, a two-phase current value (Id, Iq) is calculated from the detected current value by three-phase to two-phase conversion using the following equation (Formula 3), and the process ends.
Id = √ (3/2) Iucos θ + [√ (1/2) Iu + √ (2) Iv] sin θ
Iq = −√ (3/2) Iusin θ + [√ (1/2) Iu + √ (2) Iv] cos θ (Equation 3)
In step S14 of FIG. 4, the channels to be simultaneously sampled are set to AN02 and AN11 (Iw and Iv), and the process proceeds to step S19 of FIG.
[0023]
In step S19, A / D conversion by simultaneous sampling is started, and the process proceeds to step S20. In step S20, A / D conversion completion wait is performed, and when completed, the process proceeds to step S21.
In step S21, a two-phase current value (Id, Iq) is calculated from the detected current value by three-phase to two-phase conversion using the following equation (Formula 4), and the process ends.
Id = −√ (3/2) (Iv + Iw) cos θ + √ (1/2) (Iv−Iw) sin θ
Iq = √ (3/2) (Iv + Iw) sin θ + √ (1/2) (Iv−Iw) cos θ (Equation 4)
In step S15 in FIG. 4, the channels to be simultaneously sampled are set to AN01 and AN12 (Iu and Iw), and the process proceeds to step S22 in FIG.
In step S22, A / D conversion by simultaneous sampling is started, and the process proceeds to step S23. In step S23, A / D conversion completion wait is performed, and when completed, the process proceeds to step S24.
In step S24, a two-phase current value (Id, Iq) is calculated from the detected current value by a three-phase to two-phase conversion using the following equation (5), and the process ends.
Id = √ (3/2) Iucos θ + [√ (1/2) Iu + √ (2) Iw] sin θ
Iq = −√ (3/2) Iusinθ + [√ (1/2) Iu + √ (2) Iw] cosθ (Equation 5)
With the above processing, control is performed so that the two-phase current values used for control are always read by simultaneous sampling.
[0024]
As described above, in the present embodiment, even if a failure occurs in any of the three phase current sensors, the remaining normal two-phase current sensor detection values are taken in synchronously, so that the failed phase is detected. By controlling by estimating the current value, it is possible to secure current control performance equivalent to that during normal control and to use an inexpensive microcomputer having only two A / D converter circuits, as in the case of using an inexpensive microcomputer. Even when the number of A / D converters used for the current sensor is limited, the above-described excellent functions can be realized. Further, the present invention can be realized only by processing on software without adding special hardware.
[0025]
FIG. 6 is a block diagram of a second embodiment of the present invention.
This embodiment shows a connection in a case where a combination of channels, such as AN01 and AN11, AN02 and AN12, and AN03 and AN13, is specified because there are restrictions on channels that can be simultaneously sampled in a microcomputer used.
In FIG. 6, the U-phase current sensor output Iu is connected to analog input terminals AN01 and AN02, the V-phase current sensor output Iv is connected to AN11 and AN03, and the W-phase current sensor output Iw is connected to AN12 and AN13. Then, simultaneous sampling is performed as described below.
[0026]
(1) When the U-phase current sensor fails When the U-phase is specified as the failed phase, Iv and Iw are detected by simultaneous sampling of AN03 and AN13.
(2) When the V-phase current sensor fails When the V-phase is specified as the failed phase, Iu and Iw are detected by simultaneous sampling of AN02 and AN12.
(3) When the W-phase current sensor fails, during normal operation, and when it is specified that the W-phase is the failed phase, Iu and Iv are detected by simultaneous sampling of AN01 and AN11.
As described above, in the present embodiment, the same effect as in the first embodiment can be obtained even when there is a restriction on the channels that can be simultaneously sampled in the microcomputer used.
[0027]
Next, FIG. 7 is a block diagram showing a third embodiment of the present invention.
This embodiment shows an example in which equivalent functions are realized by peripheral circuits.
In FIG. 7, the U-phase current sensor output signal Iu is connected to an analog input terminal AN01 via an analog switch SW22.
The W-phase current sensor output signal Iw is connected to the analog input terminal AN01 via the analog switch SW23, and is connected to the analog input terminal AN11 via the analog switch SW24. Is connected to the analog input terminal AN11 via the analog switch SW25.
The analog switches SW22 to SW25 are opened and closed by control signals 01 and 11 provided from I / O terminals 01 and 11, respectively. The analog switches SW22 and SW23 are opened and closed by the inverting circuit 26, and the analog switches SW24 and SW25 are opened and closed by the inverting circuit 27 in opposite phases.
[0028]
FIG. 8 is a chart showing the values of the control signals 01 and 11. By setting the control signals 01 and 11 to the values shown in FIG. 8, the analog switches SW22 to SW25 open and close in the following modes.
(1) When U phase failure analog SW22: OFF
Analog SW23: ON and W-phase current sensor connected to AN01 Analog SW24: OFF
Analog SW25: ON and V-phase current sensor connected to AN11 (2) V-phase failure Analog SW22: ON and U-phase current sensor connected to AN01 Analog SW23: OFF
Analog SW24: ON and connection of W-phase current sensor to AN11 Analog SW25: OFF
(3) Analog SW22: ON and U-phase current sensor connected to AN01 in normal or W-phase failure Analog SW23: OFF
Analog SW24: OFF, V11 phase current sensor connection to AN11 Analog SW25: ON
As described above, even if the current sensor of any phase fails, the two-phase current sensors that are not faulty are always connected to AN01 and AN11, and are always used for control without switching channels for simultaneous sampling. It is also possible to simultaneously sample current values.
As described above, in the present embodiment, the same effect as that of the first embodiment can be obtained without switching the channels for simultaneous sampling.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an example of a current feedback control device of a three-phase motor to which the present invention is applied. FIG. 2 is a block diagram of one embodiment of the present invention.
FIG. 3 is a flowchart showing the contents of a current sensor failure diagnosis process.
4 is a part of a flowchart for explaining operations from detection of a three-phase current value to calculation of two-phase current values Id and Iq in the current control of FIG. 1 when the control of FIG. 3 is performed.
5 is another part of the flowchart for explaining the operation from the detection of the three-phase current value to the calculation of the two-phase current values Id and Iq in the current control of FIG. 1 when the control of FIG. 3 is performed.
FIG. 6 is a block diagram of a second embodiment of the present invention.
FIG. 7 is a block diagram showing a third embodiment of the present invention.
FIG. 8 is a table showing values of control signals 01 and 11;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Current command calculation part 2 ... Current PI control part 3 ... Two-phase three-phase converter 4 ... PWM conversion part 5 ... Inverter 6 ... Three-phase motors 7-1, 7-2, 7-3 ... Current sensor 9 ... A / D converter 10: three-phase two-phase converter 21: A / D controllers 22 to 25: analog switches SW 26, 27: inverting circuit

Claims (3)

A failure phase identification unit that identifies a failure phase corresponding to the failed current sensor when a failure occurs in the current sensor that detects the current of each phase in the three-phase AC motor;
A first A / D conversion circuit which takes in a first phase current sensor detection value and performs A / D conversion;
A second A / D conversion circuit that takes in the detected value of the second phase current sensor and performs A / D conversion.
The detected value of the current sensor of the third phase can be taken in by either the first A / D conversion circuit or the second A / D conversion circuit, and the fault phase specified by the fault phase specifying means can be obtained. A control device for a three-phase AC motor configured to take in two phases except for the first and second A / D conversion circuits in synchronization with each other. The failure phase identification means captures values detected by the first A / D conversion circuit and the second A / D conversion circuit captured at a first time and a second time delayed from the first time. Identify a faulty phase by comparing each of the detected values by the first A / D conversion circuit or the second A / D conversion circuit with a current command value for commanding a current value to be passed to each phase. The control device for a three-phase AC motor according to claim 1, wherein: Each input terminal of the first A / D conversion circuit and the second A / D conversion circuit is connected to the current sensor of each phase via an analog switch. Accordingly, by controlling the opening and closing of each analog switch, two phases except for the fault phase specified by the fault phase specifying means are connected to the input terminals of the first and second A / D conversion circuits. The control device for a three-phase AC motor according to claim 1 or 2, which is configured.

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