JPH0937405A - Self-diagnostic apparatus for motor controller for electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cut and separate a control command issuing device and a motor controller, at the time of checking the cause of a malfunction. SOLUTION: A control command issuing device 30 receives the output of an accelarator sensor 8, and outputs a control command. A detachable malfunction diagnostic apparatus 20 is connected to the motor controller 5, and a motor 4 is controlled by a control command from the diagnostic apparatus. Limits are set on a control command value and a control command generating time. Also when the control issuing apparatus 30 is malfunctioning, the motor can be driven by the control command from the malfunction diagnostic apparatus 20, and malfunction diagnosis of the motor controller becomes possible. It is possible to prevent the speeding of a vehicle caused by misoperation by limiting the command value and the command generating time at the time of malfunction diagnosis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric vehicle, and more particularly to a control device and a control method for coping with a failure of the electric motor of the electric vehicle or its control device.

[0002]

2. Description of the Related Art In recent years, an electric motor of vector control type has been widely used in order to use an induction motor driven by an inverter for vehicle propulsion and to control the induction motor at high speed and with high accuracy. Generally, an electric vehicle includes an inverter that converts a DC power source of a battery into an AC power source of a variable voltage and a variable frequency, a three-phase AC electric motor for driving a vehicle, a current sensor that detects a current and a rotation speed of the three-phase AC electric motor, and An encoder, a control command device that determines a control command for the three-phase AC motor according to the accelerator opening, and a control command device that controls the current flowing through the winding of the three-phase AC motor based on the outputs of the control command device and the current sensor. A control microcomputer that generates a phase AC current command, and P that is applied to the gate of the inverter based on the three-phase AC current command and the motor winding current
And a driver that generates a WM signal. Usually, the control microcomputer and the driver are integrally configured as a motor control unit.

In such electric vehicle control, vector control is performed in order to feed back the output of the encoder and thereby control the speed and torque with high accuracy. For this vector control, an accelerator switch for detecting the accelerator opening, a current sensor for detecting the current of the three-phase AC motor, and an encoder for detecting the rotation speed are indispensable. Therefore, if any of these sensors fails, vector control becomes uncontrollable,
When the encoder fails, the torque may be excessive or excessive, and stable control of current and electric power may become impossible.

In such a case, in order to stably control the electric vehicle, Japanese Patent Laid-Open No. 3-277101 discloses that if a failure occurs in the rotation sensor, the vehicle speed sensor is switched to and the electric motor is based on the information obtained from this sensor. The scheme for driving the is shown. Further, Japanese Patent Application Laid-Open No. 5-91601 discloses a technique of switching the control method from vector control to v / f control when the rotation sensor (encoder) is abnormal in an electric vehicle.

On the other hand, even if the sensors are normal, if the torque command device or the motor control unit is abnormal, the electric vehicle cannot be safely driven, so it is always necessary to check whether these are normal. Therefore, JP-A-5-33660
As described in Japanese Patent Publication No. 3 and Japanese Patent Application Laid-Open No. 6-261404, there is known a failure diagnosis device that periodically checks the operation of the control command device and the electric motor control unit at the time of starting the electric vehicle and during traveling. There is. A conventional failure diagnosis device inputs a signal corresponding to an accelerator opening command to drive an electric motor,
From the relationship between the input and the output current of the electric motor detected by various sensors, it is diagnosed whether there is an abnormality in the control command device or the electric motor control unit.

[0006]

In the conventional fault diagnosis apparatus, the fault diagnosis is performed by using the control command device and the electric motor control unit as one electric motor control device. In this case, when the electric motor does not move in spite of the control command given from the failure diagnosis device, it is not possible to directly diagnose whether the control command device has a defect or the motor control unit has a defect.

However, the control command device and the electric motor control unit are generally designed and manufactured separately in advance, selected according to the characteristics of the vehicle, and generally assembled together. This is because the opening characteristic required by the control command device strongly depends on the operation characteristic peculiar to each vehicle model such as the accelerator and the shift lever, and it is desirable to design it together with the vehicle. The control characteristics of the control unit are
Because it strongly depends on the characteristics of each motor model, it is desirable to design with the motor.

Therefore, in order to take appropriate measures against the failure,
In some cases, it is necessary to separately diagnose the control command device and the motor control unit. However, even when making a failure diagnosis individually, it must always be safe.

It is an object of the present invention to provide an electric vehicle diagnostic device capable of diagnosing a failure of a motor control unit regardless of whether the control command device is normal or abnormal.

Another object of the present invention is to provide a diagnostic apparatus for an electric vehicle that prevents the risk of excessive torque being generated in the electric motor during failure diagnosis.

Another object of the present invention is to provide a diagnostic device capable of diagnosing a motor control device even if the control command device in operation is malfunctioning.

Another object of the present invention is to prevent the electric vehicle drive system from stopping when the failure diagnosis device is in operation.

[0013]

In order to achieve the above object, the present invention provides an inverter for converting a DC power source of a battery into an AC power source of a variable voltage and a variable frequency, and a current of a three-phase AC motor for driving a vehicle. A current sensor for detecting the rotational speed of the three-phase AC motor, an encoder for detecting the rotational speed of the three-phase AC motor, a control command device for determining a control command of the three-phase AC motor according to the accelerator opening, the control command, the current sensor And a motor control that generates a current command for controlling the current of the three-phase AC motor based on each output of the encoder, and generates a voltage signal based on the current command and the current flowing in the three-phase AC motor. Section and driver means for generating a signal for controlling the inverter based on the voltage signal, and the control command device and the motor control section are configured separately. A self-diagnosis device for performing a failure diagnosis on a motor control device of a vehicle, the fault being provided independently of the motor control device and connectable to a motor control unit of the motor control device via a communication line. The failure diagnosis device includes a diagnosis device, outputs a control command equivalent to the control command device to the electric motor control unit, and the electric motor control unit receives the control command and generates the control signal for the electric motor. The present invention is characterized by diagnosing whether or not there is a failure in the electric motor control unit based on the operating state of the electric motor.

Another feature of the present invention is that the control command value or the control command generation time from the failure diagnosis device is limited to a predetermined value or less.

Another feature of the present invention is that, when a diagnostic control command is given from the diagnostic device, the processing of the electric motor control unit is executed even if the diagnostic control command is not synchronized with the control command device. Another feature of the present invention is to notify the monitoring microcomputer that a diagnosis control command is given from the failure diagnosis device.

[0016]

According to the present invention, a control command is given from a removable fault diagnosing device, and the electric motor is moved based on the control command so that the fault diagnosis of the electric motor control section can be performed regardless of whether the control command device is normal or abnormal. .

According to another feature of the present invention, it is possible to prevent a risk that an excessive torque is generated in the electric motor at the time of failure diagnosis. That is, the generation amount of the diagnostic control command output from the diagnostic device is limited. For example, take the sum of command values every 2 ms,
Keep within a predetermined value. A small torque requires a long time, and a large torque requires a short diagnosis time. Although the embodiment has been described in which the sum of the command values is taken, a method of simply calculating the generation time of the diagnostic control command may be used. Further, the control command for diagnosis may be suppressed to a value lower than that of the normal control command to prevent the risk of excessive torque generation.

According to another feature of the present invention, when the diagnostic control command is given from the diagnostic device, the process of the electric motor control section is executed even if the diagnostic control command is not synchronized with the control command device. Also, even if the control command device is malfunctioning, the motor control unit can be diagnosed.

According to another feature of the present invention, the fact that the diagnostic control command is given to the monitoring microcomputer from the failure diagnosing device causes the monitoring microcomputer to become inconsistent as a calculation based on the signal from the control command device. , Prevent from shutting down the system. It is also possible to obtain a calculated value for controlling the electric motor based on the command value from the control command device and output it to the monitoring microcomputer so that the system does not stop.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a control device for an electric vehicle, in which 1 is a battery which is a main power source of the electric vehicle, 2 is a contactor, and 3 is a power switching element for converting direct current of the battery 1 into alternating current. An inverter, 4 is a three-phase AC electric motor for driving an electric vehicle, 5 is an electric motor controller that controls the three-phase AC electric motor 4 in a normal state, and 6 is an electric motor 4.
It is an encoder for detecting the rotation speed N of the. In addition, 7 is a current sensor, which flows through the primary winding of the AC motor 2 3
The primary current i (iu, iv, iw) of the phase alternating current is detected. 8
Is an accelerator sensor that outputs an output θA corresponding to the amount of depression when the accelerator is depressed. Reference numeral 9 denotes a shift lever switch that outputs an output corresponding to the position of the shift lever.

Reference numeral 20 is a failure diagnosing device, which is a diagnostic control unit 2
1, a display unit 22, and an operation unit 23. The operation unit 23 is used to specify a device to be diagnosed and to input a command, data, and the like for performing a predetermined diagnosis process in the diagnosis control unit 21.

Reference numeral 30 denotes a control command device, which is provided with an accelerator opening calculation means 31 and a control command calculation means 32, which inputs accelerator and shift lever position signals and, in addition to these signals, gives them from the motor control section 5. Motor rotation speed N
Then, the target torque of the electric motor is calculated.

The electric motor control unit 5 is provided with a control microcomputer 50 including a speed detection unit 10, a primary frequency command generation unit 40, a vector control unit 52, an AC current command generation unit 60, and a motor current control unit 70. In response to the control command given from 30, the control microcomputer 50 is a driver P so that the electric motor 4 outputs the torque of the control command.
The inverter 3 is controlled via the WM signal generation means 90.

The electric motor control section 5 further comprises a monitoring microcomputer 80 for monitoring the control microcomputer 50 for abnormalities. The monitoring microcomputer 80 includes a control unit 81 having the same calculation function as the control microcomputer 50 and a monitoring unit 8 having a monitoring function.
2 and. The control unit 81 is configured to receive the same control command as the control microcomputer 50, detect the motor rotation speed N, and perform the same calculation as the control microcomputer 50. The monitoring unit 82 compares the calculation result of the control unit 81 with the calculation result of the control microcomputer 50, and when they do not match, opens the contactor 2 and cuts off the power supplied from the battery 1 to the inverter 3.

The electric motor controller 5, the control command device 30, and the failure diagnosis device 20 are connected to the optical fiber communication line 110, 1.
They are connected to each other by 10.

In the control command device 30, the accelerator opening degree θA is taken into the control command calculating means 32 via the accelerator opening degree calculating means 31, and the control command τr * corresponding to the accelerator opening degree θA is calculated.

The control microcomputer 50 is usually the encoder 6
A. The rotation speed N ₁ of the electric motor is fetched via the speed detection means 10. The vector control unit 52 generates the control current command It * and the exciting current command Im * based on the input of the control command τr * and the rotation speed N ₁ . Further, the primary frequency command generating means 40 generates the primary frequency ω ₁ * corresponding to this rotation speed N ₁ . The alternating current command generating means 60 uses It
Based on *, Im *, ω ₁ *, the current command Iu *,
Iv *, Iw * are generated. In the motor current control means 70, voltage commands Eu *, Ev *, Ew for obtaining the motor control τM based on these current commands and the three-phase alternating currents (iu, iv, iw) detected by the current sensor 7. * Is generated and output to the PWM signal generating means 90.

The control microcomputer 50 has a 2 ms job started every 2 ms using an internal timer, a 100 μs job started every 100 μs, and a torque command device interrupt job started by a communication interrupt from the control command device. , There is a fault diagnosis device interrupt job started by a communication interrupt from the fault diagnosis device.

In the 2 ms job 200 of the control microcomputer 50 shown in FIG. 2, it is judged whether or not the synchronization processing with the control command device 30 at the time of startup is completed (step 201), and when not completed, the synchronization processing shown in FIG. 4 is executed. Execute (step 20)
5).

At the end of synchronization, it is judged whether or not a diagnostic control command is given from the failure diagnostic device (step 20).
2). After the completion of the synchronization process, if the diagnostic control command is given, the inverter drives the 2 ms job and the 100 μs job. 2 when the diagnostic control command is given
The diagnostic control command is added every ms to determine whether the upper limit value has been reached (step 207). When the upper limit is reached, the diagnostic torque command is set to 0 to prevent the torque from being continuously output indefinitely (step 208). That is, for safety, the sum of command values is taken every 2 ms to limit the generation amount of the diagnostic control command. Then, the command value for motor control is calculated using the diagnostic control command as a control command (step 20).
9). The command values for motor control are the exciting current and the torque current.

When the diagnostic control command is not given, the addition value of the diagnostic control command every 2 ms is cleared,
A command value for motor control is calculated by a control command from the control command device (steps 203 to 204).

FIG. 4 shows an example of the synchronization processing at the time of starting.
(A) shows the control command from the control command device, and (b) shows the operation of the failure diagnosis device. When the key switch is turned on, a command for memory check is output from the control command device 30 to perform the memory check. When a command to turn on the inverter drive relay is subsequently output, the relay is turned on and it is checked whether the capacitor is charged to a predetermined value, and when the charge is completed, the control command device 30
The control command device outputs a command to turn on the inverter relay. After the inverter relay is turned on, the monitoring microcomputer 80 checks the monitoring function. The notification of the completion of the check ends the synchronization processing.

Thereafter, "READ" indicating that the display device is ready
When the diagnostic control command is given after the synchronization process is completed, the inverter is driven by the 2 ms job and the 100 μs job as described above. The 2 ms job is shown in FIG. As shown, the control command value of the electric motor is calculated every 2 ms for 0.6 ms.

In the case of the 100 μs job, FIGS.
As shown in (b), inverter control, that is, electric motor control for giving a three-phase command of U, V, W to the inverter is performed based on the command value of the motor control determined by the 2 ms job (step 301). Further, the calculation result is transmitted to the monitoring microcomputer 80, and the monitoring microcomputer side compares the results (step 302). When the control command is given from the failure diagnosis device 20, the command is given to the monitoring microcomputer 80 so that the monitoring microcomputer does not stop the system.

That is, the monitoring microcomputer is notified that the diagnostic control command is given from the failure diagnosis device, and the monitoring microcomputer is prevented from stopping the system due to a mismatch in the calculation based on the signal from the control command device. To do. It is also possible to obtain a calculated value for controlling the electric motor based on the command value from the control command device and output it to the monitoring microcomputer so that the system does not stop.

As shown in FIG. 6, it is judged whether or not there is a communication abnormality in the communication interrupt processing from the command device (step 60).
2). When normal, the received data is used as a control command value (step 763).

FIG. 7 shows a communication procedure between the failure diagnosis device 20 and the motor control microcomputer, and FIG. 8 shows the failure diagnosis device 20.
On the motor control microcomputer side when data is sent from
It is a flowchart of a diagnostic device communication interruption job.

When an interrupt occurs from the fault diagnosis device 20 to the motor control microcomputer, the diagnosis device communication interrupt job (8
00) starts and returns an answer back signal. The procedure is that the diagnostic device sends the number assigned to the motor control microcomputer and selects the motor control microcomputer. When instructing diagnostic control, a code for instructing diagnostic control is transmitted, and then a diagnostic control instruction is transmitted.

In the communication interruption job from the failure diagnosis device 20, it is judged whether or not there is a control command for diagnosis (step 80).
1) If there is a command, the diagnostic control that follows is received and stored in the memory as a diagnostic control command value (step 802). On the fault diagnosis device 20 side, when all the data is sent, the code of the END signal indicating the end is output, the answer control signal confirms that the motor control microcomputer has received the END signal, and the series of processes is ended.

The received diagnostic control command value exceeds the upper limit value that may be output for diagnosis, for example, 8 kgm,
Check in step 803.

When the diagnostic control command value exceeds the upper limit of the diagnostic command, it is limited to the upper limit value so that excessive torque is not output during the diagnosis in order to prevent danger (steps 803 to 8).
04).

Further, a flag indicating that the synchronization process with the control command device is completed is set so that the electric motor drive system starts up without synchronization with the control command device. As a result, the 2 ms task is put into the electric motor control state (step 805).

When the diagnostic control command is given from the diagnostic device, the electric motor control process is executed even if the control command device is not synchronized. Therefore, even if the control command device is out of order, the electric motor control device can be diagnosed.

The command from the diagnostic device is not only a diagnostic control command but also a request for transmission of rotational speed and failure information. In step 806, it is determined whether the request is for transmission of rotation speed information, and if true, transmission of rotation speed information is performed in step 807. In step 808, it is determined whether or not the request is a failure information transmission request, and if true, the failure information is transmitted in step 809.

As described above, it is possible to operate the electric motor control unit 5 based on the diagnosis control command from the failure diagnosis device 20 to drive the electric motor 4 and perform the failure diagnosis of the electric motor control unit 5. The command value calculation process of the motor control in the motor control unit 5 when the control command is given is as follows. Here, the vector control calculation means 52
The operations from to PWM signal generating means 90 will be described using arithmetic expressions.

The motor torque τM is obtained by the following equation using the torque current It and the exciting current Im.

ΤM = (3/2) · P · (M ² / (M + 1 ₂ )) · Im · It ………… (1) where P: number of poles M: exciting inductance 1 ₂ : secondary Leakage Inductance Next, the maximum value I ₁ of the AC current command is calculated based on the torque current command It * and the exciting current command Im *. Corresponding to the rotational angular velocity ωr obtained via the velocity detecting means 10,
The magnetic flux φR * to be generated in the secondary circuit of the electric motor 4 is generated.
Multiply the magnetic flux φR * by the load factor α in the following equation 2 to obtain the secondary magnetic flux command φ *
Is required. α = It * / It0 ……………………………………………… (2) However, It0: Rated torque current Next, the secondary magnetic flux command φ *, The deviation of the secondary magnetic flux generated in the secondary circuit of the AC motor 2 from φ ₂ estimated by the following expression 3 is obtained, and the exciting current command Im * is generated. φ ₂ = (M · Im *) / (1 + T ₂ · s) …………………………………… (3) However, T ₂ (= (M + 1 ₂ ) / r ₂ ): Secondary Constant r ₂ : Secondary resistance Using the torque current command It * and the exciting current command Im * obtained as described above, the slip angular frequency ωs and the phase θ ₁ are calculated by the following equations (4) and (5), respectively. Desired. ωs = Ks ・ (It * / Im *) ……………………………………………… (4) where Ks = r ₂ / (M + 1 ₂ ) θ ₁ = tan- ¹ ( It * / Im *) …………………………………… (5) The angular frequency (primary angular frequency) ω ₁ * of the AC current command is the slip angular frequency ωs and the rotational speed N ₁ It is obtained by adding ωr obtained from The instantaneous phase of the AC current command is obtained by integrating the primary angular frequency ω ₁ *.

The phase of the AC current command is obtained by adding the instantaneous phase and the phase θ ₁ . In the AC current command generator 60, the three-phase AC current commands iu *, i based on these values are used.
Generate v * and iw *.

The electric motor current control means 70 responds to these alternating current commands (iu *, iv *, iw *) with three-phase alternating currents iu,
The PI compensator generates voltage commands Eu *, Ev *, Ew * so that iv, iw follow. PWM signal generating means 9
0 generates a PWM signal by comparing the voltage commands Eu *, Ev *, Ew * with the triangular wave signal of the carrier wave. Based on this PWM signal, the six power elements forming the arm of the inverter 3 are driven. As a result, a three-phase AC voltage having a variable frequency and a variable voltage is generated from the battery 1 power supply, and the torque of the three-phase AC motor 4 is controlled.

According to the present invention, the removable fault diagnosis device 20 gives a control command to the electric motor control unit 5, and the electric motor control unit 5 operates based on the control command to drive and control the electric motor 4. Therefore, even if the control command device 30 is defective, the failure diagnosis of the electric motor control unit 5 can be performed.

In the fault diagnosis, for safety, the generation amount of the diagnostic control command is limited. In the embodiment, the sum of the command values is taken every 2 ms to keep it at a predetermined value. A small torque requires a long time, and a large torque requires a short diagnosis time.
As a simpler method, a method of calculating the generation time of the diagnostic control command may be used.

Further, for safety, the diagnostic control command is suppressed to a value lower than the normal control command to prevent the risk of excessive torque generation.

When the diagnostic control command is given from the diagnostic device, the electric motor control process is executed even if the control command device is not synchronized.

Further, even if the control command device is out of order, the motor control device can be diagnosed. The monitoring microcomputer is notified that the diagnostic control command is given from the failure diagnosis device, and the monitoring microcomputer is prevented from stopping the system due to a mismatch in the calculation based on the signal from the control command device. It is also possible to obtain a calculated value for controlling the electric motor based on the command value from the control command device and output it to the monitoring microcomputer so that the system does not stop.

[0055]

According to the present invention, a control command is given from a removable fault diagnosing device, and the electric motor is made to operate based on the control command, so that even if the control command device is defective, the electric motor control unit can independently diagnose the fault. You can Further, by limiting the generation amount of the diagnostic control command and limiting the command value and command generation time at the time of failure diagnosis, it is possible to prevent vehicle runaway due to erroneous operation.

Further, when the diagnostic control command is given from the diagnostic device, the electric motor control process is executed even if the control command device is not synchronized. Further, even if the control command device is out of order, the motor controller can be diagnosed.

[0057]

[Brief description of drawings]

FIG. 1 is a diagram showing a drive control device for an electric vehicle according to an embodiment of the present invention.

FIG. 2 is a flow chart of processing of a 2 ms job in the failure diagnosis apparatus of FIG.

3 is a flow chart of processing of a 100 μs job in the failure diagnosis apparatus of FIG.

FIG. 4 is a diagram illustrating a synchronization process in the process flow of FIG.

5 is an explanatory diagram of a 2 ms job and a 100 μs job of FIG. 2. FIG.

FIG. 6 is a flowchart of communication interrupt processing from the torque command device.

FIG. 7 shows a communication procedure between the failure diagnosis device and the motor control microcomputer.

FIG. 8 is a flowchart of communication interrupt processing from the failure diagnosis device.

[Explanation of symbols]

1 ... Battery, 2 ... Three-phase AC motor, 3 ... Inverter, 4 ... Electric motor, 5 ... Electric motor control unit, 6 ... Encoder,
7 ... Current sensor, 8 ... Accelerator sensor, 10 ... Speed detection means, 20 Failure diagnosis device, 30 ... Control command device, 5
0 ... Control microcomputer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Yokoyama 2520 Takaba, Hitachinaka City, Ibaraki Prefectural Automobile Equipment Division, Hitachi Ltd. (72) Toshisada Mitsui 2520 Takaba, Hitachinaka City, Ibaraki Prefecture Company Hitachi, Ltd. Automotive Equipment Division (72) Hiroyuki Yamada Inventor Hironaka, Hitachinaka City, Ibaraki Takaba 2477 Kashima Yatsu 3 Hitachi Automotive Engineering Co., Ltd. (72) Inventor Atsushi Kunimi, Ibaraki Hitachinaka Kashima Yatsu 2477 3 Hitachi Automotive Engineering Co., Ltd.

Claims (4)

[Claims] 1. An inverter for converting a DC power source of a battery into an AC power source of a variable voltage and a variable frequency, a current sensor for detecting a current of a three-phase AC motor for driving a vehicle, and a rotation speed of the three-phase AC motor. An encoder to detect, a control command device that determines a control command of the three-phase AC motor according to the accelerator opening, and the current of the three-phase AC motor based on the control command, the output of the current sensor and the encoder. A motor control unit that generates a voltage command based on the current command and a current flowing through the three-phase AC motor, and a signal that controls the inverter based on the voltage signal. A driver unit for generating a fault, and a self-diagnosis unit for performing a failure diagnosis with respect to an electric motor control device of an electric vehicle in which the control command device and the electric motor control unit are separately configured. The diagnostic device includes a failure diagnostic device that is provided independently of the electric motor control device and that can be connected to an electric motor control unit of the electric motor control device via a communication line, and the failure diagnostic device includes the control command device. A control command equivalent to the above is output to the electric motor control unit, and the presence or absence of a failure of the electric motor control unit is diagnosed by the operating state of the electric motor with respect to the control signal of the electric motor generated by the electric motor control unit receiving the control command. A self-diagnosis device for an electric motor control device of an electric vehicle. 2. The self-diagnosis device for an electric motor control device of an electric vehicle according to claim 1, wherein the control command value or the control command generation time from the failure diagnosis device is limited to within a predetermined value. 3. The electric motor control process according to claim 1, wherein when a control command for diagnosis is given from the failure diagnosis device, the motor control process is executed even if the control command device is not synchronized. A self-diagnostic device for the motor controller of a car. 4. An inverter for converting a DC power source of a battery into an AC power source of variable voltage and variable frequency, a current sensor for detecting a current of a three-phase AC motor for driving a vehicle, and a rotation speed of the three-phase AC motor. An encoder to detect, a control command device that determines a control command of the three-phase AC motor according to the accelerator opening, and the current of the three-phase AC motor based on the control command, the output of the current sensor and the encoder. A control microcomputer that generates a voltage signal based on the current command and the current flowing in the three-phase AC motor, and a signal that controls the inverter based on the voltage signal. And a driver unit for controlling the electric motor control device of the electric vehicle in which the control command device and the electric motor control unit are separately configured. The diagnostic device includes a failure diagnostic device that is provided independently of the electric motor control device and is connectable to the control microcomputer of the electric motor control device via a communication line, and the electric motor control device is the same as the control microcomputer. A control unit having a function and a monitoring unit that compares the output of the control unit with the output of the control microcomputer to monitor whether the output is normal or not, and outputs a control command equivalent to the control command device to the control microcomputer. The motor control unit diagnoses the presence / absence of a failure of the control microcomputer based on an operating state of the motor with respect to a control signal of the motor generated by receiving the control command, and the monitoring microcomputer performs a diagnosis from a failure diagnosis device. Prevents the monitoring microcomputer from notifying that the control command is given and causing the monitoring microcomputer to become inconsistent in the calculation based on the signal from the control command device and stop the system. Self-diagnosing apparatus for a motor control device for an electric vehicle, characterized by.