JP2003219675A - Motor driver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a power supply current fed from a power supply to a driving circuit accurately. <P>SOLUTION: A power supply current sensor 9 for detecting the level of a power supply current flowing through a feeder path from a power supply 3 to a motor drive circuit 1 comprises a current sensor of low detection accuracy and a detection signal from the power supply current sensor 9 is provided to a microcomputer 2. The microcomputer 2 corrects the detection value of the power supply current sensor 9 based on detection signals from a phase U current sensor 6U and a phase V current sensor 6V, compares a corrected value with a predetermined threshold value and makes a decision whether an overcurrent is supplied from the power supply 3 to the motor drive circuit 1 or not. If the corrected value is larger than the threshold value and a decision is made that an overcurrent is supplied to the motor drive circuit 1, a relay 10 is turned off as its fail-safe thus interrupting the feeder path from the power supply 3 to the motor drive circuit 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor drive device for driving an electric motor used as a drive source for an electric power steering device.

[0002]

2. Description of the Related Art For example, an electric motor provided in an electric power steering apparatus is driven and controlled by an electronic control unit (ECU) for the electric power steering apparatus based on an operation of a steering wheel. . That is, the electronic control unit is provided with a drive circuit connected to the battery power source of the vehicle, and by controlling the power element in this drive circuit with a duty according to the operation of the steering wheel,
The electric power according to the duty is supplied to the electric motor, and the steering assist force according to the operation of the steering wheel is generated from the electric motor.

In such a configuration, for example, when a short circuit failure occurs in the power element in the drive circuit, an overcurrent is supplied from the battery power supply to the drive circuit, and heat is generated on the power supply path from the battery power supply to the drive circuit. Or other power elements may be destroyed. Therefore, on the power supply path from the battery power supply to the drive circuit, a current sensor for detecting a power supply current value flowing through the power supply path and a relay for disconnecting the power supply path are provided.
Then, when the detection value of the current sensor exceeds a predetermined threshold value, it is determined that an overcurrent is being supplied from the battery power source to the drive circuit, and as a failsafe thereof,
The power supply path is cut off by the relay, and the power supply from the battery power supply to the drive circuit is stopped.

[0004]

As a current sensor for detecting a power supply current, for example, a current sensor using a shunt resistor is often adopted. The current sensor using the shunt resistor is inexpensive, but the current detection accuracy is low because the resistance value of the shunt resistor is designed as small as about 1 mΩ for the purpose of suppressing power loss. Therefore, in a configuration that employs a current sensor that uses a shunt resistor, the overcurrent supply state cannot be properly detected, and there is a possibility that problems such as heat generation due to overcurrent cannot be avoided. In order to solve this problem, a current sensor using a Hall element with high detection accuracy may be adopted, but the current sensor using the Hall element is expensive and therefore costly.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above technical problems and to improve the detection accuracy of the power supply current value supplied from the power supply to the drive circuit without increasing the cost. It is to provide a device.

[0006]

The invention according to claim 1 for achieving the above object is a motor drive device for driving an electric motor (M), which comprises a power supply (3). And a drive circuit (1) for supplying a drive current to the electric motor and a power supply current detection means (9) for detecting a power supply current supplied from the power supply to the drive circuit using a current sensor. ), Drive current detection means (6U, 6V) for detecting the drive current supplied from the drive circuit to the electric motor with higher detection accuracy than the current detection accuracy of the power supply current detection means, and the drive current detection means. And a correction means (2) for correcting the detection value of the power supply current detection means on the basis of the detection value of.

The alphanumeric characters in parentheses represent corresponding constituent elements in the embodiments described later. The same applies in this section below. According to the present invention, the detection value (power supply current detection value) of the power supply current detection means is corrected based on the detection value (drive current value) of the drive current detection means. Since the drive current detection means has higher current detection accuracy than the power supply current detection means, for example, the power supply current value is calculated (estimated) based on the drive current value detected by the drive current detection means, and the calculated power supply current value is calculated. By correcting the power supply current detection value by the power supply current detection means based on the (power supply current calculation value), the accuracy of detection of the power supply current value by the power supply current detection means can be increased. Moreover, in this configuration, there is no possibility of causing a problem of cost increase as in the case where the current sensor using the Hall element is adopted as the power supply current detecting means.

According to a second aspect of the present invention, a circuit disconnecting means (10) is provided on a power supply path from the power source to the drive circuit for disconnecting the power supply circuit, and after correction by the correcting means. The motor drive device according to claim 1, further comprising fail-safe means (2) for activating the circuit disconnecting means to disconnect the power supply circuit when the value exceeds a predetermined value. . According to the present invention, when the value corrected by the correction unit exceeds a predetermined value, the power supply circuit is disconnected (determined that an overcurrent is being supplied from the power supply to the drive circuit). The circuit breaking means is activated.

The value corrected by the correction means has an error (a difference from the actual power supply current value) than the value detected by the power supply current detection means.
Therefore, by comparing the corrected value with a predetermined value to determine whether the overcurrent is being supplied from the power supply to the drive circuit, the overcurrent supply state to the drive circuit can be accurately measured. The detection can be performed well, and the occurrence of problems such as heat generation due to the supply of overcurrent to the drive circuit can be favorably avoided.

[0010]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram schematically showing a configuration of a motor drive device according to an embodiment of the present invention. This motor drive device includes a motor drive circuit 1 for supplying a drive current to an electric motor M.
And a microcomputer 2 including a CPU 21, a RAM 22 and a ROM 23.

The electric motor M is a three-phase brushless motor, and the motor drive circuit 1 includes a power MOSFET 11 between a power source (for example, a vehicle battery) 3 and a ground 4.
U, 12U series circuit, power MOSFET 11V,
12V series circuit and power MOSFETs 11W, 12
It is composed of an inverter circuit in which a series circuit of W is connected in parallel. The series circuit of the power MOSFETs 11U and 12U is composed of these two power MOSFETs 11U and 12U.
It is connected to the U-phase winding of the electric motor M at the U connection point. In addition, the series circuit of the power MOSFETs 11V and 12V is composed of these two power MOSFETs 11V and 12V.
Is connected to the V-phase winding of the electric motor M.
The series circuit of the power MOSFETs 11W and 12W is connected to the W-phase winding of the electric motor M at the connection point of these two power MOSFETs 11W and 12W.

In relation to the electric motor M, a rotation angle sensor 5 for detecting the rotation angle (rotational position of the rotor) of the electric motor M is provided. As the rotation angle sensor 5, for example, a resolver that outputs a sine-waveform signal whose phase changes in response to a change in the rotation angle of the electric motor M can be adopted. The output signal of the rotation angle sensor 5 is supplied to the microcomputer 2.
A U-phase current sensor 6U and a V-phase current sensor 6V are provided on the power supply paths from the motor drive circuit 1 to the U-phase winding and the V-phase winding of the electric motor M, respectively.
For the U-phase current sensor 6U and the V-phase current sensor 6V, for example, a current sensor with a high detection accuracy using a hall element is used. The detection signals of these U-phase current sensor 6U and V-phase current sensor 6V , Are provided to the microcomputer 2.

The microcomputer 2 sets the target current value of each phase of the electric motor M based on the detection signal of the rotation angle sensor 5, and the target current value and the U-phase current sensor 6U and the V-phase current sensor 6V. On / off of each power MOSFET of the motor drive circuit 1 is controlled based on the detection signal. For example, when the motor drive device is used to drive the electric motor M of the electric power steering device, the microcomputer 2 further includes a vehicle speed for detecting the vehicle speed of the vehicle in which the electric power steering device is mounted. The detection signal of the sensor 7 and the detection signal of the torque sensor 8 for detecting the steering torque input from the steering wheel are given. Then, the microcomputer 2 sets the target current value based on the detection signals of the vehicle speed sensor 7 and the torque sensor 8. Further, the microcomputer 2 sets the target current value of each phase of the electric motor M by subjecting the set target current value to three-phase phase separation processing based on the detection signal of the rotation angle sensor 5, and further PWM for controlling the power MOSFET (power MOSFET corresponding to the rotation direction of the electric motor M) of the motor drive circuit 1 based on the phase target current value and the detection signals of the U-phase current sensor 6U and the V-phase current sensor 6V (Pulse Width Modulation) Generates control signal. As a result, the power MOSFE of the motor drive circuit 1 is
T is turned on / off with the duty Du, Dv, Dw of the PWM control signal, and a current according to the vehicle speed and the steering torque flows through the electric motor M. From this electric motor M, the driving force (steering Assisting force) is generated.

Further, the motor driving device includes a power source 3
A power supply current sensor 9 for detecting a value of a power supply current flowing from a power supply path to the motor drive circuit 1 and a relay 10 for disconnecting the power supply path from the power supply 3 to the motor drive circuit 1. The power supply current sensor 9 is a current sensor that uses a shunt resistor and has low detection accuracy, and the detection signal of the power supply current sensor 9 is supplied to the microcomputer 2. The microcomputer 2 uses the detected value of the power supply current sensor 9 as the U-phase current sensor 6U and V
Correction is made based on the detection signal of the phase current sensor 6V, and the corrected value is compared with a predetermined threshold value to determine whether or not an overcurrent is being supplied from the power supply 3 to the motor drive circuit 1. . When it is determined that the corrected value is larger than the threshold value and the overcurrent is being supplied to the motor drive circuit 1, the relay 1 is set as the fail safe.
0 is turned off, and the power supply path from the power supply 3 to the motor drive circuit 1 is cut off.

FIG. 2 is a flow chart showing the flow of processing for setting a correction value for correcting the detection value of the power supply current sensor 9. After the ignition key switch of the vehicle is turned on, the microcomputer 2 detects, for example, that the detection value of the power supply current sensor 9 (power supply current detection value) is 30 Arm.
When a predetermined current value is reached (steps S1 and S2), such as in response to s (effective value 30A), the correction value setting process described below is performed.

In this correction value setting process, first, the U-phase current sensor 6U and the V-phase current sensor 6V are used to measure the U-phase current value Iu flowing in the U-phase winding of the electric motor M and the V-phase current flowing in the V-phase winding. The value Iv is detected (step S
3). Then, the detected U-phase current values Iu and V
The V-phase current value Iw flowing in the W-phase of the electric motor M is calculated based on the phase current value Iv (step S
4). That is, since the sum of the currents flowing in the U-phase, V-phase and W-phase of the electric motor M becomes zero, the current Iw flowing in the W-phase is calculated according to the following equation (1).

Iw = 0-Iu-Iv (1) Next, the U-phase current value Iu detected by the U-phase current sensor 6U and the V-phase current value detected by the V-phase current sensor 6V Based on Iv and the W-phase current value Iw calculated according to the above equation (1), the effective value of the power supply current being supplied from the power supply 3 to the motor drive circuit 1 at this time is calculated (step S5). The effective value of the power supply current is the regenerative current generated in the electric motor M from the total current flowing in the direction from the motor drive circuit 1 to the electric motor M (two powers associated with each phase winding of the electric motor M). MOSF
It corresponds to a value obtained by subtracting the current induced during the period when both ETs are off. Therefore, when a positive sign is attached to the value of the current flowing from the motor drive circuit 1 toward the electric motor M, one of the U-phase current value Iu, the V-phase current value Iv, and the W-phase current value Iw having a positive value is given. Corresponding to PW
By multiplying the Duty Du, Dv, and Dw of the M control signal and adding the respective multiplied values, the effective value of the power supply current can be obtained. For example, when the U-phase current value Iu and the V-phase current value Iv are positive values, the effective value of the power supply current is the multiplication value of the U-phase current value Iu and the duty Du of the U-phase PWM control signal, and the V-phase It is calculated as Iu · Du + Iv · Dv obtained by adding the current value Iv and the product of the duty Dv of the V-phase PWM control signal.

As described above, the U-phase current sensor 6U and the V-phase current sensor 6V are current sensors having relatively high detection accuracy. Therefore, the calculated value (power supply current calculation value) It of the effective value of the power supply current based on the detection signals of the U-phase current sensor 6U and the V-phase current sensor 6V is the power supply current supplied from the power supply 3 to the motor drive circuit 1. It is almost equal to the effective value. Therefore, the difference between the power supply current calculation value It and the detection value of the power supply current sensor 9 can be regarded as a detection error of the power supply current sensor 9.

Therefore, when the power supply current calculation value It is obtained as described above, the difference between the power supply current calculation value It and the detection value of the power supply current sensor 9 is calculated, and the difference is calculated by the power supply current sensor 9. The correction value of the detection value is set (step S6). After that, the detected value of the power supply current sensor 9 is corrected by adding the correction value to the detected value of the power supply current sensor 9, and the corrected value is transferred from the power supply 3 to the motor drive circuit 1. The supplied power supply current value (effective value thereof) is compared with the above threshold value in order to determine whether or not an overcurrent is supplied to the motor drive circuit 1. As a result, the overcurrent supply state to the motor drive circuit 1 can be satisfactorily detected, and the occurrence of problems such as heat generation due to the overcurrent supply to the motor drive circuit 1 can be avoided.

Here, while the ignition key switch of the vehicle is turned on, the power supply current calculation value It is repeatedly calculated, and the calculated power supply current calculation value It is used as a power supply current value to the motor drive circuit 1. A configuration used to determine whether or not current is supplied is conceivable. However, in this configuration, if the power supply current value sharply increases and exceeds the threshold value between the first and second calculations of the power supply current calculation value It, the overcurrent supply The state cannot be immediately detected, and the overcurrent continues to be supplied to the motor drive circuit 1 during that time.

On the other hand, the process of correcting the detection value of the power supply current sensor 9 is a simple calculation process of adding the correction value to the detection value of the power supply current sensor 9, and therefore can be executed in a short cycle. Therefore, according to the configuration of this embodiment, when an overcurrent supply state is encountered, the overcurrent supply state can be quickly detected, and the fail-safe processing for the overcurrent supply can be promptly executed. .
Furthermore, if the failsafe process is executed immediately when the detected value of the power supply current sensor 9 exceeds the threshold value, the failsafe process for overcurrent supply can be executed more quickly. .

Although one embodiment of the present invention has been described above, the present invention can be implemented in other forms.
For example, in the above-described embodiment, the currents flowing in the U-phase winding and the V-phase winding of the electric motor M are detected by the current sensors, respectively, and the current flowing in the W-phase winding is calculated. The current flowing in the V-phase winding may be obtained by calculating the current flowing in the V-phase winding by detecting the current flowing in the W-phase winding and the current flowing in the W-phase winding. Alternatively, the current flowing through the U-phase winding may be calculated by detecting the current with a current sensor. Further, the U-phase winding, the V-phase winding, and the W of the electric motor M
The currents flowing through the phase windings may be detected by current sensors.

Further, in the above-mentioned embodiment, the current sensor using the shunt resistor is adopted as the power supply current sensor 9, but the power supply current sensor 9 may be another current sensor such as a current sensing MOS. May be adopted. In addition, various design changes can be made within the scope of the matters described in the claims.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing a configuration of a motor drive device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a flow of processing for setting a correction value for correcting the detection value of the power supply current sensor.

[Explanation of symbols]

1 Motor drive circuit 2 microcomputer 3 power supplies 4 earth 5 Rotation angle sensor 6U U-phase current sensor 6V V phase current sensor 7 vehicle speed sensor 8 Torque sensor 9 Power supply current sensor 10 relays

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B62D 119: 00 H02P 6/02 371D F term (reference) 3D032 CC35 DA15 DA23 DA64 DA99 DB11 DC33 DD02 DE09 EB30 EC23 GG01 3D033 CA13 CA16 CA20 CA31 5G044 AA01 AC01 CA01 5H560 AA08 BB04 DC03 DC12 JJ02 SS02

Claims (2)

[Claims] 1. A motor drive device for driving an electric motor, comprising: a drive circuit connected to a power source for supplying a drive current to the electric motor; and a drive circuit supplied from the power source to the drive circuit. And a drive current for detecting the drive current supplied from the drive circuit to the electric motor with higher detection accuracy than the current detection accuracy of the power supply current detection means. A motor drive device comprising: a detection unit; and a correction unit that corrects the detection value of the power supply current detection unit based on the detection value of the drive current detection unit. 2. A circuit cutting means provided on a power feeding path from the power source to the driving circuit for cutting the power feeding circuit, and a value after correction by the correction means exceeds a predetermined value. The motor drive device according to claim 1, further comprising: fail-safe means for activating the circuit disconnecting means to disconnect the power supply circuit.