JP2003244988A - Motor drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the generation of a regenerative current by eliminating deviation between driving timings of a pair of FETs of a bridge circuit 22, in an electric power steering device which includes an assist motor 8 and the bridge circuit 22 formed by bridge-connecting the FETs 22a to 22d for driving the assist motor 8 by switching operations. <P>SOLUTION: A driving timing determination means for determining timing for driving the motor 8 based on a triangle wave with a prescribed frequency and a plurality of thresholds are provided at a main microcomputer 24M. The driving timings of the pair of FETs (FETs 22a, 22d for clockwise driving or FETs 22b, 22c for counter-clockwise driving) on upper and lower stages of the bridge circuit 22 are determined based on the same threshold as the thresholds. The FET 22c which forms one pair is on-controlled during driving the FETs 22a, 22d forming the other pair and at the off-timing of duty control. <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 driving device for driving a motor by current feedback control,
In particular, the present invention relates to an electric motor drive device of an electric power steering device having an assist motor that generates a steering assist force for a steering system of a vehicle.

[0002]

2. Description of the Related Art Generally, an electric power steering apparatus is constructed as shown in FIG. In FIG. 3, the steering wheel 1 is a first steering shaft 2a.
And is connected to the second steering shaft 2b via the universal joint 3.

The second steering shaft 2b is
It is connected to a tie rod 6 of a steering wheel via a pinion 4 and a rack 5. Second steering shaft 2
A torque sensor 7 for detecting the steering torque of the steering wheel 1 is provided at b, and an assist motor 8 for assisting the steering force of the steering wheel 1 is coupled to the second steering shaft 2b via a reduction gear 9.
Reference numeral 10 denotes a vehicle state detection device that detects a running state of the vehicle such as engine speed, vehicle speed, and steering wheel load by a sensor.

Reference numeral 11 denotes a motor drive current (target current command value) from the detection output of the vehicle state detection device 10, the detection torque of the torque sensor 7, the detection current obtained from a current detector (not shown), a voltage detector, detection voltage, etc. ) Is obtained and the current supplied to the assist motor 8 is controlled based on the target current command value, and is composed of, for example, a microcomputer.

Reference numeral 12 is a relay which is turned on by turning on a key switch of an ignition key and is turned off, for example, in case of a malfunction. The controller 11 and the assist motor 8 are driven by the power source of the battery 13 supplied via the relay 12.

In the apparatus constructed as described above, the motor drive control section of the controller 11 drives the assist motor 8 to add the assist torque to the steering torque to improve the operability of the steering wheel 1.

An example of an electric motor drive device for an electric power steering device constructed as described above is, for example, Japanese Patent Laid-Open No.
There is a device disclosed in Japanese Patent Application No. 01-58578.
This device forms an H-bridge circuit with four transistors and controls the drive of the electric motor by PWM (pulse width modulation) control. As described in the specification of the above publication, PWM control in the H-bridge circuit includes a method of PWM driving only one of the upper and lower stages and a method of PWM driving both the upper and lower stages.

Among them, the method of PWM driving both upper and lower stages has an advantage that the braking action is less likely to occur in the electric motor as compared with the method of PWM driving only one of the upper and lower stages.

In this upper and lower PWM drive control, a threshold value is set for a triangular wave (carrier wave of a predetermined frequency), and the drive timing of the transistor is determined by, for example, turning on the duty during a period when the triangular wave is at or above the threshold value.

This threshold is provided with two different values so that the upper and lower stages on the same side of the H-bridge circuit do not turn on at the same time. Based on one threshold value, the left and right upper stage transistors are driven and controlled, and the other threshold value is set. Based on this, the lower transistors on the left and right sides are drive-controlled.

The difference in drive timing caused by the different thresholds is called dead time, which secures a time during which both upper and lower stages are not turned on.

[0012]

However, the dead time causes a deviation in the upper and lower driving timings of the right (left) driving transistor, resulting in a regenerative current in the H bridge circuit.

Therefore, in the drive circuit of the electric motor in which the current detection resistor is provided on the upstream side or the downstream side of the H bridge circuit and the current feedback control is performed based on the current value detected by the current detection resistor, An error is generated between the value of the current value detected by the detection resistor and the value of the current flowing through the electric motor by the amount of the regenerative current.

Therefore, there is a problem in that the desired current feedback control is not performed and the steering feeling may be deteriorated.

The present invention has been made in view of the above points, and an object thereof is to shift a drive timing of a semiconductor element (upper-stage element for left driving or upper-stage element for right driving) forming a pair of bridge circuits. It is an object of the present invention to provide a motor drive device capable of performing appropriate current feedback control by eliminating the occurrence of regenerative current to prevent generation of regenerative current, thereby matching the current value flowing in the motor with the detected current value.

[0016]

An electric motor drive apparatus of the present invention for solving the above problems is an electric motor, a bridge circuit for driving the electric motor by a switching operation of a plurality of bridge-connected semiconductor elements, and the bridge. Of the current detection means provided on the upstream side or the downstream side of the circuit, the current command value calculation means for calculating the current command value given to the electric motor, the current command value, and the current value detected by the current detection means. In a motor drive device including a current feedback unit that corrects the current command value based on a deviation, the current command value calculation unit is a timing for driving the motor based on a carrier signal of a predetermined frequency and a plurality of threshold values. A driving timing determining means for determining, and the upper and lower semiconductor elements forming a pair of the bridge circuit are both the threshold value and Is characterized in that driving timing is determined based on one threshold value.

Further, the semiconductor element of the bridge circuit is constituted by an antiparallel connection body of a transistor and a diode or a field effect transistor, and the drive timing determining means drives the semiconductor element forming one pair of the bridge circuit. It is characterized in that the semiconductor element forming the other pair is ON-controlled at time and at the OFF-timing of the duty control.

Further, the electric motor is characterized by being composed of an assist motor for generating an assist torque for assisting the steering torque.

[0019]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment in which the present invention is applied to the electric power steering apparatus of FIG. 1, the same parts as those in FIG. 3 are indicated by the same reference numerals.

In FIG. 1, the positive electrode side of the battery 13 is connected to the F circuit via the relay circuit 12a and the current detecting resistor 21.
It is connected to a bridge circuit 22 formed by bridge-connecting ETs (field effect transistors) 22a to 22d.

A common connection point P of the FETs 22a and 22c
_The assist motor 8 is connected between ₁ and the common connection point P ₂ of the FETs 22b and 22d. FET 22c
The common connection point of 22 and 22d is grounded (connected to the negative electrode side of the battery 13).

Reference numeral 24 _M denotes a motor drive current (target current command value) from the voltage detected by the current flowing through the current detecting resistor 21 through the operational amplifier 25, the torque detection signal of the torque sensor 7, and the like. It is a main microcomputer that calculates and controls the current supplied to the assist motor 8 based on the target current command value.

This main microcomputer 24
_M is a current feedback control function for performing current value feedback control of the drive of the assist motor 8 based on the target current command value and the current value detected by the current detection resistor 21, and a carrier signal of a predetermined frequency (for example, triangular wave). PWM assist motor 8 based on multiple thresholds
It has a drive timing determining function for determining the drive timing.

Reference numeral 24 _S is a sub-microcomputer having a function of judging an abnormality of the apparatus based on the running state of the vehicle detected by the vehicle state detecting apparatus 10 of FIG. 3, for example.

26 is a main microcomputer 24 _M
And on the sub-microcomputer 24 _S to the control signal introduced via the AND gate 27a, a relay to turn off the contact point and the contact point or on, the coil as a non-energized by energizing the coil of the relay circuit 12a It is a drive circuit.

A control signal for an enable signal is input to the AND gate 27b from the main microcomputer 24 _M and the sub microcomputer 24 _S , and the gate output (enable signal) of the AND gate 27b is supplied to each of the AND gates 27c and 27d. It is input to one of the input terminals.

The target current command signal from the main microcomputer 24 _M is supplied to the other input terminal of each of the AND gates 27c and 27d, and each output terminal is connected to the predrivers 28a and 28b.

28a, 28b and 28c, 28d
Is the main microcomputer 24 _MGoal calculated by
Pulse with duty ratio determined based on current command value
The width modulation (PWM) signal is fed to the FE of the bridge circuit 22.
Supply to each gate of T22a, 22b, 22c, 22d
Is a pre-driver that controls the FET to be turned on and off.

Signals are exchanged between the main microcomputer 24 _M , the sub microcomputer 24 _S and its peripheral circuits via an interface (not shown).

In the apparatus constructed as described above, during the normal operation, the main microcomputer 24 _M and the sub microcomputer 24 _S to the AND gate 27.
For example, a high level signal is supplied to a, the coil of the relay circuit 12a is excited by the relay drive signal output from the relay drive circuit 26, the contact is turned on, and the battery 13 supplies power to the bridge circuit 22. Is being supplied.

A high-level signal is supplied from the main microcomputer 24 _M and the sub-microcomputer 24 _S to the AND gate 27b, and the AND gates 27c and 27d are output by the output signal (high-level enable signal) of the AND gate 27b. A high level signal is input to one of the input gates.

The bridge circuit 22 includes, for example, the upper and lower stage simultaneous P
In the case of the WM drive system, the FETs 22a and 22d forming one pair are subjected to pulse width modulation control by the pre-drivers 28a and 28d in the case of right rotation, and the FETs 22b and 22c forming the other pair are in the pre-driver 28b in case of left rotation. , 2
The pulse width modulation is controlled by 8c.

Therefore, from the battery 13 to the relay circuit 12
bridge circuit 22 via a and the current detection resistor 21.
The current supplied to the FET flows in a path of FET 22a (or 22b) → assist motor 8 → FET 22d (or 22c) → ground, and the assist motor 8 rotates to the right (or to the left). As a result, the steering wheel 1 rotates in the direction in which the steering operation is performed, and assists the steering force.

In this embodiment, as shown in FIG. 2, the drive timing of each FET is determined by comparing a triangular wave signal of a predetermined frequency with a plurality of threshold values, for example, X _H and X _L.

That is, for example, when the assist motor 8 is driven to rotate to the right, one pair of F is formed during the period when the triangular wave level exceeds the threshold value X _H (for example, the period from time t _{2 to} t ₄ ).
The ETs 22a and 22d are turned on at the same timing as shown by the solid line.

The lower FET22c of this time FET forming the other pair, the triangular wave level controls (period for example, time t ₁ ~t ₅₎ Medium-off period exceeding the threshold value X _L, upper FET22b Constantly off control I'll do it.

In this way, since the pair of FETs 22a and 22d are on-controlled at the same timing by the same threshold value X _H , the bridge circuit 22 does not generate a regenerative current due to a drive timing shift.

As a result, the value of the current flowing through the assist motor 8 matches the value of the current detected by the current detecting resistor 21, and appropriate current feedback control can be performed.

The FETs 22a and 22d forming one pair
Is off-controlled at the same timing in a period in which the triangular wave level is equal to or lower than the threshold value X _H (for example, in the period from time t _{4 to} t ₈ ). There has been a medium on control threshold X _L or less and consisting period (e.g. a period of time t ₅ ~t _7).

In this way, one pair of FETs (22
a, 22d) is being driven and the other pair of FETs (22c) are on-controlled at the duty control OFF timing, the return current flowing by the counter electromotive force when the FETs 22a, 22d are OFF is: It flows through the FET 22c without flowing through the diode of the FET, and the amount of heat generation is suppressed. Furthermore, no regenerative current is generated.

Dead time (for example, between times t ₁ and t ₂ ,
Times t ₄ and t ₅ and times t ₇ and t ₈ ) are easily created by different thresholds X _H and X _L.

The control timing of each FET when the assist motor 8 is driven to rotate counterclockwise is shown by the broken line in FIG.

That is, during the period when the triangular wave level is below the threshold value X _L (for example, the period from time t _{5 to} t ₇ ), the FET 22
b and 22c are turned on at the same timing, and at this time, F
ET22d is off-controlled in a period (e.g. a period of time t ₄ ~t ₈₎ triangular wave level is equal to or less than the threshold X _H,
The FET 22a is always off-controlled.

[0044] Further FET22b, Among OFF period of 22c (e.g. a period of time t ₁ ~t _5), triangular wave level threshold X
Only FET22d are on-controlled in _H or become period (e.g. a period of time t ₂ ~t _4).

The action and effect at the time of such counterclockwise rotation are similar to the above.

In order to adopt a system in which the upper (or lower) FET is PWM-driven and the lower (or upper) FET is always on-driven, the lower FET 22d is always on-controlled (to the FET 22d) during right rotation. Control signal is fixed to a high level), and in the case of left rotation, the lower FET 22c is always on-controlled (the control signal to the FET 22c is fixed to a high level).

Further, in the method in which both the upper and lower FETs are PWM-driven and in the method in which one of the upper and lower FETs is PWM and the other is always ON, for example, it is determined whether the current direction of the assist motor and the rotation direction match. It may be configured to switch as a condition.

As described above, since the upper and lower FETs forming a pair of the bridge circuit are both driven with the same threshold value, the dead time can be determined at the same time on the register which gives the duty, which makes it complicated. Since it is not necessary to create dead time with various software, the load on software can be reduced.

That is, the U phase of the inverter control circuit is FET 22a, the U'phase is FET 22c, and the V phase is FET2.
2d, V ′ phase is connected to FET 22b (U-phase is FET 22a, U ′ phase is FET 22c, V phase is FET
By connecting the 22b and V'phases to the FET 22d), the PWM output can be easily performed by setting the FET 22a / 22c register and the FET 22b / 22d register to the same value during the upper and lower stage simultaneous PWM drive.

Incidentally, the main microcomputer 24
_{The M} and the sub-microcomputer 24 _S may be combined to form a single unit.

The semiconductor element forming the bridge circuit is not limited to the FET, but may be another semiconductor element, for example, an antiparallel connection body of a transistor and a diode.

Furthermore, the present invention is not limited to being applied to the assist motor of the electric power steering device, but may be applied to other electric motor drive devices, and in that case, the same operation and effect as described above can be obtained.

[0053]

As described above, according to the present invention as set forth in claim 1, semiconductor elements forming a pair of bridge circuits (upper and lower semiconductor elements for left rotation driving, or right rotation driving). Since the upper and lower semiconductor devices are controlled at the same drive timing, a regenerative current due to the drive timing deviation is not generated. Therefore, the value of the current flowing through the electric motor matches the value of the current detected by the current detecting means, and appropriate current feedback control can be performed.

Further, since the upper and lower semiconductor elements forming a pair of the bridge circuit are both driven at the same threshold value, the dead time can be determined at the same time on the register giving the duty, which allows complicated software. This eliminates the need to create dead time and reduces the load on software. (2) According to the present invention described in claim 2, since the return current at the off timing of the duty control does not pass through the diode but passes through the transistor side, it is possible to suppress the amount of heat generation. (3) According to the third aspect of the present invention, in the assist motor driving device of the electric power steering device, the regenerative current due to the drive timing deviation is not generated. Therefore, the value of the current flowing through the assist motor matches the value of the current detected by the current detecting means, and appropriate current feedback control can be performed. Therefore, the steering feeling is improved by the good current feedback control.

[Brief description of drawings]

FIG. 1 is a motor control block diagram showing an embodiment of the present invention.

FIG. 2 is an FE of a bridge circuit according to an embodiment of the present invention.
The time chart which shows the state of control of T.

FIG. 3 is a configuration diagram showing an example of an electric power steering device.

[Explanation of symbols]

1 ... steering wheel 7 ... torque sensor 8 ... assist motor 12a ... relay circuit 13 ... Battery 21 ... current detection resistor 22 ... bridge circuit 22a to 22d ... FET 24 _M ... main microcomputer 24 _S ... sub microcomputer 25 ... operational amplifier 26 ... relay drive circuits 27a to 27d ... AND gates 28a to 28d ... pre-driver

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B62D 137: 00 B62D 137: 00 F term (reference) 3D032 CC08 CC22 CC24 DA15 DA21 DA64 DA65 DB11 DC09 DC31 DD02 DD17 DE14 EB11 EB30 EC23 EC40 GG01 3D033 CA12 CA13 CA14 CA15 CA16 CA17 CA18 CA19 CA20 CA21 5H571 AA03 BB10 CC04 FF01 FF09 GG04 HA09 HD02 JJ03 LL22 LL46 MM02 MM16

Claims (3)

[Claims] 1. An electric motor, a bridge circuit for driving the electric motor by a switching operation of a plurality of bridge-connected semiconductor elements, a current detection means provided upstream or downstream of the bridge circuit, and the electric motor. A motor including a current command value calculating means for calculating a current command value, and a current feedback means for correcting the current command value based on a deviation between the current command value and the current value detected by the current detecting means. In the drive device, the current command value calculation means has drive timing determination means for determining timing for driving the electric motor based on a carrier wave signal of a predetermined frequency and a plurality of threshold values, and forms a pair of the bridge circuit. In the lower semiconductor elements, the drive timing is determined based on the same threshold value as the threshold value. Machine drive. 2. A semiconductor element of the bridge circuit is constituted by an antiparallel connection body of a transistor and a diode or a field effect transistor, and the drive timing determining means is a semiconductor element forming one pair of the bridge circuit. 2. The electric motor drive device according to claim 1, wherein the semiconductor elements forming the other pair are turned on at the time of driving and when the duty control is turned off. 3. The electric motor drive device according to claim 1, wherein the electric motor comprises an assist motor that generates an assist torque that assists the steering torque.