JP2001136788A - Motor drive apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a switching element in a drive part from being damaged due to excessive current, using a low-cost constitution. SOLUTION: A shunt resistance SH, which detects a current flowing in an inverter IV, is installed. A second comparator CP2, in which a detection current by the shunt resistance SH is compared with a cutoff value, is installed. When the detection current reaches a second threshold as cutoff value, a signal at high level as an abnormal signal is output from the second comparator CP2. A second D-FFD2 and AND gates AG1 to AG6 as a cutoff part BR, which cuts off a control signal to all switching elements S1 to S6 in the inverter IV and which turns off the switching elements S1 to S6 by the control of a control part CO on the basis of the abnormal signal are installed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor drive for driving a motor by switching a plurality of switching elements constituting a drive unit in accordance with a control signal of a control unit and controlling opening and closing of a current path to a winding of the motor. Related to the device.

[0002]

2. Description of the Related Art Conventionally, a motor driving device for driving a three-phase DC brushless motor is configured as shown in FIG. 3, for example, and has a control unit (not shown) composed of a microcomputer.
The six switching elements that make up the three-phase bridge inverter IV are switched by the control signal output from the controller, and the conduction path from the DC power supply E to each winding of the three-phase DC brushless motor M is opened and closed by a plurality of switching elements. Then, the motor M is driven.

In this three-phase bridge inverter IV, as shown in FIG. 3, a first arm A1 is formed by a series circuit of two switching elements S1 and S2 composed of, for example, a field effect transistor. Each of the second and third switching elements S3 and S4 and the two switching elements S5 and S6 are connected in series.
Third arms A2 and A3 are formed, and flywheel diodes D1 to D6 are provided in each of the switching elements S1 to S6.
Are connected in opposite polarities.

The respective arms A1 to A1 of the inverter IV
Connection point P of both switching elements in each of A3
1, P2, and P3 are connected to the star-connected three-phase windings M1, M2, and M3 of the stator of the motor M, respectively.
One end of each of the switching elements S1, S3, S5 of the upper switching element group HT above the connection points P1, P2, P3 is connected to the positive terminal of the DC power supply E, and the inverter IV
The other ends of the switching elements S2, S4, S6 of the lower switching element group LT below the connection points P1, P2, P3 are connected to the negative terminal of the DC power supply E.

[0005] In such a configuration, as shown in FIG. 4, each of the switching elements S 1, S 3, S 5 of the upper switching element group HT is shifted by 120 ° by a control signal shifted by 120 ° from the control unit. Similarly, the switching elements S2, S4, S6 of the lower switching element group LT are turned on by 120 ° by a control signal having a phase shifted by 120 ° from the control unit.

At this time, in the control unit, the switching elements of the lower switching element group LT different from the ON switching arm of the switching elements S1, S3, S5 of the upper switching element group HT are turned ON. A combination of a switching element of the upper switching element group HT and a switching element of the lower switching element group LT to be turned on is detected by a rotation detector (not shown) composed of a Hall element. The switching is performed in relation to the position of the rotor of the motor M to be performed. Thus, the direction of current flow to each of the windings M1 to M3 is switched, and the magnetic poles of the stator rotate in one direction, so that the rotational force of the rotor is obtained.

Normally, a control signal from the control unit to the lower switching element group LT of the inverter IV is subjected to pulse width modulation (PWM).
, The current control of the motor M is performed.

Although not shown in FIG. 3, in the motor driving device having the above-described configuration, an excessive current is prevented from flowing through each of the switching elements S1 to S6 of the inverter IV so that each of the switching elements S1 to S6 is To protect
A current limiting unit is provided for limiting the current flowing through each of the switching elements S1 to S6 to a value equal to or less than a threshold.

This current limiting section is provided with a current detector in a current path between the DC power supply E and the inverter IV, and the current detected by the current detector is used to switch the switching elements S1 to S1.
When the threshold value for preventing damage to the inverter 6 is reached, the control signal to the lower switching element group LT of the inverter IV is interrupted at a control cycle based on, for example, the clock frequency of the control unit, thereby flowing through the inverter IV. Limit the current value.

However, in such a configuration, when any one of the switching elements of the inverter IV or any one of the windings of the motor M is short-circuited, for example, when the switching elements S1 and S2 in FIG.
Both ends of the DC power supply E are short-circuited by the switching elements S1 and S2, so that a so-called through current flows.

In the above-described current limiting section, the inverter IV
Switching element S of lower switching element group LT
2, since there is no function to stop the current flowing through the inverter IV only by interrupting the control signals to S4 and S6, the short-circuited switching elements such as the switching elements S1 and S2 and the windings M1 to M3 of the motor M are damaged. There is a risk of causing burnout. Therefore, in order to prevent such a problem, as shown in FIG.
A current fuse F is provided in an energizing path between V and V.

[0012]

However, in the above-described current fuse F, when the windings M1 to M3 of the motor M are rarely short-circuited, that is, short-circuited with a certain number of turns remaining,
The current flowing through the current fuse F does not reach the operating current,
The current fuse F may not operate, and the inverter I
There is a problem that the switching elements S1 to S6 of V cannot be sufficiently protected and lack reliability.

Further, since the current fuse F is expensive,
There is also a problem that the cost of the entire apparatus is increased.

An object of the present invention is to provide an inexpensive configuration that can prevent damage to a switching element of a drive unit and burning of a motor winding due to an excessive current.

[0015]

In order to solve the above-mentioned problems, the present invention provides a current detecting section for detecting a current flowing through the driving section, and a current detecting section for detecting a current value detected by the current detecting section below a predetermined limit value. A current limiting unit that interrupts a control signal from the control unit to the switching element at a constant cycle to limit the current, and compares the current detected by the current detecting unit with a cutoff value larger than the limit value to perform the detection. An abnormal signal generating unit that generates an abnormal signal when the current becomes equal to or greater than the cutoff value; and a control signal to the drive unit under control of the control unit based on the abnormal signal to turn off the switching element. And a cut-off portion.

According to such a configuration, when the current value detected by the current detecting section reaches the limit value, the current limiting section interrupts the control signal to the switching element at a constant cycle, and the current value is limited to the limit value or less. When the current detected by the current detector rises to a cutoff value higher than the limit value due to a short circuit of the switching element or the motor winding, an abnormal signal is output from the abnormal signal generator, and the control of the control unit based on the abnormal signal is performed. As a result, the cutoff unit operates to cut off the control signal to the drive unit.

Therefore, even if an excessive current suddenly flows due to, for example, a short circuit in the winding of the motor, an abnormal signal is output from the interrupting section, and the control signal to the driving section is interrupted. It is turned off, and the switching element of the drive unit is protected.

Furthermore, the switching element can be protected with a low-cost configuration by cutting off the current flowing through the driving section in a circuit without using expensive components such as a conventional current fuse.

At this time, applicable motors include DC brushless motors, induction motors, and linear motors.

In the present invention, the control unit determines whether or not the abnormal signal continues a predetermined number of times within a predetermined time period. The switching device is controlled to be turned off.

According to such a configuration, it is possible to determine whether the abnormal signal from the abnormal signal generating unit is an excessive current due to an abnormality such as a short-circuit of the motor, and to determine whether the excessive signal is an excessive current due to an abnormality such as a short-circuit of the winding. However, if the current is noise-like, the current of the drive unit is not interrupted, and the current of the drive unit is ensured only when it is determined that an excessive current due to abnormality such as winding short-circuit flows through the drive unit. Can be shut off.

Here, when the control section is constituted by a microcomputer, for example, the time for judging whether or not the current is excessive due to an abnormality is preferably a time corresponding to several control cycles. A timer or an external timer means may be used to measure the time.

In the present invention, the motor may include a plurality of the windings, and the driving unit may include an arm formed by connecting the two switching elements in series with the same number as the number of the windings. A first switching element group on one side of the connection point of the inverter and a second switching element on the other side, each of the windings being connected to a connection point between the two switching elements in each arm; Control the group, and by turning on one of the switching elements of the one-side switching element group and turning on the switching elements of the other-side switching element group on an arm different from the arm of the switching element, The switching element of the one-side switching element group to be turned on while the current flows and the other-side switch Switching the combination of the switching element group and the switching element in relation to the position of the rotor of the motor detected by the detection means, thereby switching the direction of current flow to each winding to rotate the rotor. Force, wherein the cut-off unit turns off at least one of the one-side switching element group or the other-side switching element group of the driving unit to cut off the current path. And

According to such a configuration, the current flowing to the drive section can be cut off by the cutoff section, and especially when all the switching elements of the drive section are turned off, the cutoff can be more reliably performed.

Further, in the present invention, the current limiting section cuts off a control signal from the control section to one of the one of the one-side switching element group and the other-side switching element group. I have.

According to such a configuration, during normal operation, the current flowing through each switching element of the drive section can be suppressed to a predetermined limit value or less, and each switching element of the drive section can be protected.

In addition, by interrupting the control signal to the switching element at a constant cycle in this manner, the circulating current can be continuously supplied to the motor even while the control signal to the switching element is interrupted. When the control signal that has been input to the switching element, the current of the motor can be recovered immediately.

[0028]

1 and 2 show an embodiment in which the present invention is applied to a power steering of a vehicle.
This will be described with reference to FIG. However, FIG. 1 is a connection diagram of the motor drive device of the present invention, and FIG. 2 is a waveform diagram for explaining the operation.

A motor drive device applied to a power steering for a vehicle such as an automobile is configured as shown in FIG. 1, for example. A detector SD including a rotary encoder or the like is provided on a steering (not shown). In response to the operation of the steering, a two-phase pulse signal having a 90 ° phase shift is output from the detector SD as a detection signal by a signal conversion unit in a subsequent stage. The signal is output to the WS, and the detection signal is shaped by the signal conversion unit WS.

When the waveform-shaped detection signal is input to a control unit CO comprising a microcomputer (hereinafter simply referred to as a microcomputer), the control unit CO controls the steering angular velocity, that is, the speed at which the steering is operated, based on the detection signal. Is detected by the control unit CO, and the assist amount of the steering operation torque is determined according to the high / low of the steering angular velocity, and the three-phase DC brushless motor M is driven to generate the determined assist torque.

The drive unit for driving the three-phase DC brushless motor M is composed of, for example, a three-phase bridge inverter IV having the same configuration as that shown in FIG. 3, and a control signal having a phase shift of 120 ° from the control unit CO. As a result, each of the switching elements S1, S3,
S5 (see FIG. 3) is turned on with a shift of 120 °, and in the same manner, the control signals from the control unit CO are shifted by 120 ° with each other, so that each of the switching elements S2, S4, S6 of the lower switching element group LT is switched. (See FIG. 3) are turned on by 120 °.

Here, the control unit CO controls the switching elements S of the arms A1 to A3 of the upper switching element group HT.
1, the lower switching element group LT of an arm different from the ON of the switching element arm among S3 and S5
A control signal is output so that the switching element of the upper switching element group HT and the switching element of the lower switching element group LT to be turned on are combined with the switching element of the lower switching element group LT. (Not shown) is switched in relation to the position of the rotor of the motor M detected. Note that a PWM control signal is output from the control unit CO to the lower switching element group LT of the inverter IV, and the duty cycle in the PWM is controlled to control the current of the motor M.

Further, as shown in FIG.
In order to prevent an overcurrent from flowing through each of the switching elements S1 to S6 to protect each of the switching elements S1 to S6, a shunt resistor SH as a current detection unit, an amplifier A, and a first comparator CP1 , A first D-flip-flop (hereinafter, flip-flop is referred to as FF) D1,
The current flowing through each of the switching elements S1 to S6 is formed by three 3-input AND gates AG1 to AG3, and the current flowing through each of the switching elements S1 to S6 is a first threshold value TH1 which is a predetermined limit value (see FIG. 2)
A current limiting unit CR for limiting the following is provided.

As shown in FIG. 1, a shunt resistor SH is provided on the negative current path from the DC power supply E to the inverter IV, and a current flowing through the inverter IV is detected by the shunt resistor SH. SH
Is amplified by the amplifier A, the output of the amplifier A is input to the non-inverting input terminal of the first comparator CP1, and the voltage between the positive power supply (not shown) and the ground is
The potential of the connection point of the resistors R2 and R3 among the voltage dividing resistors R1, R2 and R3 is set to a first comparator CP1 as a first reference value.
, And the first comparator CP1 compares the potentials of both input terminals.

As shown in FIG. 1, the first D-FF
An input terminal D of D1 is connected to a positive power supply (not shown), and a clock terminal CK has a frequency of, for example, 16 kHz from the control unit CO.
, And an output signal of the first comparator CP1 is input to a reset terminal R connected to a positive power supply (not shown) via a pull-up resistor R4.

Further, the first of the AND gates AG1 to AG3
Is connected to the output terminal of a control signal from the control unit CO to each of the switching elements S2, S4, S6 of the lower switching element group LT, and the second input terminal is connected to a second D-FF to be described later. The third input terminal is connected to the Q bar output terminal, the third input terminal is connected to the Q output terminal of the first D-FFD1, and each AND gate AG1 to AG3 is connected to each AND gate only when the AND condition of its input is satisfied. AG1 to AG
3, a control signal is input to each of the switching elements S2, S4, S6 of the lower switching element group LT, and AND
When the condition is not satisfied, the control unit CO sends the switching elements S2, S4, S4 of the lower switching element group LT.
The control signal to 6 is cut off by each of the AND gates AG1 to AG3.

Therefore, as shown in FIG. 2, when the current flowing through the shunt resistor SH increases and reaches the first threshold value TH1, the output of the amplifier A on the non-inverting input terminal side of the first comparator CP1. If the potential exceeds the first reference value on the inverting input terminal side, the output of the first comparator CP1 becomes low level (hereinafter, referred to as
L) to a high level (hereinafter, referred to as H). As a result, as described above, each of the AND gates AG1 to AG1
The AND condition of each input of AG3 is not satisfied,
The control signal to each of the switching elements S2, S4, S6 of the lower switching element group LT via each of the AND gates AG1 to AG3 is cut off, and the current flowing from the inverter IV through the shunt resistor SH is cut off.

At this time, in the inverter IV, a circulating current flows through the windings of the motor M via the switching elements in the ON state of the upper switching element group HT and the flywheel diode, and the first current until the circulating current disappears. At the timing of outputting a clock pulse from the control unit CO to the clock terminal CK of the D-FFD1, each AND gate A
The AND condition of both inputs of G1 to AG3 is satisfied,
A control signal is output to each of the switching elements S2, S4, S6 of the lower switching element group LT via each of the AND gates AG1 to AG3, and a current starts to flow again to the shunt resistor SH. The flowing current recovers.

By repeatedly supplying and interrupting the control signal to each of the switching elements S2, S4, S6 of the lower switching element group LT, a current having a waveform as shown in FIG. The current flowing through the IV is limited to the first threshold value TH1 or less.

The clock terminal C of the first D-FFD1
The clock pulse from the control unit CO to K is not limited to 16 kHz as described above, and may be any frequency that can recover the current flowing through each of the windings M1 to M3 of the motor M until the circulating current disappears. .

As described above, the control signal to each of the switching elements S2, S4, S6 of the lower switching element group LT is cut off by the action of the current limiting section CR, and the current flowing through the shunt resistor SH is cut off. Inverter IV
Current value flowing through each of the switching elements S1 to S6 is prevented from becoming an overcurrent equal to or more than the first threshold value TH1 which may cause damage to the switching elements S1 to S6, and The demagnetization of the motor M is prevented.

Further, while each of the switching elements S2, S4, S6 of the lower switching element group LT is off,
By the time the circulating current is passed through the motor M and the circulating current disappears, the switching elements S2, S4, S4 of the lower switching element group LT are operated by the action of the current limiting section CR.
6 is supplied with the control signal again, and the windings M1 to M1 of the motor M are supplied again.
The current flowing through M3 is restored.

Further, as shown in FIG.
Switching elements S1 to S6 and the winding M1 of the motor M
In order to prevent an excessive current such as a through current when a short circuit occurs in M3, a second comparator CP2 as an abnormal signal generation unit is provided, and a second D-FFD2 is provided.
And three two-input AND gates AG4 to AG6 that constitute a blocking unit BR together with the second D-FFD2 and the above-described AND gates AG1 to AG3. The switching unit S1 is provided by the blocking unit BR. The second threshold value TH2 (see FIG. 2) in which the current flowing through .about.S6 is almost twice as large as the above-mentioned first threshold value TH1 which is the cutoff value.
, The control signal to each of the switching elements S1 to S6 of the inverter IV is cut off.

The non-inverting input terminal of the second comparator CP2 is connected to the output terminal of the amplifier A, and the potential at the connection point between the resistors R1 and R2 is used as a second reference value for the inverting input terminal of the second comparator CP2. The second comparator CP2 compares the potentials of the two input terminals. At this time, the current detected by the shunt resistor SH is equal to the second threshold T, which is approximately twice the first threshold.
The resistance values of the voltage dividing resistors R1 to R3 are set such that the output potential of the amplifier A when H2 is equal to the potential of the inverting input terminal of the second comparator CP2 at that time. I have.

Further, as shown in FIG. 1, the second D-FF
An input terminal D of D2 is connected to a positive power supply (not shown), and an output signal of the second comparator CP2 is supplied to a clock terminal CK connected to a positive power supply (not shown) via a pull-up resistor R5. A reset pulse from the control unit CO (for example, a control cycle of the control unit CO of 4 m
s) is input.

One input terminal of each of AND gates AG4 to AG6 is connected to an output terminal of a control signal from control unit CO to each of switching elements S1, S3, S5 of upper switching element group HT, and the other input terminal. Is the second D-
When the AND condition of the input of each of the AND gates AG4 to AG6 is not satisfied, the control unit CO sends the upper switching element group H to the Q bar output terminal of the FFD2.
The control signal to each of the switching elements S1, S3, S5 of T is cut off. Thus, the upper switching element group H
When the control signal to each of the switching elements S1, S3, S5 of T is cut off, the above-described AND gates AG1 to AG1 are output.
Since the AND condition of each input of AG3 is not satisfied,
Each switching element S of the lower switching element group LT
2, and the control signals to S4 and S6 are also cut off.

Therefore, as shown in FIG. 2, the current flowing through the shunt resistor SH is reduced to the first threshold value T due to, for example, a short circuit between the switching elements S1 to S6 or the windings M1 to M3.
When the voltage exceeds H1 and reaches the second threshold value TH2, the output potential of the amplifier A on the non-inverting input terminal side of the second comparator CP2 becomes equal to the second reference value on the inverting input terminal side. Of the comparator CP2 is inverted from L to H.

When the output H from the second comparator CP2 is input to the second D-FFD2, the second DF
The Q output of FD2 becomes H, and the Q bar output becomes L. When the output H of the second comparator CP2 is input to the second D-FFD2, the Q bar output of the second D-FFD2 becomes L,
The control unit CO outputs, for example, one reset pulse to the second D-FFD2 in a control cycle of 4 ms, and outputs the second D-F
Control is performed so that the Q bar output of the FD 2 is normally H. Further, the Q output of the second D-FFD2 is input to the control unit CO, and during the period of, for example, 500 ms counted by the built-in timer or the external timer means of the control unit CO, the second D-FFD2 is output. Q output goes from L to H 100
When the number of times changes, the control unit CO stops outputting the reset pulse, so that the Q-bar output of the second D-FFD2 becomes L.

Therefore, all AND gates AG1 to AG1
The AND condition of the input of AG6 is no longer satisfied, and all the switching elements S1 to S6 via AND gates AG1 to AG6 are not satisfied.
The control signal to S6 is cut off, and the current flowing from the DC power supply E via the inverter IV to the shunt resistor SH is cut off.

However, the control unit C is controlled within the above-mentioned 500 ms.
O from L of the Q output of the second D-FFD2 input to O
Is less than 100 times, the switching element S
It is determined that no short circuit has occurred between the windings M1 to S6 or the windings M1 to M3, and the control signal from the control unit CO to each of the switching elements S1 to S6 of the inverter IV is not interrupted.

Therefore, according to the above-described embodiment, for example, the inverter I is not connected due to the rare short of the winding of the motor M.
Even if an excessive current flows through V, an abnormal signal of H is output from the second comparator CP2 in response to the excessive current due to an abnormality such as a short circuit, so that each switching element S1 of the inverter IV
To S6 to shut off each switching element S1.
To S6 can be reliably turned off for protection.

When the current flowing through the inverter IV increases to the first threshold value TH1 during the normal operation, the current limiter CR controls the control signals to the switching elements S2, S4, S6 of the lower switching element group LT. Can be turned off to turn off these switching elements S2, S4, S6.
The switching elements S1 to S6 can be protected by preventing an overcurrent exceeding 1 from flowing, and at the same time, demagnetization of the motor M due to the overcurrent can be prevented.

Further, the switching elements S2 and S2 of the lower switching element group LT are operated by the action of the current limiting section CR.
4. Even while S6 is off, the windings M1 to M1 of the motor M
A circulating current flows through M3. By the time the circulating current disappears, the switching elements S2 and S2 are switched by the current limiting unit CR.
4, the control signal to S6 is released, so that the switching elements S2, S4,
S6 returns to the ON state again, and the current of the motor M can be recovered immediately.
An assist torque corresponding to the steering operation can be generated with good response.

In the above embodiment, 500 ms
Of the second D-FFD2 input to the control unit CO during the
It is determined whether or not an excessive current is flowing due to a short circuit of the switching element of the inverter IV based on whether the change from L to H from the output is 100 times or more. Is 500ms and 1
The number of times is not limited to 00, but may be set to a length and number of times in consideration of the duration of noise and the like.

Also, the abnormal signal from the second comparator CP2 serving as the abnormal signal generator described above is used to directly control the control unit C.
O to all switching elements S1 to S6 of inverter IV
The blocking unit BR may be configured so as to block the control signal to the controller.

Further, in the above-described embodiment, a case is described in which the control signals to all the switching elements S1 to S6 are cut off when the switching elements S1 to S6 and the motor winding are short-circuited. Upper switching element group HT or lower switching element group LT
The control signal to either one of the switching elements may be cut off, and in this case, the same effect as in the above-described embodiment can be obtained.

In the above embodiment, the case where the control signal to the switching elements S2, S4 and S6 of the lower switching element group LT is intermittently controlled by the current limiting section CR has been described. H
The control signals to the T switching elements S1, S3, S5 may be intermittent.

Further, in the above-described embodiment, the case where the current limiting section CR is provided is described, but such a current limiting section CR is not necessarily required.

In the above-described embodiment, the case where the three-phase DC brushless motor M is used has been described. However, the present invention can be similarly applied to an induction motor or a linear motor. Therefore, the same effect as the above-described embodiment can be expected.

In the above-described embodiment, the control unit CO and the current limiting unit CR may be implemented by a microcomputer.

Further, in the above-described embodiment, the case where the present invention is applied to a power steering for a vehicle such as an automobile is described. However, the scope of application of the present invention is not limited to such a power steering. The present invention can be applied to any other device that drives a motor.

The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the gist of the present invention.

[0063]

As described above, according to the first aspect of the present invention, when an excessive current flows through the drive unit due to a short circuit of the switching element or the motor winding of the drive unit, the current detection unit detects By comparing the detected current with the cutoff value, the abnormal signal generator can output an abnormal signal in response to an excessive current caused by an abnormality such as a short circuit. As a result, the switching element of the drive unit can be reliably turned off, and the switching element can be protected.

Furthermore, the switching element can be protected with a low-cost configuration by cutting off the current flowing through the driving section in a circuit without using expensive components such as a conventional current fuse.

According to the second aspect of the present invention, it is possible to determine whether or not the abnormal signal from the abnormal signal generating section is an excessive current due to an abnormality such as a short-circuit of a motor winding. When the current is not noise due to excessive current due to abnormalities, the current of the drive unit is not interrupted, and only when it is determined that excessive current due to abnormalities such as winding short-circuit flows through the drive unit. It is possible to reliably cut off the current of the section, and it is possible to improve the reliability of the cutoff operation.

According to the third aspect of the invention, it is possible to cut off the current flowing through the drive unit, and it is possible to cut off the current more reliably if all the switching elements of the drive unit are turned off. Become.

According to the fourth aspect of the present invention, the current flowing through each switching element of the drive unit can be suppressed to a predetermined limit value or less, and each switching element can be protected, and at the same time, the motor can be permanently mounted. In the case of the magnet type, demagnetization due to overcurrent can be prevented.

[Brief description of the drawings]

FIG. 1 is a connection diagram of an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the embodiment of the present invention.

FIG. 3 is a connection diagram of a conventional example.

FIG. 4 is a timing chart for explaining the operation of the conventional example.

[Explanation of symbols]

 E DC power supply CO control section IV 3-phase bridge inverter (drive section) SH shunt resistor (current detection section) CR current limit section CP2 second comparator (abnormal signal generation section) BR cutoff section D2 second D-FF AG3 To AG6 AND gate S1 to S6 Switching element A1 to A3 Arm M Motor M1 to M3 Winding

Continuation of the front page F term (reference) 5H576 AA15 BB06 BB10 CC01 DD02 DD04 DD05 DD10 EE11 GG04 HB02 JJ18 JJ19 JJ28 LL22 MM02

Claims (4)

[Claims] 1. A motor drive device for driving a motor by switching a plurality of switching elements constituting a drive unit in accordance with a control signal of a control unit and controlling opening and closing of a current path to a winding of the motor to drive the motor. A current detector that detects a current flowing through the current detector; and a current limiter that interrupts a control signal from the control unit to the switching element at regular intervals so as to limit a current value detected by the current detector to a predetermined limit value or less. An abnormality signal generating unit that compares a detection current detected by the current detection unit with a cutoff value larger than the limit value and generates an abnormality signal when the detection current is equal to or greater than the cutoff value; A motor drive device comprising: a cut-off unit that cuts off the control signal to the drive unit based on a signal to control the control unit and turns off the switching element. . 2. The control section determines whether or not the abnormal signal continues for a predetermined number of times within a predetermined time. The motor drive device according to claim 1, wherein the element is turned off. 3. The motor has a plurality of the windings, and the driving unit has a bridge inverter having the same number of arms as the number of the windings, the arm including two switching elements connected in series. Connecting each of the windings to a connection point of the two switching elements in each of the arms to control a one-side switching element group on one side of the connection point of the inverter and a second-side switching element group on the other side. By turning on one of the switching elements of the one-side switching element group and turning on the switching elements of the other-side switching element group on an arm different from the arm of the switching element, a current flows through the winding. And the switching element of the one-side switching element group and the switching element of the other-side switching element group to be turned on. Combination with the switching element
By switching in relation to the position of the rotor of the motor detected by the detecting means, the direction of current flow to each winding is switched to obtain the rotational force of the rotor, and 3. The motor drive according to claim 1, wherein at least one of the one-side switching element group and the other-side switching element group of the driving unit is turned off to cut off the current path. apparatus. 4. The current limiting unit according to claim 3, wherein the control unit cuts off a control signal from the control unit to one of the one of the one-side switching element group and the other-side switching element group. A motor drive device according to claim 1.