JP2017169346A - Motor controller, and method for controlling motor drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit off-set correction of a current detector from being set on the basis of a false current detection value when short-circuit failure occurs in a switching element of an inverter.SOLUTION: A current detector for each phase is arranged between a lower arm switching element of an inverter and a ground point, respectively. When the difference between the sum of a first current detection value detected by each phase current detector, respectively, in a state where upper arm switching elements of all phases are on control and the sum of a second current detection value detected by each phase current detector, respectively, in a state where the lower arm switching elements of all phases are on control is smaller than a threshold, off-set correction of detection output of each current detector is set on the basis of the first current detection value.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a motor control device and a control method for a motor drive circuit, and more particularly to a technique for detecting a phase current of a three-phase brushless motor.

  Patent Document 1 discloses a current that flows between a DC power source, a bridge circuit, and a motor when all the lower arm switching elements of the bridge circuit are on and all the upper arm switching elements are off, or vice versa. , And a motor control method configured to correct and output the current measurement value based on the difference between the current measurement value and the ideal value at this time is disclosed.

Japanese Patent No. 5653779

  By the way, in the motor control that includes a current detector for detecting the phase current and performs PWM control of the inverter based on the output of the current detector, when all of the upper arm switching element or the lower arm switching element are in the on-control state When detecting the offset error of the current detector based on the current detection value of the current, if a short fault has occurred in any of the switching elements that are to be controlled off, the offset error is erroneously detected. Setting correction will reduce the detection accuracy of the phase current.

  The present invention has been made in view of the above-described problems, and is capable of suppressing an offset correction from being set based on an erroneous current detection value when a short circuit failure has occurred in an inverter switching element. And it aims at providing the control method of a motor drive circuit.

  Therefore, the motor control device according to the present invention includes, as one aspect thereof, a three-phase brushless motor, an inverter provided with a series connection circuit of an upper arm switching element and a lower arm switching element for each phase of the three-phase brushless motor, Control of a motor drive circuit comprising: a current detector that is arranged between the lower arm switching element of each phase of the inverter and a ground point and detects a current flowing through the lower arm switching element of each phase. A total sum of first current detection values detected by the current detectors when the upper arm switching elements of all phases are in the ON control state, and the lower arm switching elements of all phases are ON. The difference between the second current detection values detected by the current detectors in the control state is smaller than the threshold value. Occasionally, an offset correction unit for setting said current detector offset correction of each of the detection output on the basis of the first current detection value.

  The motor drive circuit control method according to the present invention includes, as an aspect thereof, a three-phase brushless motor and a series connection circuit of an upper arm switching element and a lower arm switching element for each phase of the three-phase brushless motor. A motor drive comprising: an inverter; and a current detector that is disposed between the lower arm switching element of each phase of the inverter and a ground point and detects a current flowing through the lower arm switching element of each phase. A method for controlling a circuit, comprising: detecting a current detection value by each of the current detectors as a first current detection value when the upper arm switching elements of all phases are in an on-control state; When the arm switching element is in the ON control state, the current detection value by each of the current detectors is detected as the second current detection. Detecting the difference between the sum of the first current detection values and the sum of the second current detection values and a threshold, and when the difference is smaller than the threshold, the first current Setting an offset correction of the detection output of each of the current detectors based on a detection value.

  According to the above-described invention, it is possible to suppress the offset correction from being erroneously set based on the current detection value in a state where the short-circuit failure has occurred in the switching element of the inverter, and to suppress a decrease in the detection accuracy of the phase current.

It is a circuit diagram which shows the one aspect | mode of the drive circuit of the three-phase brushless motor in embodiment of this invention. It is a functional block diagram which shows the one aspect | mode of the PWM control of the three-phase brushless motor in embodiment of this invention. It is a time chart which shows the one aspect | mode of the detection timing of the phase current in embodiment of this invention. It is a flowchart which shows the one aspect | mode of the setting process of the offset correction value in embodiment of this invention. It is a time chart which shows the one aspect | mode of the detection timing of the offset error in embodiment of this invention.

Embodiments of the present invention will be described below.
FIG. 1 is a circuit diagram showing an aspect of a drive circuit 2 of a three-phase brushless motor 1.
The three-phase brushless motor 1 shown in FIG. 1 is used, for example, as an electric actuator that generates steering assist torque or an electric actuator that drives various pumps of a vehicle in an electric power steering device of the vehicle.
The motor drive circuit 2 that drives the three-phase brushless motor 1 includes a drive unit 212 and a control device (control unit) 213.

The control device 213 includes an A / D converter 213a and a microcomputer 213b. The microcomputer 213b is a microprocessor (arithmetic processing unit) such as a CPU and MPU, and a memory device (storage medium) such as a ROM and RAM. It is comprised including.
The three-phase brushless motor 1 includes a U-phase, V-phase, and W-phase three-phase windings 215u, 215v, and 215w that are star-connected to a cylindrical stator (not shown), and is formed at the center of the stator. This is a three-phase DC brushless motor that includes a permanent magnet rotor (rotor) 216 that can rotate in space.

The three-phase brushless motor 1 does not include a sensor that detects the position information of the rotor 216, and the control device 213 controls the drive of the three-phase brushless motor 1 without using a sensor that detects the position information of the rotor 216. Do by.
However, the three-phase brushless motor 1 includes a magnetic pole position sensor, and the control device 213 can control the driving of the three-phase brushless motor 1 by detecting the rotor angle (magnetic pole position) based on the output of the magnetic pole position sensor. .

The drive unit 212 includes an inverter 212a in which switching elements 217a to 217f including antiparallel diodes (parasitic diodes) 218a to 218f are connected in a three-phase bridge, and a DC power supply circuit 219.
The inverter 212a includes a series connection circuit of the upper arm switching elements 217a, 217c, 217e and the lower arm switching elements 217b, 217d, 217f for each phase of the three-phase brushless motor 1, and supplies AC power to the three-phase brushless motor 1. To do.
The switching elements 217a to 217f of the inverter 212a are configured by, for example, FETs, and each control terminal (gate terminal) of the switching elements 217a to 217f is connected to an output port of the control device 213. The switching devices 217a to 217f are turned on / off by the control device 213.

The control device 213 controls on / off of the switching elements 217a to 217f of the inverter 212a by a triangular wave comparison type PWM (Pulse Width Modulation) to control a voltage applied to the three-phase brushless motor 1.
In the triangular wave comparison type PWM control, a timing at which each switching element 217a to 217f is turned on / off by comparing a triangular wave (carrier) and a PWM timer set according to a command duty ratio (command voltage), In other words, the rising and falling timings of the PWM pulses, which are control signals for the switching elements of each phase, are detected.

The control device 213 controls on / off of the lower arm switching elements 217b, 217d, and 217f of each phase in response to the PWM pulse that controls the on / off of the upper arm switching elements 217a, 217c, and 217e of each phase. PWM control is performed on the switching elements 217a to 217f of the inverter 212a by a complementary method in which the PWM pulse has a reverse phase.
That is, when the control device 213 controls the PWM pulse for controlling ON / OFF of the upper arm switching elements 217a, 217c, and 217e of one phase to a logic level high, the lower arm switching elements 217b, 217d, The PWM pulse that controls on / off of 217f is controlled to be low at the logic level.
Therefore, when the upper arm switching elements 217a, 217c, and 217e in all phases are in the on control state, the lower arm switching elements 217b, 217d, and 217f in all phases are in the off control state, and the upper arm switching elements 217a and 217c in all phases. When 217e is in the off control state, the lower arm switching elements 217b, 217d, and 217f of all phases are in the on control state.

The inverter 212a is provided with current detectors 220U, 220V, and 220W for detecting currents flowing through the lower arm switching elements 217b, 217d, and 217f, respectively.
Current detectors 220U, 220V, and 220W are respectively disposed between lower arm switching elements 217b, 217d, and 217f of each phase of inverter 212a and ground point GND.

The current detectors 220U, 220V, and 220W include shunt resistors 220aU, 220aV, and 220aW connected in series to the lower arm switching elements 217b, 217d, and 217f, and detection circuits 220bU, 220bV, and 220bW including operational amplifiers, respectively. The
Each detection circuit 220bU, 220bV, 220bW detects a voltage proportional to the current generated by the resistance of the shunt resistor 220aU, 220aV, 220aW, and outputs an analog signal (current detection signal) of the voltage to the control device 213. To do.
The voltage analog signals of the detection circuits 220bU, 220bV, and 220bW, that is, the detection signals of the currents flowing through the lower arm switching elements 217b, 217d, and 217f are A / D converted by the A / D converter 213a, and the microcomputer 213b is read.

For example, the control device 213 determines the three-phase command voltages Vu, Vv, and Vw by a vector control method based on the rotor position and the command torque, and performs PWM control of the inverter 212a based on the command voltage.
The control device 213 receives the outputs of the current detectors 220U, 220V, and 220W, detects the phase currents Iu, Iv, and Iw of each phase, and performs vector control using the detected phase currents Iu, Iv, and Iw. To do.

From the outputs of current detectors 220U, 220V, and 220W and the PWM pulses for each phase, control device 213 detects the phase current for each phase.
For example, when the U-phase upper arm switching element 217a is on and the V-phase upper arm switching element 217c and the W-phase upper arm switching element 217e are both off, the currents flowing in the U-phase are the V-phase and W-phase currents. It flows in phases.

Therefore, when the U-phase upper arm switching element 217a is on and the V-phase upper arm switching element 217c and the W-phase upper arm switching element 217e are both off, the control device 213 controls the current detector 220V. From the output of the output and current detector 220W, the phase current Iv of the V phase and the phase current Iw of the W phase can be directly detected, and from the phase current Iv of the V phase and the phase current Iw of the W phase The U-phase phase current Iu can be obtained by calculation.
That is, in a combination state of PWM pulses in which one of the upper arm switching elements of each phase is on and the other two are off, the phase currents of two of the three phases are current detectors 220U, 220V, and 220W. Directly detected, the control device 213 can obtain the remaining one-phase current by calculation from the detected current values of the two phases.

For example, when both the U-phase upper arm switching element 217a and the V-phase upper arm switching element 217c are on and the W-phase upper arm switching element 217e is off, the current flowing in the U-phase and the V-phase Thus, the control device 213 can detect the W-phase current Iw from the output of the current detector 220W.
Further, when both the U-phase upper arm switching element 217a and the W-phase upper arm switching element 217e are on and the V-phase upper arm switching element 217c is off, the current flowing in the U-phase and the current flowing in the W-phase Therefore, the control device 213 can directly detect the phase current Iv of the V phase from the output of the current detector 220V.

Then, the control device 213 can obtain the U-phase phase current Iu by calculation from the W-phase phase current Iw and the V-phase phase current Iv.
That is, in a combination state of PWM pulses in which two of the upper arm switching elements 217a, 217c, and 217e of each phase are on and the other one is off, the phase current of one of the three phases is the current detector 220U. , 220V, 220W, and the control device 213 calculates the remaining one-phase current from the detected two-phase current when the combination of the upper arm switching elements to be turned on is different. Can be sought.

  Thus, in the combination state of the PWM pulse in which one or two of the upper arm switching elements of each phase are on, the control device 213 determines the phase current of each phase from the output of the current detectors 220U, 220V, and 220W. Can be detected, and the detected phase currents Iu, Iv, Iw of each phase are used for PWM control.

FIG. 2 is a functional block diagram showing an aspect of the control function of the control device 213, and shows the setting process of the three-phase command voltages Vu, Vv, Vw by the vector control method.
In FIG. 2, a phase current detector 501 receives A / D conversion values of outputs of the current detectors 220U, 220V, and 220W, and detects phase currents Iu, Iv, and Iw of the phases.

  In other words, the phase current detection unit 501 sets a PWM pulse period in which one or two of the upper arm switching elements 217a, 217c, and 217e of each phase is on as a phase current detection period, and which phase's upper arm switching Based on whether the elements 217a, 217c, and 217e are on, the phase current detection section identifies the phase in which the phase current is directly detected by the current detectors 220U, 220V, and 220W, and the phase currents Iu, Iv, Iw is detected and output.

The angle / angular velocity calculator 502 estimates the motor angle (magnetic pole position) and angular velocity (motor rotation speed).
Here, when the control device 213 performs PWM control of the three-phase brushless motor 1 by the sensorless driving method, the angle / angular velocity calculation unit 502 estimates the rotor position based on the counter electromotive force of the motor, and sets the estimated rotor position to the estimated rotor position. Based on this, the angular velocity is calculated.
On the other hand, when the three-phase brushless motor 1 has a magnetic pole position sensor, the angle / angular velocity calculator 502 detects the rotor position from the output of the magnetic pole position sensor, and calculates the angular velocity based on the detected rotor position.

  Further, the three-phase to two-axis converter 503 uses the phase current detection values Iu, Iv, and Iw obtained by the phase current detection unit 501 as the two-axis rotational coordinate system (d) based on the motor angle (magnetic pole position) θ at that time. -Q coordinate system) real currents Id and Iq.

The vector control unit 504 includes a d-q coordinate system obtained by the d-axis command current and the q-axis command current according to the command torque, the angular velocity calculated by the angle / angular velocity calculation unit 502, and the three-phase / two-axis converter 503. Real currents Id and Iq are input.
Then, the vector control unit 504 determines the command voltages Vq and Vd of the dq coordinate system based on the d-axis, q-axis command current, angular velocity, and actual currents Id and Iq, and sets the determined command voltages Vq and Vd to 2 Output to the axis-3 phase converter 505.

The two-axis to three-phase converter 505 converts the command voltages Vq and Vd output from the vector control unit 504 into three-phase command voltages Vu, Vv, and Vw and outputs them to the PWM modulation unit 506.
The 2-axis to 3-phase converter 505 has a pulse shift processing function that shifts the PWM pulse generated around the valley of the triangular wave carrier back and forth by correcting the command voltages Vu, Vv, and Vw. The above-described pulse shift process is a process performed to generate a phase current detection interval, and will be described in detail later.

  In the PWM modulation unit 506, the rising and falling timings of the switching gate waveform (PWM pulse) for driving the switching elements (upper arm and lower arm) of each phase are converted into three-phase command voltages as modulated waves. The switching gate waveform (PWM pulse) determined by comparing Vu, Vv, Vw and the triangular wave carrier is output to each control terminal of the switching elements 217a to 217f of the inverter 212a.

The setting of the switching gate waveform by the PWM modulation unit 506 is performed as follows, for example.
The PWM modulation unit 506 compares the U-phase command voltage Vu with the triangular wave carrier, and generates a switching gate waveform for driving the U-phase upper arm switching element 217a when the U-phase command voltage Vu is larger than the triangular wave carrier. The logic level is set to the high level, and when the U-phase command voltage Vu is smaller than the triangular wave carrier, the switching gate waveform for driving the U-phase upper arm switching element 217a is set to the low level as the logic level.
Further, the PWM modulation unit 506 generates an inverted signal of the switching gate waveform for driving the U-phase upper arm switching element 217a as a switching gate waveform for driving the U-phase lower arm switching element 217b.

  Similarly, the PWM modulation unit 506 generates a switching gate waveform for driving the V-phase upper and lower arm switching elements 217c and 217d and a switching gate waveform for driving the W-phase upper and lower arm switching elements 217e and 217f. Generate.

Next, detection processing of the phase currents Iu, Iv, and Iw in the phase current detection unit 501 will be described in detail.
If the two-phase phase current of the three phases of the three-phase brushless motor 1 can be directly detected based on the outputs of the current detectors 220U, 220V, and 220W, the remaining one-phase phase current has a total phase current of zero. Can be obtained by calculation.

Therefore, the 2-axis to 3-phase converter 505 controls the phase of the PWM pulse for each phase, and performs a pulse shift for detecting the two-phase current from the outputs of the current detectors 220U, 220V, and 220W.
For example, when the phase of the PWM pulse is advanced, the 2-axis to 3-phase converter 505 increases and corrects the command voltage in the half cycle before the carrier valley and commands in the half cycle after the carrier valley. Reduce the voltage. Also, when retarding the phase of the PWM pulse, the 2-axis to 3-phase converter 505 corrects the command voltage to decrease in the half cycle before the carrier valley, and commands in the half cycle after the carrier valley. Correct the voltage increase.

Here, the phase current detection unit 501 detects the two-phase phase current by sampling the output of the current detector 220 in two phase current detection sections having different combinations of PWM pulses generated by the pulse shift described above. .
The vector control unit 504 performs the calculation processing of the command voltages Vq and Vd on the two-phase phase current detection values detected from the outputs of the current detectors 220U, 220V, and 220W, and the remaining one-phase phase calculated based on these values. This is performed using the current detection value.
The phase current detection unit 501 directly detects the phase current of each of the three phases from the outputs of the current detectors 220U, 220V, and 220W in two PWM cycles by switching the pulse shift processing pattern for each PWM cycle. Is possible.

FIG. 3 is a time chart showing one mode of pulse shift. A U-phase PWM pulse is generated around a carrier valley, but a V-phase PWM pulse is advanced in phase than the carrier valley. The W-phase PWM pulse is generated around the position where the phase is retarded and delayed from the valley of the carrier.
With this pulse shift, the current detection period in which the U-phase upper arm switching element 217a and the V-phase upper arm switching element 217c are on and the W-phase upper arm switching element 217e is off in the period before the carrier valley. In the current detection period (time t2), the phase current detection unit 501 can detect the W-phase phase current Iw from the output of the current detector 220W.

In the period after the carrier valley, a current detection period in which the U-phase upper arm switching element 217a and the W-phase upper arm switching element 217e are on and the V-phase upper arm switching element 217c is off is generated. In the current detection period (time t4), the phase current detection unit 501 can detect the V-phase phase current Iv from the output of the current detector 220V.
Furthermore, the phase current detection unit 501 calculates the remaining U-phase phase current Iu from the W-phase phase current detection value Iw and the V-phase phase current detection value Iv based on the fact that the sum of the phase currents of each phase becomes zero. The phase currents Iu, Iv, and Iw of all three phases are calculated to obtain.

Further, the control device 213 includes an offset correction unit 507 for correcting offset errors (zero error) of the current detectors 220U, 220V, and 220W.
The offset correction unit 507 is configured to detect each current detector when the upper arm switching elements 217a, 217c, and 217e of each phase are all in an on-control state and the lower arm switching elements 217b, 217d, and 217f of each phase are all in an off-control state. The offset correction amount for each phase for correcting the output of each current detector 220U, 220V, 220W is set so that the current detection value by 220U, 220V, 220W becomes zero.

  That is, when the upper arm switching elements 217a, 217c, and 217e of each phase are all in the on control state and the lower arm switching elements 217b, 217d, and 217f of each phase are all in the off control state, the upper arm switching elements 217a, 217c, The current flows back through 217e, and theoretically no current flows through the shunt resistors 220aU, 220aV, and 220aW. However, in reality, a small current flows through the shunt resistors 220aU, 220aV, and 220aW, and the current corresponding to the minute current flows. An error (zero error, offset error) of the detected value occurs.

  Therefore, the offset correction unit 507 is configured so that each of the upper arm switching elements 217a, 217c, and 217e in each phase is in an on control state and each of the lower arm switching elements 217b, 217d, and 217f in each phase is in an off control state. A deviation from zero of each of current detection values (detection values without offset correction) by the current detectors 220U, 220V, and 220W is detected as an offset error of each phase, and an offset correction amount for canceling the offset error is detected for each phase. Set to update.

The offset correction unit 507 corrects the output of each of the current detectors 220U, 220V, and 220W with the offset correction amount for each phase, and causes the phase current detection unit 501 to input the corrected detection output, thereby offset error. The phase currents Iu, Iv, and Iw are detected based on the compensated outputs, and the PWM control of the inverter 212a is performed based on the phase currents Iu, Iv, and Iw with compensated offset errors.
The offset correction process is not limited to the correction of the output signals of the current detectors 220U, 220V, and 220W, and the current value obtained by converting the output signals of the current detectors 220U, 220V, and 220W in the phase current detector 501. And various processes for compensating for the offset error, such as a process for correcting the conversion table for converting the output signal into a current value in the phase current detection unit 501.

By the way, when a short failure has occurred in any of the lower arm switching elements 217b, 217d, and 217f of each phase, the upper arm switching elements 217a, 217c, and 217e of each phase are all in the ON control state. Even when the lower arm switching elements 217b, 217d, and 217f are all in the OFF control state, a current flows through the shunt resistor 220a through the lower arm switching elements 217b, 217d, and 217f that are short-circuited.
For this reason, when any of the lower arm switching elements 217b, 217d, and 217f is short-circuited (short-circuited), the offset correction unit 507 flows to the shunt resistor 220a due to the short-circuit failure for the phase in which the short-circuit has occurred. The detected current is erroneously detected as an offset error, and the detected current value is erroneously corrected.

Furthermore, if the PWM control of the inverter 212a (the operation of the inverter 212a) is continued in the failure state of the inverter 212a in which a short-circuit failure has occurred in any of the switching elements constituting the inverter 212a, the three-phase brushless motor 1 There is a case where the control accuracy deteriorates and an assist torque abnormality occurs, and the steering performance of the vehicle is lowered.
Accordingly, the offset correction unit 507 suppresses erroneous detection of an offset error due to a short-circuit failure of the switching element constituting the inverter 212a (incorrectly performing the offset correction process), and a short-circuit failure of the switching element occurs. The inverter 212a is controlled to be driven (the inverter 212a in the short-circuit failure state is operated).

  Specifically, in the offset correction unit 507, the upper arm switching elements 217a, 217c, and 217e in each phase are all turned on, and the lower arm switching elements 217b, 217d, and 217f in each phase are all turned off. A sum S1 of current values detected by the current detectors 220U, 220V, and 220W (hereinafter referred to as first current detection values A1u, A1v, and A1w) is obtained. Further, the offset correction unit 507 is used when the lower arm switching elements 217b, 217d, and 217f of each phase are all turned on and the upper arm switching elements 217a, 217c, and 217e of each phase are all turned off. A sum S2 of current values detected by the current detectors 220U, 220V, 220W (hereinafter referred to as second current detection values A2u, A2v, A2w) is obtained.

  Then, the offset correction unit 507 compares the sum S1 and the sum S2, detects from the comparison result whether or not a short fault has occurred in any of the switching elements that constitute the inverter 212a, and the short fault has occurred. If not, the offset correction amount for each phase is updated and set based on the first current detection values A1u, A1v, A1w, and the PWM control of the inverter 212a (operation of the inverter 212a) is stopped when a short circuit failure occurs.

Hereinafter, detection of a short fault (offset correction setting / cancellation switching control) based on the sum S1 and S2 by the offset correction unit 507 will be described in detail.
When any one of the lower arm switching elements 217b, 217d, and 217f in each phase is short-circuited, the upper arm switching elements 217a, 217c, and 217e in each phase are all controlled to be off, and the lower arm switching elements in each phase When all of 217b, 217d, and 217f are controlled to be on, the sum S2 of the second current detection values A2u, A2v, and A2w theoretically becomes zero without being affected by the short-circuit failure.

That is, in the above control state, the current flows back through the lower arm switching elements 217b, 217d, and 217f, and the second current depends on the difference in the current direction of whether the current flows toward the upper arm or toward the ground. When the detected values A2u, A2v, A2w are indicated by plus / minus, the sum S2 theoretically becomes zero.
On the other hand, when there is a short circuit failure in any one of the lower arm switching elements 217b, 217d, and 217f of each phase, all the upper arm switching elements 217a, 217c, and 217e of each phase are controlled to be turned on. When all of the arm switching elements 217b, 217d, and 217f are controlled to be off, a current flows through the lower arm switching element in which the short circuit failure occurs, and the detection current of the current detector 220 in the phase in which the short circuit failure has occurred is zero. Therefore, the sum S1 of the first current detection values A1u, A1v, A1w by the current detectors 220U, 220V, 220W is deviated from zero (S1 ≠ 0).

Further, when a short circuit failure has occurred in any of the upper arm switching elements 217a, 217c, 217e, the first current detection values A1u, A1v, A1w and the sum S1 are not affected, but the upper arm switching elements 217a, Even in the off-control state of 217c and 217e, the supply current flows into the lower arm through the shorted upper arm switching element, and therefore the sum S2 of the second current detection values A2u, A2v and A2w deviates from zero. (S2 ≠ 0).
That is, when all of the switching elements constituting the inverter 212a are not short-circuited, the sum S1 and the sum S2 are both zero, and the difference between the sum S1 and the sum S2 is theoretically zero.

On the other hand, when a short-circuit failure occurs in any of the upper arm switching elements 217a, 217c, and 217e of the inverter 212a, the sum S2 deviates from zero, and a short-circuit failure occurs in any of the lower arm switching elements 217b, 217d, and 217f of the inverter 212a. Then, the sum S1 deviates from zero.
Therefore, when a short circuit failure occurs in any of the switching elements constituting the inverter 212a, the sum S1 and the sum S2 do not coincide with each other, and a difference occurs between the two.

Therefore, when the sum S1 and the sum S2 match and there is no difference between them, the offset correction unit 507 detects (estimates) that all of the switching elements constituting the inverter 212a are not short-circuited. Then, the offset error learning is executed to update and set the offset correction amount of each phase based on the first current detection values A1u, A1v, A1w.
On the other hand, when a difference exceeding the variation error of the current detection occurs between the sum S1 and the sum S2, the offset correction unit 507 has a short circuit failure on the upper arm side or the lower arm side of the switching element constituting the inverter 212a. It detects (estimates) that it has occurred, stops updating the offset correction amount, and further stops the operation of the inverter 212a.

  With the processing function of the offset correction unit 507, the inverter 212a is PWM-controlled in an abnormal state in which a short circuit has occurred in the switching element constituting the inverter 212a, and the three-phase brushless motor 1 is prevented from generating abnormal assist torque. Further, it is possible to prevent the offset correction unit 507 from erroneously detecting an offset error based on the first current detection values A1u, A1v, and A1w affected by the short-circuit failure of the switching element and performing an incorrect offset correction. it can.

The flowchart of FIG. 4 shows one mode of update processing (offset correction setting processing) of the offset correction value (zero point correction value) by the control device 213 (offset correction unit 507).
In step S101, the control device 213 first controls the upper arm switching elements 217a, 217c, and 217e of each phase to be on, and controls the lower arm switching elements 217b, 217d, and 217f of each phase to be off. A process of sampling the current values detected by the current detectors 220U, 220V, and 220W at the first current detection values A1u, A1v, and A1w and storing (storing) them in the memory is performed.

The state where all the upper arm switching elements 217a, 217c, and 217e of each phase are controlled to be on and all the lower arm switching elements 217b, 217d, and 217f of each phase are controlled to be off is, for example, time t2 in FIG. The control device 213 (offset correction unit 507) determines the current values of the respective phases detected from the outputs of the current detectors 220U, 220V, and 220W at the time t2 as the first current detection values A1u, A1v, Store as A1w.
The first current detection values A1u, A1v, A1w are the current detection values when the offset correction is canceled, and the stored values of the first current detection values A1u, A1v, A1w are the upper arm of each phase. It is assumed that the current value when the switching elements 217a, 217c, and 217e are all turned on is updated to the latest value every time a new value is detected.

Next, the control device 213 proceeds to step S102, where all the upper arm switching elements 217a, 217c, 217e of each phase are controlled to be off, and the lower arm switching elements 217b, 217d, 217f of each phase are all controlled to be on. In this state, the current detection value by the current detector 220 is sampled as the second current detection values A2u, A2v, A2w and stored (stored) in the memory.
The state where all the upper arm switching elements 217a, 217c, and 217e of each phase are controlled to be off and the lower arm switching elements 217b, 217d, and 217f of each phase are all controlled to be on is, for example, time t3 in FIG. The control device 213 (offset correction unit 507) determines the current values of the respective phases detected from the outputs of the current detectors 220U, 220V, and 220W at time t3 as second current detection values A2u, A2v, Store as A2w.

The second current detection values A2u, A2v, A2w are current detection values in a state where the offset correction is canceled, and the stored values of the second current detection values A2u, A2v, A2w are the lower arm of each phase. It is assumed that the current value is updated to the latest value every time the switching elements 217b, 217d, and 217f are all controlled to be on.
The first current detection values A1u, A1v, A1w and the second current detection values A2u, A2v, A2w are data with a plus / minus sign corresponding to the direction of the current.

When the control device 213 samples the first current detection values A1u, A1v, A1w and the second current detection values A2u, A2v, A2w as described above, the process proceeds to step S103, and the first current detection values A1u, A1v, A1w The absolute value of the value obtained by subtracting the sum S2 of the second current detection values A2u, A2v, A2w from the sum S1 of the current and the threshold SL (SL> 0) is compared.
In addition, the absolute value of the value obtained by subtracting the sum S2 from the sum S1 is, in other words, the difference between the sum S1 and the sum S2, which is a value obtained by subtracting the smaller one of the sum S1 and the sum S2. .

The threshold value SL is a state in which the difference between the total sum S1 and the total sum S2 is a value within the variation range of the current detection, or exceeds the variation range, and a circuit abnormality such as a short circuit failure has occurred in the inverter 212a. It is a value for discriminating whether it is a value to be shown, adapted beforehand based on experiments and simulations, and stored in the memory of the control device 213.
Here, when the absolute value of the value obtained by subtracting the sum S2 from the sum S1 (difference between the sum S1 and the sum S2) is equal to or less than the threshold SL, the switching element of the inverter 212a has no abnormality such as a short circuit failure, and the first current Since the detection values A1u, A1v, and A1w indicate offset errors of the current detectors 220U, 220V, and 220W, the control device 213 proceeds to step S104 for performing update setting of the offset correction value.

In step S104, the control device 213 updates and sets the offset correction values HOSu, HOSv, HOSW of each phase based on the first current detection values A1u, A1v, A1w.
Since the first current detection values A1u, A1v, A1w theoretically become zero when there is no offset error, the control device 213 corrects the first current detection values A1u, A1v, A1w after correction. The offset correction values HOSu, HOSv, and HOSW for each phase are set as correction values for bringing the detected current value close to zero.

For example, when the U-phase first current detection value A1u is A1u> 0, the U-phase current Iu detected by the current detector 220U is subtracted and corrected by the absolute value of the first current detection value A1u (shift in the decreasing direction). In other words, when the actual U-phase current Iu is zero, the offset-corrected U-phase current detection value Iu becomes zero and the offset error is compensated.
Therefore, when the U-phase first current detection value A1u is A1u> 0, the control device 213 reduces the subtraction correction value (minus correction) by the absolute value of the first current detection value A1u (or a value close to the absolute value). Value) is set to the U-phase offset correction value HOSu.

In addition, when the offset correction values HOSu, HOSv, and HOSW are updated, the control device 213 calculates the offset calculated based on the previous offset correction values HOSuold, HOsvold, HOswold, and the latest first current detection values A1u, A1v, A1w. The correction values HOSunew, HOSunew, and HOSWnew are averaged by weighted averaging or the like, and the averaged values can be set as offset correction values HOSu, HOSu, and HOSW used for offset correction.
Further, the control device 213 compensates for the offset error based on plus / minus of the first current detection values A1u, A1v, A1w corrected by the previous offset correction values HOSu, HOSV, HOSW. Can be specified, and the offset correction values HOSu, HOSv, and HOSW can be changed by a predetermined step width in this direction.

Further, the variable range of the offset correction values HOSu, HOSu, and HOSW can be limited to an area between the preset negative limit value and the positive limit value.
In addition, for the phase in which the absolute values of the first current detection values A1u, A1v, A1w are larger than the upper limit value (predetermined value), the control device 213 stops updating the offset correction value HOS corresponding to the phase. Can do. Thereby, it can suppress that an offset correction value is erroneously set with the erroneous detection of 1st electric current detection value A1u, A1v, A1w.

  Further, the control device 213 operates the inverter 212a (three-phase brushless by the inverter 212a) when at least one of the absolute values of the first current detection values A1u, A1v, A1w is larger than the upper limit value (predetermined value). Supply of AC power to the motor 1) can be stopped. Thereby, for example, when an abnormality occurs in the current detectors 220U, 220V, and 220W and the detection accuracy of the phase current is reduced, the three-phase brushless motor 1 is controlled based on the phase current detection value different from the actual value. This can be suppressed.

  On the other hand, if the absolute value of the value obtained by subtracting the sum S2 from the sum S1 (difference between the sum S1 and the sum S2) exceeds the threshold SL, an abnormality such as a short circuit failure has occurred in the switching element of the inverter 212a. 1 Current detection values A1u, A1v, A1w may have different values from the offset errors of the current detectors 220U, 220V, 220W, and the three-phase brushless motor 1 is abnormal due to an abnormality in the inverter 212a. There is a possibility of generating assist torque.

Therefore, if the absolute value of the value obtained by subtracting the total sum S2 from the total sum S1 exceeds the threshold value SL, the control device 213 proceeds to step S105, and offset correction values HOSu, HOSv, based on the first current detection values A1u, A1v, A1w, The update setting of HOSW is stopped and the operation of the inverter 212a is stopped.
Thus, when an abnormality such as a short circuit failure has occurred in the switching element of the inverter 212a, and the first current detection values A1u, A1v, A1w show values different from the actual offset error, the first current detection value concerned Based on A1u, A1v, and A1w, the offset correction values HOSu, HOSv, and HOSW are prevented from being erroneously updated.

In addition, since the operation of the inverter 212a in which an abnormality such as a short fault has occurred in the switching element is stopped, it is possible to suppress a current different from the command current from flowing through the three-phase brushless motor 1 due to an abnormality such as a short fault, Thus, the three-phase brushless motor 1 is suppressed from generating abnormal assist torque.
The control device 213 controls the operation of the inverter 212a (supply of AC power to the three-phase brushless motor 1 by the inverter 212a), off control of the power supply relay of the inverter 212a, and stop of PWM output (set the duty ratio to 0%). For example).

Although the contents of the present invention have been specifically described above with reference to the preferred embodiments, it is obvious that those skilled in the art can take various modifications based on the basic technical idea and teachings of the present invention. is there.
For example, the control device 213 samples the first current detection values A1u, A1v, A1w and the second current detection values A2u, A2v, A2w, and sets the offset correction values HOSu, HOSv, HOSw based on the sampled current detection values. Need not be performed every PWM cycle, and the control device 213 performs sampling of the current detection value and setting of the offset correction value once every plural cycles of the PWM cycle, or every predetermined time. It can be carried out when the three-phase brushless motor 1 is started.

Here, the technical idea that can be understood from the above-described embodiment will be described below.
In one aspect thereof, the motor control device includes a three-phase brushless motor, an inverter provided with a series connection circuit of an upper arm switching element and a lower arm switching element for each phase of the three-phase brushless motor, and each phase of the inverter. A motor drive circuit control device comprising: current detectors that are respectively disposed between the lower arm switching element and a ground point and detect currents flowing through the lower arm switching elements of the respective phases; The sum of the first current detection values detected by the current detectors when the upper arm switching elements of the phases are in the on-control state, and the lower arm switching elements of all phases are in the on-control state When the difference from the sum of the second current detection values detected by the current detectors is smaller than a threshold value, the first current Based on the detection value includes an offset correction unit for setting said current detector offset correction of each of the detection output.

In a preferred aspect of the motor control device, the offset correction unit stops setting the offset correction and stops the operation of the inverter when the difference is larger than the threshold value.
In another preferable aspect, the offset correction unit stops setting offset correction for a phase in which the first current detection value is larger than a predetermined value.
In still another preferred aspect, the offset correction unit stops the operation of the inverter when the first current detection value is larger than a predetermined value in at least one phase.

In one aspect, the motor drive circuit control method includes a three-phase brushless motor, an inverter provided with a series connection circuit of an upper arm switching element and a lower arm switching element for each phase of the three-phase brushless motor, A method for controlling a motor drive circuit, comprising: a current detector that is arranged between the lower arm switching element of each phase of the inverter and a grounding point and detects a current flowing through the lower arm switching element of each phase. A step of detecting a current detection value by each of the current detectors as a first current detection value when the upper arm switching elements of all phases are in an on-control state, and the lower arm switching elements of all phases The current detection value by each of the current detectors is detected as the second current detection value when in the on-control state. A step of comparing a difference between a sum of the first current detection values and a sum of the second current detection values with a threshold value, and based on the first current detection value when the difference is smaller than the threshold value. Setting offset correction of detection output of each of the current detectors.
In a preferred aspect of the method for controlling the motor drive circuit, when the difference is larger than the threshold value, the step of stopping the setting of the offset correction based on the first current detection value and stopping the operation of the inverter is further provided. Including.

In one aspect, the motor control device includes a three-phase brushless motor, an inverter provided with a series connection circuit of an upper arm switching element and a lower arm switching element for each phase of the three-phase brushless motor, and each of the inverters A motor drive circuit control device comprising a current detector for detecting a current flowing in a phase,
A correction unit for correcting an offset of a current detection value by the current detector;
A first current detector for obtaining a current detection value detected by the current detector as a first current detection value when the upper arm switching elements of all phases are in an on-control state;
A setting unit for setting offset correction by the correction unit based on the first current detection value;
A second current detection unit for obtaining a current detection value detected by the current detector as a second current detection value when the lower arm switching elements of all phases are in an on-control state;
A comparator for comparing the first current detection value and the second current detection value;
A switching unit that switches between setting and canceling the offset correction by the setting unit based on the comparison result of the comparison unit;
including.

In a preferred aspect of the motor control device, the current detector is disposed between the lower arm switching element of each phase of the inverter and a grounding point, and the current flowing through the lower arm switching element of each phase is respectively To detect.
In another preferable aspect, the comparison unit compares the sum of the first current detection values for each phase with the sum of the second current detection values for each phase.

In still another preferred aspect, the switching unit includes an offset by the setting unit when a difference between the sum of the first current detection values for each phase and the sum of the second current detection values for each phase is smaller than a threshold value. The correction setting is permitted, and the setting of the offset correction by the setting unit is stopped when the difference is larger than the threshold value.
In still another preferred aspect, the switching unit stops the operation of the inverter when the setting of the offset correction by the setting unit is stopped.

  DESCRIPTION OF SYMBOLS 1 ... Three-phase brushless motor, 2 ... Motor drive circuit, 212 ... Drive part, 212a ... Inverter, 213 ... Control device, 213a ... A / D converter, 213b ... Microcomputer, 220U, 220V, 220W ... Current detector, 220aU, 220aV, 220aW ... shunt resistor, 220bU, 220bV, 220bW ... detection circuit

Claims (6)

An inverter comprising a three-phase brushless motor, a series connection circuit of an upper arm switching element and a lower arm switching element for each phase of the three-phase brushless motor, and the lower arm switching element and the ground point of each phase of the inverter A motor drive circuit control device comprising: current detectors that respectively detect currents that flow through the lower arm switching elements of the respective phases that are disposed between the current detectors;
When the sum of the first current detection values detected by the current detectors when the upper arm switching elements of all phases are in the on-control state and the lower arm switching elements of all phases are in the on-control state When the difference between the second current detection values detected by the current detectors and the sum of the second current detection values is smaller than a threshold value, the offset correction of the detection outputs of the current detectors is set based on the first current detection values. A motor control device including an offset correction unit.   The motor control device according to claim 1, wherein when the difference is larger than the threshold value, the offset correction unit stops setting the offset correction and stops the operation of the inverter.   The motor control device according to claim 1, wherein the offset correction unit stops setting offset correction for a phase in which the first current detection value is larger than a predetermined value.   The motor control device according to claim 1, wherein the offset correction unit stops the operation of the inverter when the first current detection value is larger than a predetermined value in at least one phase. An inverter comprising a three-phase brushless motor, a series connection circuit of an upper arm switching element and a lower arm switching element for each phase of the three-phase brushless motor, and the lower arm switching element and the ground point of each phase of the inverter A current detector for respectively detecting a current flowing in the lower arm switching element of each phase that is arranged between each phase, and a method for controlling a motor drive circuit,
Detecting a current detection value by each of the current detectors as a first current detection value when the upper arm switching elements of all phases are in an on-control state;
Detecting a current detection value by each of the current detectors as a second current detection value when the lower arm switching elements of all phases are in an on-control state;
Comparing the difference between the sum of the first current detection values and the sum of the second current detection values with a threshold;
Setting an offset correction of the detection output of each of the current detectors based on the first current detection value when the difference is smaller than the threshold;
A method for controlling a motor drive circuit.   The control of the motor drive circuit according to claim 5, further comprising: stopping setting of the offset correction based on the first current detection value and stopping the operation of the inverter when the difference is larger than the threshold value. Method.