JP2017060218A - Motor controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor controller capable of suitably determining the presence/absence of a ground fault on overcurrent side.SOLUTION: An upper-limit threshold value Imax and a lower-limit threshold value Imin are set according to a duty ratio D of a duty signal (S101). When a detection value of a motor current I is not less than the upper-limit threshold value Imax or not more than the lower-limit threshold value Imin (S102: YES), it is determined that a ground fault has occurred in a power supply line of a motor (S104).SELECTED DRAWING: Figure 5

Description

  The present invention relates to a motor control device that performs drive control of a motor installed in an electric power steering system.

  In a vehicle, in an electric power steering system (hereinafter referred to as EPS), the steering force of a driver is assisted by transmitting the rotational force of a motor to a steering shaft or a rack shaft via a speed reduction mechanism. In such EPS, in order to generate an accurate assist force, feedback control is performed on a current (hereinafter, referred to as a motor current) that flows to the motor. The motor current feedback control adjusts the motor terminal voltage according to the deviation between the current command value and the detected motor current value. In many cases, the terminal voltage is adjusted by pulse width modulation (PWM). This is done through adjustment of the duty ratio of the duty signal in width modulation) control.

  On the other hand, if a ground fault occurs in a power supply line that supplies power to such an EPS motor, an excessive current may flow through the motor and its drive circuit. Therefore, conventionally, Patent Document 1 describes a ground fault determination technique for determining whether or not a ground fault has occurred based on a motor terminal voltage and the duty ratio. Specifically, in the ground fault determination technique of Patent Document 1, the difference between the detected value of the terminal voltage and the estimated value of the terminal voltage estimated from the duty ratio continues to be a predetermined value for a predetermined time or longer. When exceeded, it is determined that there is a ground fault.

Japanese Patent Laid-Open No. 11-263240

  By the way, the ground fault of the power line of the motor as described above includes a ground fault on the dead short side where current does not flow through the motor, and a ground fault on the over current side where excessive current flows through the motor. The above-mentioned conventional ground fault determination technique has a problem that although it is possible to determine the presence or absence of the ground fault on the dead short side, it is not possible to determine the presence or absence of the ground fault on the overcurrent side. Further, since the internal resistance of the motor changes depending on the load applied to the motor, the terminal voltage of the motor changes with some variation with respect to the estimated value from the duty ratio even during normal operation. For this reason, in order to avoid erroneous determination, a large margin for setting the determination value must be taken, and the determination accuracy deteriorates accordingly.

  The present invention has been made in view of such circumstances, and the problem to be solved is a motor control capable of suitably determining the occurrence of an overcurrent-side ground fault in which excessive current flows in the motor. To provide an apparatus.

  A motor control device that solves the above problem generates a duty signal according to a current command value calculated for power supply to the motor, and performs drive control of the motor according to the duty signal. Then, the motor control device includes a current detection unit that detects a current flowing through the motor, and a current that is equal to or higher than an upper limit threshold that is set according to a duty ratio of the duty signal. A ground fault determination unit that determines that a ground fault has occurred in the power line of the motor.

  When an overcurrent-side ground fault that causes excessive current to flow through the motor occurs, the current flowing through the motor shows a value that deviates to a value that is excessive with respect to a value assumed from the duty ratio. Therefore, if an upper limit threshold is set according to the duty ratio and it is determined that a ground fault has occurred when it is detected that a current equal to or greater than the upper limit threshold has flowed to the motor, the occurrence of an overcurrent-side ground fault will occur. Presence / absence can be determined. Also, during normal operation, the current flowing through the motor does not show a value that deviates too much from the value assumed from the duty ratio. Judgment can be avoided. Therefore, the accuracy of determination can be increased. Further, the determination can be performed in a shorter time after the occurrence of the ground fault.

  Further, the ground fault determination unit in the motor control device further sets a lower limit threshold smaller than the upper limit threshold according to a duty ratio of the duty signal, and a current equal to or lower than the lower limit threshold is detected by the current detection unit. Even in such a case, it is desirable to determine that a ground fault has occurred in the power supply line of the motor. In such a case, it is possible to preferably determine whether or not the ground short on the dead short side where current does not flow to the motor due to the occurrence thereof.

  The motor control device may further include a power supply stopping unit that stops power supply through the power line in which a ground fault has occurred when the ground fault determination unit determines that a ground fault has occurred. desirable. If it does in this way, it will become possible to control that an excessive current flows into a motor or its drive circuit by generation of a ground fault.

  According to the motor control device of the present invention, it is possible to suitably determine whether or not an overcurrent-side ground fault has occurred.

1 is a schematic diagram schematically showing a configuration of a power steering system to which an embodiment of a motor control device is applied. The figure which shows the structure of the motor drive circuit provided in the same electric power steering system. 1 is a schematic diagram schematically showing the configuration of a motor control device according to the embodiment. (A) is a figure which shows the current flow of the said motor drive circuit at the time of generation | occurrence | production of a dead short side ground fault, (b) shows the current flow of the motor drive circuit at the time of generation | occurrence | production of an overcurrent side ground fault. FIG. The flowchart of the ground fault determination process performed in the motor control apparatus of the said embodiment. The graph which shows the relationship between the detected value and duty ratio of a motor current in the determination map referred by the ground fault determination process, and an upper limit threshold value and a lower limit threshold value.

  Hereinafter, an embodiment of a motor control device will be described in detail with reference to FIGS. The motor control device of this embodiment is installed in an electric power steering system mounted on a vehicle.

  As shown in FIG. 1, in an electric power steering system in which the motor control device of the present embodiment is installed, a steering shaft 11 is coupled to a handle 10 so as to be integrally rotatable. The steering shaft 11 is divided into three parts connected in order of a column shaft 12, an intermediate shaft 13 and a pinion shaft 14 from the handle 10 side. The pinion of the pinion shaft 14 is meshed with the rack portion 16 of the rack shaft 15. Both ends of the rack shaft 15 are connected to the knuckle arms 19 of the left and right steered wheels 18 via tie rods 17, respectively. The rotation of the steering shaft 11 according to the operation of the handle 10 is converted into a reciprocating linear motion of the rack shaft 15 by a rack and pinion mechanism constituted by a pinion shaft 14 and a rack portion 16. The reciprocating linear motion of the rack shaft 15 is transmitted to the knuckle arm 19 so that the steering angle of the left and right steered wheels 18 is changed.

  On the other hand, a motor 20 is connected to the column shaft 12 via a reduction gear mechanism 21. Then, the rotational force generated by the motor 20 is transmitted to the column shaft 12 after being decelerated by the reduction gear mechanism 21, whereby the assist force for assisting the driver's steering operation is transmitted to the steering shaft 11. It is like that. In the present embodiment, a single-phase DC motor is employed as the motor 20.

  The motor control device that performs drive control of the motor 20 includes an electronic control unit 23 that performs drive control of the motor 20. The electronic control unit 23 includes a central processing unit that performs various arithmetic processes related to the drive control of the motor 20, a read-only memory that stores control programs and data, the calculation results of the central processing unit, and the sensors described below. The microcomputer is configured with a readable memory that temporarily stores detection results and the like. The electronic control unit 23 includes a vehicle speed sensor 24 that detects the vehicle speed V, a torque sensor 25 that detects the steering torque γ applied to the handle 10, and a motor rotation angle sensor that detects the rotation angle of the motor 20 (motor rotation angle θm). 26 is connected. The electronic control unit 23 is also connected to a motor drive circuit 22 that supplies power to the motor 20.

(Motor drive circuit)
As shown in FIG. 2, the motor drive circuit 22 includes an H-bridge circuit configured by four field effect transistors (FETs) FET1 to FET4. Specifically, the H bridge circuit is a circuit in which a series circuit of FET1 and FET3 and a series circuit of FET2 and FET4 are connected in parallel. One end of the H bridge circuit is connected to the battery BATT, and the other end is grounded via the shunt resistor Rs.

  The plus terminal (+) of the motor 20 is connected to the portion between the FET1 and FET3 via the power supply line L1, and the minus terminal of the motor 20 is connected to the portion between the FET2 and FET4 via the power supply line L2. It is connected. Further, a motor relay 27 that is opened and closed by the electronic control unit 23 is installed on the power supply line L1. The power supply line L1 becomes conductive when the motor relay 27 is closed, and becomes cut-off when it is opened.

  On the other hand, both ends of the shunt resistor Rs are connected to the electronic control unit 23 via the current detection circuit 28. Further, both terminals of the motor 20 are connected to the electronic control unit 23 via voltage detection circuits 29a and 29b, respectively. Then, the electronic control unit 23 obtains the voltage across the shunt resistor Rs through the current detection circuit 28, and thus the current flowing through the motor 20 (motor current I). Further, the electronic control unit 23 acquires the terminal voltages M1 and M2 on the plus side and the minus side of the motor 20 via the voltage detection circuits 29a and 29b, respectively. In the present embodiment, the current detection circuit 28 corresponds to a current detection unit.

  The gates of the FET1 to FET4 are connected to the gate drive circuit 30. The gate drive circuit 30 generates a duty signal according to the duty ratio D from the electronic control unit 23 and a command value in the rotation direction, and drives the FETs 1 to 4 to open and close.

(Electronic control unit)
As shown in FIG. 3, the electronic control unit 23 includes a current command value calculation unit 31, a duty ratio calculation unit 32, a ground fault determination unit 33, and a power supply stop unit 34. As an alternative to these configurations, the functions of these configurations may be realized by the central processing unit performing an integrated process.

  The current command value calculation unit 31 generates assist force to be applied based on the vehicle speed V, the steering torque γ, and the motor rotation angle θm detected by the vehicle speed sensor 24, the torque sensor 25, and the motor rotation angle sensor 26, respectively. Therefore, the command value (current command value Ip) of the motor current I and the rotation direction of the motor 20 necessary for the calculation are calculated. Then, the current command value calculation unit 31 commands the calculated rotation direction to the gate drive circuit 30. In the following description, the rotation direction of the motor 20 when a current is passed from the plus terminal side to the minus terminal side of the motor 20 is described as a positive rotation direction, and the minus terminal side is changed to the plus terminal side. The direction of rotation of the motor 20 when a current is passed is described as the reverse direction.

  The duty ratio calculation unit 32 calculates the duty ratio D of the duty signal based on the current command value Ip calculated by the current command value calculation unit 31 and the detected value of the motor current I acquired through the current detection circuit 28. The duty ratio D is calculated so as to feedback control the motor current I with the current command value Ip as a target. Specifically, the value of the duty ratio D is obtained by adding a feedforward term obtained from the current command value Ip and a feedback term obtained in accordance with a deviation between the current command value Ip and the detected value of the motor current I. It is calculated by combining. Then, the duty ratio calculation unit 32 commands the calculated duty ratio D to the gate drive circuit 30.

  The gate drive circuit 30 has a duty signal of a duty ratio D commanded by the duty ratio calculation unit 32 with respect to the gate of the FET necessary for rotating the motor 20 in the rotation direction commanded by the current command value calculation unit 31. Is output. Specifically, the gate drive circuit 30 outputs a duty signal to the gates of the FET 2 and FET 3 when the rotation of the motor 20 in the forward rotation direction is commanded, and the rotation of the motor 20 in the reverse rotation direction is performed. When commanded, a duty signal is output to the gates of FET1 and FET4.

  On the other hand, the ground fault determination unit 33 determines whether or not a ground fault has occurred in the power supply lines L1 and L2 based on the duty ratio D calculated by the duty ratio calculation unit 32 and the detected value of the motor current I. . The power supply stopping unit 34 stops power supply to the motor 20 by opening the motor relay 27 and turning off the power supply line L1 when the ground fault determination unit 33 determines that a ground fault has occurred. .

(Ground fault judgment)
Next, details of ground fault determination by the ground fault determination unit 33 will be described. When a ground fault occurs in the power supply lines L1 and L2, one of the following two states occurs. That is, there are a dead short state in which no current flows through the motor 20 and an overcurrent state in which an excessive current flows through the motor 20.

  FIG. 4A shows the flow of current in the motor drive circuit 22 when a ground fault occurs in the power supply line L2 while the FET 1 and FET 4 are driven to open and close to rotate the motor 20 in the reverse direction. ing. The current at this time flows from the battery BATT to the ground fault path LE after passing through the FET 1 and the power supply line L2, so that the motor 20 is in a dead short state in which almost no current flows. Hereinafter, such a ground fault that causes a decrease in the motor current I is referred to as a dead short-side ground fault.

  FIG. 4B shows the current flow in the motor drive circuit 22 when a ground fault occurs in the power supply line L2 when the FET2 and FET3 are driven to open and close to rotate the motor 20 in the forward rotation direction. Show. The current at this time flows from the battery BATT to the ground fault path LE after passing through the FET 2, the power supply line L1, the motor 20, and the power supply line L2. Therefore, since the current flows without passing through the shunt resistor Rs, an excessive current flows through the motor 20, and as a result, the assist force generated by the motor 20 becomes excessive. Hereinafter, such a ground fault that causes an increase in the motor current I is referred to as an overcurrent-side ground fault.

In the motor control device of the present embodiment, the ground fault determination unit 33 determines whether or not the occurrence of ground faults on both the dead short side and the overcurrent side occurs in the following manner.
FIG. 5 is a flowchart of the ground fault determination process performed by the ground fault determination unit 33. This process is repeatedly executed every prescribed control period while the drive control of the motor 20 is being performed.

  When this process is started, first, in step S100, the duty ratio D calculated by the duty ratio calculator 32 and the detected value of the motor current I acquired by the electronic control unit 23 through the current detection circuit 28 are read. Subsequently, in step S101, based on the duty ratio D, two threshold values for determination, that is, an upper limit threshold value Imax and a lower limit threshold value Imin are calculated. These threshold values are calculated using the ground fault determination map MAP stored in the read-only memory of the electronic control unit 23. The ground fault determination map MAP stores the relationship between the duty ratio D, the upper limit threshold value Imax, and the lower limit threshold value Imin.

  FIG. 6 shows the relationship between the duty ratio D, the upper limit threshold value Imax, and the lower limit threshold value Imin in the ground fault determination map MAP. As shown in the figure, the upper limit threshold value Imax and the lower limit threshold value Imin are set to take larger values as the duty ratio D increases. Further, the lower limit threshold Imin is set to be a value smaller than the upper limit threshold Imax. The upper limit threshold Imax is set to a value obtained by adding a margin ΔI to the value of the motor current I assumed from the duty ratio D during normal operation (the estimated motor current Is). The lower limit threshold Imin is set as a value obtained by subtracting the margin ΔI from the estimated motor current value Is.

  When the upper limit threshold value Imax and the lower limit threshold value Imin are calculated, it is determined in step S102 whether or not the detected value of the motor current I is greater than or equal to the upper limit threshold value Imax or less than or equal to the lower limit threshold value Imin. Here, when a negative determination is made (S102: NO), that is, when the detected value of the motor current I is larger than the lower limit threshold Imin and smaller than the upper limit threshold Imax, in step S103, “ After it is determined that there is no connection, the current routine is terminated. On the other hand, if an affirmative determination is made (S102: YES), that is, if the detected value of the motor current I is equal to or greater than the upper threshold Imax, or if the detected value is equal to or smaller than the lower threshold Imin, in step S104, “with ground fault” It is determined. In step S <b> 105, the power supply stopping unit 34 is instructed to stop power supply to the motor 20, and then the process of this routine is terminated.

(Function)
In the motor control apparatus of the present embodiment described above, feedback control of the motor current I is performed through adjustment of the duty ratio D of the duty signal supplied to each gate of the FET1 to FET4 of the motor drive circuit 22. During normal operation, the motor current I maintains a high correlation with the duty ratio D. That is, the motor current I does not deviate much from the value assumed from the duty ratio D (the motor current assumed value Is).

  On the other hand, when a ground fault occurs in the power supply line L1 or L2, the motor current I shows a value greatly deviating from the expected motor current Is. When the generated ground fault is a dead short side ground fault, the motor current I becomes a value greatly deviating to the side where the motor current is assumed to be too small, and the generated ground fault is an over current side ground fault. In some cases, the motor current I is a value that is greatly deviated to an excessive side with respect to the estimated motor current value Is.

  In the present embodiment, when determining the ground fault, an upper limit threshold Imax and a lower limit threshold Imin are set according to the duty ratio D, respectively. If the detected value of the motor current I is equal to or higher than the upper threshold Imax or lower than the lower threshold Imin, it is determined that there is a ground fault, and the driving of the motor 20 is stopped. For this reason, it is determined that there is a ground fault when either the overcurrent side or dead short side ground fault occurs. Note that, as described above, the motor current I during normal operation does not deviate too much from the estimated motor current Is, and therefore it is erroneously determined even if the margin ΔI required for setting the upper limit threshold Imax and the lower limit threshold Imin is not increased too much. It is possible to avoid.

According to the motor control apparatus of the present embodiment described above, the following effects can be obtained.
(1) Whether or not the occurrence of ground faults on both the overcurrent side and the dead short side can be suitably determined.

  (2) Since power supply to the motor 20 is stopped according to the determination that a ground fault has occurred, it is possible to prevent an excessive current from flowing to the motor 20 and the motor drive circuit 22 due to the ground fault. As a result, it becomes possible to protect those components from overcurrent.

  (3) Since the erroneous determination can be avoided even if the margin for setting the determination value is reduced, the determination accuracy can be increased. Moreover, the determination can be performed in a shorter time from the occurrence of the ground fault.

  (4) If the motor control device performs feedback control of the motor current I, since the motor current I is detected from the start, it can be realized without adding a hardware configuration to the existing device. .

In addition, the said embodiment can also be changed and implemented as follows.
-Although the motor control apparatus of the said embodiment was applied to EPS comprised so that the assist force with respect to handle operation may be given by transmitting the rotational force which the motor 20 generate | occur | produces to the column shaft 12. The invention can be similarly applied to EPS having other configurations such as transmitting the rotational force of the motor 20 to the rack shaft 15.

  In the above embodiment, the current command value Ip and the motor rotation direction are calculated based on the vehicle speed V, the steering torque γ, and the motor rotation angle θm. A steering angle sensor for detecting the steering angle of the handle 10 is provided, and the current command value Ip and the motor rotation direction are calculated based on detection values other than the above, such as using the steering angle instead of the motor rotation angle θm. Good.

  -Although the motor drive circuit 22 of the motor control apparatus of the said embodiment was comprised so that motor current I might be adjusted by opening / closing drive of FET, it replaced with FET and provided the other switching element in the motor drive circuit 22 You may do it.

In the above embodiment, a single-phase DC motor is employed as the motor 20, but other motors such as a three-phase motor may be employed.
In the above embodiment, a single-phase DC motor is adopted as the motor 20, and when it is determined that there is a ground fault, the power supply to the motor 20 is completely stopped, and as a result, the steering operation assist by EPS is also stopped. It was supposed to be. If EPS is provided with a plurality of motors that apply assist force, it is possible to stop only the motor in which a ground fault has occurred and continue assisting steering operation by EPS with the remaining motors. In addition, when using a three-phase motor, the assist of steering operation by EPS is continued by the two-phase driving of the motor using two phases excluding the phase where power is supplied through the power line in which a ground fault has occurred. You can also

  In the above embodiment, the EPS motor control device that assists the steering operation by adding the motor power to the steering force applied to the steering wheel 10 by the driver has been described. The ground fault determination in the above embodiment can be similarly applied to a motor control device adopted in such a system other than EPS.

  BATT: battery, FET1 to FET4: field effect transistor, L1, L2 ... power supply line, Rs ... shunt resistor, 10 ... handle, 11 ... steering shaft, 12 ... column shaft, 13 ... intermediate shaft, 14 ... pinion shaft, 15 DESCRIPTION OF SYMBOLS ... Rack shaft, 16 ... Rack part, 17 ... Tie rod, 18 ... Steering wheel, 19 ... Knuckle arm, 20 ... Motor, 21 ... Reduction gear mechanism, 22 ... Motor drive circuit, 23 ... Electronic control unit, 24 ... Vehicle speed sensor, 25 ... Torque sensor, 26 ... Motor rotation angle sensor, 27 ... Motor relay, 28 ... Current detection circuit (current detection unit), 29a, 29b ... Voltage detection circuit, 30 ... Gate drive circuit, 31 ... Current command value calculation unit, 32 ... Duty ratio calculation part, 33 ... Ground fault determination part, 34 ... Power supply stop part.

Claims (3)

In a motor control device that generates a duty signal according to a current command value calculated for power supply to the motor and performs drive control of the motor according to the duty signal,
A current detector for detecting a current flowing through the motor;
A ground fault determination unit that determines that a ground fault has occurred in the power line of the motor when a current equal to or higher than an upper limit threshold set according to a duty ratio of the duty signal is detected by the current detection unit;
A motor control device comprising: The ground fault determination unit further sets a lower limit threshold value smaller than the upper limit threshold value according to a duty ratio of the duty signal, and when a current equal to or lower than the lower limit threshold value is detected by the current detection unit, The motor control device according to claim 1, wherein it is determined that a ground fault has occurred in the power line of the motor. 3. The motor control device according to claim 1, further comprising: a power supply stopping unit that stops power supply through the power line in which a ground fault has occurred when the ground fault determination unit determines that a ground fault has occurred.