JP4967767B2 - Electric power steering control device - Google Patents

Description

  The present invention relates to an electric power steering control device that applies a steering assist force by a motor to a steering mechanism of a vehicle such as an automobile.

  An electric power steering device used as a steering assist device for a vehicle such as an automobile energizes a steering assist force by transmitting the rotational torque of a motor to a steering shaft and a rack shaft directly connected to a steering handle via a reduction gear. It is supposed to be. The electric power steering apparatus includes an electric power steering control apparatus including a control circuit that controls the motor to generate a desired torque, a motor drive circuit that supplies current to the motor, and the like.

  FIG. 8 is a block diagram showing a schematic configuration of a general electric power steering control device. The electric power steering control device 2 includes a phase compensator 21 that calculates a torque command value that is phase-compensated based on the steering torque detected by the torque sensor 31, and a motor based on the steering torque and the vehicle speed detected by the vehicle speed sensor 32. A current command calculator 22 that calculates a current command value I that is a control target value of a current that drives the motor 20, and a current command value I and a motor current (current detection value) i detected by a motor current detection circuit 29 described later. A subtractor 23 that calculates the deviation current ΔI, a differential compensator 24 that differentiates the current command value I to improve the transient response, and a proportional calculator 25 that proportionally processes the deviation current ΔI by multiplying a predetermined proportional gain. In addition, the outputs of the integration calculator 26 that performs a predetermined integration process to improve the characteristics of the feedback system, the differential compensator 24, the proportional calculator 25, and the integration calculator 26 are added. An adder 27 that calculates a current control value E, a motor drive circuit 28 that generates a current to be supplied to the motor 20 based on the current control value E, and a motor current detector 29 that detects a motor current i flowing through the motor 20. It is composed of The battery 33 is a power source for the motor drive circuit 28.

  In the electric power steering control device 2 configured in this way, the motor current i detected by the motor current detection unit 29 is fed back to the subtractor 23 and controlled so that the deviation current ΔI becomes zero, thereby assisting the steering assist. Control is realized.

  FIG. 9 is a diagram showing a schematic configuration of the motor drive circuit 28. In the figure, the motor drive circuit 28 is a PWM (pulse width modulation) signal having a duty ratio determined based on the field effect transistors FET1 to FET4 constituting the H-bridge circuit and the current control value E sent from the adder 27. And a dead time circuit 282, 283, and an FET gate drive circuit 284 for driving the gates of the FETs 1 to 4, and the power source 33 is connected to drive the high side of the FETs 1 and 2. Has been.

  Here, the upper and lower arms FET1 and FET3 constituting the H bridge circuit are alternately turned on and off, and similarly, FET2 and FET4 are alternately turned on and off. However, the FETs 1 to 4 are not instantaneously turned on and off by the input of the gate signal, but always have a turn-on time and a turn-off time. For this reason, when the ON signal to the gate of FET1 and the OFF signal to the gate of FET3 are input simultaneously, FET1 and FET3 are simultaneously turned on, and the upper and lower arms are short-circuited. Therefore, a dead time circuit 282 for inserting a predetermined short-circuit prevention time (dead time) is inserted between the PWM controller 281 and the FET gate drive circuit 284 so that the FET 1 and the FET 3 do not turn on simultaneously. . Similarly, a dead time circuit 283 is inserted so that FET2 and FET4 do not turn on simultaneously.

  By the way, the presence of dead time in the electric power steering control device causes distortion in the motor current, which causes torque ripple and abnormal noise. As a method for solving this problem, conventionally, in order to avoid the influence of the dead time, a method of applying a dead time compensation amount to the command value of the motor has been proposed (see, for example, Patent Document 1).

  In addition, when applying the dead time compensation amount, it is necessary to make the polarities of the dead time compensation amount and the motor current coincide with each other and to accurately determine the timing at which the zero crossing of the motor current occurs.

JP 2006-199140 A

  As for the determination of this timing, a method that is performed when the motor current i is directly detected and the detected value crosses zero, or a method that is performed when the current command value I crosses zero is known. Among these, in the former method, if there is a delay in the motor current detection circuit, the timing is delayed from the zero cross of the motor current i, and in addition to this, the detection value includes noise and the detection accuracy is impaired. There was a problem. In the latter method, the motor current i often lags behind the current command value I due to the responsiveness of the motor drive circuit. Therefore, the timing is earlier than the zero cross of the motor current i. was there.

  In addition, general dead time compensation is applied individually to each phase even when the motor has a plurality of phases. For this reason, the voltage balance with other phases deteriorates. As a result, the motor current may be distorted, which causes the timing of dead time compensation to deviate, which is a factor that impairs the stability of dead time compensation.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electric motor that can suppress the distortion of the motor current, reduce the occurrence of torque ripple and abnormal noise, and perform stable dead time compensation. It is to provide a power steering control device.

  In order to achieve the above-described object, an electric power steering control device according to the present invention is characterized by the following (1) and (2).

  (1) A motor for applying a steering assist force to the steering mechanism, a current command value calculation means for calculating a current command value based on the detected steering torque, and a current control value for the motor based on the current command value An electric power steering control device comprising: current control means for controlling the motor current based on the current control value; motor drive means for controlling the current of the motor; and dead time compensation means for compensating for the dead time of the motor drive means. The dead time compensation means estimates a current applied to the motor based on the current command value, and outputs a current control model that outputs the estimation result as a model current value, and determines a zero cross of the model current value Zero-cross determination means, zero-cross determination means for determining the polarity of the model current value, and a deck based on the model current value. A dead time compensation amount calculating means for calculating a time compensation amount, a dead time compensation waveform signal generating means for generating a dead time compensation waveform signal that changes at a gentle slope based on the determined polarity, and a dead time compensation waveform signal Multiplying means for multiplying the determined polarity and the calculated dead time compensation amount, and adding the output of the multiplying means to the current control value.

  (2) In the electric power steering control device described in (1) above, when the motor has a plurality of phases, the dead time compensation means further outputs the output of the multiplication means for each phase. An averaging means for averaging is provided, and an output of the averaging means is added to the current control value.

  According to the electric power steering control device described in (1) above, based on the model current value generated based on the current command value, the polarity and the zero cross are determined and the compensation amount is calculated. For example, a stepped dead time compensation signal that changes slowly with respect to the reference is generated, and the dead time compensation amount obtained by multiplying the signal by the polarity and the compensation amount is added to the current control value. Is suppressed, torque ripple and abnormal noise are reduced, and stable dead time compensation can be performed.

  In addition, according to the electric power steering control device described in (2) above, in addition to the characteristics of (1) above, the dead time compensation amount of each phase is added and averaged, and the resulting dead time compensation amount is obtained. Is added to the current control value, so if the motor has multiple phases, the balance between the applied voltages of each phase is improved, distortion of the motor current is further suppressed, and torque ripple and abnormal noise are generated. Therefore, more stable dead time compensation can be performed.

  According to the present invention, it is possible to provide an electric power steering control device that can suppress the distortion of motor current, reduce the occurrence of torque ripple and abnormal noise, and perform stable dead time compensation.

  Hereinafter, an embodiment of an electric power steering control device according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an electric power steering control device according to the present embodiment.

  In FIG. 1, an electric power steering control device 1 drives a motor 10 based on a steering torque signal detected by a torque sensor, and calculates a current command value calculation unit 11 that calculates a current command value I that is a current control target value. A subtractor 12 that calculates a deviation current ΔI between a current command value I and a current detection value i detected by a motor phase current detection unit 17 described later. In order to control the drive of the motor, the deviation current ΔI is controlled to be zero. The current control unit 13 for performing the control, the dead time compensation unit 14 for generating the dead time compensation amount of the motor phase current based on the current command value I, and adding the dead time compensation amount to the output of the current control unit 13 to obtain the current control value E , The motor drive circuit 16 for generating a phase current to be supplied to the motor 10 based on the current control value E, and the phase current applied to the motor 10 as the current detection value i. As shown in FIG.

  In the electric power steering control device 1 configured as described above, the current detection value i detected by the motor phase current detection unit 17 is fed back to the subtractor 12, and a deviation current ΔI between the current command value I and the current detection value i is detected. Steering assist control is realized by performing control so as to be zero. The motor 10 is a three-phase brushless DC motor, and steering assist control is performed in accordance with each phase of the motor 10.

  FIG. 2 is a block diagram showing a schematic configuration of the dead time compensation unit 14 in the electric power steering control apparatus 1 described above.

  In FIG. 2, the dead time compensator 14 predefines the relationship between the current command value I and the phase current applied to the motor as, for example, a first-order lag model (transfer function) that also considers the control period. Based on the output value of the current control model unit 140, the current control model unit 140, the polarity determination unit 141 that determines the polarity to be given to the dead time compensation amount, and the zero crossing based on the output value of the current control model unit 140 A zero cross determination unit 142 that determines timing (zero cross point), a dead time compensation amount calculation unit 143 that calculates a dead time compensation amount from the output value of the current control model unit 140, and a staircase pattern based on the determined zero cross point The dead time compensation waveform signal generator 144 for generating the dead time compensation waveform signal and the dead time compensation waveform signal A multiplier 145 that multiplies the dead time compensation amount calculated by the time compensation amount calculation unit 143 and the polarity determined by the polarity determination unit 141 individually for each phase, and averages the output of each phase of the multiplier 145. And an averaging unit 146.

  The current control model unit 140 uses the current command value I (without the influence of detection noise) to avoid the influence of the detection noise included in the current detection value i of the motor phase current detection unit 17, for example. The current detection value i is estimated from the value I. That is, the current control model unit 140 converts the current command value I using a first-order lag transfer function, and generates a model current value that is substantially equivalent to the detected current value i of the motor 10 as an estimated value. , Output to the polarity determination unit 141, the zero cross determination unit 142, and the dead time compensation amount calculation unit 143, respectively. Thereby, the polarity of the actual motor current and the accuracy of determining the zero crossing can be improved.

  The polarity determination unit 141 determines the polarity of the model current value corresponding to the current command value I of the current control model unit 140 using a comparator or the like, and thereby determines the polarity of the actual motor current (detected current value) i. A result almost equivalent to the above can be obtained.

  Here, an operation flow of the polarity determination unit 141 will be described. FIG. 3 is a flowchart for explaining the processing procedure of the polarity determination unit 141.

  First, it is determined whether or not the model current value input from the current control model unit 140 exceeds a preset threshold value (ie, S101). As a result, when it is determined that the threshold value is exceeded, it is determined that the polarity of the actual motor current i is positive, and the polarity (+1) is output (that is, S102).

  On the other hand, if the result of determination in S101 is that the model current value does not exceed the threshold value, it is determined that the polarity of the motor current i is negative, and the polarity (-1) is output (ie, S103).

  The zero-cross determination unit 142 determines a time when the motor current i corresponding to the current command value I of the current control model unit 140 passes through the zero point, that is, a time when the polarity of the motor current i is switched (zero-cross). Thereby, the timing of the zero crossing of the motor current i can be estimated.

  Here, an operation flow of the zero cross determination unit 142 will be described. FIG. 4 is a flowchart for explaining the processing procedure of the zero-cross determination unit 142.

  First, it is determined whether or not the sign of the model current value input from the current control model unit 140 is the same as the sign of the model current value input last time (ie, S201). As a result, when it is determined that the codes are the same, it is determined that there is no zero cross (that is, S202). Thereafter, the sign of the model current value input last time is updated to the current input (ie, S204).

On the other hand, if the sign of the model current value input from the current control model unit 140 is different from the sign of the model current value input last time as a result of the determination in S201, it is determined that there is a zero cross (that is, S203). Thereafter, the sign of the model current value inputted last time is updated (ie, S204).
As a result, the zero cross determination unit 142 can determine the zero cross point and output the determination result to the dead time compensation waveform signal generation unit 144.

  The dead time compensation waveform signal generation unit 144 generates a dead time compensation amount waveform signal to be added to the output of the current control unit 13, and determines the zero cross point of the model current value based on the determination result of the zero cross determination unit 142. As a reference, a dead time compensation waveform signal having, for example, a stepped waveform, which changes at a gentle slope, is generated. That is, the dead time compensation waveform signal generation unit 144 measures the timing for performing the dead time compensation at the time of the zero crossing, and even if the processing is delayed and the timing is shifted, the dead time compensation waveform signal is a stepped waveform. Therefore, it also has a function of suppressing the influence of the deviation.

  FIG. 5 is a diagram showing the dead time compensation waveform signal generated by the dead time compensation waveform signal generator 144 in comparison with the conventional dead time compensation waveform signal.

The conventional dead time compensation waveform signal shown in FIG. 5 (a) is a step-like waveform signal whose polarity is inverted at the time of zero crossing. On the other hand, the dead time compensation waveform signal shown in FIG. The time-compensated waveform signal is a signal having a waveform that changes stepwise with respect to the zero-cross point.
The dead time compensation waveform signal preferably takes a unit value such as 1 as the absolute value of the maximum value and the minimum value in consideration of the relationship with the dead time compensation amount calculation unit described later.

  Based on the model current value corresponding to the current command value I of the current control model unit 140, the dead time compensation amount calculation unit 143 sets the dead time compensation amount to be given to the output of the current control unit 13 according to a preset relational expression. Calculate according to each phase and output to each. The relational expression may be defined as a model of a predetermined transfer function or a conversion table obtained experimentally.

  The multiplier 145 multiplies the dead time compensation waveform signal by the polarity of the model current value determined by the polarity determination unit 141 and the dead time compensation amount calculated by the dead time compensation amount calculation unit 143 to obtain the polarity. The amount of dead time compensation is calculated. These dead time compensation amounts are output according to each phase.

  The averaging unit 146 outputs the output of each phase of the multiplier 145 in order to stabilize the balance of the dead time compensation amount of each phase given to the output of the current control unit 13 in each phase current of the motor 10. It is to be averaged. FIG. 6 is a diagram illustrating a schematic configuration of the averaging unit 146.

  In FIG. 6, each phase output from the multiplier 145 is input to adders 147a and 147b and subtracters 148u, 148v and 148w corresponding to the respective phases.

  The adders 147a and 147b add all the phase outputs of the multiplier 145, and the divider 149 divides the added output and averages each phase output of the multiplier 145, for example, 1 / The average value is calculated by dividing by 3 and input to the subtracters 148u, 148v and 148w corresponding to each phase of the motor 10. The subtracters 148u, 148v, and 148w subtract the average value obtained by the divider 149 from the output of the multiplier 145 for the corresponding phase to generate a dead time compensation amount for each phase.

  The dead time compensation amount generated by the dead time compensation unit 14 configured as described above is added to the output of the current control unit 13 by the adder 15 to generate a current control value E to be supplied to the motor drive circuit 16.

  FIG. 7 is a diagram showing the waveform of the dead time compensation amount of each phase output from the averaging unit 146 in comparison with the phase current i of the motor 10. As shown in FIG. 7B, the timing of applying the dead time compensation amount is synchronized with the actual motor current zero crossing shown in FIG. 7A, so that the current balance of each phase of the motor is improved. At the same time, distortion in the vicinity of the zero cross of the motor current is improved, and the occurrence of torque ripple and abnormal noise can be reduced to stably perform dead time compensation.

  As described above, according to the electric power steering control apparatus according to the embodiment of the present invention, the determination of the polarity and zero cross timing and the compensation amount are performed based on the model current value of the current control model, and the determination is made. Each phase is averaged by multiplying the dead time compensation waveform signal generated based on the zero crossing time point by the polarity and the compensation amount. Then, this is added to the output of the current control unit as a dead time compensation amount to obtain a current control value, which is supplied to the motor drive circuit to control the motor current. Thereby, distortion of the motor current is reduced, occurrence of torque ripple and abnormal noise is reduced, and dead time compensation can be performed stably.

  The description of the specific embodiments is finished above, but the aspect of the present invention is not limited to these embodiments, and modifications, improvements, and the like can be made as appropriate. For example, in the present embodiment, most of the processing is performed by software, but a part or all of the processing may be realized by hardware such as FPGA (Field Programmable Gate Array).

  Further, the present invention can be applied to any type of electric power steering apparatus (column type, pinion type, rack type).

  Furthermore, in the embodiments, the three-phase brushless DC motor has been described as an example. However, the present invention is not limited to this, and single-phase is, of course, applicable to a motor having a plurality of various phases such as a synchronous motor. can do.

It is a block diagram showing a schematic structure of an electric power steering control device concerning an embodiment of the present invention. It is a block diagram which shows schematic structure of the dead time compensation part which concerns on embodiment of this invention. It is a flowchart for demonstrating the process sequence of the polarity determination part which concerns on this embodiment. It is a flowchart for demonstrating the process sequence of the zero cross determination part which concerns on this embodiment. (A) is a figure which shows the conventional dead time compensation waveform signal, (b) is a figure which shows the dead time compensation waveform signal which concerns on embodiment of this invention. It is a figure which shows schematic structure of the averaging part which concerns on this embodiment. (A) is a figure which shows the waveform of a motor phase electric current, (b) is a figure which shows the waveform of the dead time compensation amount which concerns on embodiment of this invention. It is a figure which shows schematic structure of a general electric power steering apparatus. It is a block diagram which shows schematic structure of the conventional motor drive circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering control apparatus 10 Motor 11 Current command value calculating part 12 Subtractor 13 Current control part 14 Dead time compensation part 15 Adder 16 Motor drive circuit 17 Motor phase current detection part 140 Current control model part 141 Polarity determination part 142 Zero cross Determining unit 143 Dead time compensation amount calculating unit 144 Dead time compensation waveform signal generating unit 145 Multiplier 146 Averaging unit

Claims (2)

A motor for applying a steering assist force to the steering mechanism; a current command value calculating means for calculating a current command value based on the detected steering torque; and a current control for generating a current control value for the motor based on the current command value An electric power steering control device comprising: means; motor driving means for controlling the current of the motor based on the current control value; and dead time compensation means for compensating for dead time of the motor driving means,
The dead time compensation means is
A current control model that estimates the current applied to the motor based on the current command value, and outputs the estimation result as a model current value;
Polarity determination means for determining the polarity of the model current value;
Zero-cross determination means for determining the timing of occurrence of zero-cross in the model current value;
Dead time compensation waveform signal generating means for generating a dead time compensation waveform signal that changes at a gentle slope with respect to the timing at which the zero cross occurs, and
A dead time compensation amount calculating means for calculating a dead time compensation amount based on the model current value;
Multiplication means for multiplying the dead time compensation waveform signal by the determined polarity and the calculated dead time compensation amount, and adding the output of the multiplication means to the current control value. Electric power steering control device. If the motor has multiple phases,
The dead time compensation means further includes:
Averaging means for averaging the output of the multiplication means for each phase;
The electric power steering control device according to claim 1, wherein the output of the averaging means is added to the current control value.

Images