JP5205973B2 - Control device for electric power steering device - Google Patents

Description

  The present invention relates to a control device for an electric power steering device that drives and controls a steering assist electric motor based on a steering assist command calculated based on a steering torque.

  In order to reduce the steering force of vehicles such as passenger cars and trucks, there is a so-called electric power steering (EPS) device that assists steering by a steering assist motor. In this electric power steering apparatus, the driving force of the steering assist motor is applied to the steering shaft or the rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer.

  In the control device for controlling the electric power steering device, feedback control of the current flowing through the steering assist motor is performed in order to accurately generate the steering assist torque. In this feedback control, the voltage applied to the steering assist motor is adjusted so that the difference between the current command value and the detected value of the current flowing through the steering assist motor becomes small. A PWM inverter is generally used for controlling the steering assist motor. When the PWM inverter is used, the voltage applied to the steering assist motor is adjusted by controlling the duty ratio of the PWM signal applied to the PWM inverter.

  The PWM inverter includes, for each phase, an arm circuit in which an upper switching element (upper arm element) and a lower switching element (lower arm element) are connected in series. For this reason, the PWM signal for controlling the PWM inverter is provided with a short-circuit prevention time called a dead time so that the upper and lower arm elements constituting each arm circuit are not turned on simultaneously. On the other hand, when a dead time is provided in the PWM signal, it is known that the output voltage and the output current are distorted due to an error generated between the voltage command applied to the PWM inverter and the actual output voltage. Note that the distortion of the output current appears as torque ripple, and thus has a considerable influence on the control characteristics of the electric power steering apparatus.

  As one of the conventional techniques for improving such a problem caused by dead time, there is, for example, the following Patent Document 1. In Patent Document 1, in order to compensate for distortion of the output voltage due to dead time, a square-wave compensation voltage is added to the voltage command applied to the PWM inverter in synchronization with the point where the output current of the PWM inverter crosses zero. Technology is disclosed.

JP 05-316737 A

  By the way, according to the prior art including the above-mentioned Patent Document 1, the dead time provided in the PWM signal is set to a predetermined value in a memory of a microcomputer as a control device and output. On the other hand, when a temperature change occurs in the switching element or the vicinity of the switching element, a substantial switching time in the switching element changes. For this reason, when controlling the electric power steering apparatus, there is a problem that a torque ripple increases due to a state of overcompensation or undercompensation due to a change in temperature environment around the switching element.

  The present invention has been made in view of the above, and is a control device for an electric power steering device capable of suppressing substantial dead time fluctuation caused by a change in temperature environment and suppressing occurrence of torque ripple. The purpose is to provide.

In order to solve the above-described problems and achieve the object, the present invention uses a PWM inverter to convert a steering assist electric motor based on a current command value calculated based on a steering torque generated in a steering system of a vehicle. In a control device for an electric power steering device that assists steering of the vehicle by driving control, a current control unit that receives the current command value and a PWM signal that generates a PWM signal necessary for controlling the PWM inverter A generation unit, a dead time compensation unit that generates and outputs a compensation voltage for suppressing an influence caused by a dead time provided in the PWM signal based on the current command value, and a voltage command value from the current control unit And a command duty for determining a command duty to be applied to the PWM signal generator based on the compensation voltage from the dead time compensation unit. A tee determination unit, based on said detected temperature detected temperature or ambient temperature of the switching element provided in the PWM inverter, the dead time corrected for dead time designated value which is set in advance imparted to the PWM signal generating unit A dead time correction unit that determines a correction value , and the functions of the current control unit, the dead time compensation unit, the command duty determination unit, and the dead time correction unit are embodied by software processing, whereas The function of the PWM signal generation unit is embodied by hardware processing. The PWM signal generation unit includes a first input for receiving the command duty from the command duty determination unit, and the dead time correction value from the dead time correction unit. A second input for receiving the current control unit, the dead time compensation unit, and the finger A control path of the duty determination unit, and a control path of the dead time compensation unit, characterized in that are separated from each other.

  Also, according to a preferred aspect of the present invention, the dead time correction unit corrects the dead time specified value to increase when the detected temperature fluctuates in a direction that increases, and the detected temperature decreases. It is desirable to correct so that the specified dead time becomes smaller.

  According to a preferred aspect of the present invention, it is desirable that the correction of the designated dead time value is further performed based on a detection voltage obtained by detecting a DC voltage applied to the PWM inverter.

  According to the control device for the electric power steering apparatus according to the present invention, the preset value is given to the PWM signal generation unit based on the detected temperature obtained by detecting the temperature of the switching element or the ambient temperature of the PWM inverter. Since the designated dead time value is corrected, a substantial change in dead time due to a change in temperature environment is suppressed, and the occurrence of torque ripple can be suppressed.

  Hereinafter, a control device for an electric power steering apparatus according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by the following embodiment. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or that are substantially the same.

<Embodiment>
FIG. 1 is a diagram illustrating a general configuration of an electric power steering apparatus. In FIG. 1, a column shaft 2 of a steering handle 1 is connected to a tie rod 6 of a steering wheel via a reduction gear 3, universal joints 4a and 4b, and a pinion rack mechanism 5. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque T of the steering handle 1, and a steering assist motor 20 that assists the steering force of the steering handle 1 is connected to the column shaft via the reduction gear 3. 2 is connected. Here, the steering assist motor 20 is, for example, a brushless motor or a brush motor. The control unit 30 that controls the electric power steering device is supplied with electric power from the battery 14 via the built-in power supply relay 13 and is supplied with an ignition signal from the ignition key 11. Further, the control unit 30 calculates a current command value for the steering assist motor 20 based on the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12, and the current of the steering assist motor 20 is calculated. Based on the detected value and the current command value, the steering assist motor 20 is drive-controlled so that the current detected value of the steering assist motor 20 follows the current command value.

(control unit)
FIG. 2 is a diagram showing a functional configuration of the control unit (control device) 30 according to the embodiment of the present invention. In the figure, for the sake of explanation, the steering assist motor 20, a drive unit such as an inverter circuit 66 for controlling the steering assist motor 20, a shunt resistor 68, a current detection circuit 70, a voltage detector 72, a temperature detector. Various sensors such as 74 are also shown.

  As shown in FIG. 2, the control device according to the present embodiment includes a control unit (software (SW) processing unit) 40 and a control unit (hardware (HW) processing unit) 42. The control unit (SW processing unit) 40 is a functional unit configured using, for example, a general-purpose processor such as a microcomputer, and each of these functions is embodied as software processing in which the CPU executes a program stored in the ROM. It becomes. On the other hand, the function of the control unit (HW processing unit) 42 is embodied as hardware processing by dedicated hardware. It goes without saying that a dedicated IC for a specific application such as an ASIC (Application Specific Integrated Circuit) may be used to realize the function of the control unit (HW processing unit) 42.

(Configuration of control unit-control unit (SW processing unit))
In FIG. 2, the control unit 40 includes a steering assist current command value calculation unit 44 that receives a torque signal, a dead time compensation unit 46 that receives the output of the steering assist current command value calculation unit 44, and a steering assist current command value calculation. The output of the unit 44 and the output signal of the AD converter 64 are input, and the outputs of the current control unit 48, the dead time compensation unit 46, and the current control unit 48 are input. And the command duty (hereinafter referred to as “command DUTY”) determination unit 50 that receives the output of the adder 82 as input, and the output signals of the dead time designation unit 52 and AD converters 60 and 62 And an adder 84 that receives the outputs of the dead time correction unit 54, the dead time specification unit 52, and the dead time correction unit 54, and a command DUTY determination unit 5 The output of the output of adder 84 is configured to be input to the control unit (HW processor) 42 provided in the next stage.

(Configuration of control unit-control unit (HW processing unit))
Further, the control unit 42 receives two outputs from the control unit 40, that is, the output of the command DUTY determination unit 50 and the output of the adder 84, and the output of the PWM signal generation unit 56 as an input. Detection output via the voltage detector 72 of the DC driver applied to the AD converter 60 and the inverter circuit 66 that receive the temperature detected by the gate driver 58 and the temperature detector 74 (hereinafter referred to as “detected temperature”). A detection output (hereinafter referred to as “detection current”) of the current flowing through the AD converter 62 (hereinafter referred to as “detection voltage”) and the current flowing through the shunt resistor 68 (hereinafter referred to as “motor current”) 70. And an output of the gate driver 58 is input to the inverter circuit 66. That is, the steering assist motor 20 is controlled by the output of the gate driver 58 via the inverter circuit 66, and the detected current (current corresponding to the motor current) is fed back to the current control unit 48, so that the detected voltage (inverter The voltage corresponding to the DC voltage applied to the circuit 66) and the detected temperature are fed back to the dead time correction unit 54.

  2 illustrates a configuration in which the gate driver 58 is provided inside the control unit 42 and the inverter circuit 66 is provided outside the control unit 42. However, the gate driver 58 may be provided outside the control unit 42. The gate driver 58 may be integrated with the inverter circuit 66. Further, both the gate driver 58 and the inverter circuit 66 may be incorporated in the steering assist motor 20. This latter configuration is as illustrated in FIG.

(Control unit operation)
Next, the operation of the control unit (control device) will be described. In FIG. 2, a steering assist current command value calculation unit 44 calculates and outputs a current command value for performing steering assist based on at least the torque signal (T). The current command value calculated by the steering assist current command value calculation unit 44 is input to the dead time compensation unit 46 and the subtractor 80. The subtractor 80 calculates a difference value between the input current command value and the detected current value and outputs the difference value to the current control unit 48. The dead time compensation unit 46 generates a compensation voltage for suppressing the influence due to the dead time based on the current command value, and outputs the compensation voltage to the adder 82. The compensation voltage generation processing performed by the dead time compensation unit 46 is appropriately disclosed in, for example, Japanese Patent Application No. 2005-12881, and detailed description thereof is omitted here.

  The adder 82 corrects an added value obtained by adding the input voltage command value (voltage command value before correction, hereinafter referred to as “first voltage command value”) and the compensation voltage (hereinafter referred to as “voltage command value after correction”). To the command DUTY determination unit 50 as a “second voltage command value”. The command DUTY determination unit 50 determines a command DUTY value based on the input second voltage command value, and outputs the determined command DUTY value as a parameter value to be given to the PWM signal generation unit 56.

  Also, the dead time correction unit 54 calculates a dead time correction value based on the detected voltage and the detected temperature, and outputs it to the adder 84. The adder 84 is an output of the dead time specifying unit 52 and is a fixed dead time specified value (hereinafter referred to as “first dead time specified value”). An added value obtained by adding the time correction value is calculated as a corrected dead time specified value (hereinafter referred to as “second dead time specified value”), and the calculated second dead time specified value is supplied to the PWM signal generation unit 56. Output as the parameter value to be assigned.

  The PWM signal generator 56 generates PWM signals (U, V, and W phases) to be given to the gate driver 58 based on the input command DUTY and the input second dead time designation value. To the inverter circuit 66. The inverter circuit 66 converts the PWM signal in each UVW phase into a positive / negative energization signal for each phase and outputs the converted signal to the steering assist motor 20.

  Next, supplementary matters regarding the operation of the control unit (control device) and the operation characteristics of the inverter circuit when a dead time is provided in the PWM signal for controlling the inverter circuit will be described with reference to FIGS. explain. In addition to this description, the effect of the control device according to the present embodiment will also be described.

  FIG. 3 is a diagram illustrating a command DUTY output from the command DUTY determination unit 50 and a PWM signal generated based on the command DUTY. In FIG. 3, waveforms K1 and K2 are reference signals for generating a PWM signal. Of these reference signals, the waveform K1 is used for generating a switching pattern for the high-side (upper arm side) switching element, and the waveform K2 is used for generating a switching pattern for the low-side (lower arm side) switching element. It is done. For example, in the case of the reference signal shown in the figure, if the command DUTY is about 70%, the on-time of the high-side switching element is long and the on-time of the low-side switching element is long as shown in the waveforms K3 and K4. A switching pattern (PWM signal) that is shortened is generated in the PWM signal generation unit 56. Incidentally, if the command DUTY is 100%, the high-side switching elements are all on and the low-side switching elements are all off. If the command DUTY is 0%, the high-side switching elements are all off and the low-side switching elements are all on.

  If the time difference between the falling portion of the waveform K3 and the rising portion of the waveform K4 is T1, and the time difference between the falling portion of the waveform K4 and the rising portion of the waveform K3 is T2, the dead time in the PWM signal shown in this example Td is given by Td = T1 + T2. When the waveform K1 and the waveform K2 are matched (corresponding to the case where the second dead time designation value output from the adder 84 is “zero” in FIG. 2), the dead time Td is zero. Become.

  FIG. 4 is a diagram for explaining a dead band (dead band) generated near the zero ampere cross by setting the dead time. In FIG. 4, the horizontal axis represents the command DUTY, and the vertical axis represents the current.

  When controlling an inverter circuit with a PWM signal waveform having a dead time, a dead band of a predetermined width called a dead band near the zero cross as shown in FIG. 4 (region where the current direction is switched from negative to positive or from positive to negative). An area appears. The width of this dead band varies depending on the characteristics of the switching element used in the inverter circuit, the body diode connected in parallel to the switching element, or the characteristics of the gate driver that drives the switching element, and is set to the PWM signal. It also changes depending on the dead time. On the other hand, when such a dead band exists, even if the command DUTY determination unit 50 gives the desired command DUTY to the PWM signal generation unit 56, the current switching is not performed appropriately, so the PWM signal generation unit 56 An error occurs between the voltage command value for and the actual output voltage value, and the output current (phase current) is distorted. Therefore, in the presence of such a dead band, it is preferable to perform control to change the command DUTY according to the width of the dead band in the vicinity of the zero cross where the current flowing through the inverter circuit is switched.

  In the present embodiment, as described above, the second voltage command generated by adding the compensation voltage generated by the dead time compensation unit 46 to the first voltage command value generated by the current control unit 48. This is realized by outputting the value to the command DUTY determination unit 50.

  FIG. 5 is a diagram showing a typical example of the dead band width with respect to the temperature of the switching element or the ambient temperature. In FIG. 5, the horizontal axis represents temperature, and the vertical axis represents dead band width (see FIG. 4). As shown in FIG. 5, the dead band width varies depending on the temperature environment. Further, the fluctuation has a characteristic that it becomes smaller when the temperature becomes higher and becomes larger when the temperature becomes lower.

  FIG. 6 is a diagram showing current characteristics during overcompensation in the vicinity of the zero ampere cross. That is, the current characteristics shown in FIG. 6 correspond to a case where the temperature changes in a direction in which the temperature increases, for example, without the dead time specifying unit 52, the dead time correcting unit 54, and the adder 84 shown in FIG. Is. In the waveform shown in FIG. 6, a distortion current as shown by a broken line portion M1 in the same figure is generated near the zero cross where the current switches from the negative direction to the positive direction. Further, a portion indicated by a broken line portion M2 in the figure shows the characteristic of the current control unit 48 that attempts to restore the suddenly changed current. The current distortion is also increased by the operation of the current control unit 48 indicated by the broken line portion M2.

  FIG. 7 is a diagram illustrating the concept of the dead time correction table, in which the horizontal axis indicates temperature, and the vertical axis indicates the dead time correction value output from the dead time correction unit 54 to the adder 84 (see FIG. 2). In FIG. 7, for example, when the horizontal axis “0” and the vertical “0” cross each other, the dead time correction value output from the dead time correction unit 54 is “zero”. is there. That is, the specified value by the dead time specifying unit 52 is output as a parameter value for the PWM signal generating unit 56.

  On the other hand, for example, when the temperature fluctuates in the direction of increasing, the dead time specified value is corrected, and when the temperature fluctuates in the direction of decreasing, the dead time specified value is corrected. . The operation at this time can be explained as follows.

  As shown in FIG. 6, when the temperature becomes high, an overcompensation state is established. This is due to the characteristic (see FIG. 5) that the dead band width decreases when the temperature increases. That is, when the temperature increases, the compensation amount (compensation voltage) by the dead time compensation unit 46 is overcompensated by the amount corresponding to the reduction of the dead band. Therefore, in the present embodiment, for example, when the temperature becomes high, the dead time correction value is increased so that the value of the dead time itself is increased. As the dead time increases, the dead band becomes wider and is offset by the reduced component due to the temperature rise, and the substantial dead time can be made constant before and after the temperature change. In addition, when the temperature is low, the idea of dead time correction is the same except that the compensation is insufficient. In other words, the dead time correction value may be reduced and the dead time itself may be controlled so as to cancel out the dead band expansion component due to the temperature drop.

  In the present embodiment, as shown in FIG. 2, not only the detected temperature information but also the detected voltage information for detecting the magnitude of the DC voltage applied to the inverter circuit 66 is input. ing. The gist of this configuration is that dead band fluctuations are caused not only by temperature fluctuations but also by DC voltage fluctuations. However, in general, in a normal steering state, the fluctuation of the DC voltage is smaller than the temperature fluctuation, and therefore the configurations of the voltage detector 72 and the AD converter 62 may be omitted.

  As described above, according to the control device according to the present embodiment, the PWM signal generation unit 56 is provided based on the detected temperature at which the temperature of the switching element provided in the inverter circuit 66 or the ambient temperature is detected. Since the specified dead time value is corrected, a substantial change in dead time due to a change in temperature environment is suppressed, and the occurrence of torque ripple can be suppressed.

  Moreover, according to the control apparatus concerning this Embodiment, there exists an advantage that desired temperature compensation is attained, without changing the control program of a dead time compensation part. In other words, in the control device according to the present embodiment, the change of the dead time according to the change of the temperature environment is given to the PWM signal generation unit 56 using the second dead time designation value as a parameter, that is, the hardware Since it is realized by the function, it is not necessary to change the control program including the dead time compensation unit. In addition, by adopting a functional configuration based on this concept of control processing, it is not necessary to consider changes in the temperature environment in the function unit that performs software processing using the control program, minimizing the impact on existing functions. It becomes possible to do.

  Further, in the conventional configuration, the dead time tends to increase in a low temperature environment, so that the passage time of the current flowing through the body diode of the switching element becomes long and the loss increases. On the other hand, according to the control device according to the present embodiment, the substantial dead time when driving the switching element can be kept substantially constant regardless of the temperature environment, so that a stable increase in loss can be suppressed. Control can be performed.

  As described above, the control device for the electric power steering apparatus according to the present invention is useful as an invention capable of suppressing the fluctuation of the substantial dead time due to the change of the temperature environment and suppressing the occurrence of torque ripple. is there.

It is a figure which shows the general structure of an electric power steering apparatus. It is a figure which shows the function structure of the control unit (control apparatus) concerning embodiment of this invention. It is a figure explaining the PWM signal produced | generated based on the instruction | command DUTY output from the instruction | command DUTY determination part, and the instruction | command DUTY. It is a figure explaining the dead band (dead zone) which arises near zero ampere crossing by the setting of dead time. It is a figure which shows a typical example of the dead band width with respect to temperature. It is a figure which shows the electric current characteristic at the time of the overcompensation in the zero-ampere cross vicinity. It is a figure which shows the concept of a dead time correction table.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering handle 2 Column shaft 3 Reduction gear 4a, 4b Universal joint 5 Pinion rack mechanism 6 Tie rod 10 Torque sensor 11 Ignition key 12 Vehicle speed sensor 13 Power supply relay 14 Battery 20 Steering auxiliary motor 30 Control unit 40 Control part (SW processing part)
42 Control unit (HW processing unit)
44 Steering Auxiliary Current Command Value Calculation Unit 46 Dead Time Compensation Unit 48 Current Control Unit 50 Command Duty Determination Unit 52 Dead Time Designation Unit 54 Dead Time Correction Unit 56 PWM Signal Generation Unit 58 Gate Driver 60, 62, 64 AD Converter 66 Inverter Circuit 68 Shunt resistor 70 Current detection circuit 72 Voltage detector 74 Temperature detector 80 Subtractor 82, 84 Adder

Claims (3)

An electric power steering apparatus for assisting steering of the vehicle by driving and controlling a steering assist electric motor using a PWM inverter based on a current command value calculated based on a steering torque generated in a steering system of the vehicle. In the control device,
A current control unit that inputs the current command value;
A PWM signal generator for generating a PWM signal necessary for controlling the PWM inverter;
A dead time compensator that generates and outputs a compensation voltage for suppressing the influence of the dead time provided in the PWM signal based on the current command value;
A command duty determination unit that determines a command duty to be applied to the PWM signal generation unit based on a voltage command value from the current control unit and a compensation voltage from the dead time compensation unit;
Based on a detected temperature obtained by detecting the temperature of the switching element provided in the PWM inverter or the ambient temperature, a dead time correction value that is set in advance and corrects the dead time specified value given to the PWM signal generation unit is determined . A dead time correction unit;
Equipped with a,
The functions of the current control unit, the dead time compensation unit, the command duty determination unit, and the dead time correction unit are realized by software processing, whereas the function of the PWM signal generation unit is realized by hardware processing. ,
The PWM signal generation unit has a first input for receiving the command duty from the command duty determination unit, and a second input for receiving the dead time correction value from the dead time correction unit,
The electric power steering apparatus characterized in that a control path of the current control unit, the dead time compensation unit and the command duty determination unit and a control path of the dead time correction unit are separated from each other. Control device. The dead time correction unit is
When the detected temperature fluctuates in the direction of increasing, correct the dead time specified value to be large,
The control device for an electric power steering apparatus according to claim 1, wherein when the detected temperature fluctuates in a decreasing direction, the dead time specified value is corrected to be small.   2. The control device for an electric power steering apparatus according to claim 1, wherein the correction of the dead time specified value is further performed based on a detection voltage obtained by detecting a DC voltage applied to the PWM inverter.

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