JP4617895B2 - Control device for electric power steering device - Google Patents

Description

  The present invention relates to a control device for an electric power steering device in which a steering assist force by a motor is applied to a steering system of an automobile or a vehicle, and in particular, an electric power in which dead band control of an inverter for driving a motor is improved according to a steering state. The present invention relates to a control device for a steering device.

  An electric power steering device that energizes an automobile or vehicle steering device with the rotational force of a motor assists the steering shaft or rack shaft with a transmission mechanism such as a gear or a belt via a reduction gear. Energize power. In order to supply current to the motor so that the motor generates a desired torque, an inverter or the like is used in the motor drive circuit.

  Here, FIG. 9 shows a basic configuration of a control device of a conventional electric power steering device disclosed in Japanese Patent Laid-Open No. Hei 8-142288 (Patent Document 1), and the operation thereof will be described.

  Torque detected by the torque sensor 103 is input to the phase compensator 121, and a torque command value is calculated. Further, the torque command value is input to the current command calculator 122, and the current command value Iref is calculated by the current command calculator 122 in consideration of the vehicle speed detected by the vehicle speed sensor 112. In this control, feedback control is employed, and the current i of the motor 110 to be controlled is detected by the motor current detection circuit 142 and fed back to the subtractor 123. A subtractor 123 calculates a deviation (= Iref−i) between the current command value Iref and the motor current. The deviation is subjected to so-called proportional integration control by the proportional calculator 125 and the integral calculator 126 and is input to the adder 127. The current command value is input to the differential compensator 124 for improving the transient response, and the outputs of the differential compensator 124, the proportional calculator 125, and the integral calculator 126 are added by the adder 127 to calculate the current control value E. The current control value E is input to the motor drive circuit 141. The motor drive circuit 141 supplies current to the motor 110 based on the current control value E. The battery 114 is a power source for the motor drive circuit 141.

  The motor drive circuit 141 is configured as shown in FIG. 10, and the motor drive circuit 141 includes an inverter unit composed of FETs 1 to 4 serving as switching elements and a gate control unit that controls each gate of the FETs 1 to 4. It is configured. The inverter part is composed of an upper and lower arm made up of FET1 and FET3 and an upper and lower arm made up of FET2 and FET4 to form an H bridge. The current control value E is input to the conversion unit 130 of the gate control unit, and the conversion unit 130 generates a timing signal for each of the FETs 1 to 4, and the timing signal is input to the gate drive circuits 133 a, 134 a, 133 b, and 134 b. A gate signal capable of driving each of the four gates is generated. However, the timing signal generated by the conversion unit 130 is not directly input to the gate drive circuits 134a and 134b but is input to the dead time circuit 131 and the dead time circuit 132, respectively, for the following reason.

  The upper and lower arms constituting the inverter unit, for example, FET1 and FET3 are alternately turned on and off, and similarly, FET2 and FET4 are alternately turned on and off. However, the FET is not an ideal switch and does not turn on and off instantaneously as instructed by the gate signal, and requires a turn-on time and a turn-off time. For this reason, when an instruction to turn on FET1 and an instruction to turn off FET3 are simultaneously issued, there is a problem in that FET1 and FET3 are simultaneously turned on and the upper and lower arms are short-circuited. Therefore, when an off signal is given to the gate drive circuit 133a so that the FET1 and FET3 are not turned on at the same time, an on signal is not given immediately to the gate drive circuit 134a, and the dead time circuit 131 has a predetermined time of dead time. By giving an ON signal to the gate drive circuit 134a at an interval, the upper and lower short circuits of the FET1 and FET3 are prevented. This applies to FET2 and FET4 as well.

  However, the existence of this dead time causes a problem of torque shortage and torque ripple for the control of the electric power steering apparatus. Hereinafter, this problem will be described in detail.

  First, the dead time, turn-on time, and turn-off time will be described with reference to the time chart of FIG. A signal K from the conversion unit 130 illustrated in FIG. 11A is an on / off signal for the FET1 and FET3. However, actually, the gate signal K1 shown in FIG. 11B is given to the FET1, and the gate signal K2 shown in FIG. 11C is given to the FET3. That is, the dead time Td is ensured for both the gate signals K1 and K2. A terminal voltage composed of the FET1 and the FET3 is assumed to be Van shown in FIG. Even if an ON signal by the gate signal K1 is given, the FET 1 is not immediately turned on, and it is turned on taking a turn-on time Ton. Even if an OFF signal is given, the FET 1 is not turned off immediately, and a turn-off time Toff is needed. is doing. Vdc is the power supply voltage of the inverter (the voltage of the battery 114).

Therefore, the total delay time Ttot is expressed by the following equation (1).

Ttot = Td + Ton−Toff (1)

Here, the turn-on time Ton and the turn-off time Toff vary depending on the type and capacity of the FET and IGBT to be used. The dead time Td is generally larger than the turn-on time Ton and the turn-off time Toff.

  Next, the influence of the dead time Td will be described.

First, the influence on the voltage is as follows. As shown in FIG. 11, the actual gate signals K1 and K2 with respect to the ideal gate signal K are different from the gate signal K due to the influence of the dead time Td. As a result, distortion occurs in the voltage. The distortion voltage ΔV is expressed by the following equation (2) when the direction of the motor current is positive (when the direction of the current flows from the power source to the motor), and the direction of the current is negative. In the case (when the direction of current flows from the motor to the power source), the following equation (3) is obtained.

−ΔV = − (Ttot / Ts) · (Vdc / 2) (2)
Here, Ts is the reciprocal Ts = 1 / fs of the PWM frequency Fs when the inverter is PWM-controlled.

ΔV = (Ttot / Ts) · (Vdc / 2) (3)

When the above equations (2) and (3) are expressed by one equation, the following equation (4) is obtained.

ΔV = −sign (Is) · (Ttot / Ts) · (Vdc / 2) (4)
Here, sign (Is) represents the polarity of the motor current.

What is derived from the above equation (4) is that the distortion voltage ΔV has a higher frequency fs, and the larger the power supply voltage Vdc, the greater the influence of the dead time Td.

  Although the influence of the dead time Td on the voltage distortion has been described, the current or torque also has an undesirable influence due to the dead time Td. Regarding the current distortion, a phenomenon (zero clamping phenomenon) in which the current sticks to near zero when the current changes from positive to negative or from negative to positive is caused by the dead time Td. This is because the load (motor) is an inductance, and the voltage decrease due to the dead time Td tends to keep the current at zero.

  Further, the influence of the dead time Td on the torque appears in a shortage of torque output and an increase in torque ripple. That is, current distortion generates low-order harmonics, which leads to an increase in torque ripple. Further, the torque output shortage occurs because the actual current affected by the dead time Td is smaller than the ideal current.

In order to prevent such an undesirable effect of the dead time Td, various measures, so-called dead band compensation, have been considered. The basic idea is to compensate for the distortion voltage ΔV shown in the above equation (4). Therefore, in order to compensate the equation (4), it is corrected by the correction value (voltage) Δu shown by the following equation (5).

Δu = sign (Is) · (Ttot / Ts) · (Vdc / 2) (5)

JP-A-8-142848 Ben Brahim, “Dead Time Compensation Analysis of Three-Phase PWM Inverters,” IEICE-IECON98, Vol. 2, pp. 792-797 (Ben-Brahim, Analysis and compensation of dead-time effects in the three phase JP 2002-294441 A

  The problem with deadband compensation is that the polarity sign (Is) of the current Is cannot be detected correctly. When measuring the polarity of the current Is, the noise of PWM control and the above-described zero clamping phenomenon of the current make it difficult to measure the polarity of the current Is correctly.

  Many conventional deadband compensations (for example, Non-Patent Document 1) have complicated methods, require additional hardware, and take measures that take into account changes in the load current such as motor current (steering state). Absent. For this reason, the dead band compensation for preventing the short circuit between the upper and lower arms of the inverter has problems such as the distortion or vibration of the motor voltage, the motor current, or an increase in torque ripple.

  Japanese Patent Laying-Open No. 2002-29441 (Patent Document 2) determines whether the steering wheel has been added or turned off, but does not describe any deadband compensation.

  The present invention has been made for the above-described circumstances, and an object of the present invention is to provide dead band compensation with respect to the voltage command value with a simple configuration and taking into consideration the influence of the motor load current and the steering state. By doing so, an object of the present invention is to provide a control device for an electric power steering device with less motor voltage, motor current distortion and vibration, and torque ripple.

  The present invention provides a steering assist force to a steering mechanism based on a current command value calculated based on a steering torque signal generated in a steering shaft and a voltage command value from a current control unit that receives the current command value. The above-described object of the present invention relates to a control unit for calculating a dead band characteristic based on the current command value, and a steering state for determining a steering state of a steering wheel. A determination unit; a gain unit that varies the gain of the dead band characteristic according to the determination of the steering state determination unit; and a polarity determination unit that switches a polarity determination method according to the determination of the steering state determination unit. By applying the polarity determined by the polarity determination unit to the voltage command value as a dead time correction value. Alternatively, a calculation unit that calculates a dead band characteristic based on the current command value, a steering state determination unit that determines a steering state of a steering wheel, and a gain unit that varies the gain of the dead band characteristic according to the determination of the steering state determination unit And calculating a dead band characteristic based on the current command value by giving a polarity to the output of the gain unit and giving the voltage command value as a dead time correction value, and a handle A steering state determination unit that determines a steering state and a polarity determination unit that switches a polarity determination method according to the determination of the steering state determination unit are provided, and the polarity determined by the polarity determination unit is added to the dead band characteristics to thereby apply the voltage This is achieved by giving the command value as a dead time correction value.

  The above object of the present invention is to provide an increase / return determination unit in the steering state determination unit that determines whether the steering wheel is increased or decreased, and sets the gain to “1” when the increase is detected. Polarity determination that makes the gain “0” or small when a return is detected, or that the steering state determination unit determines an open state and makes the polarity determination method variable based on the determination of the open state The polarity determination unit determines the polarity with hysteresis based on the detected current of the motor or the current command value, or the model current value based on the current command value, and the release determination unit is in the open state. The hysteresis width is switched to be large when it is determined to be small, and it is switched to be small otherwise, or the increase / return determination unit is In addition, by determining whether to increase / return using at least one of a motor angular velocity signal and a steering torque signal, or for determining the open state, a vehicle speed signal, a steering wheel or motor angular signal, a steering wheel or motor angular velocity signal, This is achieved more effectively by using at least one of a steering torque signal, a detected current signal, and the current command value.

  According to the control device for the electric power steering apparatus according to the present invention, since the dead band compensation is performed for the voltage command value, unlike the conventional dead band compensation based on the actually measured current including noise, the motor voltage and current are controlled. It is possible to provide a control device for an electric power steering apparatus that performs dead band compensation with less distortion and less torque ripple.

  In addition, because dead band compensation is performed in consideration of changes in motor current according to the steering state, unlike conventional dead band compensation using only fixed values, there is little distortion in motor voltage and current, and dead band with less torque ripple. Compensation is possible.

  In the present invention, the dead band correction value is calculated according to the model current and the steering state such as the steering wheel being increased, switched back, and opened, and the dead band compensation is performed for the voltage command value of the inverter that drives the motor. Do. For this reason, unlike the conventional dead band compensation based on the actually measured current including noise, it is possible to realize the dead band compensation with less distortion of the motor voltage and current and less torque ripple.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a configuration example of the present invention for a brushed motor 1A, in which a steering torque T from a torque sensor and a vehicle speed V from a vehicle speed sensor are input to a steering assist command value calculation unit 4 and calculated. The auxiliary command value Iref1 is input to the adding unit 7. The compensation signal CM from the compensation unit 8 is input to the addition unit 7, and the addition result Iref2 (= Iref1 + CM) is input to the current control unit 3, and the voltage command value u for PWM is output and added. Input to the unit 9. The compensating unit 8 adds the self-aligning torque and inertia data by the adding unit 81, adds the convergence data to the added value by the adding unit 82, and outputs the addition result as a compensation value CM.

  On the other hand, the current Imes of the motor 1 is detected by the current detector 6 and fed back to the current control unit 3 to calculate a deviation from the current command value Iref2 from the adding unit 7, and a voltage command value u based on the deviation is obtained. Is output. The voltage command value u is input to the adding unit 9. The current command value Iref2 is input to the dead time compensator 5A together with the steering torque T, the vehicle speed V, the angle θ, and the angular velocity ω. The dead time compensation unit 5A outputs the calculated dead time correction value Δu, and the voltage command value u ′ (= u + Δu) added by the adding unit 9 is input to the inverter 2. The inverter 2 is PWM-controlled based on the input voltage command value u 'and drives the motor 1A. As an input to the dead time compensation unit 5A, a voltage command value u may be used instead of the current command value Iref2.

  FIG. 1 shows the configuration in the case of the brushed motor 1A, but the configuration in the case of the brushless motor 1 is as shown in FIG. In the expression of FIG. 2, the compensation unit 8 of FIG. 1 is included in the steering assist command value calculation unit 4. In FIG. 2, the steering assist command value Iref <b> 3 from the steering assist command value calculation unit 4 is input to the dead time compensation unit 5.

  The configuration of the inverter 2 may be a single-phase inverter having two upper and lower arms as shown in FIG. 10 (in the case of a two-phase motor), or a three-phase inverter having three upper and lower arms (of a three-phase motor). Case).

  Here, a configuration example of the dead time compensation unit 5 will be described with reference to FIG.

The current command value Iref3 from the steering assist command value calculation unit 4 is input to the steering state determination unit 53 and also input to the dead band characteristic unit (calculation unit) 56. The dead band characteristic from the dead band characteristic unit (calculation unit) 56 is input to the gain unit 55. The dead band characteristic unit (arithmetic unit) 56 outputs a dead time correction value DB having a dead band characteristic as shown in FIG. 4 with respect to the current command value Iref3. The polarity determination unit 52 determines the input signal polarity with a characteristic with hysteresis. The polarity determination unit 52 is input with a motor detected current or a current command value Iref3 or a model current based on the current command value Iref. The hysteresis width is changed based on the steering state signal ST1 from the steering state determination unit 53. The model current is obtained by converting the current command value Iref with a transfer function of the following equation (6) (for example, Japanese Patent Application No. 2003-310131).

MR (s) = 1 / (1 + Tc · s) (6)
Here, Tc = 1 / (2π · fc), and fc is a cutoff frequency of the current control loop.

The first-order lag function of the above equation (6) is a model function of a current control loop in which the transfer function 1 / (R + s · L) indicating the motor 1 is derived based on the current control unit 3, the inverter 2, and the current detector 6. is there.

  Here, an example of the relationship between the current command value Iref and the actual motor current Imes is shown in FIG. The actual motor current Imes contains a lot of noise, which makes it difficult to determine the polarity near zero current. For this reason, it is more effective if the model current of the motor 1 is generated through the first-order lag circuit based on the current command value Iref without noise and the polarity is determined based on the model current without using the actual current Imes. Is.

  The steering state determination unit 53 has an opening determination function and an increase / return determination function, and the motor angular speed ω, the steering torque T, the vehicle speed V, the motor angle θ, and the current command value Iref3 are input, and the steering state determination unit 53 Is determined to be open, the steering state signal ST1 is input to the polarity determination unit 52, and when it is determined to increase or return, the steering state signal ST2 is input to the gain unit 55. The polarity sign (Pi) determined by the polarity determination unit 52 is input to the multiplication unit 57, multiplied by the gain-adjusted DBa from the gain unit 55, and output as a dead time correction value Δu.

  The opening determination function of the steering state determination unit 53 is based on the vehicle speed V, the motor angular speed ω, and the current command value Iref3. The signal ST1 is output, and the increase / return determination function determines that the motor angular velocity ω and the steering torque T are in the same direction based on the motor angular velocity ω and the steering torque T as shown in FIG. If the two are different, it is determined that the switch is returned, and the steering state signal ST2 is output.

  In such a configuration, the operation will be described.

  The detected current of the motor or the current command value Iref3 or the model current based on the current command value Iref is input to the polarity determination unit 52 together with the steering state signal ST1, and the polarity is determined. The sign (Pi) that is the output of the polarity determination unit 52 is output in the form of (+1) or (−1) as shown in the following equation (7).

It is very difficult to correctly determine the polarity by measuring the actual motor current and inverter current due to noise as described above, but there is no such concern if the determination is made using the model current.

sign (Pi) = (+ 1) or (−1) (7)

The polarity determination unit 52 has a polarity determination with hysteresis, and sets the hysteresis width of the polarity determination as follows based on the steering state signal ST1 when the steering wheel open (hand-off) state is determined.

When released (ST1 = 1): Large hysteresis width During steering (ST1 = 0): Small hysteresis width

The reason why the hysteresis width is made variable by determining the opening of the handle is as follows. When the fluctuation of the current command exceeds the dead time correction hysteresis width, the output direction of the dead time correction is switched from positive → negative or negative → positive, and this causes self-excited vibration by a closed loop including torque control, resulting in sound. This is a problem that may occur in a situation where the command value fluctuates due to a disturbance around 0A. Since the command value exceeds a certain value in the steering state, self-excited vibration does not occur. Therefore, in an open state where the current command value is difficult to be determined, the hysteresis width is increased in order to eliminate the sensitivity to the command value fluctuation, and a dead time compensation delay is generated at the time of steering to generate a torque ripple. Make it smaller.

The opening determination function in the steering state determination unit 53 receives the vehicle speed V, the motor angular speed ω, and the current command value Iref3, and outputs a state determination signal ST = 1 when the following equation (8) is satisfied. ing.

Vehicle speed V <predetermined value α and angular velocity ω <predetermined value β
And | current command value Iref3 | <predetermined value γ (8)

The predetermined value α is a vehicle speed that does not bother the sound caused by self-excited vibration, the predetermined value β is a small value that does not detect noise, and the predetermined value γ is a small value that does not detect noise. .

  The dead time correction value DB from the dead band characteristic unit 56 is input to the gain unit 55, and the gain is adjusted in accordance with the steering state signal ST2 from the increase / return determination function in the steering state determination unit 53. The increase / return is determined as shown in FIG. That is, when the steering torque T (or current command value) and the angular velocity ω (steering direction of the steering wheel) coincide with each other, the steering wheel is increased. Otherwise, it is determined that the steering wheel is turned back. The gain of the gain unit 55 is set to “1” by the steering state signal ST2, and no correction is required at the time of switching back, so the gain of the gain unit 55 is set to “0” or small by the steering state signal ST2.

  In addition, the determination of the increase / return can be performed by only the steering torque T as disclosed in, for example, JP-A-2003-170856.

  As described above, the dead time correction value DBa whose gain is adjusted by the steering state signal ST2 from the increase / return determination function is given a polarity according to the polarity (positive / negative) from the polarity determination unit 52 by the multiplication unit 57 and is dead. It is output as a time correction value Δu.

  The correction value Δu calculated in this way is added by the adding unit 9 to the voltage command value u which is the output of the current control unit 3 shown in FIG. The meaning that the correction value Δu is added to the voltage command value u is that the basic control indicated by the voltage command value u is a correction value Δu that improves voltage, current distortion, and torque ripple due to dead time to prevent the upper and lower arms from being short-circuited. Is to control.

  In the above description, the dead time compensation for the brushless motor 1 has been described. However, compensation for the brushed motor 1A is also possible. In this case, the current notation and Iref3 in FIG. 3 are set to Iref2 in FIG.

  In the above description, an example in which the steering state determination unit 53 has an opening determination function and an increased switchback determination function has been described. However, as shown in FIG. 7, the steering state determination unit 53 has only an increase switchback determination function, Only the gain of the gain unit 55 may be changed by the steering state signal ST2. Further, as shown in FIG. 8, the steering state determination unit 53 may have only an opening determination function, and only the hysteresis of the polarity determination unit 52 may be changed by the steering state signal ST1.

  According to the present invention, since dead time can be compensated according to the steering state, demands for severe noise and vibration can be cleared, and a high-performance power steering device can be realized.

It is a block block diagram which shows an example (motor with a brush) of the control apparatus of this invention. It is a block block diagram which shows the other example (brushless motor) of the control apparatus of this invention. It is a block diagram which shows the structural example of the dead time compensation part which concerns on this invention. It is a figure which shows an example of a dead band characteristic. It is a figure which shows the relationship between an actual electric current and a model electric current. It is a figure for demonstrating the steering wheel additional cut-back determination. It is a block diagram which shows the other structural example of the dead time compensation part which concerns on this invention. It is a block diagram which shows the other structural example of the dead time compensation part which concerns on this invention. It is a block block diagram which shows the example of a control apparatus of a general electric power steering apparatus. It is a block block diagram which shows an example of a motor drive circuit. It is a time chart for demonstrating the relationship between dead time, turn-on time, and turn-off time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Brushless motor 1A Brushed motor 2 Inverter 3 Current control part 4 Steering assistance command value calculation part 5, 5A Dead time compensation part 6 Current detector 7 Subtraction part 8 Compensation part 9 Addition part 52 Polarity determination part 53 Steering state determination part 55 Gain unit 56 Dead band characteristic unit 57 Multiplication unit

Claims (8)

A motor that provides a steering assist force to the steering mechanism based on a current command value calculated based on a steering torque signal generated in the steering shaft and a voltage command value from a current control unit that receives the current command value. In a control device for an electric power steering apparatus controlled by an inverter, a calculation unit that calculates a dead band characteristic based on the current command value, a steering state determination unit that determines a steering state of a steering wheel, and a determination of the steering state determination unit A gain unit that varies the gain of the dead band characteristic according to the above, and a polarity determination unit that switches a polarity determination method according to the determination of the steering state determination unit, and gives the polarity determined by the polarity determination unit to the output of the gain unit And providing the voltage command value as a dead time correction value. Location of the control device. A motor that provides a steering assist force to the steering mechanism based on a current command value calculated based on a steering torque signal generated in the steering shaft and a voltage command value from a current control unit that receives the current command value. In a control device for an electric power steering apparatus controlled by an inverter, a calculation unit that calculates a dead band characteristic based on the current command value, a steering state determination unit that determines a steering state of a steering wheel, and a determination of the steering state determination unit And a gain unit that varies the gain of the dead band characteristic according to the control unit, wherein a polarity is given to the output of the gain unit and the voltage command value is given as a dead time correction value. apparatus. A motor that provides a steering assist force to the steering mechanism based on a current command value calculated based on a steering torque signal generated in the steering shaft and a voltage command value from a current control unit that receives the current command value. In a control device for an electric power steering apparatus controlled by an inverter, a calculation unit that calculates a dead band characteristic based on the current command value, a steering state determination unit that determines a steering state of a steering wheel, and a determination of the steering state determination unit And a polarity determination unit that switches a polarity determination method according to the electric power steering, wherein the polarity determined by the polarity determination unit is added to the dead band characteristic and the voltage command value is added as a dead time correction value. Control device for the device. When the increase / return determination unit in the steering state determination unit determines whether the steering wheel is increased or decreased, the gain is set to “1” when the increase is detected, and when the return is detected. The control device for the electric power steering apparatus according to claim 1 or 2, wherein the gain is set to "0" or small. 4. The control device for an electric power steering apparatus according to claim 1, further comprising a polarity determination unit that determines whether the steering state is in an open state and makes a polarity determination method variable based on the determination in the open state. 5. . The polarity determination unit determines the polarity with hysteresis based on the detected current of the motor or the current command value, or a model current value based on the current command value, and the hysteresis is determined when the release determination unit determines the open state. 6. The control device for an electric power steering apparatus according to claim 5, wherein the control is performed so that the width is increased and the width is decreased otherwise. The control of the electric power steering apparatus according to claim 4, wherein the increase / return determination unit performs determination of increase / return using at least one of a steering wheel, a motor angular velocity signal, and a steering torque signal. apparatus. The determination of the open state is performed using at least one of a vehicle speed signal, a steering wheel or motor angle signal, a steering wheel or motor angular speed signal, a steering torque signal, a detected current signal, and the current command value. Item 6. A control device for an electric power steering device according to Item 5.

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