KR102253168B1 - Motor Driven Power Steering System and Method for the Vehicles - Google Patents

Abstract

The present invention relates to an electric power steering system for a vehicle and a method thereof, and in controlling a motor of an electric power steering (MDPS, Motor Driven Power Steering) of a vehicle that transmits steering force to a wheel in response to manipulation of a steering wheel, calculation By estimating and compensating for errors in the position of the motor rotor caused by delays due to time, the accuracy of motor control is improved, the reactive power caused by errors is minimized, and the generation of noise, vibration and heat is reduced, thereby improving the control efficiency It works.

Description

Motor Driven Power Steering System and Method for the Vehicles}

The present invention relates to an electric power steering system and method of a vehicle, and in particular, in the driving direction control using a motor, the present invention relates to an electric power steering system and method of a vehicle for effectively controlling the steering direction of the vehicle in response to manipulation of a steering wheel. will be.

Recently, in the power steering system in a vehicle, an electric power steering system (MDPS, Motor Driven Power Steering System) that controls the driving direction of a vehicle using the rotational force of a motor from battery power is expanding.

In this MDPS system, a motor controller that generates an output corresponding to an input according to a driver's steering wheel manipulation plays an important role.

Important control factors for a three-phase AC motor include phase current measurement, motor rotor position, dead time, and decoupling. In particular, the position of the motor rotor becomes the most important control factor when converting from 3-phase to 2-phase for vector control.

When driving the motor, the PWM switching frequency should be 20Khz (less than 50us) higher than the human audible frequency. Therefore, it is good to take the period of the motor controller equal to the PWM (Pulse Width Modulation) frequency, but for this, a separate controller must be provided.

Accordingly, conventionally, the period of the motor controller was driven more than several times the PWM period, and a method of driving the PWM with the same rotor position was used until the next rotor position was calculated.

However, considering the SW operation time until the PWM output for driving the motor after calculating the motor output by a complex formula with the position of the motor rotor initially sensed, the actual output is calculated by the rotation of the motor after the actual initial calculated motor position. There will be an error in the position to be given out.

This means that the error of the rotor increases as the motor of 3000rpm or more operates at high speed such as field weakening control. This is an error that accumulates over time with respect to the rotor position initially calculated in a rotating motor. This accumulated error causes noise, heat, and torque ripple due to reactive power. It degrades performance and can also cause noise, vibration, harshness (NVH) problems.

An object of the present invention is to provide an electric power steering system for a vehicle and a method for reducing an error by estimating and compensating for a rotor position of a motor in controlling a driving direction of a vehicle using a motor.

The electric power steering system of a vehicle according to the present invention is an electric power steering system of a vehicle that transmits steering power to a wheel in response to an operation of a steering wheel, wherein the electric power steering (MDPS) includes: a steering gear A motor for operating the motor, a position sensing unit for sensing the position of the rotor of the motor, an angular velocity sensing unit for measuring an angular velocity according to the operation of the motor, a motor driving unit for supplying operating power to the motor, and the position sensing unit and the angle A motor control unit for inputting a control command to the motor driving unit in response to a measured value of the speed sensing unit, and the motor control unit is the rotor of the motor in response to an operation time required to calculate a control signal for controlling the motor. It is characterized in that it compensates for the error of the position.

In addition, the method of the electric power steering system for a vehicle according to the present invention is the position of a rotor of a motor provided in an electric power steering (MDPS) of a vehicle that transmits steering force to the wheel in response to manipulation of the steering wheel. Sensing, calculating a control signal for controlling the motor, estimating a position of the rotor that changes during an operation time required for calculating the control signal, and using the estimated value for the rotor position Compensating the electronic position and controlling the motor in response to the compensated rotor position.

The electric power steering system and method thereof for a vehicle according to the present invention greatly reduce errors caused by delays due to calculation time by estimating and compensating the position of a motor rotor in controlling a three-phase AC motor, and By minimizing reactive power and reducing the generation of noise, vibration and heat, the efficiency of control is improved, and more precise control is possible, thereby improving the safety of the vehicle.

1 is a schematic diagram of a vehicle equipped with an electric power steering system according to the present invention.
2 is a block diagram showing a control configuration of an electric power steering system for a vehicle according to the present invention.
3 is a flowchart illustrating a control flow of an electric power steering system for a vehicle according to the present invention.
4 is a diagram illustrating a first example of an output characteristic through compensation of a rotor position of an electric power steering system for a vehicle according to the present invention.
5 is a view showing a second example of an output characteristic through compensation of a rotor position of an electric power steering system for a vehicle according to the present invention.
6 is a diagram showing a third example of an output characteristic through compensation of a rotor position of an electric power steering system for a vehicle according to the present invention.

Advantages and features of the present invention, and a method of achieving them will become apparent with reference to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in a variety of different forms, and only these embodiments make the disclosure of the present invention complete, and are common knowledge in the technical field to which the present invention pertains. It is provided to completely inform the scope of the invention to those who have, and the invention is only defined by the scope of the claims. The same reference numerals refer to the same elements throughout the specification.

1 is a schematic diagram of a vehicle equipped with an electric power steering system according to the present invention.

Referring to FIG. 1, a vehicle 1 according to the present invention includes a steering wheel 2 that changes the driving direction of the vehicle according to a driver's manipulation, and an electric power steering (MDPS) that controls the steering. ), and a steering gear 5 connected to the wheel 4 to transmit steering force.

The automobile 1 is a torque sensor (not shown) and angle sensor (not shown) that senses torque and rotation angle according to the steering input of the steering wheel 2, a speed sensor that measures the speed of the vehicle, inside and outside the vehicle. It further includes a plurality of sensors that are installed to detect the state of the vehicle, and further includes a main control unit (not shown) for controlling overall operation of the vehicle driving.

In addition, the automobile 1 is provided with an engine (or motor) (not shown) as a power source, an accelerator (not shown) and a brake (not shown) for acceleration or reduction of the vehicle, and a transmission ( (Not shown), a plurality of sensors (not shown) installed inside and outside the vehicle are further included, but a description thereof will be omitted below.

The electric power steering (MDPS) 3 is a device that adjusts the steering feeling by using the power of a motor provided in setting the driving direction of the vehicle according to the operation of the steering wheel 2.

The electric power steering (MDPS) 3 is configured in various forms depending on the connection structure, and in FIG. 1, a C-MDPS, which is provided in a column and directly turns the steering wheel 2, is described as an example. At this time, since the electric power steering (MDPS) 3 is provided with a motor, it does not use the engine power of the vehicle and thus can be driven with a small output.

In the electric power steering (MDPS) 3, when operation of the steering wheel 2 is detected by the torque sensor and the rotation angle sensor, the sensor data on the torque and rotation angle according to the operation of the steering wheel 2 and the vehicle It receives the speed and state data of the vehicle and drives the motor to control the gearbox of the column. The steering force is thus transmitted from the column through the steering gear 5 to the wheels 4.

Accordingly, the driver can easily operate the steering wheel 2 and the driving direction of the vehicle is changed according to the operation of the steering wheel 2.

2 is a block diagram showing a control configuration of an electric power steering system for a vehicle according to the present invention.

As shown in Fig. 2, the electric power steering (MDPS) 3 is a motor 140, a motor drive unit 130, a current controller 120, a motor control unit 110, a position sensing unit 150, and a sense of angular velocity. It includes a branch unit 170 and a current sensing unit 160.

The motor 140 is driven according to an input operation power, and operates a gearbox of a column connected to the steering wheel 2.

The current sensing unit 160 senses the current with respect to the three-phase power applied to the motor 140. The position sensing unit 150 detects the position of the rotor of the motor 140, and the angular velocity sensing unit 170 measures the angular velocity according to the rotation of the motor.

The motor driving unit 130 controls the operation of the motor 140 in response to a signal input from the current controller 120 according to a control command of the motor control unit 110. At this time, the motor driving unit 130 performs PWM control according to the switching period according to the voltage command input from the current controller 120 and drives an inverter (not shown) accordingly to apply three-phase operation power to the motor 140. By doing so, it controls the operation of the motor.

The motor driving unit 130, when driving the motor 140, sets the PWM switching frequency to 20Khz (50us or less) higher than the human audible frequency, and accordingly, the control period of the motor 140 is also set equal to the PWM frequency. .

The motor control unit 110 controls the electric power steering (MDPS) 3 to operate in response to the operation of the steering wheel 2 or the driving state of the vehicle.

The motor control unit 110 controls the electric power steering (MDPS) 3 to operate by causing the motor 140 to operate in response to the state of the vehicle, the torque sensor, and the input of each sensor. At this time, the motor control unit 110 applies a current command for controlling the motor 140 to the current controller 120.

In addition, the motor control unit 110 estimates the position of the rotor in response to inputs from the current sensing unit 160, the position sensing unit 150, and the angular velocity sensing unit 170, and compensates for errors in the position of the rotor. Accordingly, the compensated data is applied to the current controller 120 and the motor driving unit 130 to cause the motor 140 to operate.

When the motor driving unit 130 converts two-phase power to three-phase power for vector control, the motor control unit 110 compensates for the error of the position of the motor rotor acting as an important control element. ) To be precisely controlled.

When controlling the motor 140, the motor driving unit 130 uses a method of driving the PWM with the same rotor position until the next rotor position is calculated by setting the control period to several times or more of the PWM period.

At this time, the position of the rotor measured by the position detecting unit 150 is a value measured in the last control cycle, and an error is accumulated over time. In addition, it takes time to calculate the output of the motor 140 based on the actual motor rotor position.

The motor control unit 110 estimates and compensates the position of the motor rotor in consideration of such an operation time, so that the motor drive unit 130 controls the motor 140 based on the compensated rotor position.

In order to estimate the position of the rotor, the motor control unit 110 may calculate by mixing the estimation using the position, the estimation using the speed, and the position and the speed estimation. Hereinafter, a description will be given of estimating and compensating the rotor position of the motor using the speed.

The motor control unit 110 estimates the position of the rotor by using the speed of the motor 140. The motor control unit 110 may estimate the position of the rotor by using the angular velocity of the motor 140 sensed by the angular velocity detecting unit 170.

At this time, the motor control unit 110 applies the calculation according to the motor control and the required time according to the control execution to be different, and thus applies this to the motor control. In motor control, the calculation time can be measured using a timer, or can be measured and input separately using an oscilloscope or a tool such as SymTa.

The motor control unit 110 uses this calculation time as a constant value T_sw for estimating and compensating the position of the motor rotor.

In addition, in estimating the rotor position, the motor control unit 110 assumes that the speed of the motor 140 is constant for one control period due to inertia, and uses the calculation time T_sw described above to determine the motor position by the following equation: Calculate like 1.

Here, Δθ_est is an estimated value of the rotor position, T_sw is a constant value for the calculation time, ω is the angular velocity of the motor, and P is the number of poles of the motor.

Position estimation using this speed can be applied when the speed is variable. In the case of constant velocity, the estimation using position may be more advantageous.

In addition, the motor control unit 110 compensates the estimated value of the rotor position calculated as described above through Equation 2 below.

Here, Δθ_est is an estimated value of the rotor position, and θ_real is a value measured by the position sensing unit 160 of the motor.

That is, the motor control unit 110 compensates the position of the motor rotor by adding the estimated value to the value measured by the position sensing unit 160.

As described above, the output of the motor 140 is calculated based on the rotor position of the motor 140 measured by the position sensing unit 160, and data on the output of the motor is fed back to control the motor. It takes time.

In other words, considering the calculation time from the initially sensed position of the motor rotor to the PWM output for driving the motor after calculating the motor output, it is at the position that produces the actual output after the calculation by the rotation of the motor after the actual initial calculated motor position. There is an error.

For example, when the motor 140 rotates at a rated 1200 rpm, the calculation time is about 25 us, and accordingly, an error of up to 0.54 degrees occurs.

Since the position of the rotor is changed as long as the calculation time, an error occurs, the motor control unit 110 compensates for the rotor position by adding an estimated value to the actual rotor position.

3 is a flowchart illustrating a control flow of an electric power steering system for a vehicle according to the present invention.

The motor control unit 110 generates a current command for controlling the motor 140 (S120), adds the current value for the feedback of the motor output to the current command (S123, S124), and applies it to the current controller 120. . At this time, the motor control unit 110 applies a current command to the Q-axis and D-axis (S121, S122).

The current value fed back at this time is also data on the Q-axis and D-axis currents.

The current controller 120 applies a voltage command to the motor driving unit 130 in response to the input current command (S130). The current controller 120 generates a voltage command from the obtained rotor position and the phase current value of the current sensing unit 160 in response to the input current command.

The motor driving unit 130 controls the motor 140 through PWM control by converting the input voltage command (S140). The motor driving unit 130 performs switching control in response to a signal input from the current controller 120, and accordingly converts the two-phase power into three-phase power and applies it to the motor 140.

The motor 140 of the electric power steering (MDPS) 3 rotates with the supplied operating power (S150).

While the motor 140 is operating, the position detecting unit 150 of the motor 140 calculates the rotor position of the motor from the measured value of the position sensor (S181). In addition, the angular velocity detection unit 170 measures the angular velocity according to the rotational motion of the motor.

The motor control unit 110 receives an angular velocity measurement value from the angular velocity detection unit 170 and estimates the rotor position of the motor (S182). The motor control unit 110 estimates the position of the rotor based on Equation 1 according to the estimation of the position of the rotor according to the speed described above (S182).

In addition, the motor control unit 110 compensates the rotor position of the motor by adding the actual rotor position and the estimated rotor position (S183).

The rotor position of the motor compensated in this way is input to the current controller 120 and the motor driving unit 130 and is used as a control factor when controlling the motor.

Meanwhile, while the motor 140 is operating, the current sensing unit 160 senses the current of the motor 140.

In addition, the motor control unit 110 calculates the output of the motor from the calculated rotor position (S160), and calculates the current values for the Q-axis and D-axis (S170). The current value calculated as described above is fed back and added to the current command in the next control cycle (S123 and S124).

The motor control unit 110 repeats such control so that the electric power steering (MDPS) 3 operates.

4 is a diagram illustrating a first example of an output characteristic through compensation of a rotor position of an electric power steering system for a vehicle according to the present invention. 4 is an embodiment to which a position estimation method using a position is applied.

The electric power steering (MDPS) 3 estimates and compensates the motor rotor position in the motor control unit 110, and controls the motor 140 based on the compensated rotor position.

When the motor control unit 110 uses a position estimation method, the following equation is applied.

This estimation method is used under the assumption that there is no change in speed due to inertia at constant speed.

As shown in FIG. 4, the motor 140 is driven and the position S1 of the motor rotor measured by the position sensing unit 150 increases in proportion to time. On the other hand, the compensated motor rotor position S2 gradually increases in rotation angle in units of the control period dt as time elapses. At this time, the difference E1 (A, B) between the actual motor rotor position S1 and the compensated motor rotor position S2 becomes an error.

In the case of using position estimation, if the position calculation is started at the first time t1, the position of the motor rotor at the time of calculation increases from the rotation angle Δ_advance(n-1) to Δ_advance(n), and the second position It increases to Δ_advance(n+1) at the second time t2 at which the operation is started.

At this time, the actual motor rotor position is θ(n) at the first time t1 and θ(n+1) at the second time.

At the first time t1, the compensated motor rotor position is larger than the actual motor rotor position, and at the second time t2, the actual motor rotor position becomes larger than the compensated motor rotor position.

Also, between the first time t1 and the second time t2, the actual motor rotor position and the compensated motor rotor position coincide.

Although the error E1 exists between the actual motor rotor position and the compensated motor rotor position, it is reduced by 1/2 compared to the conventional one.

5 is a view showing a second example of an output characteristic through compensation of a rotor position of an electric power steering system for a vehicle according to the present invention.

FIG. 5A is a position of the motor rotor according to the prior art, and FIG. 5B is a diagram illustrating the position of the motor rotor when the above-described speed estimation method is used.

As shown in FIG. 5A, the measured motor rotor position S12 increases step by step following the actual motor rotor position S11. That is, since the calculation is performed at the measured point and the same value is maintained until the next measurement, the error increases as time passes.

When the position calculation is performed at the third time t11, at this time, the measured motor rotor position is 0 to θ_real, and the same value as the actual motor position is used.

When the time passes and the fifth time t13 of the next control period dt2 is reached, the position calculation is started, and the position calculation is started based on the actual motor rotor position. At this time, the difference θ_err between the measured motor rotor positions increases significantly. Accordingly, the accumulated error corresponds to the area C between the measured motor rotor position D11 and the actual motor rotor position S12.

According to the first position calculation at the third time t11, the PWM is applied at the fourth time t12 after the calculation time T_sw (dt3) has elapsed.

Since the calculation takes a predetermined time, PWM control is performed after the calculation time has elapsed. At this time, the PWM control at the fourth time (t12) is based on the rotor position measured at the third time (t11). , Since the actual motor rotor position at the fourth time t12 and the rotor position used for the controlling PWM signal are different, an error occurs accordingly.

That is, when the PWM control is performed at the fourth time t12, since the rotor position of the last third time t11 is used, the control signal and the rotor position at the control point are different, so an error occurs accordingly. . In particular, the longer the operation time, the larger the error.

On the other hand, as shown in FIG. 5B, when compensation is performed for the position of the motor rotor using the speed of the present invention, when the position is calculated at the third time t11, the actual motor rotor position is measured. Perform position calculation. At this time, the rotor position becomes θ_real.

At this time, the motor control unit 110 performs an operation based on the measured motor rotor position, but considers the operation time T_sw and estimates the corresponding motor rotor position, and this is performed at the third time t11. Compensate by adding it to the motor rotor position.

Accordingly, PWM control is performed at a fourth time t12 in which the operation time T_sw dt3 has elapsed from the first position operation of the third time t11.

At this time, the PWM control signal is a signal to which Δ_advance, which is the compensated motor rotor position, is applied in consideration of the position calculation time (T_sw) (dt3) as described above. That is, by estimating and compensating the position by the error D at the fourth time t12, the error is minimized, and further, the position is matched with the actual motor rotor position.

In the fifth time t13, which is the next control period dt2, the position of the motor rotor is measured, and as described above, the position of the rotor is estimated in consideration of the operation time, and the position of the rotor is compensated to perform the next PWM control.

Accordingly, the error between the actual motor rotor position and the compensated motor rotor position applied to the PWM signal at the fourth time t12, which is the PWM control time point, decreases. Furthermore, the compensated motor rotor position applied to the PWM signal matches the actual motor rotor position, and accordingly, motor control is possible without error.

6 is a diagram illustrating a third example of an output characteristic through compensation of a rotor position of an electric power steering system for a vehicle according to the present invention.

As described above, it is possible to control according to the actual motor rotor position at the time of PWM control through error compensation.

Hereinafter, a case of performing motor control through error compensation in the case of a controller having a long operation time will be described.

As shown in FIG. 6, when the calculation time T_sw (dt4) is long, when the position calculation starts based on the position of the motor rotor at the sixth time t21, the seventh time when the stretching time elapses. At time t22, an error greatly increases between the actual motor rotor position and the motor rotor position at the sixth time.

Accordingly, when the PWM control is performed at the seventh time t22, as an error increases, a problem may occur in the motor control accordingly.

On the other hand, the electric power steering (MDPS) 3 of the present invention estimates and compensates for the measured rotor position of the motor by estimating the changed rotor position in consideration of the elongation time, as shown in FIG. 6B.

Even if the operation starts at the sixth time t21 and the operation time takes a long time, the PWM control is performed at the seventh time t22 through position compensation corresponding to the operation time, so that the motor ( 140). Even if the operation time is long, it is compensated accordingly, so precise control can be performed regardless of the length of the operation time.

As described above, the present invention configures the electric power steering system of a vehicle, thereby minimizing an error due to operation time when controlling the motor of the MDPS, and compensating in consideration of the operation time, thereby enabling precise motor control.

The terms such as "include", "consist of" or "have" described above mean that the corresponding component may be embedded, unless otherwise specified, and thus other components are not excluded. It should be construed as being able to further include other components.

In the above, preferred embodiments have been illustrated and described, but the present invention is not limited to the specific embodiments described above, and common knowledge in the technical field to which the present invention pertains without departing from the gist of the present invention claimed in the claims. Of course, various modifications may be made by the possessor, and these modifications should not be understood individually from the technical spirit or prospect of the present invention.

1: car 2: steering wheel
3: Electric Power Steering (MDPS) 4: Wheels
110: motor control unit 120: current controller
130: motor drive unit 140: motor
150: current sensing unit 160: position sensing unit
170: angular velocity detection unit

Claims (14)

In the electric power steering system of a vehicle that transmits steering force to the wheel in response to the operation of the steering wheel,
The electric power steering (MDPS, Motor Driven Power Steering),
A motor that operates the steering gear;
A position sensing unit that detects the position of the rotor of the motor;
An angular speed sensing unit that measures an angular speed according to the operation of the motor;
A motor driving unit supplying operating power to the motor; And
Including; a motor control unit for inputting a control command to the motor driving unit in response to the measured value of the position detection unit and the angular velocity detection unit,
The motor control unit compensates for an error of the rotor position of the motor in response to an operation time required to calculate a control signal for controlling the motor,
The motor control unit compensates for the rotor position by summing an estimated value of the rotor position changed during the calculation time to an operation value according to the rotor position of the motor sensed by the position detection unit at the start of operation. Electric power steering system of a vehicle, characterized in that. The method of claim 1,
The motor control unit calculates a control signal for controlling the motor according to the rotor position of the motor sensed by the position sensing unit, and estimates the rotor position changed during the calculation time, and the rotor position Electric power steering system of a vehicle, characterized in that to compensate for. The method of claim 1,
The motor driving unit PWM control of the motor in response to the compensation value of the rotor position input from the motor control unit. delete The method of claim 1,
The motor control unit estimates the position of the rotor that is changed during the calculation time by using the rotor position sensed by the position sensing unit and the angular velocity sensed by the angular velocity sensing unit. Steering system. The method of claim 1,
The motor control unit, in response to a delay due to the calculation time, estimates the position of the rotor according to the following equation.
Δθ_est = ω*T_sw * P/2
(Here, Δθ_est is an estimated value for the rotor position, T_sw is a constant value for the calculation time, ω is the angular velocity of the motor, and P is the number of poles of the motor.) The method of claim 1,
The motor control unit compensates for the position of the rotor according to the calculation time, so that an error with respect to the position of the rotor becomes zero at a time when PWM control is performed by the motor driving unit. Power steering system. The method of claim 1,
Further comprising a timer for counting the calculation time,
The motor control unit receives the calculation time measured by the timer and estimates the rotor position with respect to the calculation time. The method of claim 1,
The motor control unit receives the calculation time from the outside and estimates the position of the rotor with respect to the calculation time. Calculating a control signal for controlling the motor by detecting the rotor position of a motor provided in an electric power steering (MDPS, Motor Driven Power Steering) of a vehicle that transmits steering force to the wheel in response to the manipulation of the steering wheel ;
Estimating a position of the rotor that is changed during an operation time required for calculating the control signal;
Compensating for the rotor position using an estimated value for the rotor position; And
Including the step of controlling the motor in response to the compensated rotor position,
In response to the angular speed of the motor input from the angular speed detecting unit and the calculation time, estimating the position of the rotor that is changed during the calculation time
Control method of electric power steering system of automobile. delete The method of claim 10,
The control method of an electric power steering system for a vehicle, comprising compensating for the rotor position by summing an estimated value for the rotor position with the calculated value for the initially detected rotor position. The method of claim 10,
The control method of an electric power steering system for a vehicle, characterized in that the calculation time is measured in advance to calculate an estimated value for the rotor position. The method of claim 10,
A control method of an electric power steering system for a vehicle, comprising performing PWM control for the motor according to the compensated rotor position at a point in time when the operation on the control signal is terminated.

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