Apparatus and method for estimating speed of dc motor in mdps system

Abstract

An apparatus to estimate a speed of a DC motor in an MDPS system can include a motor speed estimator configured to estimate a motor speed based on a DC link voltage driving the motor, a motor current flowing through the motor, and a voltage command; and a limiter configured to generate a current command based on the estimated motor speed, a torque command, and the DC link voltage.

Description

TECHNICAL FIELD

[0001] Example embodiments of the present disclosure relate to an apparatus and method of estimating a speed of a Direct Current (DC) motor in a Motor Driven Power Steering (MDPS) system, and more particularly, to an apparatus and method of estimating a speed of a DC motor in an MDPS system, which can estimate a motor speed using a voltage command and a measured motor current in the MDPS system. BACKGROUND

[0002] An MDPS of a vehicle is used to reduce steering effort by providing an assist torque in a steering direction of a driver using a motor.

[0003] Unlike a conventional Hydraulic Power Steering (HPS), the MDPS can automatically control an operation of the motor according to a driving situation of the vehicle, thereby improving steering performance and steering feel.

[0004] The MDPS system uses a DC motor without a position sensor to reduce manufacturing costs. When there is no position sensor, a method of calculating a speed by measuring a change in a rotation angle cannot be applied. Therefore, a motor speed estimation method capable of replacing the speed calculation method is being developed.

[0005] A conventional MDPS system using a DC motor uses a method of estimating a motor speed by using a voltage across the motor and a measured current.

[0006] However, since the conventional MDPS system uses a low pass filter configured as an analog circuit to measure the voltage across the motor, a cost of a circuit configuration is generated, and an accuracy of the motor speed estimation varies according to a passband setting. Therefore, the MDPS system is difficult to cope with various operating situations, and when the passband is changed, the measurement circuit needs to be modified.

[0007] In addition, since the conventional MDPS system uses a speed-voltage-current relationship equation for speed estimation in a normal state, the number of errors in the speed estimation increases in a portion in which the current and the voltage rapidly change.

[0008] The related art of the present disclosure relates to Korean Patent Application No. 2008-0078441, entitled "Apparatus for estimating angular velocity of DC motor for power steering system," published on August 27, 2008. SUMMARY

[0009] Various embodiments are directed to an apparatus and method of estimating a speed of a DC motor in an MDPS system, which can estimate the motor speed using a voltage command and a measured motor current in the MDPS system.

[0010] In one embodiment, an apparatus of estimating a speed of a DC motor in an MDPS system can include a motor speed estimator configured to estimate a motor speed based on a DC link voltage driving the motor, a motor current flowing through the motor, and a voltage command, and a limiter configured to generate a current command based on the estimated motor speed, a torque command, and the DC link voltage.

[0011] The motor speed estimator can include a stalling time voltage calculation unit configured to calculate a stalling time voltage using the voltage command, the DC link voltage, and the motor current, a motor resistance and inductance voltage calculation unit configured to calculate a motor resistance voltage through a resistance of the motor and a motor inductance voltage through an inductance of the motor, and a calculation unit configured to calculate the motor speed based on the stalling time voltage, the voltage command, the motor resistance voltage, the motor inductance voltage, and a preset motor back EMF constant.

[0012] The stalling time voltage calculation unit can include a stalling time voltage limit calculator configured to calculate a stalling time voltage limit by applying a sign of the motor current, the DC link voltage, and a stalling time ratio over a switching period, and a stalling time voltage determiner configured to determine the stalling time voltage according to a state of the voltage command and the stalling time voltage limit.

[0013] The stalling time voltage limit calculator can calculate the stalling time voltage limit by multiplying the sign of the motor current, the DC link voltage, and the stalling time ratio.

[0014] The stalling time voltage determiner can determine the stalling time voltage as a value of the voltage command when an absolute value of the voltage command is less than an absolute value of the stalling time voltage limit, determine the stalling time voltage as a positive stalling time voltage limit when the absolute value of the voltage command is not less than the absolute value of the stalling time voltage limit and both the voltage command and the stalling time voltage limit are positive, determine the stalling time voltage as a negative stalling time voltage limit when the absolute value of the voltage command is not less than the absolute value of the stalling time voltage limit and both the voltage command and the stalling time voltage limit are negative, determine the stalling time voltage as the positive stalling time voltage limit when the voltage command is negative and the stalling time voltage limit is positive, and determine the stalling time voltage as the negative stalling time voltage limit when the voltage command is positive and the stalling time voltage limit is negative.

[0015] The computing unit can include a first computing unit configured to output a voltage applied to the motor by performing a subtraction operation on the command voltage and the stall time voltage, a second computing unit configured to subtract the motor resistance voltage and the motor inductance voltage from the voltage applied to the motor, and a third computing unit configured to calculate the motor speed by dividing an output value of the second computing unit by a motor back-EMF constant.

[0016] The apparatus can further include a noise removing unit configured to estimate a final motor speed by removing noise from the motor speed calculated by the computing unit.

[0017] The limiter can include a torque current conversion unit configured to convert a torque command into a current command, a current limit value calculation unit configured to receive the motor speed and the DC link voltage and calculate a current command limit value, and a current command output unit configured to limit a size of the current command by using the current command output from the torque current conversion unit and the current command limit value calculated by the current limit value calculation unit.

[0018] The current limit value calculation unit can include a first current limit value calculator configured to calculate a positive current limit value by subtracting a back-EMF based on the motor speed from the positive DC link voltage and dividing a resulting value by a motor resistance, and a second current limit value calculator configured to calculate a negative current limit value by subtracting a back-EMF based on the motor speed from the negative DC link voltage and dividing a resulting value by the motor resistance.

[0019] In one embodiment, a method of estimating a speed of a DC motor in an MDPS system can include a motor speed estimator estimating a motor speed based on a DC link voltage driving the motor, a motor current flowing through the motor, and a voltage command, and a limiter generating a current command based on the estimated motor speed, a torque command, and the DC link voltage.

[0020] The estimation of the motor speed can include a stall time voltage calculation unit calculating a stall time voltage using the voltage command, the DC link voltage, and the motor current, a motor resistance and inductance voltage calculation unit calculating a motor resistance voltage through a resistance of the motor and calculating a motor inductance voltage through an inductance of the motor, and a computing unit calculating the motor speed based on the stall time voltage, the voltage command, the motor resistance voltage, the motor inductance voltage, and a preset motor back-EMF constant.

[0021] The calculation of the stall time voltage can include: the stall time voltage calculation unit calculating a stall time voltage limit value by applying the sign of the motor current, the DC link voltage, and the stall time ratio in the switching period; and the stall time voltage calculation unit determining the stall time voltage according to the stall time voltage limit value and the state of the voltage command.

[0022] In the calculation of the stall time voltage limit value, the stall time voltage calculation unit calculates the stall time voltage limit value by multiplying the sign of the motor current, the DC link voltage, and the stall time ratio.

[0023] In the determination of the stall time voltage, when the absolute value of the voltage command is less than the absolute value of the stall time voltage limit value, the stall time voltage calculation unit can determine the stall time voltage as the value of the voltage command, when the absolute value of the voltage command is not less than the absolute value of the stall time voltage limit value and both the voltage command and the stall time voltage limit value are positive, the stall time voltage calculation unit can determine the stall time voltage as the positive stall time voltage limit value, when the absolute value of the voltage command is not less than the absolute value of the stall time voltage limit value and both the voltage command and the stall time voltage limit value are negative, the stall time voltage calculation unit can determine the stall time voltage as the negative stall time voltage limit value, when the voltage command is negative and the stall time voltage limit value is positive, the stall time voltage calculation unit can determine the stall time voltage as the positive stall time voltage limit value, and when the voltage command is positive and the stall time voltage limit value is negative, the stall time voltage calculation unit can determine the stall time voltage as the negative stall time voltage limit value.

[0024] The calculation of the motor speed can include: the calculation unit outputting a motor applied voltage by performing a subtraction operation on the command voltage and the stall time voltage; and the calculation unit calculating the motor speed by subtracting the motor resistance voltage and the motor inductance voltage from the motor applied voltage and dividing the result value by the motor back-EMF constant.

[0025] The method can further include the noise removal unit estimating a final motor speed by removing noise from the motor speed calculated by the calculation unit.

[0026] The generation of the current command can include: a torque current conversion unit converting the torque command into the current command; a current limit value calculation unit receiving the motor speed and the DC link voltage and calculating a current command limit value; and a current command output unit limiting the size of the current command using the current command output from the torque current conversion unit and the current command limit value calculated by the current limit value calculation unit.

[0027] In the calculation of the current limit value, the current limit value calculation unit calculates the positive current limit value by subtracting the back electromotive force based on the motor speed from the positive DC link voltage and dividing the resulting value by the motor resistance, and calculates the negative current limit value by subtracting the back electromotive force based on the motor speed from the negative DC link voltage and dividing the resulting value by the motor resistance.

[0028] The apparatus and method of estimating the speed of a DC motor in an MDPS system according to an aspect of the disclosure can estimate the motor speed using a voltage command and a measured motor current, thus not requiring a voltage measurement circuit, thereby reducing cost.

[0029] In addition, the apparatus and method of estimating the speed of a DC motor in an MDPS system according to another aspect of the disclosure can estimate the motor speed by considering the dynamic state of the motor and a stall time voltage generated by a Pulse Width Modulation (PWM) generator, thereby improving the accuracy of motor speed estimation. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 FIG. 1 is a diagram for describing an apparatus for estimating the speed of a DC motor in an MDPS (Motor Driven Power Steering) system according to an embodiment of the disclosure.

[0031] Figure 2 FIG. 2 is a diagram for describing Figure 1 FIG. 3 is a diagram for describing a DC motor and a motor drive unit in an Electronic Control Unit (ECU) shown in FIG. 1.

[0032] Figure 3 FIG. 4 is a diagram for describing a stall time according to an embodiment of the disclosure.

[0033] Figure 4 FIG. 5 is a diagram for describing Figure 1 FIG. 6 is a diagram for describing a motor speed estimator shown in FIG. 1.

[0034] Figure 5 FIG. 7 is a diagram for describing Figure 4 FIG. 8 is a diagram for describing a stall time voltage calculation unit shown in FIG. 1.

[0035] Figure 6 FIG. 9 is a diagram for describing Figure 1 FIG. 10 is a diagram for describing a limiter shown in FIG. 1.

[0036] Figure 7 FIG. 11 is a graph for describing a current limit value of a current limit value calculation unit 420 shown in FIG. 1. Figure 6

[0037] Figure 8 ​is a flowchart for describing a method of estimating a speed of a DC motor in an MDPS system according to an embodiment of the disclosure.

[0038] Figure 9 is a flowchart for describing a method of estimating a motor speed by a motor speed estimator according to an embodiment of the disclosure.

[0039] Figure 10 is a flowchart for describing a method of generating a current command by a limiter according to an embodiment of the disclosure. DETAILED DESCRIPTION

[0040] According to the conventional in the respective fields, some exemplary embodiments can be described in the accompanying drawings according to functional blocks, units and / or modules. The blocks, units and / or modules can be understood by those of ordinary skill in the art as being physically implemented by electronic (or optical) circuits (e.g., logic circuits, discrete elements, processors, processors, memory elements, wired connections, etc.). When the blocks, units and / or modules are implemented by a processor or similar hardware, they can be programmed and controlled using software (e.g., code) to perform various functions discussed herein. Alternatively, each block, unit and / or module can be implemented by dedicated hardware or as a combination of dedicated hardware to perform some functions and can be executed by a processor (e.g., one or more programmed processors and related circuitry) to implement other functions. Each block, unit and / or module of some exemplary embodiments can be physically divided into two or more interacting and discrete blocks, units and / or modules without departing from the scope of the inventive concept. In addition, the blocks, units and / or modules of some exemplary embodiments can be physically combined into more complex blocks, units and / or modules without departing from the scope of the inventive concept.

[0041] Hereinafter, an apparatus and a method of estimating a speed of a DC motor in an MDPS (Motor Driven Power Steering) system will be described below by various exemplary embodiments with reference to the accompanying drawings. It should be noted that the accompanying drawings are not drawn to scale precisely, and the thickness of lines or the size of components can be exaggerated only for the purpose of description and clarity. In addition, the terms used herein are defined by considering the functions of the present invention, and can be changed according to the habits or intentions of users or operators. Therefore, the terms should be defined according to the entire disclosure set forth herein.

[0042] For example, the embodiments described in the specification can be implemented with, for example, a method or a procedure, an apparatus, a software program, a data stream, or a signal. Although a certain function is discussed only in a single context (for example, only in a method), the discussed function can be implemented in another type (for example, an apparatus or a program). The apparatus can be implemented with suitable hardware, software, or firmware. For example, the method can be implemented in an apparatus such as a processor, which generally refers to a processing device including a computer, a microprocessor, an integrated circuit, or a programmable logic device. The processor includes a communication device such as a computer, a cell phone, a personal digital assistant (PDA), and another device that can facilitate communication of information between end users.

[0043] Figure 1 is a graph for describing an apparatus for estimating a speed of a DC motor in an MDPS (Motor Driven Power Steering) system according to an embodiment of the disclosure, Figure 2 is a graph for describing Figure 1 is a graph of a DC motor and a motor drive unit in an electronic control unit (ECU) shown in Figure 3 is a graph for describing a stall time according to an embodiment of the disclosure, Figure 4 is a graph for describing Figure 1 is a graph of a motor speed estimator shown in Figure 5 is a graph for describing Figure 4 is a graph of a stall time voltage calculation unit shown in Figure 6 is a graph for describing Figure 1 is a graph of a limiter shown in Figure 7 is a graph for describing Figure 6 is a graph of a current limit value of a current limit value calculation unit 420 shown in

[0044] Referring to Figure 1 , the apparatus for estimating a speed of a DC motor in an MDPS system according to an embodiment of the disclosure includes a DC motor 100, an ECU 200, a motor speed estimator 300, a limiter 400, and a motor controller 500.

[0045] The DC motor 100 is installed on a steering shaft and operates by a voltage applied from the ECU 200. In the present embodiment, the motor can be a DC motor 100. However, the disclosure is not limited to the above-described embodiment.

[0046] The ECU 200 measures a direct current link voltage V dcThe measured DC link voltage and motor current flowing through the DC motor 100 are also measured. The ECU 200 can transmit the measured DC link voltage and motor current to the motor speed estimator 300, and can also transmit the DC link voltage to the motor controller 500.

[0047] ECU 200 can receive voltage commands from motor controller 500 and drive DC motor 100. Therefore, ECU 200 may include... Figure 2 The electric motor drive unit 210 is shown. (Reference) Figure 2 The motor drive unit 210 may include a PWM generator 212, a gate driver 214, and a converter 216.

[0048] The PWM generator 212 can calculate the duty cycle of the DC motor 100 based on the voltage command and generate PWM pulses to apply voltage to the DC motor 100. The PWM generator 212 can transmit the PWM pulses to the converter 216 through the gate driver 214.

[0049] Converter 216 can turn multiple switching elements on / off according to the PWM signal generated by PWM generator 212 to provide DC power input from a power supply unit or battery (not shown) to DC motor 100. That is, converter 216 can apply a DC link voltage to DC motor 100 according to the PWM signal to drive DC motor 100. Such converter 216 may include multiple power switching elements, for example, using a full-bridge (F-bridge) circuit to drive DC motor 100.

[0050] The converter 216 has an output voltage determined by the complementary switching operations of two power switching elements (e.g., insulated-gate bipolar transistors, IGBTs) at its top and bottom. In this case, a short-circuit fault may occur when both power switching elements are turned on. Therefore, as... Figure 3 As shown, the two power switching elements can be turned on with a tiny time difference between them. This tiny time difference is called the dwell time. Therefore, the converter 216 can convert the voltage command V... c and the voltage V during the dwell time d The voltage corresponding to the difference between them is applied to the DC motor 100.

[0051] When the DC motor 100 is represented as an equivalent circuit, such as Figure 2 As shown, the equivalent circuit can be implemented using the motor resistance R as a parameter of the motor. a 120 and motor inductance L a110. When the equivalent circuit of the DC motor 100 is used, a relationship with the voltage applied from the motor drive unit 210 can be identified. That is, the voltage applied from the motor drive unit 210 can be equal to the motor voltage generated by the equivalent circuit of the DC motor 100. This can be expressed as Equation 1 below.

[0052] Equation 1:

[0053]

[0054] In Equation 1, v a may represent the applied voltage, V c may represent the voltage command, v d may represent the stall voltage, R a may represent the motor resistance 120, i a may represent the motor current, L a may represent the motor inductance, K b may represent the motor back EMF constant, and ω m may represent the motor speed.

[0055] In Equation 1, the voltage command, the motor resistance 120, the motor current, the motor inductance 110, and the motor back EMF constant can be predetermined values or calculated values. However, the stall voltage and the motor speed are not determined values, and thus need to be calculated.

[0056] Accordingly, the motor speed estimator 300 estimates the motor speed based on the DC link voltage driving the DC motor 100, the motor current measured from the DC motor 100, and the voltage command.

[0057] That is, the motor speed estimator 300 can receive the DC link voltage and the motor current from the ECU 200, receive the voltage command from the motor controller 500, and estimate the motor speed using the received DC link voltage, motor current, and voltage command. The motor speed estimator 300 can estimate the motor speed ω m using Equation 2 below.

[0058] Equation 2:

[0059]

[0060] Equation 1 is transformed into a motor speed equation, resulting in Equation 2.

[0061] Accordingly, the motor speed estimator 300 can estimate the motor speed using the stall voltage generated by the motor drive unit 210 and the voltage determined by the motor resistance 120 and the motor inductance 110.

[0062] Referring to Figure 4 , the motor speed estimator 300 can include a stalling time voltage calculation unit 310, a first calculation unit 320, a motor resistance and inductance voltage calculation unit 330, a second calculation unit 340, a third calculation unit 350, and a noise removal unit 360.

[0063] The stalling time voltage calculation unit 310 can calculate a stalling time voltage using a voltage command, a DC link voltage, and a motor current.

[0064] Referring to Figure 5 , the stalling time voltage calculation unit 310 includes a stalling time voltage limit calculator 312 and a stalling time voltage determiner 314.

[0065] The stalling time voltage limit calculator 312 can calculate a stalling time voltage limit V d_lim by applying a direction (sign) of a motor current, a DC link voltage, and a stalling time ratio to a switching period.

[0066] For example, the stalling time voltage limit calculator 312 can calculate a stalling time voltage limit V d_lim by multiplying a direction (sign) of a motor current, a DC link voltage, and a stalling time ratio to a switching period.

[0067] The stalling time voltage determiner 314 can determine a stalling time voltage V c according to a state of a voltage command V d_lim and the stalling time voltage limit V d .

[0068] For example, when an absolute value of the voltage command V c is less than an absolute value of the stalling time voltage limit V d_lim , the stalling time voltage determiner 314 can determine the stalling time voltage V d as a value equal to the voltage command, denoted as 'A'. Also, when both the voltage command V c and the stalling time voltage limit V d_lim exceed '0' or are positive, the stalling time voltage determiner 314 can determine the stalling time voltage V d as a positive stalling time voltage limit +V d_lim , denoted as 'B'. Also, when both the voltage command V c and the stalling time voltage limit V d_lim are less than '0' or are negative, the stalling time voltage determiner 314 can determine the stalling time voltage V d as a negative stalling time voltage limit -V d_limIt is represented by 'C'. Furthermore, when the voltage command V... c Less than '0' or negative, and the voltage limit value V during the dwell time. d_lim When the value exceeds '0' or is positive, the stall time voltage determiner 314 can determine the stall time voltage V. d Determined as the positive dwell time voltage limit value +V d_lim It is represented by 'D'. Furthermore, when the voltage command V... c When the value exceeds '0' or is negative, and the voltage limit value V during the dwell time is... d_lim When the value is less than '0' or negative, the stall time voltage determiner 314 can determine the stall time voltage V. d The negative stall time voltage limit value -V was determined. d_lim , represented by 'E'.

[0069] The first calculation unit 320 uses the voltage command and the dwell time voltage to calculate the voltage v applied by the motor. a In other words, the first calculation unit 320 can output the voltage v applied to the motor by performing a subtraction operation on the voltage command and the voltage during the dwell time. a .

[0070] The motor resistance and inductance voltage calculation unit 330 can calculate the voltage determined by the motor resistance 120 and the motor inductance 110 in the equivalent circuit of the motor. Therefore, the motor resistance and inductance voltage calculation unit 330 may include a motor resistance voltage calculator 332 and a motor inductance voltage calculator 334.

[0071] The motor resistance voltage calculator 332 can calculate the motor resistance voltage using the motor resistance 120Ω and the motor current. In other words, the motor resistance voltage calculator 332 can calculate the motor resistance voltage by using the motor resistance R... a 120 and motor current i a Multiply them to calculate the motor resistance voltage.

[0072] The 334 motor inductance voltage calculator can reflect the motor inductance L a The effect of 110 is used to calculate the motor inductance voltage. The motor inductance voltage calculator 334 can calculate the motor inductance voltage in the following ways: through unit delay, subtraction, low-pass filter (LPF), and 1 / T. s Differentiate the motor current and convert the differentiated motor current to a different value. Multiplied by the motor inductance L a 110.

[0073] For example, in Figure 2In the case of the equivalent circuit of the motor, the motor resistance voltage calculator 332 can calculate the motor resistance voltage, such as R a L a , the motor inductance voltage calculator 334 can calculate the motor inductance voltage, such as

[0074] The second calculation unit 340 can perform a subtraction operation on the motor applied voltage calculated by the first calculation unit 320, the motor resistance voltage calculated by the motor resistance voltage calculator 332, and the motor inductance voltage calculated by the motor inductance voltage calculator 334. That is, the second calculation unit 340 can subtract the motor resistance voltage and the motor inductance voltage from the motor applied voltage.

[0075] The third calculation unit 350 can calculate the motor speed by dividing the output value of the second calculation unit 340 by a preset back-EMF constant. At this time, since the calculated motor speed can contain noise, it is necessary to remove the noise.

[0076] Therefore, the noise removal unit 360 can remove the noise from the motor speed calculated by the third calculation unit 350. At this time, the noise removal unit 360 can be implemented as an LPF.

[0077] The limiter 400 limits the size of the current command input to the motor controller using the motor speed estimated by the motor speed estimator 300.

[0078] The limiter 400 converts the torque command into the current command, receives the DC link voltage and the motor speed estimated by the motor speed estimator 300, calculates the current command limit value, and outputs the limited current command. The torque command can be received from the MDPS control logic.

[0079] Referring to Figure 6 , the limiter 400 includes a torque-current conversion unit (conversion into a current command) 410, a current limit value calculation unit 420, and a current command output unit (limiting function) 430.

[0080] The torque-current conversion unit 410 can convert the torque command into the current command. That is, since the torque is proportional to the product of the magnetic flux and the current, and the magnetic flux has a fixed value depending on the motor, the torque-current conversion unit 410 can convert the torque command into the current command.

[0081] The current limit value calculation unit 420 receives the DC link voltage and the motor speed estimated by the motor speed estimator 300, and calculates the current command limit value. At this time, the current limit value calculation unit 420 can calculate the positive current limit value and the negative current limit value.

[0082] Accordingly, the current limit value calculation unit 420 can include a first current limit value calculator 422 configured to calculate a positive current limit value and a second current limit value calculator 424 configured to calculate a negative current limit value.

[0083] The first current limit value calculator 422 can calculate the positive current limit value by subtracting the back electromotive force from the positive DC link voltage, the motor speed being reflected to the back electromotive force, and then dividing the resulting value by the motor resistance 120. That is, the first current limit value calculator 422 can calculate the positive current limit value i a_lim .

[0084] Equation 3:

[0085] + i a_lim = (V dc - K b ω m ) / R a .

[0086] Then, the first current limit value calculator 422 can calculate the positive current limit value, for example, the positive limit shown in Equation 3. Figure 7

[0087] The second current limit value calculator 424 can calculate the negative current limit value by subtracting the back electromotive force from the negative DC link voltage, the motor speed being reflected to the back electromotive force, and dividing the resulting value by the motor resistance 120. That is, the second current limit value calculator 424 can calculate the negative current limit value -i a_lim .

[0088] Equation 4:

[0089] - i a_lim = (-V dc - K b ω m ) / R a .

[0090] Then, the second current limit value calculator 424 can calculate the negative current limit value, for example, the negative limit shown in Equation 4. Figure 7

[0091] ​​The current command output unit 430 can output a final current command using the current command output from the torque current conversion unit 410 and the current command limit value calculated by the current limit value calculation unit 420. That is, the current command output unit 430 can limit the size of the current command so that the current command output from the torque current conversion unit 410 is included within the range of the current command limit value. For example, when the current command exceeds the current command limit value, the current command output unit 430 can output the corresponding current command as the current command limit value.

[0092] The motor controller 500 receives the current command and the DC link voltage from the limiter 400 and the ECU 200, respectively, and outputs a voltage command to operate the DC motor.

[0093] As described above, the MDPS system using the DC motor 100 can estimate the motor speed using the voltage command and the motor current.

[0094] Figure 8 is a flowchart for describing a method of estimating a speed of a DC motor in an MDPS system according to an embodiment of the disclosure.

[0095] Referring to Figure 8 In step S810, the motor speed estimator 300 estimates the motor speed based on the DC link voltage driving the DC motor 100, the motor current flowing through the DC motor 100, and the voltage command. Referring to Figure 9 The method in which the motor speed estimator 300 estimates the motor speed will be described in more detail.

[0096] When step S810 is performed, in step S820, the limiter 400 generates a current command based on the estimated motor speed, the torque command, and the DC link voltage. Referring to Figure 10 The method in which the limiter 400 generates the current command will be described in detail.

[0097] Figure 9 is a flowchart for describing a method of estimating a motor speed by a motor speed estimator according to an embodiment of the disclosure.

[0098] Referring to Figure 9 In step S910, the stall time voltage calculation unit 310 calculates a stall time voltage using the voltage command, the DC link voltage, and the motor current. That is, the stall time voltage calculation unit 310 can calculate a stall time voltage limit value by applying the sign of the motor current, the DC link voltage, and the stall time ratio within a switching period. Then, the stall time voltage calculation unit 310 can determine the stall time voltage according to the state of the stall time voltage limit value and the voltage command.

[0099] When step S910 is performed, the motor resistance and inductance voltage calculation unit 330 calculates a motor resistance voltage by the resistance 120 of the DC motor 100, and in step S920, a motor inductance voltage by the inductance 110 of the DC motor 100.

[0100] When step S920 is performed, in step S930, the calculation unit outputs a motor applied voltage by performing a subtraction operation on the command voltage and the stall time voltage.

[0101] When step S930 is performed, in step S940, the calculation unit calculates a motor speed using the motor applied voltage, the motor resistance voltage, the motor inductance voltage, and the motor back-EMF constant. That is, the calculation unit can calculate the motor speed by subtracting the motor resistance voltage and the motor inductance voltage from the motor applied voltage, and dividing the result value by the motor back-EMF constant.

[0102] Figure 10 is a flowchart for describing a method of generating a current command by a limiter according to an embodiment of the disclosure.

[0103] Referring to Figure 10 In step S1010, the torque current conversion unit 410 converts a torque command into a current command, and in step S1020, the current limit value calculation unit 420 receives a motor speed and a DC link voltage, and calculates a current command limit value. At this time, the current limit value calculation unit 420 can calculate a positive current limit value by subtracting a back-EMF based on the motor speed from the positive DC link voltage, and dividing the result value by the motor resistance 120. In addition, the current limit value calculation unit 420 can calculate a negative current limit value by subtracting a back-EMF based on the motor speed from the negative DC link voltage, and dividing the result value by the motor resistance 120.

[0104] When step S1020 is performed, in step S1030, the current command output unit 430 limits the size of the current command using the current command output by the torque current conversion unit 410 and the current command limit value calculated by the current limit value calculation unit 420.

[0105] As described above, the apparatus and method of estimating a speed of a DC motor 100 in an MDPS system according to an aspect of the disclosure can estimate a motor speed using a voltage command and a measured motor current, and thus does not need a voltage measurement circuit, thereby reducing costs.

[0106] Further, the apparatus and method of estimating the speed of the DC motor 100 in the MDPS system according to another aspect of the present disclosure can estimate the motor speed by considering the dynamic state of the motor 100 and the stall time voltage generated by the PWM generator 212, thereby improving the accuracy of the motor speed estimation.

[0107] While exemplary embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the present disclosure as defined by the following claims. Accordingly, the true technical scope of the present disclosure should be defined by the appended claims.

Claims

1. An apparatus of estimating a speed of a DC motor in a motor-driven power steering (MDPS) system, comprising: a motor speed estimator configured to estimate a motor speed based on a DC link voltage driving a motor, a motor current flowing through the motor, and a voltage command; and a limiter configured to generate a current command based on the estimated motor speed, a torque command, and the DC link voltage, wherein the motor speed estimator comprises: a stalling time voltage calculation unit configured to calculate a stalling time voltage using the voltage command, the DC link voltage, and the motor current; a motor resistance and inductance voltage calculation unit configured to calculate a motor resistance voltage by a resistance of the motor and a motor inductance voltage by an inductance of the motor; and a calculation unit configured to calculate the motor speed based on the stalling time voltage, the voltage command, the motor resistance voltage, the motor inductance voltage, and a preset motor back EMF constant.

2. The apparatus of claim 1, wherein, the stalling time voltage calculation unit comprises: a stalling time voltage limit calculator configured to calculate a stalling time voltage limit by applying a sign of the motor current, the DC link voltage, and a stalling time ratio over a switching period; and a stalling time voltage determiner configured to determine the stalling time voltage according to a state of the stalling time voltage limit and the voltage command.

3. The apparatus of claim 2, wherein, the stalling time voltage limit calculator calculates the stalling time voltage limit by multiplying the sign of the motor current, the DC link voltage, and the stalling time ratio.

4. The apparatus of claim 2, wherein, when an absolute value of the voltage command is less than an absolute value of the stalling time voltage limit, the stalling time voltage determiner determines the stalling time voltage as a value of the voltage command, when the absolute value of the voltage command is not less than the absolute value of the stalling time voltage limit and both the voltage command and the stalling time voltage limit are positive, the stalling time voltage determiner determines the stalling time voltage as a positive stalling time voltage limit, when the absolute value of the voltage command is not less than the absolute value of the stalling time voltage limit and both the voltage command and the stalling time voltage limit are negative, the stalling time voltage determiner determines the stalling time voltage as a negative stalling time voltage limit, when the voltage command is negative and the stalling time voltage limit is positive, the stalling time voltage determiner determines the stalling time voltage as the positive stalling time voltage limit, and when the voltage command is positive and the stalling time voltage limit is negative, the stalling time voltage determiner determines the stalling time voltage as the negative stalling time voltage limit.

5. The apparatus of claim 1, wherein, the calculation unit comprises: a first calculation unit configured to output a motor applied voltage by performing a subtraction operation on the voltage command and the stalling time voltage; a second calculation unit configured to subtract the motor resistance voltage and the motor inductance voltage from the voltage applied to the motor; and a third calculation unit configured to calculate the motor speed by dividing an output value of the second calculation unit by the motor back-EMF constant.

6. The apparatus of claim 1, further comprising a noise removal unit configured to estimate a final motor speed by removing noise from the motor speed calculated by the calculation unit.

7. The apparatus of claim 1, wherein, The limiter includes: a torque-to-current conversion unit configured to convert the torque command to the current command; a current limit value calculation unit configured to receive the motor speed and the DC link voltage and calculate a current command limit value; and a current command output unit configured to limit a magnitude of the current command by using the current command output from the torque-to-current conversion unit and the current command limit value calculated by the current limit value calculation unit.

8. The apparatus of claim 7, wherein, The current limit value calculation unit includes: a first current limit value calculator configured to calculate a positive current limit value by subtracting a back-EMF based on the motor speed from a positive DC link voltage and dividing a resulting value by a motor resistance; and a second current limit value calculator configured to calculate a negative current limit value by subtracting the back-EMF based on the motor speed from a negative DC link voltage and dividing a resulting value by the motor resistance.

9. A method of estimating a speed of a DC motor in a motor-driven power steering (MDPS) system, the method comprising: a motor speed estimator estimating a motor speed based on a DC link voltage driving the motor, a motor current flowing through the motor, and a voltage command; and a limiter generating a current command based on the estimated motor speed, a torque command, and the DC link voltage, wherein the estimation of the motor speed includes: a stall time voltage calculation unit calculating a stall time voltage using the voltage command, the DC link voltage, and the motor current; a motor resistance and inductance voltage calculation unit calculating a motor resistance voltage by a resistance of the motor and a motor inductance voltage by an inductance of the motor; and a calculation unit calculating the motor speed based on the stall time voltage, the voltage command, the motor resistance voltage, the motor inductance voltage, and a preset motor back-EMF constant.

10. The method of claim 9, wherein, The calculation of the stall time voltage includes: the stall time voltage calculation unit calculating a stall time voltage limit value by multiplying a sign of the motor current, the DC link voltage, and a stall time ratio within a switching period; and the stall time voltage calculation unit determining the stall time voltage according to a state of the stall time voltage limit value and the voltage command.

11. The method of claim 10, wherein, In the calculation of the stall time voltage limit value, the stall time voltage calculation unit calculates the stall time voltage limit value by multiplying the sign of the motor current, the DC link voltage, and the stall time ratio.

9. A method of estimating a speed of a DC motor in a motor-driven power steering (MDPS) system, the method comprising: a motor speed estimator estimating a motor speed based on a DC link voltage driving the motor, a motor current flowing through the motor, and a voltage command; and a limiter generating a current command based on the estimated motor speed, a torque command, and the DC link voltage, wherein the estimation of the motor speed includes: a stall time voltage calculation unit calculating a stall time voltage using the voltage command, the DC link voltage, and the motor current; a motor resistance and inductance voltage calculation unit calculating a motor resistance voltage by a resistance of the motor and a motor inductance voltage by an inductance of the motor; and a calculation unit calculating the motor speed based on the stall time voltage, the voltage command, the motor resistance voltage, the motor inductance voltage, and a preset motor back-EMF constant. The calculation of the stall time voltage includes: the stall time voltage calculation unit calculating a stall time voltage limit value by multiplying a sign of the motor current, the DC link voltage, and a stall time ratio within a switching period; and the stall time voltage calculation unit determining the stall time voltage according to a state of the stall time voltage limit value and the voltage command. In the calculation of the stall time voltage limit value, the stall time voltage calculation unit calculates the stall time voltage limit value by multiplying the sign of the motor current, the DC link voltage, and the stall time ratio.

12. The method of claim 10, wherein, In the determination of the stalling time voltage, when the absolute value of the voltage command is smaller than the absolute value of the stalling time voltage limit value, the stalling time voltage calculation unit determines the stalling time voltage as the value of the voltage command, when the absolute value of the voltage command is not smaller than the absolute value of the stalling time voltage limit value and both the voltage command and the stalling time voltage limit value are positive, the stalling time voltage calculation unit determines the stalling time voltage as the positive stalling time voltage limit value, when the absolute value of the voltage command is not smaller than the absolute value of the stalling time voltage limit value and both the voltage command and the stalling time voltage limit value are negative, the stalling time voltage calculation unit determines the stalling time voltage as the negative stalling time voltage limit value, when the voltage command is negative and the stalling time voltage limit value is positive, the stalling time voltage calculation unit determines the stalling time voltage as the positive stalling time voltage limit value, and when the voltage command is positive and the stalling time voltage limit value is negative, the stalling time voltage calculation unit determines the stalling time voltage as the negative stalling time voltage limit value.

13. The method of claim 9, wherein, The calculation of the motor speed includes: the calculation unit outputs a motor applied voltage by performing a subtraction operation on a voltage command and the stalling time voltage; and the calculation unit calculates the motor speed by subtracting the motor resistance voltage and the motor inductance voltage from the motor applied voltage and dividing a resulting value by the motor back electromotive force constant.

14. The method of claim 9, further comprising: A noise removal unit estimates a final motor speed by removing noise from the motor speed calculated by the calculation unit.

15. The method of claim 9, wherein, The generation of the current command includes: a torque current conversion unit converts the torque command to the current command; a current limit value calculation unit receives the motor speed and the DC link voltage and calculates a current command limit value; and a current command output unit limits the size of the current command using the current command output from the torque current conversion unit and the current command limit value calculated by the current limit value calculation unit.

16. The method of claim 15, wherein, In the calculation of the current command limit value, the current limit value calculation unit calculates a positive current limit value by subtracting a back electromotive force based on the motor speed from a positive DC link voltage and dividing a resulting value by a motor resistance, and calculates a negative current limit value by subtracting the back electromotive force based on the motor speed from a negative DC link voltage and dividing a resulting value by the motor resistance.

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