MOTOR CONTROLLING METHOD, MOTOR CONTROLLING SYSTEM, AND ELECTRONIC POWER STEERING SYSTEM

Abstract

A motor controlling method includes a step of obtaining an armature magnetic flux, a resultant magnetic flux, a stator current, and a stator voltage, which are represented by a phasor, with respect to an - fixed coordinate system or a d-q rotating coordinate system, a step of calculating an angle () between the stator current and the stator voltage, a step of calculating a torque angle () according to:

=90tan.sup.1[(.sub.s.sub.a sin())/(.sub.a cos())],

where .sub.a indicates a magnitude of the armature magnetic flux and .sub.s indicates a magnitude of the resultant magnetic flux, and a step of controlling the surface permanent magnet motor based on the torque angle ().

Claims

1-7. (canceled)

8. A motor controlling method of controlling a surface permanent magnet motor, the motor controlling method comprising the step of: acquiring an armature magnetic flux, a resultant magnetic flux, a stator current, and a stator voltage, which are represented by a phasor, with respect to an - fixed coordinate system or a d-q rotating coordinate system; calculating an angle () between the stator current and the stator voltage; calculating a torque angle () according to:
=90tan.sup.1[(.sub.s.sub.a sin())/(.sub.a cos())], where .sub.a indicates a magnitude of the armature magnetic flux and .sub.s indicates a magnitude of the resultant magnetic flux; and controlling the surface permanent magnet motor based on the torque angle ().

9. A motor controlling method of controlling a surface permanent magnet motor, the motor controlling method comprising the step of: acquiring a resultant magnetic flux, a stator current, and a stator voltage, which are represented by a phasor, with respect to an - fixed coordinate system or a d-q rotating coordinate system; calculating an angle () between the stator current and the stator voltage; calculating a torque angle () according to:
=tan.sup.1[(LI.sub.s cos())/(.sub.sLI.sub.s sin())], where L is an armature inductance, .sub.s indicates a magnitude of the resultant magnetic flux, and I.sub.s indicates a magnitude of the stator current; and controlling the surface permanent magnet motor based on the torque angle ().

10. The motor controlling method of claim 8, further comprising a step of calculating torque T based on the torque angle (); wherein in the step of controlling the motor, the surface permanent magnet motor is controlled based on the torque T.

11. The motor controlling method of claim 10, further comprising a step of calculating a phase angle () based on a component on an -axis and a component on a -axis of the resultant magnetic flux in the - fixed coordinate system and calculating a rotor angle () based on the torque angle () and the phase angle (); wherein in the step of controlling the motor, the surface permanent magnet motor is controlled based on the rotor angle () and the torque (T).

12. A motor controlling system for controlling a surface permanent magnet motor, the motor controlling system comprising; a surface permanent magnet motor; and a control circuit configured to control the surface permanent magnet motor; wherein the control circuit acquires an armature magnetic flux, a resultant magnetic flux, a stator current, and a stator voltage, which are represented by a phasor, with respect to an - fixed coordinate or a d-q rotating coordinate system; calculates an angle () between the stator current and the stator voltage; calculates a torque angle () according to:
=90tan.sup.1[(.sub.s.sub.a sin())/(.sub.a cos())], where .sub.a indicates a magnitude of the armature magnetic flux and .sub.s indicates a magnitude of the resultant magnetic flux; and controls the surface permanent magnet motor based on the torque angle ().

13. A motor controlling system for controlling a surface permanent magnet motor, the motor controlling system comprising; a surface permanent magnet motor; and a control circuit which controls the surface permanent magnet motor; wherein the control circuit acquires a resultant magnetic flux, a stator current, and a stator voltage, which are represented by a phasor, with respect to an - fixed coordinate or a d-q rotating coordinate system; calculates an angle () between the stator current and the stator voltage; calculates a torque angle () according to:
=tan.sup.1[(LI.sub.s cos())/(.sub.sLI.sub.s sin())], where L is an armature inductance, .sub.s indicates a magnitude of the resultant magnetic flux, and I.sub.s indicates a magnitude of the stator current; and controls the surface permanent magnet motor based on the torque angle ().

14. An electronic power steering system comprising the motor controlling system of claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a block diagram illustrating a hardware block of a motor controlling system according to an example embodiment of the present disclosure.

[0014] FIG. 2 is a block diagram illustrating a hardware configuration of an inverter 300 of a motor controlling system according to an example embodiment of the present disclosure.

[0015] FIG. 3 is a block diagram illustrating a hardware block of a motor controlling system 1000 according to a modified example of an example embodiment of the present disclosure.

[0016] FIG. 4 is a functional block diagram illustrating a functional block of a controller.

[0017] FIG. 5 is a phasor diagram showing variables (I.sub.s, .sub.s, , and V.sub.s).

[0018] FIG. 6 is a phasor diagram showing a resultant magnetic flux (.sub.s) on an - fixed coordinate system or d-q rotating coordinate system.

[0019] FIG. 7 is a phasor diagram showing a rotor magnetic flux (.sub.m), an armature magnetic flux (.sub.a), and a resultant magnetic flux (.sub.s).

[0020] FIG. 8 is a graph showing a waveform of torque (top), waveforms of three-phase currents (middle), and waveforms of three-phase voltages (bottom) within a certain period.

[0021] FIG. 9 is a graph showing a waveform of a torque angle (degree) estimated using a calculation equation according to an example embodiment of the present disclosure and a measured value of a torque angle within a certain period.

[0022] FIG. 10 is a schematic diagram illustrating a typical configuration of an electric power steering (EPS) system according to an example embodiment of the present disclosure.

DETAILED DESCRIPTION

[0023] Hereinafter, example embodiments of motor controlling methods, motor controlling systems, and electronic power steering systems each including a motor controlling system according to an example embodiment of the present disclosure will be described with reference to the accompanying drawings. However, there will be instances in which unnecessarily detailed description is omitted. This is to prevent the following description from being unnecessarily lengthy, in order to facilitate understanding for a person of ordinary skill in the art. For example, detailed descriptions of subject matter that is already well-known, as well as a redundant description of components that are substantially the same will be omitted in some cases.

[0024] FIG. 1 schematically shows a hardware block of a motor controlling system 1000 according to the present example embodiment.

[0025] The motor controlling system 1000 typically includes a motor M, a controller (control circuit) 100, a driving circuit 200, an inverter (also referred to as an inverter circuit) 300, a plurality of current sensors 400, an analog-to-digital conversion circuit (hereinafter, referred to as an AD converter) 500, and a read only memory (ROM) 600. The motor controlling system 1000 may be modularized. Thus, for example, the motor controlling system 1000 may be manufactured and sold as a motor module including a motor, a sensor, a driver, and a controller. In the present specification, the motor controlling system 1000 will be described by exemplifying a system having the motor M as a component. However, the motor controlling system 1000 may be a system for driving the motor M which does not include the motor M as a component.

[0026] The motor M is a surface permanent magnet (SPM) motor, for example, a surface permanent magnet synchronous motor (SPMSM). The motor M includes three-phase coils (U-phase coil, V-phase coil, and W-phase coil) (not shown). The three-phase coils are electrically connected to the inverter 300. The present disclosure is not limited to a three-phase motor, but multiphase motors such as a five-phase motor and a seven-phase motor are also within the scope of the present disclosure. In the present specification, example embodiments of the present disclosure will be described by exemplifying a motor controlling system for controlling a three-phase motor.

[0027] The controller 100 is, for example, a microcontroller unit (MCU). Alternatively, the controller 100 may also be implemented, for example, as a field programmable gate array (FPGA) equipped with a central processing unit (CPU) core.

[0028] The controller 100 controls the entirety of the motor controlling system 1000 and controls, for example, torque and a rotational speed of the motor M through a vector control. The present disclosure is not limited to the vector control, and the motor M may also be controlled though other closed loop controls. The rotational speed is expressed in revolutions per minute (rpm) at which a rotor rotates for a unit time (for example, for one minute) or revolutions per second (rps) at which the rotor rotates for a unit time (for example, for one second). The vector control is a method of dividing a current flowing in a motor into a current component contributing to the generation of torque and a current component contributing to the generation of a magnetic flux and independently controlling the current components orthogonal to each other. The controller 100 sets, for example, a target current value according to an actual current value measured by the plurality of current sensors 400 and a rotor angle estimated based on the actual current value. The controller 100 generates a pulse width modulation (PWM) signal based on the target current value and outputs the generated PWM signal to the driving circuit 200.

[0029] The driving circuit 200 is, for example, a gate driver. The driving circuit 200 generates a control signal for controlling a switching operation of a switching element in the inverter 300 according to the PWM signal output from the controller 100. As will be described below, the driving circuit 200 may be mounted on the controller 100.

[0030] For example, the inverter 300 converts direct current (DC) power supplied from a DC power source (not shown) into alternating current (AC) power and drives the motor M with the converted AC power. For example, the inverter 300 converts DC power into three-phase AC power which is a pseudo-sinusoidal wave having a U-phase, a V-phase, and a W-phase based on a control signal output from the driving circuit 200. The motor M is driven by the converted three-phase AC power.

[0031] The plurality of current sensors 400 include at least two current sensors configured to detect at least two currents flowing in the U-phase, V-phase, and W-phase coils of the motor M. In the present example embodiment, the plurality of current sensors 400 include two current sensors 400A and 400B (see FIG. 2) configured to detect currents flowing in the U-phase and the V-phase. Of course, the plurality of current sensors 400 may include three current sensors configured to detect three currents flowing in the U-phase, the V-phase, and the W-phase coils. For example, the plurality of current sensors 400 may include two current sensors configured to detect currents flowing in the V-phase and the W-phase or currents flowing in the W-phase and the U-phase. The current sensor includes, for example, a shunt resistor and a current detection circuit (not shown) configured to detect a current flowing in the shunt resistor. A resistance value of the shunt resistor is, for example, about 0.1 .

[0032] The AD converter 500 samples an analog signal output from the plurality of current sensors 400, converts the analog signal into a digital signal, and outputs the converted digital signal to the controller 100. The controller 100 may also perform AD conversion. In this case, the plurality of current sensors 400 directly output an analog signal to the controller 100.

[0033] The ROM 600 is, for example, a writable memory (for example, a programmable read only memory (PROM)), a rewritable memory (for example, a flash memory), or a read-only memory. The ROM 600 stores a control program having a command group for controlling the motor M in the controller 100. For example, the control program is first loaded in a random access memory (RAM, not shown) at the time of booting. The ROM 600 need not be mounted outside the controller 100 but may be mounted on the controller 100. The controller 100 equipped with the ROM 600 may be, for example, the above-described MCU.

[0034] A hardware configuration of the inverter 300 will be described in detail with reference to FIG. 2.

[0035] FIG. 2 schematically shows the hardware configuration of the inverter 300 of the motor controlling system 1000 according to the present example embodiment.

[0036] The inverter 300 includes three low side switching elements and three high side switching elements. As shown, switching elements SW_L1, SW_L2, and SW_L3 are the low side switching elements, and switching elements SW_H1, SW_H2, and SW_H3 are the high side switching elements. For example, a semiconductor switching element such as a field effect transistor (FET, typically a metal-oxide semiconductor field-effect transistor (MOSFET)) or an insulated gate bipolar transistor (IGBT) may be used as the switching element. The switching element includes a reflux diode configured to allow a regenerative current flowing toward the motor M to flow therefrom.

[0037] FIG. 2 shows shunt resistors Rs of two current sensors 400A and 400B configured to detect currents flowing in the U-phase and the V-phase. As shown, for example, the shunt resistor Rs may be electrically connected between the low side switching element and a ground. Alternatively, for example, the shunt resistor Rs may be electrically connected between the high side switching element and a power source.

[0038] For example, the controller 100 may drive the motor M by performing a control through three-phase conduction (hereinafter, referred to as a three-phase conduction control) based on a vector control. For example, the controller 100 generates a PWM signal for performing a three-phase conduction control and outputs the PWM signal to the driving circuit 200. The driving circuit 200 generates a gate control signal for controlling a switching operation of each FET of the inverter 300 based on the PWM signal and supplies the generated gate control signal to a gate of each FET.

[0039] FIG. 3 schematically shows a hardware block of a motor controlling system 1000 according to a modified example of the present example embodiment.

[0040] As shown in the drawing, the motor controlling system 1000 may not include a driving circuit 200. In this case, a controller 100 includes a port capable of directly controlling a switching operation of each FET of an inverter 300. Specifically, the controller 100 may generate a gate control signal based on a PWM signal. The controller 100 may output the gate control signal through the port and supply the gate control signal to a gate of each FET.

[0041] As shown in FIG. 3, the motor controlling system 1000 may further include a position sensor 700. The position sensor 700 is disposed in a motor M, detects a rotor angle, and outputs the detected rotor angle to the controller 100. The position sensor 700 is implemented, for example, by a combination of a magnetoresistive (MR) sensor including an MR element and a sensor magnet. The position sensor 700 is implemented by using, for example, a Hall integrated circuit (IC) including a Hall element or a resolver.

[0042] The motor controlling system 1000 may include, for example, a speed sensor or an acceleration sensor instead of the position sensor 700. When the speed sensor is used as the position sensor, the controller 100 may calculate a rotor angle, i.e., a rotation angle, by performing integral treatment or the like on a rotational speed signal or an angular speed signal. An angular speed is expressed in radians per second (rad/s) at which a rotor rotates for one second. In addition, when the acceleration sensor is used as the position sensor, the controller 100 may calculate a rotation angle by performing integral treatment or the like on an angular acceleration signal.

[0043] The motor controlling system of the present disclosure may be used, for example, as a motor controlling system for performing a sensorless control, which does not include a position sensor as shown in FIGS. 1 and 2. In addition, the motor controlling system of the present disclosure may be used, for example, as a motor controlling system for performing a sensor control which includes a position sensor as shown in FIG. 3.

[0044] Hereinafter, by exemplifying a motor controlling system for controlling a sensorless control, a specific example of a motor controlling method used in the system will be described with reference to FIGS. 4 to 7, and calculations used to estimate a torque angle will be mainly described. The motor controlling method of the present disclosure may be used in various motor controlling systems for controlling an SPM motor in which a torque angle estimation is required.

[0045] An outline of a controlling method of a motor controlling system 1000 is as follows.

[0046] First, three-phase currents I.sub.a, I.sub.b, and I.sub.c measured by a current sensor 400 are transformed into a current I.sub. and a current I.sub. on an -axis and a -axis of an - fixed coordinate system. Next, a phase angle is calculated based on the current I.sub. and the current I.sub.. In addition, a stator current I.sub.s, a resultant magnetic flux .sub.s, and an angle ((hereinafter, referred to as a phase angle ) between the stator current I.sub.s and the resultant magnetic flux .sub.s are calculated. After that, a torque angle is estimated based on the stator current I.sub.s, the resultant magnetic flux .sub.s, and the phase angle . In addition, torque T and a rotor angle required for controlling a motor are determined based on the torque angle . Finally, a motor M is controlled based on the torque T and the rotor angle .

[0047] An algorithm for implementing the motor controlling method according to the present example embodiment may be implemented, for example, only by hardware such as an application specific integrated circuit (ASIC) or an FPGA or may also be implemented by a combination of hardware and software.

[0048] FIG. 4 schematically shows a functional block of a controller 100 for estimating a torque angle . In the present specification, each block in a functional block diagram is shown in a functional block unit rather than a hardware unit. A motor control software may be, for example, a module constituting a computer program for executing specific processing corresponding to each functional block. Such a computer program is stored, for example, in a ROM 600.

[0049] As shown in FIG. 4, the controller 100 includes, for example, a pre-calculation unit 110, a torque angle calculation unit 120, a phase angle calculation unit 130, a rotor angle calculation unit 140, a torque calculation unit 150, and a motor control unit 160. The controller 100 may calculate a torque angle based on a stator current I.sub.s, a resultant magnetic flux .sub.s, and a phase angle . In the present specification, for convenience of description, each functional block will be expressed as a unit. Of course, the Equation is not intended to be used to limit each functional block to hardware or software.

[0050] When each functional block is implemented in the controller 100 as software, an execution subject of the software may be, for example, a core of the controller 100. As described above, the controller 100 may be implemented as an FPGA. In this case, all or some of the functional blocks may be implemented in hardware.

[0051] Processing may be distributed using a plurality of FPGAs, and thus, it is possible to distribute a calculation load of a specific computer. In this case, all or some of the functional blocks shown in FIG. 4 may be distributed and mounted in the plurality of FPGAs. For example, the plurality of FPGAs are connected through a control area network (CAN) for a vehicle so as to be able to communicate with each other, and thus, transmission/reception of data is performed.

[0052] For example, in a three-phase conduction control, the sum of currents flowing in respective phases ideally becomes zero. In the present specification, a current flowing in a U-phase coil of a motor M is denoted by I.sub.a, a current flowing in a V-phase coil of the motor M is denoted by I.sub.b, and a current flowing in a W-phase coil of the motor M is denoted by I.sub.c. The sum of the currents I.sub.a, I.sub.b, and I.sub.c is zero.

[0053] The controller 100 (for example, a CPU core) receives two currents among the currents I.sub.a, I.sub.b, and I.sub.c and obtains the remaining one current through a calculation. In the present example embodiment, the controller 100 obtains the current I.sub.a measured by a current sensor 400A and the current I.sub.b measured by a current sensor 400B. The controller 100 calculates the current I.sub.c based on the currents I.sub.a and I.sub.b using such a relationship in which the sum of the currents I.sub.a, I.sub.b, and I.sub.c is zero. The currents I.sub.a, I.sub.b, and I.sub.c may be measured using three current sensors and may be input to the controller 100 through an AD converter 500.

[0054] The controller 100 may transform the current I.sub.a, the current I.sub.b, and the current I.sub.c into a current I.sub. on an -axis and a current I.sub. on a -axis of an - fixed coordinate system using a so-called Clarke transform used for a vector control and the like. Here, the - fixed coordinate system is a stationary coordinate system. Among three phases, a direction of one phase (for example, the direction of a U-phase) corresponds to the -axis, and a direction orthogonal to the -axis corresponds to the -axis.

[0055] In addition, the controller 100 transforms reference voltages V.sub.a*, V.sub.b*, and V.sub.c* into a reference voltage V.sub.* on the -axis and a reference voltage V.sub.* on the -axis of the - fixed coordinate system using the Clark transformation. The reference voltages V.sub.a*, V.sub.b*, and V.sub.c* indicate the above-described PWM signal for controlling each switching element of an inverter 300.

[0056] For example, calculations for obtaining I.sub. and I.sub. and the reference voltages V.sub.* and V.sub.* may also be performed by the motor control unit 160 of the controller 100. The currents I.sub. and I.sub. and the reference voltages V.sub.* and V.sub.* are input to the pre-calculation unit 110 and the phase angle calculation unit 130.

[0057] In a motor control according to the present example embodiment, the stator current I.sub.s, the resultant magnetic flux .sub.s, and the phase angle are given as variables, and armature resistance R (m), armature inductance L (H), and a rotor magnetic flux .sub.m (Wb) are given as parameters. Here, the rotor magnetic flux .sub.m indicates a magnitude of a magnetic flux of a permanent magnet of a rotor.

[0058] The pre-calculation unit 110 obtains the variables I.sub.s, .sub.s, and based on the currents I.sub. and I.sub. and the reference voltages V.sub.* and V.sub.* with respect to the - fixed coordinate system or d-q rotating coordinate system. Since the pre-calculation unit 110 delivers the variables to the torque angle calculation unit 120 in rear thereof, the pre-calculation unit 110 is a unit configured to perform a pre-calculation.

[0059] FIG. 5 is a phasor diagram showing variables I.sub.s, .sub.s, , and V.sub.s. FIG. 6 is a phasor diagram showing a resultant magnetic flux .sub.s on an - fixed coordinate system or d-q rotating coordinate system. All of the shown variables are represented by a phasor. Hereinafter, each variable is treated as a phasor.

[0060] The pre-calculation unit 110 calculates a stator current I.sub.s in a phasor diagram according to Equation 1.

I.sub.s=(I.sub..sup.2+I.sub..sup.2).sup.1/2 Equation 1

Resultant Magnetic Flux

[0061] The pre-calculation unit 110 calculates a resultant magnetic flux .sub.s in a phasor diagram based on the currents I.sub. and I.sub. and reference voltages V.sub.* and V.sub.*. Specifically, the pre-calculation unit 110 calculates the resultant magnetic flux .sub.s according to Equations 2 to 4. As shown in FIG. 5, the resultant magnetic flux .sub.s is obtained by adding an armature magnetic flux .sub.a (=L.Math.I.sub.s) to a rotor magnetic flux .sub.m.

[0062] For example, the pre-calculation unit 110 calculates a component .sub. on an -axis of the resultant magnetic flux .sub.s according to Equation 2. The pre-calculation unit 110 calculates a component .sub. on a -axis of the resultant magnetic flux .sub.s according to Equation 3. Here, LPF in Equations 2 and 3 means processing by a low pass filter. For the purpose of removing harmonics, for example, a general low pass filter of the controller 100 may be used. The resultant magnetic flux .sub.s is represented by Equation 4.

.sub.=LPF(V.sub.*R.Math.I.sub.) Equation 2

.sub.=LPF(V.sub.*R.Math.I.sub.) Equation 3

.sub.s=(.sub..sup.2+.sub..sup.2).sup.1/2 Equation 4

[0063] The pre-calculation unit 110 calculates a back electromotive force component BEMF.sub. on an -axis and a back electromotive force component BEMF.sub. on a -axis based on the currents I.sub. and I.sub. and the reference voltages reference voltages V.sub.* and V.sub.*. Specifically, the pre-calculation unit 110 calculates the back electromotive force component BEMF.sub. and the back electromotive force component BEMF.sub. according to Equations 5 and 6.

BEMF.sub.=V.sub.*R.Math.I.sub.Equation 5

BEMF.sub.=V.sub.*R.Math.I.sub.Equation 6

[0064] The pre-calculation unit 110 calculates a stator voltage V.sub.s in a phasor diagram according to Equation 7. The stator voltage V.sub.s is a voltage corresponding to a back electromotive force voltage. As described above, the back electromotive force voltage is referred to as the stator voltage in the present specification.

V.sub.s=(BEMF.sub..sup.2+BEMF.sub..sup.2).sup.1/2 Equation 7

[0065] As shown in FIG. 5, for example, the phase angle is expressed as an angle between the stator current I.sub.s and the stator voltage V.sub.s in the d-q rotating coordinate system and is an angle in which a counterclockwise direction is a positive direction. Here, the d-q rotating coordinate system is a rotating coordinate system that rotates together with a rotor.

[0066] The pre-calculation unit 110 calculates the phase angle according to Equation 8. Here, arg is an operator indicating an argument of a phasor. The phase angle indicates an argument difference between two phasors.

=arg(V.sub.s)arg(I.sub.s) Equation 8

[0067] The pre-calculation unit 110 outputs the variables I.sub.s, .sub.s, and to the torque angle calculation unit 120. Other hardware (for example, an FPGA) different from the controller 100 may calculate the variables I.sub.s, .sub.s, and . The torque angle calculation unit 120 may receive and obtain the variables I.sub.s, .sub.s, and from other hardware. According to such a configuration, the calculation load of the controller 100 may be reduced.

[0068] The torque angle calculation unit 120 may receive a torque angle based on the parameters L and .sub.m and the variables I.sub.s, .sub.s, and . In FIG. 6, for example, the torque angle is expressed as an angle between the resultant magnetic flux .sub.s and a d-axis in the d-q rotating coordinate system and is an angle in which a counterclockwise direction is a positive direction.

[0069] FIG. 7 is a phasor diagram showing a rotor magnetic flux .sub.m, an armature magnetic flux .sub.a, and a resultant magnetic flux .sub.s.

[0070] A triangle including the rotor magnetic flux .sub.m, the armature magnetic flux .sub.a, and the resultant magnetic flux .sub.s is taken into account. It is considered that a length of a perpendicular line H drawn from an end point of the rotor magnetic flux .sub.m to the resultant magnetic flux .sub.s is denoted by h and a foot of the perpendicular line is denoted by f. The resultant magnetic flux .sub.s is divided into two portions by the perpendicular line H. Lengths of the respective portions are denoted by x1 and x2. The length h, the length x1, and the length x2 may be represented by Equations 9 to 11.

h=.sub.a sin(90) Equation 9

x1=.sub.a cos(90) Equation 10

x2=.sub.sx1=.sub.s.sub.a cos(90) Equation 11

[0071] When cot() (=1/tan()) is transformed using Equations 9 to 11, Equation 12 is obtained.

[00001]$\begin{array}{cc}\cot \left(\right)=x.Math..Math.2.Math.\text{/}.Math.h.Math.=\left({}_s-{}_a.Math.\cos \left(90-\right)\right)/\left({}_a.Math.\sin \left(90-\right)\right).Math.=\left({}_s-{}_a.Math.\sin \left(\right)\right)/\left({}_a.Math.\cos \left(\right)\right).Math.={}_s/\left({}_a.Math.\cos \left(\right)\right)-\tan \left(\right)& \mathrm{Equation}.Math..Math.12\end{array}$

[0072] When an arccotangent of Equation 12 is calculated using a relationship of .sub.a=L.Math.I.sub.s, is represented by Equation 13.

=cot.sup.1(.sub.s/(.sub.a cos())tan())=>=cot.sup.1(.sub.s/(LI.sub.s cos())tan()) Equation 13

[0073] A relationship of =90tan.sup.1(cot()) is obtained from a relationship of cot()=tan(90). When of Equation 13 is substituted for of the right side of such a relational Equation, Equation 14 is obtained.

[00002]$\begin{array}{cc}=90-{\tan }^{-1}\left[{}_s/\left({\mathrm{LI}}_s.Math.\cos \left(\right)\right)-\tan \left(\right)\right)].Math.=90-{\tan }^{-1}\left[{}_s/\left({}_a.Math.\cos \left(\right)\right)-\sin \left(\right)/\cos \left(\right)\right].Math.=90-{\tan }^{-1}\left[{}_s/\left({}_a.Math.\cos \left(\right)\right)-{}_a.Math.\sin \left(\right)/{}_a.Math.\cos \left(\right)\right)].Math.=90-{\tan }^{-1}\left[{}_s-\left({}_a.Math.\sin \left(\right)\right)/\left({}_a.Math.\cos \left(\right)\right)\right]& \mathrm{Equation}.Math..Math.14\end{array}$

[0074] In addition, Equation 14 is transformed into Equation 15 from a relational Equation of cot()=1/tan().

[00003]$\begin{array}{cc}={\tan }^{-1}\left(1/\cot .Math..Math.\right).Math.={\tan }^{-1}\left[1/\left({}_s/\left({\mathrm{LI}}_s.Math.\cos \left(\right)\right)-\tan \left(\right)\right)\right].Math.={\tan }^{-1}\left[\left({\mathrm{LI}}_s.Math.\cos \left(\right)\right)/\left({}_s-\tan \left(\right).Math.{\mathrm{LI}}_s.Math.\cos \left(\right)\right)\right].Math.={\tan }^{-1}\left[\left({\mathrm{LI}}_s.Math.\cos \left(\right)\right)/\left({}_s-{\mathrm{LI}}_s.Math.\sin \left(\right)\right)\right]& \mathrm{Equation}.Math..Math.15\end{array}$

[0075] The torque angle calculation unit 120 outputs the torque angle to the torque calculation unit 150 and the rotor angle calculation unit 140. As shown in Equations 14 and 15, the variables in the d-q rotating coordinate system and the rotor magnetic flux .sub.m are not required for estimating the torque angle . According to the present example embodiment, the torque angle may be calculated based on the parameters L and .sub.m and the variables I.sub.s, .sub.s, and .

[0076] A phase angle calculation unit 130 estimates a phase angle based on the currents I.sub. and I.sub. and the reference voltages V.sub.* and V.sub.*. As in the pre-calculation unit, the phase angle calculation unit 130 calculates, for example, magnetic flux components .sub. and .sub. according to Equations 2 and 3. In addition, the phase angle calculation unit 130 calculates, for example, the phase angle according to Equation 16. For example, as shown in FIG. 6, the phase angle is expressed as an angle between the resultant magnetic flux .sub.s and the -axis in the - fixed coordinate system and is an angle in which a counterclockwise direction is a positive direction. The phase angle calculation unit 130 outputs the phase angle to the rotor angle calculation unit 140.

=tan.sup.1(.sub./.sub.) Equation 16

[0077] The rotor angle calculation unit 140 calculates a rotor angle based on the torque angle and the phase angle . A relationship between the torque angle , the phase angle , and the rotor angle is as shown in FIG. 6. The rotor angle calculation unit 140 may calculate and estimate the rotor angle according to Equation 17.

=Equation 17

[0078] The torque calculation unit 150 calculates torque T based on the torque angle . When an SPM motor is used, a saliency ratio (Ld/Lq) becomes 1 (that is, L=Ld=Lq). In this case, it is known that the torque T as a reaction of torque acting on an armature is represented by Equation 18. For example, the torque calculation unit 150 may calculate the torque T based on Equation 18.

T=3/2.Math.P.Math.(.sub.m.Math..sub.s/L)sin() Equation 18,

[0079] wherein P is a parameter indicating the number of motor pole pairs.

[0080] The motor control unit 160 may control the motor M based on the torque T and the rotor angle . For example, the motor control unit 160 performs a calculation required for a general vector control. Since the vector control is well-known technology, detailed descriptions of the control will be omitted.

[0081] According to the present example embodiment, in the sensorless control, a torque angle may be obtained without depending on variables in the d-q rotating coordinate system. In addition, since a complicated calculation is not particularly required for estimating the torque angle, it is possible to reduce load of a computer and reduce memory costs.

[0082] The validity of the calculation of the torque angle according to the present disclosure was verified using a rapid control prototyping (RCP) system of dSPACE Company and Matlab/Simulink of MathWorks Company. Verification results are shown below. A model of an SPM motor controlled by a vector control was used for the verification. Values of various system parameters at the time of verification are shown in Table 1.

TABLE-US-00001 TABLE 1 Inertia moment 6.9e.sup.5 [kg .Math. m.sup.2] Friction coefficient 5.1e.sup.3 [Nm/(rad/s)] Resistance (motor + ECU) 8.50 m + 5.43 m L.sub.d (nominal) 40.7 H L.sub.q (nominal) 38.8 H Voltage range 10 to 16 V Temperature range 40 to 90 C. Motor type DC brushless motor Number of poles 8 Number of slots 12 Maximum current 77 A Rated voltage 13.5 V Rated temperature 80 C. Maximum torque 5.96 N .Math. m Diameter of coil 1.45 mm Number of turns 11.5

[0083] FIG. 8 shows a waveform of torque (top), waveforms of three-phase currents (middle), and waveforms of three-phase voltages (bottom) within a certain period (for 0.03 seconds from 0.35 seconds to 0.38 seconds). FIG. 9 shows a waveform of a torque angle (degree) estimated using a calculation equation of the present disclosure and a measured value of a torque angle within a certain period. A horizontal axis of FIGS. 8 and 9 represents a time (ms). A vertical axis of FIG. 8 represents a magnitude (N.Math.m) of torque, a current value (mA), and a voltage value (V) in order from an upper side of FIG. 8. A vertical axis of FIG. 9 represents a size (degree) of a torque angle.

[0084] It can be seen from a simulation result of FIG. 8 that a vector control is properly performed. It can be seen from a simulation result of FIG. 9 that the estimated torque angle using the calculation equation of the present disclosure is similar to the measured value. More specifically, an error between the estimated torque angle and the measured value is about one degree. In a sensorless control, an allowable value of an error thereof is generally about ten degrees. The error obtained from the simulation results is a value sufficiently satisfying a range of an allowable value.

[0085] From the simulation results, it can be seen that a torque angle is precisely estimated in the sensorless control by using a method of calculating a torque angle proposed in the present specification.

[0086] The present disclosure is not limited to the sensorless control as described above, but the method of estimating the torque angle according to the present disclosure may also be suitably used for the motor controlling system for controlling a sensor shown in FIG. 3.

[0087] The controller 100 of the motor controlling system 1000 shown in FIG. 3 may calculate the torque angle based on the variables in the d-q rotating coordinate system. For example, the controller 100 may calculate the torque angle according to Equation 18 (see FIG. 5).

=tan.sup.1[(V.sub.dR.Math.I.sub.d)/(V.sub.qR.Math.I.sub.q)]Equation 18

[0088] Here, V.sub.d is a voltage component of an armature voltage on a d-axis, and V.sub.q is a voltage component of the armature voltage on a q-axis. I.sub.d is a current component of an armature current on the d-axis, and I.sub.q is a current component of the armature current on the q-axis.

[0089] In a sensor control, when a position sensor is broken due to any cause, a rotor angle may not be measured. Therefore, it is difficult to continue the sensor control. On the other hand, when the position sensor fails, it is possible to switch a motor control from the sensor control to the sensorless control. Even when the position sensor fails, the motor control may be continued by applying the method of estimating the torque angle according to the present disclosure to the sensorless control.

[0090] FIG. 10 is a schematic diagram illustrating a typical configuration of an electric power steering (EPS) system 2000 according to the present example embodiment.

[0091] A vehicle, such as a car, generally includes an EPS system. The EPS system 2000 according to the present example embodiment includes a steering system 520 and an auxiliary torque mechanism 540 configured to generate an auxiliary torque. The EPS system 2000 generates an auxiliary torque that assists in a steering torque of the steering system generated by a driver operating a steering wheel. Operation load of the driver is reduced by the auxiliary torque.

[0092] For example, the steering system 520 includes a steering wheel 521, a steering shaft 522, universal shaft joints 523A and 523B, a rotation shaft 524, a rack and pinion mechanism 525, a rack shaft 526, left and right ball joints 552A and 552B, tie rods 527A and 527B, knuckles 528A and 528B, and left and right steering wheels 529A and 529B.

[0093] For example, the auxiliary torque mechanism 540 includes a steering torque sensor 541, an electronic control unit (ECU) 542 for a vehicle, a motor 543, and a deceleration mechanism 544. The steering torque sensor 541 detects steering torque in the steering system 520. The ECU 542 generates a drive signal based on a detection signal of the steering torque sensor 541. The motor 543 generates an auxiliary torque according to steering torque based on the drive signal. The motor 543 transfers the generated assist torque to the steering system 520 through the deceleration mechanism 544.

[0094] For example, the ECU 542 includes the controller 100 and the driving circuit 200 according to example Embodiment 1. In a car, an electronic control system is built based on the ECU. In the EPS system 2000, for example, a motor controlling system is built by the ECU 542, the motor 543, and the inverter 545. The motor controlling system 1000 according to example Embodiment 1 may be suitably used as the motor controlling system.

[0095] The example embodiments of the present disclosure are suitably used in an X-by-wire system such as a shift-by-wire system, a steer-by-wire system, or a brake-by-wire system, and a motor controlling system of a traction motor or the like, in which an ability to estimate a torque is required. For example, the motor controlling system according to the example embodiments of the present disclosure may be mounted on an autonomous vehicle corresponding to Levels 0 to 4 (standard of automation) defined by the Japanese government and the National Highway and Traffic Safety Administration (NHTSA) of the U.S. Department of Transportation.

[0096] The example embodiments of the present disclosure may be widely used in various apparatuses including various motors such as a vacuum cleaner, a dryer, a ceiling fan, a washing machine, a refrigerator, and an electronic power steering system.

[0097] Features of the above-described preferred example embodiments and the modifications thereof may be combined appropriately as long as no conflict arises.

[0098] While example embodiments of the present disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The scope of the present disclosure, therefore, is to be determined solely by the following claims.