(12) United States Patent
`Chen et al.
`
`US006498449B1
`(16) Patent N6.=
`US 6,498,449 B1
`(45) Date of Patent:
`Dec. 24, 2002
`
`(54) LOW RIPPLE TORQUE CONTROL OF A
`PERMANENT MAGNET MOTOR WITHOUT
`USING CURRENT SENSORS
`
`.
`(75) Inventors‘
`
`.
`silll'illzl’rTggiull/gugijs%ro MI
`’
`y’
`
`(US)
`
`5/1984 Whited ...................... .. 18/661
`4,447,771 A
`4/1985 Morinaga et al. ......... .. 318/254
`4,511,827 A
`4,556,811 A 12/1985 Hendricks ................. .. 310/266
`4,558,265 A 12/1985 Hayashida et al.
`4,633,157 A 12/1986 Streater .................... .. 318/723
`4,686,437 A * 8/1987 Langley e161. .
`318/138
`4,688,655 A
`8/1987 Shimizu ....... ..
`180/791
`4,745,984 A
`5/1988 Shimizu .... ..
`180/79.1
`
`_
`
`_
`
`_
`
`(73) Asslgneei Delphl Technologles, Inc» Troy, MI
`(Us)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U‘SC' 154(k)) by 5 days‘
`
`(21) App1_ NO_; 09/663,900
`_
`(22) Filed:
`
`Sep. 18, 2000
`
`Related US. Application Data
`(60) Provisional application No. 60/154,613, ?led on Sep. 17,
`1999, provisional application No. 60/154,681, ?led on Sep.
`17, 1999, and provisional application No, 60/183301, ?led
`on Feb- 17, 2000-
`(51) Int. c1.7 ...................... .. H02K 17/32; H02K 23/68;
`HOZK 27/30; H021) 7/00
`(52) US. Cl. ..................... .. 318/434; 318/805; 318/799;
`318/806
`
`,
`(58) Field of Search ....................... .. 318/434, 798—801,
`318/805 806 808 812 599
`’
`’
`_
`’
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`
`8/1975 Tanikoshi ................. .. 318/254
`3,898,544 A
`3919 609 A 11 1975 K1 t h k t
`l.
`.
`318 227
`4’027’213 A
`41977 deagaircogeere a
`315138
`47135120 A
`1/1979 Hoshimi et aL
`318/227
`4,217,508 A
`8/1980 UZuka .................... .. 310/46
`4,240,020 A 12/1980 Okuyama et al. .
`318/721
`4,392,094 A
`7/1983 Kuhnlein .................. .. 318/254
`
`4,814,677 A
`
`3/1989 Plunkett . . . . . . . . .
`
`. . . .. 318/254
`
`...... .. 318/254
`5/1989 Dishner et al. .
`4,835,448 A
`6/1989 Shimizu .............. .. 364/424.05
`4,837,692 A
`9/1989 Anderson et al. ......... .. 318/696
`4,868,477 A
`9/1989 Schultz et al. .............. .. 29/596
`4,868,970 A
`.
`.
`(List continued on neXt page.)
`Primary Examiner—Robert E. Nappi
`Assistant Examiner—Edgardo San Martin
`(74) Attorney, Agent, or Firm—Edmund P. Anderson
`(57)
`ABSTRACT
`.
`A method and apparatus for Controlhng the torque of and
`reducing torque ripple in a pelmflnellt magnet motor Without
`using current sensors. By eliminating the need for current
`sensors, loW frequency torque ripple is reduced. A voltage
`mode Control method is implemented to Control the mom
`In response to the position and speed of the rotor and a
`torque Command Signal’ a Controller develops motor Voltage
`command signals indicative of the voltage required to pro
`duce the desired motor torque. A rotor position encoder
`-
`-
`-
`determines the angular positions of the rotor. From the
`angular positions of the rotor, a speed measuring circuit
`determines the ‘speed of the rotor. The position and speed
`signals are applied to the controller. The controller uses this
`information and develops the motor voltage command sig
`nals indicative of the voltage needed to produce the desired
`motor torque An inverter is Coupled between a power Source
`'
`.
`.
`.
`and the controller. The circuit applies phase voltages to the
`motor, in response to the motor voltage command signals, to
`Produce the desired motor t0rqlle
`
`18 Claims, 3 Drawing Sheets
`
`22
`10 V ll:
`\ DC I
`
`20
`EL‘
`POWER
`CIRCUIT
`
`\
`
`J
`
`________________ __ 32-_
`
`32
`
`F
`Va Vb v6
`1
`:
`va =Vsin (9)
`i
`38 Q 8
`|
`vb=vsin (9-120 )
`:
`LOOKUP
`i
`Vc=Vsin(0-240) {
`TABLE
`-—36
`a,
`=
`6
`1
`2
`2
`l girl
`: ‘0
`R + (9L)
`1
`l
`_____+ __s T +14 comR |
`(
`:
`28
`RQOS§+(G)LS) S1116
`3Kc
`Cmd e
`l 26
`l
`
`l
`
`“'24
`
`SPEED
`MEASURING —
`CIRCUIT
`\16
`
`Nidec Motor Corporation
`IPR2014-01121
`
`Exhibit 2009 - 1
`
`

`

`US 6,498,449 B1
`Page 2
`
`US. PATENT DOCUMENTS
`
`4,882,524 A 11/1989 Lee .......................... .. 318/254
`4,912,379 A
`3/1990 Matsuda er a1-
`318/254
`4988273 A * 1/1991 Faig er a1
`318/138
`4,992,717 A
`2/1991 Marwin er a1-
`318/696
`5,006,774 A
`4/1991 Rees ------------- --
`318/721
`5,040,629 A
`8/1991 Matsuoka er al-
`180/79-1
`5,063,011 A 11/1991 Ruiz er a1
`264/126
`5,069,972 A 12/1991 Versic ----- --
`-- 428/407
`5,076,381 A 12/1991 Daido et a1.
`. 180/791
`5,122,719 A
`6/1992 Bessenyei et a1.
`.. 318/629
`5,223,775 A
`6/1993 Mongeau ------- --
`-- 318/432
`5,239,490 A
`8/1993 Masaki er a1
`-- 364/565
`5331245 A
`7/1994 Burgbacher er a1-
`-- 310/186
`5,345,156 A * 9/1994 Moreira ............ ..
`318/254
`5,349,278 A
`9/1994 Wedeen -
`318/632
`5,361,210 A 11/1994 Fu ............. ..
`364/424.05
`5,428,285 A
`6/1995 Koyama et a1.
`318/799
`5,433,541 A
`7/1995 Hieda er a1
`400/279
`5444341 A
`8/1995 Kneifel, 11 er a1- -
`318/432
`5,460,235 A 10/1995 Shimizu ........ ..
`180/791
`5,461,293 A * 10/1995 Roman er a1- -
`318/603
`5,467,275 A 11/1995 Takamoto et a1.
`364/426.01
`5,469,215 A 11/1995 Nashiki .................... .. 318/432
`5,475,289 A 12/1995 McLaughlin er a1-
`-- 318/432
`5,493,200 A * 2/1996 Roman er 91-
`~322/10
`5,517,415 A * 5/1996 Miller er a1- -
`701/43
`5,554,913 A
`9/1996 Ohasawa .................. .. 318/434
`5,568,389 A 10/1996 McLaughlin et a1. .. 364/424.05
`5569994 A 10/1996 Taylor et a1- - - - -
`- - - -- 318/700
`5,579,188 A 11/1996 Dun?eld 618.1. .
`360/9908
`5,585,708 A 12/1996 Richardson et a1. ...... .. 318/800
`
`4/1997 Matsumura et a1. ...... .. 318/632
`5,616,999 A
`4/1997 Miller ................. .. 364/424.05
`5,623,409 A
`6/1997 vveber _________________ u 324/207_25
`5,642,044 A
`8/1997 Nakayana et a1.
`318/718
`5,656,911 A
`9/1997 Chandy .......... ..
`.. 701/41
`5,668,721 A
`9/1997 GOkhale et a1. ..
`. 318/254
`5,672,944 A
`5,701,065 A 12/1997 Ishizaki .......... ..
`318/701
`5,739,650 A * 4/1998 Kimura et a1. .
`318/254
`5,777,449 A
`7/1998 Schlager ...... ..
`318/459
`5,780,986 A
`7/1998 Shelton et a1. .
`318/432
`5,803,197 A
`9/1998 Hara et a1_
`_ “30/248
`5,811,905 A
`9/1998 Tang
`5,852,355 A 12/1998 Turner ...................... .. 318/701
`5,881,836 A
`3/1999 Nishimoto et a1. ..
`180/446
`5,898,990 A
`5/1999 Henry ............... ..
`.. 29/598
`5919241 A
`7/1999 Bolourchi et a1_
`701/41
`5,920,161 A
`7/1999 Obara et a1. .............. .. 318/139
`5929590 A
`7/1999 Tang
`5962999 A 1O/1999 Nakamura et a1_
`5,963,706 A 10/1999 Baik ........................ .. 388/804
`5,977,740 A 11/1999 McCann ......... ..
`.318/701
`5,984,042 A 11/1999 Nishimoto et aL
`_ 180/446
`5,992,556 A 11/1999 Miller ...................... .. 180/446
`6,002,226 A 12/1999 CO11ier_Ha11man et aL _ 318/439
`6,002,234 A 12/1999 Ohm et a1_ _______________ __ 318/729
`6,009,003 A 12/1999 Yeo .......... ..
`.. 363/37
`6,034,460 A
`3/2000 Tajima ..... ..
`.310/179
`6,034,493 A
`3/2000 Boyd et a1. ............... .. 318/254
`6,043,624 A
`3/2000 Masaki et aL
`6,049,182 A
`4/2000 Nakatani et a1_
`6,129,172 A 10/2000 Yoshida et a1. ........... .. 180/446
`
`* cited by examiner
`
`Nidec Motor Corporation
`IPR2014-01121
`
`Exhibit 2009 - 2
`
`

`

`U.S. Patent
`
`Dec. 24, 2002
`
`Sheet 1 of3
`
`US 6,498,449 B1
`
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`
`Nidec Motor Corporation
`IPR2014-01121
`
`Exhibit 2009 - 3
`
`

`

`U.S. Patent
`
`Dec. 24, 2002
`
`Sheet 2 of3
`
`US 6,498,449 B1
`
`FIG. 2
`
`FIG. 3
`
`20
`
`(
`INVERTER
`
`_ Tc _ F lllllllllll 11L
`
`253%: R“ _ 3_ a b c __ _ _ V V V V _
`_ _ " MT,“
`
`_ nnnA d _ b .m .m .m m _
`wncwww A. + _
`
`
`
`
`
`1.11.1 lllll II l...|_ " 2 _
`
`_ 6% w _
`)) m
`
`. L T06 _
`
`2
`
`w 2
`
`6
`
`18
`
`/24
`
`gm
`mnm D EUw\
`SEC M
`
`G
`
`Nidec Motor Corporation
`IPR2014-01121
`
`Exhibit 2009 - 4
`
`

`

`U.S. Patent
`
`Dec. 24, 2002
`
`Sheet 3 of3
`
`US 6,498,449 B1
`
`FRICTION
`
`FIG. 4
`
`10
`O
`-10
`-20
`-30
`-40
`-50
`-6O
`-70
`-8O
`-9O
`
`- 100
`-1 10
`~12O
`
`0
`
`40
`
`30
`
`120 160 200 240 280 320 360 (DEGREES)
`ROTOR ANGLE
`
`FIG. 5
`
`~20
`
`FRICTION
`
`-11O
`
`0
`
`40
`
`30
`
`120 160 200
`
`240 280 320 360 (DEGREES)
`
`ROTOR ANGLE
`
`Nidec Motor Corporation
`IPR2014-01121
`
`Exhibit 2009 - 5
`
`

`

`US 6,498,449 B1
`
`1
`LOW RIPPLE TORQUE CONTROL OF A
`PERMANENT MAGNET MOTOR WITHOUT
`USING CURRENT SENSORS
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is based upon, and claims the bene?t of,
`US. Provisional Patent Application No. 60/154,613, ?led
`Sep. 17, 1999; No. 60/154,681, ?led Sep. 17, 1999; and No.
`60/183,301, ?led Feb. 17, 2000, the disclosures of all three
`of Which are incorporated by reference herein in their
`entirety.
`
`TECHNICAL FIELD
`
`This invention relates to torque control of a sinusoidally
`eXcited permanent magnet motor, and more particularly to
`reducing the loW frequency torque ripple, or smoothing the
`torque, in such a motor.
`
`BACKGROUND OF THE INVENTION
`
`It is knoWn in the art relating to electric motors that
`polyphase permanent magnet (PM) brushless motors With a
`sinusoidal ?eld offer the capability of providing loW torque
`ripple, noise, and vibration in comparison With those With a
`trapeZoidal ?eld. Theoretically, if a motor controller can
`produce polyphase sinusoidal currents With the same fre
`quency as that of the sinusoidal back-emfs (also knoWn as
`“back-voltages”), the torque output of the motor Will be a
`constant, and Zero torque ripple can be achieved. HoWever,
`due to practical limitations of motor design and controller
`implementation, there are alWays deviations from those
`assumptions of pure sinusoidal back-emf and current Wave
`forms. The deviations Will usually result in parasitic torque
`ripple components at various frequencies and magnitudes.
`The methods of torque control can in?uence the level of this
`parasitic torque ripple.
`One method for torque control of a permanent magnet
`motor With a sinusoidal back-emf is accomplished by con
`trolling the motor phase currents so that its current vector is
`aligned With the back-emf. This control method is knoWn as
`the current mode control method. In such a method, the
`motor torque is proportional to the magnitude of the current.
`The current mode control method requires a compleX con
`troller for digital implementation. The controller requires
`tWo or more A/D channels to digitiZe the current feedback
`from current sensors. In a three-phase system, it is conve
`nient to transform the three-phase variables into a tWo
`dimensional d-q synchronous frame Which is attached to the
`rotor and design the controller in the d-q frame. But, due to
`considerable calculations and signal processing involved in
`performing the d-q transformation, reverse d-q transforma
`tion and P-I loop algorithms, a high speed processor such as
`a digital signal processor (DSP) has to be used to update the
`controller information every data sampling cycle.
`
`SUMMARY OF THE INVENTION
`
`A method and system for controlling the torque of a
`sinusoidally excited PM motor to reduce loW frequency
`torque ripple, or smooth torque, is disclosed. The loW
`frequency torque ripple is reduced by a controller Which
`calculates the voltage required for producing the desired
`torque based on motor equations. The controller is imple
`mented using only feedback of the rotor position and speed.
`The method and system of the invention preserve the
`smoothness of sinusoidal commutation While eliminating
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`the sensitivity of torque ripple due to current sensors of the
`prior art. The controller of the invention features a loW cost
`implementation that not only eliminates the hardWare of
`current sensors and A/D converters of the prior art, but also
`considerably reduces the softWare computation needs, e.g.,
`no d-q transformations and P-I loops are necessary. A loW
`cost microprocessor may be used With the invention instead
`of the DSPs of the prior art.
`The method of the invention senses angular positions of
`a rotor and determines its rotational speed. In response to the
`position and speed of the rotor and a torque command signal,
`a controller develops varying motor voltage command sig
`nals indicative of the voltage needed to produce a desired
`motor torque. Phase voltages are applied across the motor
`Windings in response to the motor voltage command signals
`to develop the desired motor torque.
`The system disclosed herein includes a rotor position
`encoder coupled to the motor for sensing the angular posi
`tions of the rotor and outputting a position signal. A speed
`measuring circuit is connected to the position encoder for
`determining the speed of the rotor and outputting a speed
`signal. The position and speed signals are applied to a
`controller. The controller develops varying motor voltage
`command signals in response to the position signal, speed
`signal, and a torque command signal indicative of a desired
`motor torque. A poWer circuit is coupled betWeen a poWer
`source and the controller for applying phase voltages across
`the motor in response to the motor voltage command signals
`to develop the desired motor torque.
`One application for the voltage mode control method and
`system disclosed herein is in a poWer steering controller for
`an electric poWer steering system. The motor is coupled
`directly into the steering column to provide steering assist
`torque. Therefore, even a small level of loW frequency
`torque ripple produced by the motor can be felt at the
`steering Wheel. By using the voltage mode control method
`disclosed herein, the loW frequency torque ripple is reduced
`and a smooth steering feel is achieved.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a system for controlling the
`torque of a sinusoidally eXcited permanent magnet motor;
`FIG. 2 is a phasor diagram of a permanent magnet motor
`under constant voltage excitation;
`FIG. 3 is a block diagram of a system for controlling the
`torque of a sinusoidally eXcited permanent magnet motor
`according to another embodiment;
`FIG. 4 is a graph of torque vs. rotor angle for a motor
`controlled by a voltage mode control method at 20% torque
`command; and
`FIG. 5 is a graph of torque vs. rotor angle for a motor
`controlled by a current mode control method at 20% torque
`command.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`Referring noW to FIGS. 1 and 2, a system for controlling
`torque is generally shoWn at 10. The system 10 controls
`torque of a sinusoidally eXcited permanent magnet motor 12.
`The system includes a rotor position encoder 14, a speed
`measuring circuit 16, a controller 18, an inverter 20 and a
`poWer source 22.
`
`Nidec Motor Corporation
`IPR2014-01121
`
`Exhibit 2009 - 6
`
`

`

`US 6,498,449 B1
`
`3
`Unlike the prior art, the torque of the motor 12 is
`controlled Without the use of current sensors. By eliminating
`the current sensors, the loW frequency torque ripple is
`reduced so that the output torque is smoother. Instead of
`controlling the torque producing current, the controller 18
`determines a voltage required for producing a desired torque
`based on motor equations, described beloW. This voltage
`mode control method is based on machine operation phasor
`diagram as shoWn in FIG. 2. Under steady state operating
`condition, the voltage phasor V, back-emf phasor E and
`current phasor T) of a sinusoidally excited PM motor are
`governed by:
`
`(1)
`
`Where R is the Winding resistance, X5 is the phase reactance
`Which is equal to the product of motor inductance LS and the
`excitation frequency u)(rad./sec.). Here, it is assumed that
`the angle betWeen back-emf phasor E and current phasor —I>
`is 0t and the angle betWeen the voltage phasor V and the
`back-emf phasor E is 6.
`Neglecting motor iron losses, friction and Windage losses,
`the output poWer of the PM motor is equal to
`
`a
`
`P=3IE cos or
`
`and the output torque is
`
`T=P/0Jm
`
`(2)
`
`(3)
`
`Where uum=u)/(no. of pole pairs). Based on the phasor
`diagram, it can be derived that
`
`Vcos 6=E+IR cos OL+IXS sin or
`
`Vsin 6=—IR sin OL+IXS cos or
`
`Solving equations 4 and 5 yields
`
`COSII :
`
`(4)
`
`(5)
`
`(6)
`
`45
`
`By substituting equation 6 into equation 2, it is obtained
`that
`
`P _ 3E(Vcos6 — E)R + XSVsin6
`_ T}
`
`(7)
`
`From equation 7 and equation 3, the motor torque can be
`expressed as
`
`(Vcosé — KEwm)R + XSVsin6
`T = 3K,—
`R2 + X}
`
`(8)
`
`Where Ke=E/u)m is the EMF constant. It can be seen from
`equation 8 that the motor torque is dependent on the motor
`input voltage V, the motor parameters and operating speed.
`Hence, given the motor parameters and speed, by controlling
`the voltage magnitude V and its phase angle 6 relative to
`back-emf E, it is possible to control the motor torque to a
`desired value. Equation 8 forms the basis of the control
`method. The voltage required for any given torque command
`
`60
`
`m 5
`
`4
`Tcmd can be calculated by substituting Tcmd into equation 8
`and solving for V:
`
`1
`V _
`_ Rcosé + Xssiné
`
`ER
`R2 + X3 T
`3K,
`and +
`
`(9)
`
`3K
`
`2
`
`cmd + KEwmR]
`
`Equation 9 (FIG. 1) shoWs that, for a ?xed angle 6 (e.g.,
`6 at a line 36 from a lookup table 38) betWeen the back-emf
`and the terminal voltage, to maintain a torque equal to the
`commanded torque With varying speed, the amplitude of
`motor input voltage must change. Thus, information of
`motor parameters, rotor speed, and position angle is
`required, but no current feedback is needed for the controller
`to develop a signal to produce a desired motor torque.
`In the voltage mode control, the angle 6 has to be chosen
`properly. By referring to FIG. 2, it can be seen that the phase
`angle a betWeen the current and the back-emf depends on the
`angle 6. By choosing proper phase angles ot, the motor
`armature current can induce a magnetic ?ux component
`opposed to the magnet ?eld. Therefore, the choice of 6 can
`cause the voltage control to mimic in performance the
`equivalent current control With ?eld Weakening.
`Referring to FIG. 3, in a preferred embodiment the
`voltage mode control method is implemented for a perma
`nent magnet (synchronous) motor With slotless Windings
`having a sinusoidal air gap ?ux distribution. This type of
`motor has a large effective air gap and thus, armature
`currents produce a ?ux that is negligible compared to the
`permanent magnet ?eld. As a result, saturation or demag
`netiZation of the permanent ?eld is unlikely to occur in
`normal operation and a ?xed value of 6 can be used. Thus,
`for slotless Winding machines, the voltage mode control is
`particularly suitable. For this exemplary motor, the motor
`parameters are listed beloW:
`
`Motor Type
`Pole Number
`Input Voltage
`Effective Phase Resistance
`Inductance
`Maximum No Load Speed
`Maximum Reactance
`EMF Constant
`Encoder Resolution
`
`PM, Sinusoidal, three-phase
`Np = 4
`Vdc = 12 V
`R = 55 m9
`L5 = 38.5 ,uH
`2800 RPM
`22.5 mg
`Ke = 0.023 V/(rad/s)
`2.5 degree (electrical)
`
`Based on these motor parameters, the Winding reactance
`of the motor at the maximum speed is relatively small in
`comparison With its effective Winding resistance. This means
`that, for any given voltage, the angle 6 betWeen the voltage
`and back-emf phasors is very small and so is the angle 0t
`betWeen V and E and the current. Therefore, a suitable
`choice of the angle 6 betWeen V and E is a constant Zero.
`Based on this condition, the control equation can be reduced
`to
`
`For a hardWare implementation, further simpli?cation is
`preferred. Since the motor reactance is much smaller than
`the resistance, the initial implementation can ignore the
`inductance term in equation 10. Therefore, the folloWing
`
`Nidec Motor Corporation
`IPR2014-01121
`
`Exhibit 2009 - 7
`
`

`

`US 6,498,449 B1
`
`5
`simpli?ed control equation may be implemented by the
`controller 18:
`
`R
`Tcmd + Kewm
`V :
`3K,
`
`(11)
`
`The poWer inverter 20 is coupled betWeen poWer source
`22 and the controller 18 to supply the phase voltages across
`the motor Windings. The inverter is controlled by space
`vector pulse Width modulated signals generated by the
`controller 18. Taking the gain of the inverter into account
`using a space vector pulse Width modulation scheme, the
`normaliZed voltage amplitude is given by: V,ef=V/(VdC/\/ 6).
`By substituting Vref for V in equation 11, the folloWing
`simpli?ed control equation is preferably implemented by the
`controller 18 (FIG. 3):
`
`10
`
`15
`
`(12)
`
`Where K1=(\/6R)/(3KeVdC) and K2=(x/6Ke)/Vdc. The maXi
`mum and minimum values of Vref are clamped to +1 and —1.
`Thus, for a given PM motor and ?xed battery voltage, K1
`and K2 are constant and can be stored in the controller
`memory alloWing the control equation to be implemented
`Without using current sensors.
`For the controller 18 to develop the correct voltage
`needed to produce the desired torque, the position and speed
`of the rotor are needed. A rotor position encoder 14 is
`connected to the motor 12 to detect the angular position of
`the rotor. The encoder 14 may sense the rotary position
`based on optical detection or magnetic ?eld variations, such
`being knoWn. The encoder 14 outputs a position signal 6 at
`a line 24 indicating the angular position of the rotor.
`From the position signal 6, the speed measuring circuit 16
`determines the speed of the rotor and outputs a speed signal
`00 at a line 26. The speed measuring circuit 16 may include
`a counter that counts the position signal pulses for a prede
`termined duration. The count value is proportional to the
`speed of the motor. For eXample, if a counter counts the
`position signal pulses in time intervals of 5 ms and the
`encoder has a resolution of 2.5 degrees, then the speed
`measurement Will have a resolution of about 41.7 rpm. The
`speed signal can also be obtained by any other method, such
`as the derivative of the position signal from the equation
`(nm=A6m/At Where At is the sampling time and Aem is the
`change in position during the sampling interval.
`The position and speed signals 6, u), and a torque com
`mand signal Tcmd at a line 28 are applied to the controller 18.
`The torque command signal Tcmd is indicative of the desired
`motor torque. The controller 18 determines a voltage ampli
`tude at a line 30 required to develop the desired torque by
`using the position, speed and torque command signals 6, u),
`Tcmd and other ?Xed motor parameter values in the control
`equation. For a three-phase motor, three sinusoidal reference
`signals that are synchroniZed With the motor back-emf are
`required to generate the required motor input voltages. The
`controller transforms the voltage amplitude signal into three
`phase by determining phase voltage command signals Va,
`Vb, and VC from the voltage amplitude signal and the
`position signal 6 according to the folloWing equations:
`
`25
`
`35
`
`45
`
`55
`
`(13)
`Va=VVEf sin(6)
`(14)
`v,,=vvef sin(6—120°)
`(15)
`vc=vvef sin(6—240°)
`Motor voltage command signals 32 of the controller 18
`are applied to poWer inverter 20 Which is coupled With
`
`65
`
`6
`poWer source 22 to apply phase voltages at lines 34 to the
`stator Windings of the motor 12 in response to motor voltage
`command signals at lines 32. But in order to generate phase
`voltages With an average sinusoidal shape, sWitching
`devices (not shoWn) of the inverter 20 must be turned on and
`off for speci?c durations at speci?c rotor angular positions.
`Control of the inverter 20 can be implemented according to
`any appropriate pulse Width modulation (PWM) scheme.
`HoWever, since space vector modulation (SVM) has the
`advantages of higher output voltage, loW harmonic
`distortion, loW sWitching poWer losses and easy micropro
`cessor implementation, SVM-based control is preferred. The
`duty cycle of each phase voltage command signal is given
`by:
`
`and the space vector voltages sVa, SVb, sVC are obtained
`from the folloWing logic equations:
`
`This modulation scheme provides a rms fundamental line
`to line voltage of 0.7071 Vdc, Which is 15.5% higher than
`that of a simple sine modulation scheme.
`By using this voltage mode control method, the loW
`frequency torque ripple is reduced. FIG. 4 shoWs the results
`of a test performed to measure the torque ripple performance
`of the voltage control method of the invention. The test Was
`performed on a rotor of a PM motor that Was locked and the
`rotor angle varied sloWly. Thus, the test can be considered to
`be conducted at Zero speed. FIG. 4 shoWs that there is still
`some torque ripple in the voltage mode. But the character
`istic of torque ripple is different from that of the current
`mode that is shoWn in FIG. 5. Unlike the current mode, the
`
`Nidec Motor Corporation
`IPR2014-01121
`
`Exhibit 2009 - 8
`
`

`

`US 6,498,449 B1
`
`7
`frequency of the torque ripple is at the motor commutation
`frequency Which is six times the fundamental frequency.
`Also, there are no fundamental or 2nd harmonic components
`as seen in FIG. 5. The fact that the torque ripple frequency
`is six times higher than the current mode alloWs the voltage
`mode control method to provide a smoother torque as the
`higher frequency component is easily ?ltered out by the
`system inertia.
`The voltage mode control method is not expected to
`provide the same precise torque control as the current mode.
`This is because the voltage mode control is a feed-forWard
`control, instead of a closed-loop regulation, and changes in
`the motor parameters can directly in?uence the output level.
`Therefore, it should be applied to only those applications
`Where precise torque level control is not critical.
`One such application is in an electrical poWer steering
`system. The motor is coupled directly into the steering
`column to provide assisted steering torque. The desired
`torque has only to provide the “right feel.” Also, since the
`voltage mode control reduces the loW frequency torque
`ripple felt at the steering Wheel, a very smooth steering feel
`is achieved.
`While preferred embodiments have been shoWn and
`described, various modi?cations and substitutions may be
`made thereto Without departing from the spirit and scope of
`the invention. Accordingly, it is to be understood that the
`present invention has been described by Way of illustration
`only, and such illustrations and embodiments as have been
`disclosed herein are not to be construed as limiting to the
`claims.
`What is claimed is:
`1. A method of controlling a sinusoidally excited perma
`nent magnet motor having knoWn motor parameters, com
`prising:
`generating a motor angular position signal indicative of an
`angular position of the motor;
`generating a motor speed signal indicative of a speed of
`the motor;
`determining, in response to the knoWn motor parameters,
`the motor angular position signal, the motor speed
`signal, a torque command signal, and amplitudes for
`input motor phase voltages, the torque command signal
`being indicative of a desired torque on the motor; and
`applying the input motor phase voltages at the amplitudes
`determined to the motor, Wherein the desired torque on
`the motor is produced.
`2. An apparatus for controlling a sinusoidally excited
`permanent magnet motor having knoWn motor parameters,
`comprising:
`a position encoder associated With the motor for sensing
`an angular position of the motor and providing a motor
`angular position signal indicative thereof;
`a speed measurement circuit associated With the position
`encoder for measuring a speed of the motor and pro
`viding a motor speed signal indicative thereof;
`a controller in communication With the position encoder
`for receiving the motor angular position signal and in
`communication With the speed measurement circuit for
`receiving the motor speed signal, the controller
`providing, in response to the knoWn motor parameters,
`the motor angular position signal, the motor speed
`signal, and a torque command signal, voltage command
`signals, the torque command signal being indicative of
`a desired torque on the motor; and
`an inverter in communication With the controller for
`receiving the voltage command signals and in commu
`
`15
`
`25
`
`35
`
`45
`
`55
`
`8
`nication With a poWer source, the inverter applying, in
`response to the voltage command signals, input motor
`phase voltages to the motor, Wherein the desired torque
`on the motor is produced.
`3. An apparatus for controlling a sinusoidally excited
`permanent magnet motor having knoWn motor parameters,
`comprising:
`a position encoder associated With the motor for sensing
`an angular position of the motor and providing a motor
`angular position signal indicative thereof;
`a speed measurement circuit associated With the position
`encoder for measuring a speed of the motor and pro
`viding a motor speed signal indicative thereof;
`a controller in communication With the position encoder
`for receiving the motor angular position signal and in
`communication With the speed measurement circuit for
`receiving the motor speed signal, the controller
`providing, in response to the knoWn motor parameters,
`the motor angular position signal, the motor speed
`signal, and a torque command signal, voltage command
`signals, the torque command signal being indicative of
`a desired torque on the motor; and
`an inverter in communication With the controller for
`receiving the voltage command signals and in commu
`nication With a poWer source, the inverter applying, in
`response to the voltage command signals, input motor
`phase voltages to the motor, Wherein the desired torque
`on the motor is produced; and
`Wherein said controller does not employ current or volt
`age feedback.
`4. A method of controlling a sinusoidally excited perma
`nent magnet motor having knoWn motor parameters, com
`prising:
`generating a motor angular position signal indicative of an
`angular position of the motor;
`generating a motor speed signal indicative of a speed of
`the motor;
`determining, in response to the knoWn motor parameters,
`the motor angular position signal, the motor speed
`signal, a torque command signal, and amplitudes for
`input motor phase voltages, the torque command signal
`being indicative of a desired torque on the motor;
`applying the input motor phase voltages at the amplitudes
`determined to the motor, Wherein the desired torque on
`the motor is produced; and
`Wherein the determining the amplitudes for the input
`motor phase voltages comprises calculating the ampli
`tudes according to a control equation comprising:
`
`Where
`V=amplitude of the input voltage of the motor;
`R=resistance of the motor Windings;
`Xs=reactance of motor phase Winding;
`Ke=E/uum Which is EMF constant;
`uum=speed of the motor;
`Tcmd=torque command signal; and
`6=angle betWeen EMF phasor F) and voltage phasor
`V.
`5. A method of controlling a sinusoidally excited perma
`nent magnet motor having knoWn motor parameters, com
`prising:
`
`a
`
`Nidec Motor Corporation
`IPR2014-01121
`
`Exhibit 2009 - 9
`
`

`

`US 6,498,449 B1
`
`9
`generating a motor angular position signal indicative of an
`angular position of the motor;
`generating a motor speed signal indicative of a speed of
`the motor;
`determining, in response to the knoWn motor parameters,
`the motor angular position signal, the motor speed
`signal, a torque command signal, and amplitudes for
`input motor phase voltages, the torque command signal
`being indicative of a desired torque on the motor;
`applying the input motor phase voltages at the amplitudes
`determined to the motor, Wherein the desired torque on
`the motor is produced; and
`Wherein the determining the amplitudes for the input
`motor phase voltages comprises calculating the ampli
`tudes according to a control equation comprising:
`
`Where
`Vref=normalized voltage for generating the pulse Width
`modulation signals to control the inverter;
`
`T =torque command signal;
`cmd
`
`2 —
`
`.
`
`Vdc
`
`Ke=E/u)m Which is EMF constant;
`R=resistance of the motor Windings;
`Vdc=the DC supply voltage; and
`uum=speed of the motor.
`6. A poWer steering assist system comprising:
`a steering Wheel and column;
`an electric motor comprising a motor controller, said
`electric motor adapted to impart rotational force to said
`steering column;
`a poWer steering controller adapted to control said electric
`motor in a manner effective in providing poWer steering
`assist to an operator of said steering Wheel; and
`Wherein said electric motor controller operates by a
`method comprising:
`generating a motor angular position signal indicative of
`an angular position of the motor;
`generating a motor speed signa