Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OP THE INVENTION
System and method for controlling a pennaner~t magnet
electric motor.
FIELD OF THE.INVENTION
DD01 ,The present invention relates to permanent magnet electric
t 1
motors. More preciselY~ the present invention rs related to a system and a
method for controlling a Permanent magnet elecuic motor.
gpCKGR4UND OP THE 1NVENTIDN
(D002'( Generally. in order to control a permanent magnet motor,
charactenstics~ of the permanent magnet motor such as the phase, . the
frequency and the amplitude of the electric motive force ("emu') voltage
generated by the rotation of the motor rotor, need to be determined to yield a
voltage to be applied to the motor terminals_
These characteristics of the permanent magnet motor may be
obtained by usn9 a position sensor, which results in increased costs and
reduces the reliability of the method because feedbag signals ai a subject to
changes in the ambient environment such as noise and temperature and to the
presence of impurity for example. ' Y
[0004] A possible method involves estimating the emf of the
permanent magnet motor. However, in case of a high sPead motor this method
requires a high compu~tion speed. which may result cos~tlY. Moreover, since
the characteristics of the motor are dependent on the ambient ~nvironement,
such a control method can be ~mplex.
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[0005] European Patent EP0944164 teaches a system and a
method for controlling a permanent magnet electric motor using an induced
voltage estimator.
j0006j From the foregoing, it appears that although a number of
methods are known to control permanent magnet motors, these methods either
require position sensors and complicated computation or must be adapted to
the environment accora~n9 to each design of permanent magnet motors.
[OQO~ Therefore, there is a need for a system and a method, which
allow controlling a permanent magnet electric motor in a simple, reliable way
and which automat~calty adapts to environmental changes.
OBJECTS OF THE INVENTION
[OaO~j An object of the present invention, is therefore to provide an
improved controlter system and method for a permanent magnet electric motor.
SUMMARY OF THE INVENTION
[0009] More specifically, in accordance with the present invention,
there is provided a system for controlling a permanent magnet etectric motor,
comprising a motor controller and a power stage, the motor controller using
phase currents of the permanent magnet electric motor to generate. voltage-
controlling signals in relation to both changes in speed aid tarque of the
permanent magnet electric motor, which are fed pack to the permanent magnet
electric motor via the power stage.
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[pp1 pl Moreover, there is provided a method for controNing a
pemnanent magnet electric motor comprising determining a current of each
phase of the permanent magnet electric motor; obtaining voltage controlling
signals in relation to both changes iri speed and torque of the permanent
magnet electric motor; and feeding the voltage controlling signal kfack to the
permanent magnet electric motor.
[001'I~ 'There is further provided a circuit for controlling a permanent
magnet three-phases electric motor provided with a rotor and a stator,
comprising a rotator allowing rotation of current signals of the phases of the
permanent magnet electric motor from a Stationary frame to two decvupled
current components in a tutor synchronous frame along a direct axis (la) and a
quadrature axis (Iq) respectively; a proportional and integral operator fur
deriving a voltage (Vq) 'along the quadrature axis and a voltage (V,,) along
the
direct axis; a rotator allowing rotating the voltages Vq and Va back from the
rotor
ynchronous frame to the stationary frame to yield terminal voltages Va, Vc and
V~ of the permanent magnet electric motor.
[p012j There is still further provided a method fur controlling a
permanent magnet three-phases electric motor provided with a rotor and a
stator, comp~5in9 rotating current signals of the phases of the permanent
magnet electric motor from a stationary frame to two decoupled current
components in a rotor synchronous frame along a direct axis (lo) and a
quadrature axis (1~) respectively; ~ deriving a voltage (V~) along the
quadrature
axis therefrom; deriving a voltage (Vc) along the direct axis; rotating the
voltages Vq and Va back from the rotor synchronous frame to the stationary
frame to yield terminal voltages Va. Vp and V~ of the permanent magnet
electric
motor.
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~0013j There is also provided a method for controlling a permanent
magnet electric motor having three-phases each supporting a current ia, ip and
it respectively, comprising determining the currents ia, is and i~; rotating
the
currents ia, ip and i~ by art angle -e~ to yield currents to and Iq; computing
a
current torque of the permanent magnet electric motor; computing a current
rotating angle 8~~,; computing a voltage output Vq; computing a voltage output
Va; rotating the voltages Vq and Va by the rotating angle 9n+1 to yield three
voltage controlling signals Va, VQ and V~; and applying the voltage
controlling
signals Va, Vo and V~ to the permanent magnet electric motor.
[0014j tJther opjects, advantages arid fealutes of the present
invention will become more apparent upon reading of the fotiowing non-
restrictive description of embodiments thereof, given by way of e;campie only
W th reference to the accompanying drawings. 1
BRIEF DESCRIPTION OF THE DRAWINGS
[t101 Sj . In the appended drawings:
~OI116] Figure 1 is a simplified diagram of a motor controller system
according to an embodiment of a first aspect of the present invention; and
[4417] Figure 2 is a flowchart of a method for controlling an electric
riiotor according to an embodiment of a second aspect of the present
invention.
DESCRIPT1C1N t7t= THE EMBODIMENT
[0a18j Generally stated, the present invention provides a system
and method for controlling a three-phased electric motor, ay monitoring the
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terminal voltages thereof in relation to both changes in speed and torque of
the
m4tor.
[OQ19~ More specifically, the present invention provid~;s that the
phase currents of a permanent magnet electric motor are Fret rotated from a
stationary frame into twcr decoupled current components in a rotor synchronous
frame, which enable to derive a voltage along a quadraTUre axis and a voltage
along a direct axis thereof, before rotating back the quadrdture and direct
axis
voltages from the rotor synchronous frame to the stationary frame to yield the
motor terminal voltages.
~0020~ The system 10 shown in Fgure 1 comprises a permanent
magnet motor, referred to hereinafter as PM motor 12; a power stage 14: and a
motor controller 'i fi.
[002'1 The PM motor 12 is a three-phase electric motor provided
with a rotor and a stator (not shown, each ono of the phases ranging a
current, ia. ip and i~, respectively. These phases currents are sensed and
used
t3y the park vector rotator unit 16 tv generate three voltage-contr~3liing
signals
Va, Vp and V~, which are then supplied to the power stage 14.
~Q022] . For example, the power stage 14 may be of the type provided
dy 5emikron, in particular the SKiiPACKt"" 342 GA 120-314 CTV for example.
j0023~ The angular speed "~" of tfie motor is controlled by a user by
setting a value representing the speed of the PM motor 12 into the system 1 D.
The user chooses a reference cement value "1"", normally set at 0, but other
values may be selected.
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[0024 The motor controller 7 B is in the form of a patlc vector rotator
unit. The park vector rotator unit 16 generates two continuously rotating
angles
having instantaneous values 8"r, and -6~. wherein the negative sign represents
an apposite direction of rotation, the subscript "n+1 P labels a current.
computing
angle, and the subscript "n" labels the previous computing angle.
_ [0025 For clarity purposes, the main steps of a method for
controlling a permanent magnet electric motor using the system 10 according
to a second aspect of the invention will now De descrit~ed in reference tv
Figure
2.
[QOZ6] In a first step 100, the three currents ia, io and i~, from the
three phases of the PM motor 12 are determined by the use of standard current
sensors.
~p02T] Then, in a following step (200), the three currents ia, ip arid i~
are processed in an inverse patio vector rotator 18, which mtates them by an
angle -e", to output two currents l~ and IQ.
[0028] fn step 300, the two currents Id and Iq are used to compute a
current torque "T° of the PM motor 12, which is in tum used to compute
the
current rotating angle 8",.~ (step 400).
[0029] AGditionally, the two currents la and Iq ate used to compute
two voltag$ outPu~ Vq and Vc (steps 500 and 600). The voltage outputs VQ and
Va are then rotated in a park ve~or rotator 20 by the rotating angle 9",.~ to
yield
three voltage controlling signals Va, Vp and V~ (step 700).
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[0030] Returning now to Figure 1, the steps of the method of the
present invention will now ~e described in more details.
[0031j The current computing angle is derived in response to
changes of the speed c~ and of the torque T of the PM motor 12 from the
following equation:
8"t~=A" ~-k~ xcu +kzxT~o
where k, and k2 are constants.
[0032] As seen in Figure 1, the phase currents ia, id and i~ are
directed through lines '12a, 12b and 12c to a first inverse park Y~CtGr
rDtatOr ') 8,
which rotates them by the angle -e", to output the tw4 currents t~ and iq,
according to the following relations on the d-q axis fixed on the rotor- axis:
Ic = 2I3 x ~a x cos(A~j -~ i~ x cos(9" +120°) + i~ x cas(9~ -.120~)~
c2y
Iq = 2I3 x [ia x sin(8~) + is X 51t'1(Q~ +i 20°)+ i° x sin(~" -
120°)j cs~
[0033j It is to be noted that either the three currents ia, rp and i~ from
the three phases of the PM motor '12 are measured, or only two of them, the
third phase current being ~calcutated from the other tyvo phases since, as is
,..
known in the art, the following relation holds:
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~pp34~ The la and Iq rotated values are further used tv generate a
first voltage output Vq which takes into account an error between the preset
value I' and la, according to the following equation on the d-q axis tired on
the
rotor axis:
V~ = PI (I" - la) '~' ~ x Iq ts~
where ks is a constant, "PI" refers to a proportional and intel~ral operator,
defined as follows:
PI(x)=axtbj~dt ~s1
vuhere a and b are constants and the integration is over time.
~pp35J The to and Iq rotated, values are also used to generate the
second voltage output Vu, according to the following equation on the d-q axis
fixed on the rotor axis:
Va = li5 x Id 'f k4 x ly X W (7)
where k4 and I~ are constants.
[p036~ Moreover, the speed w is set by the user as stated
hereinabave, whereas the torque T can be calculated by the following formula:
Ts(Vaxlai-~Iq~Clq)/f~~e~
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using the Ic and !q currents and Va and Vq on the d-q axis fixed on the rotor
frame, as determined hereinabove by equations (2~(3).
~typ37~ 'The two voltages Vu and Vq in the continuously rotating
reference frame are then submitted to a second park vector rotamr 20, whereby
they ors rotated by the angle 8~~~, to produce three voltage controlling
signals,
namely Va , vD and V~, which control the power unit 14, according to the
fo~iowing equations:
va = va x coS(e".,) + Va x Sin(B~r~) (9?
Vp - Va x cos(8",.i+120°) + Va x sin(9~,T~+120°) c~o1
v~=va X coS(6"r,-12~°) + Vq X sin(8"Trl2g°) t»f
~pp3g~ It is to be noted that the values k~ to ks are constants that the
user sets, when designing the system 10, based on a number of parameters,
including the sampling rate of the computer to t'e used, condition of the
power
drive, sensitivity of the current sensors, the characteristics of the motor
etc....
(0039 From the foregoing. it should be apparent that the present
invention provides for a system and a method wherepy the motor terminal
voltages are self-adapting. More specifically, three current s~gnats are first
rotated from a stationary frame tv two decvupled current components in a rotor
synchronous frame, along a direct axis (!a) and a quadralure axis (Iq)
respectively. Then, on the first hand, a voltage (Vq) along the quadrature
axis is
derived therefrom. by aPPiyin9 a ProPo~ional and integral operator on the
direct
axis current component added with a product of a constant and the current
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components along the quadrature axis (see equation 5). on the other hand, a
voltage (Va) along the direct axis is derived, as a product of the direct axis
current component added to a product of the speed of the motor by the
quadrature current component (see equation 7). Finally, the qua~irature and
direct axis voltages (Vq and Vd) thus computed are rofated back from the rotor
synchronous frame to the stationary frame to yield the motor terminal voltages
Na, V~ and V~, see equations 9-17 }.
[0040 Therefore, the present system and method allow tar a
continuously updating value of the angle in response to changes of speed and
variations in the torque as welt as to changes in ambient conditions
~00~41~ From the foregoing, it is now also apparent that the present
invention provides a circuit for controlling a permanent magnet three-phases
electric motor provided with a rotor and a stator, comprising a rotator
allowing
rotation of current signals of the phases of the permanent magnet electric
motor from a stationary frame to two decoupled current components in a rotor
synchronous frame along a direct axis (la) and a quadrature axis (1q)
respectively; a proportional and integral operator for deriving a voltage (Va)
along the quadrature axis and a voltage (Vd) along the direct axis; a rotator
allowing rotating the voltages VQ and Va back from the rotor synchronous frame
to the stationary frame to yield terminal voltages Va, Va and V~ of the
permanent
magnet electric motor.
j0042~ )n particular, people in the art wilt appreciate that the method
and system of the present invention allows controlling a permanent magnet
mofior without resorting to position sensors or charactsristirs of the
permanent
magnet motor such as the emf, which are liable to depend on the environment,
thereby adaptable to en~ironmentat conditions.
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~ppe~3~ Although the present invention has been described
hereinabove by way of specific embodiments thereof, it cari pa mo~~fied,
without departing from the spirit and nature of the subject invention as
aefinecl
in the appended claims.
~AMEN~DEp HE~Tf
