FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
CONTROL DEVICE FOR ROTATING MACHINE
MITSUBISHI ELECTRIC CORPORATION A CORPORATION ORGANISED AND
EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
Field
[0001] The present disclosure relates to a control device
for a rotating machine with magnetic saliency, specifically5
a control device that controls a rotating machine whose
inductance varies with a rotor position by obtaining rotor
position information without using a position sensor that
detects the rotor position.
10
Background
[0002] In order for a rotating machine to be driven with
its performance fully brought out, rotor position
information is necessary. To this end, a conventional
control device for a rotating machine uses position15
information that is detected by a position sensor attached
to the rotating machine. However, position sensor–less drive
techniques have been developed for rotating machines from
the perspectives of further reducing manufacturing costs of
rotating machines, downsizing rotating machines, and20
improving reliability of rotating machines.
[0003] Position sensor–less control methods for rotating
machines include a method of estimating a rotor position by
applying high-frequency voltages to a rotating machine and
a method of estimating the rotor position from, for example,25
induced voltages or flux linkages without applying high-
frequency voltages. Patent Literature 1 mentioned below
discloses a method of estimating the rotor position on the
basis of flux linkages of a rotating machine. Specifically,
the background section of Patent Literature 1 below discloses30
the technique of estimating the rotor position by performing
control that makes armature current magnetic flux estimates,
the flux linkages computed on the basis of a voltage equation
3
for the rotating machine, converge to apparent armature
current magnetic fluxes, the flux linkages computed using
stator currents and inductances.
Citation List5
Patent Literature
[0004] Patent Literature 1: Japanese Patent Application
Laid-open No. 2009-095135
Summary of Invention10
Problem to be solved by the Invention
[0005] According to the above-mentioned technique of
Patent Literature 1, the flux linkages are computed by a
flux observer on the basis of both stator voltages and the
stator currents. For this reason, a problem with the15
technique described in Patent Literature 1 is complexity of
position estimation control design. For example, when the
computed flux linkages and the stator currents are used for
the rotor position estimation, the stator currents are used
not only in the rotor position estimation but also in the20
flux linkage computation, causing interference between the
rotor position estimation and the flux linkage computation.
Therefore, with the technique described in Patent Literature
1, highly responsive and highly accurate rotor position
estimation is difficult.25
[0006] The present disclosure has been made in view of
the above, and an object of the present disclosure is to
obtain a control device for a rotating machine that is
capable of highly responsive and highly accurate rotor
position estimation while preventing interference between30
flux linkage computation and position estimate computation.
Means to Solve the Problem
4
[0007] In order to solve the above-stated problem and
achieve the object, a control device for a rotating machine
according to the present disclosure includes a current
detector that detects stator currents flowing through a
stator of the rotating machine and a position estimator that5
computes, on the basis of computed flux linkages of the
rotating machine, a rotor position estimate that is an
estimated position of a rotor of the rotating machine and a
rotational speed estimate that is an estimated speed. The
control device for the rotating machine also includes a10
control unit that outputs stator voltage command values based
on the stator currents and the rotor position estimate for
driving the rotating machine and a voltage application unit
that applies drive voltages to the rotating machine on the
basis of the stator voltage command values. The position15
estimator updates the computed flux linkages on the basis of
stator voltage command values, the rotational speed estimate,
and the most recent computed flux linkages.
Effect of the Invention20
[0008] The control device for the rotating machine
according to the present disclosure has an effect of
estimating the rotor position with high responsiveness and
high accuracy while preventing interference between the flux
linkage computation and the position estimate computation.25
Brief Description of Drawings
[0009] FIG. 1 is a diagram illustrating an exemplary
configuration of a control device for a rotating machine
according to a first embodiment.30
FIG. 2 is a diagram illustrating a control method for
converging a rotor position estimation error to zero in the
first embodiment.
5
FIG. 3 is a diagram illustrating an exemplary
configuration of a control device for a rotating machine
according to a second embodiment.
FIG. 4 is a diagram illustrating a first exemplary
hardware configuration of the control device for the rotating5
machine according to each of the first and second embodiments.
FIG. 5 is a diagram illustrating a second exemplary
hardware configuration of the control device for the rotating
machine according to each of the first and second embodiments.
10
Description of Embodiments
[0010] With reference to the accompanying drawings, a
detailed description is hereinafter provided of control
devices for rotating machines according to embodiments of
the present disclosure.15
[0011] First Embodiment.
FIG. 1 is a diagram illustrating an exemplary
configuration of a control device for a rotating machine
according to a first embodiment. The control device 1A for
the rotating machine according to the first embodiment is a20
control device that controls operation of the rotating
machine 3A. As illustrated in FIG. 1, the control device 1A
includes a voltage application unit 2, a current detector 4,
a control unit 5, and a position estimator 6A. The current
detector 4 is disposed between the voltage application unit25
2 and the rotating machine 3A and detects stator currents
isu, isv, and isw that flow through a stator 7 of the rotating
machine 3A. The voltage application unit 2 applies drive
voltages to the rotating machine 3A in accordance with stator
voltage command values vsu*, vsv*, and vsw* output from the30
control unit 5. Although not illustrated, a direct-current
power supply, an inverter circuit, a pulse-width modulation
(PWM) unit, and others are included in the voltage
6
application unit 2. The inverter circuit converts a direct-
current voltage output from the direct-current power supply
into alternating-current voltages. The PWM unit generates
PWM signals that drive switching elements of the inverter
circuit.5
[0012] The rotating machine 3A in the first embodiment
is a rotating machine whose inductance includes a variable
inductance component that varies with a rotor position and
whose rotor 8 includes no magnets. An example of this type
of rotating machine 3A is a synchronous reluctance motor.10
A direction of the rotor 8 in which the inductance is
maximized is defined herein as a d-axis, and a direction of
the rotor 8 in which the inductance is minimized is defined
herein as a q-axis. For the rotor position, the d-axis of
the rotor 8 is used as a reference. Both the inverter15
circuit and the rotating machine 3A are configured herein
to be three-phase.
[0013] Using stator voltage command values vsd*and vsq* in
a rotating frame and d- and q-axis currents isd and isq in
the rotating frame, the position estimator 6A computes a20
rotor position estimate θ^r that is an estimated position of
the rotor 8. On the basis of the stator currents isu, isv,
and isw and the rotor position estimate θ^r, the control unit
5 generates and outputs the stator voltage command values
vsu*, vsv*, and vsw* for driving the rotating machine 3A.25
Specifically, the control unit 5 uses the stator currents
isu, isv, and isw and the rotor position estimate θ^r to
generate the stator voltage command values vsu*, vsv*, and vsw*
in order for the rotating machine 3A to output a desired
torque command value T*.30
[0014] Next, a more detailed description of the operation
of the control unit 5 is provided. As illustrated in FIG.
1, the control unit 5 includes a current command computation
7
unit 501, a three-phase to two-phase transformation unit 502,
a rotating frame transformation unit 503, a d-q current
control unit 504, an inverse rotating frame transformation
unit 505, and a two-phase to three-phase transformation unit
506.5
[0015] The current command computation unit 501 computes
current command values isd*and isq* in the rotating frame that
are needed for the rotating machine 3A to generate an output
corresponding to the torque command value T*. The current
command values isd*and isq* in the two-phase rotating frame10
are selected herein to minimize a root-mean-square current
value, that is to say, copper loss of the rotating machine
3A for the torque.
[0016] The three-phase to two-phase transformation unit
502 performs three-phase to two-phase transformation of the15
stator currents isu, isv, and isw in a three-phase frame into
rotating machine currents isα and isβ in a two-phase
stationary frame, as expressed by Formula (1) below.
[0017] Formula 1:
20
[0018] In the first embodiment, a transformation matrix
C32 shown in Formula (1) above is used for the three-phase
to two-phase transformation.
[0019] Using the rotor position estimate θ^r, the rotating
frame transformation unit 503 performs rotating frame25
transformation of the rotating machine currents isα and isβ
in the two-phase stationary frame into the d- and q-axis
currents isd and isq in the two-phase rotating frame, as
expressed by Formula (2) below.
8
[0020] Formula 2:
[0021] In the first embodiment, a transformation matrix
Cdq(θ^r) shown in Formula (2) above is used for the rotating
frame transformation.5
[0022] The d-q current control unit 504 performs control
that causes the d- and q-axis currents isd and isq from the
rotating frame transformation unit 503, which has performed
the rotating frame transformation, to match the current
command values isd*and isq* and computes the stator voltage10
command values vsd*and vsq* in the two-phase rotating frame.
For example, proportional-integral (PI) control is used for
this current control.
[0023] Using the rotor position estimate θ^r computed by
the position estimator 6A, the inverse rotating frame15
transformation unit 505 performs inverse rotating frame
transformation of the stator voltage command values vsd*and
vsq* in the two-phase rotating frame into stator voltage
command values vsα* and vsβ* in the two-phase frame, as
expressed by Formula (3) below. In the first embodiment, a20
transformation matrix Cdq-1(θ^r) shown in Formula (3) below is
used for the inverse rotating frame transformation.
[0024] Formula 3:
[0025] The two-phase to three-phase transformation unit25
506 transforms the stator voltage command values vsα* and vsβ*
in the two-phase frame into the stator voltage command values
vsu*, vsv*, and vsw* in the three-phase frame, as expressed by
Formula (4) below.
9
[0026] Formula 4:
[0027] In the first embodiment, a transformation matrix
C23 shown in Formula (4) above is used for the two-phase to
three-phase transformation.5
[0028] Next, a description is provided of how the position
estimator 6A estimates the rotor position, that is to say,
computes the rotor position estimate θ^r. To begin with, a
model of the rotating machine 3A is expressed in the two-
phase frame by Formulas (5) and (6) below.10
[0029] Formula 5:
Formula 6:
[0030] In Formula (5) above, “vsαβ“ represents stator15
voltages, and “isαβ” represents the stator currents. The
superscript “αβ” indicates that the values are in the two-
phase frame. In Formula (5) above, “Rs” represents winding
resistance, and “Ψsαβ” represents flux linkages of the
rotating machine 3A that can be expressed using a matrix, as20
shown in Formula (6) above. As mentioned earlier, the
inductance of the rotating machine 3A varies with the rotor
position. Accordingly, the inductance of the rotating
machine 3A is divided into two components: a mean component
and a variable component. “Lsavg” represents the mean25
inductance component that does not vary with the rotor
10
position, while “Lsvar” represents the variable inductance
component that varies at twice an electrical angular
frequency at which the rotor position changes. The mean
inductance component Lsavg and the variable inductance
component Lsvar are expressed respectively by Formulas (7)5
and (8) below, where d-axis inductance Lsd and q-axis
inductance Lsq are used.
[0031] Formula 7:
Formula 8:10
[0032] Rotating frame transformation of the flux linkages
Ψsαβ of above Formula (6) on the basis of the rotor position
estimate θ^r gives Formula (9) below.
[0033] Formula 9:15
[0034] The superscript “dq” in Formula (9) above indicates
that the values are in the two-phase rotating frame. In
above Formula (9), the first term relates to the inductance’s
mean inductance component Lsavg, which does not vary with the20
rotor position, and the second term relates to the
inductance’s variable inductance component Lsvar, which
varies at twice the electrical angular frequency where the
rotor position changes. Components generated by the variable
inductance component Lsvar and the stator currents isdq, as25
described in the second term, are referred to as the “flux-
linkage inductance variation components”. In the first
embodiment, the flux-linkage inductance variation components
11
are used in the rotor position estimation. Estimates of the
flux-linkage inductance variation components are represented
herein by “Ψ^svardq”. The estimates Ψ^svardq of the flux-linkage
inductance variation components can be derived from the
second term of above Formula (9) and expressed by Formula5
(10) below.
[0035] Formula 10:
[0036] As shown in Formula (10) above, the estimates
Ψ^svardq of the flux-linkage inductance variation components10
can be obtained by using the rotor position estimate θ^r and
the stator currents isdq. It is to be noted here that the
rotating machine 3A in the first embodiment is the
synchronous reluctance rotating machine with the rotor 8
that has no magnets, not allowing for the use of rotor flux15
in the rotor position estimation. Therefore, another method
that does not use the rotor flux is required to accurately
compute the estimates Ψ^svardq of the flux-linkage inductance
variation components.
[0037] Above Formula (10) is simplified here into Formula20
(11) below when the rotor position estimate θ^r approximates
a true rotor position θr, that is, θ^r≈θr.
[0038] Formula 11:
[0039] If there are computed values serving as references25
for the estimates Ψ^svardq of the flux-linkage inductance
variation components, the rotor position can be estimated by
comparing the estimates Ψ^svardq and the reference computed
values. Accordingly, an approach described below is proposed.
[0040] Firstly, applying rotating frame transformation30
12
based on the rotor position estimate θ^r to above Formula
(5), which is a voltage equation, gives Formula (12) below.
[0041] Formula 12:
[0042] In Formula (12) above, “ω^r“ represents an5
estimated rotational speed and is called herein the
“rotational speed estimate”. The rotational speed estimate
ω^r is computed by the position estimator 6A, as described
later. In Formula (12) above, “J” represents a
transformation matrix expressed by Formula (13) below.10
[0043] Formula 13:
[0044] Rearranging above Formula (12) gives Formula (14)
below.
[0045] Formula 14:15
[0046] Theoretically, flux linkages Ψsdq can be computed
by integrating Formula (14) above; however, unknown initial
values are a problem. Furthermore, since response of Formula
(14) itself is oscillatory, an observer is commonly used for20
stable computation. From these perspectives, a flux observer
that computes the flux linkages Ψsdq can be configured on the
basis of above Formula (14) to be Formula (15) below.
Voltage drops due to the winding resistance Rs in the second
term of Formula (14) can be ignored when the rotational speed25
of the rotating machine 3A is above a certain level.
[0047] Formula 15:
[0048] In Formula (15) above, “Ψs,calcdq” represents
13
computed values of the flux linkages Ψsdq, and “H” represents
feedback gain of the flux observer. “Ψs,objdq” represents
target values to which the computed flux linkages Ψs,calcdq
should converge and are needed for the flux observer to
achieve convergence. Formula (16) below, derived by setting5
differentials of the flux linkages Ψsdq, that is, the left
side of above Formula (14) representing a voltage equation
to zero, can be used for computation of the target values
Ψs,objdq.
[0049] Formula 16:10
[0050] Since the target values Ψs,objdq are computed on the
basis of the voltage equation, the target values Ψs,objdq are
called herein the “voltage-based target values”. For the
purpose of designing responsiveness of the flux observer,15
transforming above Formula (15) so that the computed flux
linkages Ψs,calcdq become variables gives Formula (17) below.
[0051] Formula 17:
[0052] Since the true rotor position θr is unknown here,20
the approximation, θr≈θ^r, gives Formula (18) below.
[0053] Formula 18:
[0054] Using above Formula (18) and setting the feedback
14
gain H of the flux observer, for example, to Formula (19)
below allows the responsiveness of convergence to be designed
as ωobs.
[0055] Formula 19:
5
[0056] A summary of the above description is as follows.
Firstly, the flux observer of the first embodiment is
represented by Formulas (15), (16), and (19). In Formulas
(15) and (16), the voltage drops Rsisdq due to the winding
resistance Rs can be ignored when the rotational speed is10
above the certain level. The stator voltage command values
vsdq* are used as stator voltages vsdq. From the above
perspectives, the flux observer is used in the first
embodiment to compute the flux linkages Ψs,calcdq on the basis
of the stator voltage command values vsdq*, the rotational15
speed estimate ω^r, and the most recent computed flux
linkages Ψs,calcdq. The phrase “the most recent” refers to
being temporally close and may refer to, for example, being
closest to the current point in time. In other words, “the
most recent computed flux linkages Ψs,calcdq“ mentioned here20
may be the latest values among past computed flux linkages
Ψs,calcdq. The same meaning is used in subsequent descriptions.
[0057] A more detailed computation method is explained as
follows. The flux observer of the first embodiment computes
the flux linkages Ψs,calcdq on the basis of the stator voltage25
command values vsdq*, the products of the rotational speed
estimate ω^r and the most recent computed flux linkages
Ψs,calcdq, and the quotients of the stator voltage command
values vsdq* by the rotational speed estimate ω^r. “The
products of the rotational speed estimate ω^r and the most30
15
recent computed flux linkages Ψs,calcdq” correspond to the
third term in above Formula (15). “The quotients of the
stator voltage command values vsdq* by the rotational speed
estimate ω^r” correspond to above Formula (16).
[0058] An even more detailed computation method is5
explained as follows. The flux observer of the first
embodiment computes the flux linkages Ψs,calcdq on the basis
of the stator voltage command values vsdq*, the products of
the rotational speed estimate ω^r and the most recent
computed flux linkages Ψs,calcdq, and differences between the10
most recent computed flux linkages Ψs,calcdq and the quotients
of the stator voltage command values vsdq* by the rotational
speed estimate ω^r. The “differences between the most recent
computed flux linkages Ψs,calcdq and the quotients of the
stator voltage command values vsdq* by the rotational speed15
estimate ω^r” correspond to the fourth and fifth terms in
above Formula (15).
[0059] A yet more detailed computation method is
explained as follows. The flux observer of the first
embodiment computes the flux linkages Ψs,calcdq on the basis20
of first differences between the stator voltage command
values vsdq* and the products of the rotational speed estimate
ω^r and the most recent computed flux linkages Ψs,calcdq and
second differences between the most recent computed flux
linkages Ψs,calcdq and the quotients of the stator voltage25
command values vsdq* by the rotational speed estimate ω^r.
The first differences correspond to the first and third terms
of above Formula (15), and the above-mentioned second
differences correspond to the fourth and fifth terms of above
Formula (15). It is to be noted that the first differences30
are based on the differentials of the flux linkages Ψs, as
shown in above Formula (14), while the second differences
are based on steady-state values of the flux linkages Ψs, as
16
shown in above Formula (15). In other words, the flux
observer of the first embodiment computes the flux linkages
Ψs on the basis of both the differentials and the steady-
state values of the flux linkages Ψs. Unlike the flux
observer of above-mentioned Patent Literature 1, the flux5
observer of the first embodiment does not use flux linkages
computed using the stator currents and the inductances.
[0060] The computation methods for the flux linkages
Ψs,calcdq according to the first embodiment have been described
above. However, the terms in above Formula (15), which forms10
the basis of the computation methods, can have their signs
reversed depending on polarities of the stator voltages vs,
the stator currents is, and the flux linkages Ψs. Furthermore,
various modifications of above Formula (16) are possible,
depending on how the flux observer is configured. A vital15
point of the flux observer in the first embodiment is that
components essential for computing the flux linkages Ψs,calcdq
are the stator voltage command values vsdq*, the rotational
speed estimate ω^r, and the most recent computed flux
linkages Ψs,calcdq. In view of this perspective, the computed20
flux linkages Ψs,calcdq are updated in the first embodiment by
computing new flux linkages Ψs,calcdq on the basis of the stator
voltage command values vsdq*, the rotational speed estimate
ω^r, and the most recent computed flux linkages Ψs,calcdq.
[0061] Computed values of the flux-linkage inductance25
variation components are represented by “Ψsvar,calcdq”. The
flux-linkage inductance variation components Ψsvar,calcdq can
be computed using Formula (20) below, where the flux linkages
Ψs,calcdq computed by the flux observer are used.
[0062] Formula 20:30
[0063] Above Formula (20) can be derived from the
17
relations given by Formulas (9) and (10).
[0064] For the flux-linkage inductance variation
components, using Formula (21) below, estimation errors can
be computed from the computed flux-linkage inductance
variation components Ψsvar,calcdq expressed by above Formula5
(20) and the flux-linkage inductance variation component
estimates Ψ^svardq expressed by above Formula (11).
[0065] Formula 21:
[0066] Above Formula (21) can be expressed as Formula10
(22) below when the rotor position estimate θ^r approximates
the true rotor position θr, that is, θ^r≈θr in above Formula
(21).
[0067] Formula 22:
15
[0068] Above Formula (22) is a formula expressing a rotor
position estimation error {-(θ^r-θr)}. FIG. 2 illustrates a
control method for converging this estimation error {-(θ^r-
θr)} to zero. FIG. 2 is a diagram illustrating the control
method for converging the rotor position estimation error {-20
(θ^r-θr)} to zero in the first embodiment. In the first
embodiment, the position estimator 6A follows the procedure
shown in FIG. 2. Specifically, as illustrated in FIG. 2,
the estimation error {-(θ^r-θr)} has only to undergo PI
control and then be further integrated to converge to zero.25
In this procedure, an input to an integrator, that is to say,
the output from the PI control is the rotational speed
estimate ω^r, and an output of the integrator is the rotor
position estimate θ^r.
[0069] Next, the approach of the first embodiment and the30
18
technique described in Patent Literature 1 are compared. In
Patent Literature 1, as described earlier, values computed
from the stator currents and the inductances are used as
target values in the flux observer. These target values are
called herein the “current-based target values” and are5
represented by “Ψs,objdq’”. As mentioned earlier, the approach
of the first embodiment uses the voltage-based target values
Ψs,objdq.
[0070] The current-based target values Ψs,objdq’ used in
Patent Literature 1 can be computed using Formula (23) below.10
Formula (23) below can be obtained by using the approximation,
θ^r≈θr, in above Formula (9) and using the relations given by
above Formulas (7) and (8).
[0071] Formula 23:
15
[0072] When the variable inductance component Lsvar is used
for position estimation as in the first embodiment, the flux
linkages Ψs in the rotating frame need to be computed on the
basis of the rotor position estimate θ^r, which includes the
estimation error. For this computation, the voltage equation20
relating to the stator voltages vsdq is used, as shown in
above Formula (14). By comparing the computed values with
the flux-linkage inductance variation component estimates
Ψ^svardq, which are the estimates computed using the rotor
position estimate θ^r and the stator currents isdq as in25
Formulas (10) and (11), the estimation error {-(θ^r-θr)} can
be extracted.
[0073] Meanwhile, if the computed flux linkages Ψs are
made to converge to the current-based target values Ψs,objdq’,
which are computed from the stator currents isdq, as shown in30
above Formula (23), on the assumption that the rotor position
estimate θ^r is true, the estimation error {-(θ^r-θr)} cannot
19
be extracted. More specifically, if the flux-linkage
inductance variation components are computed using above
Formula (20) through the use of the computed values from
above Formula (23), the flux-linkage inductance variation
components will become equal to the estimates from above5
Formula (11). This means that the error in the rotor
position estimate θ^r, as expressed in the second term of
above Formula (9), and variations in the flux linkages Ψs
due to the variable inductance component Lsvar are ignored.
However, if the flux observer is designed to have a slow10
response speed for causing the convergence to the current-
based target values Ψs,objdq’, the flux linkages Ψs computed on
the basis of the voltage equation will slowly follow the
current-based target values Ψs,objdq’, mitigating the effects.
Meanwhile, designing for the slow response speed causes the15
flux linkages Ψs, which are computed on the basis of the
voltage equation represented by above Formula (14), to be
oscillatory. Therefore, the response speed of the flux
observer needs to be at least a certain value. This is how
the control design using the flux observer interferes with20
the position estimation control design, resulting in a
problem with the technique described in Patent Literature 1
and making stable and highly responsive rotor position
estimation difficult.
[0074] By contrast, the approach of the first embodiment25
includes computing the flux linkages Ψs on the basis of the
voltage equation using the stator voltages vs and making the
computed flux linkages Ψs converge to the voltage-based
target values Ψs,objdq given by Formula (16). Therefore, the
approach of the first embodiment allows for highly responsive30
and highly accurate rotor position estimation through the
computation of the flux-linkage inductance variation
components, with the computation of the position estimate
20
not interfering with the computation of the flux linkages Ψs.
[0075] Besides Patent Literature 1, Japanese Patent
Application Laid-open No. 2006-288083 (hereinafter referred
to as “Patent Literature 2”), for example, shows another
conventional technique. The technique described in Patent5
Literature 2 uses what are called herein the voltage-based
target values Ψs,objdq directly for position estimate
computation without using a flux observer. A problem with
this technique is that using only the steady-state values of
the flux linkages Ψs results in time-consuming convergence10
of the computed flux linkages Ψs and also leads to a slow
response in position estimation.
[0076] By contrast, the approach of the first embodiment
uses not only the steady-state values of the flux linkages
Ψs but also the differentials of the flux linkages Ψs for the15
computation of the flux linkages Ψs. Therefore, the approach
of the first embodiment allows for the rotor position
estimation through the highly responsive computation of the
flux linkages Ψs.
[0077] Yet another conventional technique is shown, for20
example, in Japanese Patent Application Laid-open No. 2018-
183005 (hereinafter referred to as “Patent Literature 3”).
The technique described in Patent Literature 3 involves
computing the flux linkages Ψs on the basis of the voltage
equation in the two-phase frame, which is the stationary25
frame. Rearranging above Formula (5) gives following Formula
(24) for the differentials of the flux linkages Ψs.
[0078] Formula 24:
[0079] Since the parameters of the rotating machine 3A in30
the stationary frame are alternating current, their steady-
state values are zero. Furthermore, if initial values of
21
the flux linkages Ψs are set to zero, the flux linkages Ψs
can be computed by integration. In that case, the technique
described in Patent Literature 3 applies a high-pass filter,
such as the one shown in Formula (25) below, to remove a
direct-current component and low-frequency components.5
[0080] Formula 25:
[0081] In Formula (25) above, “ωhpf” represents a cutoff
angular frequency of the high-pass filter. The use of the
high-pass filter in Patent Literature 3 solves the problem10
of the initial values. Furthermore, using the high-pass
filter restrains drift of the integral that is caused by
disturbances and others. However, since the parameters of
the rotating machine 3A are alternating current, high
rotational speeds and high frequencies of the parameters of15
the rotating machine 3A result in fewer sampling points for
the control computation. As a result, oscillations occur in
the integration of the flux linkages Ψs, problematically
causing the rotor position estimation, which uses the
integration, to become unstable. Another problem with the20
technique described in Patent Literature 3 is that using the
high-pass filter to remove the low-frequency components,
which should ideally be included in the computed values,
results in a reduced response speed and reduced accuracy,
particularly during a transient response.25
[0082] By contrast, the approach of the first embodiment
allows for the computation of the flux linkages Ψs in the
rotating frame by using the flux observer and the voltage-
based target values Ψs,objdq. Since the parameters of the
rotating machine 3A in the rotating frame are direct current,30
the problem of sampling points is mitigated even at high
rotational speeds. Furthermore, using the flux observer
22
enables the flux linkages Ψs to converge to the voltage-based
target values Ψs,objdq, eliminating the need to remove low-
frequency components. Therefore, the approach of the first
embodiment allows for the rotor position estimation through
the highly accurate, highly responsive, and highly stable5
computation of the flux linkages Ψs.
[0083] As described above, the control device for the
rotating machine according to the first embodiment includes
the current detector that detects the stator currents flowing
through the stator of the rotating machine and the position10
estimator that computes the rotor position estimate and the
rotational speed estimate on the basis of the computed flux
linkages of the rotating machine. The position estimator
updates the computed flux linkages on the basis of the stator
voltage command values, the rotational speed estimate, and15
the most recent computed flux linkages. This enables the
rotor position to be estimated with high responsiveness and
high accuracy.
[0084] The approach of the first embodiment can use the
flux-linkage inductance variation components when the flux20
linkages are computed. The flux-linkage inductance
variation components are the flux components generated by
the variable inductance component and the stator currents.
When the inductance of the rotating machine is divided into
the mean component, which does not vary with the rotor25
position, and the variable component, which varies at twice
the electrical angular frequency where the rotor position
changes, the variable inductance component refers to the
latter component. Using this variable inductance component
in the rotor position estimation allows for highly responsive30
and highly accurate rotor position estimation, a remarkable
effect not conventionally seen.
[0085] Second Embodiment.
23
FIG. 3 is a diagram illustrating an exemplary
configuration of a control device for a rotating machine
according to a second embodiment. Compared with the first
embodiment’s configuration illustrated in FIG. 1, the
configuration of the second embodiment has the control device5
1B replacing the control device 1A and the rotating machine
3B replacing the rotating machine 3A. Furthermore, the
control device 1B has a position estimator 6B replacing the
position estimator 6A. The configuration is otherwise
identical or equivalent to that of FIG. 1, and identical or10
equivalent constituent elements have the same reference
characters. In the second embodiment, descriptions of
details identical or equivalent to those in the first
embodiment are omitted as appropriate.
[0086] The rotating machine 3B in the second embodiment15
is a rotating machine whose inductance includes a variable
inductance component that varies with a rotor position and
whose rotor 8 includes magnets. An example of this type of
rotating machine 3B is an interior permanent magnet motor
with magnets embedded in the rotor 8. In the second20
embodiment, an N-pole direction of the magnets of the rotor
8 is defined as a d-axis. For the rotor position, the d-
axis of the rotor 8 is used as a reference. A q-axis is in
a direction that is electrically 90° ahead of the d-axis in
a direction of rotation. As in the first embodiment, both25
the inverter circuit and the rotating machine 3B are
configured to be three-phase.
[0087] Next, a description is provided of how the position
estimator 6B estimates the rotor position, that is to say,
computes the rotor position estimate θ^r. To begin with, a30
model of the rotating machine 3B is expressed in a two-phase
frame by Formulas (26) and (27) below.
24
[0088] Formula 26:
Formula 27:
[0089] In Formula (27) above, “Ψm” represents flux linkage5
created by the permanent magnets and is called herein “magnet
flux”. Rotating frame transformation of the flux linkages
Ψsαβ of above Formula (27) on the basis of the rotor position
estimate θ^r gives Formula (28) below.
[0090] Formula 28:10
[0091] “Ψmdq” in the third term of above Formula (28)
represents components of the magnet flux Ψm in a two-phase
rotating frame. In Formula (28) above, the first term
relates to the inductance’s mean inductance component Lsavg,15
which does not vary with the rotor position, and the second
term relates to the inductance’s variable inductance
component Lsvar, which varies at twice the electrical angular
frequency where the rotor position changes. In the second
embodiment, the q-axis component of the magnet flux Ψm20
described in the third term is used for the rotor position
estimation.
[0092] Given safety, the environment, and costs, rotating
machines with small magnet flux and high reluctance torque
(i.e., a large variable inductance component) have started25
to prevail in recent products, such as those for automobiles.
25
Therefore, flux linkages based on the variable inductance
component Lsvar, as described in the second term, need to be
accurately computed for accurate computation of the magnet
flux in the third term.
[0093] Next, a description is provided of how the flux5
linkages are computed in the second embodiment. Firstly,
applying rotating frame transformation based on the rotor
position estimate θ^r to above Formula (26), which is a
voltage equation, followed by rearrangement, gives Formula
(29) below.10
[0094] Formula 29:
[0095] Theoretically, the flux linkages Ψsdq can be
computed by integrating Formula (29) above; however, unknown
initial values are a problem. Furthermore, since response15
of Formula (29) itself is oscillatory, an observer is
commonly used for stable computation. From these
perspectives, a flux observer that computes the flux linkages
Ψsdq can be configured on the basis of above Formula (29) to
be Formula (30) below. Voltage drops due to the winding20
resistance Rs in the second term of Formula (29) can be
ignored when rotational speed of the rotating machine 3B is
above a certain level.
[0096] Formula 30:
25
[0097] Formula (31) below, derived by setting
differentials of the flux linkages Ψsdq, that is, the left
side of above Formula (29) representing a voltage equation
to zero, can be used here for computation of the target
values Ψs,objdq.30
[0098] Formula 31:
26
[0099] Since the target values Ψs,objdq are computed on the
basis of the voltage equation, the target values Ψs,objdq are
called the “voltage-based target values” in the second
embodiment as well. For the purpose of designing5
responsiveness of the flux observer, transforming above
Formula (30) so that the computed flux linkages Ψs,calcdq
become variables gives Formula (32) below.
[0100] Formula 32:
10
[0101] Since the true rotor position θr is unknown here,
the approximation, θr≈θ^r, gives Formula (33) below.
[0102] Formula 33:
[0103] Using above Formula (33) and setting the feedback15
gain H of the flux observer, for example, to Formula (34)
below allows the responsiveness of convergence to be designed
as ωobs.
[0104] Formula 34:
20
[0105] A summary of the above description is as follows.
27
Firstly, the flux observer of the second embodiment is
represented by Formulas (30), (31), and (34). In Formulas
(30) and (31), the voltage drops Rsisdq due to the winding
resistance Rs can be ignored when the rotational speed is
above the certain level. The stator voltage command values5
vsdq* are used as the stator voltages vsdq. From the above
perspectives, the flux observer is used in the second
embodiment to compute the flux linkages Ψs,calcdq on the basis
of the stator voltage command values vsdq*, the rotational
speed estimate ω^r, and the most recent computed flux10
linkages Ψs,calcdq.
[0106] A more detailed computation method is explained as
follows. The flux observer of the second embodiment computes
the flux linkages Ψs,calcdq on the basis of the stator voltage
command values vsdq*, the products of the rotational speed15
estimate ω^r and the most recent computed flux linkages
Ψs,calcdq, and the quotients of the stator voltage command
values vsdq* by the rotational speed estimate ω^r. “The
products of the rotational speed estimate ω^r and the most
recent computed flux linkages Ψs,calcdq” correspond to the20
third term in above Formula (30). “The quotients of the
stator voltage command values vsdq* by the rotational speed
estimate ω^r” correspond to above Formula (31).
[0107] An even more detailed computation method is
explained as follows. The flux observer of the second25
embodiment computes the flux linkages Ψs,calcdq on the basis
of the stator voltage command values vsdq*, the products of
the rotational speed estimate ω^r and the most recent
computed flux linkages Ψs,calcdq, and differences between the
most recent computed flux linkages Ψs,calcdq and the quotients30
of the stator voltage command values vsdq* by the rotational
speed estimate ω^r. The “differences between the most recent
computed flux linkages Ψs,calcdq and the quotients of the
28
stator voltage command values vsdq* by the rotational speed
estimate ω^r” correspond to the fourth and fifth terms in
above Formula (30).
[0108] A yet more detailed computation method is
explained as follows. The flux observer of the second5
embodiment computes the flux linkages Ψs,calcdq on the basis
of first differences between the stator voltage command
values vsdq* and the products of the rotational speed estimate
ω^r and the most recent computed flux linkages Ψs,calcdq and
second differences between the most recent computed flux10
linkages Ψs,calcdq and the quotients of the stator voltage
command values vsdq* by the rotational speed estimate ω^r.
The first differences correspond to the first and third terms
of above Formula (30), and the second differences correspond
to the fourth and fifth terms of above Formula (30). It is15
to be noted that the first differences are based on the
differentials of the flux linkages Ψs, as shown in above
Formula (29), while the second differences are based on
steady-state values of the flux linkages Ψs, as shown in
above Formula (30). In other words, the flux observer of20
the second embodiment computes the flux linkages Ψs on the
basis of both the differentials and the steady-state values
of the flux linkages Ψs. Unlike the flux observer of above-
mentioned Patent Literature 1, the flux observer of the
second embodiment does not use the flux linkages computed25
using the stator currents and the inductances.
[0109] The computation methods for the flux linkages
Ψs,calcdq according to the second embodiment have been
described above. However, the terms in above Formula (30),
which forms the basis of the computation methods, can have30
their signs reversed depending on the polarities of the
stator voltages vs, the stator currents is, and the flux
linkages Ψs. Furthermore, various modifications of above
29
Formula (31) are possible, depending on how the flux observer
is configured. A vital point of the flux observer in the
second embodiment is that components essential for computing
the flux linkages Ψs,calcdq are the stator voltage command
values vsdq*, the rotational speed estimate ω^r, and the most5
recent computed flux linkages Ψs,calcdq. In view of this
perspective, the computed flux linkages Ψs,calcdq are updated
in the second embodiment by computing new flux linkages
Ψs,calcdq on the basis of the stator voltage command values
vsdq*, the rotational speed estimate ω^r, and the most recent10
computed flux linkages Ψs,calcdq.
[0110] A computed value of the q-axis component of the
magnet flux Ψmdq described in the third term of Formula (28)
above is represented by “Ψmq,calc”. This value Ψmq,calc can be
computed using Formula (35) below, where the flux linkage15
Ψsq,calc computed by the flux observer is used.
[0111] Formula 35:
[0112] Above Formula (35) can be derived from the
approximation, θ^r≈θr, in above Formula (28) and the relations20
given by Formulas (9) and (10).
[0113] The q-axis component in the third term of above
Formula (28) corresponds to the computed q-axis component
Ψmq,calc on the left side of Formula (35) above and thus can
be expressed by Formula (36) below.25
[0114] Formula 36:
[0115] Using the relation, θ^r≈θr, in above Formula (36)
allows above Formula (36) to be expressed as Formula (37)
below.30
30
[0116] Formula 37:
[0117] Above Formula (37) is a formula expressing the
rotor position estimation error {-(θ^r-θr)}. As in the first
embodiment, the estimation error {-(θ^r-θr)} undergoes PI5
control and is then integrated to converge to zero. This
allows for the estimation of the rotor position. In this
case as well, an input to an integrator is the rotational
speed estimate ω^r, and an output of the integrator is the
rotor position estimate θ^r.10
[0118] Next, the approach of the second embodiment and
the technique described in Patent Literature 1 are compared.
When the technique described in Patent Literature 1 is
applied to the second embodiment, the current-based target
values Ψs,objdq’ used in Patent Literature 1 can be expressed15
by Formula (38) below.
[0119] Formula 38:
[0120] However, if the computed flux linkages Ψs are made
to converge to the current-based target values Ψs,objdq’, which20
are computed from the stator currents isdq, as shown in above
Formula (38), on the assumption that the rotor position
estimate θ^r is true, the q-axis component of the magnet flux
Ψm, shown in the third term of above Formula (28) and which
is used for the position estimation, cannot be extracted.25
Furthermore, the error in the rotor position estimate θ^r,
as shown in the second term of above Formula (28), and
variations in the flux linkages Ψs due to the variable
inductance component Lsvar are ignored. The effects are
particularly significant for rotating machines with small30
magnet flux Ψm and a large variable inductance component Lsvar.
31
Even using the measure to adjust the response of the flux
observer, as described in the first embodiment, results in
complexity where the control design using the flux observer
interferes with the position estimation control design,
making stable and highly responsive rotor position5
estimation difficult.
[0121] By contrast, the approach of the second embodiment
includes computing the flux linkages Ψs on the basis of the
voltage equation using the stator voltages vs and making the
computed flux linkages Ψs converge to the voltage-based10
target values Ψs,objdq given by Formula (31). Therefore, the
approach of the second embodiment allows for highly
responsive and highly accurate rotor position estimation
through the computation of the flux-linkage inductance
variation components, with the computation of the position15
estimate not interfering with the computation of the flux
linkages Ψs.
[0122] As described in the first embodiment, the
technique described in Patent Literature 2 uses what are
called herein the voltage-based target values Ψs,objdq directly20
for position estimate computation without using a flux
observer. A problem with this technique is that using only
the steady-state values of the flux linkages Ψs results in
time-consuming convergence of the computed flux linkages Ψs
and also leads to a slow response in position estimation.25
[0123] By contrast, the approach of the second embodiment
uses not only the steady-state values of the flux linkages
Ψs but also the differentials of the flux linkages Ψs for the
computation of the flux linkages Ψs. Therefore, the approach
of the second embodiment allows for the rotor position30
estimation through the highly responsive computation of the
flux linkages Ψs.
[0124] As described above, even when the rotating machine
32
has the permanent magnets, the position estimator included
in the control device for the rotating machine according to
the second embodiment updates the computed flux linkages on
the basis of the stator voltage command values, the
rotational speed estimate, and the most recent computed flux5
linkages. This enables the rotor position to be estimated
with high responsiveness and high accuracy even when the
magnet flux of the rotating machine is used for rotor
position estimation.
[0125] The functions of each of the control devices 1A10
and 1B for the rotating machines, as described in the first
and second embodiments, can be implemented with processing
circuitry. The functions of the control device 1A or 1B
refer to the functions of the control unit 5 and the position
estimator 6A or 6B.15
[0126] FIG. 4 is a diagram illustrating a first exemplary
hardware configuration of the control device for the rotating
machine according to each of the first and second embodiments.
FIG. 5 is a diagram illustrating a second exemplary hardware
configuration of the control device for the rotating machine20
according to each of the first and second embodiments. A
rotating machine 3 illustrated in FIGS. 4 and 5 refers to
either the rotating machine 3A described in the first
embodiment or the rotating machine 3B described in the second
embodiment. The processing circuitry may be dedicated25
hardware, such as dedicated processing circuitry 10
illustrated in FIG. 4, or may include, as illustrated in FIG.
5, a processor 11 and a memory 12 storing programs that
operate the processor 11.
[0127] The dedicated processing circuitry 10, which is30
used as the dedicated hardware, corresponds to a single
circuit, a composite circuit, a programmed processor, a
parallel programmed processor, an application-specific
33
integrated circuit (ASIC), a field-programmable gate array
(FPGA), or a combination of these. The functions of each of
the control devices 1A and 1B may be implemented individually
or collectively with the processing circuitry.
[0128] When the processor 11 and the memory 12 are used,5
the functions of each of the control devices 1A and 1B are
implemented with software, firmware, or a combination of
these. The software or the firmware is described as programs
and is stored in the memory 12. The processor 11 reads and
executes the programs stored in the memory 12. These10
programs can be said to cause a computer to execute the steps
and the method that the processor 11 performs. The memory
12 corresponds to a semiconductor memory, such as a random-
access memory (RAM), a read-only memory (ROM), a flash memory,
an erasable programmable read-only memory (EPROM), or an15
electrically erasable programmable read-only memory (EEPROM)
(registered trademark). The semiconductor memory may be
either a nonvolatile memory or a volatile memory. Besides
the semiconductor memory, a magnetic disk, a flexible disk,
an optical disk, a compact disk, a mini disk, a digital20
versatile disc (DVD), or a different option may be used as
the memory 12. The functions of each of the control devices
1A and 1B may be implemented partly with hardware and partly
with software or firmware.
[0129] The voltage application unit 2 described herein25
includes the three-phase inverter circuit. However, the
voltage application unit 2 may include an inverter with a
different number of phases. The voltage application unit 2
to be used can be any of various voltage application units
that include multi-level inverters, such as a three-level30
inverter and a five-level inverter.
[0130] While the stator currents is for the torque of each
of the rotating machines 3A and 3B are set to minimize the
34
root-mean-square current value, the stator currents is may
be set to minimize the flux linkages or maximize efficiency
of the voltage application unit 2 or each rotating machine
3A or 3B.
[0131] The above configurations illustrated in the5
embodiments are illustrative, can be combined with other
techniques that are publicly known, and can be partly omitted
or changed without departing from the gist.
Reference Signs List10
[0132] 1A, 1B control device; 2 voltage application
unit; 3, 3A, 3B rotating machine; 4 current detector; 5
control unit; 6A, 6B position estimator; 7 stator; 8 rotor;
10 dedicated processing circuitry; 11 processor; 12
memory; 501 current command computation unit; 502 three-15
phase to two-phase transformation unit; 503 rotating frame
transformation unit; 504 d-q current control unit; 505
inverse rotating frame transformation unit; 506 two-phase
to three-phase transformation unit.
20
35
WE CLAIM:
[Claim 1] A control device (1A, 1B) for a rotating machine
(3A, 3B), the control device (1A, 1B) comprising:
a current detector (4) to detect stator currents flowing
through a stator (7) of the rotating machine (3A, 3B);5
a position estimator (6A, 6B) to compute a rotor
position estimate and a rotational speed estimate on a basis
of computed flux linkages of the rotating machine (3A, 3B),
the rotor position estimate being an estimated position of
a rotor (8) of the rotating machine (3A, 3B), the rotational10
speed estimate being an estimated speed;
a control unit (5) to output stator voltage command
values based on the stator currents and the rotor position
estimate for driving the rotating machine (3A, 3B); and
a voltage application unit (2) to apply drive voltages15
to the rotating machine (3A, 3B) on a basis of the stator
voltage command values, wherein
the position estimator (6A, 6B) updates the computed
flux linkages on a basis of the stator voltage command values,
the rotational speed estimate, and the computed flux linkages20
that are the most recent.
[Claim 2] The control device (1A, 1B) for the rotating
machine (3A, 3B) according to claim 1, wherein
the position estimator (6A, 6B) updates the computed25
flux linkages on a basis of the stator voltage command values,
products of the rotational speed estimate and the computed
flux linkages that are the most recent, and quotients of the
stator voltage command values by the rotational speed
estimate.30
[Claim 3] The control device (1A, 1B) for the rotating
machine (3A, 3B) according to claim 1 or 2, wherein
36
the position estimator (6A, 6B) updates the computed
flux linkages on a basis of the stator voltage command values,
the products of the rotational speed estimate and the
computed flux linkages that are the most recent, and
differences between the computed flux linkages that are the5
most recent and the quotients of the stator voltage command
values by the rotational speed estimate.
[Claim 4] The control device (1A, 1B) for the rotating
machine (3A, 3B) according to any one of claims 1 to 3,10
wherein
the position estimator (6A, 6B) updates the computed
flux linkages on a basis of first differences between the
stator voltage command values and the products of the
rotational speed estimate and the computed flux linkages15
that are the most recent and second differences between the
computed flux linkages that are the most recent and the
quotients of the stator voltage command values by the
rotational speed estimate.
20
[Claim 5] The control device (1A, 1B) for the rotating
machine (3A, 3B) according to any one of claims 1 to 4,
wherein
inductance of the rotating machine (3A, 3B) includes a
variable inductance component that varies with a rotor25
position, the rotor position being a rotational position of
the rotor (8).
[Claim 6] The control device (1A) for the rotating machine
(3A) according to claim 5, wherein30
the rotor (8) of the rotating machine (3A) is permanent
magnet–free.
37
[Claim 7] The control device (1B) for the rotating machine
(3B) according to claim 5, wherein
the rotor (8) of the rotating machine (3B) includes a
permanent magnet.
5
[Claim 8] The control device (1A, 1B) for the rotating
machine (3A, 3B) according to any one of claims 5 to 7,
wherein
the position estimator (6A, 6B) estimates the rotor
position from flux-linkage inductance variation components10
that are included in flux linkages of the rotating machine
(3A, 3B) and generated by the variable inductance component
and the stator currents.
[Claim 9] The control device (1A, 1B) for the rotating15
machine (3A, 3B) according to claim 8, wherein
the inductance of the rotating machine (3A, 3B) is
divided into a mean component that does not vary with the
rotor position and the variable inductance component that
varies at twice an electrical angular frequency where the20
rotor position changes, and
the flux-linkage inductance variation components are
magnetic fluxes generated by the stator currents and the
variable component.