1
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
ROTATING MACHINE CONTROL DEVICE;
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 rotating
machine control device that controls a rotating machine.5
Background
[0002] To operate an alternating-current motor that is a
type of rotating machine (hereinafter referred to as the
rotating machine) at variable speeds, power that is10
supplied to the rotating machine needs to be converted to a
desired voltage and frequency. For the power conversion,
an inverter device is used. A typical inverter device is
composed of a main circuit using semiconductor switching
elements and a control device that controls the15
semiconductor switching elements. The inverter device
obtains the desired frequency and voltage through on-off
control of the semiconductor switching elements. Pulse-
width modulation (PWM) control is widely used as a method
of switching the semiconductor switching elements.20
[0003] Pulses used in the PWM control are generated by
comparing a command for voltage to be applied to the
rotating machine (hereinafter referred to as the voltage
command) with a carrier wave used for the pulse generation.
The carrier wave to be used is, for example, a triangular25
wave. With an increasing carrier wave frequency, output
pulses include fewer harmonics, resulting in reduced
harmonic losses when applied to the rotating machine.
[0004] However, as the carrier wave frequency is
increased, the semiconductor switching elements are30
switched more frequently, leading to heat generation
associated with increased switching losses. Therefore,
from the perspective of thermal design, an upper limit for
3
the carrier wave frequency is determined.
[0005] If the carrier wave frequency is fixed regardless
of the rotating machine’s rotational speed, the switching
frequency increases when the rotational speed of the
rotating machine increases, leading to heat generation that5
cannot be tolerated. Accordingly, control is performed
such that the carrier wave frequency is fixed when the
rotational speed of the rotating machine is lower and
changed in synchronization with the voltage command’s
frequency when the rotational speed of the rotating machine10
is higher. A PWM method where a carrier wave frequency
does not synchronize with the frequency of the voltage
command is referred to as an asynchronous PWM mode, while a
PWM method where a carrier wave frequency synchronizes with
the frequency of the voltage command is referred to as a15
synchronous PWM mode (the asynchronous PWM mode and the
synchronous PWM mode may be simply referred to as the
asynchronous PWM and the synchronous PWM below). For the
synchronous PWM, there is a method that adopts plural
carrier wave frequencies to change a count of pulses20
included in one cycle of the voltage command.
[0006] Switching between the PWM methods (hereinafter
referred to as the PWM modes) without any consideration
causes oscillations in current flowing through the rotating
machine (hereinafter referred to as the current25
oscillations). When the current oscillations occur, the
current flowing through the rotating machine, that is, the
machine current may deviate from an allowable current of
each semiconductor switching element, potentially causing
the switching elements to break. Furthermore, depending on30
the current oscillations’ frequency, there is a possibility
of conflicting with regulations on current harmonics, in
which case installation of an additional filter circuit may
4
be required. Furthermore, mechanical vibrations and noise
in the rotating machine may become problematic when the
rotating machine’s torque oscillates in proportion to
current oscillations.
[0007] Various measures have been taken so far to5
address such current oscillations that occur during
switching between the PWM modes. For example, Patent
Literature 1 discloses a technique of switching between a
variable voltage operation method using pulse-width
modulation and a one-dash pulse control method near a phase10
angle at which centers of primary magnetic flux
trajectories in a stationary reference frame of the
rotating machine deviate the least from each other.
Citation List15
Patent Literature
[0008] Patent Literature 1: Japanese Patent No. 2911734
Summary of Invention
Problem to be solved by the Invention20
[0009] However, the technique described in Patent
Literature 1, which effects switching between PWM modes at
a prespecified phase, has a problem in that the technique
cannot be applied to switching between the asynchronous
PWM, which operates without synchronization with voltage25
phase, and the synchronous PWM, which operates in
synchronization with the voltage phase.
[0010] The present disclosure has been made in view of
the above, and an object of the present disclosure is to
obtain a rotating machine control device capable of30
restraining current oscillations when switching the PWM
mode used to control generation operation of voltage to be
applied to a rotating machine between the asynchronous PWM
5
and the synchronous PWM.
Means to Solve the Problem
[0011] In order to solve the above-described problem and
achieve the object, a rotating machine control device5
according to the present disclosure includes: a voltage
application unit to generate three-phase voltages to be
applied to a rotating machine; and a control unit to
control voltage generation operation of the voltage
application unit in a first pulse-width modulation mode or10
a second pulse-width modulation mode, the first pulse-width
modulation mode being a pulse-width modulation method where
a carrier wave frequency is asynchronous with a frequency
of a voltage command, the second pulse-width modulation
mode being a pulse-width modulation method where a carrier15
wave frequency is synchronous with a frequency of a voltage
command. On a basis of a first carrier wave used in
generating a signal that controls the voltage application
unit in the first pulse-width modulation mode, a second
carrier wave used in generating a signal that controls the20
voltage application unit in the second pulse-width
modulation mode, and an output voltage phase command
commanding a phase of each of voltages to be output to the
rotating machine, the control unit selects one of the first
pulse-width modulation mode and the second pulse-width25
modulation mode as a pulse-width modulation method to be
used for controlling the voltage generation operation.
Effect of the Invention
[0012] The rotating machine control device according to30
the present disclosure has an effect of restraining current
oscillations when switching the PWM mode used to control
the generation operation of the voltage to be applied to
6
the rotating machine between the asynchronous PWM and the
synchronous PWM.
Brief Description of Drawings
[0013] FIG. 1 is a diagram illustrating an exemplary5
configuration of a rotating machine control device
according to a first embodiment.
FIG. 2 is a diagram illustrating an exemplary
configuration of a timing generator included in the
rotating machine control device according to the first10
embodiment.
FIG. 3 is a diagram illustrating an exemplary
configuration of a voltage application unit included in the
rotating machine control device according to the first
embodiment.15
FIG. 4 is a diagram illustrating an example of a
storage unit that stores comparison values that the timing
generator according to the first embodiment uses in a
process of generating a timing signal.
FIG. 5 is a diagram illustrating another example of20
the storage unit that stores the comparison values that the
timing generator according to the first embodiment uses in
the process of generating the timing signal.
FIG. 6 is a diagram illustrating an exemplary
configuration of a timing generator included in a rotating25
machine control device according to a second embodiment.
FIG. 7 is a diagram illustrating an example of a
storage unit that stores comparison values and a delayed
phase that the timing generator according to the second
embodiment uses in a process of generating a timing signal.30
FIG. 8 is a diagram illustrating another example of
the storage unit that stores the comparison values and the
delayed phase that the timing generator according to the
7
second embodiment uses in the process of generating the
timing signal.
FIG. 9 is a diagram illustrating a variation of the
storage unit illustrated in FIG. 7.
FIG. 10 is a diagram illustrating a variation of the5
storage unit illustrated in FIG. 8.
FIG. 11 is a diagram illustrating a first example of
current oscillations that occur during switching between
PWM modes.
FIG. 12 is a diagram illustrating a second example of10
current oscillations that occur during switching between
the PWM modes.
FIG. 13 is a diagram illustrating examples of carrier
waves used respectively in two synchronous PWM modes
between which switching is performed.15
FIG. 14 is a diagram illustrating a magnetic flux
evaluation function generated by synchronous carrier waves
#1 and #2 illustrated in FIG. 13.
FIG. 15 is a diagram illustrating examples of carrier
waves used respectively in two PWM modes when switching is20
performed from an asynchronous one of the PWM modes to a
synchronous one.
FIG. 16 is a diagram illustrating a magnetic flux
evaluation function generated by the asynchronous and
synchronous carrier waves illustrated in FIG. 15.25
Description of Embodiments
[0014] With reference to the drawings, a detailed
description is hereinafter provided of rotating machine
control devices according to embodiments of the present30
disclosure.
[0015] First Embodiment.
Before details of a rotating machine control device
8
according to the present embodiment are explained, a
description is first provided of current oscillations that
become problematic during switching between PWM modes.
[0016] FIG. 11 is a diagram illustrating a first example
of current oscillations that occur during switching between5
PWM modes, specifically the example of current oscillations
that occur when a conventional rotating machine control
device, which is a comparative example, switches between
the PWM modes. FIG. 11 illustrates currents expressed in a
rotating reference frame (by dq transformation) on the10
basis of a magnetic pole position of a rotating machine
after three-phase to two-phase transformation of three-
phase alternating currents of the rotating machine. The
current oscillations that occur during the switching
between the PWM modes can be extracted by passing the d-15
axis and q-axis machine currents through a band pass filter
(BPF) centered around a frequency of a voltage command. A
first row from the top in FIG. 11 illustrates the d-axis
current, namely the d-axis machine current, and a second
row illustrates oscillations in the d-axis current (the d-20
axis current after passing through the BPF). A third row
illustrates the q-axis current, namely the q-axis machine
current, and a fourth row illustrates oscillations in the
q-axis current (the q-axis current after passing through
the BPF). A dotted vertical midline indicates a timing of25
the switching between the PWM modes.
[0017] A description is provided of a factor that
contributes to the occurrence of the current oscillations
illustrated in FIG. 11. When the rotating machine, which
is to be controlled, is an interior permanent magnet30
synchronous motor (IPMSM), voltage equations in the
rotating reference frame are represented by Formula (1).
[0018] Formula 1:
9
[0019] In Formula (1), vd and vq respectively represent
voltages applied to the d-axis and the q-axis of the IPMSM,
and id and iq respectively represent currents flowing along
the d-axis and the q-axis of the IPMSM. Ld and Lq5
respectively represent d-axis and q-axis inductances of the
IPMSM, and φd and φq respectively represent d-axis and q-
axis magnetic fluxes of the IPMSM. φm represents magnet
flux, R represents winding resistance, and ω represents an
angular frequency of a fundamental wave of voltage applied10
to the IPMSM. d/dt represents a differentiation operation.
id (t) and iq (t) are time functions. Time is represented
by t.
[0020] Suppose Formula (1) represents the voltage
equations in a transient state immediately after switching15
between the PWM modes, while Formula (2) below represents
voltage equations in a steady state. Voltage equations for
differences are represented by Formula (3) below.
[0021] Formula 2:
20
[0022] Formula 3:
[0023] In Formulas (2) and (3), the d-axis and q-axis
currents in the steady state are represented by id' and
iq', and the d-axis and q-axis magnetic fluxes in the25
10
steady state are represented by φd' and φq'. In Formula
(3), each term expressing a difference between Formula (1)
and Formula (2) is denoted with Δ, with the differences in
the d-axis and q-axis currents represented by Δid and Δiq
and the differences in the d-axis and q-axis magnetic5
fluxes represented by Δφd and Δφq. The voltages applied to
the IPMSM are assumed to remain unchanged between the
transient state and the steady state; therefore, the
difference in each voltage between Formulas (1) and (2) is
0. id'(t) and iq'(t) in Formula (2) and Δid (t) and Δiq (t)10
in Formula (3) are also time functions.
[0024] Using the Laplace transform to solve Formula (3)
for the currents as the time functions, Formula (4) can be
derived. In Formula (4), e is Napier’s constant, which is
used to represent an exponential function.15
[0025] Formula 4:
[0026] According to Formula (4), the currents Δid and
Δiq during the switching between the PWM modes are sine and
cosine waves proportional to the differences in the motor’s20
magnetic fluxes, Δφd and Δφq, along the axes before and
after the switching. When combined with exponential terms,
the currents Δid and Δiq become damped oscillations.
Furthermore, the d-axis and q-axis currents are inversely
proportional to the motor’s d-axis and q-axis inductances25
Ld and Lq. Among the variables included in Formula (4),
only the differences in the motor’s magnetic fluxes, Δφd
11
and Δφq, can be manipulated through control without
modifying the motor. Therefore, if switching between the
PWM modes is performed to reduce the differences Δφd and
Δφq in the motor’s magnetic fluxes, current oscillations
can be restrained. The current oscillations’ frequency is5
the angular frequency ω of an inverter, and the current
oscillations’ phase is determined by performing an
arctangent operation on the differences Δφd and Δφq in the
motor’s magnetic fluxes.
[0027] A method for computing motor fluxes is described10
here. The flux linkages (motor fluxes) φu, φv, and φw of u,
v, and w phases can be computed from phase voltages vu, vv,
and vw of the three phases, phase currents iu, iv, and iw of
the three phases, and the winding resistance R. Equations
for computing the motor fluxes are represented by Formula15
(5).
[0028] Formula 5:
[0029] When the rotating machine’s rotational speed is
higher than or equal to a medium speed, the second term on20
each right side of Formula (5) is smaller than the first
term on each right side and thus can be ignored.
Therefore, the computation of the motor fluxes only needs
to use integrals of the voltages of the phases. Since
voltages applied from the inverter to the motor are each25
the product of a corresponding PWM pulse applied to a gate
of a semiconductor switching element in the inverter and
half a supply voltage, the integral of the voltage for each
12
phase of the motor and an integral of the corresponding PWM
pulses applied to the gate have similar waveforms.
Therefore, quantities equivalent to the motor fluxes can be
computed from the PWM pulses applied to the inverter.
[0030] To express the motor fluxes in the rotating5
reference frame, three-phase to two-phase transformation
shown in Formula (6) below is performed. Furthermore,
rotating frame transformation based on the magnetic pole
position θm of the motor is performed, as shown in Formula
(7).10
[0031] Formula 6:
[0032] Formula 7:
[0033] According to Formula (4) above, reducing the15
differences Δφd and Δφq in the motor’s magnetic fluxes
before and after the switching between the PWM modes can
restrain the current oscillations during the switching
between the PWM modes. The term for the differences in the
motor’s magnetic fluxes in Formula (4) is defined as a20
magnetic flux evaluation function Ef, as shown in Formula
(8) below.
[0034] Formula 8:
[0035] FIG. 12 illustrates motor currents during25
switching between the PWM modes when the magnetic flux
evaluation function Ef is made smaller. FIG. 12 is a
diagram illustrating the second example of current
13
oscillations during the switching between the PWM modes.
As in FIG. 11, a first row from the top illustrates the d-
axis current, a second row illustrates oscillations in the
d-axis current (the d-axis current after passing through
the BPF), a third row illustrates the q-axis current, and a5
fourth row illustrates oscillations in the q-axis current
(the q-axis current after passing through the BPF). A
dotted vertical midline indicates a timing of the switching
between the PWM modes. The current oscillations
illustrated in FIG. 12 correspond to an example of current10
oscillations resulting from the application of the first
embodiment. As illustrated in FIG. 12, making the magnetic
flux evaluation function Ef defined by Formula (8) smaller
can restrain current oscillations during switching between
the PWM modes compared to the case illustrated in FIG. 11.15
[0036] Next, a description is provided of
characteristics of a magnetic flux evaluation function
associated with switching between synchronous PWM modes and
a magnetic flux evaluation function associated with
switching from an asynchronous PWM mode to a synchronous20
PWM mode.
[0037] FIG. 13 is a diagram illustrating examples of
carrier waves used respectively in the two synchronous PWM
modes between which the switching is performed. The
carrier waves are referred to as synchronous carrier waves25
#1 and #2. FIG. 14 is a diagram illustrating the magnetic
flux evaluation function Efss generated by synchronous
carrier waves #1 and #2 illustrated in FIG. 13.
[0038] In a synchronous PWM, a carrier wave synchronizes
with a phase of the u-phase voltage (hereinafter referred30
to simply as the voltage phase); therefore, the voltage
applied to the IPMSM synchronizes with the voltage phase,
and the motor flux, which is expressed by the integral of
14
the voltage applied to the IPMSM, also synchronizes with
the voltage phase. Since the motor flux synchronizes with
the voltage phase before and after the switching between
the PWM modes, the magnetic flux evaluation function Efss,
as a result, synchronizes with the voltage phase, as5
illustrated in FIG. 14. The magnetic flux evaluation
function Efss, which is associated with the switching
between the synchronous PWM modes that respectively use
synchronous carrier waves #1 and #2 illustrated in FIG. 13,
has a waveform that repeats every 60 degrees as illustrated10
in FIG. 14. Therefore, for switching between the
synchronous PWMs, a phase at which the magnetic flux
evaluation function Efss is minimized can be easily
precomputed from a relationship between the respective
carrier waves of the synchronous PWMs.15
[0039] FIG. 15 is a diagram illustrating examples of
carrier waves used respectively in the two PWM modes (the
asynchronous and synchronous PWMs) when the switching is
performed from the asynchronous PWM to the synchronous PWM.
The carrier wave used in the asynchronous PWM refers to an20
asynchronous carrier wave, and the carrier wave used in the
synchronous PWM refers to a synchronous carrier wave. FIG.
16 is a diagram illustrating the magnetic flux evaluation
function Efas generated by the asynchronous and synchronous
carrier waves illustrated in FIG. 15.25
[0040] In an asynchronous PWM, a carrier wave
(corresponding to the asynchronous carrier wave illustrated
in FIG. 15) does not synchronize with the voltage phase;
therefore, the voltage applied to the IPMSM does not
synchronize with the voltage phase, and the motor flux,30
which is expressed by the integral of the voltage applied
to the IPMSM, also does not synchronize with the voltage
phase. Therefore, when computed on the basis of the motor
15
flux obtained when the IPMSM is controlled in the
synchronous PWM and the motor flux obtained when the IPMSM
is controlled in the asynchronous PWM, the magnetic flux
evaluation function Efas does not synchronize with the
voltage phase. Furthermore, a waveform that repeats every5
60 degrees, as observed with the switching between the
synchronous PWM modes, is not seen. Since the carrier wave
of the asynchronous PWM does not synchronize with the
voltage phase, the magnetic flux evaluation function Efas
changes its form over one cycle of the voltage phase,10
depending on a phase of the carrier wave of the
asynchronous PWM. Therefore, for switching from the
asynchronous PWM mode to the synchronous PWM mode,
identifying a phase at which the magnetic flux evaluation
function Efas is minimized is not possible. Since a15
difference in the magnetic flux remains the same even for
switching from the synchronous PWM mode to the asynchronous
PWM mode, identifying a phase at which the magnetic flux
evaluation function is minimized is not possible. In other
words, for the switching between the asynchronous PWM and20
the synchronous PWM, identifying the phase at which the
magnetic flux evaluation function is minimized is not
possible.
[0041] Next, a description is provided of the rotating
machine control device according to the first embodiment.25
FIG. 1 is a diagram illustrating an exemplary configuration
of the rotating machine control device 1 according to the
first embodiment.
[0042] The rotating machine control device 1 includes a
voltage application unit 3 and a control unit 4. The30
voltage application unit 3 is connected to a rotating
machine 2 and generates three-phase voltages Vu, Vv, and Vw
to be applied to the rotating machine 2. The control unit
16
4 is connected to the voltage application unit 3 and
generates PWM pulses Vug, Vvg, and Vwg as PWM signals to
control voltage generation operation of the voltage
application unit 3 in a first PWM mode or a second PWM
mode. In the present embodiment, the first PWM mode is5
described as an asynchronous PWM, and the second PWM mode
is described as a synchronous PWM.
[0043] The control unit 4 includes a timing generator 5,
a PWM mode selector 6, a modulation wave generator 7, a
carrier wave selector 8, and a PWM pulse generator 9.10
[0044] First carrier waves cru1, crv1, and crw1, second
carrier waves cru2, crv2, and crw2, and an output voltage
phase command θ are input to the timing generator 5. The
output voltage phase command θ indicates a command value
for a phase of each of the three-phase voltages Vu, Vv, and15
Vw to be output from the voltage application unit 3 to the
rotating machine 2. The timing generator 5 determines
whether or not a timing qualifies for switching between the
PWM modes on the basis of the first carrier wave cru1, crv1,
or crw1, the second carrier wave cru2, crv2, or crw2, and the20
output voltage phase command θ. Upon determining that the
timing qualifies for switching between the PWM modes, the
timing generator 5 generates a timing signal Tr indicating
that the timing qualifies for switching between the PWM
modes.25
[0045] A fundamental frequency FINV of the voltage output
from the voltage application unit 3, voltage commands Vu*,
Vv*, and Vw* used for controlling the rotating machine 2,
and the timing signal Tr output from the timing generator 5
are input to the PWM mode selector 6. The PWM mode30
selector 6 generates a PWM mode selection signal Pmode based
on the fundamental frequency FINV, the voltage commands Vu*,
Vv*, and Vw*, and the timing signal Tr.
17
[0046] The voltage commands Vu*, Vv*, and Vw*, the output
voltage phase command θ, and the PWM mode selection signal
Pmode are input to the modulation wave generator 7. The
modulation wave generator 7 generates modulation waves vu*,
vv*, and vw* based on the voltage commands Vu*, Vv*, and Vw*,5
the output voltage phase command θ, and the PWM mode
selection signal Pmode.
[0047] The first carrier waves cru1, crv1, and crw1, the
second carrier waves cru2, crv2, and crw2, and the PWM mode
selection signal Pmode are input to the carrier wave10
selector 8. On the basis of the PWM mode selection signal
Pmode, the carrier wave selector 8 selects the first carrier
waves cru1, crv1, and crw1 or the second carrier waves cru2,
crv2, and crw2 to output as the carrier waves cru, crv, and
crw.15
[0048] The modulation waves vu*, vv*, and vw* and the
carrier waves cru, crv, and crw are input to the PWM pulse
generator 9. On the basis of the modulation waves vu*, vv*,
and vw* and the carrier waves cru, crv, and crw, the PWM
pulse generator 9 generates the PWM pulses Vug, Vvg, and Vwg,20
which serve as the PWM signals for controlling the voltage
application unit 3. In the following description, PWM
pulses that the PWM pulse generator 9 generates when
operating in the asynchronous PWM may be referred to as the
asynchronous PWM pulses, and PWM pulses that the PWM pulse25
generator 9 generates when operating in the synchronous PWM
may be referred to as the synchronous PWM pulses.
[0049] The PWM pulses Vug, Vvg, and Vwg generated by the
PWM pulse generator 9 are input to the voltage application
unit 3. On the basis of the PWM pulses Vug, Vvg, and Vwg,30
the voltage application unit 3 generates the three-phase
voltages Vu, Vv, and Vw to be applied to the rotating
machine 2.
18
[0050] The rotating machine 2 is driven by the three-
phase voltages Vu, Vv, and Vw output from the voltage
application unit 3. The rotating machine 2 may be the
aforementioned IPMSM, an induction motor (IM), or a
synchronous reluctance motor (SynRM).5
[0051] The first carrier waves cru1, crv1, and crw1 input
to the timing generator 5 and the carrier wave selector 8
are the carrier waves corresponding to the first PWM mode
and are asynchronous carrier waves that do not synchronize
with the output voltage phase command θ. The second10
carrier waves cru2, crv2, and crw2 are the carrier waves
corresponding to the second PWM mode and are synchronous
carrier waves that synchronize with the output voltage
phase command θ. The first carrier waves cru1, crv1, and
crw1 may be carrier waves that are in phase or carrier15
waves that are out of phase among the three phases.
Similarly, the second carrier waves cru2, crv2, and crw2 may
be carrier waves that are in phase or carrier waves that
are out of phase among the three phases. The first carrier
waves cru1, crv1, and crw1 and the second carrier waves cru2,20
crv2, and crw2 are unitless signals, and their respective
values change between -1 and +1.
[0052] FIG. 2 is a diagram illustrating an exemplary
configuration of the timing generator 5 included in the
rotating machine control device 1 according to the first25
embodiment.
[0053] The timing generator 5 includes a first
determiner 50, a second determiner 51, operators 52 to 54,
and a logical conjunction operator 55.
[0054] The first carrier wave cru1 and a computed result30
crst1, which is a precomputed sign of slope of the first
carrier wave cru1 and is retained in a memory, are input to
the first determiner 50. The computed result crst1 retained
19
in the memory is a comparison value. The first determiner
50 compares a sign of slope of the input first carrier wave
cru1 to the comparison value crst1. The first determiner 50
outputs a value indicating true when both match and a value
indicating false when both do not match. Specifically, the5
first determiner 50 outputs “1” when the sign of the slope
of the first carrier wave cru1 and the comparison value
crst1 match and “0” when the sign of the slope of the first
carrier wave cru1 and the comparison value crst1 do not
match.10
[0055] The second carrier wave cru2 and a computed
result crst2, which is a precomputed sign of slope of the
second carrier wave cru2 and is retained in the memory, are
input to the second determiner 51. The computed result
crst2 retained in the memory is a comparison value. The15
second determiner 51 compares a sign of slope of the input
second carrier wave cru2 to the comparison value crst2. The
second determiner 51 outputs a value indicating true when
both match and a value indicating false when both do not
match. Specifically, the second determiner 51 outputs “1”20
when the sign of the slope of the second carrier wave cru2
and the comparison value crst2 match and “0” when the sign
of the slope of the second carrier wave cru2 and the
comparison value crst2 do not match.
[0056] The first carrier wave cru1 and a result crnt1 of25
precomputing the first carrier wave cru1, which is retained
in the memory, are input to the operator 52. The computed
result crnt1 retained in the memory is a comparison value.
The operator 52 computes an instantaneous carrier wave
value difference Δcr1 between an instantaneous value of the30
input first carrier wave cru1 and the comparison value
crnt1. The operator 52 outputs a value indicating true when
the instantaneous carrier wave value difference Δcr1 is 0
20
or within an acceptable range of deviation and a value
indicating false when the instantaneous carrier wave value
difference Δcr1 is not within the acceptable range of
deviation. Specifically, the operator 52 outputs “1” as
the value indicating true when the instantaneous carrier5
wave value difference Δcr1 is less than a predetermined
threshold and “0” as the value indicating false when the
instantaneous carrier wave value difference Δcr1 is greater
than or equal to the threshold.
[0057] The second carrier wave cru2 and a result crnt2 of10
precomputing the second carrier wave cru2, which is
retained in the memory, are input to the operator 53. The
computed result crnt2 retained in the memory is a comparison
value. The operator 53 computes an instantaneous carrier
wave value difference Δcr2 between an instantaneous value15
of the input second carrier wave cru2 and the comparison
value crnt2. The operator 53 outputs a value indicating
true when the instantaneous carrier wave value difference
Δcr2 is 0 or within an acceptable range of deviation and a
value indicating false when the instantaneous carrier wave20
value difference Δcr2 is not within the acceptable range of
deviation. Specifically, the operator 53 outputs “1” as
the value indicating true when the instantaneous carrier
wave value difference Δcr2 is less than a predetermined
threshold and “0” as the value indicating false when the25
instantaneous carrier wave value difference Δcr2 is greater
than or equal to the threshold.
[0058] The output voltage phase command θ and a result
θt of precomputing the output voltage phase command θ,
which is retained in the memory, are input to the operator30
54. The computed result θt retained in the memory is a
comparison value. The operator 54 computes a phase
difference Δθ between the input output voltage phase
21
command θ and the comparison value θt. The operator 54
outputs a value indicating true when the phase difference
Δθ is 0 or within an acceptable range of deviation and a
value indicating false when the phase difference Δθ is not
within the acceptable range of deviation. Specifically,5
the operator 54 outputs “1” as the value indicating true
when the phase difference Δθ is less than a predetermined
threshold and “0” as the value indicating false when the
phase difference Δθ is greater than or equal to the
threshold.10
[0059] The signals output respectively from the first
determiner 50, the second determiner 51, and the operators
52 to 54 are input to the logical conjunction operator 55.
The logical conjunction operator 55 outputs a value
indicating true as the timing signal Tr when every input15
signal is the value indicating true, that is, “1” and a
value indicating false as the timing signal Tr when the
input signals include any values indicating false.
Specifically, the logical conjunction operator 55 outputs
“1” as the timing signal Tr when every input signal is the20
value indicating true and “0” as the timing signal Tr when
the input signals include any values indicating false.
[0060] The aforementioned precomputed comparison values,
namely crst1, crst2, crnt1, crnt2, and θt, may be retained
within the timing generator 5 or in an external storage25
means.
[0061] In the example described in the present
embodiment, the timing generator 5 determines, on the basis
of the first and second carrier waves cru1 and cru2 for the
u phase and the output voltage phase command θ, whether or30
not the timing qualifies for switching between the PWM
modes and changes the state of the timing signal Tr upon
determining that the timing qualifies for switching between
22
the PWM modes. However, the timing generator 5 may
determine the timing for switching between the PWM modes on
the basis of the first and second carrier waves for the v
phase and the output voltage phase command θ or on the
basis of the first and second carrier waves for the w phase5
and the output voltage phase command θ.
[0062] On the basis of the fundamental frequency FINV of
the voltage output from the voltage application unit 3 and
the voltage commands Vu*, Vv*, and Vw* used for controlling
the rotating machine 2, the PWM mode selector 6 generates10
the PWM mode selection signal Pmode selecting the first PWM
mode or the second PWM mode and outputs the PWM mode
selection signal Pmode to the modulation wave generator 7
and the carrier wave selector 8. The PWM mode selector 6
switches a value of the PWM mode selection signal Pmode at a15
timing when the timing signal Tr input from the timing
generator 5 logically reverses from false to true.
[0063] The modulation waves vu*, vv*, and vw* generated by
the modulation wave generator 7 are three-phase sine waves
for the u phase, the v phase, and the w phase,20
respectively. A phase difference of 120 degrees is
established between the modulation waves vu*, vv*, and vw*.
Amplitudes of the modulation waves vu*, vv*, and vw* are
determined by the voltage commands Vu*, Vv*, and Vw* input to
the modulation wave generator 7. Each of the voltage25
commands Vu*, Vv*, and Vw* has a magnitude of 0 to 4/π, with
a maximum amplitude of a fundamental wave obtained from
Fourier series expansion of a square wave being 4/π.
[0064] Each of the modulation waves vu*, vv*, and vw* may
include a superimposed third harmonic with a frequency30
three times that of the modulation wave to improve a
utilization rate of the voltage output from the voltage
application unit 3. When the rotating machine 2 is driven
23
with the magnitudes of the voltage commands Vu*, Vv*, and Vw*
each exceeding 1, gains may be multiplied to correct
relationships between fundamental voltages determined from
the Fourier series expansion of the voltages vu, vv, and vw
applied to the rotating machine 2 and the corresponding5
voltage commands Vu*, Vv*, and Vw*. The aforementioned third
harmonics and correction gains may differ between
modulation waves corresponding to the asynchronous PWM
pulses and modulation waves corresponding to the
synchronous PWM pulses. For this reason, the modulation10
wave generator 7 switches between the modulation waves
corresponding to the asynchronous PWM pulses and the
modulation waves corresponding to the synchronous PWM
pulses on the basis of the PWM mode selection signal Pmode
to output as the modulation waves vu*, vv*, and vw*.15
[0065] On the basis of the PWM mode selection signal
Pmode, the carrier wave selector 8 selects the first carrier
waves cru1, crv1, and crw1, which correspond to the
asynchronous PWM pulses, or the second carrier waves cru2,
crv2, and crw2, which correspond to the synchronous PWM20
pulses, to output as the carrier waves cru, crv, and crw.
[0066] The PWM pulse generator 9 compares magnitudes of
the modulation waves vu*, vv*, and vw* input from the
modulation wave generator 7 and the carrier waves cru, crv,
and crw input from the carrier wave selector 8 separately25
for the u phase, the v phase, and the w phase. For the u
phase, the PWM pulse vug output to the voltage application
unit 3 is true, that is, “1” when the modulation wave vu*
is greater than the carrier wave cru and false, that is,
“0” when the modulation wave vu* is less than or equal to30
the carrier wave cru. Similarly, for the v phase and the w
phase, magnitudes of the modulation and carrier waves for
each phase are compared, and a value (“1” or “0”) based on
24
a comparison result is output as the PWM pulse vvg or vwg to
the voltage application unit 3.
[0067] The voltage application unit 3 has, for example,
a configuration illustrated in FIG. 3. FIG. 3 is a diagram
illustrating the exemplary configuration of the voltage5
application unit 3 included in the rotating machine control
device 1 according to the first embodiment, specifically
illustrating the exemplary circuit configuration when the
voltage application unit 3 is a three-phase PWM inverter.
[0068] The voltage application unit 3 includes a leg 30A10
where an upper-arm semiconductor element UP and a lower-arm
semiconductor element UN are connected in series, a leg 30B
where an upper-arm semiconductor element VP and a lower-arm
semiconductor element VN are connected in series, and a leg
30C where an upper-arm semiconductor element WP and a15
lower-arm semiconductor element WN are connected in series.
[0069] The legs 30A to 30C are connected in parallel,
and a bus voltage is applied to the legs 30A to 30C through
direct-current buses 35a and 35b. The voltage application
unit 3 converts direct-current power supplied from a power20
source 36 to the legs 30A to 30C through the direct-current
buses 35a and 35b into alternating-current power and
supplies the converted alternating-current power to the
rotating machine 2, thus driving the rotating machine 2.
[0070] In FIG. 3, the semiconductor elements UP, UN, VP,25
VN, WP, and WN are exemplified by metal-oxide-semiconductor
field-effect transistors (MOSFETs). The semiconductor
element UP includes a transistor 30a and a diode 30b
connected in antiparallel to the transistor 30a. The other
semiconductor elements UN, VP, VN, WP, and WN have the same30
configuration as the semiconductor element UP. The term
“antiparallel” means that an anode side of the diode 30b is
connected to a first terminal corresponding to a source of
25
the MOSFET, while a cathode side of the diode 30b is
connected to a second terminal corresponding to a drain of
the MOSFET.
[0071] The semiconductor elements UP, UN, VP, VN, WP,
and WN to be used may be, for example, insulated gate5
bipolar transistors (IGBTs) instead of the MOSFETs.
[0072] A connection point 32 between the upper-arm
semiconductor element UP and the lower-arm semiconductor
element UN of the leg 30A is connected to a first phase
(for example, the u phase) of the rotating machine 2. A10
connection point 33 between the upper-arm semiconductor
element VP and the lower-arm semiconductor element VN of
the leg 30B is connected to a second phase (for example,
the v phase) of the rotating machine 2. A connection point
34 between the upper-arm semiconductor element WP and the15
lower-arm semiconductor element WN of the leg 30C is
connected to a third phase (for example, the w phase) of
the rotating machine 2. The connection points 32, 33, and
34 of the voltage application unit 3 constitute alternating
current terminals.20
[0073] A description of voltage vectors that the voltage
application unit 3 outputs is provided here. The voltage
application unit 3 is, as mentioned earlier, the three-
phase PWM inverter, serving as a power conversion unit that
obtains desired voltage by performing PWM control on the25
direct-current power with voltage VDC supplied from the
power source 36 through the direct-current buses 35a and
35b. The three-phase PWM inverter has the two vertically
arranged semiconductor switching elements for each phase,
and the upper and lower semiconductor switching elements30
operate such that one of the semiconductor switching
elements is in an ON state. Therefore, the three-phase PWM
inverter has two cubed (eight) possible switching states.
26
[0074] Next, a description is provided of the
aforementioned precomputed comparison values crst1, crst2,
crnt1, crnt2, and θt, which are used in the timing generator
5 illustrated in FIG. 2.
[0075] When, for example, the asynchronous and5
synchronous carrier waves, assumed for switching between
the PWM modes during operation of the rotating machine 2,
are in the relationship illustrated in FIG. 15, the
magnetic flux evaluation function Efas illustrated in FIG.
16 is precomputed outside the rotating machine control10
device 1. This precomputation is done by integrating
three-phase asynchronous PWM pulses, which are obtained
from magnitude comparison between the modulation waves
corresponding to the asynchronous PWM and the asynchronous
carrier waves, and three-phase synchronous PWM pulses,15
which are obtained from magnitude comparison between the
modulation waves corresponding to the synchronous PWM and
the synchronous carrier waves, and then performing
computations described in Formulas (6), (7), and (8) above.
[0076] As described first in the present embodiment, the20
phase at which the magnetic flux evaluation function Efas,
represented on a vertical axis in FIG. 16, reaches a
minimum value is a phase that minimizes amplitudes of
current oscillations. In FIG. 16, the u-phase voltage
phase at 223 degrees is the phase that minimizes the25
amplitudes of the current oscillations. Therefore, by
extracting and utilizing a sign of slope and an
instantaneous value of each of the asynchronous and
synchronous carrier waves at the 223-degree u-phase voltage
phase from FIG. 15, the current oscillations can be30
restrained during switching between the PWM modes, even
without the computation of the motor fluxes during the
operation of the rotating machine 2. In other words, the
27
signs of the slopes and the instantaneous values of the
asynchronous and synchronous carrier waves, which
correspond to when the magnetic flux evaluation function
Efas reaches its minimum and can be identified from the
relationship between the asynchronous and synchronous5
carrier waves, are precomputed and used as the
aforementioned comparison values crst1, crst2, crnt1, and
crnt2. Furthermore, the u-phase voltage phase at which the
magnetic flux evaluation function Efas reaches its minimum
is used as the aforementioned comparison value θt. As10
described, the comparison values crst1, crst2, crnt1, crnt2,
and θt needed when the timing generator 5 generates the
timing signal Tr can be precomputed.
[0077] Since the three-phase PWM pulses are generated by
comparing the modulation waves vu*, vv*, and vw* with the15
carrier waves cru, crv, and crw, their respective average
values over one cycle may not equal 0, unlike with a sine
wave. Integrating the three-phase PWM pulses with their
respective average values over one cycle not equaling 0
causes the integrals to diverge positively or negatively,20
depending on signs of the three-phase PWM pulses’ average
values over one cycle. Accordingly, the integrals of the
three-phase PWM pulses may be computed after the average
value of the PWM pulses corresponding to each phase over
one cycle is subtracted from the three-phase PWM pulses.25
[0078] As illustrated in FIG. 4, the above comparison
values crst1, crst2, crnt1, crnt2, and θt are stored in a
storage unit 58 and are output from the storage unit 58
when the timing generator 5 generates the timing signal Tr.
FIG. 4 is a diagram illustrating the storage unit 58 given30
as an example to store the comparison values that the
timing generator 5 according to the first embodiment uses
in a process of generating the timing signal Tr. The
28
storage unit 58 may be provided inside or outside the
timing generator 5.
[0079] The above comparison values crst1, crst2, crnt1,
crnt2, and θt may be fixed values or may be variables stored
in a table, being outputs that change depending on input5
conditions. FIG. 5 illustrates an exemplary configuration
of a storage unit 58 where the comparison values crst1,
crst2, crnt1, crnt2, and θt are the variables. FIG. 5 is a
diagram illustrating the storage unit 58 given as another
example to store the comparison values that the timing10
generator 5 according to the first embodiment uses in the
process of generating the timing signal Tr. The storage
unit 58 that is illustrated as the different example in
FIG. 5 includes a table 59. In the table 59 illustrated in
FIG. 5, an asynchronous carrier wave frequency FAS within15
one cycle of the output voltage phase command θ, a
synchronous carrier wave frequency FSY within one cycle of
the output voltage phase command θ, and the voltage
commands Vu*, Vv*, and Vw* are input, and a linear search is
performed to output the precomputed and retained comparison20
values crst1, crst2, crnt1, crnt2, and θt.
[0080] As described above, the rotating machine control
device 1 according to the present embodiment is configured
to appropriately use one of the two PWM modes, namely the
asynchronous PWM and the synchronous PWM, to control the25
rotating machine 2. The rotating machine control device 1
includes the timing generator 5 that detects the timing for
switching to the PWM mode to be used, which restrains
current oscillations, and generates the signal indicating
this timing. The timing generator 5 detects the timing for30
the switching between the PWM modes on the basis of the
first carrier wave used for the PWM pulse generation in the
asynchronous PWM, the second carrier wave used for the PWM
29
pulse generation in the synchronous PWM, and the output
voltage phase command. The timing generator 5 then changes
the timing signal being output to the state that indicates
that the timing qualifies for switching between the PWM
modes. Specifically, the timing generator 5 detects, on5
the basis of the first carrier wave cru1, the second
carrier wave cru2, the output voltage phase command θ, and
the precomputed comparison values crst1, crst2, crnt1, crnt2,
and θt, the timing at which the relationship established
between the first carrier wave cru1, crv1, or crw1 and the10
second carrier wave cru2, crv2, or crw2 causes a difference
between the integral of the asynchronous PWM pulses and the
integral of the synchronous PWM pulses to become less than
a predetermined value. The timing generator 5 then changes
the output state of the timing signal. The control unit 415
of the rotating machine control device 1 switches the PWM
mode used for controlling the rotating machine 2 when the
state of the timing signal output from the timing generator
5 changes. In this way, the PWM mode can be switched at
the timing when the difference between the magnetic flux of20
the rotating machine 2 in the asynchronous PWM and the
magnetic flux of the rotating machine 2 in the synchronous
PWM becomes smaller, resulting in restrained current
oscillations during the switching between the PWM modes.
[0081] Second Embodiment.25
Next, a description of a second embodiment is
provided. For convenience’s sake, a rotating machine
control device according to the second embodiment is
referred to as the rotating machine control device 1a, to
be distinguished from the rotating machine control device 130
according to the first embodiment. The rotating machine
control device 1a according to the present embodiment
includes a timing generator 5a illustrated in FIG. 6 in
30
place of the timing generator 5 (refer to FIGS. 1 and 2)
included in the rotating machine control device 1 according
to the first embodiment. Constituent elements other than
the timing generator 5a are the same as those in the first
embodiment and thus are not described. FIG. 6 is a diagram5
illustrating an exemplary configuration of the timing
generator 5a included in the rotating machine control
device 1a according to the second embodiment.
[0082] The timing generator 5a includes the operators 52
to 54, a logical conjunction operator 55a, a phase holder10
56, and an operator 57. The operators 52 to 54 are the
same as the operators 52 to 54 of the timing generator 5
according to the first embodiment and thus are not
described. In the present embodiment, θt1 is input to the
operator 54 as a result of computing the output voltage15
phase command θ.
[0083] Signals output respectively from the operators 52
to 54 are input to the logical conjunction operator 55a.
The logical conjunction operator 55a outputs a value
indicating true as a timing signal Tr’ when every input20
signal is a value indicating true, that is, “1” and a value
indicating false as the timing signal Tr’ when the input
signals include any values indicating false. Specifically,
the logical conjunction operator 55a outputs “1” as the
timing signal Tr' when every input signal is the value25
indicating true and “0” as the timing signal Tr' when the
input signals include any values indicating false.
[0084] The timing signal Tr' output from the logical
conjunction operator 55a and the output voltage phase
command θ are input to the phase holder 56. The phase30
holder 56 retains a phase of the output voltage phase
command θ at a timing when the timing signal Tr' changes
from false to true and outputs the retained phase as a
31
reference phase θb. This means that the phase holder 56
keeps outputting the value of the output voltage phase
command θ that corresponds to the timing when the timing
signal Tr' has changed from false to true as the reference
phase θb.5
[0085] The reference phase θb output from the phase
holder 56 and a precomputed delayed phase θt2 retained in
the memory are input to the operator 57. The operator 57
computes a phase difference between the input reference
phase θb and the input delayed phase θt2. The operator 5710
outputs a value indicating true as the timing signal Tr
when the computed phase difference is 0 or within an
acceptable range of deviation and a value indicating false
as the timing signal Tr when the computed phase difference
is not within the acceptable range of deviation.15
Specifically, the operator 57 outputs “1” as the timing
signal Tr when the computed phase difference is less than a
predetermined threshold and “0” as the timing signal Tr
when the computed phase difference is greater than or equal
to the threshold.20
[0086] The timing generator 5a according to the second
embodiment, which is illustrated in FIG. 6, uses the
specific phase at which the asynchronous and synchronous
carrier waves each peak at -1 or +1 (a maximum or minimum
value) as the reference phase θb and outputs the timing25
signal Tr at a phase delayed by a fixed amount relative to
the reference phase θb.
[0087] The operators 52 and 53 respectively detect peaks
of the carrier waves cru1 and cru2. Since each carrier wave
has a slope of 0 at its peak, there is no need to determine30
a sign of the slope. Therefore, the precomputed comparison
value crnt1 for the first carrier wave cru1 and the
precomputed comparison value crnt2 for the second carrier
32
wave cru2 are set to -1 or +1. The precomputed comparison
value θt1 for the output voltage phase command θ is set to
a phase at which the synchronous carrier wave peaks. For
example, in the example illustrated in FIG. 15 used above,
since the asynchronous and synchronous carrier waves each5
reach -1 at 150 degrees, the reference phase θb can be set
to 150 degrees.
[0088] A description is provided of the precomputed
delayed phase θt2. Consider that the first carrier wave
cru1 and the second carrier wave cru2 that are input to the10
timing generator 5a are respectively the asynchronous and
synchronous carrier waves illustrated in the example of
FIG. 15. In this case, the asynchronous and synchronous
carrier waves generate the magnetic flux evaluation
function Efas that is illustrated in FIG. 16. In FIG. 16,15
the phase at which the magnetic flux evaluation function
Efas reaches its minimum is 223 degrees. Therefore, when
the reference phase θb is set to 150 degrees, the delayed
phase θt2 is set to 223 degrees. The timing generator 5a
outputs the timing signal Tr based on this setting, and the20
PWM mode selector 6 switches the PWM mode at a timing in
line with this timing signal Tr. Consequently, current
oscillations during switching between the PWM modes are
restrained.
[0089] As illustrated in FIG. 7, the precomputed25
comparison values crnt1, crnt2, and θt1 and the precomputed
delayed phase θt2 in FIG. 6 are stored in a storage unit 60
and are output from the storage unit 60 when the timing
generator 5a generates the timing signal Tr. FIG. 7 is a
diagram illustrating the storage unit 60 given as an30
example to store the comparison values and the delayed
phase that the timing generator 5a according to the second
embodiment uses in a process of generating the timing
33
signal Tr. The storage unit 60 may be provided inside or
outside the timing generator 5a.
[0090] The above comparison values crnt1, crnt2, and θt1
and the delayed phase θt2 may be fixed values or may be
variables stored in a table, being outputs that change5
depending on input conditions. FIG. 8 illustrates an
exemplary configuration of a storage unit 60 where the
comparison values crnt1, crnt2, and θt1 and the delayed phase
θt2 are the variables. FIG. 8 is a diagram illustrating
the storage unit 60 given as another example to store the10
comparison values and the delayed phase that the timing
generator 5a according to the second embodiment uses in the
process of generating the timing signal Tr. The storage
unit 60 that is illustrated as the different example in
FIG. 8 includes a table 61. In the table 61 illustrated in15
FIG. 8, the asynchronous carrier wave frequency FAS within
one cycle of the output voltage phase command θ, the
synchronous carrier wave frequency FSY within one cycle of
the output voltage phase command θ, and the voltage
commands Vu*, Vv*, and Vw* are inputs, and a linear search is20
performed to output the precomputed and retained comparison
values crnt1, crnt2, and θt1 and the precomputed and retained
delayed phase θt2.
[0091] The storage unit 60 may be configured as
illustrated in FIG. 9 or FIG. 10. FIG. 9 is a diagram25
illustrating a variation of the storage unit 60 illustrated
in FIG. 7. FIG. 10 is a diagram illustrating a variation
of the storage unit 60 illustrated in FIG. 8.
[0092] The configuration illustrated in each of FIGS. 9
and 10 differs in that information stored in the storage30
unit 60 partly differs from the information stored in the
storage unit 60 illustrated in each of FIGS. 7 and 8 and
that operators 62 and 63 are included downstream of the
34
storage unit 60. While the storage unit 60 illustrated in
each of FIGS. 7 and 8 stores, as mentioned above, the
comparison values crnt1, crnt2, and θt1 and the delayed phase
θt2, the storage unit 60 illustrated in each of FIGS. 9 and
10 stores the comparison values crnt1, crnt2, and θt1 and the5
delayed phase θt2'. In other words, the storage unit 60
illustrated in each of FIGS. 9 and 10 stores the delayed
phase θt2' instead of the delayed phase θt2, which is stored
in the storage unit 60 illustrated in each of FIGS. 7 and
8.10
[0093] In the configuration illustrated in each of FIGS.
9 and 10, the operator 62 computes a phase difference Δθ
between the output voltage phase command θ and the
comparison value θt1 retained in the storage unit 60.
Furthermore, the operator 63 adds the phase difference Δθ15
output from the operator 62 to the delayed phase θt2'
retained in the storage unit 60 and outputs a result of
this addition operation as a corrected delayed phase θt2.
When the phase difference Δθ is not 0, the reference phase
θb will be misaligned with the peak of the synchronous20
carrier wave, so that the phase at which the magnetic flux
evaluation function Efas reaches the minimum value will also
be misaligned. For this reason, the operator 63 adds the
phase difference Δθ to the delayed phase θt2' to correct
the delayed phase θt2', thus obtaining the corrected25
delayed phase θt2.
[0094] The rotating machine control device 1a to which
the timing generator 5a described in the present embodiment
is applied can switch the PWM mode at the same timing as
the rotating machine control device 1 according to the30
first embodiment and can restrain current oscillations
during switching between the PWM modes.
[0095] The above configurations illustrated in the
35
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. The
embodiments can be combined with each other.
5
Reference Signs List
[0096] 1 rotating machine control device; 2 rotating
machine; 3 voltage application unit; 4 control unit; 5,
5a timing generator; 6 PWM mode selector; 7 modulation
wave generator; 8 carrier wave selector; 9 PWM pulse10
generator; 30A, 30B, 30C leg; 30a transistor; 30b diode;
32, 33, 34 connection point; 35a, 35b direct-current bus;
36 power source; 50 first determiner; 51 second
determiner; 52, 53, 54, 57, 62, 63 operator; 55, 55a
logical conjunction operator; 56 phase holder; 58, 6015
storage unit; 59, 61 table.
36
WE CLAIM:
[Claim 1] A rotating machine control device (1) comprising:
a voltage application unit (3) to generate three-phase
voltages to be applied to a rotating machine (2); and
a control unit (4) to control voltage generation5
operation of the voltage application unit (3) in a first
pulse-width modulation mode or a second pulse-width
modulation mode, the first pulse-width modulation mode
being a pulse-width modulation method where a carrier wave
frequency is asynchronous with a frequency of a voltage10
command, the second pulse-width modulation mode being a
pulse-width modulation method where a carrier wave
frequency is synchronous with a frequency of a voltage
command, wherein
on a basis of a first carrier wave used in generating15
a signal that controls the voltage application unit (3) in
the first pulse-width modulation mode, a second carrier
wave used in generating a signal that controls the voltage
application unit (3) in the second pulse-width modulation
mode, and an output voltage phase command commanding a20
phase of each of voltages to be output to the rotating
machine (2) , the control unit (4) selects one of the
first pulse-width modulation mode and the second pulse-
width modulation mode as a pulse-width modulation method to
be used for controlling the voltage generation operation,25
wherein
when switching a pulse-width modulation method used
for controlling the voltage generation operation, the
control unit (4) detects, on the basis of the first carrier
wave, the second carrier wave, and the output voltage phase30
command, a timing at which a difference between a flux
linkage of the rotating machine (2) during the control of
the voltage generation operation in the first pulse-width
37
modulation mode and a flux linkage of the rotating machine
(2) during the control of the voltage generation operation
in the second pulse-width modulation mode is minimized and
uses the detected timing as a timing for switching the
pulse-width modulation method.5
[Claim 2] The rotating machine control device (1) according
to claim 1 , wherein
the control unit (4) includes
a timing generator (5) to determine a timing for10
switching a pulse-width modulation method used for
controlling the voltage generation operation on the basis
of the first carrier wave, the second carrier wave, and the
output voltage phase command and
a pulse-width modulation mode selector (6) to select15
the one of the first pulse-width modulation mode and the
second pulse-width modulation mode as a pulse-width
modulation method to be used for controlling the voltage
generation operation when the timing generator (5)
determines that the timing qualifies for switching the20
pulse-width modulation method.
[Claim 3] The rotating machine control device (1)
according to claim 2, comprising a storage unit (58) to
retain a sign of slope of the first carrier wave, a sign of25
slope of the second carrier wave, an instantaneous value of
the first carrier wave, an instantaneous value of the
second carrier wave, and a phase of a voltage to be output
to the rotating machine (2) that correspond to when a
difference between a flux linkage of the rotating machine30
(2) during the control of the voltage generation operation
in the first pulse-width modulation mode and a flux linkage
of the rotating machine (2) during the control of the
38
voltage generation operation in the second pulse-width
modulation mode is minimized, wherein
the timing generator (5)
determines that the timing qualifies for switching the
pulse-width modulation method when a sign of slope of the5
first carrier wave and a sign of slope of the second
carrier wave respectively match a sign of slope of the
first carrier wave and a sign of slope of the second
carrier wave that are retained in the storage unit (58), a
difference between an instantaneous value of the first10
carrier wave and an instantaneous value of the first
carrier wave that is retained in the storage unit (58) and
a difference between an instantaneous value of the second
carrier wave and an instantaneous value of the second
carrier wave that is retained in the storage unit (58) are15
each less than a predetermined threshold, and a difference
between a value of the output voltage phase command and a
phase of a voltage to be output to the rotating machine (2)
that is retained in the storage unit (58) is less than a
predetermined threshold.20
[Claim 4]The rotating machine control device (1) according
to claim 3, wherein
the storage unit (58) includes
a table (59) where a frequency of the first carrier25
wave, a frequency of the second carrier wave, and the
voltage command are input, and a linear search is performed
to output a sign of slope of the first carrier wave, a sign
of slope of the second carrier wave, an instantaneous value
of the first carrier wave, an instantaneous value of the30
second carrier wave, and a phase of a voltage to be output
to the rotating machine (2) that are retained.
39
[Claim 5] The rotating machine control device (1a)
according to claim 2, comprising
a storage unit (60) to retain an instantaneous value
of the first carrier wave, an instantaneous value of the
second carrier wave, and a phase of a voltage to be output5
to the rotating machine (2) that correspond to when a
difference between a flux linkage of the rotating machine
(2) during the control of the voltage generation operation
in the first pulse-width modulation mode and a flux linkage
of the rotating machine (2) during the control of the10
voltage generation operation in the second pulse-width
modulation mode is minimized, and a delayed phase derived
from a relationship between the first carrier wave and the
second carrier wave, wherein
at a moment when a difference between an instantaneous15
value of the first carrier wave and an instantaneous value
of the first carrier wave that is retained in the
storage unit (60) and a difference between an
instantaneous value of the second carrier wave and an
instantaneous value of the second carrier wave that is20
retained in the storage unit (60) are each less than a
predetermined threshold and a difference between a value of
the output voltage phase command and a phase of a voltage
to be output to the rotating machine (2) that is retained
in the storage unit (60) is less than a predetermined25
threshold, the timing generator (5a) uses a value of the
output voltage phase command as a reference phase, and the
timing generator (5a) determines that the timing qualifies
for switching the pulse-width modulation method when a
difference between the reference phase and the delayed30
phase retained in the storage unit (60) is less than a
predetermined threshold.
40
[Claim 6] The rotating machine control device (1a)
according to claim 5, wherein
the storage unit 60) includes
a table (61) where a frequency of the first carrier
wave, a frequency of the second carrier wave, and the5
voltage command are input, and a linear search is performed
to output the instantaneous value of the first carrier
wave, the instantaneous value of the second carrier wave,
a phase of a voltage to be output to the rotating machine
(2) , and the delayed phase that are retained.10
[Claim 7] The rotating machine control device (1a)
according to claim 5 or 6, wherein
a phase difference between a value of the output
voltage phase command and a phase of a voltage to be output15
to the rotating machine (2) that is output from the storage
unit (60) is computed, the phase difference computed is
added to the delayed phase output from the storage unit
(60) to correct the delayed phase, and the timing
generator (5a) determines the timing for switching, using20
the delayed phase corrected.