1
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POWER CONVERSION 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
TITLE OF THE INVENTION: POWER CONVERSION DEVICE
TECHNICAL FIELD
[0001] The present disclosure relates to a power5
conversion device.
BACKGROUND ART
[0002] As a power conversion device for driving an AC
motor, there is known a power conversion device that includes10
a rectifier which rectifies AC power inputted from a three-
phase AC power supply such as a commercial power supply to DC
power, and an inverter which converts the DC power to AC
power suitable for an AC motor and outputs the AC power to
the AC motor. In general, it is known that, when three-phase15
AC voltages are rectified by a rectifier composed of diodes,
pulsation having a frequency that is six times the frequency
of an AC power supply occurs in the rectified DC voltage.
Here, a smoothing capacitor is provided in a DC
link section connecting the DC output side of the rectifier20
and the DC input side of the inverter. An inductance
component on the AC power supply and the smoothing capacitor
form an LC resonance circuit. If the resonant frequency of
the LC resonance circuit coincides with the frequency that is
six times the power supply frequency, DC voltage at the DC25
3
link section greatly pulsates. In particular, in a case
where a small-capacity film capacitor is used as the
smoothing capacitor for the purpose of device size reduction
or the like, great pulsation of DC voltage and distortion of
power supply current are likely to occur, so that it might5
become difficult to continuously operate the power conversion
device. For solving this problem, an inverter device having
the following configuration as a power conversion device is
disclosed.
[0003] That is, the conventional inverter device includes10
an inductor connected between a diode bridge as a rectifier
and an inverter unit, and a capacitor connected to an input
terminal of the inverter unit. A control unit for the
inverter unit multiplies voltage across the inductor detected
by a voltage detector by a gain (k). The voltage across the15
inductor multiplied by the gain (k) is subtracted from an
initial value of a voltage control ratio or a signal from a
PI controller (see, for example, Patent Document 1).
CITATION LIST20
PATENT DOCUMENT
[0004] Patent Document 1: Japanese Laid-Open Patent
Publication No. 2008-29151 (FIG. 18 and FIG. 19)
SUMMARY OF THE INVENTION25
4
PROBLEM TO BE SOLVED BY THE INVENTION
[0005] In the conventional inverter device described
above, after the voltage across the inductor provided between
the diode bridge and the smoothing capacitor is detected and
multiplied by the gain (k), a current command which is a5
signal from the PI controller or a modulation factor which is
a voltage control ratio is corrected. Thus, pulsation of
power supply current and DC voltage can be reduced.
However, in such a correction method based on a
detected value of the voltage across the inductor, the effect10
of control for suppressing pulsation becomes smaller in a
condition in which the impedance on the power supply side is
greater. In addition, in a case of correcting the current
command, it is difficult to reduce pulsation unless a current
control system is designed to have extremely high response.15
Further, on the DC link voltage, high-order pulsation that is
due to rectification operation of the rectifier, resonance of
the LC resonance circuit, and the like and is higher than
sixth order, for example, is superimposed, in addition to
pulsation having a frequency that is six times the power20
supply frequency. The conventional correction method has a
problem that the effect of suppressing such pulsation is
small and the effect of suppressing distortion of power
supply current is also small.
[0006] The present disclosure has been made to solve the25
5
above problem, and an object of the present disclosure is to
provide a power conversion device that can effectively
suppress pulsation occurring in power supply current and a DC
link section.
5
MEANS TO SOLVE THE PROBLEM
[0007] A power conversion device according to the present
disclosure includes: a rectification unit which converts
inputted three-phase AC voltages to DC voltage and outputs
the DC voltage to a DC bus; a power converter which converts10
the DC voltage on the DC bus converted by the rectification
unit, to AC voltage, to control an electric motor; and a
control unit which controls the power converter. The control
unit converts current flowing through the electric motor to
D-axis current and Q-axis current in an orthogonal two-axis15
coordinate system, generates a D-axis voltage command so that
the D-axis current follows a D-axis current command,
generates a Q-axis voltage command so that the Q-axis current
follows a Q-axis current command, and controls the power
converter on the basis of the generated D-axis voltage20
command and the generated Q-axis voltage command. The
control unit derives, as a pulsation voltage prediction
value, pulsation contained in the DC voltage obtained through
full-wave rectification of the three-phase AC voltages, on
the basis of a detected value of the three-phase AC voltages,25
6
and derives pulsation contained in the DC voltage, as a
pulsation voltage actual measured value, on the basis of a
detected value of the DC voltage. The control unit corrects
at least one of the D-axis voltage command or the Q-axis
voltage command by a voltage correction command generated so5
as to reduce a deviation between the pulsation voltage
prediction value and the pulsation voltage actual measured
value.
EFFECT OF THE INVENTION10
[0008] With the power conversion device according to the
present disclosure, it is possible to effectively suppress
pulsation occurring in power supply current and the DC link
section.
15
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] [FIG. 1] FIG. 1 is block diagram showing a
schematic configuration of a power conversion device
according to embodiment 1.
[FIG. 2] FIG. 2 is a control block diagram showing20
an internal configuration of a control unit of the power
conversion device according to embodiment 1.
[FIG. 3] FIG. 3 is a control block diagram showing
a configuration of a pulsation suppression control unit of
the power conversion device according to embodiment 1.25
7
[FIG. 4] FIG. 4 shows an example of a hardware
configuration of the control unit as a control device
according to embodiment 1.
[FIG. 5] FIG. 5A and FIG. 5B show operation
waveforms in a power conversion device of a comparative5
example.
[FIG. 6] FIG. 6A and FIG. 6B show operation
waveforms in the power conversion device according to
embodiment 1.
[FIG. 7] FIG. 7A and FIG. 7B show operation10
waveforms in the power conversion device according to
embodiment 1.
[FIG. 8] FIG. 8 is a control block diagram showing
an internal configuration of a pulsation suppression control
unit of a power conversion device according to embodiment 2.15
[FIG. 9] FIG. 9 is a control block diagram showing
an internal configuration of a pulsation suppression control
unit of the power conversion device according to embodiment
2.
20
DESCRIPTION OF EMBODIMENTS
[0010] Embodiment 1
A power conversion device 100 according to the
present embodiment 1 will be described with reference to the
drawings.25
8
FIG. 1 is a block diagram showing the schematic
configuration of the power conversion device 100 according to
embodiment 1.
The power conversion device 100 is provided between
a three-phase AC power supply 1 such as a commercial power5
supply and a motor 7 as an electric motor. The power
conversion device 100 converts AC power from the AC power
supply 1 to DC power once, converts the converted DC power to
AC power, and supplies the AC power to the motor 7 as a load.
The power conversion device 100 includes a10
rectifier 2 as a rectification unit, a DC link section 5, an
inverter 6 as a power converter, and a control unit 50.
[0011] The rectifier 2 is composed of diodes and converts
three-phase AC voltages inputted from the three-phase AC
power supply 1, to DC voltage, through full-wave15
rectification.
The DC link section 5 is provided between the
rectifier 2 and the inverter 6, and supplies DC power
converted by the rectifier 2, to the inverter 6. The DC link
section 5 includes positive and negative DC buses P, N20
connecting the DC output side of the rectifier 2 and the DC
input side of the inverter 6, a DC reactor 3 connected in
series on the positive DC bus P, and a smoothing capacitor 4
provided between the positive and negative DC buses P, N.
[0012] The inverter 6 includes six semiconductor elements25
9
(not shown). While the semiconductor elements are driven by
drive signals G from the control unit 50, the inverter 6
converts DC voltage from the DC link section 5 to AC voltage
with variable voltage and a variable frequency, thus
controlling the motor 7 at an arbitrary rotational speed.5
[0013] The power conversion device 100 further includes a
voltage sensor 10 for detecting line voltage Vab of the AC
voltages on the AC power supply 1, a voltage sensor 11 for
detecting DC bus voltage Vdc between the DC buses P, N, and a
load current sensor 12 for detecting load currents Iu, Iv, Iw10
flowing in the respective phases of the motor 7.
[0014] As inputs to the control unit 50, information about
the DC bus voltage Vdc, information about the load currents
Iu, Iv, Iw flowing through the motor 7, and information about
an angular velocity ω of the motor 7, are inputted, and in15
addition, there is a feature that information about the line
voltage Vab on the AC power supply 1 side detected by the
voltage sensor 10, which is used for suppressing pulsation
occurring in the AC power supply 1 and the DC link section 5,
is further inputted, as described later in detail. The20
control unit 50 generates the drive signals G for controlling
the inverter 6, on the basis of the inputted detected values.
[0015] It has been described that the load current sensor
12 acquires all the load currents Iu, Iv, Iw for three
phases. However, if currents for two phases among the three25
10
phases are detected, current for the other one phase can be
calculated. Therefore, currents to be actually detected may
be for only two phases. As another method, a current sensor
may be provided on the input negative side of semiconductor
elements of the inverter 6 and sampling is performed a5
plurality of times, whereby each of three-phase currents can
be calculated.
[0016] It is general that the DC reactor 3 is interposed
on the DC bus P, for reducing harmonic noise. However, in
the power conversion device 100 of the present embodiment, it10
is not always necessary to use the DC reactor 3, and
therefore the DC reactor 3 may be omitted.
[0017] Next, the control unit 50 will be described.
FIG. 2 is a control block diagram showing an
internal configuration of the control unit 50 of the power15
conversion device 100 according to embodiment 1. In the
present embodiment, a control block for performing vector
control is adopted.
[0018] The control unit 50 includes PI control units 22,
23, 24 which perform feedback control on the basis of20
inputted deviations, a coordinate conversion unit 25 which
converts a D-axis voltage command Vd* and a Q-axis voltage
command Vq* for two phases to voltage commands Vu*, Vv*, Vw*
for three phases, a PWM control unit 26 which generates the
drive signals G for driving the semiconductor elements of the25
11
inverter 6 on the basis of the converted voltage commands
Vu*, Vv*, Vw*, a pulsation suppression control unit 30 which
performs control for suppressing pulsation in the power
supply current and the DC link section 5, and subtractors
21A, 21B, 21C, 21D, 21E.5
[0019] In the control unit 50, the detected load currents
Iu, Iv, Iw of the motor 7 are converted to D-axis current Id
and Q-axis current Iq in an orthogonal two-axis coordinate
system by a converter (not shown).
The subtractor 21A calculates a deviation between10
an angular velocity command ω* which is a speed command and
the angular velocity ω estimated through position-sensorless
control, and the PI control unit 22 performs PI control so
that the calculated deviation becomes small, thereby deriving
a Q-axis current command Iq*.15
[0020] The subtractor 21B calculates a deviation between
the Q-axis current command Iq* and the detected Q-axis
current Iq, and the PI control unit 23 performs PI control so
that the calculated deviation becomes small, i.e., the Q-axis
current Iq follows the Q-axis current command Iq*, thereby20
calculating the Q-axis voltage command Vq*.
Similarly for D axis, the subtractor 21D calculates
a deviation between a D-axis current command Id* and the
detected D-axis current Id, and the PI control unit 24
performs PI control so that the calculated deviation becomes25
12
small, i.e., the D-axis current Id follows the D-axis current
command Id*, thereby calculating the D-axis voltage command
Vd*.
[0021] The pulsation suppression control unit 30
calculates a D-axis voltage correction command ΔVd* as a5
voltage correction command and a Q-axis voltage correction
command ΔVq* as a voltage correction command. The pulsation
suppression control unit 30 will be described later in
detail.
Then, the subtractor 21E subtracts the D-axis10
voltage correction command ΔVd* from the D-axis voltage
command Vd*, to correct the D-axis voltage command Vd*. In
addition, the subtractor 21C subtracts the Q-axis voltage
correction command ΔVq* from the Q-axis voltage command Vq*,
to correct the Q-axis voltage command Vq*. The corrected D-15
axis voltage command Vd* and Q-axis voltage command Vq* are
inputted to the coordinate conversion unit 25.
[0022] The coordinate conversion unit 25 performs
coordinate conversion from a D, Q-axis rotating coordinate
system to a U, V, W coordinate system at rest corresponding20
to actual output voltage commands. The voltage commands Vu*,
Vv*, Vw* for the respective phases obtained through the
coordinate conversion are inputted to the PWM control unit
26.
The PWM control unit 26 generates the drive signals25
13
G for the semiconductor elements of the inverter 6, on the
basis of the inputted voltage commands Vu*, Vv*, Vw* for the
respective phases.
[0023] The coordinate conversion unit 25 and the PWM
control unit 26 are means used in general inverter control,5
and therefore the detailed description thereof is omitted
here.
In the control block described here, DQ-axis
decoupling control for inhibiting coupling of D and Q axes is
not described, but DQ-axis decoupling control may be10
performed before voltage command correction is performed by
the D-axis voltage correction command ΔVd* and the Q-axis
voltage correction command ΔVq* from the pulsation
suppression control unit 30.
[0024] Next, the details of the pulsation suppression15
control unit 30 which is a major part of the power conversion
device 100 of the present embodiment will be described.
FIG. 3 is a control block diagram showing a
configuration of the pulsation suppression control unit 30 of
the power conversion device 100 according to embodiment 1.20
[0025] The pulsation suppression control unit 30 performs
pulsation suppression control for suppressing voltage
pulsation and current distortion occurring from the AC power
supply 1 to the DC link section 5.
The pulsation suppression control unit 30 includes25
14
an amplitude-and-phase calculation unit 31, a pulsation
voltage command calculation unit 32, a D-axis feedback
control unit 35 and a Q-axis feedback control unit 36 which
perform feedback control on the basis of inputted deviations,
gain adjustment units 37, 38, and high-pass filters 33A, 33B.5
[0026] The pulsation suppression control unit 30 receives
two inputs, i.e., the detected line voltage Vab on the AC
power supply 1 side and the detected DC bus voltage Vdc.
Then, the pulsation suppression control unit 30 outputs two
values, i.e., the D-axis voltage correction command ΔVd* and10
the Q-axis voltage correction command ΔVq*.
[0027] Hereinafter, pulsation suppression control
performed by the pulsation suppression control unit 30 will
be described sequentially from an input of the line voltage
Vab.15
First, the amplitude-and-phase calculation unit 31
calculates an amplitude Vs and a phase θs from an analog
voltage signal. As a calculation method, a method called
enhanced phase locked loop (ePLL) can be used. The amplitude
Vs and the phase θs of AC voltage may be derived using a20
zero-cross signal of the line voltage Vab. In a case of
detecting only a zero-cross point from negative to positive,
a zero-cross signal is inputted once per power supply cycle.
Using a time T1 between zero-cross points and a time T2
between zero-cross points in the previous cycle, a phase25
15
angle can be calculated as shown by the following Formula
(1). The unit thereof is radian [rad].
[0028] [Mathematical 1]
[0029] The magnitude of the amplitude Vs can be calculated5
by integrating the absolute value of the power supply line
voltage Vab between zero-cross points and then taking an
average value thereof, as shown by the following Formula (2).
[0030] [Mathematical 2]
10
[0031] In Formula (2), π/2 is a coefficient for converting
an average value to an effective value. As described above,
the amplitude Vs and the phase θs can be derived from the
zero-cross signal using the above formulae (1) and (2).
[0032] Without detecting the line voltage Vab in an analog15
manner, it is possible to calculate the amplitude Vs and the
phase θs by only a zero-cross signal. In this case, the
amplitude Vs can be derived by the following Formula (3)
16
using an average value Vdcave of the DC bus voltage.
[0033] [Mathematical 3]
[0034] Here, K1 is a gain, and normally, K1 is set at π/3.
In a case where a resistance component such as a power supply5
impedance is great, K1 may be slightly adjusted to be a
little greater.
The amplitude Vs and the phase θs of AC voltage
calculated by the amplitude-and-phase calculation unit 31 are
inputted to the pulsation voltage command calculation unit10
32.
[0035] The pulsation voltage command calculation unit 32
can reproduce phase voltages Va, Vb, Vc of the three-phase AC
power supply 1, using the inputted amplitude Vs and phase θs,
as shown by the following Formulae (4) to (6).15
[0036] [Mathematical 4]
[0037] [Mathematical 5]
17
[0038] [Mathematical 6]
[0039] Then, regarding the reproduced phase voltages Va,
Vb, Vc of the three-phase AC power supply 1, for every phase,5
the smallest phase voltage Va, Vb, Vc is subtracted from the
greatest phase voltage Va, Vb, Vc at each phase, whereby a DC
bus voltage prediction value Vdc* can be derived. This is
expressed by Formula (7).
[0040] [Mathematical 7]10
[0041] Then, a DC component of the DC bus voltage
prediction value Vdc* is removed by the high-pass filter 33A,
whereby a pulsation voltage prediction value ΔVdc* extracted
as an AC component can be calculated.15
18
The pulsation voltage prediction value ΔVdc* is a
prediction value of an AC component contained in the DC bus
voltage between the DC buses P, N obtained through full-wave
rectification of the three-phase AC voltages, and is
pulsation that oscillates at a frequency that is six times5
the frequency of AC voltage of the AC power supply 1.
[0042] Next, description will be given sequentially from
the DC bus voltage Vdc inputted on the lower side in FIG. 3.
The DC bus voltage Vdc detected by the voltage
sensor 11 passes through the high-pass filter 33B in which a10
DC component is removed, and thus the pulsation voltage
actual measured value ΔVdc extracted as an actual AC
component on the DC buses P, N is derived.
[0043] The reason why the high-pass filters 33A, 33B are
provided is that, if DC components are contained in the15
pulsation voltage prediction value ΔVdc* and the pulsation
voltage actual measured value ΔVdc that are derived, they
interfere with current control shown in FIG. 2, so that motor
control might not work appropriately. Therefore, it is
necessary to interpose the high-pass filters 33A, 33B.20
Then, the subtractor 34 subtracts the pulsation
voltage actual measured value ΔVdc from the pulsation voltage
prediction value ΔVdc*, to calculate a deviation ΔVerr.
[0044] Here, the pulsation voltage actual measured value
ΔVdc which is the actual measured value of actual pulsation25
19
in the DC link section 5 has a higher crest value than the
pulsation voltage prediction value ΔVdc* which is predicted
through calculation and oscillates at a frequency that is six
times the power supply frequency. Further, the pulsation
voltage actual measured value ΔVdc has a waveform also5
containing high-order pulsation that has a frequency higher
than six times the power supply frequency and is due to
actual rectification operation of the rectifier 2, resonance
of the LC resonance circuit formed in the actual circuit, and
the like. Therefore, the deviation ΔVerr derived by10
subtracting the pulsation voltage actual measured value ΔVdc
from the pulsation voltage prediction value ΔVdc* has a
waveform containing sixth-order pulsation and high-order
pulsation for higher than sixth order.
[0045] Then, so as to reduce the deviation ΔVerr, i.e.,15
reduce pulsation containing sixth-order pulsation and high-
order pulsation for higher than sixth order, on D axis, the
D-axis feedback control unit 35 performs feedback control to
derive a controlled variable 35C.
Then, the gain adjustment unit 37 multiplies the20
controlled variable 35C by a gain 37G (Vdc/Id) as a first
gain which is proportional to the DC bus voltage Vdc and
inversely proportional to the D-axis current Id, to calculate
the D-axis voltage correction command ΔVd*.
[0046] As the feedback control, normally, proportional (P)25
20
control is used. In a case where a control band is raised,
proportional differential (PD) control may be used.
The P control can be represented by the following
Formula (8), and the PD control can be represented by the
following Formula (9).5
[0047] [Mathematical 8]
[0048] [Mathematical 9]
[0049] In the above Formula (8) and Formula (9), Kp is a10
proportional gain as a control gain, and Kd is a differential
gain as a control gain. Instead of performing PD control, P
control and phase-lead control using a phase-lead
compensation filter may be performed. The phase-lead control
is control for advancing a phase of the controlled variable15
derived through P control by a set phase amount, so as to
compensate for control lag that occurs depending on the
control cycle for performing feedback control, whereby the
effect of pulsation suppression can be improved.
[0050] Similarly for Q axis, so as to reduce the deviation20
ΔVerr, i.e., reduce pulsation containing sixth-order
pulsation and high-order pulsation for higher than sixth
order, the feedback control unit 36 performs feedback control
21
to calculate a controlled variable 36C.
Then, the gain adjustment unit 38 multiplies the
controlled variable 36C by a gain 38G (Vdc/Iq) as a first
gain which is proportional to the DC bus voltage Vdc and
inversely proportional to the Q-axis current Iq, to calculate5
the Q-axis voltage correction command ΔVq*.
[0051] In a case where the DC bus voltage Vdc has
increased, the D-axis voltage correction command ΔVd* and the
Q-axis voltage correction command ΔVq* as described above are
to perform correction so that d-axis voltage and q-axis10
voltage increase, in order to increase output power of the
inverter 6. In a case where the DC bus voltage Vdc has
decreased, the D-axis voltage correction command ΔVd* and the
Q-axis voltage correction command ΔVq* are to perform
correction so that d-axis voltage and q-axis voltage15
decrease, in order to decrease the output power of the
inverter 6. In this way, pulsation suppression control for
suppressing pulsation in power supply current and the DC link
section 5 is performed.
[0052] The magnitudes of the controlled variables 35C, 36C20
in the present embodiment are adjusted by the gains 37G, 38G
as first gains.
The gains 37G, 38G provide an effect of making the
control effect of the pulsation suppression control constant.
Hereinafter, description will be given using the gain 37G as25
22
an example.
[0053] First, output power of the inverter 6 is defined as
Pout + ΔPout. A DC component of the output power is Pout,
and pulsation power of the output power is ΔPout. Pout means
DC power that is generated through normal motor control, and5
ΔPout means pulsation power generated for suppressing
resonance. The output power Pout + ΔPout can be calculated
by the following Formula (10).
[0054] [Mathematical 10]
10
[0055] Here, Vd is a DC component of D-axis voltage, ΔVd
is an AC component of D-axis voltage, Vq is a DC component of
Q-axis voltage, ΔVq is an AC component of Q-axis voltage, Id
is a DC component of D-axis current, ΔId is an AC component
of D-axis current, Iq is a DC component of Q-axis current,15
and ΔIq is an AC component of Q-axis current.
[0056] The DC component power Pout is represented by
Formula (11).
[0057] [Mathematical 11]
23
[0058] Then, ΔPout can be derived from Formulae (10) and
(11) and is represented by Formula (12).
[0059] [Mathematical 12]
5
[0060] In the above Formula (12), a term of ΔV*I which is
a product of the voltage AC component ΔV and the current DC
component I is dominant. According to the characteristics of
the motor, ΔI does not greatly change even when ΔV changes.
Therefore, a term of ΔI can be neglected, to obtain10
approximation. By the approximation, Formula (13) is
obtained.
[0061] [Mathematical 13]
[0062] Next, input current to the inverter 6 is to be15
calculated. Input power to the inverter 6 is defined as Pin
+ ΔPin and can be represented by the following Formula (14).
[0063] [Mathematical 14]
24
[0064] Here, Vdc is a DC voltage component of DC bus
voltage, ΔVdc is an AC component of DC bus voltage, Idc is a
DC component of inverter input current, and ΔIdc is an AC
component of inverter input current.5
[0065] The DC component power Pin is represented by the
following Formula (15).
[0066] [Mathematical 15]
[0067] Then, ΔPin can be derived from Formulae (14) and10
(15) and is represented by the following Formula (16).
[0068] [Mathematical 16]
[0069] Here, as long as control is appropriately performed
on the inverter 6, a term of ΔVdc which is an oscillation15
component of bus voltage becomes small, and a term of
Vdc*ΔIdc is dominant. Thus, by approximation, the following
Formula (17) is obtained.
[0070] [Mathematical 17]
20
25
[0071] By transferring ΔIdc to the left-hand side and
arranging the expression, Formula (18) is obtained.
[0072] [Mathematical 18]
[0073] Since ΔPin and ΔPout become equal to each other,5
Formula (13) is substituted into ΔPin in Formula (18),
whereby Formula (19) can be derived.
[0074] [Mathematical 19]
[0075] From a result of Formula (19), it is found that, if10
the pulsation voltage ΔVd is intentionally given to D axis in
order to suppress resonance, the input current ΔIdc having
pulsation whose magnitude is proportional to the D-axis
current Id and inversely proportional to the DC bus voltage
Vdc can be obtained with respect to the given pulsation15
voltage ΔVd. Accordingly, it is found that, if Id or Vdc
changes, a controlled variable of ΔIdc also changes.
26
[0076] Therefore, in order to make ΔIdc constant, for D
axis, using the gain 37G, the controlled variable 35C for
giving pulsation voltage to the D-axis voltage command Vd* is
multiplied by the gain 37G so as to be proportional to the DC
bus voltage Vdc and inversely proportional to the D-axis5
current Id. Similarly for Q axis, using the gain 38G, the
controlled variable 36C for giving pulsation voltage to the
Q-axis voltage command Vq* is multiplied by the gain 38G so
as to be proportional to the DC bus voltage Vdc and inversely
proportional to the Q-axis current Iq.10
[0077] The values of the DC bus voltage Vdc, the D-axis
current Id, and the Q-axis current Iq used in the gains 37G,
38G may be average values during driving of the motor 7, but
are not limited thereto. For example, the values of the
gains 37G, 38G may be updated in accordance with detected15
values of the DC bus voltage Vdc, the D-axis current Id, and
the Q-axis current Iq during driving of the motor 7, instead
of using predetermined fixed values.
The gain 37G adjusts the controlled variable of
feedback control proportionally to the detected DC bus20
voltage Vdc and inversely proportionally to the detected D-
axis current Id. By performing such adjustment of the
controlled variable, even if Vdc or Id changes, the
controlled variable of ΔIdc can be made constant, and the
effect of control can be further kept constant. Thus,25
27
variations in the control effect such as deficiency of the
controlled variable and occurrence of pulsation depending on
the condition can be suppressed, whereby resonance can be
suppressed more efficiently.
[0078] It has been described that the gain 37G is5
configured to be inversely proportional to the D-axis current
Id and the gain 38G is configured to be inversely
proportional to the Q-axis current Iq. However, the
configurations are not limited thereto. As shown by the
above Formula (19), as long as the gains 37G, 38G are both at10
least configured to be proportional to the DC bus voltage
Vdc, an effect of making ΔIdc constant is obtained to a
certain extent, even if the gains 37G, 38G are not configured
to be inversely proportional to the D-axis current Id and the
Q-axis current Iq.15
[0079] It is also possible that only one of the D-axis
voltage command Vd* and the Q-axis voltage command Vq* is
corrected by a voltage correction command. In this case, if
the D-axis voltage command Vd* need not be corrected, control
may be performed so as to disable the D-axis voltage20
correction command ΔVd*.
Alternatively, in such a case where flux weakening
control or the like is performed, if operation is performed
so as to apply current also to d axis in addition to q axis,
both of the D-axis voltage command Vd* and the Q-axis voltage25
28
command Vq* may be corrected by voltage correction commands.
Thus, even in a case where the motor 7 rotates at a high
speed, resonance can be suppressed, and sound operation of
the motor 7 can be ensured over a wide speed range.
[0080] Hereinafter, a configuration of hardware of the5
control unit 50 will be described.
As described below with reference to FIG. 4, the
control unit 50 is generally formed by means such as a
microcomputer which executes the control blocks shown in FIG.
2 and FIG. 3.10
FIG. 4 shows an example of a hardware configuration
of the control unit 50 as a control device according to
embodiment 1.
[0081] As shown in the hardware example in FIG. 3, the
control device is composed of a processor 51 and a storage15
device 52. The storage device 52 is provided with a volatile
storage device such as a random access memory and a
nonvolatile auxiliary storage device such as a flash memory,
although not shown.
Instead of the flash memory, an auxiliary storage20
device of a hard disk may be provided. The processor 51
executes a program inputted from the storage device 52. In
this case, the program is inputted from the auxiliary storage
device to the processor 51 via the volatile storage device.
The processor 51 may output data such as a calculation result25
29
to the volatile storage device of the storage device 52, or
may store such data into the auxiliary storage device via the
volatile storage device.
[0082] Hereinafter, with reference to the drawings,
effectiveness of the pulsation suppression control will be5
confirmed using actual operation waveforms.
FIG. 5 shows operation waveforms in a power
conversion device of a comparative example in which the
pulsation suppression control is not performed.
FIG. 5A shows a power supply current waveform in a10
case of operating at a low torque load with Id = 0 A and Iq =
30 A. FIG. 5B shows a power supply current waveform in a
case of operating at a high torque load with Id = 0 A and Iq
= 100 A.
In both cases, great pulsations are occurring and15
thus it can be confirmed that resonance is occurring.
[0083] FIG. 6 shows operation waveforms in the power
conversion device 100 of the present embodiment in which the
pulsation suppression control is performed.
FIG. 6A shows a power supply current waveform in a20
case of operating at a low torque load with Id = 0 A and Iq =
30 A. FIG. 6B shows a power supply current waveform in a
case of operating at a high torque load with Id = 0 A and Iq
= 100 A.
As the feedback control in the pulsation25
30
suppression control unit 30, only P control is performed, and
the Q-axis feedback gain is set as Kp = 0.3. On D axis,
since Id is 0 A, the effect of compensation is small, and
therefore feedback is not performed in the case of these
waveforms. That is, in the case of these waveforms, the5
power conversion device 100 corrects only one Q-axis voltage
command Vq* by the Q-axis voltage correction command ΔVq*.
With reference to both waveforms in FIG. 6A and
FIG. 6B, pulsation has successfully been reduced in both
waveforms, and the effect of the pulsation suppression10
control can be confirmed.
[0084] FIG. 7 shows operation waveforms in a case where
the gains 37G, 38G are set at fixed values.
FIG. 7A shows a power supply current waveform in a
case of operating at a low torque load with Id = 0 A and Iq =15
30 A. Under this condition, the gains are adjusted so as to
obtain the same waveform as in FIG. 6A. In this case, when
operation is performed at a high torque load with Id = 0 A
and Iq = 100 A, the waveform shown in FIG. 7B is produced,
and it can be found that the power supply current waveform20
oscillates.
From the above, it can be confirmed that the gains
37G, 38G are important components for enabling stable
operation in various operation conditions.
[0085] The gain 37G is configured to perform division by25
31
the D-axis current Id, and therefore the D-axis voltage
correction command ΔVd* becomes extremely great when the
value of the D-axis current Id is small. In this case, clamp
control described below may be performed so that the value of
the D-axis current Id does not become extremely small, or if5
the D-axis current Id is 0 or infinitely small, control of
disabling the D-axis voltage correction command ΔVd* may be
performed. The same applies to the Q-axis current Iq of the
gain 38G.
[0086] In a case of performing clamp control, for example,10
when the D-axis current Id or the Q-axis current Iq has
become a value within a set first value range, the value of
the D-axis current Id used in the gain 37G or the value of
the Q-axis current Iq used in the gain 38G may be adjusted to
be a value above the first value range. For example, in a15
case where the first value range is set as -10 to +10, clamp
control is performed such that, if the D-axis current Id is -
2, the value thereof is clamped at -10.1, and if the Q-axis
current Iq is +3, the value thereof is clamped at +10.1.
In particular, when the motor 7 is rotating at a20
low or middle speed, control is often performed with Id set
at 0 A, and therefore the above situation applies.
[0087] The power conversion device of the present
embodiment configured as described above includes:
a rectification unit which converts inputted three-25
32
phase AC voltages to DC voltage and outputs the DC voltage to
a DC bus;
a power converter which converts the DC voltage on
the DC bus converted by the rectification unit, to AC
voltage, to control an electric motor; and5
a control unit which controls the power converter,
wherein
the control unit converts current flowing through
the electric motor to D-axis current and Q-axis current in an
orthogonal two-axis coordinate system, generates a D-axis10
voltage command so that the D-axis current follows a D-axis
current command, generates a Q-axis voltage command so that
the Q-axis current follows a Q-axis current command, and
controls the power converter on the basis of the generated D-
axis voltage command and the generated Q-axis voltage15
command,
the control unit derives, as a pulsation voltage
prediction value, pulsation contained in the DC voltage
obtained through full-wave rectification of the three-phase
AC voltages, on the basis of a detected value of the three-20
phase AC voltages, and derives pulsation contained in the DC
voltage, as a pulsation voltage actual measured value, on the
basis of a detected value of the DC voltage, and
the control unit corrects at least one of the D-
axis voltage command or the Q-axis voltage command by a25
33
voltage correction command generated so as to reduce a
deviation between the pulsation voltage prediction value and
the pulsation voltage actual measured value.
[0088] As described above, the control unit derives, as
the pulsation voltage prediction value, pulsation contained5
in the DC voltage obtained through full-wave rectification of
the three-phase AC voltages, on the basis of the detected
value of the three-phase AC voltages. In addition, the
control unit derives pulsation contained in the DC voltage of
the DC bus as the pulsation voltage actual measured value, on10
the basis of the detected value of the DC voltage, and
calculates the deviation between the pulsation voltage
prediction value and the pulsation voltage actual measured
value. The calculated deviation contains sixth-order
harmonic pulsation components due to a crest value difference15
between the pulsation voltage prediction value and the
pulsation voltage actual measured value, and also contains
high-order pulsation for higher than sixth order due to
rectification operation of the rectifier, resonance of the LC
resonance circuit, and the like contained in the pulsation20
voltage actual measured value. The control unit generates
the voltage correction command so that the calculated
deviation is reduced, and corrects at least one of the D-axis
voltage command or the Q-axis voltage command. Thus,
pulsation of the power supply current and pulsation on the DC25
34
bus containing high-order noise can be effectively
suppressed, whereby the inverter can be continuously operated
stably and soundly.
[0089] In particular, on the basis of the deviation
between the pulsation voltage prediction value and the5
pulsation voltage actual measured value, the voltage
correction command is generated so as to reduce the
deviation. Therefore, irrespective of the impedance on the
power supply side, pulsation can be effectively suppressed,
and the controlled variable therefor can be made small, so10
that the target value is readily followed. Thus, it becomes
possible to effectively suppress also high-order noise for
higher than sixth order.
The configuration is made such that the voltage
commands for D axis and Q axis are corrected, instead of15
correcting current commands. Therefore, even in a case where
a current control system is not designed to have high
response, pulsation can be effectively suppressed. Thus,
high-order noise can be effectively reduced.
[0090] In the power conversion device of the present20
embodiment configured as described above,
the control unit subtracts, for every phase,
smallest phase voltage from greatest phase voltage among the
three-phase AC voltages at each phase, to derive the
pulsation voltage prediction value.25
35
[0091] As described above, a prediction value of pulsation
contained in the DC voltage obtained through full-wave
rectification is derived from phase voltages of the three-
phase AC voltages. Thus, it is possible to accurately derive
a prediction value of pulsation having a frequency that is5
six times the power supply frequency, from which pulsation
due to rectification operation of the rectifier which occurs
in the actual circuit, pulsation due to LC resonance of the
LC circuit formed in the actual circuit, and the like are
excluded.10
[0092] In the power conversion device of the present
embodiment configured as described above,
the control unit performs feedback control using a
set control gain so that the deviation is reduced, to derive
a controlled variable, and multiplies the controlled variable15
by a first gain configured to be proportional to the voltage
of the DC bus, to generate the voltage correction command.
[0093] By performing the feedback control as described
above, control response to a target value can be enhanced and
thus high-order noise can be effectively suppressed.20
In addition, by using the first gain configured to
be proportional to the voltage of the DC bus, the D-axis
voltage command and the Q-axis voltage command can be
corrected with an appropriate controlled variable.
Therefore, such a situation that correction is performed25
36
excessively or correction is insufficient can be avoided.
Thus, it becomes possible to continuously operate the power
converter stably and soundly. In addition, pulsation having
a small amplitude in a case where the resonant frequency does
not coincide with six times the power supply frequency can be5
suppressed accurately.
[0094] In the power conversion device of the present
embodiment configured as described above,
the control unit generates the voltage correction
command for correcting the D-axis voltage command, by10
multiplying the controlled variable by the first gain
configured to be inversely proportional to the D-axis
current, and
the control unit generates the voltage correction
command for correcting the Q-axis voltage command, by15
multiplying the controlled variable by the first gain
configured to be inversely proportional to the Q-axis
current.
[0095] By using the first gain configured as described
above, the D-axis voltage command and the Q-axis voltage20
command can be corrected with a more appropriate controlled
variable, whereby the controlled variable of ΔIdc is made
constant and the effect of control can be kept constant.
Thus, pulsation occurring in the power supply current and the
DC link section is stably eliminated, whereby it becomes25
37
possible to continuously operate the power converter stably
and soundly.
[0096] In the power conversion device of the present
embodiment configured as described above,
a value of at least one of the voltage of the DC5
bus, the D-axis current, or the Q-axis current composing the
first gain is updated in accordance with a detected value
thereof during operation of the power converter.
[0097] Thus, in various operation conditions such as a
load current varying condition, deficiency of the controlled10
variable and variations in the control effect are suppressed,
whereby pulsation can be efficiently suppressed.
[0098] In the power conversion device of the present
embodiment configured as described above,
when the D-axis current or the Q-axis current15
becomes a value within a set first value range, the control
unit performs clamp control for making adjustment so that a
value of the D-axis current or the Q-axis current to be used
in the first gain becomes a value above the first value
range.20
[0099] Thus, in various operation conditions, application
of an excessive controlled variable and the like is
prevented, whereby it becomes possible to continuously
operate the power converter more stably and soundly.
[0100] Embodiment 225
38
Hereinafter, embodiment 2 of the present disclosure
will be described focusing on a difference from the above
embodiment 1, with reference to the drawings. The same parts
as those in the above embodiment 1 are denoted by the same
reference characters and the description thereof is omitted.5
A circuit configuration of the power conversion
device of the present embodiment 2 is the same as that shown
in FIG. 1 in embodiment 1. A configuration of the control
unit 50 of the present embodiment is also the same as that
shown in FIG. 2 in embodiment 1, but an internal10
configuration of the pulsation suppression control unit 30 is
different.
[0101] FIG. 8 is a control block diagram showing an
internal configuration of a pulsation suppression control
unit 230 of the power conversion device according to15
embodiment 2.
The pulsation suppression control unit 230 of the
present embodiment 2 is different from the pulsation
suppression control unit 30 of embodiment 1 in that a
feedback control unit 235, a gain adjustment unit 237, and20
positive/negative determination units 239d, 239q as sign
functions are provided.
[0102] In particular, unlike embodiment 1, the feedback
control unit 235 for suppressing resonance is characterized
by having the same configuration between D axis and Q axis,25
39
and derives a controlled variable 235C to be used in common
for generating the D-axis voltage correction command ΔVd* and
the Q-axis voltage correction command ΔVq* for respectively
correcting the D-axis voltage command Vd* and the Q-axis
voltage command Vq*.5
As the feedback control in the feedback control
unit 235, normally, proportional (P) control is used. In a
case where a control band is raised, proportional
differential (PD) control may be used. Instead of PD
control, control using a phase-lead compensation filter for10
advancing a phase of the controlled variable by a set phase
amount and proportional (P) control may be performed in
combination.
[0103] Then, with respect to the controlled variable 235C
used in common between D axis and Q axis as described above,15
the gain adjustment unit 237 multiplies the controlled
variable 235C by a gain 237G (Vdc/(|Id| + |Iq|)) as a first
gain used in common between D axis and Q axis.
The gain 237G is configured to be proportional to
the DC bus voltage Vdc and inversely proportional to the sum20
of the absolute value of D-axis current Id and the absolute
value of Q-axis current Iq.
[0104] Next, on D axis, with respect to the controlled
variable multiplied by the gain 237G, the positive/negative
determination unit 239d multiplies the controlled variable by25
40
a sign function Sign(Id) which takes only the polarity of the
D-axis current Id which is a variable, to generate the
voltage correction command ΔVd*. Next, on Q axis, with
respect to the controlled variable multiplied by the gain
237G, the positive/negative determination unit 239q5
multiplies the controlled variable by a sign function
Sign(Iq) which takes only the polarity of the Q-axis current
Iq which is a variable, to generate the voltage correction
command ΔVq*.
The D-axis voltage command Vd* and the Q-axis10
voltage command Vq* are corrected by the D-axis voltage
correction command ΔVd* and the Q-axis voltage correction
command ΔVq* generated as described above.
[0105] Hereinafter, the configurations of the gain 237G
and the positive/negative determination units 239d, 239q in15
the present embodiment will be described.
In embodiment 1, it has been confirmed that ΔIdc is
derived by the above Formula (19).
[0106] Here, in the present embodiment, ΔVd to be given to
the voltage command in order to suppress pulsation, i.e., the20
D-axis voltage correction command ΔVd*, is represented by the
following Formula (20). In addition, ΔVq to be intentionally
given to the voltage command in order to suppress pulsation,
i.e., the Q-axis voltage correction command ΔVq*, is
represented by the following Formula (21).25
41
[0107] [Mathematical 20]
[0108] [Mathematical 21]
[0109] Here, ΔVerr is a deviation between the pulsation5
voltage prediction value ΔVdc* and the pulsation voltage
actual measured value ΔVdc, and corresponds to an output of
the subtractor 34. In addition, as the feedback control
performed for deriving ΔVd*, ΔVq*, only proportional (P)
control using the proportional gain Kp is performed.10
[0110] Then, the D-axis current Id is 0 or a negative
value, and Iq is a positive value in a normal state.
Therefore, the above Formulae (20) and (21) can be rewritten
as shown by the following Formulae (22) and (23).
[0111] [Mathematical 22]15
42
[0112] [Mathematical 23]
[0113] By substituting Formulae (22) and (23) into Formula
(19), Formula (24) is obtained.5
[0114] [Mathematical 24]
[0115] That is, the characteristics of output power of the
inverter 6 shown by the above Formula (19) can be made into
simple characteristics in which the influence of physical10
parameters Vdc, Id, Iq is canceled out, as shown by the above
Formula (24).
43
Through such adjustment, the controlled variable of
ΔIdc can be made constant, and deficiency of the controlled
variable, occurrence of pulsation, and variations in the
control effect depending on the condition can be suppressed,
and resonance can be efficiently suppressed.5
[0116] Next, another gain calculation method will be
described. The internal configuration of the pulsation
suppression control unit may be replaced with that of a
pulsation suppression control unit 230A shown in FIG. 9.
FIG. 9 is a control block diagram showing an10
internal configuration of the pulsation suppression control
unit 230A of the power conversion device according to
embodiment 2.
A difference from the pulsation suppression control
unit 230 shown in FIG. 8 is that the controlled variable 235C15
is multiplied by gains in the gain adjustment units 237A,
238A.
[0117] On D axis, the gain adjustment unit 237A multiplies
the controlled variable 235C by the gain 237G (Vdc/(|Id| +
|Iq|)) as a first gain and in addition, a gain 237AG20
(|Id|/Id’) as a second gain.
On Q axis, the gain adjustment unit 238A multiplies
the controlled variable 235C by the gain 237G (Vdc/(|Id| +
|Iq|)) as a first gain and in addition, a gain 238AG
(|Iq|/Iq’) as a second gain.25
44
[0118] The gain 237AG is configured to be proportional to
the absolute value of D-axis current Id and inversely
proportional to the value of the D-axis current Id clamp-
controlled to be a value above the set first value range.
The gain 238AG is configured to be proportional to5
the absolute value of Q-axis current Iq and inversely
proportional to the value of Q-axis current Iq clamp-
controlled to be a value above the set first value range.
The denominator Id’ of the gain 237AG is the D-axis
current Id that has undergone limiter processing by clamp10
control, and the denominator Iq’ of the gain 238AG is the Q-
axis current Iq that has undergone limiter processing by
clamp control.
[0119] The limiter processing by the clamp control is to
clamp the output so that the absolute value of each of the D-15
axis current Id and the Q-axis current Iq does not become a
value within the set first value range. For example, in a
case where the first value range is set as -9 A to 9 A, when
7 A is inputted, the output is clamped at 9.1 A. Conversely,
when -7 A is inputted, the output is clamped at -9.1 A.20
Thus, even if the absolute values of D-axis current
Id and Q-axis current Iq are small, the voltage commands are
not excessively corrected.
With this block, for example, in a case of Id = 0
A, when clamp control is performed, the voltage correction25
45
command ΔVd* becomes 0 V. Conversely, in a case of not
performing clamp control on both of D axis and Q axis,
operation is the same as in the pulsation suppression control
having the configuration shown in FIG. 8.
[0120] In the power conversion device of the present5
embodiment configured as described above,
the control unit generates the voltage correction
commands for correcting the D-axis voltage command and the Q-
axis voltage command, by multiplying the controlled variable
by the first gain configured to be inversely proportional to10
a sum of an absolute value of the D-axis current and an
absolute value of the Q-axis current.
In the power conversion device of the present
embodiment configured as described above,
in the feedback control, the control unit derives15
the controlled variable to be used in common for generating
the voltage correction commands for correcting the D-axis
voltage command and the Q-axis voltage command.
[0121] By using the first gain configured as described
above, the D-axis voltage command and the Q-axis voltage20
command can be corrected with an appropriate controlled
variable, and also, feedback control can be implemented with
one configuration for both of D axis and Q axis. Thus,
feedback control executed in the control unit can be reduced,
the same first gain can be used for D axis and Q axis, and25
46
the controlled variable that can be used in common for
generating the voltage correction commands for correcting D-
axis and Q-axis voltage commands is derived. Therefore, the
control configuration can be simplified, and the control load
on the control unit can be reduced. Thus, high-speed5
response is achieved in feedback control and high-order
pulsation can be effectively suppressed.
[0122] In the power conversion device of the present
embodiment configured as described above,
in the configuration in which the first gain is10
inversely proportional to the sum of the absolute value of
the D-axis current and the absolute value of the Q-axis
current,
with respect to the controlled variable to be used
in common for correcting the D-axis voltage command and the15
Q-axis voltage command, the control unit multiplies the
controlled variable by a sign function that takes only a
polarity of the D-axis current which is a variable, to
generate the voltage correction command for correcting the D-
axis voltage command, and multiplies the controlled variable20
by the sign function that takes only a polarity of the Q-axis
current which is a variable, to generate the voltage
correction command for correcting the Q-axis voltage command.
[0123] As described above, with respect to the same
controlled variable to be used in common for D axis and Q25
47
axis, the voltage correction commands are generated by
multiplying the controlled variable by the sign functions
that take only the polarities of the D-axis and Q-axis
currents, whereby the output of the power converter can be
controlled with simple characteristics in which the deviation5
ΔVerr is multiplied by the gain Kp. Thus, in various
operation conditions, it becomes possible to continuously
operate the power converter stably and soundly.
[0124] In the power conversion device of the present
embodiment configured as described above,10
in the configuration in which the first gain is
inversely proportional to the sum of the absolute value of
the D-axis current and the absolute value of the Q-axis
current,
the control unit multiplies the controlled variable15
to be used in common for correcting the D-axis voltage
command and the Q-axis voltage command, by a second gain in
addition to the first gain, and
the second gain is
configured to be proportional to the absolute20
value of the D-axis current and inversely proportional to a
value of the D-axis current clamp-controlled to be a value
above a set first value range, or
configured to be proportional to the absolute
value of the Q-axis current and inversely proportional to a25
48
value of the Q-axis current clamp-controlled to be a value
above a set first value range.
[0125] Thus, even in a case where the driving condition of
the electric motor is changed, excessive correction is
prevented, pulsation is suppressed, and the inverter can be5
continuously operated stably and soundly.
[0126] Although the disclosure is described above in terms
of various exemplary embodiments and implementations, it
should be understood that the various features, aspects, and
functionality described in one or more of the individual10
embodiments are not limited in their applicability to the
particular embodiment with which they are described, but
instead can be applied, alone or in various combinations to
one or more of the embodiments of the disclosure.
It is therefore understood that numerous15
modifications which have not been exemplified can be devised
without departing from the scope of the present disclosure.
For example, at least one of the constituent components may
be modified, added, or eliminated. At least one of the
constituent components mentioned in at least one of the20
preferred embodiments may be selected and combined with the
constituent components mentioned in another preferred
embodiment.
25
49
DESCRIPTION OF THE REFERENCE CHARACTERS
[0127] 2 rectifier (rectification unit)
6 inverter (power converter)
7 motor (electric motor)
50 control unit5
37G, 38G gain (first gain)
100 power conversion device
P, N DC bus
50
We Claim:
[Claim 1] A power conversion device (100) comprising:
a rectification unit (2) which converts inputted
three-phase AC voltages to DC voltage and outputs the DC
voltage to a DC bus (P, N);5
a power converter which converts the DC voltage on
the DC bus (P, N) converted by the rectification unit (2), to
AC voltage, to control an electric motor (7); and
a control unit (50) which controls the power
converter, wherein10
the control unit (50) converts current flowing
through the electric motor (7) to D-axis current and Q-axis
current in an orthogonal two-axis coordinate system,
generates a D-axis voltage command so that the D-axis current
follows a D-axis current command, generates a Q-axis voltage15
command so that the Q-axis current follows a Q-axis current
command, and controls the power converter on the basis of the
generated D-axis voltage command and the generated Q-axis
voltage command,
the control unit (50) derives, as a pulsation20
voltage prediction value (ΔVdc*), pulsation contained in the
DC voltage obtained through full-wave rectification of the
three-phase AC voltages, on the basis of a detected value of
the three-phase AC voltages, and derives pulsation contained
in the DC voltage, as a pulsation voltage actual measured25
51
value (ΔVdc), on the basis of a detected value of the DC
voltage, and
the control unit (50) corrects at least one of the
D-axis voltage command or the Q-axis voltage command by a
voltage correction command generated so as to reduce a5
deviation between the pulsation voltage prediction value
(ΔVdc*) and the pulsation voltage actual measured value
(ΔVdc).
[Claim 2] The power conversion device (100) according to10
claim 1, wherein
the control unit (50) subtracts, for every phase,
smallest phase voltage from greatest phase voltage among the
three-phase AC voltages at each phase, to derive the
pulsation voltage prediction value (ΔVdc*).15
[Claim 3] The power conversion device (100) according to
claim 1 or 2, wherein
the control unit (50) performs feedback control
using a set control gain so that the deviation is reduced, to20
derive a controlled variable, and multiplies the controlled
variable by a first gain configured to be proportional to the
voltage of the DC bus (P,N), to generate the voltage
correction command.
25
52
[Claim 4] The power conversion device (100) according to
claim 3, wherein
the control unit (50) generates the voltage
correction command for correcting the D-axis voltage command,
by multiplying the controlled variable by the first gain5
configured to be inversely proportional to the D-axis
current, and
the control unit (50) generates the voltage
correction command for correcting the Q-axis voltage command,
by multiplying the controlled variable by the first gain10
configured to be inversely proportional to the Q-axis
current.
[Claim 5] The power conversion device (100) according to
claim 3, wherein15
the control unit (50) generates the voltage
correction commands for correcting the D-axis voltage command
and the Q-axis voltage command, by multiplying the controlled
variable by the first gain configured to be inversely
proportional to a sum of an absolute value of the D-axis20
current and an absolute value of the Q-axis current.
[Claim 6] The power conversion device (100) according to
claim 5, wherein
in the feedback control, the control unit (50)25
53
derives the controlled variable to be used in common for
generating the voltage correction commands for correcting the
D-axis voltage command and the Q-axis voltage command.
[Claim 7] The power conversion device (100) according to5
claim 6, wherein
in the configuration in which the first gain is
inversely proportional to the sum of the absolute value of
the D-axis current and the absolute value of the Q-axis
current,10
with respect to the controlled variable to be used
in common for correcting the D-axis voltage command and the
Q-axis voltage command, the control unit (50) multiplies the
controlled variable by a sign function that takes only a
polarity of the D-axis current which is a variable, to15
generate the voltage correction command for correcting the D-
axis voltage command, and multiplies the controlled variable
by the sign function that takes only a polarity of the Q-axis
current which is a variable, to generate the voltage
correction command for correcting the Q-axis voltage command.20
[Claim 8] The power conversion device (100) according to
claim 5 or 6, wherein
in the configuration in which the first gain is
inversely proportional to the sum of the absolute value of25
54
the D-axis current and the absolute value of the Q-axis
current,
the control unit (50) multiplies the controlled
variable to be used in common for correcting the D-axis
voltage command and the Q-axis voltage command, by a second5
gain in addition to the first gain, and
the second gain is
configured to be proportional to the absolute
value of the D-axis current and inversely proportional to a
value of the D-axis current clamp-controlled to be a value10
above a set first value range, or
configured to be proportional to the absolute
value of the Q-axis current and inversely proportional to a
value of the Q-axis current clamp-controlled to be a value
above a set first value range.15
[Claim 9] The power conversion device (100) according to any
one of claims 3 to 8, wherein
in the feedback control, one of proportional
control, proportional differential control, or control in20
which control for advancing a phase of the controlled
variable by a set phase amount and proportional control are
performed in combination, is performed.
[Claim 10] The power conversion device (100) according to25
55
claim 4, wherein
when the D-axis current or the Q-axis current
becomes a value within a set first value range, the control
unit (50) performs clamp control for making adjustment so
that a value of the D-axis current or the Q-axis current to5
be used in the first gain becomes a value above the first
value range.
[Claim 11] The power conversion device (100) according to
any one of claims 3 to 10, wherein10
a value of at least one of the voltage of the DC bus
(P,N), the D-axis current, or the Q-axis current composing the
first gain is updated in accordance with a detected value
thereof during operation of the power converter.
15