[Technical Field]
[0001]
The present invention relates to a power conversion
device and a diagnosis method for a power conversion device,
and particularly, a power conversion device and a diagnosis
method for a power conversion device which are appropriate for
diagnosis of smoothing capacitor which configures a main
circuit.
[Background Art]
[0002]
A power converter which uses a semiconductor switching
element is widely used in such fields as industry, home
electronic appliances, transportation, vehicle, electric
power and company infrastructure system, and the like. For
example, in the power converter of industry where several
hundreds of kW or more are used, in order to be connected to
a load of power system or a motor, a system is configured with
a plurality of converters which serve as a forward converter
(hereinafter, will be described as a converter (CONV)) which
converts AC power to DC power or a reverse converter
(hereinafter, will be described as an inverter (INV)) which
converts DC power to AC power. In the system, there is a
1
smoothing capacitor in each of the converters (CONV and INV)
for smoothing variation that follows the power conversion. In
each of the converters, the input and output power is smoothed
by the smoothing capacitor. The power converter is described,
for example, in Patent Reference 1.
[0003]
[Patent Reference 1] JP-A-2008-11606
[Disclosure of the Invention]
[Problem that the Invention is to Solve]
[0004]
While the smoothing capacitor which smooths variation
that follows the power conversion is provided in each of the
converters (CONV and INV), the smoothing capacitor
deteriorates in accordance with an ambient temperature, an
applied voltage, and a conduction current. When the smoothing
capacitor deteriorates and electrostatic capacity decreases,
the variation in DC voltage increases, and this can cause
generation of distortion of current that flows to the power
system or load. Therefore, in order to use the power converter
for a long period of time, it is necessary to periodically
perform maintenance for confirming that the electrostatic
capacity of the smoothing capacitor does not deteriorate and
is necessary electrostatic capacity.
[0005]
For example, in order to detect deterioration of
2
electrostatic capacity according to the deterioration of the
smoothing capacitor, it is considered to set rising time of
a charging current of the smoothing capacitor or falling time
of a discharging current of the smoothing capacitor when
initiating or stopping the power converter to be a determined
value. Charging or discharging time determined by a CR time
constant is used, but it is necessary to detect rising of the
charging current of the smoothing capacitor from the state
where the power converter is stopped, and an operation time
of the power converter as much as the time for the maintenance
work becomes short. In other words, since it is not possible
to detect the deteriorated state of the electrostatic capacity
in a state where the operation of the power converter is
continuous, there is a problem that an operating ratio of the
system deteriorates.
[0006]
An object of the present invention is to provide a power
conversion device which can perform detection while
maintaining system operating ratio based on detection of
deterioration of smoothing capacitor, and a diagnosis method
for a power conversion device.
[Means for Solving the Problem]
[0007]
In order to achieve the above-described target, in the
present invention, a configuration in which there are provided
3
a plurality of power converters which convert electric power
from AC to DC or from DC to AC, the plurality of power
converters are connected to a common DC voltage portion, the
plurality of power converters respectively have a smoothing
capacitor, a function of detecting a deteriorated state of the
smoothing capacitor by analyzing an electric current that
flows from the smoothing capacitor of any of the plurality of
power converters to the smoothing capacitor of another power
converter is provided, is provided.
[0008]
Otherwise, in the power conversion device which
converts the electric power from AC to DC or from DC to AC,
a configuration in which the power conversion device is
configured with the plurality of power converters, the power
converter has the smoothing capacitor individually, the DC
voltage portion of the power converter is connected to the
common DC voltage portion, a sensor which observes or a
function which estimates the electric current that flows to
the DC voltage portion to which each of the power converters
is connected is provided, a function of detecting the
deteriorated state of the smoothing capacitor loaded on each
of the power converters by analyzing the electric current of
the DC voltage portion is provided, and a mechanism which
outputs the deteriorated state to the outside through an
external interface is provided, is provided.
4
[Advantage of the Invention]
[0009]
According to the present invention, it is possible to
detect deterioration of the smoothing capacitor while
maintaining the system operating ratio.
[Brief Description of the Drawings]
[0010]
Fig. 1 is a configuration of a power converter in a first
example in the present invention.
Fig. 2 is a flowchart for detecting a deteriorated state
of a DC smoothing capacitor in the first and fourth examples
in the present invention.
Fig. 3 is a view describing an outline in which an
electric current of a DC voltage portion is frequency-analyzed
in the first and fourth examples in the present invention.
Fig. 4a is a configuration of the power converter in a
second example in the present invention.
Fig. 4b is another configuration of the power converter
in a third example in the present invention.
Fig. 5 is a view describing an outline in which the
electric current of the DC voltage portion is
frequency-analyzed in the second, third, fifth, and sixth
examples in the present invention.
Fig. 6 is a configuration of the power converter in the
fourth example in the present invention.
5
Fig. 7 is a configuration of the power converter in the
fifth example in the present invention.
Fig. 8 is a configuration of the power converter in the
sixth example in the present invention.
[Best Mode for Carrying out the Invention]
[0011]
An aspect (example) for realizing the present invention
will be described by using the drawings hereinafter.
[First Example]
[0012]
A configuration of a power converter will be described
in Fig. 1. In the example, a three-phase two-level converter
will be described as an example. Two power converters (101a,
101b) configured with a semiconductor switching element and
a DC smoothing capacitor (will be referred to as a smoothing
capacitor. this is the same will be described) (103a, 103b)
are connected to DC voltage portions (100a, 100b). Since the
two-level converter is employed, the DC voltage portions (100a,
100b) are a positive electrode side (100a) and a negative
electrode side (100b), and in the example, a current sensor
(102) for observing an electric current of a DC portion is
provided on the negative electrode side (100b). In addition,
although the current sensor (102) is provided on the positive
electrode side (100a), the effects will be the same as
described hereinafter.
6
[0013]
Each of the power converters (101a, 101b) is controlled
by operation commands (107a, 107b) from a controller (105),
and controls input or output (104a, 104b). The controller
(105) outputs an operating state (108) of each of the power
converters to a deterioration analysis portion (106) of the
DC smoothing capacitors (103a, 103b), the output is combined
with an electric current information (109) of the DC voltage
portions (100a, 100b) in the deterioration analysis portion
(106), and a deteriorated state is detected by computing
deterioration of the electrostatic capacity of the DC
smoothing capacitors (103a, 103b). The deteriorated state
only indicates a deteriorated state of the DC smoothing
capacitors (103a, 103b) and does not include information of
a power converter operating ratio.
[0014]
Here, the operating state (108) of each of the power
converters (101a, 101b) includes a frequency, a modulation
ratio, and a gate pulse pattern of an output or input electric
current of each of the power converters (101a, 101b). In
addition, in order to specify a reason of deterioration of the
DC smoothing capacitors (103a, 103b), output or input electric
current values of each of the power converters (101a, 101b),
internal and external temperatures of a cabinet of each of the
power converters (101a, 101b), DC voltage values of each of
7
the power converters (101a, 101b), and grounding current
values of a device and a control cabinet of the power
converters (101a, 101b).
In the example, the power converter (101a) converts DC
power from the DC voltage portions (100a, 100b) to three-phase
AC by the operation command (107a) from the controller (105),
and outputs the converted power to the AC output portion (104a).
In addition, the power converter (101b) converts DC power from
the DC voltage portions (100a, 100b) to three-phase AC by the
operation command (107b) from the controller (105), and
outputs the converted power to the AC output portion (104b).
Here, the power converters (101a, 101b) may be
configured so as to input AC power from the terminals (104a,
104b), convert the AC power to DC by the power converters (101a,
101b), and supply the DC power to the DC voltage portions (100a,
100b). Otherwise, a configuration in which one of the power
converters (101a, 101b) converts electric power from AC to DC
and the other one of the power converters (101a, 101b) converts
electric power from DC to AC may be employed.
[0015]
In addition, conversion to the AC power may be connected
to a power system as a constant frequency, and may be supplied
to an electric motor or the like as a variable frequency.
[0016]
Fig. 2 illustrates a flowchart for detecting the
8
deteriorated state of the DC smoothing capacitors (103a, 103b)
executed by the deterioration analysis portion (106). The
power converters (101a, 101b) calculates a resonance
frequency of the DC voltage portions (100a, 100b) in an
operating state (S101) (S102).
[0017]
A schematic approach to the calculation of the resonance
frequency will be described first, and then, specific
calculation will be described in detail. Fig. 3 illustrates
a schematic view in which the electric current of the DC
voltage portions (100a, 100b) is frequency-analyzed. The
frequency-analysis can be obtained, for example, by
performing calculation of Fourier transform with respect to
the output of the current sensor (102) by the deterioration
analysis portion (106). The electric current of the DC voltage
portions (100a, 100b) includes not only frequency components
(200a, 200b) determined by an operation pattern of each of the
power converters (101a, 101b) and frequency components (201a,
201b) determined by a carrier frequency of each of the power
converters (101a, 101b) but also a component (202) of a
resonance current (113) between the DC smoothing capacitors
(103a, 103b) loaded on each of the power converters (101a,
101b).
[0018]
The current component determined by the operation
9
pattern and a carrier frequency of the power converters (101a,
101b) changes depending on the operation state, but
electrostatic capacity of the DC smoothing capacitors (103a,
103b) loaded on each of the power converters (101a, 101b) and
a frequency of the resonance current determined by parasitic
inductance of the DC voltage portions (100a, 100b) that
connects each of the power converters (101a, 101b) to each
other are constant regardless of the operation state in a
relatively short period of time. However, in a case where the
DC smoothing capacitors (103a, 103b) deteriorates and the
electrostatic capacity deteriorates, the resonance frequency
(202) becomes high frequency.
[0019]
Therefore, by analyzing the operating state (108) of
each of the power converters (101a, 101b) and the electric
current information (109) related to the electric current
(113) of the DC voltage portions (100a, 100b), and by comparing
the analysis result with the resonance frequency measured when
shipping the power converter, it is possible to detect the
deteriorated state of the DC smoothing capacitors (103a,
103b).
[0020]
Furthermore, the detection of the deteriorated state of
the DC smoothing capacitors (103a, 103b) executed by the
deterioration analysis portion (106) will be described in
10
detail. In the flowchart illustrated in Fig. 2, the DC
smoothing capacitors (103a, 103b) outputs an alarm about
deterioration in a case where the resonance frequency of the
DC voltage portions (100a, 100b) exceeds a specified value 1
(S104a). Here, as the resonance frequency of the DC voltage
portions (100a, 100b), after cutting a frequency lower than
the resonance frequency of the DC voltage portions (100a,
100b) when shipping the power converter illustrated as f0
hereinafter by filtering, the frequency may be compared with
the specified value 1 (this is similar when comparing the
frequency with a specified value 2 ) . The alarm is output, for
example, to a monitor and the like (112a, 112b) provided in
the power converters (101a, 101b) illustrated in Fig. 1.
[0021]
In the example, a case where the deteriorated state of
the DC smoothing capacitors (103a, 103b) is divided into two
stages and output is illustrated. A deteriorated state 1
indicates a state where the electrostatic capacity of the DC
smoothing capacitors (103a, 103b) is reduced but the operation
of the power converters (101a, 101b) can be continuous. A
deteriorated state 2 indicates a state where the power
converters (101a, 101b) are difficult to be operated in
stable.
[0022]
Here, the electrostatic capacity of the DC smoothing
11
capacitors (103a, 103b) when shipping the power converters
(101a, 101b) is set to C0, and the electrostatic capacity when
deteriorated state is set to C1 and C2 (C1 > C 2 ) . A resonance
frequency of the DC voltage portion is indicated using a
parasitic inductance L of a busbar or a wiring which connects
the power converters (101a, 101b) to each other, and the
electrostatic capacity in the following equation,
[0023]
[Equation 1]
[0024]
In a case where a state where the electrostatic capacity
of a first stage of the deteriorated state is reduced by 5%
from an initial state and a state where the electrostatic
capacity of a second stage of the deteriorated state is reduced
by 10% from the initial state, are set to be a specified value,
the specified value 1 of the change in resonance frequency
becomes 1.026 times the initial state and the specific value
12
2 is 1.054 times the initial state. In a case where the
electrostatic capacity in the initial state is set to be 2mF
and the parasitic inductance between the power converters
(101a, 101b) is set to be 500 nH, the resonance frequency in
the initial state is approximately 5 kHz, the resonance
frequency in the deteriorated state 1 is approximately 5.2
kHz(f1), and the resonance frequency in the deteriorated state
2 is approximately 5.3 kHz(f2).
[0025]
Here, for example, the specified value may be selected
from a range in which the electrostatic capacity of the first
stage of the deteriorated state (specified value 1) is reduced
by 5% to 15% from the initial state, and the specified value
may be selected from a range in which the electrostatic
capacity of the second stage of the deteriorated state
(specified value 2) is greater than that of the first stage
of the deteriorated state and reduced by 10% to 20% from the
initial state.
[0026]
After outputting the alarm (S104b), the power
converters (101a, 101b) are stopped (S105). In this manner,
by outputting the deteriorated state in a plurality of stages,
an operator of the power converters (101a, 101b) or a person
who is in charge of maintenance can recognize that a
replacement timing of the DC smoothing capacitors (103a, 103b)
13
is coming.
Here, while the operation of the power converters (101a,
101b) is continuously performed, it is possible to detect the
deteriorated state of the DC smoothing capacitors (103a, 103b)
by computing the resonance frequency with a certain or any time
interval and by consecutively observing transition of the
resonance frequency.
In this manner, the deteriorated state is analyzed by
the deterioration analysis portion (106) of the DC smoothing
capacitors (103a, 103b), and output as deterioration
information of the DC smoothing capacitors (103a, 103b) (110).
The deterioration information is notified to the person who
is in charge of maintenance by displaying the deterioration
information on the monitor (112a) provided in the power
converters (101a, 101b) or a maintenance device, such as a
personal computer connected to the power converter during the
maintenance. In addition, by notifying the deterioration
information to the monitoring center (112b) at a far location
connected by a network (111), it is possible to observe the
deteriorated state of the DC smoothing capacitors (103a, 103b)
while the operation state of the power converters (101a, 101b)
is continuously maintained.
[0027]
In the first example, deterioration diagnosis of the DC
smoothing capacitor is performed by the calculation of the
14
resonance frequency, but the deterioration diagnosis may be
performed based on other factors that correspond to the
resonance frequency for deterioration diagnosis of the DC
smoothing capacitor.
[Second Example]
[0028]
Fig. 4a illustrates an example of a three-phase
three-level converter, and Fig. 5 illustrates a schematic view
in which the electric current of the DC voltage portion is
frequency-analyzed in the example, respectively. Two power
converters (301a, 301b) configured with the semiconductor
switching element and DC smoothing capacitors (303a, 303c,
303b, 303d) are connected to the DC voltage portions (300a,
300b, 300c). In the example, a current sensor (302) of the
DC voltage portion is provided in a common portion (300c) to
which both a resonance current (313a) of the DC voltage portion
positive electrode side (300a) and a resonance current (313b)
of the DC voltage portion negative electrode side (300b) flow,
and an electric current information (309) of the DC voltage
portion is applied to the deterioration analysis portion (106)
of the DC smoothing capacitor. In the example, since there
are two resonance paths, frequency peaks (402a, 402b) which
correspond to the two resonance frequencies are expressed. In
addition, since the power converter is generally configured
to have symmetry, there are many cases where the resonance
15
frequency on the positive electrode side and the resonance
frequency on the negative electrode side substantially match
each other, but the frequency is expressed as a different
resonance frequencies in Fig. 5.
[0029]
Similar to the first example, it is possible to observe
the deteriorated state of the DC smoothing capacitors (303a,
303c, 303b, 303d) while the operation state of each of the
power converters (301a, 301b) is continuously maintained.
[Third Example]
[0030]
Fig. 4b illustrates another example of the three-phase
three-level converter, and Fig. 5 illustrates a schematic view
in which the electric current of the DC voltage portion is
frequency-analyzed in the example, respectively. In the
example, current sensors (302a, 302b) which respectively
observe the resonance current (313a) of the DC voltage portion
positive electrode side (300a) and the resonance current
(313b) of the DC voltage portion negative electrode side
(300b) are provided. In the example, since there are resonance
paths at two locations, the frequency peaks (402a, 402b) which
correspond to the two resonance frequencies are expressed. In
addition, since the power converter is generally configured
to have symmetry, there are many cases where the resonance
frequency on the positive electrode side and the resonance
16
frequency on the negative electrode side substantially match
each other, but the frequency is expressed as a different
resonance frequencies in Fig. 5.
[0031]
Similar to the first example, it is possible to observe
the deteriorated state of the DC smoothing capacitors while
the operation state of each of the power converters is
continuously maintained.
[Fourth Example]
[0032]
Fig. 6 illustrates another example of the three-phase
two-level converter. In the example, by using a signal (509)
of voltage sensors (502a, 502b) of the DC smoothing capacitor,
the electric current of DC voltage portion is estimated from
a potential difference of each of the voltage sensors. After
computing the electric current of the DC voltage portion,
similar to the first example, the resonance current that flows
to the DC voltage portion is observed, and the deteriorated
state of the DC smoothing capacitor is detected.
[Fifth Example]
[0033]
Fig. 7 illustrates another example of the three-phase
three-level converter. Similar to the fourth example, the
electric current of the DC voltage portion is estimated from
a signal (609) of voltage sensors (602a, 602c, 602b, 602d) of
17
the DC smoothing capacitors (303a, 303c, 303b, 303d). The
electric current of the DC voltage portion positive electrode
side (300a) is estimated by a potential difference of the
voltage sensor (602a) and the voltage sensor (602b), and the
electric current of the DC voltage portion negative electrode
side (300b) is estimated by a potential difference of the
voltage sensor (602c) and the voltage sensor (602d). After
computing the electric current of the DC voltage portions
(300a, 300b, 300c), similar to the second example, the
frequency peaks (402a, 402b) of the resonance current that
flows to the DC voltage portion is observed, and the
deteriorated state of the DC smoothing capacitor is detected.
[Sixth Example]
[0034]
Fig. 8 illustrates another example of the three-phase
three-level converter. Similar to the fourth and fifth
examples, the electric current of the DC voltage portion is
estimated from a signal (709) of voltage sensors (702a, 702b)
of the DC smoothing capacitors (303a, 303c, 303b, 303d). In
the example, by using the voltage sensor in which the positive
electrode and the negative electrode of the DC voltage
portions (300a, 300b, 300c) are integrated, the electric
current which combines the DC voltage portion positive
electrode side (300a) and the negative electrode side (300b)
is estimated. After computing the electric current of the DC
18
voltage portions (300a, 300b, 300c), similar to the second
example, the frequency peaks (402a, 402b) of the resonance
frequency that flows to the DC voltage portions (300a, 300b,
300c) is observed, and the deteriorated state of the DC
smoothing capacitor is detected.

WE CLAIM:
[Claim 1]
A power conversion device comprising:
a plurality of power converters which convert electric
power from AC to DC or from DC to AC,
wherein the plurality of power converters are connected
to a common DC voltage portion,
wherein the plurality of power converters respectively
have a smoothing capacitor, and
wherein a function of detecting a deteriorated state of
the smoothing capacitor by analyzing an electric current that
flows from the smoothing capacitor of any of the plurality of
power converters to the smoothing capacitor of another power
converter is provided.
[Claim 2]
The power conversion device according to claim 1,
wherein, regarding the analyzed electric current, the
electric current of the DC voltage portion which connects each
of the power converters to each other is detected by a current
sensor.
[Claim 3]
The power conversion device according to claim 1,
further comprising:
a voltage sensor which measures a voltage of the
smoothing capacitor loaded on each of the power converters,
21
wherein the analyzed electric current is estimated
based on the detection of the voltage sensor.
[Claim 4]
The power conversion device according to claim 1,
wherein the DC voltage portion has at least two common
terminals, and
wherein the power converter has a voltage sensor that
is connected to at least the two common DC voltage portions
and measures a voltage between a positive electrode and a
negative electrode of the power converter, and
wherein the analyzed electric current is estimated
based on the detection of the voltage sensor.
[Claim 5]
The power conversion device according to any one of
claims 1 to 4, further comprising:
a calculating portion which frequency-analyzes an
electric current of the DC voltage portion,
wherein the deteriorated state of the smoothing
capacitor is detected by the calculation.
[Claim 6]
The power conversion device according to any one of
claims 1 to 5,
wherein the detected deteriorated state of the
smoothing capacitor loaded on the power converter is displayed
on a monitor loaded on a power converter board.
22
[Claim 7]
The power conversion device according to any one of
claims 1 to 5,
wherein the detected deteriorated state of the
smoothing capacitor loaded on the power converter is observed
by connecting a maintenance device to a control board of the
power converter.
[Claim 8]
The power conversion device according to any one of
claims 1 to 5,
wherein the detected deteriorated state of the
smoothing capacitor loaded on the power converter is
transmitted via a network line for performing observation at
a remote location.
[Claim 9]
The power conversion device according to any one of
claims 1 to 8,
wherein the deteriorated state of the smoothing
capacitor loaded on the power converter is detected in a state
where the power converter is operated.
[Claim 10]
The power conversion device according to claim 1,
wherein an alarm is output in a case of the deteriorated
state of a first stage, and an alarm having a higher warning
degree than that of the first stage is output in a case of the
23
deteriorated state of a second stage which is the deteriorated
state where the deterioration has further proceeded than the
first stage.
[Claim 11]
The power conversion device according to claim 10,
wherein the deteriorated state of the first stage and
the deteriorated state of the second stage are obtained as
frequency component included in the electric current.
[Claim 12]
A diagnosis method for a power conversion device
including a plurality of power converters which convert
electric power from AC to DC or from DC to AC, in which the
plurality of power converters are connected to a common DC
voltage portion, and in which the plurality of power
converters respectively have a smoothing capacitor, the
method comprising:
detecting an electric current that flows from the
smoothing capacitor of any of the plurality of power
converters to the smoothing capacitor of another power
converter; and
detecting a deteriorated state of the smoothing
capacitor by analyzing the detected electric current.