FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POWER CONVERSION APPARATUS, VEHICLE AUXILIARY POWER SUPPLY,
AND METHOD FOR STOPPING POWER CONVERSION APPARATUS;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED
AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, 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 APPARATUS, VEHICLE AUXILIARY POWER SUPPLY,
5 AND METHOD FOR STOPPING POWER CONVERSION APPARATUS
Field
[0001] The present invention relates to a power
conversion apparatus that converts input power into
10 alternating-current power and supplies the alternatingcurrent power to a load, to a vehicle auxiliary power
supply including the power conversion apparatus, and to a
method for stopping the power conversion apparatus.
15 Background
[0002] Patent Literature 1 described below discloses a
vehicle auxiliary power supply configured to convert highvoltage direct-current power input from a pantograph into
alternating-current power by a three-phase inverter, supply
20 the alternating-current power output from the three-phase
inverter to a transformer via an alternating-current
reactor, and convert the alternating-current power into
desired low-voltage alternating-current power by the
transformer.
25 [0003] The vehicle auxiliary power supply supplies power
to an auxiliary load. The auxiliary load refers to a load
other than a main motor among the loads mounted on a
railroad vehicle. Examples of the auxiliary load include a
vehicle interior lighting device, a door opening and
30 closing device, an air conditioner, a safety device, a
compressor, a battery, and a control power supply. The
compressor is a device that generates air source for a
vehicle brake.
3
[0004] A typical vehicle auxiliary power supply includes
an overcurrent detector. The overcurrent detector detects
overcurrent flowing in an auxiliary load circuit. The
auxiliary load circuit is an electrical circuit for
5 supplying power to an auxiliary load from a three-phase
inverter. When the overcurrent detector detects
overcurrent, the vehicle auxiliary power supply performs a
protection operation of stopping operation of the threephase inverter.
10
Citation List
Patent Literature
[0005] Patent Literature 1: Japanese Patent Application
Laid-open No. 2011-211777
15
Summary
Technical Problem
[0006] Because the auxiliary load is mounted on a
railroad vehicle, insulation deterioration of the auxiliary
20 load develops earlier than that of home appliances or the
like. If the insulation deterioration develops, the
current flowing in the auxiliary load circuit becomes
larger than that in the case when the insulation
deterioration has not occurred. Here, the current flowing
25 in the auxiliary load circuit when the insulation
deterioration occurs is referred to as “ground fault
current”. The ground fault current is smaller than the
overcurrent described above. Thus, the ground fault
current rarely reaches a determination value for
30 overcurrent protection; therefore, the insulation
deterioration of the auxiliary load circuit is difficult to
detect with high accuracy. Although it is possible to
lower the determination value for overcurrent protection,
4
the number of false positives in overcurrent protection
increases, which is a practical problem.
[0007] The present invention has been achieved in view
of the above and an object of the present invention is to
5 provide a power conversion apparatus capable of detecting
insulation deterioration of an auxiliary load circuit early
with high accuracy.
Solution to Problem
10 [0008] In order to solve the above problems and achieve
the object, a power conversion apparatus according to the
present invention includes a three-phase inverter to
convert input power to alternating-current power and supply
the alternating-current power obtained by conversion to a
15 load via a filter circuit comprising a three-phase reactor
circuit and a three-phase capacitor circuit. The power
conversion apparatus further includes a voltage detector to
detect three-phase voltages that are voltages at respective
connection points between the three-phase reactor circuit
20 and the three-phase capacitor circuit, and a control device
to control operation of the three-phase inverter on a basis
of the three-phase voltages detected by the voltage
detector. The control device includes a calculation unit
to calculate a zero-phase voltage obtained by adding
25 together the three-phase voltages, a separation unit to
separate an instantaneous value of the zero-phase voltage
into an alternating-current signal and a direct-current
signal, and a first determination unit to determine whether
a ground fault occurs on a basis of an effective value of
30 the alternating-current signal.
Advantageous Effects of Invention
[0009] According to the present invention, an effect is
5
obtained where insulation deterioration of an auxiliary
load circuit can be detected early with high accuracy.
Brief Description of Drawings
5 [0010] FIG. 1 is a diagram illustrating an exemplary
configuration of a vehicle auxiliary power supply according
to an embodiment.
FIG. 2 is a diagram illustrating a first exemplary
configuration of a power supply that generates input power
10 for the three-phase inverter illustrated in FIG. 1.
FIG. 3 is a diagram illustrating a second exemplary
configuration of the power supply that generates input
power for the three-phase inverter illustrated in FIG. 1.
FIG. 4 is a first diagram used for explaining the
15 principle of ground fault detection according to the
present embodiment.
FIG. 5 is a second diagram used for explaining the
principle of ground fault detection according to the
present embodiment.
20 FIG. 6 is a third diagram used for explaining the
principle of ground fault detection according to the
present embodiment.
FIG. 7 is a diagram illustrating an exemplary
configuration of a control device according to the present
25 embodiment.
FIG. 8 is a diagram illustrating an exemplary
configuration of a zero-phase voltage calculation unit
illustrated in FIG. 7.
FIG. 9 is a diagram illustrating an exemplary
30 configuration of a ground fault detection unit illustrated
in FIG. 7.
FIG. 10 is a flowchart illustrating a flow of a
process by the control device in the present embodiment.
6
FIG. 11 is a block diagram illustrating an example of
a hardware configuration when the function of the control
device according to the present embodiment is implemented
by software.
5 FIG. 12 is a block diagram illustrating another
example of a hardware configuration when the function of
the control device according to the present embodiment is
implemented by software.
10 Description of Embodiments
[0011] A power conversion apparatus, a vehicle auxiliary
power supply, and a method for stopping the power
conversion apparatus according to embodiments of the
present invention will be described below in detail with
15 reference to the accompanying drawings. Note that the
embodiments described below are not intended to limit the
present invention. Moreover, the embodiments below will be
described in terms of a power conversion apparatus mounted
on a railroad vehicle as an example; however, this is not
20 intended to exclude applications to other uses. Moreover,
in the following descriptions, electrical connection and
physical connection are not distinguished from each other
and are simply referred to as “connection”.
[0012] Embodiment.
25 FIG. 1 is a diagram illustrating an exemplary
configuration of a vehicle auxiliary power supply 100
according to an embodiment. As illustrated in FIG. 1, the
vehicle auxiliary power supply 100 according to the present
embodiment includes a power conversion apparatus 1 and a
30 filter circuit 2. The power conversion apparatus 1
includes a three-phase inverter 10, a voltage detector 11,
and a control device 12. The three-phase inverter 10 and
an auxiliary load 4 are connected with each other by three
7
electrical wires 5 with the filter circuit 2 therebetween.
The three electrical wires 5 are U-phase, V-phase, and Wphase electrical wires.
[0013] The filter circuit 2 includes a three-phase
5 reactor circuit 21 and a three-phase capacitor circuit 22.
The three-phase reactor circuit 21 includes three reactor
elements. The three-phase capacitor circuit 22 includes
three capacitor elements. Each of the three reactor
elements of the three-phase reactor circuit 21 is inserted
10 into the corresponding U-phase, V-phase, or W-phase
electrical wire 5. One end of each of the three reactor
elements is connected to the three-phase inverter 10. The
other end of each of the three reactor elements is
connected to one end of a corresponding one of the
15 capacitor elements of the three-phase capacitor circuit 22
at a connection point 8a, 8b, or 8c on the electrical wire
5. The other ends of the three capacitor elements are
connected with each other at one point. This connection is
referred to as Y-connection. A connection point 7 that is
20 a connection point in the Y-connection configuration is
grounded via a ground resistor 6. The three-phase reactor
circuit 21 and the three-phase capacitor circuit 22
constitute an LC filter circuit.
[0014] As described above, examples of the auxiliary
25 load 4 include a vehicle interior lighting device, a door
opening and closing device, an air conditioner, a safety
device, a compressor, a battery, and a control power
supply. Of the examples of the auxiliary load 4, a vehicle
interior lighting device, a door opening and closing
30 device, an air conditioner, a safety device, and a
compressor are alternating-current (AC) loads that operate
upon receiving supply of AC power. A battery and a control
power supply are direct-current (DC) loads that operate
8
upon receiving supply of DC power.
[0015] As illustrated in FIG. 1, the voltage detector 11
detects three-phase voltages appearing at the connection
points 8a, 8b, and 8c. In other words, the three-phase
5 voltages are voltages at respective connection points
between the three-phase reactor circuit 21 and the threephase capacitor circuit 22. The result of detection by the
voltage detector 11 is input to the control device 12. The
control device 12 controls operation of the three-phase
10 inverter 10 on the basis of the three-phase voltages
detected by the voltage detector 11.
[0016] In FIG. 1, the voltage detector 11 detects the
voltages at the connection points 8a, 8b, and 8c between
the three-phase reactor circuit 21 and the three-phase
15 capacitor circuit 22; however, the present embodiment is
not limited thereto. Voltage may be detected at points
displaced toward the three-phase reactor circuit 21 or
toward the auxiliary load 4 from the connection points 8a,
8b, and 8c in FIG. 1. In other words, the voltage detector
20 11 may detect voltage at any position that is regarded as
having the same potential as the potential at each
connection point.
[0017] The three-phase inverter 10 converts input power
into AC power and supplies the AC power obtained by the
25 conversion to the auxiliary load 4 via the filter circuit 2
under the control of the control device 12. The filter
circuit 2 reduces harmonics contained in the output voltage
of the three-phase inverter 10. Thus, AC voltage having a
more sinusoidal shape than that when there is no filter
30 circuit 2 is applied to the auxiliary load 4.
[0018] FIG. 2 is a diagram illustrating a first
exemplary configuration of a power supply that generates
input power for the three-phase inverter 10 illustrated in
9
FIG. 1. In the first exemplary configuration illustrated
in FIG. 2, DC power supplied from a DC overhead line 30 is
received via a current collector 31. The DC power received
is converted into AC power by a single-phase inverter 50.
5 The AC power obtained by the conversion is stepped down by
a transformer 52 and is then supplied to a single-phase
converter 61. The AC power stepped down is converted into
DC power by the single-phase converter 61 and is then
supplied to the three-phase inverter 10.
10 [0019] FIG. 3 is a diagram illustrating a second
exemplary configuration of the power supply that generates
input power for the three-phase inverter 10 illustrated in
FIG. 1. In the second exemplary configuration illustrated
in FIG. 3, the DC overhead line 30 is replaced by an AC
15 overhead line 30A and the current collector 31 for DC
overhead line is replaced by a current collector 31A for AC
overhead line. Moreover, comparing the configuration
illustrated in FIG. 3 with the configuration illustrated in
FIG. 2, a transformer 41 and a single-phase converter 42
20 are arranged in this order between the current collector
31A and the single-phase inverter 50 in FIG. 3. The AC
power supplied from the AC overhead line 30A is received by
the transformer 41 via the current collector 31A. The AC
power received is stepped down by the transformer 41 and is
25 then supplied to the single-phase converter 42. The AC
power stepped down is converted into DC power by the
single-phase converter 42 and is then supplied to the
single-phase inverter 50. The subsequent operations are
the same as those in FIG. 2. Although the single-phase
30 inverter 50, the transformer 52, and the single-phase
converter 61 that are common components are each denoted by
the same reference numeral in FIG. 2 and FIG. 3, it is
needless to say that the capacity or a system of each
10
component is different depending on the difference in
overhead line voltage.
[0020] FIG. 4 is a first diagram used for explaining the
principle of ground fault detection according to the
5 present embodiment. FIG. 5 is a second diagram used for
explaining the principle of ground fault detection
according to the present embodiment. FIG. 4 is an example
of a case where the auxiliary load 4 connected to the
vehicle auxiliary power supply 100 in FIG. 1 is an AC load
10 4A. In FIG. 4, an example is illustrated where insulation
of a W-phase electrical wire deteriorates and a W-phase
ground fault has occurred. In FIG. 5, the phase relation
between three-phase voltages Vu, Vv, and Vw output from the
three-phase inverter 10 is represented by vectors. In this
15 specification, a ground fault that occurs when the
auxiliary load 4 is the AC load 4A is referred to as “AC
ground fault”.
[0021] When there is no ground fault, as illustrated in
FIG. 5, the three-phase voltages Vu, Vv, and Vw have such a
20 phase relation that they are 120° out of phase with each
other. When the three-phase voltages have such a phase
relation that they are 120° out of phase with each other,
the sum of the three-phase voltages Vu, Vv, and Vw
indicating a zero-phase voltage, or zero-sequence voltage,
25 is zero. That is, there is a relation Vu+Vv+Vw=0.
[0022] The connection point 7 is a point of
interconnection and thus has a common potential. Thus, the
three-phase voltages Vu, Vv, and Vw are applied to the
respective capacitors of the three-phase capacitor circuit
30 22. This means that when there is no ground fault, a zerophase voltage does not appear at the connection point 7.
In contrast, when an AC ground fault has occurred, the
value of the zero-phase voltage Vu+Vv+Vw does not become
11
zero and the zero-phase voltage that changes with a period
of three-phase voltage as illustrated in a broken-line
frame in FIG. 4 appears at the connection point 7.
[0023] FIG. 6 is a third diagram used for explaining the
5 principle of ground fault detection according to the
present embodiment. FIG. 6 is an example of a case where
the auxiliary load 4 connected to the vehicle auxiliary
power supply 100 in FIG. 1 is a DC load 4B. The DC load 4B
is connected to the electrical wires 5 via a rectifier 9.
10 In FIG. 6, an example is illustrated where insulation of
the electrical wires provided between the rectifier 9 and
the DC load 4B deteriorates and a ground fault has occurred
in one of the electrical wires. In this specification, a
ground fault that occurs when the auxiliary load 4 is the
15 DC load 4B is referred to as “DC ground fault”. In the
case of the DC ground fault as well, voltage appears at the
connection point 7 in a similar manner to the case of the
AC ground fault. Note that, voltage that appears in the
case of the DC ground fault is DC voltage.
20 [0024] Next, a description will be given of
configuration and operation of the control device 12
according to the present embodiment. FIG. 7 is a diagram
illustrating an exemplary configuration of the control
device 12 according to the present embodiment. As
25 illustrated in FIG. 7, the control device 12 in the present
embodiment includes a zero-phase voltage calculation unit
121 and a ground fault detection unit 122. FIG. 8 is a
diagram illustrating an exemplary configuration of the
zero-phase voltage calculation unit 121 illustrated in FIG.
30 7. As illustrated in FIG. 8, the zero-phase voltage
calculation unit 121 includes an adder 121a. In the
following descriptions, the zero-phase voltage calculation
unit 121 is in some cases simply referred to as
12
“calculation unit”.
[0025] The three-phase voltages Vu, Vv, and Vw detected
by the voltage detector 11 are input to the zero-phase
voltage calculation unit 121. The adder 121a adds together
5 the three-phase voltages Vu, Vv, and Vw to calculate a
zero-phase voltage V0. The zero-phase voltage V0
calculated is output to the ground fault detection unit
122.
[0026] FIG. 9 is a diagram illustrating an exemplary
10 configuration of the ground fault detection unit 122
illustrated in FIG. 7. As illustrated in FIG. 9, the
ground fault detection unit 122 includes an AC/DC
separation unit 122a, an effective value calculation unit
122b, an absolute value calculation unit 122c, comparators
15 122d, 122e, and 122g, an AND operation unit 122f, and an OR
operation unit 122h. In the following descriptions, the
AC/DC separation unit 122a is in some cases simply referred
to as “separation unit”.
[0027] The zero-phase voltage V0 calculated by the zero20 phase voltage calculation unit 121 is input to the AC/DC
separation unit 122a. The AC/DC separation unit 122a
separates the instantaneous value of the zero-phase voltage
V0 into an AC component and a DC component. The AC
component of the signal separated by the AC/DC separation
25 unit 122a is referred to as AC signal and is denoted by
“a1”. The DC component of the signal separated by the
AC/DC separation unit 122a is referred to as DC signal and
is denoted by “d1”. The AC signal a1 can be generated by a
high-pass filtering process, a band-pass filtering process,
30 or the like. The DC signal d1 can be generated by a lowpass filtering process or the like. The AC signal a1 is
input to the effective value calculation unit 122b and the
comparator 122e. The DC signal d1 is input to the absolute
13
value calculation unit 122c.
[0028] The effective value calculation unit 122b
calculates an effective value a2 of the AC signal a1. The
effective value a2 calculated is input to the comparator
5 122d. The comparator 122d compares the effective value a2
with a determination value 1, and outputs a comparison
result a3 thereof. The comparison result a3 is a logical
value. When the effective value a2 is larger than the
determination value 1, logic “1” is output. When the
10 effective value a2 is smaller than or equal to the
determination value 1, logic “0” is output.
[0029] In the present embodiment, the effective value
calculation unit 122b and the comparator 122d constitute a
first determination unit. With the function described
15 above, the first determination unit can determine whether
an AC ground fault that may occur on the power supply path
to the AC load 4A has occurred.
[0030] The absolute value calculation unit 122c
calculates an absolute value d2 of the DC signal d1. The
20 absolute value d2 is input to the comparator 122g. The
comparator 122g compares the absolute value d2 with a
determination value 2, and outputs a comparison result d3
thereof. The comparison result d3 is a logical value.
When the absolute value d2 is larger than the determination
25 value 2, logic “1” is output. When the absolute value d2
is smaller than or equal to the determination value 2,
logic “0” is output.
[0031] In the present embodiment, the absolute value
calculation unit 122c and the comparator 122g constitute a
30 second determination unit. With the function described
above, the second determination unit can determine whether
a DC ground fault that may occur on the power supply path
to the DC load 4B has occurred.
14
[0032] The comparator 122e compares the AC signal a1
with a determination value 3, and outputs a comparison
result a4 thereof. The comparison result a4 is a logical
value. When the AC signal a1 is larger than the
5 determination value 3, logic “1” is output. When the AC
signal a1 is smaller than or equal to the determination
value 3, logic “0” is output. The determination value 3 is
a determination value for detecting an instantaneous-value
zero point illustrated in FIG. 4.
10 [0033] The comparison result a3 from the comparator 122d
and the comparison result a4 from the comparator 122e are
input to the AND operation unit 122f. The AND operation
unit 122f performs an AND operation on the comparison
results a3 and a4. When both the comparison results a3 and
15 a4 are logic “1”, logic “1” is output. In contrast, when
at least one of the comparison results a3 and a4 is logic
“0”, logic “0” is output.
[0034] A calculation result a5 from the AND operation
unit 122f and the comparison result d3 from the comparator
20 122g are input to the OR operation unit 122h. The OR
operation unit 122h performs an OR operation S1 on the
calculation result a5 and the comparison result d3. When
at least one of the calculation result a5 and the
comparison result d3 is logic “1”, logic “1” is output. In
25 contrast, when both the calculation result a5 and the
comparison result d3 are logic “0”, logic “0” is output.
[0035] In the present embodiment, the comparator 122e
and the AND operation unit 122f constitute a zero-point
detection unit. The zero-point detection unit can detect a
30 zero point of the zero-phase voltage in the AC ground fault
on the basis of the instantaneous value of the zero-phase
voltage. With the function of the zero-point detection
unit and the function of the first determination unit, when
15
the first determination unit determines that a ground fault
has occurred, the control device 12 can stop the operation
of the three-phase inverter 10 at the timing when a zero
point is detected by the zero-point detection unit.
5 [0036] Next, a description will be given of a mode of
control by the control device 12 according to the first
embodiment. First, the control device 12 monitors the
zero-phase voltage calculated by using three-phase voltages
that are voltages at the respective connection points
10 between the three-phase reactor circuit 21 and the threephase capacitor circuit 22. In the auxiliary load circuit,
when an AC ground fault occurs, the zero-phase voltage is
generated. With the use of this principle, the control
device 12 performs a threshold-based determination on the
15 effective value of the AC component of the zero-phase
voltage, and determines that an AC ground fault has
occurred when the effective value is larger than the
threshold value.
[0037] The auxiliary load 4 connected to the vehicle
20 auxiliary power supply 100 is generally an AC load but may
be a DC load. As a method for determining the occurrence
of a DC ground fault, it is possible to use a control
circuit for determining the occurrence of an AC ground
fault. This method however has trouble with accuracy of
25 the determination. Thus, a control circuit for determining
the occurrence of a DC ground fault is separately provided.
In the auxiliary load circuit including a DC load, when a
DC ground fault has occurred, the zero-phase voltage is
generated in a similar manner to the case of an AC ground
30 fault. The control device 12 performs a threshold-based
determination on the absolute value of the DC component of
the zero-phase voltage, and determines that a DC ground
fault has occurred when the absolute value is larger than
16
the threshold value.
[0038] When an AC ground fault or a DC ground fault has
occurred, the control device 12 stops the operation of the
vehicle auxiliary power supply 100 and stops supplying
5 power to the auxiliary load 4. In this case, the voltage
in the case of three-phase imbalance may remain in the
three-phase capacitor circuit 22 as a residual voltage
depending on the timing of stopping the operation of the
vehicle auxiliary power supply 100. The residual voltage
10 may adversely affect the operation of the auxiliary load 4
when the vehicle auxiliary power supply 100 is restarted.
Thus, the timing of stopping the operation of the vehicle
auxiliary power supply 100 is controlled such that the
residual voltage is as close to zero as possible.
15 Specifically, as described above, the control device 12
stops the operation of the three-phase inverter 10 at the
timing when a zero point of the zero-phase voltage is
detected. With this control, the residual voltage of the
three-phase capacitor circuit 22 is in the same state as
20 that in the case of three-phase equilibrium; therefore, the
residual voltage can be controlled such that it has a value
close to zero.
[0039] FIG. 8 and FIG. 9 are examples of a case when the
functions of the zero-phase voltage calculation unit 121
25 and the ground fault detection unit 122 illustrated in FIG.
7 are implemented by a control circuit; however, the
present embodiment is not limited to these examples. The
function of the control device 12 according to the present
embodiment can be represented in the form of a flowchart.
30 FIG. 10 is a flowchart illustrating a flow of a process by
the control device 12 in the present embodiment.
[0040] The control device 12 calculates a zero-phase
voltage (step S101). The control device 12 separates the
17
zero-phase voltage into an AC signal that is a signal train
of the AC component and a DC signal that is a signal train
of the DC component by using calculation data of the zerophase voltage for at least one or more periods (step S102).
5 The AC signal is used in the process in step S103 and the
subsequent steps and the DC signal is used in the process
in step 105 and the subsequent steps. These processes are
performed concurrently under the control of the control
device 12.
10 [0041] (Process for AC signal)
The control device 12 calculates the effective value
of the AC signal (step S103). The control device 12
compares the effective value calculated in step S103 with
the determination value 1 (step S104). When the effective
15 value is smaller than the determination value 1 (No in step
S104), the process returns to step S101. Thereafter, the
process from step S101 is repeated. When the effective
value is larger than or equal to the determination value 1
(Yes in step S104), the control device 12 detects a zero
20 point of the zero-phase voltage (step S107). Then, the
control device 12 stops the operation of the vehicle
auxiliary power supply 100 at the timing when the zero
point of the zero-phase voltage is detected (step S108) and
ends the process flow in FIG. 10.
25 [0042] In the process in step S104 described above,
“Yes” is determined when the effective value is equal to
the determination value 1, but “No” may be determined in
such a case. That is, either “Yes” or “No” may be
determined when the effective value is equal to the
30 determination value 1.
[0043] (Process for DC signal)
The control device 12 calculates the absolute value of
the DC signal (step S105). The control device 12 compares
18
the absolute value calculated in step S105 with the
determination value 3 (step S106). When the absolute value
is smaller than the determination value 3 (No in step
S106), the process returns to step S101. Thereafter, the
5 process from step S101 is repeated. When the absolute
value is larger than or equal to the determination value 3
(Yes in step S106), the control device 12 immediately stops
the operation of the vehicle auxiliary power supply 100
(step S108) and ends the process flow in FIG. 10. In the
10 case of the DC signal, a voltage zero point is not
generated. Thus, the operation of the vehicle auxiliary
power supply 100 is immediately stopped unlike the process
in the case of the AC signal.
[0044] In the process in step S106 described above,
15 “Yes” is determined when the absolute value is equal to the
determination value 3, but “No” may be determined in such a
case. That is, either “Yes” or “No” may be determined when
the absolute value is equal to the determination value 3.
[0045] In the following descriptions, in some cases, the
20 process in step S101 is referred to as “calculation step”
and the process in step S102 is referred to as “separation
step”. Moreover, in some cases, the process in step S104
is referred to as “first determination step” and the
process in step S106 is referred to as “second
25 determination step”. Moreover, in some cases, the process
in step S107 is referred to as “zero point detection step”
and the process in step S108 is referred to as “stopping
step”.
[0046] Next, a description will be given of a hardware
30 configuration for implementing the function of the control
device 12 according to the present embodiment by software
with reference to FIG. 11 and FIG. 12. FIG. 11 is a block
diagram illustrating an example of a hardware configuration
19
when the function of the control device 12 according to the
present embodiment is implemented by software. FIG. 12 is
a block diagram illustrating another example of a hardware
configuration when the function of the control device 12
5 according to the present embodiment is implemented by
software.
[0047] In the case where the functions of the zero-phase
voltage calculation unit 121 and the ground fault detection
unit 122 in the control device 12 described above are
10 implemented by software, as illustrated in FIG. 11, the
configuration may be such that a processor 300 that
performs an arithmetic operation, a memory 302 that saves
programs to be read by the processor 300, and an interface
304 that inputs and outputs signals are included.
15 [0048] The processor 300 may be arithmetic means such as
an arithmetic unit, a microprocessor, a microcomputer, a
central processing unit (CPU), or a digital signal
processor (DSP). The memory 302 can be exemplified by a
non-volatile or volatile semiconductor memory such as a
20 random access memory (RAM), a read only memory (ROM), a
flash memory, an erasable programmable ROM (EPROM), or an
electrically EPROM (EEPROM (registered trademark)), a
magnetic disk, a flexible disk, an optical disk, a compact
disc, a mini disc, and a digital versatile disc (DVD).
25 [0049] The memory 302 stores a program for implementing
the functions of the zero-phase voltage calculation unit
121 and the ground fault detection unit 122. The processor
300 exchanges necessary information via the interface 304
and executes the program stored in the memory 302, thereby
30 enabling the functions of the zero-phase voltage
calculation unit 121 and the ground fault detection unit
122 described above to be executed.
[0050] The processor 300 and the memory 302 illustrated
20
in FIG. 11 may be replaced by processing circuitry 303 as
illustrated in FIG. 12. The processing circuitry 303
corresponds to a single circuit, a composite circuit, an
application specific integrated circuit (ASIC), a field5 programmable gate array (FPGA), or a combination thereof.
[0051] As described above, according to the present
embodiment, the control device calculates a zero-phase
voltage obtained by adding together three-phase voltages
that are voltages at respective connection points between
10 the three-phase reactor circuit and the three-phase
capacitor circuit. The control device then separates the
instantaneous value of the zero-phase voltage calculated
into an AC signal and a DC signal and determines whether a
ground fault has occurred on the basis of the effective
15 value of the AC signal separated. The ground fault current
flowing in the auxiliary load circuit when insulation
deterioration has occurred is small. Thus, with the method
of directly detecting the ground fault current, it is
difficult to detect whether a ground fault has occurred
20 with high accuracy. In contrast, the present embodiment
applies a method in which three-phase voltages are used
that are voltages at respective connection points between
the three-phase reactor circuit and the three-phase
capacitor circuit. With this method, the accuracy of
25 detecting a ground fault can be improved compared with the
method of directly detecting the ground fault current.
Therefore, insulation deterioration of the auxiliary load
circuit can be detected with high accuracy.
[0052] Moreover, according to the present embodiment,
30 the control device determines whether a ground fault has
occurred by using a determination logic different from
overcurrent protection. Thus, it is possible to use a
determination value different from overcurrent protection
21
and specialized for the determination of whether a ground
fault has occurred. Therefore, insulation deterioration of
the auxiliary load circuit can be detected early.
[0053] Moreover, according to the present embodiment,
5 the control device detects a zero point of the zero-phase
voltage on the basis of the instantaneous value of the
zero-phase voltage. When an AC ground fault is detected,
the control device performs control of stopping the
operation of the three-phase inverter at the timing when
10 the zero point of the zero-phase voltage is detected. With
this control, the residual voltage of the three-phase
capacitor circuit can be controlled such that it becomes a
value close to zero. Therefore, the adverse effect on the
operation of the auxiliary load when the vehicle auxiliary
15 power supply is restarted can be reduced.
[0054] The configurations described in the abovementioned embodiments are merely examples of the content of
the present invention. These configurations can be
combined with another known technology, and moreover, a
20 part of such configurations can be omitted and/or modified
without departing from the scope of the present invention.
[0055] For example, FIG. 1 illustrates the exemplary
configuration in which the connection point 7 of the threephase capacitor circuit 22 is grounded via the ground
25 resistor 6; however, the present embodiment is not limited
to this configuration. If the resistance value of the
electrical wires for grounding the connection point 7
satisfies the electrical equipment technical standards, the
connection point 7 may be grounded without passing through
30 the ground resistor 6.
[0056] Moreover, although FIG. 1 illustrates the example
configuration in which the three capacitor elements of the
three-phase capacitor circuit 22 are star-connected, the
22
present embodiment is not limited to this configuration.
The three capacitor elements may be delta-connected. When
the three capacitor elements are delta-connected, the
typical configuration is such that the three-phase inverter
5 10 and the three-phase capacitor circuit 22 are connected
via a Δ-Y transformer. In the case of this configuration,
the midpoint of the secondary-side coil of a transformer
(not illustrated) is grounded. Therefore, the voltage of
the midpoint of the secondary-side coil can be detected and
10 the method according to the present embodiment described
above can be applied.
Reference Signs List
[0057] 1 power conversion apparatus; 2 filter circuit;
15 4 auxiliary load; 4A AC load; 4B DC load; 5 electrical
wire; 6 ground resistor; 7, 8a, 8b, 8c connection point;
9 rectifier; 10 three-phase inverter; 11 voltage
detector; 12 control device; 21 three-phase reactor
circuit; 22 three-phase capacitor circuit; 30 DC overhead
20 line; 30A AC overhead line; 31, 31A current collector;
41, 52 transformer; 42, 61 single-phase converter; 50
single-phase inverter; 100 vehicle auxiliary power supply;
121 zero-phase voltage calculation unit; 121a adder; 122
ground fault detection unit; 122a AC/DC separation unit;
25 122b effective value calculation unit; 122c absolute
value calculation unit; 122d, 122e, 122g comparator; 122f
AND operation unit; 122h OR operation unit; 300
processor; 302 memory; 303 processing circuitry;
interface.

We Claim :
1. A power conversion apparatus comprising:
a three-phase inverter to convert input power to
alternating-current power and supply the alternating5 current power obtained by conversion to a load via a filter
circuit comprising a three-phase reactor circuit and a
three-phase capacitor circuit;
a voltage detector to detect three-phase voltages that
are voltages at respective connection points between the
10 three-phase reactor circuit and the three-phase capacitor
circuit; and
a control device to control operation of the threephase inverter on a basis of the three-phase voltages
detected by the voltage detector, wherein
15 the control device comprises
a calculation unit to calculate a zero-phase
voltage obtained by adding together the three-phase
voltages,
a separation unit to separate an instantaneous
20 value of the zero-phase voltage into an alternating-current
signal and a direct-current signal, and
a first determination unit to determine whether a
ground fault occurs on a basis of an effective value of the
alternating-current signal.
25
2. The power conversion apparatus according to claim 1,
comprising a second determination unit to determine whether
a ground fault occurs on a basis of the direct-current
signal.
30
3. The power conversion apparatus according to claim 2,
wherein
the load is an alternating-current load to operate
24
upon receiving supply of alternating-current power and a
direct-current load to operate upon receiving supply of
direct-current power,
the first determination unit determines whether an
5 alternating-current ground fault that possibly occurs on a
power supply path to the alternating-current load occurs,
and
the second determination unit determines whether a
direct-current ground fault that possibly occurs on a power
10 supply path to the direct-current load occurs.
4. The power conversion apparatus according to any one of
claims 1 to 3, wherein
the control device includes a zero-point detection
15 unit to detect a zero point of the zero-phase voltage on a
basis of an instantaneous value of the zero-phase voltage,
and
when the first determination unit determines that a
ground fault occurs, the control device stops operation of
20 the three-phase inverter at a timing when the zero point is
detected by the zero-point detection unit.
5. A vehicle auxiliary power supply comprising:
the power conversion apparatus according to any one of
25 claims 1 to 4; and
the filter circuit, wherein
the vehicle auxiliary power supply is mounted on a
railroad vehicle, and uses direct-current power or
alternating-current power supplied from an overhead line to
30 supply the alternating-current power to an auxiliary load
that is the load other than a main motor.
6. A method for stopping a power conversion apparatus
25
comprising a three-phase inverter to convert input power to
alternating-current power and supply the alternatingcurrent power obtained by conversion to a load via a filter
circuit comprising a three-phase reactor circuit and a
5 three-phase capacitor circuit, and a voltage detector to
detect three-phase voltages that are voltages at respective
connection points between the three-phase reactor circuit
and the three-phase capacitor circuit, the method
comprising:
10 a calculation step of calculating a zero-phase voltage
obtained by adding together the three-phase voltages;
a separation step of separating an instantaneous value
of the zero-phase voltage into an alternating-current
signal and a direct-current signal;
15 a first determination step of determining whether a
ground fault occurs on a basis of an effective value of the
alternating-current signal;
a zero-point detection step of detecting a zero point
of the zero-phase voltage on a basis of an instantaneous
20 value of the zero-phase voltage; and
a stopping step of, when it is determined in the first
determination step that a ground fault occurs, stopping
operation of the three-phase inverter at a timing when the
zero point is detected in the zero-point detection step.
25
7. The method for stopping a power conversion apparatus
according to claim 6, further comprising
a second determination step of determining whether a
ground fault occurs on a basis of an absolute value of the
30 direct-current signal, wherein
when it is determined in the second determination step
that a ground fault occurs, the stopping step includes
performing a process of stopping operation of the three-
26
phase inverter regardless of whether the zero point is
detected in the zero-point detection step.