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 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. 2

DESCRIPTION
Technical Field
[0001] The present disclosure relates to a power conversion apparatus.
Background Art
[0002] Some electric railway vehicles are provided with power conversion 5 apparatuses to convert DC power fed from a substation via an overhead wire into desired AC power and feed the converted power to a motor. An example of this type of power conversion apparatus is disclosed in Patent Literature 1. This power conversion apparatus includes a power converter, a filter capacitor of which both ends are connected to the primary terminals of the power converter, a discharging circuit including a 10 discharging resistor to discharge the filter capacitor, and a charging resistor to suppress inrush current during charging of the filter capacitor.
Citation List
Patent Literature
[0003] Patent Literature 1: Unexamined Japanese Patent Application Publication 15 No. 2015-050854
Summary of Invention
Technical Problem
[0004] Some electric railway vehicles are capable of braking in a dynamic braking system in addition to a mechanical brake. In order to enable the power conversion 20 apparatus disclosed in Patent Literature 1 to brake an electric railway vehicle in the dynamic braking system, the power conversion apparatus is required to include a circuit to consume electric power fed from a motor serving as an electric generator. In detail, the power conversion apparatus is required to further include a braking chopper circuit including a switching element and a braking resistor connected in series to each other. 25 The power conversion apparatus includes the discharging resistor, the charging resistor, and the braking resistor, as described above. That is, the power conversion apparatus 3

that enables braking the electric railway vehicle in the dynamic braking system includes multiple resistors dedicated to individual functions, and therefore has a complicated structure and a large size. This problem can occur in any power conversion apparatus that needs multiple resistors dedicated to individual functions.
[0005] An objective of the present disclosure, which has been accomplished in 5 view of the above situations, is to provide a power conversion apparatus having a simple structure.
Solution to Problem
[0006] In order to achieve the above objective, a power conversion apparatus according to an aspect of the present disclosure includes a filter capacitor, a power 10 converter, a circuit switcher, a chopper circuit, and a discharge switch. The filter capacitor is charged with DC power fed from a power source. The power converter has a pair of primary terminals between which the filter capacitor is connected and secondary terminals. The power converter converts the DC power fed from the power source via the filter capacitor into DC power or AC power and feeds the converted power to a motor 15 connected to the secondary terminals. The power converter converts DC power or AC power fed from the motor serving as an electric generator into DC power, outputs the converted DC power, and charges the filter capacitor. The circuit switcher includes a first resistor. The circuit switcher electrically connects the power converter and the filter capacitor to the power source or electrically disconnects the power converter and the filter 20 capacitor from the power source. The chopper circuit includes a switching element and a second resistor connected in series to each other. The chopper circuit has both ends connected between the primary terminals of the power converter. The discharge switch has one end connected to one end of the first resistor closer to the power source, and the other end connected to the point of connection between the switching element and the 25 second resistor. In order to charge the filter capacitor with the DC power fed from the power source, the circuit switcher electrically connects the power converter and the filter 4

capacitor to the power source via an electrical path passing through the first resistor. When the switching element is turned on, the chopper circuit causes the second resistor to consume the DC power fed from the power converter via the filter capacitor. The discharge switch when turned on connects the first resistor and the second resistor in series to each other and electrically connects the filter capacitor to the first resistor and the 5 second resistor connected in series to each other, thereby causing discharge of the filter capacitor.
Advantageous Effects of Invention
[0007] The power conversion apparatus according to an aspect of the present disclosure discharges the filter capacitor by connecting the first resistor and the second 10 resistor in series to each other and electrically connecting the filter capacitor to the serially connected first resistor and second resistor. The power conversion apparatus is thus not required to include a resistor dedicated to discharge of the filter capacitor. This power conversion apparatus therefore has a simple structure.
Brief Description of Drawings 15
[0008] FIG. 1 is a block diagram illustrating a power conversion apparatus according to Embodiment 1;
FIG. 2 illustrates an exemplary manner of installation of the power conversion apparatus according to Embodiment 1 in a railway vehicle;
FIG. 3 is a block diagram illustrating a power conversion apparatus according to 20 Embodiment 2;
FIG. 4 is a flowchart of an operation of determining the existence of a short-circuit fault performed by the power conversion apparatus according to Embodiment 2;
FIG. 5 is a block diagram illustrating a first modification of the power conversion apparatus according to the embodiments; and 25
FIG. 6 is a block diagram illustrating a second modification of the power conversion apparatus according to the embodiments. 5

Description of Embodiments
[0009] A power conversion apparatus according to embodiments of the present disclosure is described in detail below with reference to the accompanying drawings. In the drawings, the components identical or corresponding to each other are provided with the same reference symbol. 5
[0010] Embodiment 1
A power conversion apparatus 1 according to Embodiment 1 is described below focusing on an exemplary power conversion apparatus installed in a vehicle.
The power conversion apparatus 1 illustrated in FIG. 1 has a positive input terminal 1a to be connected to a power source, and a negative input terminal 1b to be 10 grounded. The power conversion apparatus 1 converts DC power fed from the power source via the positive input terminal 1a into three-phase AC power for driving a motor 51, and feeds the three-phase AC power via the output terminals to the motor 51. A typical example of the motor 51 is a three-phase induction motor. The three-phase AC power fed from the power conversion apparatus 1 to the motor 51 drives the motor 51, 15 thereby providing the thrust of the vehicle. The power conversion apparatus 1 also converts three-phase AC power generated at the motor 51, which serves as an electric generator during braking of the vehicle, into DC power and causes a second resistor BR (described below) to consume the DC power. This operation provides a braking force to decelerate the vehicle. 20
[0011] The power conversion apparatus 1 is described in more detail below focusing on an exemplary power conversion apparatus 1 installed in an electric railway vehicle of a DC feeding system. As illustrated in FIG. 2, a current collector 52 acquires DC power from a substation via an overhead wire 53, and feeds the electric power via a high-speed circuit breaker 54 to the power conversion apparatus 1. The current 25 collector 52 corresponds to the power source to feed electric power to the power conversion apparatus 1. The high-speed circuit breaker 54 is controlled by a circuit 6

breaker controller, which is not illustrated, and thus electrically connects the power conversion apparatus 1 to the current collector 52 or electrically disconnects the power conversion apparatus 1 from the current collector 52.
[0012] The power conversion apparatus 1 includes a power converter 11 having a pair of primary terminals 11a and 11b to convert DC power fed from the current collector 5 52 via the primary terminal 11a into three-phase AC power and feed the converted power to the motor 51, a filter capacitor FC1 of which both ends are connected to the respective primary terminals 11a and 11b of the power converter 11 and which is charged with DC power fed from the current collector 52, and a circuit switcher 12 to electrically connect the power converter 11 and the filter capacitor FC1 to the current collector 52 or 10 electrically disconnect the power converter 11 and the filter capacitor FC1 from the current collector 52.
[0013] The power conversion apparatus 1 further includes a chopper circuit 13 of which both ends are connected to the respective primary terminals 11a and 11b of the power converter 11 and which consumes electric power generated at the motor 51, which 15 serves as an electric generator during braking of the electric railway vehicle. The power conversion apparatus 1 also includes a discharge switch SW1 to connect a first resistor CHR (described below) included in the circuit switcher 12 and the second resistor BR (described below) included in the chopper circuit 13 in series and electrically connect the filter capacitor FC1 to the serially connected first resistor CHR and second resistor BR, 20 thereby causing discharge of the filter capacitor FC1. The power conversion apparatus 1 further includes a voltage measurer 14 to measure a value of the voltage at the capacitor FC1.
[0014] The power conversion apparatus 1 also includes a contactor controller 15 to control the circuit switcher 12, specifically, control switching of electrical paths of the 25 circuit switcher 12, a switching controller 16 to control the power converter 11, and a chopper controller 17 to control the chopper circuit 13. 7

[0015] The power conversion apparatus 1 discharges the filter capacitor FC1 by means of the first resistor CHR and the second resistor BR, and consumes the electric power fed from the motor 51, which serves as an electric generator during braking of the electric railway vehicle, by means of the second resistor BR. That is, the power conversion apparatus 1 is not required to include all of a resistor to be used in charging of 5 the filter capacitor FC1, a resistor to be used in discharging of the filter capacitor FC1, and a resistor to be used in consumption of electric power fed from the motor 51, which serves as an electric generator during braking of the electric railway vehicle. The power conversion apparatus 1 can thus have a reduced size. The following description is directed to the detailed structure of the power conversion apparatus 1. 10
[0016] The power converter 11 converts DC power fed via the primary terminal 11a into three-phase AC power, and feeds the three-phase AC power to the motor 51 connected to the secondary terminals. The power converter 11 also converts three-phase AC power fed from the motor 51 into DC power, and outputs the converted DC power via the primary terminal 11a. A typical example of the power converter 11 is 15 a variable voltage variable frequency (VVVF) inverter.
[0017] The filter capacitor FC1 is connected between the primary terminals 11a and 11b of the power converter 11, and charged with electric power acquired by the current collector 52 via the overhead wire 53.
[0018] The circuit switcher 12 includes the first resistor CHR, and electrically 20 connects the power converter 11 to the current collector 52 via the electrical path passing through the first resistor CHR in order to charge the filter capacitor FC1. This configuration can suppress inrush current from flowing to the filter capacitor FC1 during charging of the filter capacitor FC1. In other words, the first resistor CHR functions as a charging resistor to suppress inrush current from flowing to the filter capacitor FC1 25 during charging. The first resistor CHR may have any resistance provided that the first resistor CHR can suppress inrush current, and a resistance of several tens of ohms, for 8

example.
[0019] In detail, the circuit switcher 12 includes the first resistor CHR, a contactor MC1 serving as a first contactor of which one end is connected to the current collector 52 via the high-speed circuit breaker 54 and which is disposed in parallel to the first resistor CHR, and a contactor MC2 serving as a second contactor of which one end is connected 5 to the current collector 52 via the high-speed circuit breaker 54 and the other end is connected to one end of the first resistor CHR.
[0020] Specifically, the one end of the first resistor CHR is connected to the contactor MC2, and the other end is connected to the primary terminal 11a of the power converter 11. 10
[0021] The one end of the contactor MC1 is connected to the high-speed circuit breaker 54, and the other end is connected to the primary terminal 11a of the power converter 11. The contactor MC1 is a DC electromagnetic contactor and is controlled by the contactor controller 15. When the contactor controller 15 closes the contactor MC1, the one and the other ends of the contactor MC1 are connected to each other. 15 When the contactor MC1 is closed in the closed state of the high-speed circuit breaker 54, the power converter 11 and the filter capacitor FC1 are electrically connected to the current collector 52.
When the contactor controller 15 opens the contactor MC1, the one and the other ends of the contactor MC1 are insulated from each other. When the contactor controller 20 15 opens the contactor MC1 in the open state of the contactor MC2, the power converter 11 and the filter capacitor FC1 are electrically disconnected from the current collector 52.
[0022] The one end of the contactor MC2 is connected to the high-speed circuit breaker 54, and the other end is connected to the one end of the first resistor CHR. The contactor MC2 is a DC electromagnetic contactor and is controlled by the contactor 25 controller 15. When the contactor controller 15 closes the contactor MC2, the one and the other ends of the contactor MC2 are connected to each other. The high-speed circuit 9

breaker 54 and the first resistor CHR are thus electrically connected to each other. When the contactor MC2 is closed in the closed state of the high-speed circuit breaker 54, the power converter 11 and the filter capacitor FC1 are electrically connected to the current collector 52.
When the contactor controller 15 opens the contactor MC2, the one and the other 5 ends of the contactor MC2 are insulated from each other. The first resistor CHR is thus electrically disconnected from the high-speed circuit breaker 54.
[0023] The chopper circuit 13 includes a switching element SW2 and the second resistor BR connected in series to each other. The chopper circuit 13 in the turned-on state causes the second resistor BR to consume DC power fed from the power converter 10 11 via the filter capacitor FC1. In other words, the chopper circuit 13 functions as a braking chopper that enables braking the vehicle in a dynamic braking system, and the second resistor BR functions as a braking resistor.
[0024] The switching element SW2 is an element capable of high-speed switching and is an insulated gate bipolar transistor (IGBT), for example. In this case, the 15 collector terminal of the switching element SW2 is connected to the point of connection between the other end of the contactor MC1 and the primary terminal 11a of the power converter 11, and the emitter terminal is connected to one end of the second resistor BR. The gate terminal receives a chopper control signal S3 from the chopper controller 17, which is described below. 20
The one end of the second resistor BR is connected to the emitter terminal of the switching element SW2, and the other end is grounded. When the switching element SW2 is turned on, the filter capacitor FC1 is connected to the second resistor BR. Accordingly, the second resistor BR consumes DC power fed from the motor 51 serving as an electric generator, converted at the power converter 11, and then fed via the filter 25 capacitor FC1. The second resistor BR has any resistance provided that the second resistor BR can generate a braking force in the electric railway vehicle by consuming DC 10

power fed via the filter capacitor FC1, and a resistance of several ohms, for example.
[0025] One end of the discharge switch SW1 is connected to the one end of the first resistor CHR closer to the power source, in detail, to the point of connection between the contactor MC2 and the first resistor CHR. The other end of the discharge switch SW1 is connected to the point of connection between the switching element SW2 and the 5 second resistor BR. The discharge switch SW1 is a knife switch. The discharge switch SW1 is turned on or off when a maintenance worker responsible for maintenance of the power conversion apparatus 1 mechanically manipulates the discharge switch SW1.
[0026] In detail, the maintenance worker turns on the discharge switch SW1 in the 10 open states of both of the contactors MC1 and MC2. When the discharge switch SW1 is turned on, both ends of the discharge switch SW1 are electrically connected to each other, so that the first resistor CHR and the second resistor BR are connected in series to each other. The filter capacitor FC1 is thus electrically connected to the serially connected first resistor CHR and second resistor BR. The filter capacitor FC1 is 15 therefore discharged by the serially connected first resistor CHR and second resistor BR. When the discharge switch SW1 is turned off, both ends of the discharge switch SW1 are insulated from each other.
[0027] The voltage measurer 14 is connected to the primary terminals 11a and 11b of the power converter 11, and measures a value of the voltage between the terminals of 20 the filter capacitor FC1. The voltage measurer 14 then provides a signal indicating the measured voltage value to the contactor controller 15, the switching controller 16, and the chopper controller 17.
[0028] The contactor controller 15 is provided with an opening/closing instruction signal for instructing closing or opening of the contactors MC1 and MC2 from a cab, 25 which is not illustrated. The contactor controller 15 closes or opens the contactors MC1 and MC2 in accordance with the opening/closing instruction signal. Specifically, the 11

contactor controller 15 controls the contactors MC1 and MC2 by outputting contactor control signals S1 for instructing the closing or opening to the contactors MC1 and MC2.
[0029] The switching controller 16 is provided with a driving instruction from the cab, which is not illustrated. The driving instruction contains a power running instruction indicating a target acceleration of the electric railway vehicle or a braking 5 instruction indicating a target deceleration of the electric railway vehicle, for example. The switching controller 16 controls the switching elements included in the power converter 11 by outputting switching control signals S2 to the switching elements in accordance with the driving instruction, as is described below.
[0030] The chopper controller 17 is provided with a driving instruction from the 10 cab, which is not illustrated. The chopper controller 17 switches the turned-on and turned-off states of the switching element SW2 of the chopper circuit 13 in response to the driving instruction containing a braking instruction. In detail, in order to provide a regenerative braking force in response to the driving instruction containing a braking instruction, the chopper controller 17 outputs a chopper control signal S3 for adjusting the 15 conduction ratio of the switching element SW2 of the chopper circuit 13 to the gate terminal of the switching element SW2.
[0031] Operations of the power conversion apparatus 1 having the above-described configuration are described below.
At the start of driving of the electric railway vehicle, the current collector 52 comes 20 into contact with the overhead wire 53 in response to manipulation of an ascending switch for raising a pantograph, which is a typical example of the current collector 52, and is then supplied with electric power from the substation. In association with the manipulation of the ascending switch, the high-speed circuit breaker 54 is closed, so that the power conversion apparatus 1 is electrically connected to the current collector 52. 25
[0032] Also, in association with the manipulation of the ascending switch, an opening/closing instruction signal for instructing start of driving is fed to the contactor 12

controller 15. When receiving the opening/closing instruction signal for instructing start of driving, the contactor controller 15 outputs a contactor control signal S1 for instructing closing of the contactor MC2. Due to the closing of the contactor MC2 in response to this signal, the electric power acquired by the current collector 52 from the substation via the overhead wire 53 is fed to the filter capacitor FC1 via the high-speed circuit breaker 5 54, the contactor MC2, and the first resistor CHR, to thereby start charging of the filter capacitor FC1. The configuration in which the contactor MC2 and the first resistor CHR are connected in series to each other can suppress inrush current from flowing to the filter capacitor FC1 in response to the closing of the contactor MC2.
[0033] After sufficient charging of the filter capacitor FC1, the contactor controller 10 15 outputs a contactor control signal S1 for instructing closing of the contactor MC1. Due to the closing of the contactor MC1 in response to this signal, the electric power acquired by the current collector 52 from the substation via the overhead wire 53 is fed to the filter capacitor FC1 via the high-speed circuit breaker 54 and the contactor MC1.
[0034] The contactor controller 15 then outputs a contactor control signal S1 for 15 instructing opening of the contactor MC2. This signal causes the first resistor CHR to be electrically disconnected from the current collector 52.
[0035] After start of operation following start of driving of the electric railway vehicle, a driving instruction from the cab is input to the switching controller 16 and the chopper controller 17. The following description is directed to operations of the 20 switching controller 16 and the chopper controller 17 in accordance with the driving instruction.
[0036] When a driving instruction contains a power running instruction, that is, during power running of the electric railway vehicle, the switching controller 16 controls the switching elements of the power converter 11 and thus causes the power converter 11 25 to convert DC power into three-phase AC power for driving the motor 51.
[0037] In detail, the switching controller 16 calculates a target torque for achieving 13

the target acceleration indicated by the power running instruction. The switching controller 16 acquires the measured values of current flowing in the motor 51 from a motor current measurer, which is not illustrated, and then calculates an actual torque of the motor 51 from the acquired measured values. Specifically, the switching controller 16 acquires the measured values of phase currents flowing in the motor 51 from the 5 motor current measurer for measuring the current values in the U, V, and W phases in the motor 51, and then calculates an actual torque of the motor 51 from the values of phase currents. The switching controller 16 then outputs switching control signals S2 to the switching elements of the power converter 11 and thereby controls the switching elements such that the actual torque of the motor 51 approaches the target torque. 10
[0038] When the driving instruction contains a braking instruction, that is, during braking of the electric railway vehicle, the motor 51 functions as an electric generator and feeds three-phase AC power to the power converter 11.
In this case, the switching controller 16 controls the switching elements of the power converter 11 and thus causes the power converter 11 to convert the three-phase 15 AC power into DC power. The power conversion apparatus 1 can therefore feed electric power via the overhead wire 53 to other electric railway vehicles located in the vicinity of the electric railway vehicle. This operation yields a regenerative braking force in the electric railway vehicle, thereby decelerating the electric railway vehicle.
[0039] In an exemplary case where electric power cannot be fed to the overhead 20 wire 53 because no other electric railway vehicle during power running exists in the vicinity, a dynamic braking force can be generated in the electric railway vehicle by consuming the electric power fed from the motor 51 at the chopper circuit 13.
When the driving instruction contains a braking instruction, the chopper controller 17 switches the turned-on and turned-off states of the switching element SW2, and 25 thereby causes the second resistor BR to consume DC power output from the power converter 11. In detail, the chopper controller 17 adjusts the conduction ratio of the 14

switching element SW2 depending on the value of the voltage between the terminals of the filter capacitor FC1 acquired from the voltage measurer 14, and thereby maintains the value of the voltage between the terminals of the filter capacitor FC1 within a predetermined range. The predetermined range is determined so as to ensure power feeding to the overhead wire 53 and to be lower than the maximum voltage applicable to 5 the filter capacitor FC1.
[0040] Specifically, when the voltage between the terminals of the filter capacitor FC1 rises due to failure in power feeding to the overhead wire 53, the chopper controller 17 increases the conduction ratio of the switching element SW2. The electric power fed from the motor 51 is thus consumed at the second resistor BR, thereby providing a 10 braking force in the electric railway vehicle.
[0041] An operation of the power conversion apparatus 1 during stopping of the electric railway vehicle is described below. In order to stop the electric railway vehicle, halting of the power converter 11 is followed by opening of the high-speed circuit breaker 54 and the contactor MC1. The power converter 11 is thus electrically 15 disconnected from the current collector 52.
[0042] In the case of a maintenance work for the power conversion apparatus 1 after stopping of the electric railway vehicle, a maintenance worker mechanically manipulates the discharge switch SW1 and thereby turns on the discharge switch SW1. When the discharge switch SW1 is turned on in the open states of the contactors MC1 20 and MC2, the first resistor CHR and the second resistor BR are connected in series to each other. The filter capacitor FC1 is electrically connected to the serially connected first resistor CHR and second resistor BR, and is discharged by the first resistor CHR and the second resistor BR.
[0043] As described above, the power conversion apparatus 1 according to 25 Embodiment 1 discharges the filter capacitor FC1 by means of the first resistor CHR for suppressing inrush current during charging of the filter capacitor FC1 and the second 15

resistor BR for consuming electric power fed from the motor 51 during braking of the electric railway vehicle. The power conversion apparatus 1 is therefore not required to include another resistor for discharging the filter capacitor FC1 in addition to the first resistor CHR and the second resistor BR. This configuration can simplify the structure of the power conversion apparatus 1 that enables braking the electric railway vehicle in 5 the dynamic braking system. The configuration can also lead to a reduction in size of the power conversion apparatus 1.
[0044] The power conversion apparatus 1 discharges the filter capacitor FC1 by means of the serially connected first resistor CHR and second resistor BR. Accordingly, the discharging circuit of the filter capacitor FC1 has a resistance equal to the sum of the 10 resistance of the first resistor CHR and the resistance of the second resistor BR.
[0045] The power conversion apparatus 1 according to Embodiment 1 can reduce ground fault current caused by occurrence of a short-circuit fault in the discharge switch SW1, because of the second resistor BR connected to the other end of the discharge switch SW1. 15
[0046] The discharge current that flows during discharging of the filter capacitor FC1 is inversely proportional to the sum of the resistance of the first resistor CHR and the resistance of the second resistor BR. The first resistor CHR has a resistance high enough to suppress inrush current in response to closing of the contactor MC2, for example, a resistance of several tens of ohms. This configuration results in sufficiently 20 low discharge current, allows a switch having a small current capacity to be used as the discharge switch SW1, and can narrow the wiring of the circuitry in which the discharge current flows. In other words, the configuration can mitigate the electrical limitation of the circuitry in which current flows during discharging of the filter capacitor FC1.
[0047] Embodiment 2 25
When a short-circuit fault occurs in the discharge switch SW1, ground fault current unintentionally flows from the current collector 52 via the discharge switch SW1 to the 16

second resistor BR. The description of Embodiment 2 below is directed to a power conversion apparatus 2 capable of determining the existence of a short-circuit fault in the discharge switch SW1 on the basis of the current flowing in the second resistor BR. The manner of installation of the power conversion apparatus 2 in the electric railway vehicle is identical to that in Embodiment 1. The differences of the power conversion 5 apparatus 2 from the power conversion apparatus 1 according to Embodiment 1 are described below.
[0048] The power conversion apparatus 2 according to Embodiment 2 illustrated in FIG. 3 further includes a current measurer 18 to measure a value of the current flowing in the second resistor BR, and a fault determiner 19 to determine the existence of a 10 short-circuit fault in the discharge switch SW1 on the basis of the value measured at the current measurer 18, in addition to the components of the power conversion apparatus 1 according to Embodiment 1.
[0049] The contactor controller 15 provides the fault determiner 19 with a contactor state signal S4 indicating whether at least either of the contactors MC1 and MC2 is closed. 15 For example, the contactor controller 15 outputs a contactor state signal S4 at a low level when the contactors MC1 and MC2 are both open, and a contactor state signal S4 at a high level when at least either of the contactors MC1 and MC2 is closed.
The contactor controller 15 opens both of the contactors MC1 and MC2 when the fault determiner 19 determines that a short-circuit fault occurs in the discharge switch 20 SW1, as is described below.
[0050] The switching controller 16 turns off the switching elements included in the power converter 11 when the fault determiner 19 determines that a short-circuit fault occurs in the discharge switch SW1, as is described below.
[0051] The chopper controller 17 provides the fault determiner 19 with an element 25 state signal S5 indicating whether the switching element SW2 is turned on or off. For example, the chopper controller 17 outputs an element state signal S5 at a high level 17

when the switching element SW2 is turned on, and outputs an element state signal S5 at a low level when the switching element SW2 is turned off.
[0052] The current measurer 18 is disposed between the switching element SW2 and the second resistor BR. In detail, one end of the current measurer 18 is connected to the emitter terminal of the switching element SW2, and the other end is connected to the 5 one end of the second resistor BR. The other end of the discharge switch SW1 is connected to the point of connection between the current measurer 18 and the switching element SW2. The current measurer 18 disposed at the above-mentioned position is a current transformer (CT), and measures a value of the current flowing in the second resistor BR. The current measurer 18 then provides the fault determiner 19 with a signal 10 indicating the measured current value.
[0053] When the discharge switch SW1 is turned off and the switching element SW2 of the chopper circuit 13 is turned off, the fault determiner 19 determines whether a current value IB, which is the measured current value acquired from the current measurer 18, is at least a threshold current Th. The situation, in which the discharge switch SW1 15 is turned off, the switching element SW2 of the chopper circuit 13 is turned off, and the current value IB is at least the threshold current Th, is deemed to indicate occurrence of a short-circuit fault in the discharge switch SW1.
[0054] The threshold current Th can be defined depending on the value calculated by dividing the overhead wire voltage, which is the voltage at the overhead wire 53, by 20 the sum of the resistance of the first resistor CHR and the resistance of the second resistor BR. Specifically, the threshold current Th is preferably the value calculated by dividing the minimum possible value of the overhead wire voltage by the sum of the resistance of the first resistor CHR and the resistance of the second resistor BR.
[0055] The fault determiner 19 provides the contactor controller 15 and the 25 switching controller 16 with a determination result signal S6 based on a result of determination of whether the current value IB is at least the threshold current Th. In 18

detail, when determining that the current value IB is lower than the threshold current Th, the fault determiner 19 provides the contactor controller 15 and the switching controller 16 with a determination result signal S6 indicating no occurrence of a short-circuit fault in the discharge switch SW1. In contrast, when determining that the current value IB is at least the threshold current Th, the fault determiner 19 provides the contactor controller 5 15 and the switching controller 16 with a determination result signal S6 indicating occurrence of a short-circuit fault in the discharge switch SW1. For example, the fault determiner 19 outputs a determination result signal S6 at a low level when determining that the current value IB is lower than the threshold current, and outputs a determination result signal S6 at a high level when determining that the current value IB is at least the 10 threshold current.
[0056] A process of determining the existence of a short-circuit fault executed by the fault determiner 19 is described below with reference to FIG. 4. As described above in Embodiment 1, a maintenance worker turns on the discharge switch SW1 in the open states of the high-speed circuit breaker 54 and the contactors MC1 and MC2. In other 15 words, the discharge switch SW1 in the normal status is turned off while at least either of the contactors MC1 and MC2 is closed. The fault determiner 19 thus determines whether the discharge switch SW1 is turned off on the basis of the contactor state signal S4.
[0057] Specifically, the fault determiner 19 determines, on the basis of the contactor 20 state signal S4, whether at least either of the contactors MC1 and MC2 is turned on (Step S11). When the contactors MC1 and MC2 are both turned off (Step S11; No), the fault determiner 19 terminates the process of determining the existence of a short-circuit fault.
[0058] In contrast, when either of the contactors MC1 and MC2 is turned on (Step S11; Yes), the fault determiner 19 determines whether the switching element SW2 of the 25 chopper circuit 13 is turned off (Step S12). In detail, the fault determiner 19 determines whether the element state signal S5 indicates the turned-off state of the switching element 19

SW2. When the switching element SW2 is turned on (Step S12; No), the fault determiner 19 terminates the process of determining the existence of a short-circuit fault.
[0059] In contrast, when the switching element SW2 is turned off (Step S12; Yes), the fault determiner 19 acquires the current value IB from the current measurer 18 (Step S13). The fault determiner 19 then determines whether the current value IB is at least 5 the threshold current Th (Step S14). The current value IB lower than the threshold current Th is deemed to indicate no occurrence of a short-circuit fault in the discharge switch SW1. Thus, when the current value IB is lower than the threshold current Th (Step S14; No), the fault determiner 19 outputs a determination result signal S6 indicating no occurrence of a short-circuit fault in the discharge switch SW1 (Step S15). After 10 Step S15, the fault determiner 19 terminates the process of determining the existence of a short-circuit fault.
[0060] In contrast, the current value IB of at least the threshold current Th is deemed to indicate occurrence of a short-circuit fault in the discharge switch SW1. Thus, when the current value IB is at least the threshold current Th (Step S14; Yes), the 15 fault determiner 19 outputs a determination result signal S6 indicating occurrence of a short-circuit fault in the discharge switch SW1 (Step S16). After Step S16, the fault determiner 19 terminates the process of determining the existence of a short-circuit fault.
[0061] The fault determiner 19 repeats the above-described process at predetermined timings. For example, the fault determiner 19 may repeat the 20 above-described process at regular intervals.
[0062] When receiving the determination result signal S6 indicating occurrence of a short-circuit fault in the discharge switch SW1, the contactor controller 15 outputs contactor control signals S1 for instructing opening of both of the contactors MC1 and MC2. 25
Also, when receiving the determination result signal S6 indicating occurrence of a short-circuit fault in the discharge switch SW1, the switching controller 16 outputs 20

switching control signals S2 for instructing turning off the switching elements included in the power converter 11.
[0063] As described above, the power conversion apparatus 2 according to Embodiment 2 is capable of determining the existence of a short-circuit fault in the discharge switch SW1 on the basis of the current flowing in the second resistor BR. 5
[0064] The above-described circuit configurations are mere examples. Another exemplary circuit configuration is illustrated in FIG. 5. As illustrated in FIG. 5, a circuit switcher 12a included in a power conversion apparatus 3 may include contactors MC1 and MC2 connected in series to each other and a first resistor CHR connected in parallel to the contactor MC2. One end of the contactor MC1 is connected to the high-speed 10 circuit breaker 54. One end of the contactor MC2 is connected to the other end of the contactor MC1, and the other end of the contactor MC2 is connected to the primary terminal 11a of the power converter 11. One end of the first resistor CHR is connected to the point of connection between the contactors MC1 and MC2, and the other end is connected to the other end of the contactor MC2. One end of the discharge switch SW1 15 is connected to the point of connection between the contactors MC1 and MC2, and the other end is connected to the point of connection between the switching element SW2 of the chopper circuit 13 and the second resistor BR. The circuit switcher 12 included in the power conversion apparatus 2 may have the configuration identical to that of the circuit switcher 12a included in the power conversion apparatus 3. 20
[0065] When receiving an opening/closing instruction signal for instructing start of driving, the contactor controller 15 included in the power conversion apparatus 3 outputs a contactor control signal S1 for instructing closing of the contactor MC1. Due to the closing of the contactor MC1 in response to this signal, the electric power acquired by the current collector 52 from the substation via the overhead wire 53 is fed to the filter 25 capacitor FC1 via the high-speed circuit breaker 54, the contactor MC1, and the first resistor CHR, to thereby start charging of the filter capacitor FC1. 21

[0066] After sufficient charging of the filter capacitor FC1, the contactor controller 15 included in the power conversion apparatus 3 outputs a contactor control signal S1 for instructing closing of the contactor MC2. Due to the closing of the contactor MC2 in response to this signal, the electric power acquired by the current collector 52 from the substation via the overhead wire 53 is fed to the filter capacitor FC1 via the high-speed 5 circuit breaker 54 and the contactors MC1 and MC2.
[0067] Still another exemplary circuit configuration is illustrated in FIG. 6. A power conversion apparatus 4 illustrated in FIG. 6 further includes a filter reactor FL1 in addition to the components of the power conversion apparatus 1. The filter reactor FL1 is disposed in the circuitry between the circuit switcher 12 and the chopper circuit 13. In 10 detail, one end of the filter reactor FL1 is connected to the other end of the contactor MC1, and the other end of the filter reactor FL1 is connected to the primary terminal 11a of the power converter 11. The filter reactor FL1 can achieve smoothing of current input to the power converter 11 and smoothing of current output from the power converter 11 during regenerative braking. The filter reactor FL1 can also suppress 15 inrush current from flowing to the first resistor CHR and the second resistor BR at the start of discharge of the filter capacitor FC1. The filter reactor FL1 may also be provided in the power conversion apparatus 2 or 3.
[0068] The above-described process of determining the existence of a short-circuit fault in the discharge switch SW1 is a mere example. Steps S11 and S12 in FIG. 4 may 20 be executed in any order, for example, and the fault determiner 19 may execute Step S12 and then Step S11.
[0069] The discharge switch SW1 may have a function of outputting a signal indicating whether the discharge switch SW1 is turned on or off, and the fault determiner 19 may determine whether the discharge switch SW1 is turned off on the basis of the 25 signal acquired from the discharge switch SW1.
[0070] The fault determiner 19 may acquire current values IB from the current 22

measurer 18 at certain intervals and store the current values IB in a memory, read a current value IB from the memory in Step S13 in FIG. 4, and then execute the following Step S14 on the basis of the read current value IB.
[0071] The fault determiner 19 may include a timer, and determine whether the current value IB has been continuously at least the threshold current Th for a 5 predetermined period when the discharge switch SW1 is turned off and the switching element SW2 of the chopper circuit 13 is turned off. In this case, when determining that the current value IB has not been continuously at least the threshold current Th for the predetermined period, the fault determiner 19 preferably provides the contactor controller 15 and the switching controller 16 with a determination result signal S6 indicating no 10 occurrence of a short-circuit fault in the discharge switch SW1.
In contrast, when determining that the current value IB has been continuously at least the threshold current Th for the predetermined period, the fault determiner 19 preferably provides the contactor controller 15 and the switching controller 16 with a determination result signal S6 indicating occurrence of a short-circuit fault in the 15 discharge switch SW1. The predetermined period is preferably a period long enough to prevent the fault determiner 19 from outputting an incorrect determination result due to an instantaneous variation in the current value IB. For example, the predetermined period is preferably longer than the update period of the turned-on and turned-off states of the elements, such as the discharge switch SW1 and the switching element SW2, and 20 longer than the sampling period of the current values IB.
[0072] The fault determiner 19 may output the determination result signal S6 to a display device installed in the cab. In this case, the display device in the cab can show the existence of a short-circuit fault in the discharge switch SW1.
[0073] The motor 51 may be a motor other than the three-phase induction motor. 25 For example, the motor 51 may also be a synchronous motor or DC motor.
[0074] The power converter 11 is any power conversion circuit capable of 23

bidirectional power conversion. In an exemplary case where the motor 51 is a DC motor, the power converter 11 is preferably a direct current-direct current (DC-DC) converter.
[0075] The power conversion apparatuses 1 to 4 can be installed in any vehicle, equipment, or the like that can feed DC power to the power conversion apparatuses 1 to 4. 5 For example, the power conversion apparatuses 1 to 4 can be installed in an electric railway vehicle of an AC feeding system. In this case, the other end of the high-speed circuit breaker 54 is connected to one of the primary terminals of a transformer, and the secondary terminals of the transformer are connected to a converter, so that an output from the converter is fed to the power conversion apparatuses 1 to 4. 10
[0076] For another example, the power conversion apparatuses 1 to 4 may also be installed in an electric railway vehicle that acquires electric power via a third rail.
[0077] The power conversion apparatuses 1 to 4 are not necessarily of a dynamic braking system to brake an electric railway vehicle, and may be any power conversion apparatus including multiple resistors. For example, the power conversion apparatuses 15 1 to 4 may discharge the filter capacitor FC1 by means of a resistor for any use, instead of the first resistor CHR and the second resistor BR. These power conversion apparatuses 1 to 4 are not required to include another resistor for discharging the filter capacitor FC1 and thus have a simpler structure.
[0078] The foregoing describes some example embodiments for explanatory 20 purposes. Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the 25 scope of the invention is defined only by the included claims, along with the full range of equivalents to which such claims are entitled. 24

Reference Signs List
[0079] 1, 2, 3, 4 Power conversion apparatus
1a Positive input terminal
1b Negative input terminal
11 Power converter 5
11a, 11b Primary terminal
12, 12a Circuit switcher
13 Chopper circuit
14 Voltage measurer
15 Contactor controller 10
16 Switching controller
17 Chopper controller
18 Current measurer
19 Fault determiner
51 Motor 15
52 Current collector
53 Overhead wire
54 High-speed circuit breaker
BR Second resistor
CHR First resistor 20
FC1 Filter capacitor
FL1 Filter reactor
MC1, MC2 Contactor
S1 Contactor control signal
S2 Switching control signal 25
S3 Chopper control signal
S4 Contactor state signal 25

S5 Element state signal
S6 Determination result signal
SW1 Discharge switch
SW2 Switching element
WE CLAIM:
1. A power conversion apparatus comprising:
a filter capacitor to be charged with DC power fed from a power source;
a power converter comprising a pair of primary terminals between which the filter capacitor is connected, and secondary terminals, the power converter being configured to 5 convert the DC power fed from the power source via the filter capacitor into DC power or AC power and feed the converted power to a motor connected to the secondary terminals, the power converter being configured to convert DC power or AC power fed from the motor serving as an electric generator into DC power, output the converted DC power, and charge the filter capacitor; 10
a circuit switcher comprising a first resistor, the circuit switcher being configured to electrically connect the power converter and the filter capacitor to the power source or electrically disconnect the power converter and the filter capacitor from the power source;
a chopper circuit comprising a switching element and a second resistor connected in series to each other, the chopper circuit having both ends connected between the 15 primary terminals of the power converter; and
a discharge switch having one end and another end, the one end being connected to one end of the first resistor closer to the power source, the other end being connected to a point of connection between the switching element and the second resistor, wherein
in order to charge the filter capacitor with the DC power fed from the power source, 20 the circuit switcher electrically connects the power converter and the filter capacitor to the power source via an electrical path passing through the first resistor,
when the switching element is turned on, the chopper circuit causes the second resistor to consume the DC power fed from the power converter via the filter capacitor, and 25
the discharge switch when turned on connects the first resistor and the second resistor in series to each other and electrically connects the filter capacitor to the first 27

resistor and the second resistor connected in series to each other, thereby causing discharge of the filter capacitor.
2. The power conversion apparatus according to claim 1, wherein
the circuit switcher comprises: 5
a first contactor having one end connected to the power source and being disposed in parallel to the first resistor; and
a second contactor having one end connected to the power source and another end connected to the one end of the first resistor,
another end of the first resistor is connected to the pair of primary terminals of the 10 power converter,
the one end of the discharge switch is connected to the one end of the first resistor, and
the other end of the discharge switch is connected to the point of connection between the switching element and the second resistor of the chopper circuit. 15
3. The power conversion apparatus according to claim 1, wherein
the circuit switcher comprises a first contactor and a second contactor connected in series to each other,
one end of the first contactor is connected to the power source, 20
another end of the first contactor is connected to one end of the second contactor,
another end of the second contactor is connected to one of the primary terminals of the power converter,
the one end of the first resistor is connected to a point of connection between the first contactor and the second contactor, 25
another end of the first resistor is connected to the other end of the second contactor, 28
the one end of the discharge switch is connected to the one end of the first resistor, and
the other end of the discharge switch is connected to the point of connection between the switching element and the second resistor of the chopper circuit.
4. The power conversion apparatus according to any one of claims 1 to 3, further comprising a fault determiner to determine existence of a short-circuit fault in the discharge switch on basis of a current flowing in the second resistor.
5. The power conversion apparatus according to claim 4, wherein when the 10 discharge switch is open and the switching element of the chopper circuit is turned off, the fault determiner determines whether the current flowing in the second resistor is at least a threshold current and outputs a result of determination.
6. The power conversion apparatus according to claim 4 or 5, wherein when 15 the fault determiner determines that a short-circuit fault occurs in the discharge switch, the circuit switcher electrically disconnects the power converter from the power source.
7. The power conversion apparatus according to any one of claims 4 to 6, further comprising: 20
a switching controller to switch turned-on and turned-off states of switching elements included in the power converter, thereby causing the power converter to (i) convert the DC power fed from the power source via the filter capacitor into DC power or AC power or (ii) convert the DC power or AC power fed from the motor into DC power, wherein
when the fault determiner determines that a short-circuit fault occurs in the discharge switch, the switching controller turns off the switching elements of the power converter.
capacitor (FC1).