DC power system

Abstract

To provide a direct current feeding system which can compensate voltage drop of a direct current feeding line in line area where there is only a transformer station at one end of a track and adopts a high voltage direct current feeding system.SOLUTION: A direct current feeding line T receives supply of direct current feeding voltage VT from a transformer station 10. A high voltage direct current feeding line F is arranged in parallel to the direct current feeding line T and includes a higher direct current feeding voltage VF than the direct current feeding voltage VT. A DC / DC conversion device 20A situates between the transformer station 10 and terminal end of the direct current feeding line T. A DC / DC conversion device 20B situates between the DC / DC conversion device 20A and a terminal end of the direct current feeding line T. The DC / DC conversion device 20B executes a bidirectional direct current / direct current conversion so as to give and receive direct current power according to deviation between the direct current feeding voltage VT and a first reference voltage between the direct current feeding line T and the high voltage direct current feeding line F. The DC / DC conversion device 20A executes bidirectional direct current / direct current conversion so that the direct current feeding voltage VF becomes a second reference voltage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a DC power supply system.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2020-40455 (Patent Document 1) discloses a DC power supply system that supplies DC power to an electric vehicle running on a line via a DC power supply line. In this DC power supply system, a high-voltage DC power supply line is arranged in parallel with the DC power supply line, and a power conversion device provided between the DC power supply line and the high-voltage DC power supply line is used to transfer DC power between the DC power supply line and the high-voltage DC power supply line, thereby adopting a "high-voltage DC power supply method" in which the DC power supply voltage is increased.

[0003] In the DC power supply system described in Patent Document 1, a power conversion device is provided for each substation that supplies DC power to the DC power supply line, and a plurality of power conversion devices are arranged at intervals between the substation and another adjacent substation. Each of these plurality of power conversion devices is configured to perform control to increase or decrease the DC high-voltage power supply voltage in response to a change in the DC power supply voltage so that the DC power supply voltage of the DC power supply line and the DC high-voltage power supply voltage of the high-voltage DC power supply line have a predetermined ratio.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, a plurality of power conversion devices cooperate to adjust the DC high voltage so that the ratio of the DC low voltage to the DC high voltage is maintained at a predetermined ratio. As a result, a voltage gradient of the DC high voltage is formed between a plurality of points to which the plurality of power conversion devices are respectively connected, reflecting the DC low voltage at each point. By flowing a DC current through the DC low voltage line and the high voltage DC low voltage line according to this voltage gradient, DC power from a plurality of substations can be supplied to an electric vehicle that is powering. Also, the regenerative power generated by another electric vehicle through regenerative braking can be supplied to the electric vehicle that is powering.

[0006] However, in a section of a line (for example, a dead-end line) where there is only a substation at one end of the line and the other end (terminal) of the line is a dead end, it is feared that the application of the technology described in Patent Document 1 will become difficult.

[0007] For example, in a situation where no other electric vehicle is running on the said section, DC power will be supplied from the substation to the electric vehicle running on the line. In such a case, as the distance from the substation to the running position of the electric vehicle increases, the voltage drop in the DC low voltage line increases in proportion to the resistance of the DC low voltage line and the magnitude of the load current, which may hinder the running of the electric vehicle. Therefore, the range in which an electric vehicle can run in the said section is limited to a range where the DC low voltage does not fall below the lower limit value required for the running of the electric vehicle.

[0008] As described above, in Patent Document 1, although the DC high voltage is increased or decreased so that the DC low voltage and the DC high voltage are maintained at a predetermined ratio in response to a change in the DC low voltage by a plurality of power conversion devices arranged at predetermined intervals for each substation or between adjacent substations, the aspect of compensating for the voltage drop of the DC low voltage is not considered.

[0009] The present disclosure has been made to solve such problems, and an object of the present disclosure is to provide a DC catenary system adopting a high-voltage DC catenary system capable of compensating for the voltage drop of a DC catenary wire in a section where a substation exists only at one end of the line.

Means for Solving the Problems

[0010] According to an aspect of the present disclosure, a DC catenary system includes a first DC catenary wire, a second DC catenary wire, a first DC / DC conversion device, and at least one second DC / DC conversion device. The first DC catenary wire receives a supply of a first DC catenary voltage from a substation and supplies DC power to an electric vehicle traveling on the line. The second DC catenary wire is arranged in parallel with the first DC catenary wire and has a second DC catenary voltage higher than the first DC catenary voltage. The first DC / DC conversion device is located between the substation and the end of the first DC catenary wire and is connected between the first DC catenary wire and the second DC catenary wire. At least one second DC / DC conversion device is located between the first DC / DC conversion device and the end of the first DC catenary wire and is connected between the first DC catenary wire and the second DC catenary wire. At least one second DC / DC conversion device performs bidirectional DC / DC conversion between the first DC catenary wire and the second DC catenary wire so as to transfer DC power corresponding to the deviation between the first DC catenary voltage and a predetermined first reference voltage between the first DC catenary wire and the second DC catenary wire. The first DC / DC conversion device performs bidirectional DC / DC conversion between the first DC catenary wire and the second DC catenary wire so that the second DC catenary voltage becomes a predetermined second reference voltage.

Advantages of the Invention

[0011] According to the present disclosure, the voltage drop of the DC catenary wire in a section where a substation exists only at one end of the line can be compensated by a DC catenary system adopting a high-voltage DC catenary system.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated in principle.

[0014] [Embodiment 1] [Configuration of the DC Power Supply System] FIG. 1 is a schematic block diagram for explaining the configuration of the DC power supply system according to Embodiment 1. The DC power supply system 100 according to Embodiment 1 is a system that supplies DC power to the electric vehicle 30 running on the line R. The DC power supply system 100 can be applied to a section of the line where there is only a substation 10 at one end of the line and the other end (terminal) of the line is a dead end.

[0015] As shown in FIG. 1, the DC power supply system 100 includes a DC power supply line T that supplies DC power to the electric vehicle 30, a high-voltage DC power supply line F, a DC / DC converter 20A, and a DC / DC converter 20B.

[0016] The DC power supply line T, the high-voltage DC power supply line F, and the line R constitute a power transmission line for sending power to the electric vehicle 30 traveling on the line R. Corresponding to the end of the line R, each of the DC power supply line T and the high-voltage DC power supply line F has an end.

[0017] The DC power supply line T receives DC power supply from the substation 10. The substation 10 converts AC power sent from a power plant (not shown) into DC power and supplies it to the DC power supply line T. The substation 10 is configured to include, for example, a diode rectifier or a PWM (pulse width modulation) rectifier. The substation 10 corresponds to the substation closest to the end of the DC power supply line T. The standard value of the DC power supply voltage VT of the DC power supply line T is, for example, 1500V. The DC power supply line T corresponds to an embodiment of the "first DC power supply line", and the DC power supply voltage VT corresponds to an embodiment of the "first DC power supply voltage".

[0018] The high-voltage DC power supply line F is arranged in parallel with the DC power supply line T. The DC power supply voltage VF of the high-voltage DC power supply line F is higher than the DC power supply voltage VT. The standard value of the DC power supply voltage VF is, for example, 6000V. The high-voltage DC power supply line F corresponds to an embodiment of the "second DC power supply line", and the DC power supply voltage VF corresponds to an embodiment of the "second DC power supply voltage".

[0019] The DC / DC converters 20A and 20B are connected between the DC power supply line T and the high-voltage DC power supply line F. Each of the DC / DC converters 20A and 20B is a bidirectional DC / DC converter. Through the bidirectional DC / DC conversion in the DC / DC converters 20A and 20B, power is transferred between the DC power supply line T and the high-voltage DC power supply line F.

[0020] Specifically, the DC / DC converter 20A is located between the substation 10 and the end of the DC power line T. Preferably, the DC / DC converter 20A is located at or near the substation 10. When the DC / DC converter 20A supplies power from the DC power line T to the high-voltage DC power line F, it boosts the DC power voltage VT and outputs it to the high-voltage DC power line F. When the DC / DC converter 20A supplies power from the high-voltage DC power line F to the DC power line T, it steps down the DC power voltage VF and outputs it to the DC power line T. The DC / DC converter 20A corresponds to an embodiment of the "first DC / DC converter".

[0021] The DC / DC converter 20B is located between the DC / DC converter 20A and the end of the DC power line T. When there is one DC / DC converter 20B as shown in FIG. 1, preferably, the DC / DC converter 20B is located at or near the end of the DC power line T. When the DC / DC converter 20B supplies power from the DC power line T to the high-voltage DC power line F, it boosts the DC power voltage VT and outputs it to the high-voltage DC power line F. When the DC / DC converter 20B supplies power from the high-voltage DC power line F to the DC power line T, it steps down the DC power voltage VF and outputs it to the DC power line T. The DC / DC converter 20B corresponds to an embodiment of the "second DC / DC converter".

[0022] The control configurations of bidirectional DC / DC conversion of the DC / DC converter 20A and the DC / DC converter 20B are different. Hereinafter, the configurations and operations of the DC / DC converter 20A and the DC / DC converter 20B will be described.

[0023] <Configuration Example of DC / DC Converter 20A> FIG. 2 is a circuit block diagram showing a configuration example of the DC / DC converter 20A. As shown in FIG. 2, the DC / DC converter 20A includes a low-voltage side DC terminal T1, a high-voltage side DC terminal T3, negative side DC terminals T2 and T4, a DC / DC converter 40A, a control unit 42A, and a voltage detector 44.

[0024] The low-voltage side DC terminal T1 is connected to the DC power line T, and the low-voltage side DC terminal T2 is connected to the line R. The high-voltage side DC terminal T3 is connected to the high-voltage DC power line F, and the high-voltage side DC terminal T4 is connected to the line R.

[0025] The DC / DC converter 40A is connected between the low-voltage side DC terminals T1, T2 and the high-voltage side DC terminals T3, T4. The DC / DC converter 40A is a well-known one including a plurality of semiconductor switching elements and a plurality of diodes. In the example of FIG. 2, the DC / DC converter 40A is a chopper circuit and includes IGBTs (Insulated Gate Bipolar Transistors) Q1, Q2, diodes D1, D2, and a reactor L1.

[0026] The collector of the IGBT Q1 is connected to the high-voltage side DC terminal T3, and its emitter is connected to the node N1. The collector of the IGBT Q2 is connected to the node N1, and its emitter is connected to the negative side DC terminals T2, T4. The gates of the IGBTs Q1, Q2 receive gate signals G1, G2 from the control unit 42A, respectively.

[0027] The diodes D1, D2 are connected in anti-parallel to the IGBTs Q1, Q2, respectively. The reactor L1 is connected between the node N1 and the low-voltage side DC terminal T1 and stores electromagnetic energy.

[0028] During the step-down operation, the gate signal G1 is set to the H level and the L level at a constant period, and the IGBT Q1 is turned on and off at a constant period. The gate signal G2 is maintained at the L level, and the IGBT Q2 is maintained in the off state.

[0029] When the IGBT Q1 is turned on, current flows from the high-voltage DC power line F through the IGBT Q1, the reactor L1, and the DC power line T to the line R, DC power is supplied from the high-voltage DC power line F to the DC power line T, and electromagnetic energy is stored in the reactor L1.

[0030] When IGBT Q1 is turned off, current flows from one terminal of reactor L1 through DC power line T, line R, and diode D2 to the other terminal of reactor L1, and the electromagnetic energy of reactor L1 is released.

[0031] The ratio T2 / T1 of the time T2 during which gate signal G1 is at the H level within one period T1 of gate signal G1 is called the duty ratio D1. When the duty ratio D1 is increased, the DC power supply voltage VT rises, and when the duty ratio D1 is decreased, the DC power supply voltage VT drops. Therefore, by adjusting the duty ratio D1, it is possible to adjust the DC power supply voltage VT to a desired voltage.

[0032] During the boost operation, gate signal G2 is set to the H level and the L level at a fixed period, and IGBT Q2 is turned on and off at a fixed period. Gate signal G1 is maintained at the L level, and IGBT Q1 is maintained in the off state.

[0033] When IGBT Q2 is turned on, current flows from DC power line T through reactor L1 and IGBT Q2 to line R, and electromagnetic energy is stored in reactor L1.

[0034] When IGBT Q2 is turned off, current flows from DC power line T through reactor L1 and diode D1 to high-voltage DC power line F, DC power is supplied from DC power line T to high-voltage power line F, and the electromagnetic energy of reactor L1 is released.

[0035] The ratio T4 / T3 of the time T4 during which gate signal G2 is at the H level within one period T3 of gate signal G2 is called the duty ratio D2. When the duty ratio D2 is increased, the DC power supply voltage VF rises, and when the duty ratio D2 is decreased, the DC power supply voltage VF drops. Therefore, by adjusting the duty ratio D2, it is possible to adjust the DC power supply voltage VF to a desired voltage.

[0036] The voltage detector 44 detects the DC pulsating voltage VF. The detection signal from the voltage detector 44 is sent to the control unit 42A. The control unit 42A controls the DC / DC converter 40A by generating the gate signals G1 and G2 based on the output signal of the voltage detector 44 and the like.

[0037] The control unit 42A is configured to control the DC / DC converter 40A so that the DC pulsating voltage VF becomes constant. Specifically, the control unit 42A compares the DC pulsating voltage VF with a predetermined reference voltage VFR, and selectively executes a boosting operation and a bucking operation on the DC / DC converter 40A according to the comparison result. The reference voltage VFR is set, for example, to the standard value (6000V) of the DC pulsating voltage VF.

[0038] When VF > VFR, the control unit 42A controls the DC / DC converter 40A to execute a bucking operation. The DC pulsating voltage VF decreases by supplying power from the high-voltage DC pulsating wire F to the DC pulsating wire T. When the DC pulsating voltage VF matches the reference voltage VFR, the control unit 42A stops the bucking operation of the DC / DC converter 40A.

[0039] When VF < VFR, the control unit 42A controls the DC / DC converter 40A to execute a boosting operation. The DC pulsating voltage VF increases by supplying power from the DC pulsating wire T to the high-voltage DC pulsating wire F. When the DC pulsating voltage VF matches the reference voltage VFR, the control unit 42A stops the boosting operation of the DC / DC converter 40A.

[0040] When VF = VFR, the control unit 42A sets the DC / DC converter 40A to a stopped state.

[0041] As shown in FIG. 2, the control unit 42A includes a subtractor 50, a controller 52, and a gate signal generator 54. The control unit 42A is configured to include a CPU (Central Processing Unit), a memory, and an input / output circuit. By executing a program stored in the memory by the CPU, the functions of the subtractor 50, the controller 52, and the gate signal generator 54 can be realized. Alternatively, at least a part of the control unit 42A can be configured using a circuit such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Also, at least a part of the control unit 42A can be configured by an analog circuit.

[0042] The subtractor 50 calculates a deviation ΔVF between the DC voltage VF detected by the voltage detector 44 and the reference voltage VFR.

[0043] The controller 52 generates a duty ratio command value Da* which is a command value of the duty ratios D1, D2 by feedback control for causing the DC voltage VF to follow the reference voltage VFR. The controller 52 generates the duty ratio command value Da* by executing a control operation for making the deviation ΔVF smaller than a specified value. When VF > VFR, the duty ratio command value Da* becomes the duty ratio command value D1a* which is a command value of the duty ratio D1 during the step-down operation. When VF < VFR, the duty ratio command value Da* becomes the duty ratio command value D2a* which is a command value of the duty ratio D2 during the step-up operation. When VF = VFR, the duty ratio command value Da* = 0.

[0044] The gate signal generator 54 includes a carrier signal generator (not shown) and a comparator. The carrier signal generator generates a triangular carrier signal. The comparator compares the high and low levels of the duty ratio command value Da* and the carrier signal, and outputs gate signals G1, G2 indicating the comparison result.

[0045] During the step-down operation, the gate signal G1 has a duty ratio corresponding to the duty ratio command value Da* (Da* = D1a*), and the gate signal G2 is maintained at the L level. The DC / DC converter 40A is driven by the gate signal G1 to convert the DC intermediate voltage VF into the DC intermediate voltage VT.

[0046] During the step-up operation, the gate signal G2 has a duty ratio corresponding to the duty ratio command value Da* (Da* = D2a*), and the gate signal G1 is maintained at the L level. The DC / DC converter 40A is driven by the gate signal G2 to convert the DC intermediate voltage VT into the DC intermediate voltage VF.

[0047] FIG. 3 is a diagram for explaining the control of the DC / DC converter 40A by the control unit 42A. In FIG. 3, the relationship between the DC intermediate voltage VT and the DC intermediate voltage VF is shown. The horizontal axis of FIG. 3 indicates the DC intermediate voltage VT, and the vertical axis indicates the DC intermediate voltage VF. As described above, the control unit 42A controls the DC / DC converter 40A so that the DC intermediate voltage VF becomes constant. Therefore, regardless of the magnitude of the DC intermediate voltage VT, the DC intermediate voltage VF is maintained at a constant value (corresponding to the reference voltage VFR).

[0048] <Configuration example of the DC / DC converter device 20B> FIG. 4 is a circuit block diagram showing a configuration example of the DC / DC converter device 20B. As shown in FIG. 4, the DC / DC converter device 20B includes a low-voltage side DC terminal T1, a high-voltage side DC terminal T3, negative side DC terminals T2 and T4, a DC / DC converter 40B, a control unit 42B, a voltage detector 46, and a current detector 48.

[0049] The low-voltage side DC terminal T1 is connected to the DC intermediate wire T, and the low-voltage side DC terminal T2 is connected to the line R. The high-voltage side DC terminal T3 is connected to the high-voltage DC intermediate wire F, and the high-voltage side DC terminal T4 is connected to the line R.

[0050] The DC / DC converter 40B is connected between the low-voltage side DC terminals T1 and T2 and the high-voltage side DC terminals T3 and T4. The DC / DC converter 40B is a well-known one including a plurality of semiconductor switching elements and a plurality of diodes. In the example of FIG. 4, the DC / DC converter 40B is a chopper circuit and has the same configuration as the DC / DC converter 40A shown in FIG. 2.

[0051] The voltage detector 46 detects the DC bus voltage VT and supplies a signal indicating the detected value to the control unit 42B. The current detector 48 detects the current (reactor current) IL flowing through the reactor L1 and supplies a signal indicating the detected value to the control unit 42B.

[0052] The control unit 42B controls the DC / DC converter 40B by generating the gate signals G1 and G2 based on the output signals of the voltage detector 46 and the current detector 48 and the like. The control unit 42B is configured to control the DC / DC converter 40B so as to output DC power corresponding to the deviation between the DC bus voltage VT and a predetermined reference voltage VTR.

[0053] As shown in FIG. 4, the control unit 42B includes a voltage control unit 60, a power detection unit 62, a subtractor 64, a controller 66, and a gate signal generation unit 68. The control unit 42B is configured to include a CPU, a memory, and an input / output circuit. By the CPU executing the program stored in the memory, the functions of the voltage control unit 60, the power detection unit 62, the subtractor 64, the controller 66, and the gate signal generation unit 68 can be realized. Alternatively, at least a part of the control unit 42B can be configured using a circuit such as an FPGA or an ASIC. Also, at least a part of the control unit 42B can be configured by an analog circuit.

[0054] The voltage control unit 60 generates a DC power command value PO* which is a command value of the DC power PO output from the DC / DC converter 40B according to the deviation ΔVT between the DC voltage VT detected by the voltage detector 46 and the reference voltage VTR. FIG. 5 is a diagram for explaining the operation of the voltage control unit 60. In FIG. 5, the relationship between the DC voltage VT and the DC power command value PO* of the DC / DC converter 40B is shown. The horizontal axis of FIG. 5 indicates the DC voltage VT, and the vertical axis indicates the DC power command value PO*.

[0055] In this specification, the direction in which power (current) is supplied from the high-voltage DC wire F to the DC wire T is defined as "positive", and the direction in which power (current) is supplied from the DC wire T to the high-voltage DC wire F is defined as "negative".

[0056] As shown in FIG. 5, when VT > VTR, PO* < 0. That is, when VT > VTR, power is supplied from the DC wire T to the high-voltage DC wire F according to the negative DC power command value PO*. On the other hand, when VT < VTR, PO* > 0. That is, when VT < VTR, power is supplied from the high-voltage DC wire F to the DC wire T according to the positive DC power command value PO*.

[0057] As the deviation ΔVT between the DC voltage VT and the reference voltage VTR increases, the absolute value of the DC power command value PO* increases. When VT = VTR, PO* = 0. In this case, the DC / DC converter 40B is in a stopped state.

[0058] In FIG. 5, VTH indicates the upper limit value of the DC voltage VT, and VTL indicates the lower limit value of the DC voltage VT. The upper limit value VTH can be any voltage below the allowable voltage (breakdown voltage) of the electric vehicle 30. The lower limit value VTL can be any voltage above the lower limit value required for the electric vehicle 30 to run.

[0059] In the voltage range from the lower limit value VTL to the upper limit value VTH, the DC power command value PO* has a proportional relationship with the DC bus voltage VT. The slope of the straight line indicating this proportional relationship is determined by the control responsiveness of the DC / DC converter 40B. As the control responsiveness of the DC / DC converter 40B is increased, the slope of the straight line becomes steeper. However, as the control responsiveness of the DC / DC converter 40B increases, there is a risk of an increase in the transient fluctuations of the DC bus voltage VT and / or the DC bus voltage VF due to the power transfer between the high-voltage DC bus line F and the DC bus line T. Therefore, the slope of the straight line can be appropriately set in consideration of the stability of the DC bus voltage VT and the DC bus voltage VF.

[0060] Returning to FIG. 4, the voltage control unit 60 generates the DC power command value PO* based on the deviation ΔVT between the DC bus voltage VT and the reference voltage VTR by referring to the relationship between the DC power command value PO* and the DC bus voltage VT shown in FIG. 5. The voltage control unit 60 can generate the DC power command value PO* from the DC bus voltage VT by using a relational expression or a table prepared in advance showing the relationship between the DC bus voltage VT and the DC power command value PO*.

[0061] The power detection unit 62 calculates the DC power PO output from the DC / DC converter 40B based on the reactor current IL detected by the current detector 48 and the DC bus voltage VT detected by the voltage detector 46.

[0062] The subtractor 64 calculates the deviation ΔPO between the DC power command value PO* and the DC power PO calculated by the power detection unit 62.

[0063] The controller 66 generates a duty ratio command value Db* which is a command value for the duty ratios D1 and D2 by feedback control for causing the DC power PO to follow the DC power command value PO*. When PO*>0, the duty ratio command value Db* becomes the duty ratio command value D1b* which is the command value for the duty ratio D1 during the step-down operation. When PO*<0, the duty ratio command value Db* becomes the duty ratio command value D2b* which is the command value for the duty ratio D2 during the step-up operation. When PO* = 0, the duty ratio command value Db* = 0.

[0064] The gate signal generation unit 68 includes a carrier signal generation unit (not shown) and a comparator. The carrier signal generation unit generates a triangular carrier signal. The comparator compares the levels of the duty ratio command value Db* and the carrier signal, and outputs gate signals G1 and G2 indicating the comparison result.

[0065] During the step-down operation, the gate signal G1 has a duty ratio corresponding to the duty ratio command value Db* (Db* = D1b*), and the gate signal G2 is maintained at the L level. The DC / DC converter 40B is driven by the gate signal G1 and converts the DC boost voltage VF into the DC boost voltage VT.

[0066] During the step-up operation, the gate signal G2 has a duty ratio corresponding to the duty command value Db* (Db* = D2b*), and the gate signal G1 is maintained at the L level. The DC / DC converter 40B is driven by the gate signal G2 and converts the DC boost voltage VT into the DC boost voltage VF.

[0067] <Operation of the DC Boost System> Next, with reference to FIGS. 6 and 7, the operation of the DC boost system 100 according to Embodiment 1 will be described.

[0068] (First Operation Example) FIG. 6 is a diagram for explaining the operation of the DC power supply system 100 when the electric vehicle 30 is under power running. In FIG. 6, the electric vehicle 30 is running between the substation 10 and the end of the line R. DC power is supplied from the substation 10 to the electric vehicle 30. The arrow A1 (solid line) in FIG. 6 represents the flow of DC power by the DC power supply system 100 according to Embodiment 1. The arrow A2 (dashed line) in FIG. 6 represents the flow of DC power by a conventional DC power supply system. Note that the conventional DC power supply system is a general DC power supply system that does not have the high-voltage DC power line F.

[0069] In the conventional DC power supply system, power is supplied from the substation 10 to the electric vehicle 30 via the DC power line T. In this case, a voltage drop corresponding to the distance from the substation 10 to the running position of the electric vehicle 30 occurs in the DC power voltage VT of the DC power line T. When the DC power voltage VT falls below the lower limit value required for the running of the electric vehicle 30 due to this voltage drop, there is a possibility that the running of the electric vehicle 30 will be hindered. Therefore, the drivable range of the electric vehicle 30 is limited to a range where the DC power voltage VT does not fall below the lower limit value.

[0070] On the other hand, in the DC power supply system 100 according to Embodiment 1, in response to the DC power voltage VT becoming lower than the reference voltage VTR due to the voltage drop of the DC power line T, the DC / DC converter 20B arranged between the substation 10 and the end of the line R outputs DC power PO corresponding to the deviation ΔVT between the DC power voltage VT and the reference voltage VTR.

[0071] Specifically, inside the DC / DC converter 20B, the control unit 42B refers to the relationship between the DC power command value PO* and the DC intermediate voltage VT shown in FIG. 5, and generates the DC power command value PO* based on the deviation ΔVT between the DC intermediate voltage VT and the reference voltage VTR. Since VT < VTR, the DC power command value PO* becomes a positive value. The control unit 42B generates a duty ratio command value Db* through feedback control to make the DC power PO follow the DC power command value PO*. When PO* > 0, the duty ratio command value Db* becomes the duty ratio command value D1b* during the step-down operation. The control unit 42B compares the levels of the duty ratio command value Db* and the carrier signal, and outputs gate signals G1 and G2 indicating the comparison result. The gate signal G1 has a duty ratio with a value corresponding to the duty ratio command value D1b*, and the gate signal G2 is maintained at the L level.

[0072] The DC / DC converter 40B is driven by the gate signals G1 and G2, and converts the DC intermediate voltage VF into the DC intermediate voltage VT. Through the step-down operation of this DC / DC converter 40B, DC power is supplied from the high-voltage DC intermediate wire F to the DC intermediate wire T. Then, DC power is supplied from the DC intermediate wire T to the electric vehicle 30.

[0073] Due to the power supply to the DC intermediate wire T by the DC / DC converter 20B, when the DC intermediate voltage VF of the high-voltage DC intermediate wire F decreases and becomes lower than the reference voltage VFR, the DC / DC converter 20A arranged near the substation 10 performs DC / DC conversion so that the DC intermediate voltage VF becomes constant.

[0074] Specifically, inside the DC / DC converter 20A, the control unit 42A generates the duty ratio command value D1a* during the step-down operation through feedback control to make the DC intermediate voltage VT follow the reference voltage VTR, and generates the duty ratio command value D2a* during the step-up operation through feedback control to make the DC intermediate voltage VF follow the reference voltage VFR.

[0075] Since VF < VFR, the control unit 42A selects the duty ratio command value D2a* during the boosting operation as the duty ratio command value Da*. The control unit 42A compares the levels of the duty ratio command value Da* and the carrier signal, and outputs gate signals G1 and G2 indicating the comparison result.

[0076] The gate signal G2 has a duty ratio corresponding to the duty ratio command value D2a* during the boosting operation, and the gate signal G1 is maintained at the L level. The DC / DC converter 40A is driven by the gate signal G2 to convert the DC intermediate voltage VT into the DC intermediate voltage VF. By the boosting operation of the DC / DC converter 40A, DC power is supplied from the DC intermediate wire T to the high-voltage DC intermediate wire F.

[0077] In this way, when the DC / DC conversion device 20B performs the bucking operation and the DC / DC conversion device 20A performs the boosting operation, as shown by the arrow A1, DC power is supplied from the substation 10 to the electric vehicle 30 via the DC / DC conversion device 20A, the high-voltage DC intermediate wire F, the DC / DC conversion device 20B, and the DC intermediate wire T.

[0078] According to the above configuration, the voltage drop of the DC intermediate wire T can be compensated by the bucking operation of the DC / DC conversion device 20B. As a result, as shown in FIG. 6, by arranging the DC / DC conversion device 20B near the end of the line R, it is possible to compensate the voltage drop of the DC intermediate wire T even for the electric vehicle 30 traveling near the end. Therefore, in a section where the substation 10 is located only at one end of the line, the limitation on the travelable range of the electric vehicle 30 can be eliminated.

[0079] In addition, since DC power is sent from the substation 10 to the electric vehicle 30 through the high-voltage DC intermediate wire F, compared with the conventional DC intermediate system that sends DC power through the DC intermediate wire T, the load current is reduced, so the DC intermediate loss can be reduced.

[0080] (Second operation example) FIG. 7 is a diagram for explaining the operation of the DC power supply system 100 when a plurality of electric vehicles 30A and 30B are running between the substation 10 and the end of the line R. In FIG. 7, it is assumed that the electric vehicle 30B applies a regenerative brake near the end of the line R and the electric vehicle 30A is running near the substation 10 under power.

[0081] The arrow A3 (solid line) in FIG. 7 represents the flow of DC power by the DC power supply system 100 according to Embodiment 1. The arrow A4 (dashed line) in FIG. 7 represents the flow of DC power by a conventional DC power supply system. Note that the conventional DC power supply system is a general DC power supply system that does not have a high-voltage DC power line F.

[0082] In the conventional DC power supply system, when the electric vehicle 30B generates regenerative power by the regenerative brake and the generated regenerative power flows reversely through the DC power line T, the regenerative power can be supplied to another electric vehicle 30A running near the electric vehicle 30B through the DC power line T.

[0083] However, due to the limitation of the allowable voltage of the electric vehicle 30B, the output voltage of the regenerative power is limited to a predetermined upper limit value. Further, when the regenerative current flows through the DC power line T, a voltage drop proportional to the magnitude of the regenerative current occurs. Therefore, when the electric vehicle 30A is away from the electric vehicle 30B, the magnitude of the regenerative current is limited to suppress the voltage drop, so it becomes difficult to supply the regenerative power to the electric vehicle 30A located far from the electric vehicle 30B. In such a case, the electric energy that should be generated as regenerative power is consumed as heat of the mechanical brake in the electric vehicle 30B, and the regenerative power cannot be effectively utilized.

[0084] On the other hand, in the DC power supply system 100 according to Embodiment 1, in response to the DC power supply voltage VT rising above the reference voltage VTR due to the reverse flow of the regenerative power generated by the electric vehicle 30B, the DC / DC converter 20B arranged between the substation 10 and the end of the line R outputs DC power PO according to the deviation ΔVT between the DC power supply voltage VT and the reference voltage VTR.

[0085] Specifically, inside the DC / DC converter 20B, the control unit 42B refers to the relationship between the DC power command value PO* and the DC intermediate voltage VT shown in FIG. 5, and generates the DC power command value PO* based on the deviation ΔVT between the DC intermediate voltage VT and the reference voltage VTR. Since VT > VTR, the DC power command value PO* becomes a negative value. The control unit 42B generates a duty ratio command value Db* by feedback control to make the DC power PO follow the DC power command value PO*. When PO* < 0, the duty ratio command value Db* becomes the duty ratio command value D2b* during the boost operation. The control unit 42B compares the levels of the duty ratio command value Db* and the carrier signal, and outputs gate signals G1 and G2 indicating the comparison result. The gate signal G2 has a duty ratio with a value corresponding to the duty ratio command value D2b*, and the gate signal G1 is maintained at the L level.

[0086] The DC / DC converter 40B is driven by the gate signals G1 and G2, and converts the DC intermediate voltage VT into a DC intermediate voltage VF. By the boost operation of the DC / DC converter 40B, DC power is supplied from the DC intermediate wire T to the high-voltage DC intermediate wire F. Thereby, the voltage rise of the DC intermediate wire T is compensated.

[0087] Due to the power supply to the high-voltage DC intermediate wire F by the DC / DC converter 20B, when the DC intermediate voltage VF of the high-voltage DC intermediate wire F rises and becomes higher than the reference voltage VFR, the DC / DC converter 20A arranged near the substation 10 performs DC / DC conversion so that the DC intermediate voltage VF becomes constant.

[0088] Specifically, inside the DC / DC converter 20A, the control unit 42A generates a duty ratio command value D1a* during the buck operation by feedback control to make the DC intermediate voltage VT follow the reference voltage VTR, and generates a duty ratio command value D2a* during the boost operation by feedback control to make the DC intermediate voltage VF follow the reference voltage VFR.

[0089] Since VF > VFR, the control unit 42A selects the duty ratio command value D1a* during the step-down operation as the duty ratio command value Da*. The control unit 42A compares the levels of the duty ratio command value Da* and the carrier signal, and outputs gate signals G1 and G2 indicating the comparison result.

[0090] The gate signal G1 has a duty ratio corresponding to the duty ratio command value D1a* during the step-down operation, and the gate signal G2 is maintained at the L level. The DC / DC converter 40A is driven by the gate signal G1 and converts the DC intermediate voltage VF into the DC intermediate voltage VT. Due to the step-down operation of the DC / DC converter 40A, DC power is supplied from the high-voltage DC intermediate wire F to the DC intermediate wire T. The DC power supplied to the DC intermediate wire T is supplied to the electric vehicle 30A that is powering near the substation 10.

[0091] In this way, when the DC / DC converter device 20B performs the boost operation and the DC / DC converter device 20A performs the step-down operation, as shown by the arrow A3, the regenerative power generated by the electric vehicle 30B due to the regenerative brake is supplied to the electric vehicle 30A that is powering via the DC intermediate wire T, the DC / DC converter device 20B, the high-voltage DC intermediate wire F, the DC / DC converter device 20A, and the DC intermediate wire T.

[0092] According to the above configuration, the regenerative power generated by the electric vehicle 30B with the regenerative brake can also be supplied to the electric vehicle 30A that is powering away from the electric vehicle 30B. Therefore, the regenerative power can be effectively utilized.

[0093] In addition, since the regenerative power is sent through the high-voltage DC intermediate wire F, compared with the conventional DC intermediate system that sends the regenerative power through the DC intermediate wire T, the regenerative current becomes smaller, and as a result, the DC intermediate loss can be reduced. Therefore, it is possible to improve the utilization efficiency of the regenerative power.

[0094] [Embodiment 2] In the DC power supply system 100 described in the above-described Embodiment 1, the DC / DC converter 20B selectively executes a step-down operation and a step-up operation according to the deviation ΔVT between the DC power supply voltage VT and the reference voltage VTR, thereby compensating for the voltage drop and voltage increase of the DC power supply line T. Further, the DC / DC converter 20A selectively executes a step-up operation and a step-down operation so that the DC power supply voltage VF of the high-voltage DC power supply line F becomes constant, thereby transmitting and receiving DC power between the substation 10 or the electric vehicle 30A and the electric vehicle 30B through the high-voltage DC power supply line F.

[0095] However, if a deviation occurs in the control of DC / DC conversion between the DC / DC converter 20A and the DC / DC converter 20B, a deviation may occur between the DC power supply voltage VT and the DC power supply voltage VF at the point where the DC / DC converter 20A is connected and the DC power supply voltage VT and the DC power supply voltage VF at the point where the DC / DC converter 20B is connected. In such a case, there is a possibility that a circulating current may be generated between the DC power supply line T and the high-voltage DC power supply line F and / or between the DC / DC converter 20A and the DC / DC converter 20B. The generation of the circulating current increases the losses of the DC / DC converter 20A and the DC / DC converter 20B, so there is a concern that the efficiency of the DC power supply system 100 may be reduced.

[0096] In Embodiment 2, a method for suppressing the generation of a circulating current will be described. Since the configuration of the DC power supply system 100 according to Embodiment 2 is the same as the configuration of the DC power supply system 100 according to Embodiment 1, the description thereof will be omitted.

[0097] The DC power system 100 according to Embodiment 2 differs from the DC power system 100 according to Embodiment 1 in the control configuration of the DC / DC converter 20B. Also in Embodiment 2, as described with reference to FIG. 4, inside the DC / DC converter 20B, the control unit 42B is configured to control the DC / DC converter 40B so as to output DC power according to the deviation ΔVT between the DC power voltage VT and the reference voltage VTR. Specifically, the voltage control unit 60 generates a DC power command value PO*, which is a command value of the DC power PO output from the DC / DC converter 40B, according to the deviation ΔVT between the DC power voltage VT detected by the voltage detector 46 and the reference voltage VTR.

[0098] FIG. 8 is a diagram for explaining the operation of the voltage control unit 60 according to Embodiment 2, and is a diagram for comparison with FIG. 5. FIG. 8 shows the relationship between the DC power voltage VT and the DC power command value PO* of the DC / DC converter 40B. The horizontal axis of FIG. 8 represents the DC power voltage VT, and the vertical axis represents the DC power command value PO*.

[0099] In FIG. 8, the difference from FIG. 5 is that a dead zone is provided in the relationship between the DC power voltage VT and the DC power command value PO*. The dead zone is provided in a region where the absolute value of the deviation ΔVT between the DC power voltage VT and the reference voltage VTR is equal to or less than a predetermined threshold value Vth. In the dead zone, PO* is set to 0.

[0100] Accordingly, in the region (dead zone) where the absolute value of the deviation ΔVT is equal to or less than the threshold value Vth, the DC / DC converter 40B is controlled to stop the execution of DC / DC conversion and not output DC power. On the other hand, when the DC power voltage VT rises beyond the dead zone, the DC / DC converter 40B is controlled to perform a boosting operation according to the negative DC power command value PO*. Thereby, power is supplied from the DC power line T to the high-voltage DC power line F. Conversely, when the DC power voltage VT drops beyond the dead zone, the DC / DC converter 40B is controlled to perform a bucking operation according to the positive DC power command value PO*. Thereby, power is supplied from the high-voltage DC power line F to the DC power line T.

[0101] In a region where the absolute value of the deviation ΔVT of the DC voltage VT with respect to the reference voltage VTR is small, the DC / DC converter 20B does not output DC power, that is, by providing a dead zone in which the DC / DC converter 20B is stopped, it is possible to suppress the generation of a circulating current due to a control deviation between the DC / DC converter 20A and the DC / DC converter 20B.

[0102] [Embodiment 3] In the above-described Embodiment 1, a configuration example in which one DC / DC converter 20B is arranged between the substation 10 and the end of the line R has been described. However, a configuration in which a plurality of DC / DC converters 20B are arranged between the substation 10 and the end of the line R may also be used.

[0103] FIG. 9 is a schematic block diagram for explaining the configuration of the DC power supply system 100 according to Embodiment 3. As shown in FIG. 9, the DC power supply system 100 includes a DC power supply line T, a high-voltage DC power supply line F, a DC / DC converter 20A, and a plurality (for example, two) of DC / DC converters 20B.

[0104] The DC / DC converter 20A is located between the substation 10 and the end of the DC power supply line T. Preferably, the DC / DC converter 20A is located at or near the substation 10.

[0105] The plurality of DC / DC converters 20B are located between the DC / DC converter 20A and the end of the DC power supply line T. Preferably, the plurality of DC / DC converters 20B are arranged at intervals from each other between the DC / DC converter 20A and the end of the DC power supply line T.

[0106] FIG. 9 also shows a graph of the DC voltage VT of the DC power supply line T. The horizontal axis of the graph indicates the running position of the electric vehicle 30 traveling on the line R, and the vertical axis indicates the DC voltage VT at the running position.

[0107] A voltage drop corresponding to the distance from the substation 10 to the running position of the electric vehicle 30 occurs in the DC overhead wire T. This voltage drop is proportional to the resistance of the DC overhead wire T and the load current, and increases as the distance from the substation 10 increases.

[0108] Each of the plurality of DC / DC converters 20B is configured to output DC power according to the deviation ΔVT between the DC overhead voltage VT and the reference voltage VTR at the point where the DC / DC converter 20B is connected. Therefore, the voltage drop at each point of the DC overhead wire T can be compensated.

[0109] According to this, by arranging the plurality of DC / DC converters 20B apart from each other, the limitation on the travelable range of the electric vehicle 30 can be eliminated. Therefore, it is possible to extend the length of the section where the substation 10 exists only at one end of the line and the other end (terminal) of the line is a dead end.

[0110] It should be considered that all aspects of the embodiments disclosed this time are illustrative and not restrictive. The scope of the present disclosure is indicated not by the above description but by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

Explanation of Reference Numerals

[0111] 10 Substation, 20A, 20B DC / DC converter, 30, 30A, 30B Electric vehicle, 40A, 40B DC / DC converter, 42A, 42B Controller, 44, 46 Voltage detector, 48 Current detector, 50, 64 Subtractor, 52, 66 Controller, 54, 58 Gate signal generator, 60 Voltage control unit, 62 Power detector, 100 DC overhead system, Q1~Q4 IGBT, D1~D4 Diode, F High-voltage DC overhead wire, T DC overhead wire, R Line, T1, T2 Low-voltage side DC terminal, T3, T4 High-voltage side DC terminal, VF, VT DC overhead voltage, VFR Reference voltage, PO* DC power command value.

Claims

1. A first DC catenary wire that receives power supply of a first DC catenary voltage from a substation and supplies DC power to an electric vehicle traveling on a line, A second DC catenary wire arranged in parallel with the first DC catenary wire and having a second DC catenary voltage higher than the first DC catenary voltage, A first DC / DC converter located between the substation and the end of the first DC catenary wire and connected between the first DC catenary wire and the second DC catenary wire, At least one second DC / DC converter located between the first DC / DC converter and the end of the first DC catenary wire and connected between the first DC catenary wire and the second DC catenary wire, The at least one second DC / DC converter performs bidirectional DC / DC conversion between the first DC catenary wire and the second DC catenary wire so as to transfer DC power corresponding to a deviation between the first DC catenary voltage and a predetermined first reference voltage between the first DC catenary wire and the second DC catenary wire, The first DC / DC converter performs bidirectional DC / DC conversion between the first DC catenary wire and the second DC catenary wire so that the second DC catenary voltage becomes a predetermined second reference voltage, a DC catenary system.

2. The first DC / DC converter is arranged in the substation closest to the end of the first DC catenary wire, the DC catenary system according to claim 1.

3. The at least one second DC / DC converter includes a plurality of second DC / DC converters, The plurality of second DC / DC converters are arranged at intervals between the first DC / DC converter and the end of the first DC catenary wire, the DC catenary system according to claim 1.

4. The at least one second DC / DC converter, When the first DC catenary voltage is greater than the first reference voltage, supplies DC power corresponding to the deviation from the first DC catenary wire to the second DC catenary wire, When the first DC catenary voltage is less than the first reference voltage, supplies DC power corresponding to the deviation from the second DC catenary wire to the first DC catenary wire, the DC catenary system according to any one of claims 1 to 3.

5. The at least one second DC / DC converter does not perform bidirectional DC / DC conversion when the magnitude of the deviation is less than a threshold value, the DC catenary system according to claim 4.

6. The first DC / DC converter: When the second DC voltage is greater than the second reference voltage, supplies DC power from the second DC power line to the first DC power line; When the second DC voltage is less than the second reference voltage, supplies DC power from the first DC power line to the second DC power line. The DC power system according to any one of claims 1 to 3.

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