Patent Description:
In an electric railway, an electrical substation as a power source and a vehicle as a load are each connected to an overhead line as a positive electrode and a rail as a negative electrode to form an electric circuit, thereby supplying an electric power necessary for running of the vehicle. That is, during the vehicle running, a current flows from the electrical substation to the vehicle through the overhead line as the positive electrode, and a current flows (return current) from the vehicle to the electrical substation through the rail as the negative electrode.

The return current causes a voltage drop in the rail between the electrical substation and the vehicle, thus causing an electric potential difference (rail-to-ground voltage) between the rail and the ground as an electric potential reference in accordance with a distribution of the voltage drop on the entire train line. Since an excessive rail-to-ground voltage causes a risk of electrical shock when a railway worker touches the rail, recently, as indicated by the international standard IEC62128, it is required to keep the rail-to-ground voltage within a predetermined range (see IEC62128-<NUM>:<NUM>. Railway applications-Fixed installations-Electrical safety, earthing and the return circuit-Part <NUM>: Protective provisions against electric shock, IEC62128-<NUM>:<NUM>. Railway applications-Fixed installations-Electrical safety, earthing and the return circuit-Part <NUM>: Provisions against the effects of stray currents caused by d. traction systems, and IEC62128-<NUM>:<NUM>. Railway applications-Fixed installations-Electrical safety, earthing and the return circuit-Part <NUM>: Mutual interaction of a. traction systems).

For example, as disclosed in <CIT>, as a countermeasure to the excessive rail-to-ground voltage, a device (VLD: Voltage Limiting Device) for suppressing the rail-to-ground voltage is introduced. With this device, a short circuit switch is disposed between a rail and an earth, and a short circuit is caused between the rail and the earth when the rail-to-ground voltage exceeding a predetermined value is detected, and potential equalization is performed between the rail and the ground, thereby suppressing the rail-to-ground voltage.

However, in the conventional configuration in which the VLD is disposed as disclosed in <CIT>, there is a problem in that while the rail-to-ground voltage at the proximity of the VLD is suppressed, a fluctuation of the rail-to-ground voltage at an activated position of the VLD spreads to the entire train line, thus secondarily generating the excessive rail-to-ground voltage at a distant place from the VLD.

The present invention has been made in consideration of the above-described point, and its one object is to suppress a generation of an excessive rail-to-ground voltage at a distant place from a voltage control device due to a spread of a fluctuation of a rail-to-ground voltage at an activated position of the voltage control device to the entire train line.

To solve the above-described problem, the present invention provides a rail-to-ground voltage suppression system for an electric railway according to claim <NUM>.

The present invention can suppress, for example, the generation of the excessive rail-to-ground voltage at the distant place from the voltage control device due to the spread of the fluctuation of the rail-to-ground voltage at the activated position of the voltage control device to the entire train line.

The following describes preferred embodiments of the present invention. In the following description, the same reference numerals are attached to the same or similar elements and processes, differences are described, and repeated explanations are omitted. In the embodiments described later, differences from the previously described embodiments are described and repeated explanations are omitted.

The configurations and the processes indicated by the following description and the respective diagrams are merely examples of an outline of the embodiment necessary for understanding and exploitation of the present invention, and not intended to limit the aspects of the present invention.

Before the description of the embodiments, the problem in the conventional technique will be described. <FIG> is a drawing for describing a problem in the conventional technique. <FIG> illustrates an outline of a rail-to-ground voltage suppression system S according to the conventional technique. The rail-to-ground voltage suppression system S according to the conventional technique includes a VLD <NUM>.

A train <NUM> and an electrical substation <NUM> are each connected to an overhead line <NUM> and a rail <NUM>, and a current flows through the overhead line <NUM> as a positive electrode side and the rail <NUM> as a negative electrode, thus supplying an electric power from the electrical substation <NUM> to the train <NUM>. The rail <NUM> is connected to a ground electrode <NUM> via the VLD <NUM>. The VLD <NUM> short circuits between the rail <NUM> and the ground electrode <NUM> when a voltage exceeding a predetermined value is generated between the rail <NUM> and the ground electrode <NUM>.

As indicated by a dotted line <NUM> in a lower drawing of <FIG>, the rail-to-ground voltage deviates from an allowable range at an activated position of the VLD <NUM>. Then, when the VLD <NUM> is activated to bring the rail-to-ground voltage at the activated position close to <NUM> V as indicated by a solid line <NUM>, the rail-to-ground voltage is similarly suppressed also at positions other than the activated position. Therefore, as illustrated in the lower drawing of <FIG>, there is a problem in that the rail-to-ground voltage deviates from the allowable range to become excessive at positions farther than a predetermined position with respect to the activated position.

<FIG> is a block diagram of a rail-to-ground voltage suppression system <NUM> according to the first embodiment of the present invention. The rail-to-ground voltage suppression system <NUM> for an electric railway includes a voltage control device <NUM> and a rail-to-ground voltage acquisition device <NUM>.

The voltage control device <NUM> connects the rail <NUM> and the ground electrode <NUM>, and controls a voltage between the rail <NUM> and the ground electrode <NUM>. Details of the voltage control device <NUM> will be described later. The rail-to-ground voltage acquisition device <NUM> acquires the voltage between the rail <NUM> and the ground electrode <NUM>, and outputs it as a rail-to-ground voltage <NUM> to the voltage control device <NUM>.

<FIG> is a block diagram of the voltage control device <NUM> according to the first embodiment of the present invention. The voltage control device <NUM> includes a voltage determination unit <NUM> and a voltage control circuit <NUM>. The voltage determination unit <NUM> receives the rail-to-ground voltage <NUM> and outputs a voltage control command value <NUM>. Details of a process in the voltage determination unit <NUM> will be described later.

The voltage control circuit <NUM> receives the voltage control command value <NUM>, and controls the voltage between the rail <NUM> and the ground electrode <NUM>. For example, the voltage control circuit <NUM> includes a variable resistor having a function to feed back the voltage between the rail <NUM> and the ground electrode <NUM>, and employs a method in which a resistance value of the variable resistor is controlled such that the voltage between the rail <NUM> and the ground electrode <NUM> has the voltage control command value <NUM>.

The voltage control circuit <NUM> only needs to have a system configuration that can control the voltage between the rail <NUM> and the ground electrode <NUM>. For example, the voltage control circuit <NUM> may include a bidirectional chopper that has a function to feed back a voltage, and employ a method to control an apparent resistance value by adjusting a conduction ratio of the chopper such that the voltage between the rail <NUM> and the ground electrode <NUM> has the voltage control command value <NUM>. The bidirectional chopper is an example, and any device configured to bidirectionally step down a voltage may be employed.

<FIG> is a flowchart illustrating a process in the voltage determination unit <NUM> according to the first embodiment of the present invention. Execution of the process illustrated in <FIG> is triggered by detection of the deviation of the rail-to-ground voltage <NUM> from the allowable range by the voltage determination unit <NUM>.

At first, in Step S401, the voltage determination unit <NUM> determines the rail-to-ground voltage <NUM> to be positive or negative, advances the process to Step S402 in the case of being positive (Yes, in Step S401), and advances the process to Step S403 in the case of being negative (No, in Step S401). In Step S402, the voltage determination unit <NUM> sets the voltage control command value <NUM> to an allowable maximum value (see <FIG>) in the allowable range of the rail-to-ground voltage <NUM>, and outputs it. Meanwhile, in Step S403, the voltage determination unit <NUM> sets the voltage control command value <NUM> to an allowable minimum value (see <FIG>) in the allowable range of the rail-to-ground voltage <NUM>, and outputs it.

<FIG> is a drawing for describing the effect of the first embodiment of the present invention. In <FIG>, a dotted line <NUM> indicates the rail-to-ground voltage before activating the rail-to-ground voltage suppression system <NUM>. A solid line <NUM> indicates the rail-to-ground voltage in a state where the rail-to-ground voltage suppression system <NUM> is activated. A two-dot chain line <NUM> indicates the rail-to-ground voltage assuming that the VLD of the conventional technique is activated at the position of the voltage control device <NUM>.

While the two-dot chain line <NUM> indicates that the rail-to-ground voltage falls below the allowable minimum value at a position apart from the rail-to-ground voltage suppression system <NUM>, the solid line <NUM> indicates that the reduction amount of the rail-to-ground voltage at the position of the rail-to-ground voltage suppression system <NUM> is reduced to be minimum and the rail-to-ground voltage is kept within the allowable range also at the position apart from the rail-to-ground voltage suppression system <NUM>.

As described above, according to the embodiment, the deviation of the rail-to-ground voltage from the allowable range can be avoided at the position apart from the rail-to-ground voltage suppression system <NUM>.

In this embodiment, the example in which one pair of the voltage control device <NUM> and the rail-to-ground voltage acquisition device <NUM> is installed in the train line is indicated. However, a plurality of pairs can be installed to individually control the rail-to-ground voltage <NUM> at respective installation positions. For example, even when the rail-to-ground voltage simultaneously exceeds the allowable maximum value at one installation position and falls below the allowable minimum value at another installation position, the similar effect can be provided.

<FIG> is a block diagram of a rail-to-ground voltage suppression system <NUM> according to the second embodiment of the present invention. The rail-to-ground voltage suppression system <NUM> includes a voltage control device <NUM> and a plurality of rail-to-ground voltage acquisition devices 202a, 202b, 202c, and 202d.

The voltage control device <NUM> receives rail-to-ground voltages 211a, 211b, 211c, and 211d from the plurality of rail-to-ground voltage acquisition devices 202a, 202b, 202c, and 202d, respectively, and controls the voltage between the rail <NUM> and the ground electrode <NUM>. Details of the voltage control device <NUM> will be described later.

The rail-to-ground voltage acquisition devices 202a, 202b, 202c, and 202d are the same as the rail-to-ground voltage acquisition device <NUM> described in the first embodiment, thus omitting the description.

<FIG> is a block diagram of the voltage control device <NUM> according to the second embodiment of the present invention. The voltage control device <NUM> includes a voltage determination unit <NUM> and a voltage control circuit <NUM>.

The voltage determination unit <NUM> receives the rail-to-ground voltages 211a, 211b, 211c, and 211d, and outputs the voltage control command value <NUM>. Details of a process in the voltage determination unit <NUM> will be described later. The voltage control circuit <NUM> receives the voltage control command value <NUM> and controls an electric potential difference between the rail <NUM> and the ground electrode <NUM>. The voltage control circuit <NUM> includes a converter configured to bidirectionally step up/down a voltage. The converter configured to bidirectionally step up/down a voltage is an example, and any device configured to bidirectionally step up/down a voltage may be employed.

<FIG> is a flowchart illustrating a process in the voltage determination unit <NUM> according to the second embodiment of the present invention. The process illustrated in <FIG> is regularly executed. At first, in Step S801, the voltage determination unit <NUM> determines whether any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has exceeded the allowable maximum value in the allowable range or not. When any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has exceeded the allowable maximum value in the allowable range (Yes, in Step S801), the voltage determination unit <NUM> advances the process to Step S803, and advances the process to Step S802 in the other case.

In Step S802, the voltage determination unit <NUM> determines whether any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has fallen below the allowable minimum value in the allowable range or not. When any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has fallen below the allowable minimum value in the allowable range (Yes, in S802), the voltage determination unit <NUM> advances the process to Step S804, and the process in the voltage determination unit <NUM> according to the second embodiment ends in the other case.

In Step S803, the voltage determination unit <NUM> calculates the voltage control command value <NUM> (voltage control command value VS) based on a formula (<NUM>) below and outputs it.

In Step S804, the voltage determination unit <NUM> calculates the voltage control command value <NUM> (voltage control command value VS) based on a formula (<NUM>) below and outputs it.

While a process group of Steps S801 and S803 is executed with priority to a process group of Steps S802 and S804 in <FIG>, this should not be construed in a limiting sense. That is, the process group of Steps S802 and S804 may be executed with priority to the process group of Steps S801 and S803.

<FIG> and <FIG> are drawings for describing the effect of the second embodiment of the present invention. In the second embodiment, the voltage control by the voltage control device <NUM> includes the following four patterns.

At first, the effect provided in the situation of the pattern <NUM> in this embodiment will be described by referring to <FIG> illustrates an example in which the sign of the rail-to-ground voltage at the position at which the rail-to-ground voltage deviates from the allowable range matches the sign of the rail-to-ground voltage at the voltage control device position.

A dotted line <NUM> indicates the rail-to-ground voltage when the voltage control by the voltage control device <NUM> is not performed, and the rail-to-ground voltage at the position of the rail-to-ground voltage acquisition device 202b exceeds the allowable maximum value. A solid line <NUM> indicates the rail-to-ground voltage when a step-down control is performed in accordance with the control described in this embodiment, and the rail-to-ground voltage at the installation position of the rail-to-ground voltage acquisition device 202b is kept in the allowable range.

Thus, the rail-to-ground voltage acquisition devices 202a, 202b, 202c, and 202d are installed at the positions apart from the voltage control device <NUM>, and when the rail-to-ground voltage acquired by any of the rail-to-ground voltage acquisition devices deviates from the allowable range, the step-down control of the voltage of the voltage control device <NUM> is performed so as to keep the rail-to-ground voltage at the position of deviating from the allowable range in the allowable range. Accordingly, the rail-to-ground voltage in a wide range can be kept in the allowable range by one voltage control device.

Note that since the pattern <NUM> is a pattern in which the pattern <NUM> has the inverted signs, the illustration and the description are omitted.

Next, the effect provided in the situation of the pattern <NUM> in this embodiment will be described by referring to <FIG> illustrates an example in which the sign of the rail-to-ground voltage at the position at which the rail-to-ground voltage deviates from the allowable range does not match the sign of the rail-to-ground voltage at the voltage control device position.

A dotted line <NUM> indicates the rail-to-ground voltage when the voltage control by the voltage control device <NUM> is not performed, and the rail-to-ground voltage at the position of the rail-to-ground voltage acquisition device 202b exceeds the allowable maximum value. A solid line <NUM> indicates the rail-to-ground voltage when a step-up control in the negative direction is performed in accordance with the control described in this embodiment, and the rail-to-ground voltage of the rail-to-ground voltage acquisition device 202b is kept in the allowable range.

Thus, the rail-to-ground voltage acquisition devices 202a, 202b, 202c, and 202d are installed at the positions apart from the voltage control device position, and further, the voltage control circuit <NUM> includes the converter configured to bidirectionally step up/down the voltage. This allows the reduction of the rail-to-ground voltage even when the sign of the rail-to-ground voltage at the position at which the rail-to-ground voltage deviates from the allowable range does not match the sign of the rail-to-ground voltage at the voltage control device position. In addition, the rail-to-ground voltage in the wider range can be kept in the allowable range by one voltage control device.

Note that since the pattern <NUM> is a pattern in which in the pattern <NUM> has the inverted signs, the illustration and the description are omitted.

While the example in which the four rail-to-ground voltage acquisition devices 202a, 202b, 202c, and 202d are installed is described in this embodiment, the number of the rail-to-ground voltage acquisition devices is not limited thereto. The rail-to-ground voltage acquisition devices 202a, 202b, 202c, and 202d do not necessarily need to actually measure the rail-to-ground voltage, and for example, a configuration in which the rail-to-ground voltage is calculated to be acquired with a simulation model that calculates the rail-to-ground voltage from a train position, an electrical substation output power, and a train electric power may be employed. In this case, since the rail-to-ground voltage can be continuously calculated, the deviation of the rail-to-ground voltage from the allowable range can be reduced without fail using the rail-to-ground voltage precisely acquired at low cost compared with the case of the rail-to-ground voltage acquisition by the measurement.

While the voltage control command value <NUM> is obtained by the process illustrated in <FIG> in this embodiment, the voltage control command value <NUM> may be determined by a feedback of the rail-to-ground voltage value at the position at which the rail-to-ground voltage deviates from the allowable range and performing a PID control so as to keep the rail-to-ground voltage value in the allowable range.

<FIG> is a block diagram of a rail-to-ground voltage suppression system <NUM> according to the third embodiment of the present invention. Since the configuration other than a voltage control device <NUM> is the same as the configuration illustrated in <FIG> of the second embodiment, the description will be omitted.

<FIG> is a block diagram of the voltage control device <NUM> according to the third embodiment of the present invention. The voltage control device <NUM> includes a voltage determination unit <NUM> and the voltage control circuit <NUM>. Since the configuration other than the voltage determination unit <NUM> is the same as that of the voltage control device <NUM> of the second embodiment, the description will be omitted. The voltage determination unit <NUM> receives the rail-to-ground voltages 211a, 211b, 211c, and 211d, and outputs the voltage control command value <NUM>.

<FIG> is a flowchart illustrating a process in the voltage determination unit <NUM> according to the third embodiment of the present invention. The process illustrated in <FIG> is regularly executed.

At first, in Step S1301, the voltage determination unit <NUM> determines whether any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has exceeded the allowable maximum value in the allowable range or not. When any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has exceeded the allowable maximum value in the allowable range (Yes, in Step S1301), the voltage determination unit <NUM> advances the process to Step S1303, and advances the process to Step S1302 in the other case.

In Step S1302, the voltage determination unit <NUM> determines whether any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has fallen below the allowable minimum value in the allowable range or not. When any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has fallen below the allowable minimum value in the allowable range (Yes, in S1302), the voltage determination unit <NUM> advances the process to Step S1204, and the process in the voltage determination unit <NUM> according to the third embodiment ends in the other case.

In Step S1303, the voltage determination unit <NUM> calculates the voltage control command value <NUM> (voltage control command value VS) based on a formula (<NUM>) below such that a difference between the maximum value and the allowable maximum value of the rail-to-ground voltage becomes the same as a difference between the minimum value and the allowable minimum value of the rail-to-ground voltage, and outputs it. <MAT> <MAT>.

In Step S1304, the voltage determination unit <NUM> calculates the voltage control command value <NUM> (voltage control command value VS) based on a formula (<NUM>) below such that the difference between the maximum value and the allowable maximum value of the rail-to-ground voltage becomes the same as the difference between the minimum value and the allowable minimum value of the rail-to-ground voltage, and outputs it. <MAT> <MAT>.

<FIG> is a drawing for describing the effect of the third embodiment of the present invention. A dotted line <NUM> indicates the rail-to-ground voltage when the voltage control by the voltage control device <NUM> is not performed, and the rail-to-ground voltage at the position of the rail-to-ground voltage acquisition device 202b exceeds the allowable maximum value. A solid line <NUM> indicates the rail-to-ground voltage when a step-down control is performed in accordance with the control described in this embodiment, and the rail-to-ground voltage of the rail-to-ground voltage acquisition device 202b is kept in the allowable range and further has a value smaller than the allowable maximum value.

As illustrated in <FIG>, a difference d1 between the allowable maximum value and the rail-to-ground voltage 211b of the rail-to-ground voltage acquisition device 202b is equal to a difference d2 between the rail-to-ground voltage 211d of the rail-to-ground voltage acquisition device 202d and the allowable minimum value. By controlling the voltage control device <NUM> in this manner, a sum of absolute values of the rail-to-ground voltages in the entire train line can be decreased, thereby allowing more reducing the risk possibly caused by the rail-to-ground voltage.

<FIG> is a block diagram of a rail-to-ground voltage suppression system <NUM> according to the fourth embodiment of the present invention. The rail-to-ground voltage suppression system <NUM> includes a voltage control device <NUM>, the rail-to-ground voltage acquisition devices 202a, 202b, 202c, and 202d, and a protection target area setting unit <NUM>. Since the rail-to-ground voltage acquisition devices 202a, 202b, 202c, and 202d are the same as those illustrated in <FIG> of the second embodiment, the description will be omitted.

The voltage control device <NUM> receives rail-to-ground voltages 211a, 211b, 211c, and 211d from the plurality of rail-to-ground voltage acquisition devices 202a, 202b, 202c, and 202d. The voltage control device <NUM> receives protection target area setting information <NUM> from the protection target area setting unit <NUM>. The voltage control device <NUM> controls the voltage between the rail <NUM> and the ground electrode <NUM> based on these inputs. Details of the voltage control device <NUM> will be described later.

The protection target area setting unit <NUM> sets a position or a section to suppress the increase of the rail-to-ground voltage to a protection target area, and outputs the protection target area setting information <NUM> to the voltage control device <NUM>. The protection target area is a position or a section set to the rail <NUM> to protect a human and the like from an electric shock by suppressing a rail-to-ground voltage average value to a predetermined value (for example, <NUM> V or a value of the predetermined value or less).

<FIG> is a block diagram of the voltage control device <NUM> according to the fourth embodiment of the present invention. The voltage control device <NUM> includes a voltage determination unit <NUM> and the voltage control circuit <NUM>. Since the configuration other than the voltage determination unit <NUM> is the same as that of the voltage control device <NUM> of the second embodiment, the description will be omitted. The voltage determination unit <NUM> receives the rail-to-ground voltages 211a, 211b, 211c, and 211d and the protection target area setting information <NUM>, and outputs the voltage control command value <NUM>.

<FIG> is a flowchart illustrating a process in the voltage determination unit <NUM> according to the fourth embodiment of the present invention. The process illustrated in <FIG> is regularly executed.

At first, in Step S1701, the voltage determination unit <NUM> determines whether any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has exceeded the allowable maximum value or not. When any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has exceeded the allowable maximum value (Yes, in Step S1701), the voltage determination unit <NUM> advances the process to Step S1703, and advances the process to Step S1702 in the other case.

In Step S1702, the voltage determination unit <NUM> determines whether any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has fallen below the allowable minimum value or not. When any of the rail-to-ground voltages 211a, 211b, 211c, and 211d has fallen below the allowable minimum value (Yes, in S1702), the voltage determination unit <NUM> advances the process to Step S1706, and the process in the voltage determination unit <NUM> according to the fourth embodiment ends in the other case.

In Step S1703, the voltage determination unit <NUM> determines whether a formula (<NUM>) below is satisfied or not. When the formula (<NUM>) below is satisfied (Yes, in Step S1703), the voltage determination unit <NUM> advances the process to Step S1704, and when the formula (<NUM>) below is not satisfied (No, in Step S1703), the voltage determination unit <NUM> advances the process to Step S1705.

Step S1704 is executed when Step S1703 is Yes, that is, a value obtained by subtracting the difference between the maximum value and the allowable maximum value of the rail-to-ground voltage from the rail-to-ground voltage average value of the protection target area set by the protection target area setting unit <NUM> is negative. At this time, the rail-to-ground voltage decreased more than necessary causes the rail-to-ground voltage of the protection target area to become apart from <NUM> V to be small. That is, the absolute value of the rail-to-ground voltage increases. Therefore, in Step S1704, the voltage determination unit <NUM> calculates the voltage control command value <NUM> (voltage control command value VS) based on a formula (<NUM>) below so as to suppress the reduction amount of the rail-to-ground voltage to a minimum, and outputs it.

Meanwhile, Step S1705 is executed when Step S1703 is No, that is, the value obtained by subtracting the difference between the maximum value and the allowable maximum value of the rail-to-ground voltage from the rail-to-ground voltage average value of the protection target area set by the protection target area setting unit <NUM> is positive. At this time, as the rail-to-ground voltage is decreased, the rail-to-ground voltage average value of the protection target area can be approached to <NUM> V. Therefore, in Step S1705, the voltage determination unit <NUM> calculates the voltage control command value VS using a formula (<NUM>) below so as to make the rail-to-ground voltage average value of the protection target area <NUM> V, and outputs it.

Meanwhile, in Step S1706, the voltage determination unit <NUM> determines whether a formula (<NUM>) below is satisfied or not. When the formula (<NUM>) below is satisfied (Yes, in Step S1706), the voltage determination unit <NUM> advances the process to Step S1707, and when the formula (<NUM>) below is not satisfied (No, in Step S1706), the voltage determination unit <NUM> advances the process to Step S1708.

Step S1707 is executed when Step S1706 is Yes, that is, a value obtained by adding the difference between the allowable minimum value and the minimum value of the rail-to-ground voltage to the rail-to-ground voltage average value of the protection target area set by the protection target area setting unit <NUM> is <NUM> or more. At this time, the rail-to-ground voltage increased more than necessary causes the rail-to-ground voltage of the protection target area to become apart from <NUM> V to be large. That is, the absolute value of the rail-to-ground voltage increases. Therefore, in Step S1707, the voltage determination unit <NUM> calculates the voltage control command value VS based on a formula (<NUM>) below so as to suppress the increased amount of the rail-to-ground voltage to a minimum, and outputs it.

Meanwhile, Step S1708 is executed when Step S1706 is No, that is, a value obtained by adding the difference between the allowable minimum value and the minimum value of the rail-to-ground voltage to the rail-to-ground voltage average value of the protection target area set by the protection target area setting unit <NUM> is negative. At this time, as the rail-to-ground voltage is increased, the rail-to-ground voltage average value of the protection target area can be approached to <NUM> V. Therefore, in Step S1708, the voltage determination unit <NUM> calculates the voltage control command value VS based on a formula (<NUM>) below so as to make the rail-to-ground voltage average value of the protection target area <NUM> V, and outputs it.

<FIG> is a drawing for describing the effect of the fourth embodiment of the present invention. A dotted line <NUM> indicates the rail-to-ground voltage when the voltage control by the voltage control device <NUM> is not performed, and the rail-to-ground voltage at the position of the rail-to-ground voltage acquisition device 202b exceeds the allowable maximum value. A solid line <NUM> indicates the rail-to-ground voltage when a step-down control is performed in accordance with the control described in this embodiment, and the rail-to-ground voltage of the rail-to-ground voltage acquisition device 202b is kept in the allowable range, and further, the rail-to-ground voltage average value of the protection target area is <NUM> V. By controlling the voltage control device <NUM> in this manner, the rail-to-ground voltage of the protection target area can be decreased while keeping the rail-to-ground voltage in the allowable range, thereby allowing more reducing the risk of an electric shock due to the rail-to-ground voltage.

While the case where only one protection target area is set is described in this embodiment, a plurality of the protection target areas may be set. In this case, the control may be performed in a manner in which a priority order is given to the protection target area, and the rail-to-ground voltage average value of the protection target area having the high priority order is suppressed to a predetermined value. Alternatively, the control may be performed in a manner in which a sum of the rail-to-ground voltage average values of the plurality of protection target areas is suppressed to a predetermined value.

While the example in which the rail-to-ground voltage average value of the protection target area is decreased is described in this embodiment, the control may be performed in a manner in which the rail-to-ground voltage of the protection target area is suppressed by decreasing the maximum value, the minimum value, or the like not limiting to the average value.

While the description is omitted in the above-described first to fourth embodiments, a plurality of the voltage control devices may be disposed in the train line. In this case, the voltage control device at the position closest to a rail-to-ground voltage acquisition device having the rail-to-ground voltage deviating from the allowable range controls the rail-to-ground voltage at the installation position of itself, thus allowing to avoid competing in the control.

The voltage control device of the rail-to-ground voltage having the sign the same as that of the rail-to-ground voltage deviating from the allowable range and having the maximum absolute value controls the rail-to-ground voltage at the installation position of itself, thereby maximally ensuring the reduction range of the absolute value of the rail-to-ground voltage.

Claim 1:
A rail-to-ground voltage suppression system for an electric railway, comprising:
one or a plurality of rail-to-ground voltage acquisition devices (<NUM>) that each acquires a rail-to-ground voltage (<NUM>); and
a voltage control device (<NUM>, <NUM>, <NUM>, <NUM>) that connects a rail (<NUM>) and a ground electrode (<NUM>),
characterized in that:
the voltage control device (<NUM>, <NUM>, <NUM>, <NUM>) includes a voltage determination unit (<NUM>, <NUM>, <NUM>, <NUM>) that receives the rail-to-ground voltage (<NUM>) and outputs a voltage control command value (<NUM>), and further includes a voltage control circuit (<NUM>, <NUM>) that receives the voltage control command value, and controls the voltage between the rail and the ground electrode, wherein the voltage control circuit includes a variable resistor device configured to feed back the voltage between the rail and the ground electrode, and controls an actual or apparent resistance value of the variable resistor device such that the voltage between the rail and the ground electrode has the voltage control command value, wherein
when the rail-to-ground voltage (<NUM>) acquired by any of the rail-to-ground voltage acquisition devices (<NUM>) at an installation position of the rail-to-ground voltage acquisition device deviates from an allowable range, the voltage control device (<NUM>, <NUM>, <NUM>, <NUM>) controls the rail-to-ground voltage at the installation position of the voltage control device by connecting the rail (<NUM>) and the ground electrode (<NUM>) corresponding to the rail-to-ground voltage acquired by the rail-to-ground voltage acquisition device to keep the rail-to-ground voltage in the allowable range.