Power storage apparatus

In a power storage apparatus, for storing DC electric power, which is configured by connecting in series a plurality of modules each including a plurality of cells connected with one another, by providing two first switches at the input portion and at the output portion of the power storage apparatus and a second switch, in series with the modules, at a connection position where the modules are connected, the voltage to ground in the apparatus is lowered.

TECHNICAL FIELD

The preset invention relates to a power storage apparatus for storing DC electric power, and, for example, to a power storage apparatus that can be applied to an electric rolling stock or the like equipped with a power storage system.

BACKGROUND ART

To date, it has been known that, by applying a power storage device, such as a secondary battery or an electric double layer capacitor, to an electric railway system so as to configure the electric railway system in such away that superfluous regenerative electric power generated while the vehicle is braked (during a regenerative period) is stored in the power storage device and the stored electric power is utilized while the vehicle is accelerated (during a power running period), the kinetic energy of the vehicle can effectively be utilized (e.g., Non-Patent Document 1).

Institute of Electrical Engineers of Japan, national convention 5-176, 2005, “Development of Power Storage System for DC Rolling Stock applying Electric Double Layer Capacitor”

A smallest element of a power storage device utilized for the power storage system is referred to as a cell and a plurality of cells connected in a series-parallel fashion is referred to as a module. A necessary voltage and a necessary current are obtained by further connecting a great number of the modules.

DISCLOSURE OF THE INVENTION

Meanwhile, in the case where the power storage device is applied to an electric railway system, a great number of modules are connected in series; the voltage to ground thereof is as high as 750 V to 1500 V. When, among power storage devices, a secondary battery, in particular, is completely discharged, the lifetime thereof becomes extremely short; therefore, even while the power storage system is not in operation, the power storage device is left charged, whereby the voltage to ground is maintained as high as 750 V to 1500 V. Accordingly, it has been a problem that the deterioration in the insulators in the power storage apparatus is accelerated due to a long-term charging; in addition to that, during repair and maintenance of the power storage apparatus, stringent insulation treatment is required.

The present invention provides a power storage apparatus that lowers the voltage to ground therein while being in the stop mode so as to suppress the deterioration in the insulators, thereby allowing the insulation treatment during repair and maintenance to be simplified.

A power storage apparatus according to the present invention includes two or more modules, connected in series one another, each of which is configured with a plurality of cells connected with one another; a grounding resistor for grounding a connection position where the modules are connected to each other; and first switches inserted at an input portion and an output portion.

In the case where the power storage apparatus is not operated, the voltages to ground at given positions in the power storage apparatus can be lowered; therefore, the voltages across the insulators (unillustrated) in the apparatus can be reduced, whereby the progress of the deterioration in the insulators can be suppressed.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1is a diagram illustrating a configuration example of a power storage apparatus according to Embodiment 1 of the present invention. The configuration of a power storage apparatus30will be explained with reference toFIG. 1. As illustrated inFIG. 1, modules2ato2d, in each of which cells1are connected in a series-parallel fashion, are connected in series. A switch3a(a second switch) is provided between the negative electrode terminal of the module2band the positive electrode terminal of the module2c, thereby dividing the modules2ato2dinto two groups, i.e., a group of the modules2aand2band a group of the modules2cand2d. Additionally, a display device5ais provided between the positive electrode terminal of the module2band the negative electrode terminal of the module2c. In this case, the display device5a, which is a device for visually indicating whether or not a voltage exists, by, e.g., blinking an LED, operates when a specific voltage is generated between the positive electrode terminal of the module2band the negative electrode terminal of the module2c.

The negative electrode of the module2aand the positive electrode of the module2bare connected to the reference electric potential plane31via a grounding resistor6a; the negative electrode of the module2cand the positive electrode of the module2dare connected to the reference electric potential plane31via a grounding resistor6b. Here, the grounding resistors6aand6bare resistors each having resistance on the order of several MΩ. The reference electric potential plane31is the ground having the ground electric potential. Furthermore, the positive electrode of the module2ais connected to a P line via a fuse20aand a switch3b(a first switch), and the negative electrode of the module2dis connected to an N line via a fuse20band a switch3c(a first switch); the P line and the N line are connected to a power conversion system40having a load41.

In addition, the switches3ato3care configured in such a way that the closing and opening thereof are controlled by a control unit22. In general, in the case where the power storage apparatus30is operated, the switches3ato3care closed, and in the case where the power storage apparatus30is stopped, the switches3ato3care opened. Additionally, outside the power conversion system40, the N line is connected to the reference electric potential plane31.

Electric power accumulated in the power storage apparatus30is supplied to the load41by way of the power conversion system40; on the other hand, the power storage apparatus30is charged with electric power from the load41, by way of the power conversion system40.

Next, a method, of lowering the voltage to ground in the power storage apparatus30, which is the purpose of the present invention will be explained. By configuring the power storage apparatus30as described above, the voltages to ground at given positions illustrated inFIG. 1, i.e., VG1, VG2, VA to VD, and VP are given by the equations below. In addition, here, for the better understanding of the explanation, it is assumed that the modules2ato2deach have the same configuration; the voltages VMa to VMd across the modules2ato2d, respectively, are the same and described “VM” as follows:

In the first place, the state in which the power storage apparatus30is in operation will be explained. Because the switches3ato3care closed, the following equations are given:
VA=VP
VB=VC=½×VP
VD=0.
Moreover,
VG1=VD+(VC−VD)/2
VG2=VB+(VA−VB)/2.

As a specific numerical value, assuming that, e.g., the voltage VM across each of the modules2ato2dis 250 V, the following voltages are given:

At the output terminal of the power storage apparatus30, the voltage VP of 1000 V, which is the sum of the voltages across the respective modules2ato2d, is obtained. The maximal voltage to ground, which is VA, is 1000 V.

In the second place, the state in which the power storage apparatus30is not operated will be explained. Because the switches3ato3care opened, no closed circuit is configured, whereby neither through the grounding resistor6anor through the grounding resistor6b, any current flows; thus, because VG1=VG2=VG=0, the following equations are given:
VA=+VM
VB=−VM
VC=+VM
VD=−VM.

As a specific numerical value, assuming that, e.g., the voltage VM across each of the modules2ato2dis 250 V, the following voltages are obtained:

whereby at the output terminal of the power storage apparatus30, no voltage is generated. The maximal voltage to ground, which is VA, is 250 V.

As described above, when the power storage apparatus30is not operated, the voltages to ground VG1and VG2can be lowered to 0 V, and the voltages to ground VA to VD can be lowered to the corresponding voltages VM across the modules2ato2d, respectively; therefore, the maximal voltage to ground can be made as low as one-fourth of the maximal voltage to ground in the case where the power storage apparatus30is operated.

In contrast, the circuit described in the conventional technique (Non-Patent Document 1) is configured in such a way that, when the power storage apparatus is not operated, only the switch provided at the positive electrode of the power storage apparatus can be opened; therefore, the voltage to ground is the same, whether the power storage apparatus is operated or not operated, and the voltage value is the sum of the voltages across all the respective modules.

As described heretofore, with the configuration according to the present invention, in the case where the power storage apparatus30is not operated, the voltages to ground at the given positions in the power storage apparatus30can be made as low as one-fourth of the voltage to ground in the case where the power storage apparatus30is operated; therefore, when the power storage apparatus30is not operated, the voltage across the insulators (unillustrated) in side the apparatus can be reduced, whereby the progress of the deterioration in the insulators can be suppressed. Moreover, when the power storage apparatus30is maintained, the insulation treatment can be simplified.

In addition, the display device5ais provided in order to visually ascertain whether or not the opening operation of the switches3ato3chas securely been performed. The operation will be explained below.

The display device5ahas a function in which a voltage VL across the display device5ais detected, and in the case where a voltage that is a specific value or larger exists, a display lamp is blinked so as to indicate that the voltage exists. In addition, for example, a means in which a buzzer is sounded instead of blinking the display lamp may be utilized.

In the case where the switches3ato3care opened, the voltage VL across the display device5ais 0 V; thus, the display device5adoes not operate.

Additionally, in the case where any one of the switches3ato3cis closed, the voltage VL across the display device5ais not 0 V; thus, the display device5adetects the voltage VL and operates.

By installing the display device5a, configured as described above, inside the power storage apparatus30or at an external position where the display device5acan be viewed, it is made possible that, before maintenance, it can visually be ascertained whether or not the switches3ato3chave securely been opened and the voltage to ground in the apparatus has been lowered.

In addition, although, in Embodiment 1, a configuration in which four modules are connected in series has been described, the configuration is not limited thereto; the power storage apparatus may similarly be configured in the same manner, as long as the configuration is in such a way that two or more modules are connected in series. Moreover, the configuration described in Embodiment 1 may be implemented, by constituting a new module with a number of modules connected in series and utilizing the new module as a constituent element.

FIG. 2is a diagram illustrating a configuration example of a power storage apparatus according to Embodiment 2 of the present invention.FIG. 2illustrates a configuration example in the case where the number of modules is six; the configuration is in such a way that modules2eand2fare added. In contrast toFIG. 1which illustrates a case in which the number of modules is four, the configuration is in such a way that a switch3abis connected between the negative electrode of the module2dand the positive electrode of the module2e, a display device5bis connected between the positive electrode of the module2dand the negative electrode of the module2e, and the connection point where the module2eand the module2fare connected is grounded to the reference electric potential plane31, by way of a grounding resistor6c.

As far as the operation is concerned, in the case where the number of modules is six, the explanation is the same as that for the case where the number of modules is four; therefore, the explanation will be omitted. With the configuration according to Embodiment 2, the maximal voltage to ground in the power storage apparatus is VP while the apparatus is operated; the maximal voltage to ground in the power storage apparatus is one-sixth of VP while the apparatus is not operated.

FIG. 3is a diagram illustrating a configuration example of a power storage apparatus according to Embodiment 3 of the present invention.FIG. 3is a diagram illustrating a configuration example in the case where the number of modules is two. The same reference characters inFIG. 3denote the same or equivalent constituent elements as those inFIGS. 1 and 2. In the case where the number of modules is two, the configuration is in such a way that the connection point where the modules2aand2bare connected is connected to the reference electric potential plane31, by way of the grounding resistor6a. With the configuration according to Embodiment 3, the maximal voltage to ground in the power storage apparatus is VP while the apparatus is operated; the maximal voltage to ground in the power storage apparatus is half of VP while the apparatus is not operated.

As described above, with configurations in Embodiments 1 to 3 of the present invention, in the case where the power storage apparatus30is not operated, the voltages to ground at the given positions in the power storage apparatus30can be lowered; therefore, the voltages across the insulators (unillustrated) in the apparatus can be reduced, whereby the progress of the deterioration in the insulators can be suppressed. Moreover, when the power storage apparatus30is maintained, the insulation treatment can be simplified. Moreover, by providing the display device, it is made possible to visually ascertain whether or not the switches have securely been opened.

FIG. 4is a diagram illustrating a configuration example of a power storage apparatus according to Embodiment 4 of the present invention. Only the difference between Embodiment 4 and Embodiments 1 and 3 will be explained below.

It is the feature of Embodiment 4 that switches4aand4billustrated inFIG. 4are not capable of switching a current, but capable only of performing opening and closing, and the switch3bis a switch capable of switching a current while the current flows.

Next, the operation timing among the switches3b,4a, and4bwill be explained. When the power storage apparatus30is activated, the sequence is in such a way that the switches4aand4bare preliminarily closed, and after that closing has securely been completed, the switch3bis closed.

Additionally, when the power storage apparatus30is stopped, the sequence is in such a way that the switch3bis preliminarily opened, and after that opening has securely been completed, the switches4aand4bare opened.

As described above, by making the switch3bplay the role of eventually configuring a circuit in which a current may generated and the role of firstly opening a circuit, it is made possible to limit the roles of the switches4aand4bto the opening and closing operation in the state in which no current is generated and no circuit has been configured.

In addition, it is the main point of Embodiment 4 that a switch capable of switching a current is utilized only for the switch that eventually configures a circuit or that firstly opens a circuit; therefore, the installation positions of the switches4a,4b, and3bare not limited to the positions illustrated inFIG. 4, but may be interchanged.

In consequence, according to Embodiment 4 of the present invention, small-size switches incapable of switching a current can be utilized as the switches4aand4b; therefore, in addition to the effects of Embodiments 1 to 3, a small-size and lightweight power storage apparatus can be obtained.