1. Field of the Invention
The present invention relates to a power storage device and a power converter using same, suitable for use in a power storage device such as a capacitor, a battery or the like which comprises a power storage element and a case, and a power converter which employs the power storage device in combination with an invertor circuit.
2. Description of Related Art
Power storage devices such as a capacitor, a battery or the like are used in electric and/or electronic circuits for storing and supplying electric power. As an example of a conventional power storage device, an aluminum electrolytic capacitor will be described below. The aluminum electrolytic capacitor comprises a wound capacitor element formed of electrodes, a dielectric material and insulating sheets, accommodated in a case, and a lid having electrode terminals connected to the electrodes of the capacitor element. The lid sealingly encloses the capacitor element in the case.
The capacitor, when applied with an alternate current voltage, generates heat since a power loss occurs within the element. In this event, since the capacitor element is more deteriorated as the element itself is heated to higher temperatures, the temperature at the capacitor element must be maintained lower in order to ensure a longer effective life. On the other hand, since the amount of heat generated by a capacitor is proportional to the electric capacitance of the capacitor, a poor cooling capability of the capacitor would result in a shorter effective life thereof. In addition, since a poor cooling capability does not permit a capacitor to have a larger capacitance, the capacitor itself must be increased in size.
As can be seen, for reducing the size of a capacitor, the capacitor must be provide with an improved cooling capability. Other than the capacitor, power storage devices such as a battery or the like also require an improved cooling capability, as is the case of the capacitor, since their power storage elements also generate heat during charging and discharging.
From such a viewpoint, a capacitor described in U.S. Pat. No. 3,681,666, for example, improves the cooling capability by extending a cathode foil of a wound capacitor element and pressing the extended cathode foil into contact with a metal capacitor container.
In the capacitor disclosed in the U.S. Pat. No. 3,681,666, however, since the cathode foil of the capacitor element is extended and directly in contact with the metal capacitor container, a leak current flows through the container itself, thus causing problems such as generation of radio noise, difficulties in maintenance and inspection, and so on. For example, when the disclosed capacitor is used in a power converter for an electric car which includes a semiconductor switching element for a main circuit, a leak current flowing through the capacitor container, if any, would introduce noise into radio waves received from the outside, such as those received by a car-equipped radio. In addition, in maintenance and inspection for the power converter, wherein an operator often touches parts of the power converter by hand for the operation, if a leak current exists in a capacitor container which is a main part, the security must be ensured against the leak current before the maintenance and inspection should be done. In addition, power storage device such as a battery or the like also imply similar problems.