In recent years, owing to the rapid increase in portable devices and the development of electric automobiles, the demand for storage (secondary) batteries is greatly increasing. Storage batteries are produced by assembling the electrode made of active materials in a discharged condition. Before shipping the storage batteries in the market, the batteries must be charged with electricity or activated by repeatedly charging and discharging the same. It is also necessary to test samples of storage batteries to determine whether the batteries satisfy the intended performances such as cycle life by repeating charge/discharge operations.
This invention is directed to a power supply apparatus to be used for such purposes by charging and/or discharging storage (secondary) batteries. In the conventional technology, when charging a battery, a DC (direct current) power source converted from an AC (alternating current) source, i.e., the commercial power source is used. When discharging the battery, a discharge load is used, which is typically a resistor or an electric load. In the conventional technology noted above, the electric energy stored in the storage battery is consumed by the discharge load. As a result, a large amount of electric energy is wasted. For this reason, the conventional method is disadvantageous.
Under the circumstances, as disclosed in Japanese Laid Open Patent Publication Nos. 2-261020 and 7-222369, there has been an attempt to effectively use the energy discharged from a storage battery. In the above patent publications, it is disclosed that the energy discharged from the storage battery is recycled by feed-backing the discharged energy to an AC power source so that the AC power is converted again to a DC power to charge the storage battery.
However, since these methods convert the DC power discharged by the storage battery into the AC power by using an inverter, it is difficult to obtain an AC power with normal sine waves. In other words, the AC power inverted from the DC power involves noise and distortion. In order to obtain an AC power source having normal sine waves, i.e., low distortion or noise in the wave form, a high quality control circuit must be used, resulting in the increase of the overall cost of the apparatus.
In such a case, in order to achieve the energy saving or recycling with a simplified control circuit of relatively low cost, the recycled AC electric power tends to involve a significant amount of signal distortion or high voltage impulse (instantaneous) noise. Therefore, such a less expensive method may not be applied to noise sensitive electric apparatuses, such as computers or automatic machines which require high quality electric power. Such being the case, the method of using the recycled AC electric power is not appropriate.