1. Technical Field
The present invention relates to a power system including an operating unit which operates a plurality of DC (direct current) to DC converters (hereinafter referred to as DC-DC converters) connected in parallel to each other in such a way that power is supplied through the DC-DC converters to a predetermined power-supplied object.
2. Related Art
In a well-known power supply system, a plurality of switching power supplies (DC-DC converters) are connected in parallel to one another so as to supply power to a predetermined power-supplied object. The purpose of using this system is to increase a maximum current that can be supplied to the power-supplied object. In this system, current is outputted to the power-supplied object preferentially from a switching power supply having a higher output voltage among the plurality of switching power supplies. Accordingly, for example, some specific switching power supplies may have a higher frequency of being activated. Thus, reliability tends to be lower in a part of the switching power supplies than in other switching power supplies.
In order to cope with this, in a well-known technique as disclosed in JP-A-10-225126, current to be supplied to loads is equally shared between a plurality of switching power supplies connected in parallel to each other. Specifically, in this technique, a reference current is defined such as to be an average of the total output current of the plurality of switching power supplies. If a switching power supply has an output current larger than the reference current, the output current of the switching power supply is reduced. With this configuration, the output current of each of the switching power supplies is controlled to the reference current.
Further, in another well-known technique as disclosed in JP-A-10-248253, the larger the output current of a switching power supply becomes within a range of its rated output current, the more the output voltage of the switching power supply is reduced. With these techniques, reliability of the power supply system is enhanced.
For example, a technique of enhancing reliability of a power supply system having a plurality of switching power supplies connected in parallel to each other is also disclosed in JP-A-10-108362.
The techniques set forth above are able to enhance reliability of a power supply system but may have several inconveniences. Specifically, in the technique disclosed in JP-A-10-225126, a signal line is required to be used. The signal line is connected to the switching power supplies to share a signal, which is associated with the reference current, between the switching power supplies. Therefore, the cost and size of the power supply system may be increased.
In the technique disclosed in JP-A-10-248253, when the current to be supplied to loads becomes large, the output voltage of the switching power supplies tends to be reduced. Therefore, for example, there is a concern that, in charging a battery with the switching power supplies, the battery is not necessarily appropriately charged. In this way, there is still room for improvement in the techniques for enhancing reliability of a power supply system that includes a plurality of switching power supplies connected in parallel to each other.