In recent years, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. In addition, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery pack having a plurality of battery cells electrically connected to one another because high output and large capacity are necessary for the middle or large-sized devices. In order to provide output and capacity required by a predetermined apparatus or device, a plurality of battery cells or battery modules may be connected in series to each other.
In a case in which the above-described battery pack is mounted in a electric vehicle in a state in which the battery pack is connected to an inverter, overall output of the battery pack may be unstable due to noise generated from the inverter.
Specifically, a noise current occurs when the inverter converts an alternating current from the battery pack to a direct current through fast switching. The noise current affects an output terminal of an external input and output terminal by conduction through a power line connecting the inverter and the external input and output terminal of the battery pack, or by induction through electron induction or electrostatic induction or etc. This deteriorates the stability of the output of the battery pack, in other words, the output fluctuates.