Capacity maintenance ratio determination device, battery system and electric vehicle

摘要

A capacity maintenance ratio determination device includes an impedance measurement unit and a capacity estimation unit. An alternating signal is applied from a signal generator to a battery. Frequency characteristics of AC impedance are calculated by the impedance measurement unit based on a response signal output from the battery in response to the alternating signal. A feature frequency is determined from the calculated frequency characteristics. The capacity estimation unit includes a memory and a determination unit. A correspondence relationship among a temperature of the battery, the feature frequency and a capacity maintenance ratio is stored in the memory. The determination unit determines the capacity maintenance ratio of the battery based on the temperature of the battery detected by a temperature detector, the determined feature frequency and the correspondence relationship stored in the memory.