Abstract: A system controller acquires information on states of a plurality of storage battery strings, and based on the information, transmits bypass control information for controlling bypass switch units to string controllers. The plurality of string controllers control power converters of the corresponding storage battery strings according to charge and discharge power values or charge and discharge current values of the storage battery strings set by the system controller, and control the bypass switch units of the corresponding storage battery strings according to the bypass control information transmitted from the system controller.

Abstract: An internal resistance calculating device includes a charging unit charging a secondary battery, a voltage measuring unit measuring a both-end voltage value of the secondary battery, a capacitor holding a first voltage value predetermined by the both-end voltage value measured by the voltage measuring unit after charging is started, a capacitor holding, as a second voltage value, the both-end voltage value when charge current is changed for a predetermined current value or more within predetermined time after the both-end voltage value become the first voltage value, a current measuring unit measuring a first charge current value when the both-end voltage value become a threshold-value voltage and a second charge current value when the both-end voltage value become the second voltage value, and a ?COM calculating an internal resistance value of the secondary battery based on the first and second voltage values and the first and second charge current values.

Abstract: An internal resistance calculating device includes a charging unit charging a secondary battery, a voltage measuring unit measuring a both-end voltage value of the secondary battery, a capacitor holding a first voltage value predetermined by the both-end voltage value measured by the voltage measuring unit after charging is started, a capacitor holding, as a second voltage value, the both-end voltage value when charge current is changed for a predetermined current value or more within predetermined time after the both-end voltage value become the first voltage value, a current measuring unit measuring a first charge current value when the both-end voltage value become a threshold-value voltage and a second charge current value when the both-end voltage value become the second voltage value, and a ?COM calculating an internal resistance value of the secondary battery based on the first and second voltage values and the first and second charge current values.