u03b7 i denotes conversion efficiency of the motor power beware that during regenerative braking p all t lt 0 holds in expression 4 c calculate permissible input output power p bmin t p mmax t of the battery 41 as shown in fig8 the rechargeable battery 41 is of a cell set configuration with a plurality of cells 410 for simplicity in the description given herein it is assumed that each cell is uniform in quality each cell is equal in voltage current and output impedance and calculations are conducted on a cell by cell basis fig9 shows a cell model the cell 410 includes an output impedance element 412 and a pure cell 411 an expression for calculating the maximum and minimum electric power levels p bmin t p mmax t that the battery can input and output i e permissible input output power levels are shown as expression 6 where n denotes the number of cells and v b t r b t denotes the cell voltage output impedance since v b t r b t depends on the charge level soc t and temperature t b t of the battery v b t r b t is calculated from the soc t t b t calculated in the previous cycle d calculate.