body and thus the optimum configuration based on temperature rise simulation results is achieved the coolant after flowing in from the coolant inlet in the internal channel of the frame and absorbing the heat released from the motor body is discharged and then cooled by a radiator provided in the coolant circulation channel such water cooled structure has been adopted to improve cooling performance by about three times that of air cooling the inverter uses igbt as its power device and gives forth a maximum calorific value of several kilowatts during maximum output heat is also released from surge absorbing resistors filter capacitors and more and these components need to be controlled below a predetermined maximum allowable temperature in order to provide efficient cooling it is particularly important to cool igbt and a method available to cool igbt is either air cooling water cooling oil cooling or others in this embodiment forced water cooling has been adopted because of its ease of handling and its high efficiency the protection circuit shown in fig8 is formed in each lithium secondary battery used as the power supply in embodiments 31 to 33 this protection circuit protects the battery from overcharge and overdischarge the protection circuit as shown in fig8 includes a balance compensating circuit.