Abstract:
The Battery Management System (BMS) electronics in an electric or hybrid-electric vehicle battery are the key to performance and safety. New advances in integrated circuit design allow battery pack designers to derive more performance from Li-ion batteries. Better measurement accuracy, more robust data links, and the active balancing of cells results in lower cost, longer drive cycles, and quicker charging. Self-test and diagnostic circuitry enhances safety and reliability.
AFE IC measurement accuracy has a direct impact on the cost of the system. Accurate cell voltage measurements provided by the BMS AFE IC are needed for useful state of charge (SOC) computations. Uncertainty in the SOC calculation results in the need to over-size the battery pack proportional to the magnitude of that uncertainty. The AFE IC must provide laboratory equipment grade accuracy at low cost while operating in an automobile for 15 years. These measurements are made in an operating environment which includes significant electrical noise and transients from inverters, actuators, switches, relays, etc. IC technologies employed by the BMS IC including the voltage reference technology, ADC architecture and filtering capabilities must be carefully chosen to meet these challenges. High accuracy cell measurements also impact system level design for safety and reliability.
Modular BMS design requires robust digital board-to-board communication which can withstand electromagnetic interference and provide isolation at economical cost. Advanced BMS ICs include protocols such as isoSPI® as an alternative to CAN to provide this capability.