This presentation discusses challenges of automated test equipment (ATE) for testing battery management systems (BMS) in electric vehicles (EV) and stationary battery energy storage systems (BESS) and introduces novel system-architectural solutions based on highly integrated system-on-a-chip (SOC) parametric measurement units (PMUs).
BMS measure temperature, voltage and current in the battery-pack, and balance battery cell charge. However, ATE for testing BMS in EVs and BESS has several challenges: Since a BMS device-under-test (DUT) may support a battery module with a series-connected stack of 16 or more Lithium-Ion cells, traditional ATE based on discrete devices has low density since it requires a high number of voltage and/or current source stimuli to emulate individual cell outputs. Second, since the DUT needs to be tested to microVolt (uV) and microAmpere (uA) accuracy, the ATE needs low-noise, precision voltage and current sources which increases implementation complexity, size, and cost of discrete solutions. Moreover, the test stimuli to the BMS-DUT may require 100’s of Volts common-mode voltage relative to the channel differential voltage. Finally, since discrete-device-based ATE is not readily scalable, testing various BMS and battery-module configurations requires custom-designs which take longer time to build.
As a solution to the above challenges, this work first presents a series-connected stack of floating-ground PMUs which connect to the DUT and test if its cell-voltage (CV) and cell-balance (CB) terminal characteristics meet their specifications. The floating-ground-based topology meets both the high common-mode and the uV/uA precision requirements noted above. Each PMU has an isolated power supply for galvanic isolation from the system input power supply. In this configuration, 20-bit digital-to-analog converters (DACs) integrated in each PMU drive the DUT CV and CB terminals in force-voltage (FV) or force-current (FI) mode and validate the DUT battery-cell-measurement, input-current and CB switch-transistor on-resistance capabilities from the DUT measure-current (MI) and measure-voltage (MV) responses. Each PMU FV or FI stimulus can be independently programmed by ATE software, thereby enabling test coverage of any battery cell condition. Following the above discussion, a second topology is presented which extends the testable DUT voltage range up to its absolute maximum rating by connecting each PMU in series with a high-voltage common-mode (CM), efficient switching-mode-power-supply (SMPS). The system is reconfigurable between the first high-precision and the second extended-voltage-range topologies using switching matrices. These switching matrices may be discrete to support more flexibility, or integrated with the PMU, e.g., as co-packaged Micro-Electromechanical Systems (MEMS) switches. At the circuit level, integrated clamps in the PMU limit the voltage and current across the DUT. Additionally, each PMU has alarm features which detect temperature, voltage, current and force/sense Kelvin faults.
BMS future trends include support for higher-voltage battery-packs, higher precision, various pack topologies as well as several new functions including active management and active cell balance. The presented architecture is scalable and readily addresses these trends because of design choices such as the integrated PMU SOC, series-connected PMUs / stacking of PMU on CM power supply, and reconfigurability between the two topologies via the MEMS switching-matrix.
