Solid-state relays simplify monitoring electric-car battery voltage

摘要

Figure 1 shows the propulsion system of an electric vehicle. It includes an electric motor, drive electronics, a mechanical transmission, vehicle control/power management, a charging system, and a battery. The long-term performance of the electric vehicle depends on ensuring the electrical health of the battery and its charging system. The battery system in an electric or a hybrid-electric car comprises a series connection of 75 to 150 individual 2V cells. This series connection generates a potential voltage of 150 to 300V. The measurement of an individual cell's terminal voltage creates a testing dilemma. The high electrical potential precludes the use of standard differential op amps connected across each cell. The measurement of each cell's voltage entails using a switching network that interconnects an isolated or floating A/D converter between the two terminals of each cell in the string. A measurement method also needs a switching system to sequence this "voltmeter" across each of the 150 cells.