A battery management system adapted for an energy harvester with a low-power state of charge monitoring method and a 24 microwatt intermittently enabled Coulomb counter

This paper presents a battery management system with methods for monitoring both the battery state of charge (SOC) and the discharge amount consumed by a wireless sensor device. The proposed SOC estimation method achieves a low-power operation by using a pulse-shaped input current to obtain the frequency-dependent internal impedance of a battery, and by eliminating the AC-source and sample-hold circuits which are conventionally required. The discharge amount from the battery is monitored with a proposed discharge-estimation algorithm that enables an intermittently enabled Coulomb counter (CC), which leads to low-power operation, keeping the error as low as 2.5 percent - the same result from an always-on CC. Measured power consumption has shown a reduction from 340 microwatt with a conventional always-on CC to 24 micro watts using the proposed method. These two techniques enable the power management system to achieve sub-milliwatt operation.