Universal Current-Mode Control Schemes to Charge Li-Ion Batteries under DC/PV Source

A pair of universal current mode control schemes for charging a Li-ion battery for mobile applications are discussed in this paper. The peak-current mode control schemes, based on a single control loop, is universal because it is designed with a single-stage buck charger for both a conventional wall adapter dc source as well as a solar photovoltaic (PV) module of comparable specifications. The charging schemes remove the need for an extra MPPT (maximum power point tracking) power converter stage. This control scheme is non-linear and incorporates all possible scenarios: mode of operation of a battery, current charging rate and power characteristic of input source. The algorithm uses need-based MPPT and ensures minimal battery discharge, and also uses minimum number of sense variables in the circuit. The methods differ in the way MPPT is implemented: perturb and observe (P&O) and fractional open circuit voltage. Simulation results demonstrating battery charge profile, validity of the algorithm under varying insolation conditions and platform workloads are presented, along with a discussion of the trade-offs of the two methods. Proof-of-concept hardware results are also provided.