Optimal Charging Strategy With Complementary Pulse Current Control of Lithium-Ion Battery for Electric Vehicles

Although the pulse charging strategy has many advantages, it is still controversial. The paradox is that it prolongs the charging time to eliminate the polarization voltage by the pulse interval, and the ac component in pulse current will increase the ohmic losses. In this article, an optimal charging strategy with a complementary pulse current of lithium-ion is proposed to address and alleviate these issues. For the pulse frequency, the optimization can be achieved through the electrochemical impedance spectroscopy (EIS) analysis to reduce the battery’s ac impedance. For the pulse amplitude, based on the battery’s internal resistance characteristics, minimize the ohmic losses to obtain the optimal amplitude. For the pulse duty cycle, it is adjusted to achieve a state of charge (SOC) balancing in the early charging stage, and the battery’s terminal voltage balancing in the later stage. Based on the optimized charging strategy, a pulse charger concept is proposed, which can flexibly control the pulse charging currents and use complementary pulses to completely eliminate the prolonged charging time caused by the pulse interval. In the end, an experimental platform for pulse chargers of lithium-ion batteries is designed, and the theoretical analysis is verified by the comparative experiments.

I. Introduction

As an important means to reduce environmental pollution, the development of renewable energies (REs) and electric vehicles (EVs) promote each other [1], [2]. EVs are not only a load of the smart grid but also can be used as energy storage to increase the penetration of REs [3]. Lithium-ion batteries have become the main choice for EVs or other storage systems due to their many advantages [4]–[6]. In order to maximize the potential of the batteries, charging technologies have increasingly become one of the focuses [7], [8].