Voltage-Feedback Internal Heating Strategy of Lithium-Ion Battery in an Extremely Cold Environment Implemented With Drive System of Electric Vehicle

The formation mechanism of alternating current (ac) of a battery is analyzed theoretically for a typical motor drive circuit model. The effect of a direct current link (dc-link) capacitor on battery current is calculated and discussed, and the result showed that the presence of this capacitor will weaken the amplitude of ac current, especially when the heating frequency is close to the resonance point of the resistor and inductor paralleled with capacitor (RL-
${C}$
) of the dc-link capacitor and motor stator circuit. Classical proportion integration (PI) control theory is introduced into in- vehicle internal heating technology of battery for the first time to propose a voltage-feedback preheating control strategy. The control frequency and the ratio of nonzero vector and dead zone are discussed and determined. The battery current is adjusted indirectly by dynamically changing the duty cycle of the zero vector to maintain the minimum voltage of the battery at a constant value and above the lower limit. The comparison experiment results show that the heating rate of the proposed strategy is improved by 45% compared with the fixed duty cycle strategy in the temperature range from −30 °C to −10 °C.