Amplitude–Frequency Decoupled Heater and Integrated Strategies for Automotive Batteries Based on Inverter and Motor

The low-temperature preheating of lithium-ion batteries is an important means for improving their fast-charging performances in electric vehicles at low temperatures. In recent years, a trend has emerged toward low-cost, small capacity, and high efficiency heaters, in which a bridge inverter self-heater is integrated into the motor inverters. However, the preheating current is limited by the power of the on-board hardware. Heating the battery under low-frequency current can easily lead to lithium precipitation. Both of these result in low heating rates. Therefore, this article proposes an amplitude–frequency decoupled ac heater (AFDH), which can well-balance the rates of the temperature rise and battery degradation. In addition, the heater can also be used to balance the batteries as an on-board equalizer. This article proposes two integrated topologies for the AFDH based on the motor inverter. Each of the two topologies can increase the preheating current to nearly 2–3 times the rate current of the motor winding. Experimental results show that the AFDH can achieve better temperature rise performance on lithium-ion batteries (LIBs). The temperature rise rate at a −20 °C, 100 Hz, and 3 C current can reach 3.871 °C/min and the energy consumption is 5.38%. Moreover, no significant capacity degradation appears after 80 heating cycles with the 3.2 C current, showing good prospects for on-board application.