Development of Preheating and Power Inverting Systems for Lithium-Ion Batteries

Abstract

A novel short-circuit self-heating (SCSH) control system was developed in this thesis to achieve the preheating of lithium-ion (Li-ion) batteries operated in extremely cold weather (<-30°C). The proposed system relies on the internal resistance of batteries and the short circuit current to heat up batteries using Joule heating. Experiments show that the SCSH control system can heat up the commercial Panasonic 18650 Li-ion batteries from-30°C to 0°C in 43 seconds, with less than 5 percent of the battery capacity consumed. The proposed heating system outperformed both external convective air heating and alternating current (AC) heating, in terms of heating time and energy consumption. Furthermore, a DC to AC battery power inverter was developed to implement the AC heating and to make the battery pack available for household appliances. This inverter employs a microcontroller using the direct pulse width modulation (DPWM) technique. The inverter achieves power output at various frequencies through programming, without changing the design of the circuit board. The optimal frequency ratio can be obtained theoretically, validated through MATLAB simulation, and was further examined through experimentation. The selected frequency ratio enables the DPWM signals to stimulate the designed inverter to produce high quality sinusoidal voltage.