SPWM Inverter Control for Wireless Constant Current and Voltage Charging

Abstract

Constant current (CC) and constant voltage (CV) charging of batteries is a crucial research area in the practical implementation of wireless power transfer (WPT) systems. The typical charging process of a battery starts from the constant current mode. As the battery’s voltage increases, the charging mode switches to the constant voltage mode. During charging, the equivalent load resistance of the battery will vary with the charging time, and the equivalent load resistance will affect the charging current or voltage and system’s efficiency. In this study, an adaptive wireless charging method of CC-CV is proposed based on sinusoidal pulse width modulation (SPWM) inverter control. The proposed WPT circuit detects the load variation by measuring the parameters of load voltage and load current, and accurately controls the system output current or voltage by adjusting the modulation depth of the SPWM inverter on the primary side. When there is relative motion between the transmitting coil and the receiving coil, the sharp change in coupling coefficient directly affects the system’s output voltage and output current, leading to output fluctuations and instability. To solve this problem, a method for estimating the coupling coefficient is proposed which estimates the coupling coefficient during the charging process by measuring system parameters. Then, the controller on the primary side adjusts the modulation depth of the SPWM inverter circuit based on the estimated new coupling coefficient, so that the system can still achieve constant current and constant voltage charging under displacement or distance changes. In this study, the CC mode output current during battery charging was set to 0.75 A, and the CV mode output voltage was set to 12 V. Simulation and experimental results demonstrate the validity and accuracy of the proposed control method.