A single-stage bi-directional series resonant DC-AC converter with fixed-frequency three-level PWM strategy is studied in this paper. With the strategy, the voltage conversion ratio can range from zero to infinity. The voltage conversion ratio depends exclusively on the duty cycle and is not related to both the magnitude and direction of the transmitted power, which means the direction and value of the power flow can be changed smoothly. So, it is suitable for the wide-voltage-range and bi-directional applications, such as single-stage DC-AC application. Additionally, both the ZVS and the ZCS can be realized among most periods of the grid. Which means low switching loss and high efficiency can be realized. The concrete operation principles, characteristics, and the control strategy are analyzed in this paper. A 600-W experimental prototype with an input voltage range of 20–60 V is built and tested to prove the correctness and feasibility of the strategy studied.