Recently, High-Voltage Direct Current transmission systems become increasingly significant in renewable energy transmission and integration. Compared to the widely used Multilevel Modular Converter, Alternate Arm Converter has great potential in the future grid systems thanks to its ability of handling dc faults. Whereas, it has energy balance challenge, and the energy imbalance between bridge arms exists under phase-shift conducting modulation. After detailed introduction about the topology schematic and basic operation principle, this article analyses the energy imbalance phenomenon and proposes a control strategy to solve this problem. Finally, simulation results verify the effectiveness of the strategy.