Due to the traditional control strategy used in modular multilevel converters and power electronic transformers, it is difficult to ensure the dynamic performance of the system during operation, which further increases the difficulty of control when the power grid is in imbalance. In order to improve the dynamic performance of the system, a nonlinear feedback linearization sliding mode composite control strategy is proposed. This composite control strategy combines the advantages of feedback linearization control （FLC） and sliding mode control （SMC） to achieve complementary advantages. Firstly, an overall simulation model for modular multilevel converters power electronic transformers （MMC-PET） is established. Secondly, a control model for feedback linearization sliding mode control is established through a mathematical model. Finally, a simulation comparison experiment is conducted using a simulation and experimental platform to compare the proposed composite control strategy with a single feedback linearization control, sliding mode control, and commonly used PI control, in order to verify that the proposed control strategy has good dynamic performance and robustness under external disturbances.