Abstract: To address the power imbalance caused by fluctuating outputs of distributed power sources and variable load demand in a photovoltaic-storage-DC-flexible load system, a power feedforward and droop composite control strategy for the power electronic transformer interface is proposed. By constructing a system model including photovoltaic cells, lithium iron phosphate batteries, a single-stage matrix-type power electronic transformer, and flexible loads, the mathematical characteristics of each unit and the system power balance mechanism are analyzed. The composite control strategy uses the power feedforward link to compensate for predicted fluctuations in photovoltaic output and load demand, and realizes multi-source coordinated operation by optimizing droop control parameters, thereby improving the dynamic response speed and steady-state accuracy of the system. A 1 kW experimental platform is built for verification. The results show that the proposed strategy controls the total harmonic distortion of the grid-connected current within 2.3%, maintains the power factor above 0.99, and limits the voltage recovery time to less than 5 ms under sudden source-load changes, effectively enhancing the operational stability and power quality of the photovoltaic-storage-DC-flexible load system.