Brushless doubly-fed machine (BDFM) is widely used in wind power, hydraulic power, marine shaft and other variable-speed constant-frequency power generation fields due to its reliable structure and flexible excitation regulation. This paper presents a double side variable frequency (DSVF) based brushless doubly-fed generator (BDFG) system with specific control strategy. Compared with the traditional brushless doubly-fed generator system, this system has the advantages of simple topology, good dynamic response and strong robustness. Moreover, the power winding frequency and control winding frequency of the BDFM are flexibly adjustable. Finally, experimental results from a 30 kW BDFM prototype verify the feasibility and reliability of the proposed system topology and control strategy.