Sensorless Starting Control Method Based on Rotor Current Characteristics of Excitation System for a Brushless Synchronous Starter/Generator at Low Speed

For an aviation brushless synchronous starter/generator system, rotors of the main exciter (ME) and main machine (MM) rotate synchronously. Meanwhile, abundant current harmonic in ME's rotor, which is caused by a rotating rectifier, contains rotor position information. Then, the rotor position of MM can be obtained indirectly by signals of ME. In this article, based on rotor current characteristics of the excitation system, the estimated rotor current of ME and MM is employed innovatively for rotor position estimation at low speed. First, the harmonic current characteristics in ME's rotor winding are analyzed, and the low-order harmonic can be used for rotor position increment estimation. However, the rotor current of ME cannot be measured directly. Fortunately, in dq coordinate, it can be estimated by the measurable signal in stator winding. Furthermore, by operations of rotation transformation and low-pass filtering, rotor position increment can be obtained. Meanwhile, by injecting low-frequency rotating signals into MM's stator, the initial rotor position of MM can be obtained by sampling the estimated main field current at a fixed point. Finally, by combining rotor position increment and initial rotor position, sensorless starting control can be realized. The proposed method can avoid the influence of MM's operating state and experiments verify the effectiveness.