A stator flux estimation method for direct torque linear control of electrical excitation flux-switching generator

The electrical excitation flux-switching (EEFS) machine, which exhibits advantages including high reliability, good flux regulation capability, bipolar flux linkage and sinusoidal back-EMF, is suitable for use as a generator in DC power systems. In this paper, a direct torque linear control (DTLC) scheme is investigated for voltage regulation of the EEFS generator. This scheme can achieve direct and smooth control of the instantaneous torque by establishing the strict linear relationship between the torque and the sine value of the torque angle, thus will improve the system steady-state and dynamic performance. However, the stator flux estimation accuracy will affect torque control quality. Hence, a simple and practical stator flux estimation method, which only contains a second-order low pass (LP) filter, a high pass (HP) filter and a simple coordinate transformation module, is proposed for both the DTLC and the direct torque control (DTC) schemes of the EEFS generator. In this estimation method, the HP filter can completely filter out the DC drift in the back-EMF, and the leading phase produced by the second-order LP filter and HP filter can be compensated by the coordinate transformation module. Hence, at any synchronous angular frequency, the amplitude-frequency and phase-frequency characteristics of the new estimation method are same as those of the pure integrator, while DC gain of this method is zero. The DTLC scheme of the EEFS generator using this estimation method exhibits good steady-state and dynamic performance, which is verified by experimental results.