This paper presents a two-degree-of-freedom (2-DOF) H speed control structure for permanent magnet synchronous motors (PMSMs). This structure consists of three parts: an H disturbance observer (DOB), an H feedback and an H feedforward controller. Firstly, the H problem and the feedback controller design method for PMSM are presented. The stability and solution are introduced. Secondly, the disturbance observer (DOB) is designed as an H disturbance tracking problem to estimate the external load torque and increase the robustness. The speed controller is adjusted and regards the estimated torque as one of the input. Finally, based on the 2-DOF structure, an H feedforward controller is designed, taking the closed loop performance into account. The proposed method has a better dynamic and stronger robustness against external disturbance and parameter variation. Several simulations and experiments of conventional PI controller, standard H speed controller and proposed method are operated in a PMSM system and compared to validate the accuracy of the disturbance observation and the effectiveness of the proposed method

Typically, permanent magnet synchronous machines (PMSMs) with small inductance can achieve a higher power density and higher power factor. Thus, in many industrial applications, more and more PMSMs are being designed with small inductance. Compared with traditional PMSMs, current harmonics in small inductance PMSMs are much more abundant, and the amplitudes are usually high. These current harmonics will cause large eddy current losses (ECLs) on the rotor, making the estimation of ECLs necessary in the design stage. Currently, ECL estimation methods are usually based on frequency order information, which cannot tell the travelling direction of the harmonic magneto-wave, resulting in the inaccuracy of the estimation. This article proposes a novel estimation method based on the mechanism of the formation of space-vector pulse width modulation (PWM), which considers both the frequency order and travelling direction of the harmonic wave, resulting in the improvement of the accuracy. Besides this, by using double Fourier analysis (DFA) instead of traditional fast Fourier analysis (FFA), the predicted frequencies of the current harmonics are more accurate and free of the troubles caused by traditional FFA-based methods. Simulation study and experiments are conducted to show the effectiveness of the proposed method.