Permanent magnet synchronous motors (PMSMs) are suitable options for high-performance applications due to their potential of high power density and torque smoothness. Nevertheless, there are some factors affecting this feature by producing unwanted pulsating torque. One of the causes of torque ripple is the presence of harmonic components in motor back EMF. This paper has presented a multiple reference frame (MRF) method improving torque characteristic in PMSM regarding nonsinusoidal back EMF. An adaptive notch filter (ANF) was used as a current estimator which can separate needed current components. Optimal current components, obtained from Lagrange multiplier method, were regulated through PI controllers which guaranteed the desired convergence. Cogging torque and rms current minimization were intended, too. Results were investigated through simulations in Matlab/Simulink environment.

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It is known that constant power load (CPL) may cause a negative impedance, which seriously affects the stability of power system. In this paper, a new control algorithm for DC–DC buck converter feeding unknown CPL is proposed. First, under the assumption of known extracted power load, the standard passivity–based control (PBC) is presented to reshape the system energy and compensate for the negative impedance and a proportion‐integration (PI) action around passive output is added to improve disturbance rejection performance, which forms the PBC plus PI (PBC+PI). Then, a parameter estimation algorithm is developed, based on immersion and invariance (I&I) technique, in order to online estimate the extracted power load. In the next step, the online estimation scheme is adopted to construct an adaptive strategy. Finally, the stability analysis of the cascaded system containing a closed‐loop control system and observer error dynamics is conducted. Simulation and experimental results are demonstrated to validate the performance of the proposed controller.

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