This paper addresses robust design of the active-power and dc-link control loops of power-synchronization control. Robustness is obtained by analytic gain selections which give large enough stability margins. The proposed design allows robust stability irrespective of the grid strength and of the operating point, the latter with one exception. The proposed design is compared to design based on the principle virtual synchronous machine. Experiments show that the time-domain results correlate well with the frequency-domain results.

A classical control approach to the design and analysis of proportional-integral (PI) speed controllers for electrical drives is presented. After vindicating the fact that traditional one-degree-of-freedom PI control generally gives unsatisfactory performance, a well-performing two-degree-of-freedom PI controller is designed, with analytical parameter selection. The robustness of the obtained closed-loop system is analyzed and is found to be satisfactory. All the proposed control designs are validated by means of experiments.

This paper deals with a speed and position estimation method for the sensorless control of permanent magnet synchronous motors. The method is based on a speed-adaptive observer. The dynamics of the system are analyzed by linearizing both the motor model and the observer, and the observer gain is selected to give improved damping and noise suppression. At low speeds, the observer is augmented with a signal injection technique, providing stable operation down to zero speed. The experimental results, obtained using a 2.2-kW interior magnet motor, are in agreement with the results of the analysis.

Power-synchronization control (PSC) and vector current control (VCC), the latter including cascaded outer loops, are, respectively, considered to be grid-forming and grid-following schemes. They have significant structural differences. Despite that, it is here shown that the two schemes can be unified by making a series of minor modifications to PSC. This results in a universal controller, allowing various combinations of the two schemes to be explored. Fundamentally, it allows PSC to be used as guideline for a robust VCC design, permitting stable and well-performing operation irrespective of the grid strength.

In high-performance control of ac machines through variable frequency drives, the knowledge of machine parameters plays a decisive role. The accuracy with which machine parameters can be known is directly related to the time and effort put in testing and commissioning process. In the ever-demanding industrial environments, the time spent on parameter identification translates into loss of production. To reduce commissioning times, research in this direction has focused on automatizing the identification procedure without loss of accuracy. This paper reviews different lines of research adopted over the past few decades for machine parameter identification. Parameter estimation of ac machines is considered because of their widespread applications from servomechanisms to traction to aviation. The surveyed works include self-commissioning schemes that have become an integral part and salient feature of modern electric drives. This feature enables the drives to automatically identify machine parameters and tune the control loops.

This paper proposes an online method for the estimation of the stator resistance and the permanent-magnet (PM) flux in sensorless PM synchronous motor drives. An adaptive observer augmented with a high-frequency signal injection technique is used for sensorless control. The observer contains excess information that is not used for the speed and position estimation. This information is used for the adaptation of the motor parameters: At low speeds, the stator resistance is estimated, whereas at medium and high speeds, the PM flux is estimated. Small-signal analysis is carried out to investigate the proposed method. The convergence of the parameter estimates is shown by simulations and laboratory experiments. The stator resistance adaptation works down to zero speed in sensorless control.