An open-end winding machine configuration and a suitable control strategy for medium-voltage ac motor drives applications are proposed in this paper in order to reduce the distortion of phase voltages in multilevel inverters (MLIs). Differently than standard open-end winding configurations, where two inverters provide active power to both sides of the stator winding, a main MLI supplies in this case the machine on one side, while an auxiliary two-level inverter acts as active power filter on the other side. A high efficiency step modulation manages the MLI, while the auxiliary unit is pulse width modulation (PWM) operated. As the phase current harmonic content is improved, the torque ripple is reduced and the drive efficiency is increased. By exploiting the proposed approach, the apparent switching frequency of the system is that typical of a PWM inverter, although the main unit is operated according to a voltage step modulation strategy. Simulation and experimental results confirm the consistency of the proposed methodology.

Considering the importance of lithium-ion (Li-ion) batteries and the attention that the study of their degradation deserves, this work provides a review of the most important battery state of health (SOH) estimation methods. The different approaches proposed in the literature were analyzed, highlighting theoretical aspects, strengths, weaknesses and performance indices. In particular, three main categories were identified: experimental methods that include electrochemical impedance spectroscopy (EIS) and incremental capacity analysis (ICA), model-based methods that exploit equivalent electric circuit models (ECMs) and aging models (AMs) and, finally, data-driven approaches ranging from neural networks (NNs) to support vector regression (SVR). This work aims to depict a complete picture of the available techniques for SOH estimation, comparing the results obtained for different engineering applications.

A new approach to compensate rotor position errors caused by parameter mismatching in model-based sensorless synchronous reluctance (SynchRel) motor drives is presented in this article. According to the proposed approach, the error in estimating the rotor position is detected by injecting some low-frequency current signals and adjusting the estimated rotor angular position through a gradient descent algorithm until minimizing the ripple generated on the estimated rotational speed. A rotor position correction can be fully online accomplished coping with saturation and cross saturation effects, as well as with unmodeled phenomena and unpredictable variations of the stator resistance with the temperature. The correction procedure can be accelerated by starting from an approximated correction table, which can be offline built using the same technique. The proposed approach neither needs additional current or voltage sensors nor motor design modifications, thus providing an inexpensive mean to improve the control performance and robustness. Although originally conceived to deal with back EMF-based sensorless control techniques, the correction procedure can be extended to other model-based sensorless SynchRel motor drives.

Multiple-Motor fed by Multiple-Converter systems feature a set of electric motor drives sharing the load through a common mechanical coupling. Such a coupling is exploited in this paper to build up a sensorless field oriented control, based on a quite common back-emf technique to estimate the rotor flux angular position and an original approach to correct estimation errors. The technique is based on the injection of a suitable, very low frequency, sinusoidal signal on the current reference of one of the motor drives. If the estimated rotor flux position is correct, the drive output torque does not show variations. Differently, a torque ripple is generated at the frequency of the injected signal, whose effects on the system speed are easily compensated by the main speed controller, however, due to the mechanical coupling, an additional component of the reference torque current at the frequency of the injected signal is generated on all the other drives. By minimizing such a component, the estimated rotor flux position can be on-line corrected. The proposed method can be also exploited to estimate actual values of the stator resistance and of the rotor time constant.

A multi-level open-end winding converter topology for multiple-motor drives is presented featuring a main multi-level inverter processing the power delivered to the motors and an active filter based on an auxiliary two-level inverter. The main inverter operates at the fundamental frequency in order to achieve low switching power losses, while the active filter is Pulse Width Modulation (PWM) operated to suitably shape the motor currents. The proposed configuration features less phase current distortion than conventional multi-level inverters operating at the fundamental frequency, while achieving a higher efficiency compared to PWM multi-level inverters. Experimental results confirm the effectiveness of such a configuration on both multiple motors-single converter and multiple motor-multiple converter drives.

An original overvoltage mitigation technique is presented in this paper for Sic based motor drives, exploiting an open-end winding motor configuration. According to the proposed solution over-voltage occurring at the terminals of the motor phases is mitigated by driving the two inverters through a modified switching pattern including a suitable dwell time. No passive RLC networks are required, thus avoiding additional costs and extra power losses. A comparison between IGBT and SiC MOSFET equipped motor drives is first provided, highlighting the difference in terms of power cable critical length and other factors affecting peak terminal over-voltages. The proposed approach is then theoretically introduced and its consistency is finally assessed by simulations and experimental results.