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.

An optimal current control strategy for asymmetrical hybrid multilevel inverters (MLIs) is proposed in this paper enabling their use on motor drives, static synchronous compensators, and photovoltaic and wind generators, where a fast and precise current regulation is required. A key feature of these highly efficient converters is that an ac machine (motor or transformer) operates according to an open-end winding configuration, connected on one side to a main MLI and, on the other side, to an auxiliary two-level inverter (TLI). The first efficiently controls the main power stream operating at a low switching frequency, while the TLI acts as an active power filter, exploiting a conventional high-frequency two-level pulsewidth modulation (PWM) technique. The proposed control scheme optimally exploits the key features of the two inverters by suitably sharing the control task. In fact, a predictive current control is assigned to the MLI, which can be accomplished by low switching frequency operations, while the high switching frequency of the PWM-operated TLI is exploited to accomplish a fast and precise closed-loop current control, processing only a part of the power stream flowing through the system, thus producing low power losses. Simulations and experimental results confirm the consistency of the proposed approach.

Capacity loss over time is a critical issue for lithium-ion batteries powering battery electric vehicles (BEVs) because it affects vehicle range and performance. Driving cycles have a major impact on the ageing of these devices because they are subjected to high stresses in certain uses that cause degradation phenomena directly related to vehicle use. Calendar capacity also impacts the battery pack for most of its lifetime with a capacity degradation. The manuscript describes experimental tests on a lithium-ion battery for electric vehicles with up to 10% capacity loss in the WLTP CLASS 3B driving cycle. The lithium-ion battery considered consists of an LMO-NMC cathode and a graphite anode with a capacity of 63 Ah for automotive applications. An internal impedance variation was observed compared to the typical full charge/discharge profile. Incremental capacitance (IC) and differential voltage (DV) analysis were performed in different states of cell health. A lifetime model is described to compute the total capacity loss for cycling and calendar ageing exploiting real data under some different scenarios of vehicle usage.

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.

A new dual T-type 13-level inverter topology is presented in this article, featuring less power switches, gate drivers, and diodes, than inverters based on traditional multilevel topologies, such as neutral point clamped, flying capacitor, T-type and cascaded H-bridge, or previously proposed reduced switch count 13-level inverter topologies. Moreover, no additional circuits are required to equalize the voltage of capacitors present in each pole, nor complex modulation strategies, leading to a reduction of cost and power losses. Exploiting a nearest level modulation technique, the proposed topology performs well in terms of efficiency and total harmonic distortion, as confirmed by experimental tests.