Gabriele Rizzoli

This paper presents a comprehensive study on voltage balancing and switching-loss minimization in dual three-phase neutral-point-clamped inverters for electric vehicle multi-motor drive applications. The increasing adoption of multi-motor drives in electric traction systems, often comprising two electric machines connected to the same battery and operating at different points, enables flexible optimization of driving profiles. Each three-phase system can be controlled independently; however, a collaborative strategy introduces new degrees of freedom to improve voltage balancing and reduce switching losses. A novel control strategy is proposed to maintain capacitor voltage balance while simultaneously reducing switching losses, thereby enhancing the overall efficiency of the inverter system. The effectiveness of the method is validated through experimental results obtained with a dual three-phase drive composed of a permanent-magnet synchronous motor and an induction motor under various operating conditions and load profiles. Results demonstrate significant reductions in switching losses and improved voltage stability, confirming the suitability of the approach for high-performance, multi-motor electric vehicle applications.

This paper presents a robust sensorless control strategy for wide-speed-range operation of a six-phase permanent magnet synchronous machine. The proposed approach exploits multi-harmonic back-EMF estimation combined with rotor permanent magnet flux synchronization to achieve accurate rotor position estimation under dynamic load conditions and in the presence of parameter uncertainties. Back-EMF components are extracted in both the fundamental and higher-order harmonic subspaces, and a dedicated harmonic synchronization strategy is introduced to guarantee correct position estimation. A smooth transition from open-loop $I$–$f$ control to sensorless closed-loop operation is implemented, ensuring stable and continuous operation over the entire speed range. The control system architecture is presented in detail, and its effectiveness is validated through an extensive set of experimental results. The experimental analysis includes full-range speed operation, synchronization and lock-in performance, dynamic response to speed and torque transients, and robustness against parameter mismatches. The impact of position estimation errors caused by parameter variations on current magnitude and Joule losses is also analyzed.

This work presents an efficiency-oriented modulation and morphing strategy for a three-phase three-level dual active bridge converter operating across both 800 V and 400 V electric vehicle battery systems. By reconfiguring the converter into a single-phase dual active bridge or a hybrid half-bridge/full-bridge structure at light-load, the proposed approach reduces current-invariant losses. A unified dual phase-shift framework is formulated to analytically model power flow and peak-current minimization across all three-level modulation variants, inner phase shift, duty-cycle control, and T-type zero-level modulation, demonstrating that all combinations produce equivalent voltage and current waveforms. Simulation efficiency maps are generated for all valid primary/secondary modulation pairs and indicate that inner and duty-cycle modulation achieve the highest efficiency across the full operating window. Hardware-in-the-loop experiments confirm stable three-phase-to-single-phase morphing and accurate power tracking between reference and measured power profiles for both voltage levels. The results validate that the proposed morphing strategy enables wide-range, auxiliary-free light-load operation suitable for next-generation EV charging architectures.

The Modular Multilevel Converter (MMC) has gained significant popularity over the past decade due to its versatility. The MMC features have been leveraged in numerous fields, including high-voltage DC transmission, electric vehicle power trains, motor drives, and wind energy conversion. In controlling the MMC, the circulating current (i.e., the current flowing through both the upper and lower converter arms without delivering power to the load) has consistently been the most critical variable. In early applications, it was perceived as a source of losses, but more recently, it has become evident that injecting a specific current could reduce voltage and energy ripples. This paper presents a theoretical framework, based on time-scale analysis, useful for modeling and controlling MMCs. The new approach is adopted for generating the circulating current reference, which is expressed as a linear combination of orthogonal functions. The goals are to decouple the control of the voltages of the upper and lower converter arms and manage additional harmonic components of the circulating current for voltage ripple reduction on module capacitors. The simulations and experimental results demonstrate the effectiveness of the proposed control strategy.

A six-phase machine can be classified according to the distribution of the magnetic axes of its stator phases, which may follow either a symmetrical or asymmetrical arrangement. These two stator configurations result in different degrees of freedom for the system, which in turn affect design criteria, control strategies, and fault management of the machine. When a six-phase machine is connected to a three-level NPC inverter, the stator configuration plays a significant role in balancing the DC bus capacitors. This paper investigates the impact of the stator layout on the low-frequency oscillations of the voltage across the capacitor. The analysis encompasses the control systems of electric machines and modulation strategies for both symmetrical and asymmetrical stator configurations. The experimental validation is carried out using a 12-phase induction machine that can be reconfigured as a six-phase machine with either symmetric or asymmetric stator winding.

This paper presents the development of a high-speed electric drive based on a three-phase synchronous reluctance motor with a bimetallic rotor manufactured via additive manufacturing. The motor features an open-end stator winding and is supplied by a dual SiC-based inverter system consisting of two three-phase, three-level T-type inverters incorporating a floating capacitor. The floating capacitor topology enables the main inverter to operate at unity power factor. A coordinated control strategy manages both converters to maximize active power output while maintaining voltage and current within their limits and ensuring DC-link voltage balancing in the three-level converter. The paper describes the drive architecture, control scheme, and technical solutions adopted to achieve high-speed operation.

This study presents a comprehensive analytical model for the real-time detection of intern-turn short circuits (ITSCs) in asymmetrical dual-three-phase permament magnet synchronous motors (DTPPMSMs). The electrical signals are decoupled into independent complex planes via vector space decomposition (VSD) and controlled using a specifically designed control system. The proposed method enables the real-time identification and diagnosis of an ITSC affecting the stator winding without further measurements, hence decreasing maintenance and monitoring costs. Moreover, it is demonstrated that the ITSC slightly alters the magnetic axis of the faulty phase, and according to this effect, the relative position of the coil within the faulty pole pair can be determined. Experiments with a prototype of a DTPPMSM are carried out to assess the effectiveness of the proposed method.