Usman Nasir

This article shares with the aerospace community a case study of turboprop mild hybridization using a recently developed integrated drive system in the University of Nottingham, U.K., within the ACHIEVE project under EU H2020 CleanSky 2 program (project No. 737814). The developed drive system enables the green taxiing of a turboprop aircraft while on the ground with its engine OFF and as an electrical generator when the turboprop is in the air. The entire system is designed to be able to integrate within the power auxiliary gearbox (PAGB) of a turboprop aircraft. Some of the key features of the developed system include a high-speed permanent magnet machine (up to 14200 rpm) with a dual-three-phase design, silicon carbide (SiC)-based high power density (11.8 kW/L for the power converter, and 35.3 kW/L and 7.2 kW/kg for the machine active parts), integrated cooling design for high-temperature operation ( $>130~^{\circ }\text{C}$ ambient temperature), fault tolerance consideration with dual-channel operation capabilities, and sensorless control for entire operational conditions. This article is giving an overview of the design process of the electrical machine, power converters, and the cooling of the entire drive. The numerical analysis [finite element method (FEM) and computational fluid dynamics (CFD)] and some experimental results are presented to demonstrate the effectiveness and the desired performance of the developed integrated drive system.

This paper discusses the analysis, design, and experimental validation of a modular isolated matrix converter (MIMC), including modulation, commutation, and control. The MIMC topology is a single-stage high power density ac-ac converter, which is attractive for traction applications and space-restricted low voltage (LV) or medium voltage (MV) future distribution networks. The topology under study utilizes bidirectional switches based dual-active-bridge cells as basic building blocks. A single cell would have limited practical application as the output frequency is locked to the input one. On the contrary, the repetition of single cells proposed in the MIMC extending the matrix converter concept, achieves variable frequency operation while also providing a modular structure. However, the presence of medium frequency transformers in each cell poses additional challenges for modulation and safe commutation that are discussed and solved in this paper. Experimental results from a proof-of-concept 6 kW laboratory scale prototype validate the practical feasibility and the operation of the MIMC.

This paper proposes a generalized commutation strategy suitable for matrix-based isolated ac/ac conversion stages in solid-state transformers for use whenever there is nonnegligible leakage inductance in the isolation transformer. The standard 4-step commutation used in matrix converters can no longer be applied when transformer leakage inductance is present, as overrated switching devices or dissipative snubbers would be necessary, reducing the attractiveness of the topologies that include matrix-based isolated ac/ac stages. A case study of a single-phase ac/ac converter has been investigated in detail to demonstrate the application of the proposed commutation method to a topology that has recently been identified as the potential building block for future multimodular ac/ac converters for grid applications. The proposed leakage-inductance-tolerant commutation strategy is based on the definition of a current decoupling phase in the commutation sequence and only needs suitable timing of the commutation steps, without high bandwidth voltage or current measurements. Matching simulations and experimental results from a 3-kW laboratory scale prototype are presented to support the effectiveness of the proposed strategy.