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As a compound structure machine, dual-winding dual-flux-concentrated magnetic-field-modulated brushless compound-structure machine (DDMFM-BCSM) could achieve function of magnetic-field modulated brushless double-rotor machine (MFM-BDRM) and permanent magnet synchronous machine (PMSM) at the same time, which means it could be applied to replace the combination of planetary gears and motors in hybrid electric vehicles (HEVs). Finite element method (FEM) could realize accurate analysis of DDMFM-BCSM while it has disadvantage of complex modeling and long computing time. To achieve fast analysis and design of DDMFM-BCSM, equivalent magnetic network (EMN) model is built in this paper. After meshing of each component, radial and tangential reluctance and magnetomotive force (MMF) could be obtained. Then EMN model could be analyzed by solving EMN equation system. Based on magnetic flux distribution from EMN model, performance of DDMFM-BCSM, including flux density, flux linkage, back EMF, torque and power factor, could be calculated. Comparison shows that result of EMN model is in good agreement with that of FEM. Finally, a DDMFM-BCSM prototype is manufactured and tested.

Free-piston linear generators (FPLGs) without a crank mechanism are promising to be used in hybrid vehicles due to their unique operation characteristics. However, the FPLG currently still faces challenges in the start-up and piston control. In this article, the start-up and operation process of FPLG are analyzed deeply and the improved thrust control strategies for the linear electric machine are presented accordingly. First, the mechanism that the vibration center shifts under the general constant thrust resonance starting method is revealed, considering the asymmetric potential energy caused by nonlinear compression spring effect in the combustion chamber. Then, a compensation thrust iteratively adjusted by the vibration offset is added to stabilize the swing center during start-up. Next, the coupling effect between the dead centers under single-stroke independent thrust control method is analyzed by modeling the piston motion from the aspect of energy flow. Accordingly, an improved thrust control method for coupling suppression is presented to enhance the accuracy and robustness of piston motion. Finally, the performance of the proposed method is verified by controlling a permanent-magnet linear synchronous machine in experiments and simulations.

Free-piston linear generator (FPLG) is considered as a potential technology in the field of hybrid vehicles due to its unique operation characteristics. However, the special structure of no crank-link also leads to the difficulty of piston control. In the presence of frequent combustion variations, the stable operation of FPLG is the biggest challenge it currently faces. In this respect, this article presents a robust piston control method by progressively updating thrust-position trajectory (PUT-PT) of permanent-magnet linear synchronous machine (PMLSM) in FPLG. According to the target points and desired speed, the required motor thrust is obtained based on the energy balance relationship. The calculation of thrust is repeated with a certain position interval in the whole target stroke, so as to obtain the updating thrust-position trajectory. A high-order fast terminal sliding-mode load force observer (HOFTSM-LFO) is designed to estimate the combustion work of an engine based on thermodynamics. Finally, a thrust compensation mechanism is added to the control scheme to counteract modeling errors to maintain high-precision dead centers positions. A sufficient theoretical analysis is provided with an emphasis on thrust calculation and observer design. The performance of the PUT-PT is successfully verified on an 18 kW PMLSM motion platform and a simulated single-cylinder FPLG.