Due to their simple structure and high efficiency, various types of linear machines are employed in direct-drive applications such as linear railway traction. The transverse flux linear machine (TFLM) can achieve high thrust density, but it has demerits of severe magnetic flux leakage and large detent force. This article investigates a tubular hybrid excitation TFLM (HE-TFLM) for a linear railway traction system. The structure and working principle of the proposed machine are described in detail. Subsequently, a magnetic circuit analysis is conducted while taking axial magnetic flux leakage into consideration. By optimizing the pole arc coefficient, the magnetic flux leakage of the machine is reduced, and performance parameters such as average thrust are improved. Based on the optimized dimensional parameters, the machine performance with different combinations of primary slots and secondary poles is compared. It is proved that employing cross-connected windings simultaneously in both the circumferential and axial directions can effectively reduce thrust ripple. Moreover, the loss and efficiency analysis and temperature field simulation results are given. Since both the primary and secondary of the HE-TFLM can be axially laminated, the motor exhibits very low eddy current losses. Despite the relatively high copper losses in the motor, its efficiency under rated conditions remains acceptable. An HE-TFLM prototype is manufactured, and an experimental platform is established to measure the no-load back electromotive force (EMF) and on-load thrust of the prototype under two conditions: reciprocal motion with a sinusoidal velocity of the secondary and linear motion with a constant velocity of the secondary. The experimental results are in good agreement with the simulation results. Compared with other TFLMs, the proposed machine achieves relatively high thrust density and extremely low thrust ripple. Additionally, by adopting a hybrid excitation method, the proposed HE-TFLM attains a wide speed regulation range, making it well-suited for application in linear railway traction systems.

A direct drive wave power generation system (DDWPGS) has the advantages of a simple structure and easy deployment, and is the first choice to provide electricity for islands and operation platforms in the deep sea. However, due to the off-grid, the source and load cannot be matched, so accommodation is an important issue. Hydrogen storage is the optimal choice for offshore wave energy accommodation. Therefore, aiming at the source-load mismatch problem of the DDWPGS, an electric-hydrogen hybrid energy storage system (HESS) for the DDWPGS is designed in this paper. Based on the characteristics of the devices in the electric-hydrogen HESS, a new dynamic power allocation strategy and its control strategy are proposed. Firstly, empirical mode decomposition (EMD) is utilized to allocate the power fluctuations that need to be stabilized. Secondly, with the state of charge (SOC) of the battery and the operating characteristics of the alkaline electrolyzer being considered, the power assignments of the battery and the electrolyzer are determined using the rule-based method. In addition, model predictive control (MPC) with good tracking performance is used to adjust the output power of the battery and electrolyzer. Finally, the supercapacitor (SC) is controlled to maintain the DC bus voltage while also balancing the system’s power. A simulation was established to verify the feasibility of the designed system. The results show that the electric-hydrogen HESS can stabilize the power fluctuations dynamically when the DDWPGS captures instantaneous power. Moreover, its control strategy can not only reduce the start-stop times of the alkaline electrolyzer but also help the energy storage devices to maintain a good state and extend the service life.

Transverse flux PM linear generator (TF-PMLG) enables a higher power density under low-speed wave characteristics. However, thrust pulsation and magnetic leakage are major issues in these generators. To address the foregoing problems, a hybrid excitation TF-PMLG is proposed. However, it presents significant control challenges due to large phase inductance and non-negligible internal resistance, particularly under conditions of insufficient bus voltage. Additionally, the necessity for electromagnetic thrust to adapt in real time to wave variations further intensifies the demands on the dynamic performance of the control system. To this end, this article proposes a model predictive thrust control (MPTC) strategy based on optimal flux linkage vector selection. It can effectively mitigate thrust fluctuations of the generator in response to wave action. Furthermore, a dynamic flux-enhancing strategy is developed, which can reduce the dependence on bus voltage magnitude, thus increasing the peak thrust of the generator. Finally, simulations and experimental results are provided to validate the effectiveness of the proposed MPTC methods in direct-drive wave energy converter system.

In this paper, a control method for a permanent magnet linear synchronous generator (PMLSG) using an improved equivalent circuit model (IECM) is proposed for maximizing energy harvesting under irregular waves. Compared with the conventional equivalent circuit model, the IECM incorporates a new impedance to characterize the radiation impulse response and provides a method for controlling the PMLSG to conjugately match the external parameters in the hydrodynamic equation in real time under irregular waves. First, the hydrodynamic equations of DDWEC and the energy harvesting mathematical model of the PMLSG were analyzed. Then, the principle of maximizing energy harvesting using the IECM-controlled PMLSG under irregular waves and the calculation of IECM parameters are explained. Finally, it is verified that the harvested energy is maximized based on the superposition principle and through simulation. The results show that the proposed method enables the PMLSG to harvest the maximum energy from irregular waves over a long period of time.