A novel finite-time control with q -axis current constrained based on time-varying second-order nonlinear disturbance observer is investigated to improve the performance of overcurrent protection and disturbance rejection for permanent magnet synchronous motor (PMSM) system. In general, the hardware could be damaged by a large transient current for achieving high-precision tracking performance when PMSM starts up. To this end, a speed-current single-loop control with q-axis current constrained is constructed by a novel finite-time controller for speed regulation of the PMSM system, which can balance well between the overcurrent protection and dynamic performance. The estimated peak generated by the high gain to ensure a precise accuracy will be integrated into the control system at the initial moment in the traditional nonlinear disturbance observer. Taking this into account, parameter uncertainties, nonmodeled dynamics, and estimated peak at the initial moment of the PMSM system are estimated by a time-varying second-order nonlinear disturbance observer. Finally, rigorous stability analysis is established for the proposed composite strategy. Comparative simulations and experiments are designed on proportion integration differentiation, sliding mode control (SMC), and the proposed method. Results demonstrate that the proposed method has better robustness and overcurrent protection property.

Conventional finite control set model-predictive control (FCS-MPC) presents a high computational burden, especially in three-level neutral-point-clamped (NPC) converters. This article proposes a low-complexity optimal switching time-modulated model-predictive control (OST-M2PC) method for a three-level NPC converter. In the proposed OST-M2PC method, the optimal switching time is calculated using a cost function. Compared with the conventional FCS-MPC, the proposed OST-M2PC method has a fixed switching frequency as well as better power quality. The proposed OST-M2PC can operate at a 20-kHz sampling frequency, reducing the computational burden of the processor. Simulation and experimental results validate the operation of the proposed method.

Litz wires are employed in high-frequency electrical machines due to their advantages of reducing the AC losses, including minimizing the skin effect and the proximity effect. In order to improve the reliability of such machines, and enable accurate thermal predictions at the design stage, accurate calculation of the thermal conductivity of Litz wire is important. In this paper, a calculation method based on the Gasar porous metal materials model is put forward. In this method, a cell model is extracted from the Litz wire, and a thermal resistance network is used to calculate the equivalent thermal conductivity. Following this, two FEA models for the same Litz wire are built, one with actual thermal conductivities for the different constituent materials and another with the calculated equivalent thermal conductivity for an equivalent material, with the two models showing similar thermal characteristics. Finally, an experimental setup is built for measuring the steady-state equivalent thermal conductivity of Litz wire. The apparatus structure and characteristics are described in detail, and the experiment uncertainty and measurement errors are analyzed. Three types of Litz wire are measured in the experimental, and the results from experiment and calculation are consistent.

Offshore wave energy can be easily predicted and is proved to be much better than other forms of ocean energy such as shoreline wave, near-shore wave, and tides. Research on offshore wave energy extraction has been carried out in many countries to meet the growing demand for clean energy and reduce the impact on natural environment. This paper reviews the development of offshore wave energy extraction systems in the recent decade. Several aspects are introduced, including a global wave energy resource assessment, offshore wave energy extraction technologies, and the interaction between wave and floating buoy as well as linear generators. Although various offshore wave energy extraction systems have been proposed and even tested, it is difficult to decide which is the best one. In fact, design of floating buoy and linear generators plays an important role in the operational efficiency of offshore wave energy extraction system. This review provides some useful guidelines for future studies in this field.

A speed controller for permanent magnet synchronous motors (PMSMs) under the field oriented control (FOC) method is discussed in this paper. First, a novel adaptive neuro-control approach, single artificial neuron goal representation heuristic dynamic programming (SAN-GrHDP) for speed regulation of PMSMs, is presented. For both current loops, PI controllers are adopted, respectively. Compared with the conventional single artificial neuron (SAN) control strategy, the proposed approach assumes an unknown mathematic model of the PMSM and guides the selection value of parameter K online. Besides, the proposed design can develop an internal reinforcement learning signal to guide the dynamic optimal control of the PMSM in the process. Finally, nonlinear optimal control simulations and experiments on the speed regulation of a PMSM are implemented in Matlab2016a and TMS320F28335, a 32-bit floating-point digital signal processor (DSP), respectively. To achieve a comparative study, the conventional SAN and SAN-GrHDP approaches are set up under identical conditions and parameters. Simulation and experiment results verify that the proposed controller can improve the speed control performance of PMSMs.

The conventional linear permanent magnet generator (CLPMG) for direct-drive wave energy conversion (WEC) has experienced many drawbacks that are difficult to overcome such as low power density and bulky system volume. To improve power density, this paper proposes a linear magnetic-geared interior permanent magnet generator (LMGIPMG) with tubular topology, which artfully incorporates a linear magnetic gear into a linear permanent magnet generator. The operating principle of the LMGIPMG is introduced, and a detailed analysis of air gap flux density, thrust force characteristics, and no-load and load performances are presented and discussed by using finite element method. The CLPMG, which produces the same power as the LMGIPMG, has about four times the volume of the latter. A prototype CLPMG is manufactured to verify simulation results against experimental tests. The design method and the operation conditions of LMGIPMG and CLPMG are both consistent; thus, the performance of LMGIPMG meets the operation requirements of the direct-drive WEC.