A 1.5 kV, 35 kW, 1 kHz silicon steel core medium-frequency transformer is designed and prototyped for a 10 kV, 0.5 MW electronic power transformer. This transformer uses 0.18 mm silicon steel as core material due to the advantages of easy processing, high saturation flux density, low noise, and low cost. The detailed design considerations and an optimal design method are presented in this paper. Different from the previous work on medium-frequency transformer design, the proposed approach takes ripples into account. Core loss model under square wave excitation with ripple and winding loss model considering side-band harmonics are established. Besides, two-dimensional finite-element simulations are adopted to obtain ac/dc resistance factors. Finally, the proposed approach is verified by experiments on prototype. The test results show performance better than expected, with desirable no-load loss and power density of 2.9623 x 10(6) W/m(3).

In order to control the cascaded H-bridges (CHB) converter with staircase modulation strategy in a real-time manner, a real-time and closed-loop control algorithm based on artificial neural network (ANN) for three-phase CHB converter is proposed in this paper. It costs little computation time and memory. It has two steps. In the first step, hierarchical particle swarm optimizer with time-varying acceleration coefficient (HPSO-TVAC) algorithm is employed to minimize the total harmonic distortion (THD) and generate the optimal switching angles offline. In the second step, part of optimal switching angles are used to train an ANN and the well-designed ANN can generate optimal switching angles in a real-time manner. Compared with previous real-time algorithm, the proposed algorithm is suitable for a wider range of modulation index and results in a smaller THD and a lower calculation time. Furthermore, the well-designed ANN is embedded into a closed-loop control algorithm for CHB converter with variable direct voltage (DC) sources. Simulation results demonstrate that the proposed closed-loop control algorithm is able to quickly stabilize load voltage and minimize the line current's THD (<5%) when subjecting the DC sources disturbance or load disturbance. In real design stage, a switching angle pulse generation scheme is proposed and experiment results verify its correctness.

This study presents a novel fundamental modulation strategy with selective harmonic elimination (SHE) for multilevel inverters. Compared with conventional schemes, more kinds of stepped waveforms can be adaptively synthesised and it is more possible to obtain the optimal solutions for the SHE problem, especially at low-modulation indices. The control purpose, SHE and fundamental voltage control, for a cascaded 11-level inverter is formulated as multi-objective optimisation problem which is solved by using shuffled frog leaping algorithm in this study. The theoretical and experimental results are presented to confirm the validity of the proposed modulation scheme.

The AC loss induced in superconducting tape may affect the performance of a superconducting device applied to power system, such as transformer, cable, motor and even Superconducting Magnetic Energy Storage (SMES). The operating condition of SMES is changeable due to the need of compensation to the active or reactive power according to the demand of a power grid. In this paper, it is investigated that the distribution of AC loss for a storage magnet on different operating conditions, which is based on finite element method (FEM) and measured properties of BSCCO/Ag tapes. This analytical method can be used to optimize the SMES magnet.

This paper proposed a control strategy based on feedback-linearization control theory to design the controller of the direct-driven permanent magnet synchronous generators (D-DPMSG) system. In order to maintain the D-DPMSG system stably operating on the optimal regimes, tracking the wind turbines’ optimal operating characteristic curve quickly, a nonlinear control strategy based on dynamic models of the components of the system is derived. Comparing to the conventional PID control strategy, this new nonlinear controller based on feedback-linearization control theory shows better performance of rotor speed with smaller overshot and faster response when subjecting to stochastic wind. Intensive simulations are shown to demonstrate the effectiveness of the proposed scheme in tracking the maximum power operating curve.

提出一种基于反馈线性化原理的控制策略来设计直驱型风力发电机组(D-DPMSG)控制系统。为了使系统稳定运行在最大功率区域和快速追踪最大功率特性曲线,建立了系统各部分的动态模型并推导出了该非线性控制策略。在随机风速扰动下,相对于传统的PID控制策略,基于反馈线性化原理设计的非线性控制器使系统的转速响应超调更小,响应速度和恢复速度更快,效果更好。最后,大量仿真证明了该控制策略在追踪最优功率曲线的有效性。