Modeling and multi-objective optimization of a stand-alone photovoltaic-wind turbine-hydrogen-battery hybrid energy system based on hysteresis band

Hybrid renewable energy system (HRES) can provide power without emission for off-grid areas. Due to intermittency of renewable energy, energy storage system (ESS) is essential for reliable power supply, while its cost is still relatively high. Appropriate power management strategy (PMS) can help to delay the degradation of energy storage devices and reduce the system cost. In this study, power management strategy and configuration optimization of the system are focused and the study includes three main contributions. First, mathematical models of the system, including photovoltaics (PVs), wind turbines (WTs), batteries, fuel cells (FCs), electrolyzers (ELZs), and hydrogen tanks are developed. The degradation of fuel cells and electrolyzers is considered in the modeling process. Second, power management strategy considering hysteresis band is employed to control energy flow to delay fuel cell and electrolyzer degradation. Third, a multi-objective optimization function including the system net annual value (NAV), loss of power supply probability (LPSP) and excess energy (E_excess) is established. Non-dominating Sorting Genetic Algorithm II (NSGA-II) is used to solve objective function. The results demonstrate that using hysteresis band help improve the system performance and reduce the cost. In addition, by setting the goal of excess energy, system reliability is well preserved with a LPSP as low as 0.92%. Compared with other optimization algorithms such as MOEA/D, NSGA-II has a smaller SI value of 422.10 and a larger DI value of 830.78, therefore the Pareto solution obtained by NSGA-II has a more uniform distribution and larger coverage.     

配流阀结构特征对微型高压柱塞泵流量输出特性的影响

为满足航空泵高功率密度化要求，微型高压柱塞泵采用阀配流方式能够有效减少泄漏，提高容积效率。针对影响微型高压柱塞泵流量输出特性的主要因素，建立阀配流微型高压柱塞泵数学模型，通过AMESim搭建不同结构的单向阀配流模型，将球阀、锥阀、平板阀等不同形式的单向阀芯进行不同组合结构的建模及仿真试验，对微泵的余隙容积、斜盘倾角、负载压力及单向阀的弹簧刚度、阀芯质量等影响因素进行仿真分析。结果表明：在现有结构下，吸液阀和排液阀均为平板阀时是最优配流阀组合形式；微泵在变转速工况下容积效率稳定，阀芯质量对配流阀迟滞性影响较小；增大斜盘倾角及减小负载压力和余隙容积能够有效改善配流阀开启滞后角，进而提高容积效率。     

磁滞回线测试系统的改进

本文对磁滞回线测量的原理和方法进行了介绍，并对通常的测量系统进行了改进使系统有较小的测量噪声，测试结果可以方便地由计算机输出并计算磁滞回线面积，经和专业测量设备的结果比较，结果非常吻合，适合实验室应用。     

Dynamic hysteresis relation for guiding poling condition of high-performance KNN-based ceramics

Currently, the poling condition selection for KNN-based ceramics still requires an inefficient and time-consuming empirical attempt process owing to the lack of relevant theoretical guidance. Herein, the dynamic hysteresis relations and polarization reversal behavior of KNNS-BNZ-Ba ceramics were explored to guide the poling condition selection. The scaling relations of the loop area <A> on electric field amplitude E₀ and frequency f were determined. The three-stages E₀-dependent scaling relation and two-stages f-dependent scaling relation (at the high electric field) were clarified. The relevance between hysteresis dynamics and poling process was analyzed. It suggested that the optimal poling field amplitude corresponds to the terminal electric field of non-180° domain switching. Meanwhile, excellent electromechanical properties (d₃₃ = 408 pC/N, k_p = 51%, and k₃₃ = 69%) were achieved in KNNS-BNZ-Ba ceramics. Our work provides a scientific theory to guide the poling technology in KNN-based ceramics by exploring the polarization reversal kinetics.