High-efficient C3N4-viologen charge transfer systems for promoting photocatalytic H2 evolution through band engineering

Accelerating the charge transfer (CT) capability of photocatalysts is an efficient way to improve the overall photocatalytic performance, yet the precise regulation of CT in photocatalyst systems is still lacking. In this paper, a series of hybrid photocatalysts composed of graphitic carbon nitride (CN) and various viologens (V) were prepared for the photocatalytic hydrogen evolution (PHE) from water splitting under visible-light irradiation. Considering the fixed energy structure of CN, the different electron-withdrawing substituents were introduced to engineer the band structure of V delicately and modulate the CT process between CN and V. It was shown that all the hybrid photocatalysts CN-x%V_y exhibited higher photocatalytic performance, of which CN–1%V₃, possessing the strongest electron withdrawing group (-NO₂), demonstrated the best PHE performance (3572.3 μmol g⁻¹ h⁻¹), exceeding 29 times over the unmodified CN. It was proposed that the introduction of V can optimize the interfacial photogenerated electron transfer (CN→V→Pt) of the whole photocatalytic system effectively. We highlighted the V as an efficient chemical segment to modify semiconductors toward enhanced activity due to the following unique characteristics: (i) the unique redox ability, (ii) the easy synthetic methods for controlling the band structures precisely, and (iii) the inherent positively charged feature. This work provides a deep understanding of CT for the rational design of high-performance photocatalysts through band engineering.     

可实现低频输电系统不对称故障穿越的M3C电容电压均衡控制策略

低频输电作为一种新型输电技术，在海上风电送出、新能源场站送出等多个场景具有良好的应用前景。但在不对称故障下，故障侧功率不对称将严重影响模块化多电平矩阵变换器(modular multilevel matrix converter, M3C)的电容电压均衡，对低频输电系统安全稳定运行产生不利影响。为此，提出了一种可实现低频输电系统不对称故障穿越的M3C电容电压均衡控制策略。首先，介绍M3C的系统结构及双αβ0数学模型，并分析不对称故障下电容电压不均衡的原因。然后，基于双αβ0数学模型针对输电线路不对称故障情况计算桥臂功率不均衡分量的表达式，通过M3C功率平衡关系引入电流补偿分量，消除桥臂功率的不均衡，并得到适用于不对称故障的环流控制目标，进而通过环流控制实现故障下M3C电容电压的均衡。最后，搭建基于M3C的低频输电系统仿真模型验证所提控制方案的可行性和有效性。     

基于自抗扰的单相PWM整流器直接功率控制

为改善单相两电平PWM整流器的动态性能，本文在传统外环采用PI控制，内环采用功率前馈解耦直接功率控制的双闭环控制方法基础上，提出一种改进控制策略，即引入基于线性自抗扰(LADRC)的电压外环，以减小直流侧电压的超调量,提高系统的响应速度，并增强其抗负载扰动能力。进一步在功率前馈解耦控制的基础上，引入二阶广义积分(SOGI)构建虚拟正交分量，以提高网侧电流对电压的追踪能力，提升系统的动态性能。最后，通过MATLAB/Simulink建立系统仿真模型并进行仿真，对所提出改进控制策略的可行性和有效性进行了验证。