直流汇聚与远距离传输并网的海上风电全直流系统与交流系统相比具有诸多优点,但目前尚有系统拓扑、运维及可靠性等诸多问题未解决.直流汇聚系统现有方案故障恢复与黑启动需要的能量多依赖于独立的反向拓扑,增大了运行成本.利用提出的新型四象限隔离型DC/DC变换器拓扑的自身特性,提出和设计实现了拓扑反向重构与能量传输,为风场故障恢复与黑启动提供了低成本辅助方案.该拓扑利用反并联晶闸管构成串联谐振DC/DC变换器二次侧电路,可实现DC/DC变换器的四象限运行.首先,重点分析了拓扑反向运行模式工作原理及参数关系,并设计了反向电压闭环控制策略.其次,利用分段状态空间方程得到变换器在电感电流连续模式(continuous current mode,CCM)以及2种电感电流断续模式(discontinuous current mode,DCM)下的谐振变量时域表达式,并利用其获得反向运行时的谐振电流应力.通过时域分析法和功率守恒推导了电压增益与品质因数、开关频率之间的数学关系,划分了反向运行时的5种工况,并设计了控制策略.最后,通过MATLAB/Simulink仿真以及样机实验验证了反向运行策略的有效性.
Reverse operation strategy of four-quadrant DC/DC converter for offshore wind power DC aggregation
DC power collection and long-distance transmission have many advantages over AC interconnection for offshore wind power systems.However,there are still many unresolved issues such as system topology,operation and reliability.Current solutions for fault recovery and black start in DC aggregation systems rely heavily on independent reverse topologies,increasing operational costs.This paper proposes and designs a new four-quadrant isolated DC/DC converter topology that leverages its inherent characteristics to achieve reverse topology reconfiguration and energy transfer.Firstly,it provides a low-cost auxiliary solution for fault recovery and black start in wind farms.The topology uses anti-parallel thyristors to form the secondary circuit of the series resonant DC/DC converter,enabling four-quadrant operation.This paper focuses on analyzing the working principles and parameter relationships of the reverse operation mode and designs a reverse voltage closed-loop control strategy.Secondly,segmented state-space equations are used to derive the time-domain expressions of resonant variables in CCM and two DCM modes.These expressions are then used to obtain the resonant current stress during reverse operation.Through time-domain analysis and power conservation,the mathematical relationship between voltage gain,quality factor,and switching frequency is derived.Five operating conditions for reverse operation are identified,and a control strategy is designed.Finally,the effectiveness of the reverse operation strategy is verified through MATLAB/Simulink simulations and prototype experiments.
万方数据
维普
