混合模块化直流固态变压器I:工作原理及稳态特性分析

Hybrid Modular DC Solid State Transformer I: Working Principle and Analysis of Steady State Characteristics

作为柔性直流配网的关键设备,直流固态变压器(DCSST)的控制性能和效率对提高系统实用性和经济性具有重要意义。不同于现有的模块化级联型 DCSST,结合移相型双有源桥(PS-DAB)变换器和串联谐振型双有源桥(SR-DAB)变换器,提出一种混合型模块化直流固态变压器(HMDCSST)。该 DCSST 融合了 PS-DAB 控制灵活以及 SR-DAB 运行效率高的优点,较原有的 DCSST 拓扑,在保持灵活的电压调节能力的同时,可提高功率传输效率,且由于 SR-DAB模块运行于开环模式,进而降低了系统设计复杂度。分析 HMDCSST 的工作原理,给出平均值数学模型以及功率损耗模型,并对该混合模型在定输出电压控制模式下的输入输出特性及功率传输效率进行详细分析。最后,通过实验结果表明,所提出混合模块化直流固态变压器的功率传输效率可达 96.4%,较单一 PS-DAB 型 DCSST,可提升约 1.0%。此外,输入侧和输出侧扰动实验进一步验证了工作原理及稳态特性分析的正确性。

As the key equipment of flexible dc distribution network, the control performance and conversion efficiency of DC solid-state transformers (DCSST) are significant for improving system practicability and economic efficiency. Unlike the existing DCSST, this paper presents a hybrid modular solid-state transformer (HMDCSST), which combines the phase shift dual active-bridge (PS-DAB) and the series resonant DAB (SR-DAB) in the way that the inputs are in series and the outputs are paralleled. The PS-DAB has the advantage of flexible voltage control while the SR-DAB features high efficiency, both of which can be inherited by the HMDCSST. Thus comparing with the original DCSST, the HMDCSST can improve power efficiency and reduce system design complexity, without sacrificing the flexible controllability. Working principle of the HMDCSST is analyzed, and the average mathematical model and power loss model are derived. Then detailed analysis of the input/output characteristics and power transmission efficiency under constant output voltage control mode are carried out. Finally, the experimental results show that the proposed HMDCSST can achieve a power efficiency of 96.4%, which is 1.0% higher than traditional PS-DAB based DCSST. In addition, experiments under the input and output disturbance further verify the correctness of working principle and steady-state characteristics.