用于分布式发电接入的交直流叠加配电网结构分析

Analysis on Structure of AC-DC Distribution Network Used for Distributed Generation Connection

针对分布式发电(DG)并网问题,提出了一种包含分布式发电、Z型变压器、变换器、超级电容、交流负荷和直流负荷的交直流叠加配电网拓扑。分布式发电以直流形式通过直流电压变换器和Z型变压器作为接口接入网络,使得线路同时传输直流和交流功率。为了验证交直流叠加情况下Z型变压器不会出现饱和现象,利用Ansoft软件对Z型变压器进行了磁场分析,得到Z型变压器的局部最大磁感应强度为1.73 T,硅钢片的饱和点为1.7 T,Z型变压器未出现过饱和现象。考虑到分布式发电具有输出电压较低、非连续和不稳定的特点,引入电压反馈环节控制直流电压变换器,保证线路上直流电压值恒定为1.64 k V。为了平衡分布式发电出力和直流负荷需求,引入超级电容和交直流双向变换器组成的储能系统用于调节能量平衡、作为直流功率和交流功率的桥梁,当系统发生故障时保证对负荷持续可靠供电。最后采用Matlab/Simulink仿真验证了该交直流叠加配电网系统的可行性。

On the basis of the access mode to grid of distributed generation（DG）, we propose the topology of AC-DC distribution network containing distributed generation, zig-zag transformer, converter, super capacitor, AC and DC load. DG is connected to network in the form of DC source by DC-DC converter and zig-zag transformer, which makes single feeder line to simultaneously transmit DC and AC power. The Ansoft software is used to verify that the saturation phe- nomenon wilt not occur under AC-DC condition by analyzing magnetic-field pattern of zig-zag transformer. The results show that the partial maximum magnetic strength is 1.73 T and saturation point of silicon is 1.7 T. In accordance with the characteristics that the output voltage is low and the non-continuity and instability of DG, voltage feedback loop is intro- duced to control DC-DC converter, which guarantees the DC voltage of distribution line is 1.64 kV. Storage system composed of super capacitor and AC-DC bidirectional converter is introduced to balance the generating capacity of DGs and capacity-need of DC loads. As a bridge of DC power and AC power, super capacitor guarantees continuous power supply to loads when accidents occur. Finally the feasibility and correctness of AC-DC distribution network are verified by Matlab/Simulink.