真双极直流配电网有功-电压分布式二级控制策略

采用下垂控制的真双极直流配电网存在负荷分配不合理以及正负极电压不平衡问题，导致换流器利用率降低、额外损耗增加，并且影响系统稳定性。为了实现负荷合理分配以及抑制正负极电压不平衡，提出了一种真双极直流配电网有功-电压分布式二级控制策略。该策略按照第二级控制功能将电压源换流器(VSC)分类，交换相邻VSC间的信息。在此基础上，逐步迭代得到相应的功率和电压收敛值，并计算得到电压调节量。由此进一步改变下垂控制参考电压值，从而实现负荷的合理分配以及抑制电压不平衡。最后，在PSCAD/EMTDC中搭建了真双极直流配电网模型，仿真结果验证了该策略的有效性和可靠性。

Distributed secondary power and voltage control strategy for a true bipolar DC distribution network

A true bipolar DC distribution network with droop control has problems with unreasonable load distribution and unbalanced positive and negative voltages. This will result in reduced converter utilization, increased additional losses, and affect system stability. In order to achieve reasonable load distribution and suppress the imbalance of positive and negative voltages, this paper proposes a distributed secondary power and voltage control strategy for a true bipolar DC distribution network. This strategy classifies voltage source converters (VSCs) according to the secondary control function, and exchanges information between adjacent VSCs. It iteratively obtains the corresponding power and voltage convergence values, and calculates the voltage regulation. This further changes the droop control reference voltage value, so as to achieve reasonable load distribution and suppress voltage imbalance. Finally, a true bipolar DC distribution network model is built in PSCAD/EMTDC, and the simulation results verify the effectiveness and reliability of the strategy. This work is supported by the General Program of National Natural Science Foundation of China (No. 51777066).