Comprehensive Voltage Regulation for Multi-Voltage Bipolar DC Distribution Systems

Asymmetric integration of photovoltaic (PV) and time-varying of DC source-load have raised diverse voltage issues such as inter-pole unbalance, violation and instability in multivoltage bipolar DC (MBDC) distribution systems. This paper proposes a comprehensive voltage regulation method for MBDC distribution systems based on multi-voltage-level bipolar power flow to ensure overall voltage performances. Firstly, an applicable bipolar DC power flow model to facilitate the optimization of multi-voltage subsystems is formulated by processing bipolar distribution systems and bipolar DC transformer (DCT) models. Then, the causes of various voltage issues under different voltage subsystems are analyzed to determine effective measures of power electronics devices for optimal solution. However, traditional voltage regulation models can only address single voltage issues within a single voltage level, which cannot handle the diverse regulation requirements under multi-voltage level systems. A comprehensive voltage regulation method is constructed by coordinating various heterogeneous resources across different voltage subsystems throughout the bipolar DC distribution system to improve power quality mitigation capacity and avoid device overuse. Numerical simulations on two three-voltage-level bipolar DC distribution systems with 33 and 123 nodes verify the effectiveness of the developed method.