Current Injection Power Flow Analysis and Optimal Generation Dispatch for Bipolar DC Microgrids

This article presents a current injection power flow analysis and optimal generation dispatch method for bipolar DC microgrids. In bipolar DC systems, despite a certain local voltage being balanced by the converter control, voltage unbalance can occur at buses that are electrically far from the balanced voltage. In addition, from the aspect of system operation, the optimization of operation cost and voltage unbalance has not been fully investigated yet. Herein, for steady-state analysis, the current injection Newton-Raphson power flow for a bipolar DC microgrid is developed using static models of the network, voltage balancer, sources, and loads. Afterwards, the optimization problem is formulated based on voltage sensitivity, which can be obtained from the Jacobian matrix, to reduce the operation cost while resolving the voltage unbalance. The problem of quadratic programming can be solved sequentially to find the final optimal solution. The case study validates that the power flow method is sufficiently accurate compared to the simulation in PSCAD/EMTDC and that optimal generation can be achieved while reducing the operation cost and mitigating voltage unbalance.