Linearised Bipolar Power Flow for Droop-controlled DC Microgrids

The increase in efficiency and easiness to connect renewable energy sources has brought an increased interest into DC microgrids. Bipolar DC microgrids, present advantages over unipolar DC microgrids. Yet, due to their configuration they are prone to suffer from asymmetric loading which results in voltage unbalances among poles. The traditional power flow methods used in AC microgrids do not accurately reflect the steady state of DC microgrids. Equally, The power flow methods used for unipolar DC microgrids are not applicable for bipolar DC microgrids due to the behaviour of the neutral pole. In this paper, a linearised power flow method is proposed for bipolar microgrids. The proposed method allows to calculate the power flow for the positive and negative poles and to obtain the neutral pole voltage and currents resulting from load unbalances. The proposed power flow is suitable for simulating islanded or grid-connected microgrids with droop controlled generators and non-dispatchable generators such as photovoltaic pannels. The simulation results obtained using Python prove the effective performance of the proposed approach.