Small-Signal Stability Assessment and Interaction Analysis for Bipolar DC Microgrids

Abstract

Bipolarity in dc microgrids is desirable as it enhances the system's reliability and efficiency. However, the stability assessment for bipolar dc microgrid is challenging due to the integration of three-wire dc distribution line and numerous connected power converters, which is different from the stability analysis of conventional unipolar dc microgrid. In this paper, the basic form is arranged by generalized voltage source or current source, and the simplified form is derived by looking into different bus ports of a bipolar system in detail. Then, an impedance sum criteria-based stability conditions of different bus ports in the bipolar dc microgrid are proposed. To explore the mutual influence of the stability among different bus ports as well as investigate the stability issues caused by unbalanced loads connected to the symmetrical bus port, three cases are studied: 1) ±Vdc bus ports are connected with balanced and unbalanced loads; 2) -Vdc bus port introduces the photovoltaic unit and the energy storage unit; 3) The 2Vdc bus port introduces the photovoltaic unit and the energy storage unit. Finally, a ±24 V bipolar dc microgrid platform is set up to conduct experiments, verifying the accuracy and effectiveness of the stability evaluation method.

Stability Analysis of DC Microgrid Clusters Based on Step-by-step System Matrix Building Algorithm

“…The state space model is given in (10). In this paper, three cases analyzed are ① adding a new network to an existing network via a distribution line, ② adding a new network in between a distribution line, and ③ adding a new network at one end of a distribution in a cluster.…”

“…It can be observed from a comparison of the system matrices in (10) and (11) that the system matrices of the individual networks are added diagonally. In addition, an additional row and column are introduced to accommodate the coupling due to the distribution line.…”

“…Numerous researchers have recently examined DCMG stability problems. One of the widely used techniques for assessing the dynamic stability of the DCMG is small-signal (SS) stability analysis [10]. An investigation of the SS stability of the DC-MG cluster based on impedance is performed in [11].…”

Placing Storage Energies for Enhancing Small-Signal Stability of Converter-Based-Renewable Systems

“…Substituting ( 4) and ( 5) into (3), the dynamics at the source side can be rewritten as: (6) Combining ( 1) and ( 6), the close-loop dynamic model of the multi-CBR system with SEs can be given as Fig. 2.…”

“…To address the issues of power and energy balance in the multi-CBR system, storage energies (SEs) are good choices, due to their high flexibility of bi-directional power regulation. Due to this, the large-scale applications of SEs in the multi-CBR system are recently achieving great attention [3]- [6].…”