The multi‐terminal voltage sourced converter medium‐voltage DC (VSC‐MVDC) distribution network has high prospects for future development, hence the proposed alternative for the AC distribution in commercial and industrial applications. However, a number of obstacles stand on its way in realising its immense potential in the modern power system. This study presents a review and focuses on the complexity of controlling DC voltage/power flow in the multi‐terminal DC (MTDC) grids and the possible DC voltage coordinated control approaches aimed at identifying the suitable control strategies for the proposed MVDC distribution grids. Several centralised and distributed DC voltage control strategies for MTDC have been considered. In conclusion, the droop‐based control strategies have been identified as reliable, flexible, and expandable with high dynamic performance and minimal communication needs in MTDC grids. These strategies are suitable and adaptable for stable and secure operation of the proposed multi‐terminal MVDC distribution network. The study recommends a comparative study of the key DC voltage coordination control features of the droop‐based control strategies using the multi‐terminal VSC‐MVDC distribution network dynamic model for future studies.

In this research study, a multiterminal voltage source converter (VSC) medium voltage DC (MVDC) distribution network hierarchical control scheme is proposed for renewable energy (RE) integration in a co-simulation environment of MATLAB and PSCAD/EMTDC. A DC optimal power flow (DC OPF) secondary controller is created in MATLAB. In PSCAD/EMTDC, the main circuit containing the adaptive DC voltage droop with a dead band and virtual synchronous generator (VSG) based primary controller for the VSCs is implemented. The simulation of the MVDC network under the proposed hierarchical control scheme is investigated considering variations in wind and solar photovoltaic (PV) power. The network is also connected to the standard IEEE-39 bus system and the hierarchical scheme tested by assessing the effect of tripping as well as restoration of the REs. The results show that during random variations in active power such as increasing wind and PV power generation, a sudden reduction or tripping of wind and PV power, the primary controller ensures accurate active power sharing amongst the droop-based VSCs as well as regulates DC voltage deviations within the set range of 0.98–1.02 pu with an enhanced dynamic response. The DC OPF secondary control optimizes the system’s losses by 38% regularly giving optimal droop settings to the primary controllers to ensure proper active power balance and DC voltage stability. This study demonstrates that the hierarchical control strategy is effective for RE integration in the MVDC distribution network.

Harnessing wind energy is the most rapidly growing amongst renewable energy sources. However, because of its intermittency in nature, wind power results in unfavorable influences on power system control, operation and stability. The voltage sag and flicker and grid frequency fluctuation are significant in this regard. To minimize the effect of wind power fluctuations and other contingencies on the grid frequency and AC-bus voltage, this paper presents a droop-fed vector control strategy based variable speed pumped storage (VSPS) system comprising the doubly fed induction machine. Modelling of the system is undertaken based on a phasor model technique. The case study is made by considering the droop-controlled VSPS plant in a grid containing conventional synchronous machines for hydropower and thermal power plants and an induction machine wind farm. The performance is validated and analyzed using a MATLAB/Simulink platform. The proposed droop-fed control model is compared with the conventional control strategy (without being droop-fed) and tested to wind power fluctuations, start-up transients, load variations and three-phase fault. The results show that the droop-fed vector control strategy of the VSPS plant achieves better dynamic and steady state controlling responses for grid frequency and AC-bus voltage in the power system than the conventional vector control scheme during wind power fluctuations and contingencies.

The stable operation and control of the proposed terrestrial multi‐terminal Voltage Source Converter (VSC) medium voltage DC (MVDC) distribution network is a remarkable motivation towards developing the future universal DC grid interconnecting the low voltage DC systems on one side and the high voltage DC systems on the other. The small‐signal stability analysis are important in designing these power electronic based systems (PEBS). In this study, small‐signal stability approaches for PEBS are reviewed with the aim of identifying suitable methods for the proposed MVDC distribution network. It is established that the impedance‐based methods are suitable for local stability analysis complementing very well with the state‐space modelling‐eigenvalue analysis method best for global stability analysis. The Lyapunov linearisation method offers simple, adaptable, and accurate small‐signal and large‐signal stability study. On the other hand, the bifurcation analysis is an emerging non‐linear approach with promising efficiency and precision. In conclusion, there is no single small‐signal stability criterion that encompass an acceptable level of accuracy, adaptability, and efficiency. Thus, the impedance‐based methods combined with state‐space modelling‐eigenvalue analysis, Lyapunov linearisation, and bifurcation theory can be suitable small‐signal stability approaches for the multi‐terminal MVDC distribution network.