Abstract
This paper proposes a new control scheme for the low frequency AC transmission (LFAC) system aiming at extending the point-to-point configuration to form a multi-terminal electrical energy network. The multi-terminal low frequency ac (MT-LFAC) system configuration is based on the use of modular multilevel matrix converters (M3Cs) and virtual synchronous generator (VSG) control. The M3C is the next ac/ac converter generation, which is used as an interface with the conventional AC network and the LFAC electrical energy system. Application of VSG control is proposed to enable proper power sharing, to provide synchronization of each terminal, and frequency stabilization, thus, to offer multiterminal forming capability. Two different operation modes are applied in the system to damp the frequency deviation after a dynamic perturbation, which provides additional stabilization feature to the VSG. Frequency restoration mode and commanded mode of power sharing are applied as dynamic states to validate the robustness of the VSG control system. Besides, to solve the negative impact of low X/R ratio in the LFAC electrical energy system, we enhance the VSG control by proposing a virtual-impedance-based solution, which increases the output total impedance on the low frequency side and prevents the coupling between P and Q. The operation of the proposed system is examined by simulation results with a precise model of M3Cs in the PSCAD/ EMTDC software environment (version 4.2.1, Winnipeg, MB, Canada).
Highlights
In recent years, the world has been concerned about global warming
This section evaluates the virtual synchronous generator (VSG) control scheme after transient events including the change of the power command and a power flow reversal, in addition to transition of switching modes
We proposed a control scheme to form a multi-terminal low-frequency ac (MT-low frequency AC transmission (LFAC))
Summary
The world has been concerned about global warming. Serious measures have been taken toward reducing carbon emissions by replacing fossil fuel with renewable energy sources (RES). This paper is meant to present a new control scheme for the LFAC transmission system in order to extend the point-to-point concept to form a multi-terminal LFAC (MT-LFAC) system, which has not yet been reported before in the literature This configuration is meant for applications that require an interconnection of remote power systems operating in nominal frequency via LFAC transmission lines. Since there are no previous works on forming the MT-LFAC system interconnecting remote areas, if we want to control it based on state-of-the-art solutions like [15], we need to apply the same control scheme as a master terminal, and control the other terminals as slave terminals The reliability of such a system will be determined by the master terminal, and the power flow control can only be performed in a centralized manner, which requires communication.
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