Hierarchical power control of multiterminal HVDC grids

Abstract

This article introduces a hierarchical power control structure for Multi-terminal High Voltage Direct Current (MT-HVDC) systems. The presented hierarchy is similar to the control structure used in classical AC transmission systems and is divided in primary, secondary and tertiary control actions. The voltage control in the MT-HVDC scheme acts in a way similar to the primary control action of generators in AC systems, while the secondary control action is performed by an outer power control loop. The design of the individual controllers and the interaction between these control loops is discussed in detail.Furthermore, the operational characteristics are described and the main operating points are identified. Scenarios including a power reference change and a grid side converter disconnection have been simulated in order to test and verify the proposed method. The main contribution of the paper is the development of a control methodology, providing a separation of the different control actions in different time domains, similar to what is already in use (and therefore known) within traditional power systems.

Multi-terminal DC grids: challenges and prospects

“…This very simple control technique can be also used in a generalized manner to bring enhanced flexibility to the control and operation of the MTDC grid [36]. Moreover, the operation and control structures of an MTDC grid should be hierarchized in a similar manner as traditional AC power systems do [37]. As an example, a direct voltage control and power-sharing scheme for MTDC grids, based on applying optimal power flow and generalized voltage-droop strategies, is briefly described in the following section.…”

A tool for power flow analysis of a generalized class of droop controllers for high-voltage direct-current transmission systems

“…One way to deal with this issue, that prevails in practice, is the use of hierarchical control architectures [1]- [3]. Usually, at the top of this hierarchy, a centralized controller called tertiary controlbased on power flow optimization algorithms (OPFs)-is in charge of providing the inner controllers with the operating point to which the system has to be driven, according to technical and economical constraints [1].…”

Handling of unbalanced faults in HVDC-connected wind power plants

“…It offers low transmission losses, small filter requirements resulting in less foot-print, black-start capability of the offshore grid and less raw material for the cables compared to AC [3]. In the future, interconnection between several HVDC connections might evolve into a meshed HVDC grid to integrate flawlessly offshore wind into the European grids [4,5,6]. …”