Using Decentralized Control Techniques for Interaction Analysis in Hybrid AC/DC Grids

Abstract

One of the ancillary services that can be provided by Multi-terminal Direct Current (MTDC) grid to connected ac grids is power oscillation damping (POD). However, using PODs at multiple terminals of an MTDC grid results in multi-loop, multi-variable control system. Such control systems inherently have control loop interactions challenge, which can result in reduced performance of one or more controllers. This entails that PODs installed at multiple converter terminals to damp oscillations in respective ac grids could be affected due to unfavorable interactions among the controllers. Thus, compromising the stability of the connected ac grids. This paper presents analyses of interaction between multiple POD controllers installed on MTDC. For a three-terminal study system, insights on interactions between POD controllers at two different converter terminals of an MTDC are obtained using relative gain array and performance relative gain array measures.

Operation and Control of hybrid AC/DC transmission grids

“…MT-HVDC grids can operate in various types of active power and/or DC voltage control modes such as master-slave, voltage margin, DC voltage droop and dead-band droop control modes [8], [9], [17]. PPOD is output of an optional POD (power oscillation damper) controller.…”

“…The studies referred to above on the possibilities and potential pitfalls in operation and control of hybrid AC/DC systems have motivated a more thorough analysis of stability and robustness associated with control of multi-terminal HVDC grids. In [17] a control system design study was performed based on computation and analysis of relative gain arrays (RGAs). In an earlier study [20], the main objective was to assess interactions between the subsystems in hybrid AC/DC grids using dynamic analyses:…”

Power oscillation damping with virtual capacitance support from modular multilevel converters

“…In addition to the disturbance experienced by the other ac grids, the propagation of the oscillations also indicates that there can be an inter-ac-grid dynamic coupling in the electromechanical range. This can lead to undesired interaction between power system stabilisers located in different ac grids, such as the one reported in [9]. This problem can be mitigated by leveraging the energy storage capability of the modular multilevel converter (MMC), which is currently the most flexible and preferred converter topology for HVDC.…”