Damping Performance Analysis and Control of Hybrid AC/Multi-Terminal DC Power Grids

Abstract

The voltage-source converter (VSC) based multi-terminal direct-current (MTDC) networks are currently being developed in large-scale power grids for efficient and economical transmission of electrical energy generated from remotely sited renewable energy sources (RESs). As the MTDC network is developed alongside the conventional AC grid, it has transformed the power grid to a hybrid AC/MTDC power network. However, since the MTDC network is controlled via the power electronic converters (PECs), it significantly affects the AC power grid damping and synchronising performance as it decouples the natural dynamics between various electro-mechanical systems in the power grid. This paper proposes a supplementary control scheme to improve the damping performance of the entire hybrid AC/MTDC power grid. The damping torque analysis (DTA) technique is used as the primary technique to develop the supplementary control scheme. The preliminary analysis is carried out using a two-terminal hybrid AC/DC power grid and has suggested a supplementary control loop based on the rotor speed deviation for the DC voltage controller of the VSC to improve the damping performance. With the state-space model, the synchronising and damping torque coefficients are calculated and accordingly, the feedback gain is determined to provide optimal synchronising and damping torque components. Subsequently, the fidelity of the supplementary controller is verified using a four-terminal hybrid AC/MTDC grid. Simulation studies prove that the proposed supplementary controller can improve the hybrid AC/MTDC network damping performance, and it performs very effectively with the master-slave control and the conventional droop control scheme. INDEX TERMS Damping torque analysis (DTA), high-voltage direct-current (HVDC), multi-terminal DC (MTDC), rotor angle stability, small-signal analysis, voltage-source converter (VSC).

Power System Stability with Power-Electronic Converter Interfaced Renewable Power Generation: Present Issues and Future Trends

“…More specifically, high voltage direct current (HVDC) links are constructed to transmit power generated from remotely sited wind and solar-PV plants to the AC network [12,13]. These structural changes have evolved into hybrid AC/DC power grids, hence stability of the emerging hybrid AC/DC power grids is an important aspect in regards to future power grids [14]. In addition, the distribution grid is also increasingly adopting DC technology due to increased penetration of PEC-interfaced small-scale solar-PV systems and DC loads [15].…”

“…Moreover, stability issues are also originating from the architectural changes in the power grid, such as hybrid AC/DC power grids. Therefore, stability issues emanating from hybrid AC/DC power grids must be thoroughly studied and characterized to minimize the impact on future power grids [14].…”

A Virtual Inertia Method for Stability Control of DC Distribution Systems with Parallel Converters

“…In [14], the authors extended the damping torque analysis theory to a line-commutated converter based on a voltage source converter (VSC-HVDC) auxiliary damping control to suppress the oscillation of the AC-DC hybrid system. In [15], the authors presented a detailed analytical approach to study the synchronization and damping moments of the AC-DC hybrid power grids. The authors in [16] showed that impedance matching could be used to select the resistance value and the damping controller gained to obtain the maximum damping ratio.…”

Damping Torque Analysis of VSC-HVDC Supplementary Damping Controller for Small-Signal Stability

“…Ref. [21] proposes a supplementary control scheme to improve the damping performance of the entire hybrid AC/MTDC power grid. But it only establishes the model of two-terminal AC network and thus cannot be applied to VSC-MTDC.…”