Antony Beddard

Comparison of Detailed Modeling Techniques for MMC Employed on VSC-HVDC Schemes

Modular multilevel converters (MMC) are presently the converter topology of choice for voltage-source converter high-voltage direct-current (VSC-HVDC) transmission schemes due to their very high efficiency. These converters are complex, yet fast and detailed electromagnetic transients simulation models are necessary for the research and development of these transmission schemes. Excellent work has been done in this area, though little objective comparison of the models proposed has yet been undertaken. This paper compares for the first time, the three leading techniques for producing detailed MMC VSC-HVDC models in terms of their accuracy and simulation speed for several typical simulation cases. In addition, an improved model is proposed which further improves the computational efficiency of one method. This paper concludes by presenting evidence-based recommendations for which detailed models are most suitable for which particular studies.

Analysis of Active Power Control for VSC–HVDC

This paper presents a comprehensive analysis of the limitations and the key dynamics of closed-loop active power control systems for voltage-source converter (VSC) HVDC, regarding stability, performance, and robustness. Detailed dynamic models are derived and the controllability and robustness issues for VSC active power control are identified. Limitations imposed by ac system strength, converter operating point, and current control design on the stability and performance of the two leading active power control principles are addressed, using frequency-response analysis and time-domain simulations. The dynamic interactions between the active power control design and the dc voltage droop control are examined. The simulations are performed using average-value VSC models and a high-fidelity modular multilevel converter model. Impacts of the active power control design on dynamic behaviors of multiterminal dc (MTDC) systems are investigated using a four-terminal model. This paper provides a systematic study on the key stability and performance issues associated with the active power control. Furthermore, the methodology offers a framework for the analysis of more complex active power and dc voltage droop controllers for future MTDC systems.

Improved Accuracy Average Value Models of Modular Multilevel Converters

Modular multilevel converters (MMCs) have become the converter topology of choice for voltage-source converter-high-voltage direct-current systems. Excellent work has previously been conducted to develop much needed average value models (AVM) for these complex converters; however, there a number of limitations as highlighted in this paper. This paper builds on the existing models, proposing numerous modifications and resulting in an enhanced MMC-AVM, which is significantly more accurate and which can be used for a wider range of studies, including DC faults.

Impact of Parameter Uncertainty on Power Flow Accuracy in MT Systems

Accurate power flow in a MT system can be achieved with droop controllers. However, almost all publications have assumed that the DC voltage, DC current and DC cable resistances can be measured with 100% accuracy. In this paper, a novel power flow solver is developed which enables the user to analyse the impact of these parameters on power flow accuracy. The developed Parameter Uncertainty Power Flow Solver (PU-PFS) is shown to be able to accurately calculate the power flow error for hundreds of parameter uncertainty scenarios in less than a second. The PU-PFS is employed to investigate the impact of parameter uncertainty on a potential MT system and the results show that realistic measurement errors (0.2%) can result in significant power flow error (>150MW). Finally, the paper assesses the key factors which influence the power flow accuracy resulting in a number of important conclusions.