Showing papers in "Iet Generation Transmission & Distribution in 2021"

Modelling and prediction of current harmonics generated by power converters in distribution networks

Abstract: Predicting current harmonics in distribution networks is essential to find harmonic losses and power quality indices. In order to predict the current harmonics, the effect of grid impedance and voltage distortions on grid-connected power converters need to be considered. The effects of these parameters on current harmonics can be nonlinear, which complicates the system analysis. Consequently, this paper investigates the impacts of background voltage harmonics, grid impedance, and multi-parallel grid-connected converters on current harmonics at a point of common coupling. Moreover, a novel method called combined least squares and kriging (CLSK) is proposed to predict the current harmonics after evaluating the level of system nonlinearity. In the proposed CLSK method, the prediction model is developed by measured voltage and current harmonics at the point of common coupling to identify and predict the current harmonics. This analysis shows that using the proposed CLSK method, the accuracy of the current harmonic prediction is increased compared to the existing methods. The accuracy and the efficiency of the proposed CLSK method are verified by lab experimental results and field measurement data.

Sharing reserves through HVDC: Potential cost savings in the Nordic countries

Abstract: During summer 2018, the Nordic system's kinetic energy dropped below a critical level. As a consequence, Svenska kraftnat, the Swedish transmission system operator (TSO), requested the largest production unit to reduce its power output to guarantee system's security. This action resulted in a deviation from the generation dispatch determined by the market and in high costs for the Nordic TSOs. In this regard, this paper presents a tool for comparing mitigation strategies from an economic point of view and evaluates potential economic benefits of utilizing the Emergency Power Control (EPC) functionality of HVDC lines for the provision of fast reserves as a compliment to Frequency Containment Reserves (FCR). Moreover, the analysis is extended to the years 2020 and 2025 using inertia estimations from the Nordic TSOs. The findings of the paper suggest that the frequency of redispatching actions will increase in the future and that the cost of security for Nordic TSOs could be reduced by 70\% if HVDC links are used for frequency support.

A non-singular fast terminal sliding mode control scheme for residual current compensation inverters in compensated distribution networks to mitigate powerline bushfires

Abstract: This paper presents an approach to design a non‐singular fast terminal sliding model controller for residual current compensation inverters in compensated distribution networks to compensate the fault current due to most commonly occurred single line‐to‐ground faults. The main control objective is to completely eliminate the fault current in order to mitigate the impacts of powerline bushfires. A non‐singular fast terminal sliding surface is used to design the controller so that the residual current compensation inverter can quickly ensure the desired control performance without experiencing singularity problems. In this scheme, the chattering effects are minimised by replacing the discontinuous function appearing in the control law with a continuous function and the Lyapunov stability theory is utilised to demonstrate the theoretical stability of the control law. This paper also includes an overview of the non‐singular terminal sliding model controller as the performance of the non‐singular fast terminal sliding model controller is compared with this controller through rigorous simulation results over a range of fault currents. Simulation results clearly demonstrate the faster convergence speed of the non‐singular fast terminal sliding model controller over the non‐singular terminal sliding model controller for compensating the fault current and hence, mitigating powerline bushfires.