Power Flow Calculation of Power Systems with Renewable Penetration and AC/DC grids

Power flow calculation is a mathematical approach used to determine various parameters of power systems, such as voltage magnitude and angle at each bus. As a vital area of research, power flow calculation plays an indispensable role in power system planning, operation and control. The execution of power flow calculations facilitates the comprehensive analysis of a power system and the identification of potential issues, which is crucial in enhancing the safety, reliability and economy of the power system. Power flow calculation relies on the grid topology, component parameters, loads and power supplies in a power system as essential inputs which are typically assumed to be fixed quantities in conventional power flow calculation methods. However, in recent years, the proportion of renewable power generation has experienced a marked increase, and the outputs from these renewable energy sources are often variable and fluctuating, presenting challenges that are beyond the capabilities of traditional power flow calculation methods. In addition, AC/DC grids, a new grid topology with high transmission capacity and flexible control, have been employed in modern power systems. Traditional power flow calculations are also insufficient for analysing the power flow within these modern grid configurations. This thesis aims to investigate innovative power flow calculation methods for power systems incorporating renewable energy sources and AC/DC grid configurations. Initially, it reviews the existing research studies in the context of renewable energy integration and AC/DC grids. A comparative analysis and summary of techniques employed in these studies are provided. Subsequently, a novel probabilistic power flow calculation method is proposed, which combines the concept of the desired range with the Hammersley sequence to enhance sampling efficiency. Furthermore, the continuous permutation based on eigen decomposition is employed to address the correlation problem of wind speeds in geographically adjacent areas. In addition, a novel power flow analysis method is proposed to study the mixed impacts of the interval and probabilistic uncertainties on the power flow. A probability box model is established to analyse the power flow influenced by multi-type uncertainties. A general method is then proposed to solve the power flow in power systems containing AC/DC grids, where the extended AC grid model and sensitivity analysis are adopted. Thereafter, the linear iterative process and parallel computing techniques are employed to further improve the calculational efficiency and accuracy of the proposed method. Multiple test cases are employed to thoroughly evaluate the performance of the power flow calculation methods proposed in the thesis, compared with existing representative methods. The advantages of the proposed methods and the conclusions drawn from this thesis are summarised in the final section.