Optimal Planning and Operation of Multi-Frequency HVac Transmission Systems

TL;DR

This paper introduces an optimal planning and operation framework for multi-frequency HVac transmission systems, aiming to minimize losses and improve voltage regulation by optimizing converter dispatch, voltage levels, and operating frequencies.

Contribution

It proposes novel multi-objective optimization models for both planning and operation of multi-frequency HVac systems, incorporating the effects of frequency and voltage on system losses.

Findings

Significant reduction in transmission losses achieved.

Enhanced voltage regulation during 24-hour operation.

Effective handling of parameter variations in the proposed solutions.

Abstract

Low-frequency high-voltage alternating-current (LF-HVac) transmission scheme has been recently proposed as an alternative solution to conventional 50/60-Hz HVac and high-voltage direct-current (HVdc) schemes for bulk power transfer. This paper proposes an optimal planning and operation for loss minimization in a multi-frequency HVac transmission system. In such a system, conventional HVac and LF-HVac grids are interconnected using back-to-back (BTB) converters. The dependence of system MW losses on converter dispatch as well as the operating voltage and frequency in the LF-HVac is discussed and compared with that of HVdc transmission. Based on the results of the loss analysis, multi-objective optimization formulations for both planning and operation stages are proposed. The planning phase decides a suitable voltage level for the LF-HVac grid, while the operation phase determines the optimal operating frequency and power dispatch of BTB converters, generators, and shunt capacitors. A solution approach that effectively handles the variations of transmission line parameters with the rated voltage and operating frequency in the LF-HVac grid is proposed. The proposed solutions of the planning and operation stages are evaluated using a multi-frequency HVac system. The results show a significant loss reduction and improved voltage regulation during a 24-hour simulation.