  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.
