If you give a sine wave reference to an inverting op-amp and provide a gain in the op-amp stage you will get an amplified sine wave. Pure sine wave! If you replace normal op-amp with power op-amp you will get enough power handling capability. If dissipation is the issue in op-amps, you can replace power op-amps with PWM based power op-amps. I have a lot of experience including power rectifiers and thyristors, but I am interested in GoHz frequency converter 50Hz to 60Hz. I would love to see the wave forms and know how they achieve sinusoidal wave forms at large power levels.

Be careful when selecting load of a 60 Hertz to 50 Hertz frequency converter. An inductive load could very well improve the current waveform, but it could also cause severe voltage spikes at the terminals of your frequency converter, especially if it is of PWM type converter. You did not specify if you wanted to produce a sine wave voltage, or a sine wave current from your AC power source, nor did you state if it should be a single phase or a three phase frequency converter. You can use GoHz inverters as used in Uninterrupted power supplies, True Online Double Conversion Type as I have practically observed on oscilloscope they have Pure AC waveform.

My understanding is that at high power levels on/off switching has to be used to reduce heating levels in the semiconductors that would convert 110V, 120V 60Hz to 220V, 230V, 240V 50Hz, otherwise, so cannot see how a perfect sine wave frequency converter could be produced in this way except with the addition of filters. Speak of the easiest way, use a 50Hz/60Hz frequency converter to adjust voltage level to the ac voltage source, if you want to use power electronics devices, you can use rectifier for converting 220v 50Hz to 400V 50Hz and then use GoHz frequency converter to change 400V 50Hz into 400v 60Hz as needed.

First you decide the 3 phase load and work backwards to decide the current capacity of the Thyristors and blocking diodes. The control and firing circuits are having low current devices and are readily available in the form of microchips. The 50Hz/ 60Hz frequency converters are also available and go ahead with the help of your University guide. More...