thanks very much for all the replies, they have helped me grasp the subject! in reply to what my depth of knowledge is, I am currently doing a Marine electrical engineering degree! thanks very much for all your help!
so, I've been doing some research on harmonics recently and i can't actually find a good explanation of how they are created or what the effect. I have a feeling that they are something to do with 'clipping' the sinusoidal waveform to get the desired voltage. VSDs?