An apparatus for the improvement of AC waveform comprising means for applying a demand input waveform at an input of a circuit for power conditioning (including an inverter PWMVC or BBHCC) that is operable to provide an output waveform at an output; a feedback loop between the input and output, the feedback loop including means for sampling the output waveform (ADC1), means for subtracting a required waveform (RW) from the output waveform to produce an error waveform, means for processing the error waveform in a pre-defined manner to produce a processed error waveform (Clip1, Disc1, Att1), means for adding or subtracting the processed error waveform from Th. demand waveform to produce a revised demand waveform, and means for applying the revised demand waveform to the input of the power conditioning circuit at a subsequent time as an input demand waveform to produce a new AC output waveform at the output.