A 3.3 kV variable frequency converter for retrofitting to existing motors

Variable speed control will provide significant benefits when fitted to the many fixed speed motors operating from medium voltage supplies. However, existing motors may not be rated for typical inverter output waveforms or for variable speed duty and care is required to ensure that any benefits are not diluted by problems. This paper describes a standard design for a medium voltage variable frequency inverter, which can be safely retrofitted to an existing motor, thereby realising the full benefits of conversion to variable speed operation.