Patent ID: 8672641
Filing Date: 2014-03-18
Classification: E21B,F16C,H02K,H02P

Abstract:
1. A variable speed drive system comprising a variable speed drive circuit and a multi-phase permanent magnet motor for driving an electric submersible pump, the drive circuit being adapted to drive all of the phases of the motor simultaneously and the drive circuit comprising: variable voltage supply means for supplying a voltage that can be varied as required; inverter means supplied by said voltage for producing modulated waveforms having a voltage in the range 1,000 V AC-4,000 V AC to drive all of the phases of the motor simultaneously, each modulated waveform switching between an upper voltage level and a lower voltage level; and control means for operating the inverter means so as to produce over-modulation such that each modulated waveform produced by the inverter means is distorted and is unable to follow a peak of a sinewave or other waveshape that is demanded in simple proportion and each modulated waveform produced by the inverter means has extended periods at the upper voltage level and at the lower voltage level, the control means being operable to control the speed of the motor by varying said voltage supplied by the voltage supply means to the inverter means and to permit operation of the motor at speeds above 4,500 revolutions per minute.