Deep Dive: Reliably Delivering the Benefits of CSI Variable Speed Operation for Medium Voltage Motors Over Extremely Long Distances

Medium-voltage (MV) variable frequency drives (VFDs) have been increasingly adopted in the petrochemical industry, especially for offshore applications. As offshore oil and gas deposits are often located at long distances from the centrally located production platform, electrical submersible pump (ESP) motors are supplied via extremely long cables. These cables can easily range from a few kilometers to tens of kilometers between the VFDs and motors.After a specific oil/gas deposit becomes depleted in a particular subsea region, the option is now available to simply extend to another adjacent area around the existing rig. The already installed infrastructure is leveraged, which results in the lowest cost of operation/modification.A significant challenge to overcome is the excitation, by the VFD, of the low-frequency resonance characteristic to the long cable. This resonance condition can originate with the harmonics caused by the MV Pulse Width Modulated (PWM) VFDs and may damage and/or reduce the operational life of the insulation of both the ESP motors and the subsea cables.A Current Source Inverter (CSI-PWM) VFD topology has demonstrated in numerous applications, with basic considerations (i.e. passive damping for attenuation of potential resonance), reliable control of ESP motors located at distances upwards of 30 km from the production platform. This paper elaborates on the details, advantages, and considerations associated with employing CSI-PWM VFDs for addressing the stated challenge. Simulation, experimental, and real-world applications demonstrate the effectiveness of this scenario.