Enhanced Volts-per-Hertz Starting of Permanent Magnet Motor with Heavy Loads in Long Cable Subsea Applications

Permanent Magnet (PM) motors are becoming increasingly being considered in subsea applications such as drilling, pumping, and boosting for natural gas and oil extraction. In many of these applications, PM Motors are gradually replacing induction motors. A PM motor can be controlled using an inverter that provides variable voltage and frequency, and is connected to the load through a sinewave filter, transformer, and a long cable. One of the methods to control the PM motor is by using a hybrid control strategy which starts the PM motor reliably using an open loop Volts-per-Hertz (V/Hz) control and switches to sensorless vector control once the motor reaches a safe operating speed. However, starting the PM motor with heavy loads is a key challenge. This is mainly because of the resistive voltage drop caused by the filter, transformer, and long cable. Additionally, the amount of voltage applied at the starting is limited by the transformer saturation effect. Therefore, to start the PM motor with heavy load, the voltage drop must be carefully compensated at starting without causing transformer saturation. In this paper, an enhanced V/Hz starting of the PM motor is proposed, which uses a voltage compensation method to actively compensate the voltage drop in the system without saturating the transformer. The proposed method is verified with Controller Hardware in Loop (C-HIL) real-time simulation by using Typhoon HIL-604 emulator and digital signal processor (DSP) control card TMS320F28335.