Research On Power Supply Strategy Of Offshore Oil Platform And Analysis On The Fault Characters

In offshore oil platform, high voltage and power motors (HV motor) are needed when delivering oil to onshore land. Diesel generators in platform can’t support so much power requirement, so the motors mentioned above must be supplied by onshore AC grid. In general, when there is a long distance between offshore platform and onshore land, DC transmission system is more efficient. The load consists of motors can be regarded as a passive power system with high capacity far away from the land. For this specific type of load, power supply with modulator multilevel converter is the best choice. The power supply system is required to have long-term stability and strong fault ride-through capability because the following reasons:1) the complexity of the start-up process for high power synchronous motor; 2) the inconvenience of maintenance for its long distance from mainland. Based on the above, the thesis mainly has done the related work as follows:1). The thesis analysis the mathematical model of the cable wounded synchronous motor and the modulator multilevel converter. Based on the mathematical model, a control strategy is proposed. The strategy is based on the power supply method used for power supply for the passive platforms with voltage sourced converter, combining the technology of HVDC and the studies of high voltage motor driving control,. Then the mathematical model is set for the control strategy and the thesis makes a detailed analysis for it.2). Then the thesis builds the electromagnetic transient simulation platform for the proposed system in PSCAD/EMTDC, and realizes the steady station of the power supply system. Based on the platform, the function of the motor speed regulation and the response to the load torque disturbance is tested, then the results are studied for the further research.3). The specific instantaneous metallic line to ground faults on both the sending end and the receiving end are applied to the simulation platform, and the system characters during the faults are studied. Based on the characters, the thesis adopts the DC voltage limited control to demise the effect that the loss of the active power during the ground fault on the sending end; and proposes the Q-U droop control to make the system capable to ride through the metallic line to ground fault on the receiving end. The simulation results are carefully studied and the thesis finally makes the evaluation of the control strategy.