Predictive torque control protects against gas supply interruptions

03 October 2016

ABB has released the first variable speed drive control software that uses Model Predictive Control (MPTC) to regulate the torque of a drive. 

Model Predictive Control is a control algorithm that has its roots in the process industries and that has been in use in chemical plants and oil refineries since the 1980s. In comparison with traditional control techniques, MPC intelligently predicts the future behavior of the system to be controlled via a mathematical model, and solves an optimisation problem to compute the best control action with respect to given criteria and limits of operations.

The software was initially developed to ensure the operation of compressor stations during voltage disruptions, caused by lightning strikes, winter storms or ice buildup on power lines.

The stations use large compressors, up to 50 megawatts to compress natural gas for travel through hundreds of miles of pipeline. Historically gas turbines powered the compressors. Today more efficient large synchronous electric motors are used and these are controlled by variable speed drives.

When power supply disruptions happen, protection systems quickly shut down the compressors. This halts the supply of gas. Restarting compressors lasts from a few hours to days. The resulting interruption in the gas supply can mean financial losses that range into the hundreds of millions USD per year for large facilities.

Installed in ABBs Megadrive-LCI, MPTC uses a control algorithm based on Model Predictive Control to ensure the operation of the drive during power and grid disturbances in order to provide the compressor with partial torque, preventing the compressor from going into surge.

The Megadrive-LCI application is the first where MPTC has been used to control a commercial multi-megawatt drive system with much faster dynamic behaviour, where the underlying optimisation problems need to be solved in less than a millisecond.

Live testing of the software was done over the winter at two Statoil gas facilities in Norway. It was installed on ABB Megadrive-LCIs used to power two 42.2 MW compressors at a gas processing plant in Kollsnes, and three 7.5 MW booster compressors in Kårstø. The control software successfully protected the compressor operation during voltage dips.

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