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VSD control algorithms protect gas compressors

03 October, 2016

ABB has released what it claims is the first variable-speed drive (VSD) control software that uses Model Predictive Control to regulate torque.

Model Predictive Control is an algorithm that has its roots in the process sector and has been used in chemical plants and oil refineries since the 1980s. It uses a mathematical model to predict the future behaviour of a system being controlled, and computes the best control action that meets specified criteria and operational limits.

ABB developed its Model Predictive Torque Control (MPTC) software to ensure the continuous operation of natural gas compressor stations during voltage fluctuations caused by lightning strikes, winter storms or the build-up of ice on power lines.

These stations, using compressors rated at up to 50MW, compress natural gas to send it through pipelines that can stretch for hundreds of kilometres. Historically, these compressors were powered by gas turbines but, today, most use more efficient large synchronous electric motors. These motors are controlled by VSDs – such as ABB’s largest drive, the Megadrive-LCI, about 1,000 of which are currently in operation around the world.

In the event of disruptions to a compressor’s power supply, protection systems shut it down rapidly, halting the gas supply. Restarting the compressor can take anything from a few hours to several days, and the resulting interruption to the gas supply can incur losses that run into many millions of dollars.

ABB has implemented Model Predictive Torque Control on its Megadrive-LCI system to protect against gas supply interruptions

The MPTC software running on a Megadrive-LCI drive uses an MPC-based algorithm to provide the compressor with partial torque during power and grid disturbances, thus preventing it from going into a surge condition.

ABB has already used the technology to control commercial multi-megawatt drive systems with fast dynamic behaviour, where the underlying optimisation problems needed to be solved in less than 1ms. 

The company performed live tests at two Statoil gas facilities in Norway. The first system was installed on Megadrive-LCIs used to power two 42.2MW compressors at a gas processing plant in Kollsnes. The second installation consisted of three 7.5MW booster compressors in Kårstø. The control software protected the compressors successfully during voltage dips.




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