Comparative Analysis of DTC and FOC Techniques on PHT Pump-Motor Simulating Coast-Down Speed-Time Characteristic for Nuclear Power Plant

A primary heat transport system of nuclear power plant has been incorporated for cooling nuclear reactor extracting large amount of heat energy emerging out due to nuclear fission chain reaction during reactor operation. After shutdown\tripping of reactor, fission decay heat governs the safe shutdown cooling requirements. Extraction of decay heat becomes very much essential after reactor shutdown to avoid fuel failure in reactor. A specified speed-time curve known as coast-down characteristic is to be followed by primary heat transport pump-motor using suitably designed flywheel coupled with motor shaft simulating decay power/heat profile of reactor occurred after shutdown to remove decay heat. The purpose of flywheel is to continue rotation of motor after reactor shutdown to support in extracting decay heat from reactor core to safe value. The scale down thermal hydraulic experimental facilities comprise primary heat transport pump-motor to simulate desired coast-down speed-time characteristics. The paper presents utilization of Direct Torque Control and Field Oriented Control techniques for controlling speed of primary heat transport pump-motor to obtain the desired coast-down speed-time characteristic having better dynamic response. It also describes working of Direct Torque Control as well as Field Oriented Control strategy and highlights their superiority compared to voltage/frequency method. The operating principles of these two techniques are different however their aim is controlling torque and flux effectively. The sensor less Direct Torque Control and Field Oriented Control drives requires estimation of stator and rotor flux, electromagnetic torque and speed which have been done using parametric values of stator and rotor including stator line current and voltage. The paper also discusses the estimation of flux, torque and speed of motor to model the drive. The paper presents simulation model of motor integrated with drive and results have been presented.