Accuracy study of frequency converter estimates used in the sensorless diagnostics of induction-motor-driven systems

Modern frequency converters allow energy efficient operation of induction-motor-driven systems such as pumps and fans. In addition, they can be used as a sensorless monitoring unit for the pump and fan systems, as shown by previous studies. Sensorless diagnostics of induction-motor-driven systems relies on the accurate estimation of the rotational speed, shaft torque and shaft power of the motor, which is why all frequency converters are not suitable for this use. In this paper, accuracy of the rotational speed, shaft torque and shaft power estimates is studied by laboratory tests for two different frequency converters. Using the test results, estimation accuracy of a vector- and a direct-torque-controlled frequency converter are compared with each other. The effect of erroneous motor estimates on the pump flow rate estimation is also demonstrated in the paper.

[1]  Jero Ahola,et al.  Sensorless pump operation estimation , 2009, 2009 13th European Conference on Power Electronics and Applications.

[2]  A. Binder.  Potentials for energy saving with modern drive technology — a survey , 2008, 2008 International Symposium on Power Electronics, Electrical Drives, Automation and Motion.

[3]  Juha Viholainen,et al.  Testing the accuracy of pump flow calculation without metering , 2005 .

[4]  Tero Ahonen,et al.  Monitoring of centrifugal pump operation by a frequency converter , 2011 .

[5]  Frede Blaabjerg,et al.  On the energy optimized control of standard and high-efficiency induction motors in CT and HVAC applications , 1997 .

[6]  Jussi Tamminen,et al.  Novel method for detecting cavitation in centrifugal pump with frequency converter , 2011 .

[7]  Joachim Holtz,et al.  Sensorless control of induction motor drives , 2002, Proc. IEEE.

[8]  Anibal T. de Almeida,et al.  Ecoanalysis of Variable-Speed Drives for Flow Regulation in Pumping Systems , 2011, IEEE Transactions on Industrial Electronics.

[9]  J.N. Nash.  Direct torque control, induction motor vector control without an encoder , 1996, Conference Record of 1996 Annual Pulp and Paper Industry Technical Conference.

[10]  Anibal T. de Almeida,et al.  Market transformation of energy-efficient motor technologies in the EU , 2003 .

[11]  Bimal K. Bose.  High performance control and estimation in AC drives , 1997, Proceedings of the IECON'97 23rd International Conference on Industrial Electronics, Control, and Instrumentation (Cat. No.97CH36066).

[12]  Jussi Tamminen,et al.  Estimation of pump operational state with model-based methods , 2010 .

[13]  Kaushik Rajashekara,et al.  Sensorless control of AC motor drives : speed and position sensorless operation , 1996 .

[14]  M. Orkisz,et al.  Variable frequency drive as a source of condition monitoring data , 2008, 2008 International Symposium on Power Electronics, Electrical Drives, Automation and Motion.