Laboratory evaluation of the VSD-based hybrid estimation method for the pump operational state

Operational state of a centrifugal pump directly affects the resulting energy consumption of the pump. Frequency converters (VSDs) allow the sensorless estimation of the operational state of a centrifugal pump, offering new possibilities for the diagnostics and control of pumping systems. However, estimation of the pump operational state by the QP-curve-based estimation method cannot always provide accurate results for instance because of the flat QP characteristic curve shape. In the worst case, this may prevent the detection of inefficient or even harmful pump operation. In this paper, a hybrid method with improved accuracy for sensorless estimation of the pump operational state by a frequency converter is studied through laboratory measurements. It allows more accurate estimation of the pump operational state especially at low rotational speeds and relative flow rates compared with the sole use of the known QP-curve-based estimation method.