Study of the sensorless operating point estimation for turbocompressors

Frequency converters enable energy savings and sensorless operation monitoring in pump and fan systems. This is possible with model-based estimation methods that apply frequency converter estimates of the rotational speed and the shaft power. Since compressors produce air flow similarly as fans, the same estimation methods should be applicable, if the fluid density change can be detected and analyzed. In addition, suction side air conditions have an impact on the estimation of the compressor operating point and should therefore be considered accordingly. This paper studies the use of the Q_mP and Qφ_m estimation methods for a radial-flow turbocompressor and the accuracy of the affinity laws in the case of compressors. The results show that the Qφ_m method could be applied to turbocompressors, and the affinity laws are accurate enough if the performance curves are measured with sufficiently small rotational speed steps.