Segmented energy-saving control strategy based on variable-constant frequency of beam pump motor for CBM wells

The load of beam pump motor (BPM) used in coal bed methane ( CBM) wells is dynamically alternated, which results in BPM periodically runs on electric and power status and then results in a serious waste of energy. To solve this problem,combining with beam pump load characteristics and polished rod motion law,a segmented energy- saving control strategy based on the variable and constant frequency of BPM for CBM wells is proposed. This control strategy reclassifies the operating range into variable frequency (VF) stage and constant frequency (CF) stage instead of up and down strokes divided by the traditional principle. On VF stage,beam pump runs on its own energy transfor- mation by converting potential energy on the load side into kinetic energy resulting from changing the operating fre- quency of BPM. On CF stage,BPM works on motor status and drives beam pump when electrical energy converts into mechanical energy. Taking a CYJY4-1. 5-9HB beam pump driven by an YVP180L-8,11 kW induction motor as a test platform,the comparative analysis of energy-saving effect of VF,CF and the proposed segmented control strategy based on variable and constant frequency is carried out. Field test results show that the proposed strategy makes beam pump motion and load characteristics change. Meanwhile,the control strategy can effectively solve the energy feedback and avoid the energy flowing through BPM,resulting in the system saving rate improvement by 10% compared with other two control strategies. Furthermore,the control strategy has a strong versatility,thus providing CBM extraction system energy saving a new research alternative.