Narrowband angle modulations in induction motor complex current vectors

Periodically time-varying loads such as reciprocating compressors produce torque and speed variations in grid-connected induction motors that are used to drive them. In each compression cycle, the torque and speed variations manifest themselves through periodic pulsations in induction motor's complex current vectors. Based on the concept of narrowband angle modulations, this paper analyzes the complex current vector's behavior in a typical motor-compressor system. Carson's rule is introduced to establish an empirical relationship between the complex current vector's bandwidth and the modulating frequency induced by the compressor. By reconstructing complex current vectors from raw experimental data through application of digital filters with different bandwidths, narrowband angle modulations and Carson's rule are experimentally validated.