Estimation of the Mechanical Position of Reciprocating Compressor for Silent Stoppage
Anton Dianov
Abstract
This paper proposes the solution for decreasing of the reciprocating compressor noise and vibrations, which happens at stoppage. These vibrations and resulting noise are caused by the gas pressure in the cylinder, which impacts the compressor's piston and can reverse the motor at stoppage. To avoid this situation the motor must be stopped, when the gas is not pressurized, i.e., at the desired mechanical position, however motor is not equipped with a mechanical position sensor as the control system utilizes an electrical speed and position estimator. As a rule, it is impossible to estimate the mechanical position using an electrical position, however it has been noticed that at low speeds a detrimental feature of reciprocating compressors - varying load torque can help identify the mechanical position. Load torque impacts the quadrature current, making it oscillate at the mechanical frequency of the motor, so this mechanical frequency and position can be estimated using a Phased Locked Loop (PLL) algorithm, applied to the quadrature current.