A Resonant Frequency Tracking Technique for Linear Vapor Compressors

A linear vapor compressor operates most efficiently at resonant frequency which varies with piston stroke and operation conditions. A novel resonant frequency tracking technique is proposed in order to achieve high efficiency operation of a linear compressor system. This is based on the fact that for given amplitude of the motor current, the linear compressor system reaches its maximum stroke and maximum input and output powers at its resonant frequency. By evaluation of the input power to the compressor and implementing a perturb and observe algorithm, the proposed technique can adjust the frequency of the motor current to match the resonant frequency of the compressor operation. The proposed technique does not require a position sensor, and can be easily implemented in a digital controller. Simulation and experimental results have demonstrated the validity of the proposed technique.