I. Introduction

Over the last few decades, saving energy has become a critical issue for home appliances. The compressor is the primary component that consumes electricity in air conditioners and refrigerators, which consume around 32% of the energy in households [1]. Several methods have been developed to enhance the energy efficiency of the compressor, reduce its acoustic noise and mechanical vibration that arise from the position-dependent torque, and minimize the cost of the entire system. Various alternatives of electric motor types, geometries, and control strategies have been proposed and tested to achieve this. This overview focuses on three different rotating inner-rotor motor types and their unique applications within hermetic reciprocating compressors (HRC), which are commonly used in refrigeration appliances. These compressors are well known for their small size, fractional power, and mass production. Usually, their power rating is less than 200W, their operating speed is between 1000 and 4000 rpm, and their torque output is below 0.5Nm. Due to their mass production, these compressors’ cost and energy efficiencies have become the most crucial feature of their design. The application of these motors presents specific implementation challenges, such as the absence of position sensors like hall-effect sensors due to the pressure conditions inside the compressor and the need to provide enough starting torque to prevent motor stalling due to the non-constant torque demand. Usually, HRC manufacturers do not publicly disclose in detail their technology and how they tackle these challenges. However, both independent and industry-funded academic research have also addressed these requirements with considerable success. This work provides an exhaustive review of the state-of-the-art advancements in each of these motors and highlights the research and development requirements driven by emerging future trends.