Thermal model-based torque constant compensator and active temperature limiter for actuator overheat

Abstract

Recently, actuators in various fields have brought attention to the issue of overheating due to high current application. Overheating in actuators leads to serious problems for drive systems, including decreased actuation transparency due to temperature-dependent changes, reduced lifespan, and unnecessary heat transfer to the surrounding system. This research proposes algorithms to address the overheating problem in various high-current applications: a torque constant compensator and an active temperature limiter. Firstly, the reduction in actuation transparency due to temperature changes is directly caused by magnet temperature variation. However, compensating the torque constant for magnet temperature was challenging due to the rapid rotation of the magnets. In this study, by identifying a heat transfer model and designing a robust temperature observer, the real-time temperature of the permanent magnets is estimated, and torque constant variations are compensated for. Also, overheating in actuators rapidly decreases their lifespan and is a leading cause of actuator failure but limitation existed in that the current cannot be indiscriminately reduced for cooling purposes. The active temperature limiter proposed in this study calculates the optimal current reduction between the complementary relationship of driving temperature and current reduction. This allows for maintaining the temperature while utilizing the maximum current. The torque constant compensator and active temperature controller were validated for their effectiveness across various input currents, showing improved performance compared to existing algorithms. Additionally, the research defined and verified the range of safe current inputs and the limitations of weighting factors that can be used safely.