Thermal Management of a Soft Starter: Transient Thermal Impedance Model and Performance Enhancements using Phase Change Materials

Adverse effects of starting-torque transients and high in-rush currents in induction motors are typically mitigated by employing electronically controlled soft starting voltages through silicon-controlled rectifiers (SCRs). However, the heat dissipation in the soft starter must be carefully managed in the design of motor drives. The objective of this study is both to address the heat dissipation in the soft starter by implementing analytical solutions to the heat diffusion equations inside the soft starter, and to investigate the use of a phase change material (PCM) based heat sink for thermal management of the device. The analytical modeling approach is, however, general, and can be applied to the solution of a range of thermal problems in power electronics. The transient analytical thermal model, based on the thermal quadrupole approach, allows a determination of the transient performance of a soft starter by evaluating the thyristor junction temperature. Predictions from the model are first compared to results obtained using a coupled thermal and electricalmodel based on a resistance/capacitance network approach. Experimental results obtained with the soft starter connected to a low-voltage 200 hp induction machine are then used to validate the model. Additionally, the performance improvement resulting from the use of a hybrid heat sink (plate fin heat sink immersed in a PCM) is evaluated and compared to a conventional air-cooled heat sink without a PCM under identical conditions

Reusing 60GHz Radios for Mobile Radar Imaging

The future of mobile computing involves autonomous drones, robots and vehicles. To accurately sense their surroundings in a variety of scenarios, these mobile computers require a robust environmental mapping system. One attractive approach is to reuse millimeter-wave communication hardware in these devices, e.g. 60GHz net-working chipset, and capture signals reflected by the target surface. The devices can also move while collecting reflection signals, cre-ating a large synthetic aperture radar (SAR) for high-precision RF imaging. Our experimental measurements, however, show that this approach provides poor precision in practice, as imaging results are highly sensitive to device positioning errors that translate into phase errors. We address this challenge by proposing a new 60GHz imag-ing algorithm, RSS Series Analysis, which images an object using only RSS measurements recorded along the device’s trajectory. In addition to object location, our algorithm can discover a rich set of object surface properties at high precision, including object sur-face orientation, curvature, boundaries, and surface material. We tested our system on a variety of common household objects (be-tween 5cm–30cm in width). Results show that it achieves high accuracy (cm level) in a variety of dimensions, and is highly robust against noises in device position and trajectory tracking. We be-lieve that this is the first practical mobile imaging system (re)using 60GHz networking devices, and provides a basic primitive towards the construction of detailed environmental mapping systems