Evaluation and comparison of PAM and PWM power electronics for slotless micromotors

In a world where energy is an increasingly critical resource and where engineers seek to maximize the system’s efficiency, the impact of power electronics on the motor’s performances has to be addressed. This Master’s thesis compares two well-known drive techniques for micromotors, Pulse Amplitude Modulation (PAM) and Pulse Width Modulation (PWM). More generally, it creates a simulation tool that will help future users in their electrical drive design. First, this report describes the modeling of a 3-phase, 2-pole pairs slotless Permanent Magnet Synchronous Motor (PMSM) with flex-PCB winding technology. The motor electromechanical parameters are computed with 3D Finite Element Method (FEM) in COMSOL Multiphysics, an analytical model in Python, and are then verified with real values. Then, this thesis details the implementations of the two electrical drives on Simulink, with their controller, power electronics and motor to retrieve the current waveforms. Afterwards, these waveforms are re-introduced in COMSOL to compute the different types of machine losses (i.e., eddy current, iron, copper). Finally, the last section presents the results from the two techniques as well as some parametric studies on the PWM Drive to evaluate the importance of specific design choices. In particular, the switching frequency, the operating point, the use of a choke module or the sleeve thickness and conductivity are studied. The results show that the performances of the two methods depend on the application but that some general trends can be observed. The PAM drive has the advantage of limited converter losses due to its low switching frequency, at the cost of more hardware (DC-DC converter). It also provides significantly better overall efficiency for high-speed/high-voltage applications. However, in more classical cases, the PWM Drive disposes of several tools to significantly reduce all the machine losses caused by the current ripple, at the cost of lower converter efficiency.