Design of a resonant converter for a permanent magnet synchronous machine

Abstract

This research project initially started with the hypothesis that the resonant behavior of a RLC circuit could improve the operation of a Permanent Magnet Synchronous Machine. The idea of this research project is to connect a capacitor in series to each motor phase during highspeed operation, turning the phase electrical circuits into a RLC circuits. The capacitor would be sized specially for the natural frequency of the resulting RLC circuit to match the electrical frequency of the motor at the desired operation speed. Because of the motor Back-EMF, it was found that the capacitors need to be pre-charged in order to provide the required electrical energy to the motor. This thesis presents in the first place the properties of the electrical resonance that could be valuable to benefit from and presents a high-level concept of converter that could allow to take advantage of the properties of the electrical resonance during operation of a Permanent Magnet Synchronous Motor (PMSM). Then, this thesis documents the elaboration and detailed design of the converter. The three main aspects covered in the detailed design are: the power electronics circuit of the resonant converter, the control electronics and the control algorithm. In the third place, the simulation model is presented, as well as the simulation results demonstrating the functional capabilities of the resonant converter. Finally, the simulation results are analyzed in details and conclusions about the advantages and disadvantages of the proposed resonant converter are enumerated. The simulation of the concept of resonant converter, named Resonant Power Processor (RPP), shows that the control algorithm and electronic circuit of the RPP successfully operate a PMSM at high speed and high torque simultaneously, with low THD phase current and low motor torque fluctuations. Taking advantage of the dynamic behavior of the RLC circuits of the motor phases and the recharge cycle, the RPP allows to reach 263% of the power achievable with the same battery voltage of 320V and generates a Line-Line voltage of 485.7Vrms with a battery voltage of 320V. The system successfully operates the PMSM at 5400 rpm and 14 N.m of output torque. The performances of the proposed system have been compared to a baseline system which consists of boost DC-DC conversion stages and a 3-Level inverter. The comparative analysis shows that the phase current THD and torque ripples are improved with the RPP, but the efficiency and power densities of the proposed prototype do not show improvements in terms of efficiency and power density of the global system. However, it is to be noted that the virtual prototype developed in this master’s thesis intents to be a proof of concept and that no efficiency and power density improvements have been done yet. This being said, options exist to bring the system efficiency and power density ahead of the prior art. In conclusion, the proposed RPP and its system is a promising technology, especially for high speed and high-power density operation of a PMSM.

Date	8 Dec 2021
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Kamal Al-Haddad (Supervisor)