Research Noise and vibrations produced by electric motors have gained particular importance lately as the market shifts to electrical vehicles (EVs). This work aims to evaluate the NVH (Noise, Vibration and Harshness) behavior of a Permanent Magnet Synchronous Machine (PMSM) drive system under different working conditions in the drive. The goal is to study the influence of the control strategy on the NVH performance of a PMSM to acquire general procedures to minimize its impact on EVs. Methodology The work explores different modulation and controller algorithms of the PMSM, including various control structures, different PWM (Pulse Width Modulation) strategies and load conditions. The methodology has been to define a standard test and evaluate it experimentally for the different configurations. The tests can be summarized in three groups: 1) modulation strategies and switching frequencies, 2) control approaches and 3), different load conditions. The tested modulation strategies include the well-known regular sampled PWM (sawtooth and symmetrical) and the Space Vector Modulation (SVM), all in the range from 4 kHz to 15 kHz. Moreover, advanced strategies used to control electrical drives, such as the third harmonic injection and the field weakening technique have also been tested. Finally, three control approaches are proposed: the classical PI-FOC (proportional-integral, field-oriented control) scheme has been compared with two nonlinear control techniques, a sliding mode current control and a hysteresis current control. Results It has been confirmed that higher levels of noise and vibration occur when the harmonics produced by the control strategy and the harmonics related to the motor construction interact; that, as a general rule, higher switching frequencies on the drive system led to better NVH performance of the PMSM and that control signal modulation also plays an important role on those results. It has also been tested that nonlinear approaches, which result in variable switching frequency algorithms, tend to increase the noise and vibrations in the system but improves its perception. The experiments also confirm that the levels of NVH increase as the load level of the PMSM does. Limitations of this study The study is based on a 2.2kW PMSM which has been instrumentalized with accelerometers and microphones in a laboratory test bench. Therefore, the results are neither obtained with a realistic motor used in an actual EV application nor in the final application environment. As a consequence, the results are qualitative. Nevertheless, the obtained results allow relating some controller configurations with the generated noise and vibrations of the electrical motor, which should then be exportable to an actual application. What does the paper offer that is new in the field in comparison to other works of the author? The inclusion in the study of two nonlinear control techniques allows us to compare them with traditional constant switching frequency implementations. The analysis of the NVH produced by nonlinear control techniques with variable switching frequency operation entails a contribution to this work. Conclusion The analysis of the obtained data reveals that the level of noise and vibrations of a PMSM depends on the configuration of the drive system, and it becomes important to keep these levels low. According to the results, it is possible to predict the NVH hotspot if the construction of the motor is known for a given control strategy and modulation technique. The most effective way to avoid such a hotspot seems to be the switching and the modulations used in the drive system.
Dr.-Ing. Víctor Repecho, Serra Hunter Felow - Lecturer professor, Universitat politècnica de Catalunya -BarcelonaTech