Sub-fractional Horsepower Research Articles

Noise and vibration characteristics of sub-fractional horsepower single-phase BLDC drives

Single-phase brushless DC (BLDC) drives are a cost-effective alternative for three-phase sub-fractional horsepower drives in automotive auxiliary applications. Inherent features of single-phase permanent magnet machines, such as high cogging torque and torque ripple, can, however, make them more audible than their three-phase counterparts. As some of these auxiliary drives are close to the passengers, where even a small amount of noise can be disturbing, the investigation into noise sources is essential to further address this challenge. In this paper, the dominant noise and vibration characteristics of single-phase BLDC machines are investigated for two different stator structures, i.e., salient-pole and claw-pole, and compared. Magnetic force density waves and finite element (FE) analyses are performed to analyze the electromagnetic forces resulting from the open-circuit condition as well as different switching strategies in the load condition. Structural analyses show that due to the mechanical structure’s lower stiffness and natural frequencies in the audible range, the example case machine with the claw-pole stator develops higher structure- and air-borne noise than the machine with the salient-pole stator.

Effect of Manufacturing Influences on Magnetic Performance Parameters of Sub-Fractional Horsepower Motors

Depending on the stator lamination manufacturing processes (e.g., punching, laser cutting, clamping, welding, interlocking, and bonding), the motor’s magnetic performance parameters, such as cogging torque, hysteresis torque, and iron losses, can vary significantly. In sub-fractional horsepower (SFHP) permanent magnet motors, the manufacturing influence is typically even more severe because, due to their small dimensions, practically, the whole stator material is likely to be affected. This article analyzes the magnetic performance parameters cogging torque, hysteresis torque, and iron losses of three different stator lamination stacks (i.e., M250-35A punched with interlocking, M250-35A laser cut with bonding, and NO10 laser cut with bonding) of an SFHP single-phase brushless permanent magnet motor often found in automotive fan applications. A rheometer is used for extremely accurate torque measurements in the sub-millinewton meter range, and electron backscatter diffraction measurements are performed to visualize changes in the grain morphology and crystal orientation. The findings reveal that the punched stator with interlocking is affected the most by the manufacturing process, showing the lowest cogging torque yet the highest average hysteresis torque and thus up to 40% higher iron losses. The results presented in this article allow for both making basic stator lamination design choices and translating the iron losses, as well as the hysteresis torque and cogging torque waveforms, of a laser cut and bonded prototype into those of its punched and interlocked mass-produced counterpart.

Rheometer-Based Cogging and Hysteresis Torque and Iron Loss Determination of Sub-Fractional Horsepower Motors

Accurately measuring the cogging torque, hysteresis torque, and iron losses of permanent magnet (PM) motors is a challenging task. This is especially true for sub-fractional horsepower (SFHP) variants used, e.g., in auxiliary drives for automotive fan and pump applications. Their cogging torque and hysteresis torque peak values are often in the sub-milli-Newton meter range, causing conventional measuring methods and devices to fail as especially friction impedes the measurement significantly. Moreover, their iron losses are hard to determine and usually merely estimated in the literature. This article presents an unconventional rheometer-based method to determine both 1) the cogging torque and hysteresis torque of SFHP PM motors and 2) their iron losses by evaluating the observed offset torque. Two SFHP outer-rotor PM motor topologies for fan applications are analyzed, i.e., a claw-pole motor and a salient-pole motor. The results show that, with the proposed setup, settings, and evaluation, a rheometer can successfully be used to determine the cogging torque and hysteresis torque waveforms in the sub-milli-Newton meter range and the iron losses of SFHP motors, both with excellent accuracy.

Innovative Low-Cost Sub-Fractional HP BLDC Claw-Pole Machine Design for Fan Applications

As for mass-produced sub-fractional horsepower drives, non-optimal motor behavior (e.g., high cogging torque, output torque ripple, and noise) is often accepted when cost can be reduced, provided reliability is not compromised. This paper proposes an innovative claw-pole motor design for a low-cost single-phase brushless direct current fan drive, improving motor behavior with no increase to the manufacturing cost: 1) reducing cogging torque by proposing unconventional claw-pole skewing and 2) ensuring self-starting capability by implementing air-gap asymmetry. Both measures help reduce the total output torque ripple. The goal is to reduce fan drive noise, especially at low-speed operation, where cogging torque is often the dominating noise source. The design of stator claw skewing and air-gap asymmetry is presented; their effects on motor quantities are studied via simulations and experiments. With the exception of a small reduction of about 1.8% in the back electromotive force fundamental, skewing the stator claws by 30 $^{\circ }$ can reduce the cogging torque by 23% in the simulations and by 28% in the experiments.

Improved Switching Strategy for a Single-Phase Brushless Direct Current Fan Drive and its Impact on Efficiency

Advancing the turn- off angle of the phase current of brushless direct current (BLDC) motors is a common control practice to improve the operating behavior and energy conversion efficiency of such drives by, e.g., reduction of current peaks, copper losses, and breaking torques. This paper investigates a refined switching strategy for a single-phase BLDC motor with bifilar winding to increase the energy conversion efficiency of the system. In addition to advancing the phase current turn- off angle, the turn- on angle is delayed to improve the drive's performance and increase the efficiency even further. This efficiency increase of up to 20.6% is verified experimentally for a speed range from 3000 to 8000 rpm, translating into a reduction of copper losses of up to 37.4% or a decrease of current peaks by 27.4%. The focus is on sub-fractional horsepower single-phase BLDC motors with bifilar winding which, concerning this matter, have not drawn much attention in the literature yet. The findings show that the improved switching strategy can reduce current peaks, breaking torques, copper losses, and therefore increase efficiency over the speed range of interest for fan applications.

Novel disc type motors

The use of high energy permanent magnets can lead to significantly improved efficiency and performance, especially for subfractional horsepower motors. Obviously motors with air gap windings equipped with Nd-Fe-B magnets benefit from the high remanence of this new material. Integrated designs using Nd-Fe-B magnets are cost effective. The trend towards high flux density drives will continue.