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Measurement of torque fluctuation of permanent magnet sinusoidal brushless DC motor

Chinese Library Classification Number: tm383 document identification code: a

article number: (2000) the measurement of torque

of PM Brushless DC motor Li, Yang Gui Jie, Zhang Zhi Zhong, Lu Yong Ping

KEY WORDS：brushless DC motor; torque ripple; Testing1 introduction due to the high torque performance of the permanent magnet sinusoidal brushless DC motor system, it is suitable for application in direct drive, and the fluctuation component (fluctuation torque) in its torque has a direct impact on the operation of the load, so the fluctuation torque index of the drive motor is strictly controlled [1 ~ 3]

aiming at the measurement of fluctuating torque, this paper proposes two measurement methods, namely, balanced direct measurement method and current indirect measurement method. In the balanced direct measurement method, a method different from the general structure [2, 4] is proposed, which uses the resistance strain gauge as the torque sensor, balances the constant component of the electromagnetic torque of the motor through the constant load, detects the fluctuating torque through the torque sensor, and solves the contradiction between the large range of the load torque sensor and the high resolution of the fluctuating torque sensor [4]. In the current type indirect measurement, considering that the fluctuating component of the sum of squares of stator currents of each phase represents the fluctuating torque of the motor, the corresponding measuring device is designed. For the convenience of analysis, the definition of torque fluctuation coefficient TRF is given first. Torque fluctuation coefficient is generally defined as the peak value of fluctuating torque Δ Ratio of TPP to average torque T - (1) 2 balanced direct measurement of fluctuating torque 2.1 principle and device of balanced direct measurement method in order to overcome the contradiction between the large range of the sensor and the high resolution of the sensor required by the load torque of the traditional direct measurement device, the designed direct measurement device of fluctuating torque is shown in Figure 1. Connect the load to one side of the motor shaft and the torque sensor to the other side of the motor shaft, and make the sensor push a large flywheel. In this structure, the range of the sensor can be reduced, so as to make full use of its resolution. Figure 1 Structure of the balanced direct testing bench. The mechanical equation of the system is (2), where TL is the load torque; J1 is the inertia of the motor; ω 1 is the mechanical angular speed of motor rotor; D1 is the motor damping coefficient; TT is the torque transmitted by the torque sensor to the flywheel

the load is provided by the magnetic powder brake. By controlling the excitation current and having an independent experimental force, deformation and displacement measurement control system, the brake adopts forced water cooling to keep the load torque TL constant. For the mechanical system composed of torque sensor and flywheel, there are (3) in which J2 is the moment of inertia of flywheel; ω 2 is flywheel angular speed; D2 is the flywheel damping coefficient

elastic connection is adopted between the torque sensor and flywheel to ensure that the torque sensor can produce deformation and output fluctuating torque signal

from equation (2) (4) if there is no fluctuating torque in the motor, the speed of the motor system is stable, and the flywheel and motor are at the same angular speed ω R rotation, i.e.: ω 1＝ ω 2＝ ω R = const (5) substituting equation (5) into equation (4), we can get that TT is a constant value, that is, the output torque has no fluctuation. Substituting equation (3) into equation (2), the mechanical equation of the whole measuring device can be obtained as (6). Generally, the mechanical time constant of the measuring device with flywheel is large. Therefore, if the motor has fluctuating torque, then ω R changes little. From equation (4), it can be seen that the fluctuating components ABS and PLA in te continue to meet the needs of 3D printing business enthusiasts and are more fully reflected in TT, so by measuring the torque sensor

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