Liu Mingji

Ripple torque analysis and simulation of BLDC motor with different PWM modes

Different PWM modes will influence the ripple torque of BLDC motor diversely. This paper introduced the usual PWM modes used in BLDCM and focused on the torque ripple analysis with PWM-ON mode, ON-PWM mode and PWM-ON-PWM mode. With the analysis of the commutation interval and the non-commutation zone, this paper demonstrates that the torque ripple of BLDC motor with the PWM-ON-PWM mode is better than others. Then, this paper established a novel simulation model of BLDCM with different PWM modes. The simulation results verify the analysis result.

Analysis and detection of turbo-generator stator turn-to-turn fault with multi-loop method

Turn-to-turn fault in the synchronous generator stator winding has been considered the most challenging one since the other types of stator winding related failures are usually the consequence of turn faults. In this paper we studied the turbo-generator in no load and load conditions and utilized the multi-loop method which can consider the asymmetric problem to detect the turn-to-turn fault of stator winding. The multi-loop model of the turbo-generator was established and the permeance analysis was used to calculate parameters of the model. The fault detection accuracy was improved by using the decomposition of wavelet analysis to detect the even harmonics in field current signal. The simulation results show that the stator turn-to-turn fault can be unambiguously detected from the field current signal.

Dynamic Irreversible Demagnetization Behavior of Line-start Permanent Magnet Synchronous Motors in the Starting Process

Abstract In the starting process of line-start permanent magnet synchronous motors, the relative lower flux density of the working point may cause irreversible demagnetization of permanent magnets. To research the dynamic irreversible demagnetization behavior, this article presents a sloped linear demagnetization model based on the time-stepping finite-element method. In this model, a new searching algorithm is used to quickly update the recoil line and the effective coercivity of each permanent magnet element so that the dynamic irreversible demagnetization effect can be considered effectively. Then the relationship between the demagnetization field and the rotor speed is studied, and the operation performances of the line-start permanent magnet synchronous motor after demagnetization in the starting process with different load conditions are compared. It is shown that the demagnetization field becomes larger with the rise of the rotor speed, and the demagnetization is more severe after a longer starting process with a larger load. Finally, the experimental validation on the characteristics of the dynamic irreversible demagnetization is performed by a line-start permanent magnet synchronous motor with a special rotor structure.

Comparative study on two field orientation control methods for the excitation field in the hybrid excitation synchronous generator

To solve the problem that the output voltage of permanent magnet synchronous generator (PMSG) is not easy to control, a coordinate structure hybrid excitation synchronous generator (HESG) with AC excitation is proposed and the AC excitation field orientation control (FOC) is studied. Firstly, based on the structure and principle, the mathematical model of the HESG is established. Then, two FOC methods of the excitation field, voltage-space-vector-based control and the forced orientation control strategy, are proposed. Finally, the two excitation control systems are simulated and the comparative study on the two methods is carried out.