Vector Control of Nest-Loop Secondary Linear Doubly-Fed Machine Considering Static End Effect Adapted to Urban Transit
Ge Jian1, Bao Zhen1, Xu Wei2, Tang Yirong1, Liao Kaiju2
1. State Key Laboratory of Advanced Electromagnetic Technology Huazhong University of Science and Technology Wuhan 430074 China; 2. Key Laboratory of High Density Electromagnetic Power and Systems Institute of Electrical Engineering Chinese Academy of Sciences Beijing 100190 China
Abstract Compared with the rotating machine, the linear machine has the advantages of strong climbing ability, small turning radius, low noise, light vehicle weight, and low overall energy consumption, which is especially suitable for urban rail transit drive systems. The nest-loop secondary linear doubly-fed machine (NLS-LDFM) is a new linear machine evolved from the nest-loop rotor brushless doubly-fed machine (BDFM), with a simple structure and easy operation and maintenance. It can overcome the significant thrust and power factor decrease under high speed and large slip. However, traditional control methods for BDFM are unsuitable because of the static end effect and the DC grid supply. Due to the cut-open primary iron core, the static end effect in NLS-LDFM generates the pulsating magnetic field evenly distributed along the motion direction, leading to two sets of asymmetrical three-phase windings and direct coupling. The large harmonic current, including negative sequence current and direct-coupling current, is produced. Furthermore, since the power supply of NLS-LDFM is different from that of BDFM, it is necessary to realize the close loop doubly-fed mode operation in urban transit power supply. Thus, a power winding voltage-oriented vector control strategy with static end effect compensation is proposed. Firstly, the basic structure and operation principle of NLS-LDFM, similar to the BDFM, is introduced. The static end effect and its compensation principle are analyzed. Then, the mathematical model of the three-phase static coordinate system and simplified two-phase rotating coordinate system are established. Secondly, the mathematical relationship of the primary current under the voltage orientation of the power winding is derived, and the decoupling control of two sets of winding in the electromagnetic thrust equation is realized. The power winding and control winding side converter control methods are presented. The constant voltage and frequency ratio control is employed in power winding, and the double close loop control of speed and current is applied in control winding. Simulations and experiments have demonstrated that the new method can effectively improve the steady-state drive performance of the NLS-LDFM through vector control with static end effect compensation. With the power winding voltage-oriented vector control, the electromagnetic thrust and speed can be controlled conveniently by adjusting the d-axis current of the control winding. With the static end effect compensation, the three-phase current of two winding sets is symmetrical, effectively suppressing the negative sequence current. The fast Fourier transform results show that the direct-coupling current is also suppressed. Furthermore, the noise and vibration can be decreased, and the efficiency can be improved. The following conclusions can be drawn. (1) The power winding voltage-oriented vector control easily realizes the start process and close loop doubly-fed operation in the DC power supply. The cross-coupling between power winding and control winding can be ignored. The electromagnetic thrust can be controlled directly by adjusting the d-axis current of the control winding. (2) The proposed static end effect compensation method is realized by pulsating voltage feedforward. Compared with the NLS-LDFM without compensation, the harmonic current and thrust ripple are suppressed effectively.
Ge Jian,Bao Zhen,Xu Wei等. Vector Control of Nest-Loop Secondary Linear Doubly-Fed Machine Considering Static End Effect Adapted to Urban Transit[J]. Transactions of China Electrotechnical Society, 2024, 39(24): 7752-7763.
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