A study of linear PMSM driven ropeless elevators

Abstract

In recent years, buildings have become taller and wider. The conventional approach of one roped elevator car per hoistway seems increasingly impractical. The idea of ropeless elevators using linear motors was proposed more than 30 years ago, but it was merely treated as wishful thinking by the industry at that time due to lots of safety concerns. And discussion by the industry has mainly been qualitative in nature. In recent years, an international manufacturer announced the development of a prototype and the world's first installation may probably be open to public before the end of 2018. So far, academic studies have mainly focused on the study of linear motors with generic applications, while this paper focuses on the performance of the motor drive from an elevator's point of view. In this paper, we investigate the mechanism of the drive, and the linear permanent magnet synchronous motor and, by discretizing the equations of the full mathematical model, we fine tune the parameters and design suitable controllers. We evaluate its performance by computer simulation, based on the necessary kinematics of a real elevator, so as to arrive at some design guidelines. Finally, the most critical safety concern, i.e. free fall during a total power failure, is quantitatively studied by short circuiting all motor windings. Methods to achieve a reasonably constant and low descending speed, have been studied with parameters estimated analytically, and are verified by simulation. For the sake of illustrating the concept as an initial trial, simplified circuit models, controllers and sensors are all assumed as being ideal. It is hoped that this paper will stimulate the research interest of both the academic world and the industry, while the inclusion of more losses, armature reactions, and imperfections, etc., could be tackled in a further study. Practical application: The application of one roped elevator car in taller and wider buildings seems increasingly impractical. This paper considers the analysis of the application of ropeless elevators using linear motors focusing on the performance of the motor drive from an elevator's point of view. A basic mathematical framework is developed to study and design the controllers and drive of a multi-car elevator system by using linear permanent magnet synchronous motors with emphasis on the elevator performance as a whole system. The paper is aimed at stimulating research interest to drive the appropriate analysis and application of linear permanent magnet synchronous motor driven ropeless elevators.