Research on Star-Sealing Calculation and Application of Permanent Magnet Synchronous Traction Machines

Background

Permanent Magnet Synchronous Motors (PMSMs) are widely used in modern industry and daily life due to their advantages of high efficiency, energy saving, and reliability, making them the preferred power equipment in numerous fields. Permanent magnet synchronous traction machines, through advanced control technologies, not only provide smooth lifting motion but also achieve precise positioning and safety protection of the elevator car. With their excellent performance, they have become key components in many elevator systems. However, with the continuous development of elevator technology, the performance requirements for permanent magnet synchronous traction machines are increasing, especially the application of "star-sealing" technology, which has become a research hotspot.

Research Issues and Significance

Traditional evaluation of star-sealing torque in permanent magnet synchronous traction machines relies on theoretical calculations and derivation from measured data, which struggle to account for the ultra-transient processes of star-sealing and the nonlinearity of electromagnetic fields, resulting in low efficiency and accuracy. The instantaneous large current during star-sealing poses a risk of irreversible demagnetization of permanent magnets, which is also difficult to evaluate. With the development of finite element analysis (FEA) software, these issues have been addressed. Currently, theoretical calculations are more used to guide design, and combining them with software analysis enables faster and more accurate analysis of star-sealing torque. This paper takes a permanent magnet synchronous traction machine as an example to conduct finite element analysis of its star-sealing operating conditions. These studies not only help enrich the theoretical system of permanent magnet synchronous traction machines but also provide strong support for improving elevator safety performance and optimizing performance.

Application of Finite Element Analysis in Star-Sealing Calculations

To verify the accuracy of simulation results, a traction machine with existing test data was selected, with a rated speed of 159 rpm. The measured steady-state star-sealing torque and winding current at different speeds are as follows. The star-sealing torque reaches its maximum at 12 rpm.

Figure 1: Measured Data of Star-Sealing

Next, finite element analysis of this traction machine was performed using Maxwell software. First, the geometric model of the traction machine was established, and corresponding material properties and boundary conditions were set. Then, by solving electromagnetic field equations, the time-domain current curves, torque curves, and demagnetization states of permanent magnets at different times were obtained. The consistency between simulation results and measured data was verified.

The establishment of the finite element model of the traction machine is fundamental to electromagnetic analysis and will not be elaborated here. It is emphasized that the material settings of the motor must conform to actual usage; considering subsequent demagnetization analysis of permanent magnets, nonlinear B-H curves must be used for permanent magnets. This paper focuses on how to implement star-sealing and demagnetization simulation of the traction machine in Maxwell. Star-sealing in the software is realized through an external circuit, with the specific circuit configuration shown in the figure below. The three-phase stator windings of the traction machine are denoted as LPhaseA/B/C in the circuit. To simulate sudden short-circuit star-sealing of the three-phase windings, a parallel module (composed of a current source and a current-controlled switch) is connected in series with each phase winding circuit. Initially, the current-controlled switch is open, and the three-phase current source supplies power to the windings. At a set time, the current-controlled switch closes, short-circuiting the three-phase current source and shorting the three-phase windings, entering the short-circuit star-sealing state.

Figure 2: Star-Sealing Circuit Design

The measured maximum star-sealing torque of the traction machine corresponds to a speed of 12 rpm. During simulation, speeds were parameterized as 10 rpm, 12 rpm, and 14 rpm to align with the measured speed. Regarding the simulation stop time, considering that winding currents stabilize faster at lower speeds, only 2–3 electrical cycles were set. From the time-domain curves of results, it can be judged that the calculated star-sealing torque and winding current have stabilized. The simulation showed that the steady-state star-sealing torque at 12 rpm was the largest, at 5885.3 Nm, which was 5.6% lower than the measured value. The measured winding current was 265.8 A, and the simulated current was 251.8 A, with the simulation value also 5.6% lower than the measured value, meeting design accuracy requirements.

Figure 3: Peak Star-Sealing Torque and Winding Current

Traction machines are safety-critical special equipment, and permanent magnet demagnetization is one of the key factors affecting their performance and reliability. Irreversible demagnetization exceeding standards is not allowed. In this paper, Ansys Maxwell software is used to simulate the demagnetization characteristics of permanent magnets under reverse magnetic fields induced by short-circuit currents in the star-sealing state. From the winding current trend, the current peak exceeds 1000 A at the moment of star-sealing and stabilizes after 6 electrical cycles. The demagnetization rate in Maxwell software represents the ratio of residual magnetism of permanent magnets after exposure to a demagnetizing field to their original residual magnetism; a value of 1 indicates no demagnetization, and 0 indicates complete demagnetization. From the demagnetization curves and contour maps, the permanent magnet demagnetization rate is 1, with no demagnetization observed, confirming that the simulated traction machine meets reliability requirements.

Figure 4: Time-Domain Curve of Winding Current under Star-Sealing at Rated Speed

Figure 5: Demagnetization Rate Curve and Demagnetization Contour Map of Permanent Magnets

Deepening and Outlook

Through both simulation and measurement, the star-sealing torque of the traction machine and the risk of permanent magnet demagnetization can be effectively controlled, providing strong support for performance optimization and ensuring safe operation and longevity of the traction machine. This paper not only explores the calculation of star-sealing torque and demagnetization in permanent magnet synchronous traction machines but also strongly promotes the improvement of elevator safety and performance optimization. We look forward to advancing technological progress and innovative breakthroughs in this field through interdisciplinary cooperation and exchanges. We also call on more researchers and practitioners to focus on this field, contributing wisdom and efforts to enhancing the performance of permanent magnet synchronous traction machines and ensuring the safe operation of elevators.