H∞ Robust Control Based on Internal Model Theory for Linear Permanent Magnet Synchronous Motor

For Linear permanent magnet synchronous servo motor (LPSM), the influence of mechanically driven chain from rotation motion to linear motion in rotation servo motor is cancelled by using LPSM. But the uncertainty factors in working of LPSM, such as the quality change of active cell, the variation of coefficient of friction and push ripples caused by magnetic density distribution fluctuation and time harmonic etc, greatly influence the performance of the system. Therefore, based on the internal model control (IMC) theory and robust control theory, a new H∞ speed controller with strong robust stability is designed for speed servo system by seeking the solutions to the standard H∞ control problem in the paper. The approach of output point mixed sensitivity is adopted to restrain the disturbance of speed servo system dynamically and eliminate the static error and guarantee robust stability. In the process of seeking the solutions to the standard H∞ control problem, an approximate internal model is introduced into disturbance path to simplify the design and satisfy the high-powered servo requirement. On the other hand, H∞ load disturbance observer is designed to overcome thrust ripples of LPSM more effectively. The simulation results show the proposed method is quite effective.