(A) Robust control of PM sychronous motor for high performance direct drive applications

Abstract

Robust torque and speed control techniques of a permanent magnet(PM) synchronous motor are presented for high performance direct drive applications. Some important characteristics of the PM synchronous motor are investigated and two major problems are considered as the major factors of degrading the control performance of the PM synchronous motor in the direct drive applications. One of the most serious problems is the torque pulsation or harmonics caused by the non-sinusoidal distribution of the linkage flux and the other is the load sensitivity due to the direct coupling of the external load. Therefore, the development of the novel torque and speed control techniques of the PM synchronous motor for direct drive applications are considered as a main topic of this dissertation. In order to overcome the problem first mentioned and related on the torque harmonics, a new concept of the torque control dealing with an instantaneous torque is introduced as an effective replacement of the current control technique associated with a concept of the field orientation. The mathematical model considering the flux harmonics is derived from some prior knowledges on the non-ideal construction of the PM synchronous motor. The new instantaneous torque control technique is proposed and designed based on this model. The proposed scheme consists of the adaptive torque estimator and robust torque controller using the model reference adaptive system(MRAS) and variable structure control(VSC) techniques, respectively. The linkage flux of the motor including the flux harmonics is first estimated by a flux estimator using the MRAS technique and the torque is calculated by using this estimated flux and measured stator current. Then, the estimated torque is instantaneous controlled by a robust control technique using the VSC. The undesirable torque harmonics can be effectively reduced by employing the proposed control technique. The simulation and experimental results well verify the eff...