Optimal Design Of Current Loop In PMLSM Servo System

Current loop is the inner loop of permanent magnet linear synchronous motor(PMLSM) servo system and plays a decisive role to system performances. Based on thenational natural science fund project (51075281), in order to meet the high precision andmicro feed control requirements of ac linear servo system, improve rapidity and dynamicstability of linear servo system, this thesis proposes to optimize the current loop ofpermanent magnet linear servo system.First of all, according to a large number of reference literature, linear servo systemand the developing trend of control strategy were analyzed, some kinds of disturbancewhich effect dynamic performance of linear servo system were introduced. Theimportance of linear servo system in modern society and the significance of optimizingthe current loop were explained.Secondly, this thesis analyzed the mathematical model of PMLSM, and the vectorcontrol method was used in the PMLSM servo system. The full digital control wasimplemented in the PMLSM servo system which based on DSP. The space voltage vectormodulation technology (SVPWM) and the software used in the PMLSM servo systemwere introduced.Finally, three kinds of current loop optimization strategy were proposed. When thePMLSM moves, especially at high speed and high acceleration, the motion electromotiveforce due to d-q axis coupling has important effects on system dynamic property, theinternal model decoupling control based on internal model principle was put forward tooptimize the current loop, and the performance of current loop was significantlyimproved. internal decoupling control method was used to optimize the current loop.Based on the synchronous rotating coordinate system, PWM module produces time delay,which leads to errors of inverter output voltage. Therefore an appropriate compensationmethod of current loop optimization method was put forward, i.e. multiplying the given inverter voltage by a coefficient and decoupling d-q axis coupling voltages. Experimentalresults verify the effectiveness of the proposed method. According to conventional PWMsampling sequence, there are time delay in PMLSM servo system, and they are differentin different model. Double moving current sampling and double PWM duty cycle updatewas put forward, the delay time was reduced, and the bandwidth of current loop wasexpanded, the dynamic performance of the system was improved.