Research On The Influencing Factors Of Digital Servo System Current Loop

With the servo system widely used in the field of advanced processing, robot, aerospace and so on, people have paid more and more attention to the high performance of servo system, and with the switching power devices widely used and the performance of microprocessor greatly improved, servo system has basically achieved to be digital. The control object of digital current loop mainly includes the motor and inverter, and the digital loop delay caused by the sample quantization, filter and so on has a certain effect on the current loop. The dynamic response performance of the system is determined by the bandwidth, the main influencing factor of the bandwidth is the sampling delay and the output delay of the inverter caused by the duty cycle of PWM. Predictive control is a predictive control method based on motor and inverter model, the principle shows that the strategy can improve dynamic response of the system, direct predictive control and deadbeat predictive control are typical of them, the difference mainly lies in the different voltage vector generated way.PMSM and the inverter are modeled and the principle of SVPWM is introduced, based on given servo system classical current loop structure diagram, simplify the analysis to get practical current loop diagram according to the engineering design method, with diagram analysis of main factors that influence the current loop, based on the simulation it is shown that the design is effective, then design double closed loop system according to the engineering design results for the subsequent experiments.According to theoretical derivation of the current loop bandwidth, analysis the main influencing factors, and get its exact formulation under certain constraints, compare three sampling methods and duty sequential update to get their bandwidth, showing the DSDU(double sampling and double update in single carrier cycle) in improving the current loop bandwidth is better than two modes of SSSU(single sampling single update in single carrier cycle), and further experiments prove the validity of reasoning.Detailedly introduces the current predictive control theory, mainly on direct predictive control and deadbeat control whose difference mainly lies in the way of voltage vectors generation, analysis the two kinds of strategies in control frequency and switching frequency correlation, give the torque performance contrast according to the results. Finally, it gives the two strategies in improving the system current loop bandwidth by experiments, confirming that the two strategies are better than SSSU and DSDU way and verify its effectiveness in improving the dynamic response of the system.