High-Precision Servo Control of Industrial Robot Driven by PMSM-DTC Utilizing Composite Active Vectors

In this paper, a novel direct torque control (NDTC) scheme utilizing composite active vectors based on discrete duty ratio modulation method is presented for permanent magnet synchronous motor (PMSM) in industrial robot servo control system. The errors in the PMSM driven by conventional DTC (CDTC) are compensated by single active vector during each control period, leading to unsatisfied steady-state performance. To improve the operation performance of the industrial robot servo control system effectively, the errors in the PMSM are compensated independently in NDTC. Therefore, two active vectors should be applied to compensate flux error and torque error, respectively, namely flux active vector and torque active vector. In order to maintain the merit of the fast dynamic response in CDTC, the introduced active vectors should be selected from the fixed six active vectors supplied by a two-level voltage source inverter. To describe the scheme of NDTC clearly, the angle between the applied active vector and the stator flux linkage is used to represent the error compensational effect provided by the applied active vector, namely active angle. Additionally, the compensational effect is defined as active factor. Subsequently, the duty ratio value of the active vector applied time can be derived easily. To simplify the calculations of the duty ratio values, novel discrete calculation method for the active factor by hysteresis controllers is presented in this paper. The effectiveness of the proposed NDTC strategy is verified through the experimental results on a 100-W PMSM drive system.