Zhihao Zheng

In this letter, a novel lookup table (LUT)-based direct torque control (DTC) strategy is proposed for dual-inverter fed open winding permanent magnet synchronous motor drives. Torque and flux linkage are regulated by tracking the reference voltage vector (VV) on the space VV plane according to a simplified LUT. The simplified LUT is established by dividing the space VV plane into 19 regions and each region corresponds to a basic VV. The optimal VV can be obtained by locating the corresponding region of the reference VV, which significantly decreases the complexity of LUT design and maintains the simplicity of the DTC strategy. A group of optimal switching states that minimize the transition times is selected. Meanwhile, the elimination of the hysteresis controller can further decrease the switching frequency. Experimental results show that the torque ripple, current harmonics, and switching frequency of the proposed strategy are reduced compared with the traditional DTC strategy.

This paper proposes a dual two-vector based model predictive flux control (DTV-MPFC) strategy for open winding permanent magnet synchronous motor (OW-PMSM) drives with two isolated voltage source inverters (VSIs). In MPFC strategy, the reference stator flux vector can be compensated to realize field weakening (FW) operation by controlling the value of the cost function. However, the accuracy of the cost function based FW strategy is limited when the tracking error of stator flux vector exists. In this paper, a DTV-MPFC strategy is proposed to synthesize the reference flux increment vector precisely and the FW operation boundary is kept within the linear modulation region to enhance the FW operation performance. Each inverter applies two vectors during the control period and the switching frequency of the VSIs is minimized with the proposed strategy. When the DC-link voltages of the VSIs are unequal, the number of candidate flux increment vectors and the distribution of the space vector plane are different. A generalized vector selection and duration calculation scheme is proposed to realize DTV-MPFC strategy in this case. Experimental studies are carried out to verify the validity and effectiveness of the proposed strategy.

This paper proposes a model predictive flux control (MPFC) strategy with cost function-based field weakening (FW) strategy for permanent magnet synchronous motor (PMSM). The stator flux vector is used as the control variable and the cost function of the proposed MPFC is configured in the form of flux increment, which can reflect the saturation degree of the inverter output. A novel space flux vector plane is introduced to explain the principle of optimal switching state selection in the proposed MPFC. The voltage and current limitations of the inverter in the high-speed region are analyzed in the flux plane to reveal the objective of FW compensation. The value of the cost function is controlled with a proportional integral controller in the proposed cost function-based FW strategy. Moreover, the reference flux vector is compensated with the output of the FW controller to enlarge the operation region of the stator flux vector. With the proposed FW strategy, the operation range of the PMSM is extended and the torque output in high-speed range is increased. Experimental studies are carried out to verify the validity and effectiveness of the proposed strategy.

In this paper, a simplified model predictive control (S-MPC) for open-winding permanent magnet synchronous motor (OW-PMSM) system fed by two isolated power sources is proposed in order to remove the complex tuning work of weighting factors and reduce the calculation burden in the conventional MPC. Control constraints torque and flux in the conventional MPC are converted into an equivalent flux vector for the purpose of eliminating the weighting factor in the cost function. Moreover, a novel prediction strategy and a fast voltage selection scheme are presented to reduce the system calculation burden. As a result, the optimal voltage is selected through only twice evaluations. Furthermore, a switching states distribution strategy is introduced to reduce the switching frequency of dual-inverter. Comparative experiments are conducted to verify the effectiveness of the proposed method.