Method for suppressing unreasonable torque ripple in direct torque control of permanent magnet synchronous motor

In a previous paper^[1-3], whose second author is this paper's first author, the phenomenon of unreasonable torque ripple appeared quite important. We now offer a feasible engineering method to suppress it. In the full paper, we explain our method in some detail. In this abstract, we just add some pertinent remarks to listing the three topics of explanation. The first topic is: the direct torque control (DTC). In the first topic, we analyze the increasing or decreasing effect of voltage vector on torque angle and magnitude of stator flux of a permanent magnet synchronous motor (PMSM). The second topic is: the unreasonable torque ripple. In the second topic, we give reasons for the occurrence of unreasonable torque ripple. We explain that, when the change in magnitude of stator flux is not consistent with the change of torque angle, the voltage vector makes the torque exceed the limit of hysteresis band. The third topic is: the method for suppressing unreasonable torque ripple. In this topic, we propose dividing a stator flux circle into 12 sectors to increase the number of voltage vectors, thus obtaining an improved switching table, which is Table 4 in the full paper. Then we simulate the DTC system that uses switching Table 4. The simulation results, shown in Figs.7 and 8, show preliminarily that switching Table 4 can effectively suppress the unreasonable torque ripple in some sectors, but cannot do it in the whole stator flux circle because of the limited number of voltage vectors available. The solution to the problem lies in how to increase available voltage vectors further to satisfy the requirements of the DTC system. We believe firmly that the solution is the utilization of one of the two existing solutions: (1) using the multi-level technology to add more voltage vectors, (2) using space vector modulation and DTC technology.