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In this paper, the effect of zero voltage vector in permanent magnet synchronous motors (PMSM) direct torque control (DTC) system is analyzed. As zero voltage vector decreases stator flux and torque slowly, when system decreases the amplitude of stator flux and torque at same time, zero voltage vector can be used to suppress stator flux and torque ripple at steady-state. And non-zero voltage vector is used to get quicker response at dynamic-state. As there are two switching state of zero voltage vector, a switching state selection strategy is given when zero voltage vector is used, which aims to minimize switching times. Thus, an adaptive variable voltage vector switching table is proposed. Simulation results show that PMSM DTC system can work properly under control of the proposed switching table. The switching times of the system are reduced by 55% compared with conventional switching table without zero voltage vector. And the system has quicker dynamic response compared with switching table only using zero voltage vector to decrease stator flux and torque.

In this paper, an optimal voltage vector selection strategy based on predictive control for the direct torque control (DTC) in surface permanent magnet synchronous motor (SPMSM) is reported. The proposed predictive control determines the angle of applied voltage vector from the proper voltage vector selection area according to cost function and uses space vector modulation (SVM) to generate the applied voltage vector. As the angle of applied voltage vector is selected from the proper selection area, it can always satisfy the control of stator flux and torque. Simulation results show the proposed DTC strategy can work well. Compared with conventional switching table, the reported strategy, it can suppress torque ripple and reduce cost function. And due to the use of SVM, switching frequency is constant, which isn't constant using conventional switching table.

In this paper, voltage vector selection for the direct torque control (DTC) for surface permanent magnet synchronous motor (SPMSM) based on predictive control is proposed. Firstly, based on increasing or decreasing effects of the applying voltage vector on the amplitude of stator flux and torque of SPMSM, the proper voltage vector selection area of the DTC for SPMSM is given. Then predictive control is used to determine the angle of applying voltage vector in voltage vector selection area. A cost function of stator flux and torque's errors is proposed to evaluate the performance of different angle of applying voltage vector whose amplitude is constant. The angle which results in the minimum cost function among different angles is selected as the angle of the applying voltage vector. As the applying voltage vector is selected from proper voltage vector selection area, it can always satisfy the control of stator flux and torque. Finally, space vector modulation (SVM) is used to generate the applying voltage vector. Simulation results show the DTC for SPMSM works properly under the proposed control strategy. Compared with conventional switching table, the proposed strategy can suppress torque ripple and reduce cost function and mean squared error of torque and stator flux. And due to the use of SVM, switching frequency is kept constant.

In this paper, an optimal switching table for PMSM DTC system using zero voltage vector is proposed. Zero voltage vector decreases stator flux and torque very slowly, so it can be used to suppress torque ripple when the system is at steady-state. And when the system is at dynamic-state, non-zero voltage is used to get quicker response. As both 111 and 000 can be used to generate zero voltage vector, switching state selection strategy in order to minimize switching times is given when zero voltage vector is used. Thus, an optimal switching table using zero voltage vector is proposed. Simulation results show that PMSM DTC system can work properly under control of the proposed switching table. The time of system stator flux response using optimal switching table is reduced by 73% and the time of system torque response is reduced by 82% compared with switching table only using zero voltage vector to decrease stator flux and torque. The torque ripple of the system is reduced by nearly 51% and switching times are reduced by 41% compared with conventional switching table.

In order to suppress unreasonable torque ripple of direct torque control (DTC) in surface permanent magnet synchronous motor (SPMSM), the SPMSM-DTC mode is established and the effect of voltage vectors selected by switching table on torque is analyzed. The conclusion of the change in torque is contrary to expectation when the changes of stator flux and torque angle (angle between stator and rotor flux vector) is magnitude under some conditions is proposed. The actual effect of voltage vectors on torque based on traditional switching table is opposite to the expectation and causes unreasonable torque ripple. A simplified voltage vector selection strategy for SPMSM was proposed, and the new voltage vector can avoid the condition of the torque ripple recur. Simulation results shows that the voltage vector selection strategy proposed in this paper can always satisfy the control of torque, suppress unreasonable torque ripple.