Field oriented control is a well-known instantaneous torque control method for AC motors. In this method, an integrator included in the automatic current regulator causes the deterioration of torque response due to the saturation of output voltage, and the inevitable shocks to torque response caused by switching from linear to over-modulation and single-pulse operation of the inverter. To solve these problems caused by an integrator, this paper proposes a novel torque control system without an integrator. In the proposed method, we focus on the relationship from the input voltage to the output torque, which can be expressed by a first-order differential equation (i.e., torque derivative equation); thus, the controlled plant can be regarded as consisting of a first-order differential equation and an integrator. Since the proposed method consistently controls the torque based on the torque derivative, the torque response can be specified to the time constant of the torque controller and the switching the control systems according to the operating conditions do not needed. This enables over-modulation and single-pulse driving while guaranteeing the performance of the torque response. The effectiveness of the proposed torque control system is experimentally demonstrated.
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