Among all control methods for induction motor drives, Direct Torque Control (DTC) seems to be particularly interesting being independent of machine rotor parameters and requiring no speed or position sensors. The DTC scheme is characterized by the absence of PI regulators, coordinate transformations, current regulators and PWM signals generators. In spite of its simplicity, DTC allows a good torque control in steady state and transient operating conditions to be obtained. However, the presence of hysteresis controllers for flux and torque could determine torque and current ripple and variable switching frequency operation for the voltage source inverter. This paper is aimed to analyze DTC principles, the strategies and the problems related to its implementation and the possible improvements.
This paper presents novel bi-converter structure to supply the Doubly Fed Induction Machine (DFIM). Two Voltage Source Inverters (VSI) feed the stator and rotor windings. The outputs of two VSI are combined electro-mechanically in the machine and, as a result, novel features can be obtained. For example, for high power drive applications, this configuration use two inverters dimensioned for a half of the DFIM power. A new Dual-Direct Torque Control scheme is developed with flux model of DFIM. Two Switching Tables (ST) linked to VSI are defined for stator and rotor flux vector control. Experimental and simulation results confirm good dynamic behaviour in the four quadrants of the speed-torque plane. Moreover, experimental results show the correct flux vector control behaviour and speed tracking performances.
The Synchronous Reluctance Machine (SynRM) is an electrical machine in which the useful electromagnetic torque is produced due to rotor saliency. Its high power- and torque-to-mass ratio and very good efficiency make it a cheap and simple alternative for permanent magnet or induction motors, e.g. in electromobility applications. However, because of magnetic nonlinearities, the rotational speed and torque control of a SynRM is a nontrivial task. In the paper, a control algorithm based on a Hamiltonian mathematical model is presented. The model is formulated using measurement results, obtained by the drive controller. An algorithm is tested in the drive system consisting of a SynRM with the classical rotor and a fast prototyping card. The drive dynamic response in transient states is very good, but the proposed algorithm does not ensure the best efficiency after steady state angular velocity is achieved.