Direct Torque Control Concept Research Articles

Novel Design for Direct Torque Control System of PMSM

Nowadays, with the rapid development of high-performance servo system, The conventional permanent magnet synchronous motor (PMSM) Direct Torque Control (DTC) system has large torque ripple in low speed which cannot be well adapted to today`s development. The main reason is because the number of voltage vectors provided by the two-level inverter is only six and the relationship between voltage vector and torque is not clear[1-5.10-12]. In this paper, the basic concept of direct torque control of permanent magnet synchronous motor is investigated in order to emphasize the effects produced by a given voltage vector on stator and torque variations in this paper. Modified the voltage sector switching table, a novel DTC scheme for the permanent magnet synchronous motor is proposed which is using a novel three-level inverter. An improvement of the drive performance can be obtained by using the novel DTC scheme. The simulation results showed that the scheme could reduce the torque ripple in low speed and improved the stability of the motor under the condition of keeping the system dynamic performance. DOI: http://dx.doi.org/10.11591/telkomnika.v11i4.2391

Torque Ripple Minimization for Induction Motor Drives with Direct Torque Control

Direct torque control (DTC) schemes can produce quick and robust responses, but they usually behave like hysteresis controllers. Consequently, there are similar problems like non-constant switching frequencies and high torque ripple, especially when operation conditions result in low switching frequencies. In this article, the basic concept of DTC will be improved by modifying the conventional method. Problems that arise when using standard DTC methods are explained and improvements are derived to overcome these problems. Two theoretical approaches are verified and compared with standard DTC by measurements and experiments. The proposed methods provide a constant switching frequency and solve the starting problem without dither signal. Further results are a reduction of torque pulsations, as well as a new method for stator flux estimation.

Direct Torque Control of a Doubly-Fed Induction Generator for Variable Speed Wind Turbines

This paper presents the analysis and design of a Direct Torque Control (DTC) of a Doubly-Fed Induction Generator applied to a wind generation system as an alternative to the classical field-oriented control (FOC) widely used in drive control. The aims of the control system are the control of the reactive power interchanged between the generator and the grid and the control of the power drawn from the wind turbine in order to track the wind turbine optimum operation point. DTC appeared as a control concept for squirrel cage motor drives. In this paper, DTC concept is applied to control a wound rotor induction generator by means of a rotor connected VSI. Torque and rotor flux control are used to control in an indirect way active and reactive power, respectively.

Extension of the DTC concept

The authors propose to extend the direct torque control (DTC) concept. This extension concerns voltage-vector generation. Based on this, it is possible to generate any voltage vector by the space-vector modulation method and apply DTC strategy at the same time. Experimental results are carried out to validate the proposed approach.

Implementation of a direct control algorithm for induction motors based on discrete space vector modulation

The basic concept of direct torque control of induction machines is investigated in order to emphasize the effects produced by a given voltage vector on stator flux and torque variations. The low number of voltage vectors which can be applied to the machine using the basic DTC scheme may cause undesired torque and current ripple. An improvement of the drive performance can be obtained using a new DTC algorithm based on the application of the space vector modulation (SVM) for prefixed time intervals. In this way a sort of discrete space vector modulation (DSVM) is introduced. Numerical simulations and experimental tests have been carried out to validate the proposed method.

Direct torque control for brushless doubly-fed machines

Work has illustrated the potential benefits of brushless doubly-fed machines in adjustable speed drive applications. While it has been shown that the drive is open-loop stable over a wide speed range, the resultant steady-state and dynamic performance characteristics are far from optimum. Thus, a closed-loop controller is desirable to achieve competitive drive performance. The controller proposed here is applicable for general purpose industrial drives in the medium to high power range. The nature of the doubly-fed machine, with two separate sources of excitation, only one of which is controllable, rules out field-oriented control strategies applied to conventional induction machines. However, the concept of direct torque control based on instantaneous error shows promise for this machine geometry. The present paper extends the concept of predictive torque control for induction machines to the doubly-fed machine. The controller calculates the value of converter voltage which leads to desired changes of flux and torque. Once the voltage is determined, conventional algorithms, such as space vector pulsewidth modulation (PWM), can be used to generate the inverter switching function.