PurposeThe aim of the paper is to conduct an analytical study of a new method of induction motor torque and flux direct control with nonlinear controllers.Design/methodology/approachThe method is based on the inverter state predictive determination in order to minimize the torque and flux errors.FindingsThe proposed method allows one to eliminate known DTC disadvantages, i.e. the hexagonal flux shape and nonsinusoidal current at a low motor speed, and also secures a decrease of torque and flux pulsation.Practical implicationsThis new method enables a more precise reproduction of the motor torque and flux command signals, working with the same sampling frequency of the control processor as in the case of the standard DTC method. The decreased torque pulsations cause a decrease of the motor speed pulsation.Originality/valueAn innovative optimal control method is presented. The correctness of the initial assumptions as well as the expected final results have been verified in practice.

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In the paper a new way of DTC control method analysis to explain flux and current distortion at a low speed of motor operation is discussed. As a result, a new DTC-δ algorithm is proposed. It is important that the DTC-δ algorithm uses the same switching table as the DTC method. The modified DTC algorithms are free from the disadvantages of the conventional DTC method i.e. hexagonal flux and strongly deformed current at a low speed range. The dynamical properties of the new algorithms are similar to the conventional DTC method. The correctness of the proposed methods has been confirmed by laboratory investigations.Key words: Direct torque control (DTC), Induction motor drives, Variable-speed drives Unaprije eni algoritmi za izravno upravljanje momentom. Ovaj se rad bavi novim načinom analize izravnog upravljanja momentom (DTC) radi objašnjenja distorzije toka i struje na malim brzinama vrtnje motora. Kao rezultat, predložen je novi DTC-δ algoritam. Pritom je značajno da novi DTC-δ algoritam koristi istu tablicu prekapčanja kao i DTC metoda. Modificirani DTC algoritmi su bez nedostataka karakterističnih za konvencionalne DTC metode, poput heksagonalnog toka i izrazito izobličene struje pri niskim brzinama. Dinamička svojstva novih algoritama su slična konvencionalnoj DTC metodi. Predložene metode su potvr ene laboratorijskim ispitivanjima.Ključne riječi: izravno upravljanje momentom (DTC), elektromotorni pogoni s kaveznim strojem, pogoni s promjenjivom brzinom vrtnje

The article presents comprehensive results of research on two representative topologies of converters used in the path of processing energy generated in a wind turbine and transmitted to the grid. The topology T1 uses a two-level transistor-controlled rectifier as a converter from the generator side, while the T2 topology uses DC/DC boost converter. In both topologies, a three-level back-to-back converter with a line filter L was used as a grid converter. The conclusions indicate the tendency of changes in power losses depending on the aforementioned parameters and can be used at the stage of deciding on the choice of topology, operating parameters or selection of control methods depending on the specific operating conditions of the wind turbine.