PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 NR 11/2011 239 Jawad FAIZ 1 , Mehdi MANOOCHEHRY 2 , Ghazanfar SHAHGHOLIAN 2 University of Tehran (1), Islamic Azad University (2) Performance Improvement of Permanent Magnet Linear Synchronous Motor Drive using Space Vector Modulated-Direct Thrust Force Control Abstract. This paper proposes a space vector modulation (SVM) direct thrust force control (DFC) concept to minimize the ripples of the electromagnetic thrust force and flux-linkage, and fix the switching frequency in a conventional DFC system for permanent magnet linear synchronous motors. A special method called symmetrical SVM is applied to achieve a high performance drive. Simulation results show that the proposed SVM-DFC can improve the steady-state performance considerably while keeping the dynamic performance of the conventional DFC. Streszczenie. W artykule zaproponowano wykorzystanie modulacji wektora przestrzennego SVM i bezpośrednie sterowanie siłą ciągu DFC do minimalizacji zafalowań siły ciągu w synchronicznym silniku z magnesami trwałymi. Rezuyltaty symulacji pokazały że zaproponowany system SVM- DFC pozwla na poprawę właściwości silnika w stanie ustalonym przy właściwościach dynamicznych nie gorszych niż w układach konwencjonalnych. (Poprawa parametrów liniowego silnika synchronicznego z magnesami trwałymi przy użyciu metod SVM i TFC) Keywords: PMLSM, DFC, Symmetrical SVM, DFC-SVM. Słowa kluczowe: liniowy silnik synchroniczny, SVM, DFC. Introduction Ever increasing extensive application of linear motors in transportation systems, elevators and other linear move result in a wide investigation of these types of electrical motors. Advantages of permanent magnet linear synchronous motor (PMLSM) compared to other linear motors lead to wide application of PMLSM in industrial systems particularly where a precise move is vital. The most important advantages of PMLSM include high efficiency, appropriate power factor, low friction, high axial force density and low heat losses [1-4]. To design a secure drive system for PMLSM, a control system having an appropriate performance is required to be able to compensate the parameters variations, load disturbance, friction, uncertain dynamics and difficulty of using conventional gear systems. Direct torque control (DTC) method was introduced in 1986 for controlling rotating AC motors [5]. Many advantages of this control method including simplicity, absence of speed sensors and current regulators, and needless complicated and many transformations (which required in vector control technique) and particularly lower sensitivity toward system parameters variations results in the wide application of the method in rotating AC electrical machines [6-8]. These advantages lead to the extension of the method to its counterparts- linear electrical motors particularly PMLSM. In this case the axial thrust force is directly controlled and the method is called direct thrust force control (DFC) [9-12]. In spite of many advantages of DTC and DFC methods, they have a number of drawbacks. One of these problems, which is more significant in linear motors due to their structure, is high ripples in thrust force and flux-linkage of the motor. Also switching frequency is not constant in this method. Many techniques have been so far implemented to solve these problems in DTC method applied to rotating AC motors. However, there are a few techniques to solve the similar problems in linear motors, so a wider research in this area is required. Some techniques to improve DTC or DFC are reviewed in the following part. A new integrator structure has been introduced for flux estimation in [9], and a new look-up table has been also given to reduce the torque or force ripples. In spite of implementing this system, determining controller coefficients by genetic algorithm and building a new integrator, it is practically difficult to use it. Sliding mode control can be used as a method to reduce the force ripples in DFC method [11, 13]. Although simulation results show the merit of the method, the method depends on the parameters of the motor and it is difficult to obtain an appropriate Lyapanov function. Fuzzy control can be implemented to overcome the DFC method drawbacks. This method is a new and suitable one, however design of this method requires an experienced designer. To evolve the accuracy of the Fuzzy method, a large number of cases must be processed which needs huge computations and an appropriate processor and this leads to a costly system. In [14], considering limited number of states in DTC method for three phase system, enhancement of the phase number has been proposed as solution. This method has been implemented for a prototype motor, but substituting this motor with a three phase motor in industry is not economical. DFC-SVM method consists of a DFC control system in which SVM is used for switching the drive. In this method, a combination of a three-phase inverter voltage vectors is utilized. Thus, a continuous space is used to generate voltage instead of discrete space with 6 basic voltage vector states. Consequently, this control system will be efficient in the reduction of the distortion of the drive system parameters such as developed electromagnetic force, flux-linkage and speed of the motor. Also the nature of this switching method results in fixing the switching frequency [15]. In the present paper two basic DFC and SVM-DFC are used for PMLSM. In section 2 an appropriate modeling for motor is introduced. Section 3 describes how DFC method is designed and implemented in PMLSM. In section 4, SVM method is presented and proposed system (SVM-DFC) is introduced and used in PMLSM. Simulation results and their comparisons are given in section 5. The paper is concluded in section 6. Modeling of PMLSM The following assumptions are considered in PMLSM: 1. Fundamental component is considered due to sinusoidal distribution of magnetic fields. 2. Magnetic saturation is ignored. 3. Hysteresis losses and leakage flux are neglected. 4. There is a damping winding in the primary winding of the motor.