PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 NR 8/2011 171 Asghar TAHERI 1 , Abdolreza RAHMATI 1 , Shahriyar KABOLI 2 Iran University of Science & Technology (1), Sharif University of Technology (2) Flux Search Control of Field Oriented Control of Six-Phase Induction Motor supplied by SVPWM Abstract. This paper deals with the efficiency optimization of Field Oriented Control (FOC) of a six–phase induction motor supplied by Space Vector PWM (SVPWM) using the flux Search Controller (SC) technique. The proposed technique is based on controlling flux to achieve maximum efficiency at light load or low speed. Flux search controller technique is not only cost effective and easy to implement but also robust against parameter variations. Flux control algorithm in six-phase induction machine speed controller reduces 6n±1 harmonic loss as well as other losses like that of copper and core. Simulation results are carried out and they verify the effectiveness of the proposed approach. Streszczenie. Przedstawiono metodę optymalizacji skuteczności sześciofazowego silnika indukcyjnego zasilanego za pośrednictwem SVPWM przy wykorzystaniu techniki SC. Metoda SC bazuje na kontroli strumienia w celu osiągnięcia maksimum wydajności przy małych obciążeniach i małej prędkości. Zaproponowana kontrola strumienia w silniku sześciofazowym redukuje straty. (Kontrola strumienia jako metoda optymalizacji sześciofazowego silnika indukcyjnego zasilanego za pośrednictwem SVPWM) Keywords: six phase induction motor- efficiency optimization- Field Oriented control- SVPWM- flux search control. Słowa kluczowe: silnik indukcyjny, optymalizacja wydajności, kontrola strumienia Introduction Advantages of multi-phase machines have resulted in their possible attention in some applications. These machines have some advantages compared with three or one phase machines such as higher redundancy in fault conditions [1][2]. Other advantages of these machines are lower dc-link voltage requirement, lower power per phase [3][4], and lower rotor harmonic currents and stator copper loss [4]. Multiphase induction machines are used in some applications like high marine propulsion, aerospace applications [3][5][6]. Because six-phase induction machines are recently in attention and frequently in use, efficiency improvement of these machines can be important. There are some papers proceed to this important subject. Williamson et al. [4] worked on multi- phase machine pulsating and losses. Efficiency analysis of Voltage Source Inverter (VSI) fed three-phase and dual three-phase induction machines and comparing three-phase and six-phase induction machines efficiency is reported in [7]. If the six-phase induction motor works in a speed or torque under its nominal point, the motor efficiency becomes less than nominal. While the six-phase induction motor is controlled by rotor field oriented as mentioned in [3][6][8]. Generally, in FOC of the six-phase machine mentioned above, the flux component of motor is set to maintain the rated field flux in the whole range of loading to get the best transient response. Thus, the efficiency in the light load is decreased. There are many approaches for choosing a suitable control method implanted in other machines like SC [13][14][15] and Loss Model Control (LMC)[16-20]. VSI fed six-phase induction machine can be controlled by the conventional SVPWM, SPWM, and SVPWM techniques. In the conventional SVPWM, two separated three-phase SVPWM are used. In this method, each SVPWM has two none zero and one zero voltage vector. Controlling variables in d-q plan in the conventional SVPWM causes large harmonic currents on the   1 2 - z z subspace [20]. In the SPWM technique with sine and triangular carrier waves, the voltage vector in   1 2 - z z plane is not minimum, thus large harmonics in that subspace are produced [20]. These current harmonics circulate only in the stator and cause additional losses [21]. The amplitude of these harmonics can be reduced by adding active filter or a change in the driving technique. One of the suitable techniques for the six-phase induction machine driving that minimize these harmonics is SVPWM [21][22][23]. Space vector modulation in induction machine is used to generate harmonically optimum waves at the output. The PWM switching frequency is quantitatively limited, since the SVM technique is complex and computationally intensive [21][23]. Yazdani et al. [24] proceeds full control of the voltage gain up to the maximum achievable gain with negligible low-order harmonics and utilizes a simple classification algorithm for the implementation of the space vector modulation (SVM) in both linear and over modulation modes. The innovation of this paper is to reduce loss in six- induction motors with SC technique where it is operated below its nominal torque or speed. In addition, in this paper, we implement SVPWM in the FOC. The first part of this paper is machine modeling and analysis in VSD (Vector Space Decomposition) method. Then the field oriented control of six-phase induction motor is exposed. SVPWM control of six-phase induction motor and the influence of this technique in efficiency improvement is described in next section. Then proposed losses, input power, output power, and efficiency modeling in 6PIM are presented. In the next section, the flux search control in 6PIM is investigated. Simulations results are shown finally. Six-phase Induction Motor Model The mode of 6PIM described in [8][20] has been used in this paper. Six-phase induction machine has two sets of three phase windings shifted by 30 or 60 electrical degrees and single or double neutral point (isolated neutral points or double neutral point is popular). The Six-phase induction machine considered in this paper consists of a stator with two separate windings shifted by 30 electrical degrees and a double neutral point, having similar pole numbers and parameters. The popular method in six-phase induction machine modeling is VSD (Vector Space Decomposition). In VSD method, the machine modeling is achieved in three two- dimensional orthogonal subspaces [20]. Fundamental harmonic of the machine, which produces electromechanical energy conversion and the harmonics of the order 12n±1 (n=1, 2, 3 …) are mapped to the ( ) d q  subspace. Harmonics of the order 6n±1 (n=1, 3, 5 …) are