tailieunhanh - Electric Machines and Drives Part 14

Tham khảo tài liệu 'electric machines and drives part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | The Space Vector Modulation PWM Control Methods Applied on Four Leg Inverters 249 Determination of the tetrahedrons In each TP there are six vectors these vectors define four tetrahedrons. Each tetrahedron contains three active vectors from the six vectors found in the TP. The way of selecting the tetrahedron depends on the polarity changing of each switching components included in one vector. The following formula permits the determination of the tetrahedron in which the voltage space vector is located. 3 Th 4 TP -1 1 2a 1 29 Where ai 1 if Vi 0 else ai 0 i a b c To clarify the process of determination of the TP and Th for different three phase reference system voltages cases which may occurred. Figures 13 and 14 are presenting two general cases where Figures noted as a present the reference three phase voltage system Figures noted as b present the space vector trajectory of the reference three phase voltage system Figures noted as c present the concerned TP each sampling time where the reference space vector is located Figures noted as d present the concerned Th in which the reference space vector is located. Case I unbalanced reference system voltages a 30 20 8 10 0 jk -10 -20 -30 400 400 Time s c b d Fig. 13. Presentation of instantaneous three phase reference voltages reference space vector TP and Th 250 Electric Machines and Drives Case II Unbalanced reference system voltages with the presence of unbalanced harmonics b Time s c Fig. 14. Presentation of instantaneous three phase reference voltages reference space vector TP and Th 25 20 15 10 0 Time s d Calculation of duty times To fulfill the principle of the SVPWM as it is mentioned in 9 which can be rewritten as follows 3 Vref T YT -Vi i 0 30 Where 3 Tz TT 31 i 0 In this equation the a - b - c frame components can be used either than the use of the a - p - Y frame components of the voltage vectors for the calculation of the duty times of course

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