Abstract. The effect of space vector modulation algorithm on magnitude of current vector ripples was considered on the mathematical model of a three-level three-phase voltage inverter with symmetric active inductive load. Limitations on the use of such inverters as a power supply for precision drive of optical telescopes were specified.Key words: multilevel inverter, space vector modulation, modulation algorithm, current ripples, precision AC drive.The effect of space vector modulation algorithm on characteristics of three-phase voltage inverter for drives of optical telescopes V. TOMASOV * , A. USOLTSEV, P. ZOLOV, and P. GRIBANOV ITMO University, 49 Kronverksky Pr., St. Petersburg, 197101, Russia viding the modulation period into two or three equal time intervals, within which the base vectors bounding 60-degree sector containing the modulation voltage vector are formed [16][17][18]. Thus, the number of base "vectors" increases to 12 and 56, accordingly. But it significantly complicates the control system. Eventually, VSI of AC drive must form a circular hodograph of stator flux linkage, or, equivalently, of stator current, in steady state mode. The trajectory of stator current vector between adjacent commutations of inverter switches is determined by the attitude and magnitude of active voltage base vector. Therefore, different sequences or algorithms of base vectors formation within the modulation period lead to different trajectories of current vector and different ripples. The effect of the choice of sequence of base vectors forming on the current (flux linkage) ripples during transitions of modulation vector across the segment borders is considered in [19,20]. However, the kind and magnitude of ripples depends not only on voltage jumps at the boundaries, but also on the algorithm (sequence) of vectors forming within segments. Moreover, the number of algorithms excluding redundancy of base vectors for threephase VSI is six.This work covers the investigation of effect of modulation algorithm on current ripples in the load of the inverter. Threelevel inverter was selected as an object of study, as it most clearly demonstrates this effect in different operation modes. At the same time, the findings may be extended to inverters with more levels, as well as to two-level inverters. Moreover, during deep control, which is needed to achieve ultra low velocities of the drive, current formation operates on two or three-level mode, regardless of the total number of levels of VSI. At the same time, rotating EMF is close to zero, and motor becomes active inductive load for the inverter. Therefore, symmetric RL-circuit was used as the load.
Base vectors plane of three-phase inverterAll possible states of three-phase inverter output voltage can be represented as vectors, ends of which are placed at the sides
