Instability in Inverter-Fed Induction Motor Drives

Research Project

Project/Area Number	01550345
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	計測・制御工学
Research Institution	Daido Institute of Technology
Principal Investigator	MATSUBARA Masakazu Daido Institute of Technology, Department of Electrical Engineering. Professor, 工学部, 教授 (60022969)
Project Period (FY)	1989 – 1990
Project Status	Completed (Fiscal Year 1990)
Budget Amount *help	¥1,500,000 (Direct Cost: ¥1,500,000) Fiscal Year 1990: ¥200,000 (Direct Cost: ¥200,000) Fiscal Year 1989: ¥1,300,000 (Direct Cost: ¥1,300,000)
Keywords	induction motor / stability / Routh criterion / bifurcation theory / tangential bifurcation / Hopf bifurcation
Research Abstract	In the inverter-fed induction motor drives an instability accompanied by speed fluctuations appears often in light-load and low-speed operations. This is caused not by the introduction of the inverter but by the induction motor itself. This phenomenon is such that an equilibrium point becomes unstable as the operating condition is varied and that a stable limit cycle appears around the equilibrium point. So, from the bifurcation-theoretical standpoint, this is to be dealt with as the Hopf bifurcation. However, only a few investigations based on such a standpoint have been reported so far. In this work the stability of an induction motor driven by a variable-amplitude and variable-frequency sinusoidal voltage source is investigated from the bifurcation-theoretical standpoint. The entire bifurcation set is determined in the parameter space of the frequency, slip and load torque. The following points were made clear : (1) Only four types of the hyperbolic equilibrium point, that is, _0PD, _1ND, _2PD and _3ND appear. Of these four, only the _0PD type is stable. (2) The tangential bifurcation takes place at the peak point of the torque-speed curve. _0PD and _1ND types appear in the lower-slip side (statically stable side) of the tangential bifurcation set while _2PD and _3ND types do in the other side. (3) The Hopf bifurcation accompanied by limit cycles takes place at the boundary of _0PD and _1ND regions and at the boundary of _2PD and _3ND regions. Stable limit cycles are observed within the _1ND region. (4) The tangential bifurcation set is distorted by the saturation so as to enlarge the statically stable region. (5) The Hopf bifurcation set is composed of three manifolds, but only the one located in the highest-slip side remains when the magnetic saturation is disregarded.