Pseudorotor-flux-oriented control of an induction machine for deep-bar-effect compensation

In an induction machine with deep rotor bars, the rotor parameters change due to skin effect and saturation, and the skin effect is often modeled as a ladder network. For the high-performance drive of an induction machine with deep bars, many sophisticated control strategies and machine models have been discussed. As a control strategy, a complicated airgap flux-oriented control scheme is mostly adopted, because it is not possible to define a unique rotor flux in the deep bar model. However, a unique pseudorotor flux can be defined, and it is straightforward to achieve independent control of pseudorotor flux and torque. This control scheme can be applied to any nth multiple ladder network. In this paper, it is shown how a deep-bar effect of an induction machine can be negligible by performing the proper field-oriented control. By using the concept of pseudorotor flux, the conventional rotor-flux-oriented control using equivalent rotor parameters is effective for deep-bar and/or double-cage machines. The actual insulated gate bipolar transistor (IGBT) inverter systems with a high-precision torque transducer are implemented and thoroughly tested on a 250 hp induction machine and a 5.5 kW double-cage induction machine to confirm their validity.