Energy Efficient Control of an Induction Machine Under Torque Step Changes

Abstract

Optimal control of magnetizing current for minimizing induction motor power losses during load torque step change was developed. Original problem was slightly simplified and exactly optimal control was obtained for modified formulation. Obtained strategy has feedback form and is exactly optimal for ideal speed controller performance and absence of saturation in motor. Then original and simplified problem was compared in terms of quality of result and little difference found. The impact of limited bandwidth of real speed controller is analyzed. For case of main induction saturation the sub-optimal optimal control is suggested. Relative accuracy of sub-optimality is studied. Hardware implementation of optimal strategy and experimentation conducted with induction motors under vector control.

Induction Machine Control for a Wide Range of Drive Requirements

“…A comparison between the optimal flux magnitude based on (28) and (31) is shown in Figure 1b. A similar result was presented in [14] where power losses for torque steps were considered and a function, which determines the optimal constant flux magnitude for constant torque levels, is given.…”

“…is introduced for the general case. In [14] the special case of step changes in the reference torque (or step changes filtered by a stable linear second order system) are considered. The optimization problem for the flux magnitude in order to minimize the power losses is formulated.…”

“…The online implementation requires the solution of a small static optimization problem. The problem of power loss minimization for step changes of the torque reference trajectory is also considered in [14]. In addition to [13] saturation effects of the main inductance are taken into account and a simplified suboptimal solution avoiding an online optimization is presented.…”

Online maximum torque per power losses strategy for indirect rotor flux‐oriented control‐based induction motor drives

“…Generally, there are two main approaches for efficiency optimisation in AC motor drives: model-based and search-based methods [7]. In the model-based methods, the motor loss model is derived and a loss minimisation strategy is realised on the derived model [8][9][10][11][12][13][14][15][16][17][18]. These methods are easy to implement, but they require the exact machine parameters.…”

“…The rotor current reference values are calculated according to the optimal flux and reference rotor speeds. A loss minimisation strategy applicable both in steady-state and transient conditions is proposed in [11]. In the proposed strategy, the magnetising inductance variation is taken into account.…”