The paper presents the phenomenon of directional change in LQG control of multivariable systems with amplitude constraints, as well as the impact of the latter on control performance. The interplay of directional change of the computed control vector with control performance has been thoroughly investigated, and is a result of the presence of constraints imposed on the applied control vector for different proportions of the number of control inputs to plant outputs. The impact of directional

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... nge phenomenon on the control performance has been defined, stating that performance deterioration is not tightly coupled with preservation of direction of the computed control vector. The statement has been supported by numerous simulation results for different types of plants with different LQG controller parameters.