Controller Order Reduction Using the Neighborhood of Crossover Frequency Approach

ABSTRACT A new model reduction approach is proposed. The order of a large-scale system is reduced within the neighborhood of its crossover frequency in order to closely preserve the gain and phase of the original system. The minimum and maximum allowable frequency about the crossover frequency of the system is determined using frequency dependent weights. Then the system is perturbed and reduced within the allowable frequency band. This approach targets model reduction at the crossover and within the allowable frequency band to maintain stability and performance. To illustrate the effectiveness of this approach, a fourth order plant model is considered and a fourth order H controller is designed, and then reduced to orders two and one for comparison. In addition, a second approach is taken so that order of the plant model is reduced to two, and then a second order controller is design through H synthesis.