Hai-Jiao Guo

Integral controller design based on disturbance cancellation: Partial LTR approach for non-minimum phase plants

For non-minimum phase plants, the loop transfer recovery (LTR) design of integral controllers based on the disturbance cancellation is considered. Since the design requires an unstabilizable extended plant, the standard LTR method cannot be applied. A new partial LTR method is proposed to overcome the difficulty. The target of the proposed design is a fictitious controller including a disturbance estimator based on the measurement of the minimum phase state. It is shown that the Riccati equation including the gain matrix of the disturbance estimator in the target can be used to recover the target feedback property in the output feedback controller. A simple design example is presented to show the effectiveness of the proposed method.

LTR Design of Integral Controllers for Time-Delay Plants Using Disturbance Cancellation

A design of integral controllers based on disturbance cancellation for time-delay plants is discussed. Since the extended plant used in the design is not stabilizable, the standard loop transfer recovery (LTR) method can not be applied. The new LTR method proposed by the authors to design disturbance cancellation controllers for lumped plants is extended to time-delay plants. It is shown that the new LTR technique provides a transparent two-step design.

LTR design of disturbance cancellation integral controllers for time-delay plants

For time-delay plants, the loop transfer recovery (LTR) technique for the integral controller design based on disturbance cancellation is discussed. Since the design requires an unstabilizable extended plant, the standard LTR method cannot be applied. The new LTR method proposed by the authors for lumped plants is extended to time-delay plants by introducing appropriate predictors. A simple design example is presented to illustrate the proposed design method.

Design of optimal output disturbance cancellation controllers via loop transfer recovery

The authors have introduced optimal disturbance cancellation controllers as a class of controllers minimizing a non-standard quadratic performance index explicitly including disturbances. This paper discusses the application of the classical loop transfer recovery (LTR) technique to the optimal disturbance cancellation controller for step disturbances entering the plant output. The estimation error dynamics of the Kalman filter jointly estimating the plant states and the disturbances is chosen as a target of the LTR design. The weighting coefficient of the performance index is used to recover the target which has guaranteed stability margins as in the standard LTR design. It is shown by a numerical example that the proposed design provides flexible tuning of the disturbance rejection capability with sufficient stability margins.

Partial LTR Design of Optimal Output Disturbance Cancellation Controllers for Non-Minimum Phase Plants

Abstract For non-minimum phase plants, a partial LTR design of optimal output disturbance cancellation controllers is discussed. A target recoverable by the partial LTR procedure is identified as an output injection with a frequency-shaped gain matrix. The partial LTR result is used to clarify system-theoretic meaning of enforcing the minimum phase LTR procedure. It is shown that the partial LTR procedure provides more design freedom in shaping target feedback property than the enforced minimum phase LTR procedure.

Design of optimal disturbance cancellation controllers for sinusoidal output disturbances via loop transfer recovery

This paper discusses an application of the classical loop transfer recovery technique to the design of the optimal disturbance cancellation controller for the sinusoidal output disturbance with known frequency. The optimal output feedback controller is constructed based on the separation principle. The target of the design is chosen as the estimation error dynamics including the internal model for the sinusoidal disturbance. It is shown that the target feedback property can be recovered by using the weighting parameter in the performance index. A numerical example is presented to illustrate the effectiveness of the proposed design.

Design of optimal disturbance cancellation controllers via modified loop transfer recovery

The authors proposed a modified loop transfer recovery (LTR) method for designing the disturbance cancellation controllers where the disturbances were assumed to be step functions and the optimality of the controllers was not considered. This paper discusses the extension of their work to a more general class of disturbances with optimality consideration. It is assumed that the plant is minimum phase and the disturbances entering the plant input side are generated by function generators with unknown initial conditions. A quadratic performance index explicitly representing the disturbance cancellation requirement is introduced. The optimal disturbance cancellation controller minimizing the performance index is constructed by the separation principle. As a target for the LTR design, the optimal disturbance cancellation controller based on the measurement of the plant state is chosen. It is shown that the target feedback property can be recovered in the output feedback controller by a simple modification of the standard LTR procedure. A numerical example is presented to illustrate the effectiveness of the proposed optimal design.

A Design Approach for Insensitivity to Disturbance Period Fluctuations Using Higher Order Repetitive Control

Abstract Repetitive control (RC) is well known as a method for tracking a periodic command as well as eliminating the influence of a periodic disturbance. An issue that can be encountered in applications is that the period of the disturbance can vary. In some cases one can monitor a drift in the disturbance period, but in other cases the period can fluctuate sufficiently fast that one wants an RC law that is robust to period fluctuations. Several studies address this problem using higher order RC incorporating a negative weight on errors from some previous period. This paper presents a systematic design procedure that can be used to improve RC robustness to disturbance period fluctuations. Methods are given to present the information needed to make the necessary tradeoffs when tuning the set of design parameters.

Design of generalized disturbance cancellation controllers via singular LTR

The authors proposed the singular LTR method for the integral controller design based on the step disturbance cancellation. In this paper, the singular LTR method is extended to more general class of disturbances. It is assumed that the disturbance is modeled as an output of a linear function generator. By the separation principle, the optimal disturbance cancellation controller is constructed using an observer estimating the plant state and the disturbance state. It is shown that the partial LTR method can be used for the efficient design of the disturbance cancellation controller.

Discrete-time LTR design of optimal output disturbance cancellation controllers using filtering-type Kalman filters

This paper considers a discrete-time version of the loop transfer recovery (LTR) design of the optimal output disturbance cancellation controllers proposed by the authors for continuous-time case. It is assumed that the disturbances are step functions which are estimated by a filtering-type Kalman filter jointly with the plant state variables. The separation principle is used to construct the optimal disturbance cancellation controller minimizing a quadratic performance index explicitly including the disturbances. The estimation error dynamics of the Kalman filter is chosen as a target of the LTR design. It is shown that the target feedback property can be recovered in the output feedback controller using a weighting coefficient of the performance index provided the plant is minimum phase.