A Two-Stage Robust Control Design for Damping Inter-Area Oscillations

Abstract

Robust control theories and filtering techniques provide promising solutions for damping low-frequency inter-area oscillations. The objective of this research was to develop a systematic procedure of designing a distributed two-stage damping control system for power grid inter-area oscillations by applying separation and identification filter accompanied by robust control techniques. Practical considerations were emphasized in the proposed control design. The first practical consideration was to select the control stabilizing signals and control site locations. Residual analysis were used to study the candidate signals and to evaluate their comparative strength. The most effective control signals were found to be line power flows and injected currents. The second consideration was the robustness of the designed controller. System identification and separation were used to decouple the system in presence of faults and disturbances into three variations; fault and disturbance-free, fault-dependent and disturbance-dependent. This approach minimized the stringent trade-offs inherent in the control design objectives such as reference tracking, disturbance rejection and noise attenuation. As a result, the control design could be formulated into two main objectives. The first goal was related to reference tracking and oscillation damping which was achieved using the fault-free subsystem. The second aim referred to fault and disturbance suppression which was achieved through fault and disturbancedependent subsystems. The control synthesis was formulated as mixed sensitivity H¥ outputfeedback problem with pole placement. Linear Matrix Inequality (LMI) approach was used to formulate the problem and to solve for a stabilizing controller. The design procedure of two-stage robust control damping system was illustrated by two study systems. The first study was a single machine to infinite bus system. The second one was a two-area four-machine system. The proposed architecture considerably minimized the overshoot when pole placement was not applied. For example, the overshoot was reduced by 41.98% in the first study case and by 17.60% in the second case study. If pole placement was required to achieve the minimum damping ratio, the improvement introduced by two-stage controller was less. For example, the overshoot was reduced by 0.4% only in the second case study. These results were drawn in comparison with the conventional centralized robust control. The proposed architecture successfully suppressed the impact of disturbances and faults on the operation of the system

Date of Award	May 2015
Original language	American English
Supervisor	Jimmy Peng (Supervisor)