|Title:||Damping controller designs to suppress inter-area oscillations in power systems by using novel eigenstructure-based indexes|
|Subject:||Electric power system stability.|
Electric power systems -- Control.
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Electrical Engineering|
|Pages:||xx, 164 p. : ill. ; 30 cm.|
|Abstract:||The low frequency power oscillation of inter-area modes inherently induced by interconnections of local electric networks aiming at transmission of power between different areas, over long distances, to realize stable power supply, as well as to balance the uneven distribution of primary energy sources (such as coal and renewable energy), has resulted in severe threats to safety of operations of power systems. Normally, use of damping controllers such as power system stabilizers (PSSs) and supplementary damping controllers (SDCs) for flexible AC transmission system (FACTS) devices is the most cost-effective means to alleviate the problem of inter-area oscillations, though design of them for modern power systems is never a trivial work. Therefore, on the basis of the foundation laid by the excellent pioneering research works already done, this thesis strives to make further contribution to the knowledge about design of damping controllers for suppression of inter-area oscillations. So far, limited attention has been paid to closed loop system eigenvectors in design of damping controllers as most existing designs focus only on eigenvalues. In fact, it is readily accepted that appropriate design of eigenstructure (both eigenvalues and eigenvectors) can obtain more satisfactory control effects than assignment of only eigenvalues. This thesis harnesses the eigenstructure of closed loop systems by exploring its integral and structural relationship with time domain responses. Accordingly, a novel way of constructing the eigenstructure-based index, which is equivalent to the corresponding quadratic cost function defined in time domain in terms of measuring the system dynamics objective, is proposed. Specifically, unlike the cost function, this index is not associated with the initial state of the system. Moreover, calculation of the index is independent of structures adopted by controllers. Thus, by formation of eigenstructure-based indexes for different measurement intentions, various optimization-based methods which use these indexes as objective functions can be formulated to tune the structurally constrained damping controllers for expected control effects.|
Firstly, a tuning scheme is proposed to coordinate wide-area signals based PSSs and SDCs for FACTS devices to mitigate inter-area oscillations with optimal control efforts under multiple operating conditions. This involves minimizing of an eigenstructure-based index which measures the dynamic performance of inter-area oscillations and control efforts together. Here, PSSs and SDCs are simple controllers with structural constraints, for consideration their applications in practice. Besides, SDCs and PSSs are simultaneously tuned by another proposed two-stage optimization method named IAMO-PS where an inter-area mode oriented pole placement strategy is implemented for damping of inter-area oscillations in the first stage while control efforts measured by eigenstructure-based indexes are coordinated under the constraints of such pole placement in the second stage. Subsequently, it is emphasized in this thesis that wind turbines employing doubly fed induction generators (DFIGs) have to sacrifice their dynamic performance as they are controlled to suppress inter-area oscillations. Thereby, a dual-channel SDC is proposed and tuned to drive the DFIG to offer the required damping to inter-area modes by using the method of IAMO-PS with optimizing of weighted control efforts of active and reactive power modulation, measured by eigenstructure-based indexes. Consequently, the DFIG dynamics are apparently improved because of their tight relationship with the optimized power outputs. The effectiveness of the proposed eigenstructure-based indexes and the associated tuning methods are validated in the classic two-area systems and New England and New York interconnected systems.
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