Parameter sensitivity indices of power system stabilizer(PSS) are introduced and sensitivity computation function are implemented in SSAP power system software package by two approaches;(i) the sensitivity computation function of eigenvalues associated with oscillation modes and their damping ratios via PSS controller parameters;and(ii) the sensitivity computation function of the eigenvalues of oscillation modes and their damping ratios via PSS parameters subject to the condition of constant equivalent AC gain.Low frequency oscillation damping is optimized in both approaches.The 600 MW generator in Honghaiwan power station is taken for case study.The parameter of PSS is optimized by sensitivity analysis subject to constant equivalent AC gain.The optimized results well coincide with the oscillograms recorded during the on site experiment.The sensitivity analysis by SSAP is validated not only by theoretic analysis but also by engineering practice.

Low frequency oscillation is the potential threaten to the stability and security of the large AC/DC interconnected power system.Fast and effective modulation controller is one of the effective ways to solve the problem.Introduction about the realization of user defined modulation controller(UDMC) in small signal analysis package(SSAP) developed by Shanghai Jiaotong University,which has been applied in analysis of the large power system,is present in this paper.The modeling of UDMC is based on the component connection modeling idea,and UDMC accords with the universal component connection method in SSAP to participate in the formation of system state matrix.UDMC is the foundation for future research on modulation controller.Analysis of specific case validates the correctness of the UDMC function.

The damping sensitivity analysis of interconnected power system low frequency oscillation is studied. The function of sensitivity analysis is implemented in the Small Signal Stability Analysis Package (SSAP). The paper mainly analyzes the sensitivities of oscillation modes with respect to the parameters of power system stabilizer (PSS) in the excitation systems of generators for a physical large-scale interconnected power system with AC/DC parallel transmission - China Southern Power Grid (CSG). The results show the effectiveness of this function which could direct the optimization of PSS parameters and improve the low frequency oscillation damping of the system.

As development of power systems the inter-area low frequency oscillation becomes one of the key problems which influences security and stability of the interconnected power systems.In this paper the inter-area low frequency oscillation modes of an AC/DC parallel transmission system are analyzed by Implicitly Restarted Arnoldi(IRA) method and Prony identification.In HVDC the active power modulation at rectifying side and the γ angle modulation at inverting side are taken as further countermeasures for damping the inter-area oscillation modes.The eigen-analysis shows that system damping is effectively increased and dynamic stability of the system is significantly improved.

Constant PQ model or quasi-steady-state (QSS) model are widely used for HVDC links in the large-scale AC/DC power system low frequency oscillation (LFO) analysis. An important concern of the two types of HVDC models is that to what extent the calculation results are impacted by using the constant PQ model. The differences between the two models are investigated by a modal analysis method based on the augmented system state equation (ASSE). The calculation results using the two models are compared in a LFO analysis. The theoretical and simulation results indicate that, when the HVDC system operates under the constant power!control, the active power that the converters inject into or withdraw from the AC system is approximately constant, while the reactive power drawn from the AC system is varied. For the inter-area mode, the results from the constant PQ model are more conservative than that of the QSS model. For a large-scale AC/DC power system, it is acceptable to represent the HVDC links by the constant PQ model.