Investigations On Impacts And Control Strategies Of Power System Stability With Wind Power Integration

Wind farms have been increasingly integrated into power systems over the last fewdecades because of the global energy crisis and the pressure on environmental protection, andgradually going to the road of large-scale and industrialization. In recent years, the installationof wind power energy has moved from small wind farms with a few wind turbines to largewind farms with more than hundreds of MW of capacity, and the connection point of windfarm have developed from low voltage level’s electricity distribution system to high voltagelevel’s electricity transmission system. With the penetration level increasing, the impact ofwind power on power system dynamics and stability become increasingly complicated, whichmake it necessary to research on a series of technology problems of wind power integratedsystem. Given these backgrounds, many systematic and in-depth investigations on the impactsof wind farms on power system stability have been done in this dissertation for the reasonableand stable penetrations of wind farms into power system. Meanwhile, the researching workcan provide theoretical preparation and technology support for the programming, designing,operation and policy-making of wind farms.Specifically, the main contents of this dissertation are as follows:1. To systematically examine the impacts of wind power on the small signal stability aswell as transient stability, so as to investigate the countermeasures. A comprehensive study iscarried out to compare the dynamic performances of a power system respectively with threewidely-used types of wind power generators integrated. First, the dynamic models aredescribed for three types of wind generators, i.e. the squirrel cage induction generator (SCIG),doubly fed induction generator (DFIG) and permanent magnet generator (PMG). Then, theimpacts of these three kinds of wind generators on the small signal stability and transientstability are compared with that of a substituted synchronous generator (SG) having the samecapacity at the same connection point in the WSCC three-machine nine-bus system byemploying the eigenvalue analysis and dynamic time-domain simulations.2. In order to investigate the impacts of wind power integration on the low frequencyoscillation characteristics of an interconnected power system, the damping performances of atwo-area interconnected power system with and without wind power integration are analyzedbased on the comprehensive model of the doubly fed induction generator, and the dampingincrement is given with the wind farm at the sending end and at the receiving end. Theimpacts of several factors, including the DFIG transmission distance, DFIG capacity, tie-line power of the interconnected system, with/without a power system stabilizer (PSS), on the lowfrequency oscillation characteristics of the interconnected power system are examinedsystematically. Then, a two-area four-machine system and a two-area eight-machine systemare employed to carry out detailed analysis and comparisons.3. An auxiliary damping control (ADC) static var compensator (SVC) is applied in adoubly fed induction generator (DFIG) integrated interconnected power system and theimpact of ADC-SVC on the damping characteristics of the interconnected power system isstudied. Firstly, the dynamic models of wind turbines based on DFIG is described; thereactive power limit of DFIG wind power generation system is deduced based on the powerrelationships of overall system; the energy process of area mode oscillations including SVC isanalyzed from the point of view of area transient energy using the conception of energyconservation under zero damping; the ADC at SVC is designed to improve the dampingcharacteristic of powe system, and the control parameters are determined by the eigenvaluesensitivity method. The performance was validated on an IEEE4-machine2-area system.4. To ensure the small-signal stability of a power system, power system stabilizers (PSSs)are extensively applied for damping low frequency power oscillations through modulating theexcitation supplied to synchronous machines, Up to now, various kinds of PSS designmethods have been proposed and some of them applied in actual power systems with differentdegrees, and increasing interest has been focused on developing different PSS schemes totackle the threat of damping oscillations to power system stability. Given this background,four different PSS models and investigates their performances on damping power systemdynamics using both small-signal eigenvalue analysis and large-signal dynamic simulations.The four kinds of PSSs examined include the Conventional PSS (CPSS), Single Neuron basedPSS (SNPSS), Adaptive PSS (APSS) and Multi-band PSS (MBPSS). To make thecomparisons equitable, the parameters of the four kinds of PSSs are all determined by thesteepest descent method. Finally, an8-unit24-bus power system is employed to demonstratethe performances of the four kinds of PSSs by the well-established eigenvalue analysis as wellas numerous digital simulations.