31.5
Stabilità transitoria e controlli di sistema
Il controllo della tensione del generatore è fondamentale per mantenere il funzionamento stabile di generatori sincroni e turbine eoliche. Nei modelli…
Nei generatori sincroni, l'eccitatore fornisce energia CC all'avvolgimento di campo del rotore.
I modelli più vecchi utilizzano un generatore CC azionato da un rotore come eccitatore, mentre quelli moderni utilizzano eccitatori statici o brushless.
Gli eccitatori statici rettificano l'alimentazione CA dai terminali del generatore o dal bus e la forniscono al rotore.
Gli eccitatori brushless utilizzano un generatore sincrono invertito, raddrizzando l'alimentazione CA dagli avvolgimenti dell'armatura all'avvolgimento di campo.
Gli eccitatori di tipo 1 sono dotati di un generatore CC azionato da un albero e di un regolatore di tensione che regola la corrente di campo in base alla tensione del terminale.
Nelle turbine eoliche, il controllo della tensione varia in base al tipo di eccitatore. Il tipo 1 non ha un controllo diretto, mentre il tipo 2 utilizza il controllo della resistenza per mantenere costante la potenza erogata durante le raffiche di vento.
Gli eccitatori di tipo 3 controllano la potenza reattiva, mantenendola costante o variabile con la potenza reale erogata.
I diagrammi a blocchi visualizzano il controllo della tensione del generatore nei programmi di stabilità transitoria.
Gli eccitatori ad alto guadagno e a risposta rapida aumentano la tensione di campo durante i cortocircuiti, migliorando la stabilità dei transitori.
Le equazioni del diagramma a blocchi calcolano la risposta transitoria.
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Q1: What is the difference between static and brushless exciters in synchronous generators?
Static exciters rectify AC power from generator terminals or bus and supply DC power directly to the rotor field winding. Brushless exciters use an inverted synchronous generator, rectifying AC power from armature windings via diodes mounted on the rotor, eliminating slip rings and brushes. Both replace older rotor-driven DC generators, improving reliability and reducing maintenance.
Q2: How does a Type 1 exciter control generator terminal voltage?
A Type 1 exciter uses a shaft-driven DC generator with a voltage regulator that measures terminal voltage and compares it to a reference voltage. The voltage error is processed with a gain and time constant, producing a field voltage that adjusts the rotor field current. This feedback mechanism maintains stable terminal voltage output.
Q3: Why do high-gain, fast-responding exciters improve transient stability?
High-gain, fast-responding exciters rapidly increase field voltage during short circuits, strengthening the generator's ability to maintain synchronism. This quick response enhances the simplified synchronous machine model's transient performance by providing immediate reactive power support. Faster exciter response reduces voltage dips and improves overall system stability during disturbances.
Q4: What voltage control methods are used in different wind turbine types?
Type 1 wind turbines use squirrel cage induction machines without direct voltage regulation. Type 2 systems employ wound rotor machines with adjustable external resistance to maintain constant power during wind gusts. Type 3 and Type 4 configurations manage both real and reactive power, providing enhanced control over generator output.
Q5: How do block diagrams represent generator voltage control systems?
Block diagrams visualize the feedback control loop by showing terminal voltage measurement compared against reference voltage, with the error processed through a voltage regulator with gain and time constant parameters. These diagrams compute transient response equations and standardize the representation of exciter and generator dynamics for stability analysis and system design.
Q6: What role does the field winding play in synchronous generator voltage control?
The field winding receives DC power from the exciter, creating the magnetic field that generates terminal voltage. The voltage regulator adjusts field current based on terminal voltage feedback, allowing precise control of generator output. This excitation control is essential for maintaining stable voltage and improving transient stability during system disturbances.
Q7: How does Type 2 wind turbine resistance control maintain power output stability?
Type 2 wind turbines use adjustable external resistance in the rotor circuit of wound rotor induction machines to regulate slip and power output. During wind speed variations, the resistance adjustment maintains consistent power delivery despite changing wind conditions. This resistance control mechanism provides a cost-effective alternative to direct voltage regulation in variable-speed wind turbine systems.