Congestion management: Re-dispatch and application of FACTS
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Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Publicerad
2006
Författare
Mwanza, Kennedy
Shi, You
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
This thesis deals with the transmission congestion problem arising from multiple transactions in deregulated electricity markets. Two congestion management approaches (re-dispatch and the application of Flexible ac transmission systems (FACTS)) have been studied in three market models (pool, bilateral and the combined (hybrid)). An optimal power flow (OPF) framework has been used to simulate the considered market models and the congestion problems. The IEEE 14-bus and the CIGRE 32-bus test systems have been used to demonstrate the robustness of the approaches. The objectives of congestion management are different in different market. In the pool market, the objective function is the minimisation of the amount of re-dispatched power. In the bilateral market, minimising the transaction deviations is considered as the objective. In the hybrid model, the objective function is two pronged, minimising the pool re-dispatch and minimisation of deviations of the bilateral contracts. Furthermore, the objective of minimising the cost of congestion is applied in all the market models. The use of series FACTS devices to alleviate congestion is also demonstrated. In the pool market, congestion requires re-dispatch of generation hence deviating from the market settlement. It has been shown that re-dispatch increases the system cost since the out of merit generators are involved more than scheduled. The minimisation of redispatch in the pool therefore ensures that the deviation from the economical settlement of the market is minimised. In the bilateral market, the interest is to maintain the desired transactions between contracting parties. To solve the arising congestion in this market model, the rescheduled transactions are forced to be as close to the scheduled transactions as possible. The changes to contracts are non-discriminatory, hence only contracts that affect the congestion are modified. In order to meet the load requirements, power has to be supplied from the regulation market. In the hybrid market model, a weighting factor is used between the pool and bilateral re-dispatch. The pool could be re-dispatched more than the transactions and vice versa, depending on the weighting factor. It has been found that when FACTS are included in the network, the amount of redispatched power in the pool is greatly reduced resulting in an optimal operating point closer to that dictated by the market settlement. In the bilateral market, the results show that the transactions may not need to be modified when we have FACTS. The cost of congestion to the ISO also reduces when FACTS are employed. In order to justify the use of FACTS with regards to congestion management, a simple cost benefit analysis has been proposed where the benefit from FACTS is considered as avoided congestion costs that the system would have to bear otherwise. The resulting re-dispatched generation schedules are only optimal as far as congestion is concerned under normal operating conditions i.e., N-0 contingency. The schedule is therefore tested for security under the N-1 criterion. The contingency cases have been simulated and ranked using an overload index and total power violations arising from the outages. A dc load flow and line outage distribution factors have been used for testing system behaviours under various contingency conditions. A comparison of the dc and ac load flow methods has been made and the results indicate a small average absolute error.
Beskrivning
Ämne/nyckelord
Elkraftteknik , Electric power engineering