Study On Adequacy Equivalent Model For Bulk Power System

This dissertation is sponsored by the project ("Application and Research on Theory of Power System Reliability Tracing", No. 50577072) of the national natural science fund of China.Reliability on Bulk Power System(BPS) is a very important assistant tool for power system planning, design and operation, and it can provide important information for power system planning and operation decision-making, but the computational complexity is still the biggest difficulty for the BPS adequacy evaluation(AE). With the development of power system towards UHV, long distance and huge capacity, the scale of power network enlarges continuously, which makes the solving for the computational complexity of the BPS AE more difficult. So the critical problem of AE is to improve the computational efficiency with an accepting computational precision. In other word, it is to obtain a balance point between computational complexity and computational precision.There are two ways to improve reliability evaluation efficiency: one is to reduce the number of states needed evaluating, and the other is to improve the evaluation speed for each state. The adequacy equivalent approach can evidently reduce the computational time by developing a multistate adequacy equivalent model for the interconnected area. This dissertation conducts a series of research aiming at the computational complexity of BPS reliability evaluation, the main contents are as follows:â‘ Analysis of the basic theory of BPS AE and its relevent calculation methods including power flow calculation, system island judgement and load curtailment is presented. The AE algorithm, which is from the analytical approach based on the DC power flow with the proportional load curtailment rule, is applied to the Two Area RBTS and obtain the buses and system reliability indices.â‘¡The basic theory of the AE approach is introduced and the theory how it reduces the computational complexity is analyzed. Based on these theories, the AE model is presented. The test on the Two Area RBTS shows that it evidently improves the calculation efficiency and reduces the computational time.â‘¢Using the state truncation approach analyzes the computational complexity of the AE of BPS. The analysis of algorithm complexity for the analytical approach and the adequacy equivalent approach is conducted. The analysis result shows that the computational time is the biquadratic to bicube increasment with the node number increasment while evaluating the adequacy of BPS using the analytical approach (the more computational level considered, the more computational time needed). Though the adequacy equivalent approach can evidently reduce the computational time, there are too many states which need to be evaluated when the higher level events should be considered. In order to calculating the higher level event, it's necessary to carry through the state merging technique to reduce the number of states.â‘£Based on the basic theory of the adequacy equivalent approach, the state merging (SM) equivalent model for BPS is proposed. Clustering technique is used to construct this model and reliability theory is used to obtain the equivalent probability, frequency and available capacity of each cluster. SM equivalent model can obtain very precise results and highly reduce the number of the states which need to be evaluated. The tests on the two Area RBTS, two Area RTS and Chuanyu BPS show that the proposed model evidently improves the calculation efficiency and highly reduces the computational time.