Z. FAN ET AL.

696

Table 1. Comparisons of optimal results and the initial val-

ues.

Initial

values Optimal

results

network loss(p.u.) 1.2516 1.0258

number of buses violated voltage limits 12 0

maximum voltage of PQ bus(p.u.) 1.0571 1.0789

minimum voltage of PQ bus (p.u.) 0.8927 0.9211

Table 2. Comparisons of solving results of fuzzy model and

traditional model.

fuzzy

model traditiona1

model

network loss(p.u.) 1.0258 1.0183

number of buses violated voltage limits 0 0

maximum voltage of PQ bus(p.u.) 1.0789 1.1

minimum voltage of PQ bus (p.u.) 0.9211 0.9225

computing time(s) 0.95 0.59

power optimization are shown in Table 2.

From the Table 1 and Table 2, it can be seen that the

algorithm can effectively deal with the large number of

inequality constraints of the fuzzy model of reactive

power optimization and has high compute efficiency.

After optimization calculation, there is no bus violated

voltage limit through the adjustment of the reactive pow-

er controllers. The maximum voltage of PQ bus is its

upper limit when traditiona1 model is used, however, the

voltages of PQ buses maintain specified margins when

fuzzy model is used, which improves the safety level of

the system.

Meanwhile, the network loss is decreased to 1.0183

from 1.2516 and the decreasing range is 18.63% when

traditiona1 model is used, whereas the network loss is

decreased to 1.0258 from 1.2516 and the decreasing

range is 18.04% when fuzzy model is used. So the de-

creasing range of network loss obtained by solving the

fuzzy model is less than that obtained by solving the tra-

ditiona1 model, but the level of voltage security is im-

proved when fuzzy model is used.

The example of the practical power system indicates

that the algorithm can effectively solve the fuzzy model

of reactive power optimization and satisfy the require-

ment of online calculation. After optimization calculation,

the violated voltages are corrected; the voltage soft con-

straint buses are kept specified margins; at the same time

the network loss is reduced.

5. Conclusions

This paper uses the interior point filter algorithm to solve

the formulation of fuzzy model for the power system

reactive power optimization considering the soft con-

straint characteristics of voltage constraints. Optimiza-

tion results show that the algorithm can effectively deal

with the large number of equality and inequality con-

straints of the fuzzy model for the practical power system

and satisfy the requirement of online calculation which

realizes to decrease the network loss and maintain secu-

rity margins of voltage.

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