Study Of Optimal Reactive Power Planning For Rural Power Distribution Network In Consideration Of Harmonic Distortion

Optimization of reactive power in distribution systems that can effectively reduce the system loss, improve the voltage profile and build up the stability of system is an important measure to ensure security and economy of system operation. Along with the fast and steady development of economy the large and nonlinear loads are more and more in rural power distribution network and that aggravates the burden of the rural power distribution network which hasn't enough reactive power resources. Due to the widespread use of nonlinear loads in rural power distribution network, the harmonic pollution is increasingly serious, which can cause capacitor failure or out of work. On the other hand, shunt capacitors may lead to harmonic amplification. Therefore, it is of great significance to study on reactive power optimization in rural power distribution network with harmonic consideration, aiming to make the capacitors exert their effect sufficiently and prevent harmonic amplification as well.At first, the mathematical model of optimal reactive power planning in rural power distribution network was set up, and the constraint of harmonic power flow and total harmonic distortion (THD) was included in the model's constraint conditions. Then, the branch current method based on the distribution networks layering for fundamental power flow calculation was presented, which could improve the speed of calculation greatly. The constant current source models of harmonic sources and harmonic distribution networks model were set up, and the harmonic power flow was calculated by linear analysis method. Some improvements were presented about the simple genetic algorithm (SGA). In this paper, integer strings instead of binary coding were used to represent value of control variables. The affinity and density of immune algorithm was used to improve the selection operation of genetic algorithm (GA). The crossover rate and mutation rate of excellent individuals was enhanced to prevent them from remaining the same state all the time by improving the adaptive genetic algorithm. The mutation operation of GA was guided by the sensitivity between harmonic voltage and compensation capacitances to make the shunt capacitors play the role of optimal compensation to reactive power of fundamental frequency and prevent harmonic amplification as well. The reactive power optimal planning program was programmed by VC++6.0 and applied to practical rural power distribution network. The results show that the improved genetic algorithm can enhance the search effectiveness and is easier to reach the global convergence, the system energy loss is greatly reduced and the voltage profile is enhanced evidently.