Research On Voltage Regulation Strategy For Distribution Network With DG

In order to alleviate conflicts between rapid economic development and gradual depletion of fossil energy resource and deterioration of eco-environment, distributed generation (DG) acquires vigorous development and promotion in the world due to environmental friendliness, safety, reliability, less investment and space. However, with the development of DG permeability, it cannot be ignored that DG has inevitable influence on distribution network voltage. Voltage regulation method in conventional distribution network is controlling voltage at the secondary side of substation by on-load tap changer and compensating reactive power by electrostatic capacitor. However, it has some deficiencies. When terminal voltage of long feeder surpasses its limitation, considerable change of OLTC’s tap may not meet the requirement and even cause overvoltage at substation secondary side. Furthermore, capacitor can only sent out reactive power and cannot restrain overvoltage caused by DG with high permeability effectively. In order to make up the deficiencies of conventional voltage regulation method, research on voltage regulation strategy which adapts to the connection of DG is of theoretical significance and engineering value. The main work and achievements are as follows:Firstly, the paper analyses the reactive power and voltage regulation capacity of various types of DG. Based on the processing method of DG in load flow calculation, the paper discusses the impact of DG on distribution network voltage by load flow calculation. It is concluded that the system voltage is influenced by the location, capacity and power factor of DG.Secondly, a voltage regulation method based on the cooperation of DG and D-STATCOM in active distribution network DG is proposed. As static synchronous compensator (D-STATCOM) has good ability of reactive power and voltage regulation, it is selected to coordinate with the substation on-load tap changer (OLTC) to control voltage. The working ranges of OLTC and D-STATCOM are predefined respectively to solve over-limit voltage problem caused by DG penetration or load change. In the extreme voltage violation conditions, D-STATCOM instantly brings back the voltage to the working range of OLTC by controlling its reactive power output. Then the tap position is adjusted by OLTC to maintain the system voltage violations within the permitted range. This method will not only achieve the best effect of voltage control, but also reduce the number of OLTC tap action, thus extending its service life.Finally, based on zone partition and coordinatded control, a voltage regulation strategy with active participation in voltage control of DG is proposed. To give full play to the role of the DG, as a tool of voltage regulation, DG with capacity of reactive power regulation can actively participate in voltage control. For this purpose, the node location index is defined for determining the DG’s location where DG can provide maximum voltage support. Then by load power calculation and voltage sensitivity analysis, local voltage regulation zones of DG and OLTC are divided based on the influence of DG’s power variation on each node voltage. In order to avoid unordered action of voltage regulation devices, a coordinated and sequential voltage regulation strategy based on zone partition is formulated. The results of simulation on IEEE 33-bus distribution system show that the proposed strategy can give full play to the DG capacity of supporting reactive power/voltage, achieve rapid and accurate voltage regulation and avoid invalid voltage control and the conflict among multiple voltage regulators.