Autonomous Decentralized Voltage Profile Control Method in Future Distribution Network using Distributed Generators

Abstract

To realize the sustainable energy society, it is of prime importance to introduce the renewable energy, such as Photovoltaics (PV) and Wind Turbine generators, or Cogeneration systems which can utilize the exhaust heat energy. These generators are called “Distributed Generator (DG)” and they are introduced to the distribution network mainly as shown in fig.1. However, in the distribution network with a large number of DGs, the voltage profile maintenance becomes important issue due to the reverse power flow caused by DGs. Conventionally, the voltage profile is controlled within the allowable range by the use of load-tap-changing substation transformer (LTC) or Static Capacitor (SC) in order to compensate the voltage drop caused by the demand-directional power flow. There are a lot of studies in which the voltage profile is maintained by the effective utilization of those facilities when a large number of DGs are introduced. For example, the optimization technology based on the global information of distribution network is utilized to determine the control actions of voltage control equipments. However, it should be difficult to control the high-speed voltage change by LTC or SC because those equipments work by switching. Although the utilization of SVC (Static Var Compensator) is one of effective approach to realize the high-speed voltage control, it should not be desirable from a viewpoint of increase in cost. To realize the high-speed and flexible voltage maintenance control with reducing capital investments, it should be effective to utilize the reactive power control of DGs. Supposing that a large number of DGs are introduced, it should be difficult to manage the all information of whole system and to control all DGs. Hence, the much attention is paid to the autonomous decentralized control method, for example, by P. N. Vovos or P. M. S. Carvalho. However, the cooperative work among multiple DGs is not considered in their papers because only the information of the connection node is utilized. Although Mesut E. Baran et al studied the cooperative work among DGs based on the multi-agent system, the www.intechopen.com Multi-Agent Systems - Modeling, Control, Programming, Simulations and Applications 194 method is not autonomous decentralized one because the specific control signal is generated by the optimization based on the global information. On the other hand, the authors have developed autonomous decentralized voltage control method so far using reactive power control of DGs. Specifically, voltage profile maintenance is realized by the reactive power control of inverter based on the multi-agent system. In those papers, it is supposed the agent program is installed to each DG. The agents determine their proper control actions based on the local information exchange among neighboring agents. Where, the feedback control based on integral logic is applied. The proposed method is composed by three control methods whose control purposes are different. It is possible not only to maintain the voltage profile but also to decrease the excessive reactive power. Additionally, in our other paper, the proposed method is enhanced to realize the effective utilization of free capacity. In this chapter, we will describe the outline of the voltage profile control method proposed in our previous work. First, the concept of the reactive power control of DG and voltage profile control method are described in section 2. Next, the basic and enhanced method of autonomous decentralized control are shown in section 3 and 4, respectively. Finally, a conclusion is provided in section 5.