Control coordination on the distribution power network

A two level (hierarchical) approach to controlling load voltages with under load tap changing (ULTC) transformers of radial power networks is formulated. The state of the art for controlling these devices is of the relay type and is insensitive to system-wide conditions. The proposed control law is nonlinear and employs the minimum information required to be effective in the regions classified in the past as voltage uncontrollable with the simple relay type controls. A brief review of the state of the art of ULTC controls is given. The theoretical conditions under which a two-level control approach, with the simple relay type controls at the primary level, is not effective in bringing the voltage to the required level, are discussed. The new control law is derived and illustrated using a constant power load model