Hierarchical Two-level Voltage Controller for Large Power Systems
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Keeping adequate voltage levels for each bus in a power system is a key factor for proper performance of power system equipment and reliability of the network when subject to disturbances. However, given the constant increase in loads and constraints in the operation of the grid, meeting this goal has become a challenge. Bulk power delivery substations play a key role in voltage control because they represent the primary connection points between high voltage transmission and distribution system. Proof of this is the impact of the growing renewable generation capacity in the modern power system, in which substations are expected to be a key unit in interfacing sophisticated power electronics on the distribution side to bulk transmission system of the power grid. Furthermore, Smart grid related direct load controls present enhanced control capabilities at the substation level that need to be carefully coordinated from the control center.The local character of the voltage control, the diversity of the control means and the interaction among them makes this task particularly difficult. In many European countries and in China, hierarchical voltage controllers have been proposed and implemented for automatically controlling the voltage profile of the transmission network by using different notions of primary, secondary and tertiary voltage controls. Pilot automatic voltage control projects have been implemented in the past at Bonneville Power Administration and PJM Interconnection. This dissertation proposes a hierarchical two-level controller for large power systems that uses synchrophasor measurements for voltage control decisions. The first level, the Substation Local Voltage Controller (SLVC) supervises and controls voltages at substation level with discrete devices such as capacitor/reactor banks and transformer's LTCs. Also, it monitors the reactive power output of the generators connected to the substation and keeps them in normal operation range.The second level, the Supervisory Central Voltage Controller (SCVC) coordinates the operation of the SLVCs in the system to prevent hunting between substation controllers. It also provides the voltage schedules to each SLVC.