Voltage stabilization on MV distribution lines using flywheels.

Abstract

The quality of power supply from distribution networks is dominated by electromagnetic transients, harmonics and abnormal increase or decrease of voltage levels below the grid code allowed ±6% due to variable electronic or unbalanced loads and presence of ground faults in the power grid. However, abnormal increase or decrease of voltage levels is the major power quality problem and statistically 92% of power quality problems are due to increase or decrease of voltage and 80% of these deviations in voltage last for 20ms to 50ms. At times, long and medium distribution lines experience Ferranti effect where by receiving end voltages become higher than sending end voltages. The project is derived from this background and its vital aim is to design a fly wheel energy storage system (FESS) used to stabilize voltages on MV distribution lines. The FESS acts to store energy during off-peak hours which could later be used during peak hours.

The FESS has a fast charge and discharge speed making it capable of discharging huge power over a very short time. It also has an ability to independently regulate active power and reactive power hence proving to be a soft solution to power quality problems. The project was made using Mat lab Simulink software showing the charging and discharging of the flywheel plus the dynamic nature of both the supply and the loads when the flywheel is integrated on to the power grid. The flywheel energy storage system modeled comprises of grid side converter, machine side converter, dc link capacitor, asynchronous machine, and variable torque load and control system of both the grid and machine side converters.

Two case studies in Uganda were selected and modelled using mat lab Simulink. Mat lab Simulink simulation results before and after application of FESS show that the control strategy of the FESS can accurately stabilize the voltages with flywheel's kinetic energy and the critical loads are fully protected.