Contribution / expertise:

• Smart transformer
• Expertise of smart transformer & converters.
• Development of control- and data-acquistionsoftware
• Interface with subsystems

 

Smart trafo: Stabilised LV Grid at Varying 10 kV

Due to an increasing energy demand large voltage variations in the 10 kV distribution grid of energy suppliers could occur. Especially with long 10 kV lines or with a large number of local power generation units like CHP units, the 400 V user voltage quality can no longer be guaranteed. The main problem is the fixed transformer winding ratio of the 10/0.4 kV distribution transformers. As a consequence voltage variations in the 10 kV grid will be transferred to the 400 V grid, resulting in lowered secondary voltage during periods of high energy demand and higher voltage level during periods of low energy demand.

To keep the secondary voltage level stable at 400 V, a SmartTrafo is included in the Smart MV/LV-station. The SmartTrafo adapts the transformer winding ratio to keep the LV grid stabilised. Basically the selection between the transformer fixed tap positions has to be made gradual instead of with fixed steps. In order to comply with the requirements for harmonics and cos φ, the IGBT quasi Graetz bridge topology with controlled duty cycle (PWM) is the most appropriate one for the SmartTrafo. Consequently the SmartTrafo inside the Smart MV/LV-station regulates the 400 V secondary voltage by continuous adaptation of the transformer winding ratio. It will stabilise the 400 V grid voltage independent of the varying 10 kV voltage or other 400 V user load variation.