1. Purpose of the compensator
Low efficiency of existing electrical grid consists in too big energy losses and low power quality at all levels of the grid. It is estimated that 90% of grid disturbances are provoked by voltage sags and interruptions of duration less than one second. Such interruptions of power supply cause significant losses at manufacturing processes and disturb operations of information systems. The efficiency can be improved by providing for optimal energy flows at the grid and compensation of voltage sags and interruptions.
An efficient way to improve the energy flows at the grid and to reduce losses caused by the voltage sags and interruptions is to use a compensator developed as energy/power flow controllers including fast, multilevel, high precision inverters equipped with high efficient energy storing devices such as high voltage, high power stacked supercapacitors on water electrolyte.
Only the stacked supercapacitors have parameters adequate for requirements of the grid as 28V model 60/28 [max. current 4kA, power 56kW] or 300V model 115/300 [max. current 1kA, max. power 75kW].
The parameters of prismatic supercapacitors based on a toxic organic electrolyte (acetonitrile) are much less adequate for requirements of grid.
At Gdansk Branch of the Electrotechnical Institute we developed such compensator.
2. Compensator operation.
The compensator is continuously monitoring the voltage of the grid. After detecting a voltage sag or interruption a load is disconnected from grid power supply. At the same time a sinusoidal voltage generator (implemented as cascade DC/AC converter) is started.
The converter generates supplying voltage using electric energy stored in supercapacitors. The compensator assures the required level of nominal amplitude and phase which are in conformity with parameters of the grid. When the nominal voltage occurs again at the grid, the load is back connected to the grid and the sinusoidal voltage generator is switched off. The time when the compensator is on stand-by is used to charge the supercapacitors.
3. Important features:
- the compensator includes DC/AC converters based on a novel structure of cascade inverters,
- the device enables synchronous compensation in one-phase and 3-phase system with independent compensation of each phase,
- the control is performed by three independent microprocessor-boards based on DSP (Digital Signal Processors).
4. Other effective applications of supercapacitor-based energy/power flow controllers with large potential benefits for power grid.
There are other effective applications of power flow controllers with a design similar to the compensator described above, implementing such controllers can result at large benefits for the power grid. First of all similar compensators are necessary to enable efficient connection of Renewable Energy Sources to the grid. Developing MV compensator for 1 second sag ride through is also highly desirable and can result in significant benefits for the power grid. We are now working on such MV compensator.
Other applications of such supercapacitor-based controllers with large potential benefits for power grid are:
Urban rail DC traction power supply substations:
a large scale braking energy recovery and energy saving.
Electrical vehicle charging infrastructure:
fast, high-power charging stations.