Distributed generation and frequency/load control of power systems

The frequency/load control of power systems is well established at the transmission-line level via load sharing based on droop characteristics, demand-side management, and load forecasting. The supply of power including co-generation from distributed generation (DG)--based on solar and wind--occurs at the distribution system level, and the frequency/load control is complicated due to its intermittent operation at maximum power output, and the required control at the distribution level. The joint operation of DG plants with central power stations fits into the established control paradigm only as long as the central stations can replace the power of DG plants (e.g., change of 60 MW/minute). A combination of DG plants with storage plants is feasible, if the latter can take over power generation within a few 60 Hz cycles. Long-term, hydro and compressed-air storage plants require a lead time of about 6 minutes which is too late to replace power lost from DG plants. Thus, short-term storage plants must be available to bridge the gap between the time when the DG plants are unable to deliver power and the time when the long-term storage plants can be put on- line. One advantage of combining DG plants with storage plants is that the latter can be charged with inexpensive energy during times of low power demand and high output of DG plants. Relying only on DG plants with the existing control approach is impossible due to large frequency changes with increased load. New control strategies, which must include the DG plants at the distribution level, can be based on highly adaptive biological/artificial-intelligence principles.