Researchers at the University of Birmingham are working on new ways of preventing threats to power grid stability, which result in the loss of power to millions of people, equipment damage and limit power transfer capability.
Power system frequency control and forced oscillations, which may cause widespread disruption over entire power grids, are two major technological issues observed.
The research of Professor Xiao-Ping Zhang, Chair in Electrical Power Systems at Birmingham’s Department of Electronic, Electrical and Systems Engineering, focuses on developing advanced technologies for smart grids and has developed technologies to overcome these challenges. University of Birmingham Enterprise has filed patent applications including the technologies and looking for commercial partners for licensing, collaboration or co-development.
The grid’s frequency drops to a frequency nadir when demand exceeds supply, and with a frequency second dip before recovery to a settled grid state. This grid settling process can be extended with a consequent loss of efficiency and revenue for the operator.
Zhang’s method eliminates the risk of frequency second dip with minimal (less than 1%) loss of wind power capture. It was developed for use in variable speed wind turbine systems, which operate at maximum power point tracking mode to extract the greatest amount of energy and do not regulate their active power to support the grid when its frequency deviates from its usual value.
The method includes a control system, which has been simulated in six scenarios with different wind speeds and wind power penetration levels. These simulations showed the system arrests the primary frequency dip, raises frequency to a high level close to the settling frequency within 20 seconds, and completely eliminates the risk of the secondary frequency dip.
The system can be integrated into existing wind turbine control systems and has a non-communication based central design, which links with other turbines and the grid are not required for its functionality.
The second technology addresses the issue of forced oscillations in a power system caused by malfunctioning equipment and resulting in large oscillations away from the source.
Zhang has devised a control system to be implemented in wind farms suppressing and isolating forced oscillations originating either from the grid, or the wind farm itself.
The system, which releases or absorbs power opposite to the oscillating power, has been verified by simulations with constant or varying wind speeds, different wind farm locations with respect to the source of forced oscillation, on the modified two-area and IEEE 39-bus power systems (which represent the aggregation of a large number of generators), using a real-time digital simulator and a physical modelling and simulation tool.
The results of these simulations showed that the system can suppress and isolate forced oscillations originating either from the grid, or the WTS itself. The loss of wind power capture was negligible, and the simulations showed the system also helps dampening of the intrinsic natural oscillations.
