Energy Systems and Technologies for the Coming Century ...

3 ControlThe concept is based solely on indirect control, based on four control signals, commonfor all active units:the line frequency;the local voltage;a local, dynamic price for active power; anda local, dynamic price for reactive power.All active power units respond to larger deviations of the line frequency, f, to largerdeviations of the local voltage, U, and to the local dynamic price signals for the activeand the reactive power, c P and c Q . The individual power unit’s responds to the dynamicpower prices are voluntary and will depend on the actual application, whereas theirautomatic responds to the frequency and to the voltage deviations are mandatory.3.1 Dynamic power pricesThe power system is divided into appropriate physical price areas, physically interconnectedby a number of power lines, each with individual power exchange capacity –see Figure 3. The distribution of the load flow in the interconnecting lines is partlycontrollable – through transformer tap changers, phase compensation units orAC/DC/AC connections.The local dynamic power prices, c P and c Q , must represent the local power system’sneeds for active and reactive power, and for regulation of active and reactive power, P ,and Q . In addition, the local prices should support the import from areas with relativelower prices and the export to areas with relative higher prices. The new local price, c t+1 ,is generated as a correction of the present price, c t , relative to the neighbour prices, c * t ,and the needs for regulation, : ∗ ∆ ∆ ∗ ∆ ∆ where c P* t and c Q* Pt represent the averages of the prices for the neighbouring areas, a Xand a Q X defines the sensitivity to the neighbour price levels, and b P and b Q defines thesensitivity to the needs for regulation. c P S and c Q S are local corrections, forcing anincrease or a decrease of the local prices, controlled by the power system operator, andused for the supervisory control. The local prices will to some extent follow the neighbouringprice levels, depending on the a X factors. If the local prices reduce, the importwill increase (or the export decrease), the local generating units will reduce theirgeneration and the consuming units will be motivated to increase their loads. If the localprices increase, the import will decrease (or the export increase), the local generatingunits will increase their generation, and the consuming units will be motivated to reducetheir loads. This will dynamically adjust the local prices, the import / export, the localgeneration and the local consumption to optimise local the power balances. The dynamicpower prices will be updated every second.When reconnecting an area after black-out or island operation, the local power price willbe forced relative high, giving the local generation units an incentive to provide powerand the local consuming units an incentive to reduce their demands. This is controlled bythe power system operator.The need for power regulation is determined by the power system area’s power import /export. For the active power, the need for regulation is determined by the relative highestloaded interconnecting power line – see Figure 4.Risø International Energy Conference 2011 Proceedings Page 180