The reverse distribution of wind resource and electrical load center forms the regional transmission systems with multiple types of power sources and high penetration of wind power in the Northwest

North and Northeast China. Of those systems

the wind and thermal power bundled transmission system is the most typical one. Improving its generation controllability is the key issue to increase the proportion of wind power accommodation. First

based on an understanding of characteristics of the wind and thermal power bundled transmission system

an idea of building a new optimal operation layer between the generation units and dispatch center is proposed

which is responsible for the coordinated control between local scattered wind farms and thermal units to make the total generation more controllable and increase the wind power utilization rate. The control complexity of the combined multiple types of units with different characteristics

and dealing with the variability from renewable energy in such strong rigid generation systems are the main challenges to this optimal operation layer. The entire operation control schemes are described from three aspects

i.e. the wind farm clusters coordinated control mode

the hierarchical control mode over multiple spatial scales and the detailed coordinated control over multiple temporal scales. Finally

the hierarchical coordinated optimal operation system and corresponding operation performance evaluation indices are proposed. Moreover

the key technical problems of the optimal operation system are discussed from two aspects: the coordinated layer between wind and thermal power and that inside wind power clusters.