Abstract
It is significant for power system stability to improve the operation flexibility of grid-connected units. Such improvement has always been a hot topic, especially for coal-fired units. In recent decades, it has become increasingly urgent and challenging as large-scale fluctuant renewable energy is connected to the power grid. Boiler-turbine coordinated control strategy (CCS), which is employed to perform unit load control according to automatic generation control (AGC), has a slow ramp rate in general on account of large delay and inertia of boiler, so to improve the unit operating flexibility, it is necessary to explore usable heat storage and optimize the control strategy. In combined heat and power (CHP) units with heat accumulators, their heat and power are decoupled. Therefore the extraction steam that goes to the heating station can be regulated flexibly even operating in “heat-led mode”. The change of extraction steam flow has a significant influence on the turbine power output, so we propose to improve the load-following capability of CHP units by regulating the heat source flow. In this paper, the influencing model is set up, and it is about heat source flow variations on the electric power output. The load control strategy is further optimized and designed through combinations of CCS and heat source regulation. Finally simulations and analysis are performed on a 330MW CHP unit, and the results reveal that the power ramp rate with our strategy is two times faster than that with traditional strategy.
Highlights
In recent years, large-scale of renewable energy sources (RES) such as wind and solar energy have dramatically increased around the world [1,2]
It can be seen from the curves that the power response with our strategy has shorter adjustment time and smaller overshoot compared to traditional coordinated control strategy (CCS); and the live steam pressure can recover to its set point more swiftly with smaller fluctuation
An optimized control strategy is designed through combinations of traditional CCS and heat source regulation to improve the flexibility of unit
Summary
Large-scale of renewable energy sources (RES) such as wind and solar energy have dramatically increased around the world [1,2]. Such fluctuant and intermittent RES bring great challenges to grid stability and security, which has resulted in an increasing proportion of wind curtailment all over the world [3,4], so the power system requires new solutions that can guarantee high operational flexibility to balance electrical supply and demand [5] For those countries whose dominant power is coal-fired power, coal-fired power units are the main participants in the load cycling and frequency regulation. Korpela et al [25] presented an analysis on dynamic operability of interconnected CHP plants and district heating networks in Finland His analysis was based on the fact that the heat load and electric production can be decoupled temporarily by using the heat storage capacity of DH networks and heat accumulator. Presented a model that confirms the theoretical maximum of flexibility of a combined heat and power system This system couples to a thermal energy storage solution that can be either centralized or decentralized.
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