Research On Fast Variable Load Control Of Combined Heat And Power Unit

In order to ensure the safe and stable operation of the power system,the generator units connected to the power grid need to continuously respond to the load command of the power grid through Automatic Generation Control(AGC),so as to meet the real-time energy supply and demand balance and the demand for primary frequency modulation.In order to encourage the unit to respond quickly to power grid dispatching requirements,the power grid companies in China have successively implemented "two rules" to assess the directly dispatched generator units,and the variable load performance has become an important factor in the economic benefits of power generation enterprises.At the same time,the integration of large-scale renewable energy makes the frequency regulation of power grids more and more difficult.Improving the variable load performance of grid-connected units has become the basic requirement and important guarantee for the development of energy and power transformation in China.The power structure in China is dominated by coal-fired thermal power,while in the "Three North Region",the proportion of combined heat and power(CHP)units is relatively high.Like traditional coal-fired generating units,the CHP units generally use coordinated control system to change the load output,but it is limited by the large delay and large hysteresis characteristics of the boiler side.The variable load rate is generally only about 1.5%of the rated load.Moreover,the CHP units generally operate in the mode of fixing power load by heat load,and their operational flexibility is more constrained.In order to improve the variable load performance of the CHP unit,this paper proposes a new variable load control strategy based on heating source regulation,while fully utilizing the heat storage of the heat network or heat storage device,which will not affect the thermal user demand.The main research work and innovative achievements of this paper include:(1)Based on the composite modeling theory,a dynamic characteristic model of the influence of heating source disturbance on the unit load is established.Through the field experiment,the characteristic curve of the influence of the heating source disturbance on the unit load is obtained.The "one-order inertia" description structure and time constant of the dynamic characteristic model are obtained.The static power calculation method under the condition of heating for the CHP unit is proposed,and the open-loop gain coefficient of the dynamic characteristic model is determined;(2)A new variable load control method combining source regulation and traditional coordinated control strategy is proposed,which realizes the rapid adjustment of unit load and the self-recovery control of heating source.A three-input and two-out nonlinear control model for the unit with heat source is established.Two load control loops for heating source and fuel quantity are designed.The load deviation is used as the input of the heating source regulator,and the load response speed is improved by using the characteristics of its load response speed;Besides,the um of the load deviation and the output of heating source loop has been used as the input of the fuel quantity controller to ensure the full supply of energy in the control process and realize the self-recovery control of the heating source;The thermal storage control strategy of the unit with heat accumulator is further designed to completely eliminate the impact on the heating system.(3)Taking a 330MW unit as an example,the effectiveness of the proposed control strategy is verified.Under the steady-state operation conditions,the load response of the proposed control strategy and the traditional coordinated control strategy under step disturbance and slope disturbance input are compared respectively.The load response curve,IAE?ITAE index and AGC performance index are compared.The results show that the control effect of the proposed strategy is significantly better than that of the traditional coordinated control strategy.After optimization,the load response rate of the CHP unit has doubled.