Research On Flexible Operation Characteristics And Control Of Combined Heat And Power Units

The construction of a new-type power system with new energy as the mainstay is an important means and a necessary way to achieve the goal of carbon peaking and carbon neutrality.However,the large-scale grid connection of new energy sources has posed new challenges to coal-fired units.Coal-fired units need to transform from basic power sources to flexible power sources gradually.With the gradual development of the heating transformation for pure condensing units,the proportion of combined heat and power(CHP)units in coal-fired units will also increase steadily.In the future,CHP units may need to fulfilling peaking and frequency regulation as well as the heat supply in the meantime during the heating season,which requires a quick load response rate with a large regulation depth.However,the heat-power coupling limits the flexibility supply capacity of CHP units so that it cannot meets the power grid’s increasing flexibility requirements.In this situation,this thesis aims to improve the CHP units’ operation flexibility.Research in this thesis is conducted from the following area:turbine-boiler-heating nonlinear system dynamic modeling,turbine-boiler-heating coordinated control for load response rate improvement,turbine-boiler-heating coordinated control for wide load flexible operation,and heat-power coupling-based coordinated control and scheduling.The main contents include the following four parts.1.Aiming at the modeling problem reflecting the operating characteristics between inputs and outputs of CHP units,a nonlinear dynamic model showing the operating characteristics of the turbine-boiler-heating system is established by analyzing the motion mechanism of the mass in the system during the process of heat expansion and work,based on the law of mass-balance and energy-balance,and combining the historical operating data of the system in the steady-state and dynamic processes.The accuracy of the nonlinear model is verified by open-loop and closed-loop tests.The results show that the model accuracy index of the once-through turbine-boiler-heating system is higher than 90.03%,which can provide a solid support for further control system design.2.To address the flexible control problem of CHP units near the steady-state operating point,a coordinated turbine-boiler-heating control strategy oriented to load response rate enhancement is proposed.By assigning the weight matrix to the input and state matrices in the linear quadratic regulator,the heat source can actively respond to the electric load change at the initial stage,and the unit response to the power grid load command is improved while the heat supply rate is almost not affected.Meanwhile,by reconstructing the heating quality signal and the electric-heat integration signal and designing the corresponding control loop,the fast recovery of the heat source and the accurate energy balance of the turbine-boiler-heating system is realized.Simulation results under two load conditions show that the optimized turbine-boiler-heating coordinated control strategy improves the automatic power generation control performance indexes by 22.3%and 24.1%,respectively,compared with the conventional coordinated control strategy.3.To address the flexible control problems of CHP units under a wide range of varying load conditions,an offline reinforcement learning-based coordinated turbineboiler-heating control strategy is proposed to ensure good response and tracking capability of the electric and thermal loads of the units under different operating modes.In terms of offline environment construction,multiple multi-layer perceptron network integration modes are used to solve the possible overfitting of the model in a single network mode.Considering the latency and inertia on the boiler side and the control requirements of the unit in different operation modes,appropriate environment states and rewards are set.The strategy training is implemented by a soft actor-critic algorithm with a maximum entropy model to ensure a stronger search capability under varying operating conditions and targets.The results show that with offline reinforcement learning,the unit has stronger load tracking capability than the traditional control strategy under different operation modes.4.To address the flexible control and dispatch problems of CHP units after thermal-electrical decoupling,firstly,a coordinated turbine-boiler-heating-storage control strategy with the participation of a heat storage tank is proposed to solve the recovery problem after the heat source actively responds to the grid load command through the dynamic regulation of the heat storage tank,and to reduce the impact of electric load fluctuation on the heat load.Further,based on the positive effect of the thermal storage tank and carbon capture equipment on the heat-power decoupling of CHP units,a heat-power decoupling-based coordinated scheduling strategy is proposed to quantitatively describe the promotion effect of the thermal-electrical decoupling equipment on the renewable energy consumption.The results show that the abandoned wind and solar rates of the combined heat and power energy system decreased from 3.87%and 9.69%to 1.48%and 0.08%with the effect of the thermal storage tank and carbon capture system.