跨临界CO_2热泵系统最优排气压力的极值搜索控制

Extremum Seeking Control of Discharge Pressure Optimization for Transcritical CO_2 Heat Pump Systems

ESC控制策略可以自动搜索性能指标最佳时系统所对应未知的或缓慢变化的系统输入,实际为一种基于梯度信号调制解调的动态搜索方法。本文针对空气源跨临界CO_2热泵热水器系统,选取压缩机排气压力设定值作为ESC控制器的输入,采用COP作为系统性能的输出指标,即极值搜索控制的反馈信号。通过搭建空气源跨临界CO_2热泵热水器的动态模型仿真平台,针对恒定工况,变环境温度条件和实时温度条件分别进行了模拟仿真。仿真结果表明,ESC可以搜索恒定或者系统边界变化时最佳的系统输入值,ESC控制的最优排气压力稳态误差在1.0%以内,与基于模型的控制结果相比,最优排气压力的控制偏差也在5%以内,验证了ESC控制策略的可行性和准确性。

Extremum Seeking Control（ ESC） is a class of self-optimizing control strategy that can search for the unknown or slowly varying optimum input with respect to certain performance index,which is effectively a dynamic realization of the gradient search based on a dither-demodulation scheme. For an air-source transcritical CO_2heat-pump water heater,the discharge pressure setpoint is taken as the input to the ESC controller,while the system COP is taken as the performance index,i. e. the feedback signal for the extremum seeking process. A Modelica based dynamic simulation model is developed to perform the simulation study. Simulations are conducted for several scenarios： a fixed operation condition,change of ambient condition and real time varying ambient temperature conditions. Simulation results show that ESC is able to search both fixed and slowly varying optimum. The steady-state error of optimal discharge pressure is less than 1. 0%. Compared to the optimum obtained by model based methods,the optimal discharge pressure deviations are less than 5%.The feasibility and accuracy of ESC control strategy are verified.