Research on Modeling and Deep Peak Regulation Control of a Combined Heat and Power Unit

This paper firstly proposes a nonlinear dynamic model of a combined heat and power (CHP) unit with absorption heat pump (AHP) and bypass systems, the unknown parameters are determined based on design data and perturbation test. Simulation results show that the model can reveal the couplings of AHP and bypass systems to the CHP unit, and provide model support for controller design. On the basis of the model, this paper further proposes a deep peak regulation control strategy, in which, the generalized predictive control algorithm with feedforward-feedback structure is adopted to fundamentally solve the control problems of large delay and inertia on the boiler side, and overcome known disturbances on the turbine side; the ratio of the first stage pressure to the exhaust pressure from high pressure cylinder is adopted to control the high pressure bypass. The deep peak regulation process is divided into two stages: 1) CHP and AHP are used for heating when their heating capacity can meet the heat load requirements of residents, 2) as the unit load is further reduced, bypass mode is activated for heating when the steam flow entering the low pressure cylinder is lower than its cooling flow. Simulation results show that the strategy can meet the heat load requirements of residents and ensure the safe and stable operation of the turbine when the unit is in deep peak regulation condition.