| The marine diesel engine adopts the closed-loop control of the whole range speed.Because of the working characteristics of the diesel engine,the speed control has the peculiarity such as typical nonlinearity,time-varying,uncertainty and vulnerable to interference.Moreover,the multi adjustable mechanism design of modern marine diesel engine makes the control coupling between systems more complex.Because of poor adaptability and robustness,the conventional speed control method has been difficult to meet the control performance requirements under all working conditions,and is prone to cause abnormal operation and malfunction of diesel engines due to the failure of control parameters.Therefore,according to the characteristics and requirements of diesel engine speed control system,based on the sliding mode variable structure control theory,this paper carries out the design of speed control strategy with stronger adaptability and robustness,so as to improve the speed control performance of marine diesel engine in all working conditions and all weather.In order to explore a more suitable sliding mode variable structure speed control strategy,the sliding mode variable structure controllers for diesel engine speed are designed from the perspective of finite time stability and engineering practice,and the problems of chattering and over-dependence on accurate mathematical model of the controlled system were solved.In addition,a simulation model which is more suitable for the actual operation characteristics of the diesel engine is designed,and the electronic control platform of the sliding mode variable structure control strategy is developed.Through the simulation and engine bench test,the speed closed-loop control effect of the sliding mode variable structure control method is comprehensively evaluated.The main research is state as follows:According to the peculiarity of the diesel engine which the cylinder output power is discontinuous and the fuel injection quantity changes once per cylinder working cycle,based on the mean value model of the diesel engine,a cylinder-by-cylinder mean value model is designed by introducing the cylinder pressure model,which can reflect the real speed cycle fluctuation of the diesel engine.The model is used to analyze and evaluate the performance of the speed control algorithm more accurately.In addition,a simplified continuous design model and a variable step discrete design model containing the main characteristics of the diesel engine are extracted by combining the characteristics of the mean value model and the mean value model of each cylinder,which are used for the detailed design of the sliding mode controller.Based on the terminal sliding mode control theory with finite-time convergence,the speed control strategy of diesel engine is studied.In order to solve the problem which the control performance depends on the accurate mathematical model of the diesel engine,a disturbance observer with finite time stability is designed based on the continuous design model to estimate the integrated disturbance including the model mismatch part and the unknown disturbance.A disturbance observer-based terminal sliding mode controller is proposed based on the fast terminal sliding mode variables by combining the continuous design model and the synthetic disturbance estimate.The stability analysis of the designed disturbance observer and terminal sliding mode controller is carried out,and it is proved that the control method can realize the actual finite-time stability control of the first-order continuous system.The simulation results of diesel engine mean value model control show that the terminal sliding mode controller has stronger robustness than PID control for continuous system control.Based on the discrete sliding mode control theory,the speed control strategy of diesel engine is studied.A discrete sliding mode disturbance observer based on second-order sliding mode control is proposed to estimate the synthesized disturbance for the discontinuous operation of diesel engine,combined with variable step discrete design model.According to the characteristics and requirements of diesel engine speed control,a discrete sliding mode controller based on disturbance observer is designed by analyzing the discrete sliding mode control method and selecting the discrete linear sliding mode variables and the fast power reaching law,and the monotonically decreasing region,the absolute convergence region and the quasi-sliding mode region are analyzed.The simulation results show that the designed discrete sliding mode controller can achieve the same control performance as the terminal sliding mode controller without chattering,and has better control effect and robustness than PID controller under various transient conditions,which is more suitable for the actual speed control of diesel engine.Design of sliding mode variable structure control strategy test platform.In order to explore the control performance of the designed discrete sliding mode controller on the actual diesel engine,a sliding mode variable structure control strategy based test platform is designed.Based on the high performance microprocessor,the hardware of the platform is designed,including the speed conditioning circuit with strong anti-interference ability and the three-stage high-low pressure injector driving circuit.At the same time,the platform software with the functions of condition management,phase identification,rail pressure control and sliding mode variable structure speed control is designed by using the idea of hierarchical and modular design.The test results show that the software and hardware of the platform meet the control requirements of diesel engine bench test.Based on the designed test platform,the diesel engine bench comprehensive evaluation test of sliding mode control strategy is carried out.The discrete design model parameters of the controlled diesel engine were calculated through the analysis of the diesel engine bench data and system identification,and the parameters of the disturbance observer and sliding mode controller were calibrated by optimization,and the diesel engine starting,acceleration/deceleration,steady-state and load mutation tests were completed.The test results show that the discrete sliding mode controller has better control performance than PID control in all working conditions: there is no overshoot in the starting process;The speed overshoot decreased by 69.9% on average under acceleration/deceleration conditions;The overshoot and the stability time during sudden loading decreased by 52.9% and 47.2%respectively;There is no buffeting under each steady-state condition,and the speed fluctuation rate is less than 0.59%,which meets the three-level accuracy requirements of marine main engine. |
