Study On Active Disturbance Rejection Control Theory For Marine Diesel Engine Speed Control Technique

Diesel engine is widely used as propeller prime mover and power generation equipment due to its outstanding advantages of high thermal efficiency,wide power range,excellent mobility,safety and reliability.Due to the complex structure,changeable operating environment,wide range of working conditions,and the operation includes complex physical and chemical processes such as fuel injection,oil-gas mixing,combustion,heat transferring and working,the speed control of marine diesel engine has strong nonlinearity,time variability and easy to be disturbed,which makes it harder to design proper engine speed controller.The effect of speed control not only affects the economy,power and emission performance of diesel engine,but also relates to the safety and reliability of diesel engine.Once the speed control is failed,it is possible even cause a major accident of machine destruction and human death.As a result,closed-loop speed control under all working conditions is usually necessary for marine engine.Conventional PID has some defects,such as small adaptive range of control parameters,weak anti-interference ability,difficult parameter setting etc.The modern control theory mainly depends on the mathematical model of the control object.Limited to the complexity of diesel engine,it is difficult to establish an accurate model under all working conditions under various disturbances.In the application of diesel engine speed control,it is faced with practical problems such as model parameter uncertainty,unmodeled dynamics and robustness.The Active Disturbance Rejection Control（ADRC）theory has the salient characteristics of independent of the mathematical model of the controlled object,strong anti-interference ability and simple control parameter setting,which makes it a proper choice for marine engine speed control.Hence,it is very necessary to carry out the design and research of marine diesel engine speed control strategy with stronger adaptability and robustness under the consideration of the characteristics of diesel engine speed control.The main research contents of this paper are as follows:（1）A marine diesel engine speed control test system is built.According to the characteristics of discontinuous work and cyclic speed fluctuation of diesel engine,based on the Mean Value Engine Model（MVEM）,a cylinder-by-cylinder based MVEM of high-speed diesel engine which can reflect the discontinuous torque generation process and cyclic speed fluctuation in diesel engine is established.In order to verify that the designed controller has the ability of parameter transplantation between different engine types,a low-speed two-stroke diesel engine model is built.At the same time,in order to further verify the performance of the designed speed control strategy,an embedded ADRC controller is developed based on automatic code generation technology,and a semi-physical simulation platform which can be compatible to high-speed and low-speed diesel engine is set up,and a diesel engine test-bed is built as well.（2）Time domain based ADRC and its parameter design method is studied.Based on the equivalence analysis between the bandwidth ADRC and PID,the distribution law of the zero point of the equivalent PID in the complex plane is studied,and the selection method of the ratio of observation bandwidth to control bandwidth is determined.The parameter design method of ADRC based on the recovery time of step disturbance is studied,and the influence of parameters in ADRC on the performance of closed-loop control system is studied by parameter root locus method.The gain of three common Extended State Observers（ESO）is compared by using the frequency domain analysis method,and the choice of the gain parameters of the ESO in the speed control of marine diesel engine is determined.To realize the quick transfer of control parameters between multiple types marine engine speed controllers,the existing time-scale ADRC is improved,and the time-scale and critical gain parameter b₀ are unbound to realize the telescopic transformation of control parameters.The simulation results show that compared with the traditional method,the designed time-scale based ADRC not only has better robustness and stronger anti-disturbance ability,but also meets with the requirements that different settling time is necessary for different control object,which set a base for getting different settling time for different working conditions and engine types in marine engine speed control.（3）CA-ADRC controller is designed.In order to adapt to the characteristics of large-scale variation of speed and intermittent pulsation of marine diesel engine,the bandwidth parameter design method based on the settling time of step disturbance process in time domain is extended to the crank angle domain,the control bandwidth and observation bandwidth in crank angle domain are redefined,and the design of bandwidth parameter in crank angle domain is completed.The problem of how to obtain the critical gain parameter b₀is studied and extended to the crank angle domain.At the same time,the improved time-scale method is extended to the crank angle domain,and the angle-scale is redefined in the crank angle domain as well.Through the telescopic transformation of the angle-scale in the crank angle domain,the parameter tuning between the controllers of multi-type diesel engines is realized.The advantages of the designed CA-ADRC are systematically analyzed,and its adaptive essence in marine diesel engine speed control is revealed.（4）CA-ADRC controller is verified by experimental tests.Firstly,a comprehensive performance test is carried out on the designed CA-ADRC using the semi-physical hardware in the loop simulation platform.The test shows that compared with the time domain ADRC,the CA-ADRC has excellent speed control effect under all working conditions.Under steady-state conditions,the steady-state fluctuation rate of speed can be reduced by 41.9%at most,and the speed overshoot can be reduced by 8.7%under sudden load,the recovery time can be shortened by 8.3%at most,and for different diesel engine models,the transferring of control parameters can be completed only through the telescopic transformation of crank angle scale and the adjustment of b₀,so as to realize the rapid parameter setting between different engine types.Finally,the typical working condition test is carried out on the diesel engine bench.The test results illustrate that when the speed is 1200 r/min,the speed control performance of CA-ADRC and PID controller is adjusted to be the same.After the speed increases to 1600 r/min,compared with PID controller,the steady-state fluctuation rate of speed of CA-ADRC is reduced by 31.6%,when the load changes suddenly,the overshoot is reduced by 17.4%and the recovery time is reduced by 87.5%in the CA-ADRC controller.With the same control parameters,during the acceleration/deceleration process under low speed,the CA-ADRC controller can reach to target speed almost without overshoot and the settling time is reduced by 0.5～1s.It is further proved that the CA-ADRC controller has strong robustness,adaptability to speed change,ability to suppress external disturbance and compatibility to both steady and dynamics in practical application.