Reasearch On Model Based Control Theory And Technology Of Crushed Natural Gas Engine

CNG (Crushed Natural Gas) is an effective alternative fuel due to its highcombustion efficiency, low emissions and minimum reconstruction to traditional SparkIngnition engines. Combined with signal processing, modern control and optimizationtechnology, ECU (Electronic Control Unit) greatly promoted comphrehensive engineperformance. Precise fuel injection and spark ignition timing control is the milestone oflow emission and fuel consumption. Although it is well developed and applied to manyengines in Europe and American, it has more technology and industry potential in China.Domestic enterprises need to carry out research on the nature of engine control schemeand ECU development platform.This paper focuses on the aspects such as engine modeling, simulation, controlalgorithm, emissions optimization, platform building and applicaitions of CNG enginecontrol. CNG engine is analyzed as a continuous and discrete hybrid, nonlinear andtime-delay system. First, a MVEM (Mean Value Engine Models) of CNG engineorienting for control and diagnostics is built and verified. Secondly, a nonlineardecoupling algorithm is applied to facilitate fast, stable speed and A/F (air/fuel) ratiocontrol. Based on Backstepping method, a nonlinear engine speed control algorithm isproposed to acquire excellent disturbance rejection performance. An A/F Ratio controlscheme aiming for high control frequency bandwidth as well as accuracy is presented,in which a DVSC (Discrete Variable Structure Control) observer is built. Finally, anintegrated ECU development platform is introduced as a virtual instrument. A prototypeECU is developed to demonstrate the efficiency and effectiveness of the platform,which is deployed according to V mode flow: modeling, simulation, calibration andoptimization. The main innovative works are as follows:(1) A new reaching law of the DVSC control is proposed, in which alternativeregulate factor is adopted. Two variable regulate factors are added in exponentialconvergence part and correlation term of amplitude. Its trajectory is convergenced byexponential law before it reaches the quasi-sliding mode area. After it enters theboundary layer, the chattering amplitude is convergenced according to exponential law.It is proved that the hyperbolic tangent function is feasible to act as the regulate factor.Furthermore, a factor estimation method is presented. A simple performance analysis iscarried out to prove that it achieves good balance of convergence speed and chatteringamplitude. (2) A MVEM of CNG egine is constructed which integrates Electronic Throttle，Turbo, Exhaust Gas Recycler, Inter-cooler, emission subsyst. This scheme overcomesthe disadvantages of commercial CNG engines models, such as expensive costs，poorinterface and hardware support. A new manifold pressure model is presented that isbased on an adiabatic assumption rather than an isothermal one. Furthermore, a newtime delay estimation method is proposed to calculate the time-delay of fuel injectionand prevent sudden deteriorations of transient A/F ratio.(3) Sevral algorithms are prsented to promote the stability of CNG engine speedand A/F ratio control. A nonlinear transformation decouple scheme is propsed, which isbased on nonlinear mean value model linearization policy through Lie derivative. Acontrol law for CNG engine speed control is derived from nonlinear model. Enginespeed error and intake air mass flow error are selected as2-D sliding surface, a virtualcontrol variable subsystem is used to prove the system stability by the Backsteppingmethod. The experiment performance data shows that it achieves the goals of goodresponse time and robustness. A DSMC observer is adopted to estimate the intake portair mass flow, intake manifold pressure and mass folw through throttle. Working withfeedforward and feedback control channel, a self-study control scheme is verified byreal-time contol logics to prove its high bandwidth and control accuracy in A/F controlthan PI control, which is widely used in ECU product.(4) An emission optimization policy based on Chaos particle swarm method isproposed. Firstly, the parameters of emission MVEM are verified and refined toappropriate value. The second round optimization is carried out on the ECU developplatform along with Virtual Calibration. The effectiveness of the optimization policy isproved through a CNG engine emission optimization procedure, which saved muchmore time and reduced expenses than traditional bench policy.(5) A CNG engine ECU develop platform is constructed to provide developmentflexibility through virtual instrument technology. A prototype ECU is developed on theplatform according to V mode workflow: modeling, simulation, hardware-in-loop test,code generation and ECU function test. Basic control logic is built to verify the realtimeperformance of engine control algorithm, which is independent of task scheduling,driver layer and hardware layer. The top layer models cover regular work conditions aswell as fundmental fault tolerant functions. Based on Matlab/Simulink, automatic Ccode generation is supported; therefore it can be easily modified to evaluate the codereliatility, resource consumption, scheme effectiveness and model sharpness.The main creative points focus on belows:1、A new mean value models of CNG engine is presented for ECU development.2、An algorithm based on DSMC Observerand linear feedback for A/F Ratio control is proposed. A decoupling method based onLie derivative precise linearization and Backstepping methods is adopted for enginespeed control.3、A virtual instrument develop platform for CNG engine ECU isconstructed. It consists of modeling, simulation, virtual calibration and codeauto-generation subsystem. A swarm particles algorithm is proposed for CNG enginevirtual calibration and emission optimization.The performance of MVEM, algorithm and development platform is showed bythe data of simulation and experiment analysis. The realtime quality, stability,roboustness and low development expense of proposed scheme make it possible to bewidely used for ECU industrialization. In the end of this paper, future technologytrends of the CNG engine control are summarized in the fields of algorithms, platformperformance and practice requirements.