Study on Sliding Mode Variable Structure Control in Nonlinear Coupled Systems of Diesel Engines

Abstract

In order to improve the injection quality and the performance of engine common rail system, on the basis of the measured data in bench tests, quadratic polynomial fitting method is adopted to obtain the differential equations of pressure and speed system for high pressure common rail of diesel engine. This mathematical model belongs to multi-input nonlinear systems of mutually coupled pressure and speed of common rail diesel engine. First, the nonlinear state transformation is performed using flow computation, obtaining the standard state space equations of two decoupled single input. Then, sliding mode variable structure (SMVS) control theory is used to design two sliding mode controllers for single input nonlinear systems, in order to realize the control over the common rail pressure and diesel engine speed. MATLAB/Simulink software simulation platform is then utilized to simulate the designed nonlinear high pressure common rail control system. Finally, the real time simulation of common rail pressure is conducted on a computer through prototype code conversion and Digital Signal Processor (DSP) embedding technology. Results show that the sliding mode variable structure control algorithm has satisfactory control performance over nonlinear systems, solving the problems of traditional Proportional Integral Differential (PID) control that the response is slow, the overshoot is large, and the robustness is weak.