Research On Modeling And Speed Control Method Of The Diesel Generator Set

The speed control quality of the diesel is directly responsible for the AC power qualitygenerated by the diesel generator set (DGS). For the sake of improving the performance ofthe speed control, the work mentioned as follows has been carried out in this thesis.(1) A Hardware-In-the-Loop Simulation System (HILSS) of the DGS, which can beused as a platform to conduct academic research on the speed control of DGS, is developedin this thesis. In the HILSS of DGS, the physical DGS is replaced with its mathematicalmodel, which can be regard as a virtual DGS, running in a PC. However, the electricactuator and electronic speed governor are physically installed, connected with the virtualDGS via sensors and the data acquisition card, working in with the virtual DGS toimplement the Hardware-In-the-Loop simulation. Aiming at enhancing the simulationaccuracy, an AC servomotor system is employed to imitate the output speed of the virtualDGS. Then, the speed feedback of the servomotor is transmitted to the electronic speedgovernor to implement closed-loop control of speed. It can be seen that the responses of thetwo speed control loops in the physical DGS and the HILSS of the DGS are quiet similar.(2) Based on the input-output measurements of a physical DGS, a nonlinear model,which describes the relationship between the speed of diesel and the rack displacement ofelectric actuator as well as the load exerted on the DGS, is obtained by means of NARX(Nonlinear AutoRegressive with eXogenous inputs) modeling theory in this thesis. TheNARX model reduces a lot of the computational overhead and runs very fast because of itssimple polynomial expansion model structure. The results of loading and unloadingexperiment of the HILSS indicate that the NARX model can well reproduce both the staticand dynamic characters of physical DGS accurately.(3) A new digital speed governor is designed in this thesis. Firstly, the details ofhardware design of the digital speed governor is discussed. What’s more, a performance testis conducted to assess the quality of the hardware design. The test results show that thehardware functions well and meets all expectations. With respect to the embedded controlsoftware design, the essentials of core functions are fully illustrated. An accuracy test tofrequency measurement and A/D conversation is conducted to access their performances.Moreover, for purpose of improving the speed control indexes, a modified PID speedcontroller which consists of a piecewise PI controller and an incomplete differentiation PDcontroller is designed. The simulation results of the modified PID controller show that the modified PID controller can achieve a much improved control performance than a regularPID controller.