Realization Of Low-voltage And High-current Rectifier System Based On Nonlinear Feed-forward PID Control

The commonly recruited low-voltage and high-current integrated synchronous generator has the characteristics of high-power density,small size,and good energy saving in shipping and energy industry.Rectifier module is the dominant module of DC output system of this generator.It is a nonlinear time-varying system which is susceptible to parametric changes and external disturbances during operation.Therefore,rectifier control strategies have become the focus of researches in various fields.First,a novel integrated synchronous generator which has only a half-turn coil in each slot is researched in this paper.The operating principle is illustrated from the aspects of body structure and driving modes.The PWM rectifier topology employed by the rectifier module in the integrated DC output system is explored.The mathematical model of the rectifier is built into the three-phase static coordinate system based on the equivalent circuit diagram.By exploring system model in various switching modes,the relationship between the switching function and the output voltage is determined.The mathematical model of the rectifier system built into the three-phase static coordinate system is transformed into a two-phase rotating coordinate system via coordinate transformation,which simplifies the control system design.Next,a double closed-loop control system based on nonlinear feed-forward PID algorithm is proposed in this paper for the nonlinear characteristics of the lowvoltage and high-current rectifier system.Among them,the nonlinear PID control adopts the control idea of "disturbance feed-forward compensation" to realize reasonable refinement of disturbance information.At the same time,disturbance information which is compensated to the control system achieves disturbance cancellation.However,the speed of tracking the input signal is slow for nonlinear systems.The fundamental idea of the feed-forward control algorithm is studied in depth,that is introduced into the nonlinear PID algorithm.By the fusion of open-loop and closed-loop,the optimized control algorithm greatly enhanced the adaptability and robustness and makes sure the stable output of the low-voltage and high-current DC output system.The nonlinear feed-forward PID algorithm theory is demonstrated detailedly,and the mathematical model of a nonlinear tracking differentiator is established.The mathematical model and function description of a nonlinear combination are gotten according to the structure block diagram of the control system.The parameters setting methods of the nonlinear tracking differentiator and the nonlinear combination are analyzed.The double closed-loop control system is reconstructed based on nonlinear feed-forward PID algorithm.At last,the simulation models of the low-voltage and high-current rectifier module and control system are established with Matlab/Simulink software to make sure the effectiveness of this nonlinear feed-forward PID algorithm for low-voltage and high-current rectifier system.As a result,this rectifier system which is controlled by nonlinear feed-forward PID algorithm was found to own good dynamic response characteristics,anti-interference ability and robustness.The system can continue to operate stably under the unit power factor.A test platform for the DC output system in a low-voltage and high-current integrated synchronous generator is established,and the nonlinear feed-forward PID algorithm is recruited in the rectifier module.The experimental results are basically in line with the simulation,demonstrating the feasibility of this control algorithm in practical applications.