The Algorithms Based On Internal Model Principle For Single-Phase PWM Converter Control

Single-phase two-level pluse width modulation (PWM) converter has been widely used in the railway, clean energy, chemical and metallurgical application. As the grid-side converter in the electric traction system of high-speed railway, single-phase pulse converter is coupling with traction power supply network by traction transformer. Compared with the phase-controlled thyoristor converters and un-controlled diode converters, PWM converters can achieve an more sinousiodal current with lower harmonic distoration. But there are a certain current harmonic distoration, which is influenced by all kinds of factors, the line current harmonic distortion of single-phase PWM rectifier can pollute the traction power supply system, and worsen its power quality. Moreover, there is no the LC resonant circuit in DC-link of converter, in order to reach the demand of energy conservation and environmental protection. However, it will bring an even greater challenge to the current harmonic suppression control of converters.The following work in this paper was carried out against above-mentioned background:Firstly, the current harmonics generation mechanism in single-phase PWM converter was analyzed. Specifically,the influences of the DC-link voltage ripple, dead-time and forward voltage drops, harmonic distortion in grid-voltage on line current waveform were analyzed to obtain the distribution characteristics of current harmonic. The waveform correction techniques based on principles of internal model were analyzed in end of the part.Secondly, on the basis of the principles of internal model, the traditional dual-closed loop control scheme with proportional integral (PI) controller was carried out, the reason that why the traditional control scheme fails to achieve zero steady-state error control and has a poor performance to harmonic suppression is analyzed. And then, the dual-closed loop harmonic suppression algorithm was discussed, which consists of N times notch filter (NF) in the outer voltage loop, and proportional resonant (PR) controller for harmonic compensation in the inner current loop.The PR controller in the inner loop has the advantage of achieving zero steady-state error control for the specified frequency current signal, and has a better harmonic suppression performance whether the traction network voltage harmonic is distorted or not.Thirdly, the physical model and mathematical model of repetitive control based on the internal model principle were analyzed, as well as the relationship between resonant control and repetitive control. Considering the current harmonics distribution characteristics in single-phase PWM converter, an odd-harmonic repetitive control scheme which needed less data memory than a conventional repetitive controller was adopted in the inner current loop. And then, system stability, error convergence, parameter designing and steady-state error were also discussed. A hybrid control structure incorporating repetitive control and deadbeat predictive control was proposed. Combination of these two complementary strategies presented an excellent dynamic response as well as perfect steady performance. Benefited from the zero steady-state tracking error to reference current and the increased converter input impedance, the line current harmonics caused by both PWM modulation and grid voltage harmonics were suppressed.Finally, a hardware in the loop experiment platform with RT-LAB simulator and TMS320F28335 controller was set up.The validity and effectiveness of the mentioned control schemes in this paper were compared and verified by the simulation and experiment results.