Research On Harmonic Suppression Methods Of Buck Converter

With the dramatically improvement of contemporary appliance, a daily increasing of high-quality electric source had been established. Many switching power requires low high frequency noise and ripple and the output ripple is a very important parameter for them.As a normal choice, passive filter has always been used in PWM DC/DC converter. In this paper based on the analysis of the Buck converter, the output voltage ripple was analysised and the two LC filters and filter effects on the converter stability were studied in depth.Firstly, the ripple characteristics of output voltage are researched for the PWM Buck converter.The output voltage ripple is mainly from five aspects, whose main aspects are the input low-frequency ripple and the switching frequency ripple. The former mainly caused by the former rectifier output voltage and the latter is caused by the Buck converter itself. The amplitude and phase of harmonics from output voltage caused by 6-pulse rectifier are analyzed, the content of harmonic voltage are calculated.Using the double Fourier analysis, derived Buck converter output voltage modulation harmonics.Secondly, Using state-space averaging method to establish a non-ideal conditions and ideal small signal model of Buck converter. Special derive the input and output impedance of the Buck converter in the open and closed loop and analysis Bode plot. According to the project method study the way to design the voltage loop and the voltage and current loop of the Buck converter. Through bode graph, simulation and experimental test the feasibility of the PI parameter configuration. And also compare the filtering effect of single-stage LC filter and second-stage LC filter under the close loop condition.With the analysis of the Buck converter, the factors which affect the ripple are found out using the simulation in Matlab. From four changing aspects which are capacitor change, load change, inductor change, the duty cycle change, analyses the ripple change. And also compare the filtering effect of single-stage LC filter and second-stage LC filter under the open loop condition.Finally, Finally, the analysis of the load converter characteristics which is the negative impedance to the cascaded converters and the stability problems caused by this characteristic are made. Joining the intermediate filter is the better method to solve the stability problem, which are to join a large capacitor, to plus the load resistance, to plus RLC filter.Simulation results show that, if jioning the capacitance the system bus speed of response will slow down, adding resistance will waste a lot of power, the effective way is to join RLC filter, the results show this approach feasible. In order to verify the actual operation of the system, the hardware system and software system with TI's TMS320F28335 DSP chip for the control of Buck converter are designed, and the experimental platform are built in this paper. The actual system debugging is carried out. The results proved that the theory expounded and the system design are correct in this paper.