Research On The Control Of Single-phase Boost PFC AC/DC Converters

With the rapid development of power electronic technology,the harmonic problems caused by various power equipment can’t be ignored.As a front-end ac/dc converter,power factor correction(PFC)circuit is widely applied in industrial electronics and other fields,and its related topology innovation and control algorithm have also been explored much.The single-phase boost PFC circuit has become one of the most popular topologies in medium and high power applications,which is composed of a diode bridge rectifier and a boost chopper circuit.The cascaded PI control system of the single-phase boost PFC converter is made up with inner current loop and outer voltage loop.The PI current loop controls the inductor current to be sinusoidal and in phase with the input voltage,while the PI voltage loop realizes ac-dc energy conversion and stabilizes output voltage.Thanks to the difference of bandwidth,two controllers can be designed separately.The frequency characteristics of the two control loops are derived based on the mathematical model of the converter in continuous conduction mode(CCM),and the corresponding control parameters are determined in this paper.Then,the simulation model of cascaded PI control system is built to verify the feasibility and control performance of PI algorithm.Finally,the experimental platform of 1k W single-phase boost PFC converter is set up,and the effectiveness of the PI control method is verified by experiments under different conditions.Considering that PI control has disadvantages such as complex parameter adjustment,sensitive to changes with operation mode and parameters,slow dynamic response,in order to improve the robustness and rapidity of the control system,a cascaded model-free predictive control(MFPC)method is proposed in this paper.The ultra-local models with on-line identification unify the dynamic model of the converter under CCM and discontinuous conduction mode(DCM),and accurately estimates the uncertainties and the internal and external disturbances of the system in real time.The model-free predictive controllers are designed respectively according to the ultra-local models.Based on the classical control theory,the stability of the control system is analyzed,and the corresponding rules about parameter adjustment are given.The control performance and robustness of the converter in the full power range is obviously improved with the cascaded MFPC system proven by simulation and experimental results.Aiming to further improve the robustness and rapidity of the converter,the cascade-free control for single-phase boost PFC converters is proposed complying with predictive control.Based on the established unified ultra-local model,the optimal duty cycle is calculated by designing a cost function to achieve two objectives of voltage and current control.The characteristic of the proposed control scheme is the load current estimator based on algebraic identification.The designed load current estimator is used to generate the reference current value,and the voltage control loop in the cascaded structure is removed which enhances the dynamic performance of the system by a single closed loop control.In addition,the compensation cost function is also designed,and the compensation duty cycle acts on the control system together with the optimal duty cycle to improve the control accuracy of the output voltage.Finally,the stability of cascade-free predictive control system is also analyzed and verified based on Lyapunov stability theorem.Simulation and experimental results show the technical advantages of enhancing the dynamic performance and robustness with the proposed cascaded-free control method.