Research And Implementation Of Double Boost PFC Based On Digital Control

With the wide application of power electronic devices,the harmonic pollution in power network is becoming increasingly serious.In order to reduce the harmonic pollution in power system,build the green power grid and improve energy efficiency,Factor Correction Power(PFC)technology has attracted much interest in the field of power electronics research.As a comparison to earlier analog PFC control,digital PFC control is widely used because of a series of distinguishing features,such as flexibility,reliability,easy to upgrade,and the cost is getting cheaper.In this paper,firstly,the significance,definition and research status of power factor correction are introduced,and some common topologies and control strategies are also summarized.Double Boost PFC converter is chosen as the research object of this paper,due to the specific structure of dual DC-links,the converter is commonly used for applications requiring high step-up or inverter,such as UPS systems.This paper studied the characteristics and working principle of single phase double Boost PFC,then the mathematical model of the converter is established,respectively,the digital controllers of voltage and current loop control are designed.The research emphasis of this paper is the design of current loop controller.Under variable load power,inductor current can operate in three different conduction modes,which are the continuous conduction mode(CCM),discontinuous conduction mode(DCM)and mixed conduction mode(MCM),thus different control method should be taken for each mode so as to avoid serious current distortion.This paper carries out a detailed study and deduction of each mode,the duty cycle in continuous mode is deducted from predictive current method and sliding mode control theory,and the duty cycle in discontinuous mode is obtained by adjusting the feed forward term and sampling current.Finally,a hybrid algorithm suitable for digital control is obtained,which can improve the power factor to maximum degree of full power range.The accuracy of the current loop algorithm is verified by Psim9.0 simulation.This paper also studied the current ripple character of each conduction mode,with purpose of guiding the rational choice of inductance parameters.Finally,the selection of the main circuit parameters and the program design of the PFC control algorithm are presented for a double Boost PFC prototype,which is controlled by a DSP of TMS320F28069.Experiments on the prototype show that the performance indexes of THDi and PF in various loads are all satisfied with the design objectives.