| With the development of social science and technology,power electronics has been widely used in various fields.The power topology of multi-stage DC-DC converter is increasingly complex.When a source converter cascades a load converter,the load converter under the closed-loop control can be regarded as a constant power load,At the same time,in order to reduce the harmonic pollution,power factor correction(PFC)has become an essential condition.In the design of control algorithm,the traditional PI control and a considerable number of nonlinear control methods can be applied to PFC,but there are obvious overshoot and long dynamic process adjustment time.The feedback linearization control method has the advantages of simple design,retaining the original information of the system and lower requirements for the processor in PFC application.However,for the converter system with constant power load,the control algorithm can not be calculated normally due to the loss of some parameters due to the influence of the operating characteristics of MOS transistor of constant power load It works.In this paper,buck converter is used as constant power load,boost converter is used as front stage circuit,constant voltage output is taken as important index,duty cycle algorithm derived from feedback linearization method is used as control strategy.Then,the problem that duty cycle can not be calculated normally by control algorithm due to current discontinuity under constant power load is analyzed in detail.The simulation results show that the output voltage ripple of the system has a certain corresponding relationship with the load power.Using this relationship and combining with the concept of mathematical fitting,the fitting function of the two is obtained,and the parameter variables of the output current in the control algorithm are obtained by calculation.The PSIM simulation shows that the improved control strategy can calculate normally,which overcomes the disadvantage of discontinuous output current in the original control algorithm.At the same time,when the load power has large or small jump,the improved control algorithm can quickly predict the power change,and then make fine adjustment,so that the system can achieve constant voltage output and have good power factor correction characteristics. |
