Research On High Power Factor VIENNA Rectifier

With the extensive application of power electronic devices,a large number of non-liner circuits are introduced to the power system,which will cause serious pollution of reactive and harmonic and make the power quality declining.The high power factor rectifier can restrain the harmonic pollution to a great extent and improve the energy utilization.Research on new power factor correction techniques for high voltage levels is an important way to improve the performance of equipment.Among them,VIENNA rectifier has received a great deal of attention of scholars,because it is easy to achieve high power factor,high power density,high output voltage level,high reliability and low harmonic pollution.The switching devices of VIENNA rectifier only receive half of the voltage of DC side,and the bridge arm switch without dead time.In addition,it has fewer switches.In this paper,the operation principle and the modulation algorithm of VIENNA rectifier are studied.Aiming at the power grid synchronization problem of VIENNA rectifier in non-ideal conditions,Phase-Locked Loop technology is analyzed.Finally,the scheme and simulation of VIENNA rectifier are given.The contents of the thesis are shown as follows:(1)The operation principle of VIENNA rectifier is analyzed.Dual carrier SPWM and simplified three-level SVPWM modulation methods are proposed.Simplified algorithm for key points are introduced,such as sector decision for three level,two level equivalent conversion,vector time sequence and so on,which can be realized in practical project.(2)Mathematical models of VIENNA rectifier in three kinds of coordinate systems are derived.The dual closed-loop controller which is based on feed forward decoupling control strategy is designed in dq synchronous coordinate,then,the simplified transfer function is derived and the PI parameters are calculated.For SPWM and SVPWM,the neutral point potential balancing strategy are proposed respectively,which are based on third harmonic zero sequence compensation and adjusting the time of positive and negative vector.(3)Aiming at the power grid synchronization problem of VIENNA rectifier in non-ideal conditions,The SRF-PLL,DDSRF-PLL,DSOGI-FLL,EPLL are deeply studied.Meanwhile,improved algorithm based on DSOGI-FLL and combined algorithms based on EPLL are proposed.The performance and application scenarios of different PLL are analyzed from the aspect of calculation complexity,dynamic characteristic and output accuracy.(4)Considering the system architecture and performance index,the parameters of the main circuit are analyzed and calculated,and the hardware frame construction and software flow chart of the system are given.Modeling and simulating dual carrier SPWM and SVPWM method,both of the result can meet the requirements.The THD of input three-phase current is lower than 2.5%,power factor is close to 1,and output DC voltage ripple is lower than 2.5%.In contrast,the SVPWM shows better effect on neutral point potential balancing,but the modulation process is more complex.