A 400Hz Three-Phase Four-Wire High Power Factor Rectifier Based On DQ Transformation

Conventional rectifiers usually utilize uncontrolled rectifiers or phase-controlled rectifiers, in which the input currents have a lot of harmonics. These harmonics not only affect the operation of sensitive equipments as big pollutions in the power grids, but also cause current and voltage fluctuations which decrease the reliability of the system. So power factor correction has gotten more and more attention. Pulse width modulation (PWM) is flourishing because of its advantages, and has become a trend of research and development in the recent past.The three-phase systems are more preferred in the existing medium and large power applications. Three-phase four-wire systems are widely used because of its advantages in lightning protection and insulation. So, a 400Hz three-phase four-wire PWM rectifier is studied in this paper.Due to excellent control characteristics, adjustable power factor and bidirectional power flow, three-phase six-switch rectifiers are chosen as the main circuit topology. The switching frequency is not fixed in hysteresis control method. So it is hard to design the system. The direct current control has the static error problems because of the finite gain for PI compensator in AC. This problem is more serious when the fundamental frequency is 400Hz. So dq0 rotating coordinate transformation is used to transform the input currents from abc frame to dq0 frame, in which the input current reference is DC reference. Zero static error control in the amplitude and phase of the input currents can be achieved due to the infinite DC gain in PI compensator. The voltages of the dc-link capacitors are balanced by modulating the reference of 0-axis in the rotating reference frame.The mathematic model of three-phase four-wire six-switch rectifier is presented with the control strategy mentioned above. The principle to design the main circuit and control circuits is also discussed in this paper. The simulation results show that the control method can achieve the desired results. At last, a 3kw prototype is applied in practice. The voltages of the dc-link capacitors are both equal to 200V. The three-phase input currents are in phase with their respective line voltages in the whole load range. The experiment results verify the validity of the control method well.