Research On Three-Phase Four-Wire Zero-Voltage-Switching Rectifier With A Balancing Leg

Three-phase four-wire rectifier with a balancing leg is widely used in uninterruptible power supplies(UPS)due to its capability of power factor correction and balancing the DC link voltage.However,severe switching losses and reverse recovery losses of conventional hard-switching rectifiers limits the switching frequency and results in bulky filter and higher acoustic noise.Soft-switching techniques are adopted to overcome above drawbacks.Compound-actively-clamping(CAC)soft-switching technique and minimum-voltage actively-clamping(MVAC)soft-switching technique are introduced to a three-phase four-wire rectifier with a balancing leg successively.Firstly,the operational principle of the proposed CAC rectifier is analyzed.The ZVS pulse width modulation(ZVS-PWM)scheme for three-phase four-wire ZVS soft-switching rectifiers with a balancing leg is presented.The ZVS conditions of the CAC rectifier under balanced and unbalanced load are derived.The influence of the auxiliary circuit on the modulation wave of each leg in the CAC rectifier is analyzed.The voltage stress and current stress of power semiconductor devices in the CAC rectifier are presented.The design of resonant parameters of the CAC auxiliary circuit is discussed.The closed-loop control of the rectifier is designed.A lOkW CAC rectifier experiment prototype is built to verify the theory.The operational principle of the proposed MVAC rectifier is analyzed.It is proved that when the balancing inductor current is negative(ibai<0),in order to provide the ZVS condition for the main switches in the MVAC rectifier,an extra bridge short circuit stage is needed.And when ibai?0,the main switches can realize ZVS operation without the need for an extra bridge short circuit stage.The influence of the auxiliary circuit on the modulation wave of each leg in the MVAC rectifier is analyzed.The voltage stress and current stress of power semiconductor devices in the MVAC rectifier are derived.The design of resonant parameters of the MVAC auxiliary circuit is discussed.Finally,a 10kW MVAC rectifier experiment prototype is built to verify the theory.Finally,the comparison of modulation strategies,voltage and current stress of switching devices,auxiliary circuits,losses and efficiency between the two kinds of ZVS rectifiers is given.