Research On Vienna Rectifier Under Unbalanced Power Grid

With the rapid development of power electronic technology,it has become a hot academic topic to research a PWM rectifier with high power factor and low harmonic input current has become a hot academic topic.There is growing concern about Vienna rectifier for its advantages of low harmonic content,simple structure,few driving circuits,low voltage stress of switching devices,high power density,and without any consideration of dead-zone.However,the actual power grid is in unbalanced conditions due to the power grid voltage amplitude and phase offset.Moreover the traditional control strategy under balanced condition will cause the increase of non-characteristic harmonics.In order to study the modulation method and control strategy of the Vienna rectifier under the unbalanced conditions of the power grid,the contributions of this paper are shown as follows:(1)The topological structure and equivalent circuit of Vienna rectifier are analyzed,and the current flow path and working mode under different working conditions are analyzed in detail as well.On this basis,the mathematical models under balanced and unbalanced conditions of Vienna rectifier are established,and the corresponding matrix equations and equivalent circuit are derived(2)For the inherent problems of neutral point potential imbalance and common mode noise in three-level converter,this paper researches the influence of each space vector on the neutral point potential and the corresponding magnitude of common mode voltage,Furthermore,the advantages and disadvantages are compared theoretically in respect of SVPWM and LMZVM modulation on the neutral point potential balance and common mode noise suppression in the DC side of Vienna rectifier.Therefore,on the basis of LMZVM modulation method,this paper uses six kinds of small vectors with the lowest common mode voltage to control the neutral point potential balance.Taking one sector as an example,the calculation method of duty cycle and the realization method of carrier modulation are shown in detail.The simulation results show that the modulation method can reduce the common mode voltage while controlling the neutral point potential balance(3)Based on the analysis of the power of the Vienna rectifier under instantaneous power,the influence of the unbalanced conditions of the power grid on the operation of the Vienna rectifier is obtained.In this paper,a reference current calculation method based on two-phase stationary αβ coordinate system is proposed,without the use of positive and negative component extraction.The voltage component with a phase angle delay of 90°obtained by the second-order generalized integrator replaces the positive and negative sequence component extraction in the traditional unbalanced control.The control strategy of Vienna rectifier based on proportional resonance control is designed,and the reliability of the control strategy under the condition of voltage imbalance is verified by building simulation model.Finally,the device parameter design and hardware circuit design of the Vienna rectifier are completed,and the real-time simulation system dSPACE is used as the control module to debug the hardware and software of the experimental platform...