| Three-phase three-level VIENNA rectifier is widely used because of its high power factor,low voltage stress of switch tube,and no dead-zone time setting.In this paper,the three-phase six switch rectifier is studied.Firstly,the working modes of the rectifier under different switching states with the same input current polarity are introduced,and the mathematical models under three different coordinate systems are established to facilitate the design of the controller.To achieve the control target of VIENNA rectifier,double closedloop control is used.The inner loop is a current loop,and its control goal is to make the threephase AC input current sinusoidal and in phase with the three-phase grid voltage,to achieve unit power factor operation.The current inner loop analyses PI control strategy based on feed forward decoupling and Finite Control Set Model Predictive Control with Fixed Switching Frequency(FCS-MPC-FSF)strategy.Compared with the former,the latter has the advantages of simple algorithm and no need to adjust complex control parameters.The simulation results show that the FCS-MPC-FSF strategy has better input current sinusoidal degree and lower total harmonic distortion(THD)of input current than the feedforward decoupled PI control strategy.For the outer voltage loop,its control goal is to achieve a stable output of DC voltage.Due to the strong coupling and nonlinear characteristics of the rectifier itself,when the traditional PI control is used for the voltage outer loop control,the control parameter setting is complex and fixed PI parameters will lead to large fluctuations in the DC output voltage and long adjustment time when the system has dynamic changes such as sudden load changes.Therefore,the voltage outer loop uses a fuzzy immune-single neuron adaptive PI control strategy,which improves the dynamic performance of the system by changing the PI parameters following the changes of the environment according to the self-learning and self-adaptive capabilities of a single neuron.At the same time,combining with the fuzzy immune algorithm,the neuron scale factor K is selftuned online,and the K value is adjusted in real-time to further improve the system’s steady-state and dynamic performance.Through simulation analysis,it is proved that this control strategy has smaller DC output voltage overshoot than traditional PI control strategy.At the same time,dynamic changes such as load mutation,power network voltage fluctuation,and DC given voltage mutation are analyzed,which verifies that this control strategy has better dynamic performance and anti-interference ability.The space vector pulse width modulation(SVPWM)of Vienna rectifier is introduced in detail and the realization method of converting the reference voltage vector into specific switching action is given.Analyzed the impact of various basic voltage vectors on the DC side capacitor voltage.Through analysis,it can be seen that the DC side midpoint potential is mainly affected by positive and negative small vectors.By introducing a balance factor to adjust its action time,the midpoint potential reaches equilibrium.Finally,the hardware circuit and software program are designed to build a 200W Vienna rectifier experimental device.The current inner loop uses FCS-MPC-FSF strategy,and the voltage outer loop uses PI control.The influence of different PI control parameters on the dynamic response process of the DC side output voltage was studied when the voltage outer loop adopts traditional PI control.A set of more suitable control parameters was selected,and the experimental waveforms of the system steady-state under these parameter conditions were given.The stable operation of Vienna rectifier is realized through the voltage and current double closed loop control,and the correctness of the design of the hardware and software of the system is verified. |
