| General PWM rectifiers need the sensors for data acquisition, but it will increase the size of the rectifier, reduce the product market competitiveness. What’s more, the sensor will cause loss of data, high failure rate and it may affect the stability of the system. The system needs high stability in poor environment, and therefore this thesis puts forward three-phase voltage-type PWM rectifiers control system without AC voltage sensors.Firstly, through the study of the three-phase PWM rectifier topology, the thesis determines the main circuit topology of three-phase voltage-type PWM rectifier without AC voltage sensor and then deduces the system mathematical model in the three-phase static (a,b,c) coordinates and two-phase rotating (d,q) coordinates. Finally, this thesis constructs the virtual flux of grid, learning from the flux observer of AC motor and implements the double closed-loop control strategy of voltage outer loop and current inner loop with the combination of virtual flux and SVPWM (space voltage vector pulse-width modulation).Complete the design of the three-phase voltage-type PWM rectifier control system without AC voltage sensors based on the theoretical analysis, including the hardware and software design. The hardware design includes the design of the AC-side inductance, the DC-side capacitor, the selection of power switch and the master chip in the circuit; the software design includes the observation of phase angle of grid voltage, the reconstruction of grid voltage and the implementation of SVPWM.Under MATLAB/Simulink, the thesis builds the simulation model for the three-phase voltage-type PWM rectifier without AC voltage sensors. At the same time, the thesis shows the simulation results and analyzes them.Through the research of the simulation waveforms, it proves that the three-phase voltage-type PWM rectifiers control system without AC voltage sensors has the higher power factor, stable DC voltage and better steady-state and dynamic performance. |
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