Research On Four-bridge Arm Inverter Control System Based On Three-dimensional Space Vector Modulation

The output voltage’s symmetry of three-phase inverter is the basic requirement of power quality. The traditional three-phase three-leg inverter can output low harmonic and symmetrical voltage under symmetrical load. However, it can’t solve the output voltage’s asymmetry problem under unbalanced load. In order to solve this problem, this paper chooses a three-phase four-leg inverter to study. By adding a bridge arm, it can provide access for zero-sequence current, so the symmetrical three-phase voltage on the load-side can be achieved.In order to understand, based on the detailed description of two-dimensional space vector modulation,3D space vector modulation (3D-SVPWM) is proposed. The three-dimensional space vector modulation algorithms are compared under the abc and αβγ coordinate system. Finally, three-dimensional space vector modulation in the abc coordinate system is selected as the implementation of the simulation. The implementation algorithm is based on S function, which is simple and easy to digitize..In the closed-loop control strategy, this paper uses a widely used PI controller.Combined with symmetrical component method, dq transformation and the Instantaneous Control Strategy of Voltage - Current Decoupling, The amount of traffic will become a direct flow. The negative sequence and zero sequence voltage of the load are adjusted to zero under DC, and the positive sequence voltage is adjusted to the reference value. After the PI adjustment, the DC is transformed into AC from dq inverse transformation. The three-phase modulation voltage of the three-dimensional space vector modulation is obtained by the synthesis of the sequence components.Finally, the principle of setting the PI parameters is given and the PI controller is improved, and the repetitive controller is designed by combining PI control with repetitive control.In this paper,Matlab/Simulink is chosen as the software to complete the open-loop and closed-loop simulation of four-leg inverter under different loads. The results show that the three-phase symmetrical load voltage can be obtained when the inverter is equipped with unbalanced load according to the designed scheme proposed in this paper.