Research On Control Technique Of Three-Phase Three-Wire Inverter Under Unbalance Output Voltage

With the increase of users' requirements to the quality of power supply, the power quality has been gradually become the primary selection criteria of electrical equipment industries. The inverter link based on three-phase inverter power supply is chosen as the research object in this dissertation, the overall designing of the inverter control system is carried out, and the optimization of output voltage quality is conducted through the improvement of control algorithms.After the analysis of multiple three phase inverter main circuit topologies, the three-phase and three-wire inverter is chosen as the main circuit topology of this dissertation. The inverter mathematical models under different coordinate systems are established, the coupling relationship of inverter current and voltage under rotating coordinate system is analyzed. The decoupling process is conducted, when the inverter is with unbalance loads, the output three phase unbalance voltage can be decomposed into positive sequence, negative sequence and zero sequence component, the three wire inverter is capable of depressing the zero sequence component within the unbalance voltage effectively. The negative sequence acts as the periodical harmonic component, the repetitive control can entirely eliminate this periodical disturbance, but its response is relatively low, and the conventional current and voltage double closed-loops has a quick response but its restrain on the periodical disturbance is relatively low, thus the advantages of both closed loops are combined in this dissertation, the conventional voltage and current closed-loops are in parallel connection with repetitive control closed loop, and the parameter deigning of voltage and current closed loop and repetitive control of the system is carried out.The simulation model of double closed-loop and compound control under three-phase and three-wire inverter is set up under the SIMULINK environment.Then, the output voltage waveforms comparison analysis of inverter with unbalance load under two different control strategies is carried out.Based on the theoretical analysis and simulation verification, the software and hardware designing with TMS320F2812 as the control chip is carried out. The experiments when inverter is with unbalance load are conducted, the experimental results verifies validity and feasibility of the proposed compound control strategy on the three phase inverter.