Research On Control Technique Of Three Phase-Four Legs Inverter

The same to the rectifier, the inverter is the important part of power conversion device,which is widely used in industry, aircraft power system and civil power system. However,with the development of science and technology, more and more generating equipment andelectric equipment are used in power system, and the demand of power system to the powerconverters such as capacity, security and reliability is higher than before. The theoreticalresearch of modern power electronic technology has guaranteed the demand of users.In practical applications, the inverters must have a strong loading ability when morekinds of load are used in power system, and the basic requirement of three-phase inverter isguarantee a balance output voltage. So in order to obtain the balance output, the research tothe topology and control stratagem of inverter is signality.The output voltage of traditional three-line three-phase inverters is always unbalancedwith the unbalance loads or nonlinear loads. In order to obtain the balanced output voltage inthese conditions, three-phase four-legged inverter was used. The inverter is increased a leg onthe basis of traditional three-phase inverter, and then the unbalance output voltage can becontrolled in the way of controlling the power switch of the fourth leg.In order to design the control system of the three-phase four-legged inverter withunbalance or nonlinear loads, the model of inverter was established and analyzed, andaccording to that the relationship of output voltage and the inductor current was obtained.The thesis was mainly to research the control method of three-phase four-legged inverterwith unbalance or nonlinear loads. And researchers have proposed some method, such asPWM control, SVPWM control, current tracking control, deadbeat control and sliding modelcontrol. According to the research above, the thesis has compared the PWM and SVPWMcontrol, and then the SVPWM control was chosen for the control method of three-phasefour-legged inverter with unbalance and nonlinear load to get the balanced output voltage.The control system of inverter with PWM and SVPWM was designed respectively, andthe simulation models were established and compared in MATLAB. The simulation results inseveral load condition revealed that the three-phase four-legged inverter can output thebalanced voltage when the three phase loads were unbalanced or nonlinear. Moreover, inorder to verify the control strategy proposed in this thesis, a6kW three-phase four-leggedinverter experiment platform was established, in which the TMS320F28335was used for thecontroller chip to process the data and realize the control algorithm. Finally, the experiment results shows that the output voltage of three-phase four-legged inverter controlled with themethod of SVPWM can preserve balanced and low-harmonic even when the three phaseloads ware unbalanced.The simulation and experiment results have verified the efficiency and availability ofthree-phase four-legged inverter control system...