Abstract
The inverter is extensively employed in many power electronic systems, such as uninterruptible power supplies, electronic ballasts and motor drives. To meet the required characteristics of different kinds of loads, suitable power quality control for inverter output is indispensable, even for its, voltage waveform. This thesis is mainly concerned with the study of robust waveform control of inverter and the establishment of a V-connected three-phase inverter using two single-phase modules. First, the circuit, switching control and some practical consideration issues of the inverter are studied. Then the single-phase inverter is designed and implemented. The designs of circuit constituted components, protection circuit and output filter are all introduced in detail. As to the control aspect, a two-degrees-of-freedom (2DOF) current-controlled PWM scheme is first designed to let the filter inductor current closely follow its command. Then a voltage robust waveform control scheme is designed. After determining the feedback controller parameters by trial-and-error, the intuitive approach is employed to design the other constituted controllers. Under the chosen operating point, the transfer function of voltage command feedforward controller is on-line adjusted to yield excellent waveform tracking performance. Then this transfer function is used as the inverse model being set in the robust disturbance feedforwad controller. Finally, a robust waveform controller is proposed to eliminate the waveform tracking error. Having established the single-phase inverter with good voltage waveform control performance, two modules are connected to form a V-connected three-phase inverter. In addition to the control schemes developed for single-phase module, a robust balance waveform controller is further proposed. A weighted robust compensation signal yielded from the voltage waveform tracking error of the third phase, and it is added to the waveform commands of the other two phases for performing the imbalance compensation control. The experimental results show that rather good three phase output voltage waveforms can be obtained under linear load, but the distortion will become heavier for the increase of nonlinear load component. The improvement control is considered rather difficult and thus worth further studying.