University of Macau Abstract 3-DIMENSIONAL SPACE VECTOR MODULATION IN THREE-PHASE FOUR- WIRE SYSTEM FOR SHUNT POWER QUALITY COMPENSATOR by Ning-Yi Dai Thesis Supervisor: Professor Han Ying Duo Co Supervisor: Dr. Man-Chung Wong Electrical and Electronics Engineering In the past decades, Pulse Width Modulation techniques have been the subject of the intensive research area of the developments in power electronics. There are many PWM methods that have been described and developed. However, most of them are based on the space vector representation of the voltages in Alpha-Beta plane because the Three-Phase Three- Wired Inverters as the motor drivers are the main focus for the past PWM researches. Due to the development of 'Custom Power' concept, Three- Phase Four-Wired System will play a very important role in the Distribution Site. And more and more attentions are paid to the power quality compensators for three-phase four-wire system. In this thesis, the researches are mainly focused on the 3-Dimensional Space Vector Modulation (3DSVM) techniques in 3-leg center-split inverter which is used as shunt power quality compensator to handling the current quality issues for three-phase four-wire systems. Based on the mathematical models of the 3-leg center-split inverters, the voltage vectors of two-level and tri-level systems are studied in 3D a-B-0 frame. The novel 3DSM for two-level center-split inverter is proposed and studied. And a novel 3DSVM for tri-level center-split inverter is proposed based on the two-level 3DSVM. Simulation results indicate that the harmonic, reactive and neutral currents in three-phase four-wire systems can be compensated simultaneously when the proposed ADSVM is used to control the 3-leg center split inverter as shunt power quality compensator. However, one of the drawbacks of the 3-leg center-split inverter is the d.c. voltage variation. In this thesis, the d.c. voltage variation is analyzed. Results indicate that only the zero-sequence output is affected when the d.c. voltage variation occurs. A novel 3DSVM with d.c. voltage variation consideration is proposed so that the compensation performance is not affected under the d.c. voltage unbalance situation. And since there is a limitation exists for the d.c. voltage unbalance, a valid control method for d.c. voltage unbalance is also proposed. Two prototypes of the shunt power quality compensator are implemented, in which the two-level and tri-level 3-leg center-split inverters are employed respectively. The experimental system configuration and the system parameter determination are introduced. Detailed discussions about the implementation of the novel 3DSM control strategy in the D.S.P. controller are given. With 3DSM control method, the experimental prototype has the ability to compensate the harmonic currents, reactive power, unbalance and neutral currents in steady state and dynamic state. And comparison with the 3-D Sign Cubic Hysteresis (3DSCH) control strategy is done in the thesis. The 3DSM method has better compensation performance when its switching frequency is only half of that of 3DSCH control.