An Unbalance Voltage Compensation method for the Distributed Generation System

• Main Authors: Chien-An Chen, 陳建安
• Other Authors: Po-Tai Cheng
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/75152698502882312099

碩士 === 國立清華大學 === 電機工程學系 === 95 === As regeneration sources become more and more popular, distributed generation (DG) system which integrates these small power sources has become a trend for future power system. In DG system, to balance power flow from each microsource, the power-frequency droop and reactive power-voltage droop controllers are applied in converters which interface the microsources. However, when the system is connected with imbalanced load, the droop controllers can not equally distribute the unbalanced current. Previous studies about line imbalance can maintain symmetrical line voltages under load imbalance, yet the distribution of the unbalanced current is not addressed in these literatures. Consequently, the unbalanced workload distribution among converters is still a problem to be solved. To approach this problem, a droop controller is proposed to share the unbalanced current in DG system. In this controller, a negative sequence conductance G is introduced in each converter, and the conductance command will be determined by the negative sequence reactive power Q— of each converter. Through the droop control of the conductance, the unbalanced current will be shared among converters without communication, and also the implementation of the conductance will reduce the unbalanced voltage level. The proposed controller can be seamlessly combined with P-f droop and Q-v droop controllers to share the power, reactive power and negative sequence reactive power between converters. Therefore, an automatically energy distribution proportional to the capacity of each converter can thus be achieved in the distributed generation system under imbalanced loading. To realize the control method, hardware test and simulation of DG system will be constructed and analyzed in the thesis.