Design of voltage unbalance generating device based on negative sequence injection method

Single-phase large-capacity loads, such as electrified railways, electric arc furnaces, welding machines and so on, will exert influences on the power quality of the power system. As one important problem of them, three-phase unbalance may thereby endanger the safety of various types of electrical equipments. In this paper, reasons and hazards of three-phase unbalance are analyzed. According to the measurement method based on symmetrical components, the three-phase unbalanced generating device is designed. Its main circuit topology is electric power converter of AC-DC-AC with cascaded H-bridge units. The novel method of injecting the negative sequence components is used to simulate voltage unbalance disturbances. The correctness and effectiveness of the device and control algorithms are verified through experiments. This is of great significance for the development of three-phase unbalance compensation device and power quality control equipment and thus to improve the power quality.