Application Research On Cascade SVG With Triangle Configuration

With the rapid increase of different kinds of power electronic loads, the power quality issues have become more complex and integrated. The impact on the grid and the users by the power quality increases. Therefore, the comprehensive compensation of the power quality has become a new research topic. Power quality problems at the load side mainly includes three-phase current imbalance, reactive current and harmonic current. In low voltage applications (such as 380V line voltage), power quality compensators based on the three-phase half bridge topology (such as APF) can solve these power quality problems at the same time, named as comprehensive compensation. But in high voltage applications (10kV,35kV), there is little research on the comprehensive compensation. As such, this paper presents the cascade SVG with triangle configuration applied to load comprehensive compensation.The topology of the triangle-connected cascade SVG is introduced and its theory of compensating three-phase current imbalance, reactive current and harmonic current at the same time is analyzed. Steinmetz theory is applied to the triangle-connected cascade SVG to compute the phase reference current for three-phase current imbalance and reactive current compensation. The harmonic compensation strategy with circulation being zero is introduced. The optimization strategy of compensating the harmonic and its calculation method is proposed. When the harmonic current of the load is imbalanced, it can be uniformly distributed to the three phases of the triangle-connected cascade SVG as far as possible. In order to save the equipment capacity to a certain extent, considering the fundamental current and the harmonic current, the selection principle of the two strategies is proposed.The control strategy of the triangle-connected cascade SVG is introduced. The control strategy includes the current hybrid control strategy and the DC-side voltage control strategy. In order to enhance the dynamic performance and the tracking ability to the harmonic current of the triangle-connected cascade SVG, the hybrid controller is used mixing conventional PI with repetitive controller. The PI controller can enhance the dynamic response speed and the repetitive controller can reduce the steady-state error. The hierarchical control is used in the DC-side voltage control. The upper layer control the total voltage of the cascaded H-bridges. The lower layer control the voltage of each H-bridge based on judging the H-bridge charging-discharging state and adjusting the charging or discharging rate.A triangle-connected cascade SVG was simulated using PSCAD. The simulation model applied Steinmetz theory, the optimization strategy of compensating the harmonic, the current hybrid control strategy and the DC-side voltage control strategy to compensate the load comprehensively.A experimental platform of the triangle-connected cascade SVG is designed. Its main circuit parameters, H-bridge unit and controller are introduced. The comprehensive compensation experiment was carried out on the experimental platform and the power quality parameters were compared before and after the compensation.The simulation and experimental results show that the optimization strategy of compensating the harmonic works well. Also, the triangle-connected cascade SVG has the ability to compensate the three-phase current imbalance, reactive current and harmonic current at the same time. In high voltage applications, the triangle-connected cascade SVG has broad prospects in the field of power quality comprehensive compensation.