Research On Compensation And Control System For Three-Phase Unbalanced Load In Distribution Network

In modern power system, the operation stability and power quality of the distribution network is severely influenced by the three-phase unbalance problem, which is caused by large amount of unbalanced impact loads. Compared with traditional SVC device, there are some proven advantages of all-capacitor compensation technology such as low cost, low power loss and small size. Therefore, to solve the unbalance problem in distribution network, it’s significant to do research on the compensation methodology based on all-capacitor.A novel algorithm for unbalanced loads compensation based on unequal capacitor banks is proposed, which effectively solves the problem of unbalanced active and reactive current at the distribution transformer. The algorithm relies on grouping switches in hardware to switch capacitors between phase and phase, and between phase and ground. Based on vector analysis method, the vector model of compensation network is established and the power transfer between phases is analyzed. Finally, the compensation capacity of the capacitors is derived out and the flow chart of the algorithm is presented. The characteristics and advantages of the proposed algorithm are as follows:(1) Able to transfer active power between phase and phase, thus essentially balance the three-phase current at the transformer.(2) High precision. The algorithm can configure the topology of the unequal capacitor banks to achieve highest compensation precision.(3) Low cost in hardware due to the feature of all-capacitor.In order to provide a test environment for kinds of advanced compensation algorithms, a technological test platform for unbalanced loads compensation is designed in this thesis. The hardware system consists of five parts:power distribution cabinet, control cabinet, SVC cabinet, capacitor cabinet, and load cabinet. The design work includes the electrical schematic diagrams and electrical parameters calculation of the cabinets above. Monitoring system of the upper PC is also designed. The experiment result shows that the proposed algorithm is feasible, which can be proved by the decreased unbalanced degree and improved power factor.Finally, unbalanced power flow in distribution network with distributed generators is researched. The typical static load model is established and the impact of distributed generators on feeder voltage profile is analyzed under unbalanced loads. The simulation results are given. References for the global planning of unbalance compensation in distribution network can be provided by the study.