The Positive Islanding Detection Based On Inverter

When the grid interrupts supply due to electrical appliance failure, misoperation or natural factors and so on and the generating system fails to detect power failures and breaks away the grid, the generating system and the load forms a self-supply system that the power companies did not control the state, the phenomenon is called island. In the grid-connection, the distributed generation system in the island is liable to damage the equipment, and affect the performance of the utility, seriously hazard uniformed maintenance personnel. Therefore, the study of islanding detection and protection measures to minimize harm to the island has importand practical significance.At present, the inverter islanding detection method consists of two types of active and passive detection methods. Passive detection method is simple to implement. But its non-detection zone(NDZ) is large. The power quality of unility is conficted to the stability of the system. The advantage of the active detection method is small NDZ and high sensitivity , but system stability will be affected to some extent. According to the character of the active detection method, the inverter islanding detection based on the positive feedback is brought forward.The paper analyzes the advantages and disadvantages of exiting islanding detection method, islanding not being made out reason based on the inverter and the size of non-detection zone. Then the thesis puts forward the islanding detection method combing DQ transformation mechanism and positive feedback principle through researching on the positive feedback principle based on the inverter and grandually builds the design. The theory analysis and experimental simulation shows that this method can minish the NDZ and avoid the thing that the island is not able to be detected when the inverter outputpower matches to the load power.The thesis also puts forward another islanding detection method based on the relation of the reactive power and frequency. The theory analysis and experimental simulation show the islanding detection method is valid, whatever the load is pure resistance, the paralleling resistance and inductance or the paralleling resistance, inductance and capacitance.