A delay-triggered reactive power disturbance island detection method

Abstract

The invention proposes a delayed-triggered reactive power disturbance method, which is suitable for the islanding detection technology of a grid-connected photovoltaic power generation system. In this method, the total harmonic distortion (THD) mutation is used as the trigger condition, and the frequency change of the grid-connected system common coupling point (PCC) is used as the islanding criterion. After the THD mutation is delayed for a period of time, the disturbance current is injected to realize the active mode. Island detection. The invention also provides a calculation formula for the delay time setting value, which can effectively identify the islanding phenomenon, and solves the problem of offsetting the disturbance offset and the load offset in the traditional reactive power disturbance method.

Description

technical field [0001] The invention relates to a delay-triggered reactive power disturbance island detection method, which belongs to the fault detection technology in the field of new energy. Background technique [0002] In recent years, with the rapid development of new energy power generation technology, the grid-connected scale of photovoltaic power generation (PV) systems has become larger and larger, which puts forward new requirements for the reliability and safety of power grid operation. The grid-connected inverter measures the current and voltage of the grid-connected point in real time during operation. In addition to detecting conventional faults, it also needs to consider a special operating state, that is, the islanding phenomenon. According to the definition of isolated islands in IEEE Std.929 (reference [1]: IEEE-SA Standards Board.IEEE Standard 929—2000 IEEE recommended practice for utility interface of photovoltaic (PV) systems[S].2005.), the island pheno...

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Problems solved by technology

[0007] The traditional reactive power disturbance method detects islands by periodically injecting reactive power, which not only has a great impact on power quality, but also may encounter the problem of offsetting the disturbance offset and load offset, that is, The following two special cases: A. The frequency of the PCC point has exceeded the limit within the set islanding detection period, but the effect of power disturbance stabilizes the frequency within the normal range, resulting in the failure of the islanding detection; B. The frequency of the power disturbance at the PCC point It has been injected before the limit is exceeded, but its effect makes the frequency that should have exceeded the limit no longer exceed the limit, and the island detection fails

Reference [3] (Bao Xiaoting, Chen Yongqiang, Zhang Chao, etc. An improved frequency positive feedback reactive current disturbance island detection research [J]. Electrical Measurement and Instrumentation, 2018, 55(15): 25-30.) proposed An improved reactive current disturbance method, which divides the disturbance current into traditional periodic disturbance i q1 and frequency positive feedback disturbance i q2 In order to reduce the impact of disturbance current on power quality, and introduce the sign function sign(f-f g ) to overcome the offset of the single-direction disturbance at the load end, this method can solve the above special case A, but cannot solve the second special case

Reference [4] (Ma Cong, Gao Feng, Li Ruisheng, etc. Reactive power disturbance algorithm for synchronous detection of low voltage ride-through and islanding in new energy grid-connected power generation systems[J]. Power Grid Technology, 2016, 40(5): 1406- 1414.) The reactive power disturbance algorithm proposed uses the maximum value of the PCC point frequency variation during the islanding detection period as the islanding criterion to solve the above special case A, but this method needs to use the voltage passive detection method as the trigger method, and still cannot solve the special case Case B

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