Estimation Method for Weak Power Grid and Series Compensation Power Grid Without Disturbance Signal Injection

Abstract

The invention discloses a method for estimating a weak power grid and a series-compensated power grid without disturbing signal injection. The system studied by the method includes a DC side voltage source, a three-phase full-bridge inverter circuit, a three-phase LC filter, and a three-phase line impedance. and three-phase grid. This method does not need to inject disturbance signals, and only estimates the weak grid and series compensated grid by detecting the voltage and current of the PCC point, which is then used for adaptive control of the inverter to improve the stability of the grid-connected system without increasing costs.

Description

technical field [0001] The invention belongs to the field of power grid quality analysis and signal processing, and in particular relates to a method for estimating weak power grids and series-compensated power grids without disturbance signal injection. Background technique [0002] As photovoltaic power generation, wind power generation and other new energy power generation occupy an increasing proportion in the power system, and the local consumption capacity of new energy power generation is limited, long-distance power transmission is required, and the inductive reactance of the line increases. In order to increase the transmission capacity, The series compensation capacitor will be connected to the transmission line, resulting in two states of the power grid: weak grid and series compensation grid. [0003] When the grid switches between the weak grid state and the series-compensated grid state, for inverters that cannot estimate the grid state, the grid-connected syst...

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Problems solved by technology

Using the grid impedance estimation method of injecting non-characteristic sub-harmonics and extracting the injected harmonic response by a complex filter, but it does not take into account the low stability margin of the original system itself and the working condition that it is impossible to inject disturbances

[0006] 2. Titled "Grid impedance estimation for islanding detection and adaptive control of converters", A.Ghanem, M.Rashed, M.Sumner, M.A.Elsayes, and I.I.I.Mansy, IET Power Electronics, 2017:1279-1288 ("Based on grid Converter Island Detection and Adaptive Control for Impedance Estimation", "Journal of IET Power Electronics", published online in 2017), by sampling the switching frequency level voltage and current, using the circuit equation when the switching tube is turned on and off to estimate the grid impedance , but requires high-precision sensor sampling, which is not conducive to engineering applications, and the weak grid inductive reactance and series-compensated grid capacitive reactance are both imaginary parts in the impedance expression and are mixed together, so it is impossible to estimate the weak grid and series-compensated grid

[0007] 3. The Chinese invention patent document (publication number CN 110308353 A) published "Series Compensation Sensor Tester and Test Method" on October 8, 2019. The present invention proposes a series compensation sensor tester and test method. The test The instrument obtains whether the current grid is a series-compensated grid by detecting the output information of the series-compensated sensor, but the present invention realizes the detection of the series-compensated grid on the basis of the series-compensated sensor, and is not applicable to the algorithm used in the inverter to estimate the series-compensated grid

[0009] 1. The existing impedance estimation method for weak grids based on disturbance injection does not take into account the working conditions that the original system contains harmonics and cannot inject disturbances. It is necessary to study the estimation of weak grids and series-compensated grids without disturbance injection;

[0010] 2. The existing method of estimating the impedance of the weak grid by using the harmonics of the system itself, the inductive reactance of the weak grid and the capacitive reactance of the series-compensated grid are both imaginary parts in the impedance expression, so it is impossible to estimate the weak grid and the series-compensated grid;

[0011] 3. The existing research on the estimation of series compensation grid uses external independent detection equipment and series compensation sensors on the line, which increases the cost. At the same time, it can only determine whether there is series compensation access in the transmission line, and cannot estimate the weak grid

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