Detection method for variable step length LMS (Least Mean Square) harmonic current based on versiera

Abstract

The invention discloses a detection method for a variable step length LMS (Least Mean Square) harmonic current based on versiera. The method comprises the steps of: sampling, estimating an active current of a fundamental wave, estimating a general harmonic current, updating a weight coefficient, updating the step length and iterating. According to the orthogonal characteristics of a trigonometric function, the current error output by a filter and an instantaneous cross-correlation time mean value are subtracted from a load current to eliminate interference of the harmonic current and the active current of the fundamental wave on update of the step length. Furthermore, update of the step length is controlled by an improved versiera function. Meanwhile, in the updating process of the weight coefficient, variation of the weight coefficient is imported so that the steady state error is very small and the calculated amount is smaller. The detection method for the variable step length LMS harmonic current based on versiera provided by the invention is suitable for occasion where the load current has saltus and value of the optimal parameter provided by the invention is less dependent on the load current.

Description

technical field [0001] The invention belongs to the technical field of harmonic current detection of power systems. Background technique [0002] In recent years, with the application of a large number of power electronic devices in the power grid, the problem of harmonic pollution in the power grid has become increasingly prominent, seriously affecting the quality of the power grid and the safe operation of user equipment. Therefore, it is very important to effectively control harmonics to improve power quality. Active power filter (APF) is based on the real-time detection of grid harmonics, and correspondingly injects an anti-phase harmonic current into the grid, so as to realize compensation and suppression of harmonic pollution to the grid. The quality of its performance largely depends on the real-time and accurate detection of harmonic current, so the detection method of harmonic current is very important. With the development of adaptive filter, it is applied to har...

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Problems solved by technology

2) μ is called the step size factor, and its size affects the convergence speed and steady-state error of the algorithm. If it is too large, the convergence speed will be fast but the steady-state error will be large. If it is too small, the steady-state error will be small but the convergence speed will be slow.

Although this method eliminates the interference of harmonic current, and the algorithm is universal under different grid power levels, the problems of this algorithm are: (1) When the load current is near the zero-crossing point, the algorithm will appear numerical calculation (2) The ability to track the jump system is poor; (3) The interference of the fundamental reactive current to the step size update cannot be eliminated

It is called the generalized harmonic current detection algorithm based on the S function. This method cannot eliminate the interference of the fundamental reactive current to the step size update, resulting in a large steady-state error. At the same time, the algorithm has absolute value and exponential operations, and the amount of calculation is large.

[0018] To sum up, the existing variable-step-length LMS harmonic detection method is not suitable for sudden changes, nor can it eliminate the interference of fundamental reactive current, resulting in large steady-state errors, and the accuracy of detection results needs to be improved.

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