Method for detecting and separating positive and negative sequence components of grid voltage of three-phase neutral-line-free system

Abstract

The invention provides a method for detecting and separating positive and negative sequence components of grid voltage of a three-phase neutral-line-free system. According to the method, grid voltage of each phase is sampled so as to acquire an instantaneous value and a corresponding differential value of the current grid voltage, thereby being capable of separating the positive and negative sequence components of the current voltage of the grid voltage of the phase, and calculating so as to acquire the sine and the cosine of a positive-negative sequence instantaneous phase angle of the current grid voltage. The method provided by the invention is simple in calculation, small in time delay, high in real-time performance, convenient for engineering realization, applied to a software phase-locked loop of a three-phase grid-connected converter control system, and capable of effectively avoiding overcurrent and fluctuation of DC-side voltage caused by asymmetry of three-phase voltage.

Description

technical field [0001] The invention relates to the field of power systems, in particular to a method for detecting electrical control parameters. Background technique [0002] When the grid voltage drops, to achieve good control of the three-phase grid-connected converter without a neutral line, the system is required to accurately and quickly detect the grid voltage amplitude and phase, and provide accurate system parameter information for the control system in time. This requires the phase-locked loop (PLL) to have steady-state accuracy and dynamic fastness, so that the control system can take effective measures to avoid overcurrent and DC side voltage fluctuations caused by three-phase voltage asymmetry. In order to meet the needs of the asymmetric control strategy of the three-phase grid-connected converter, the positive and negative sequence components of the instantaneous value of the grid voltage can be quickly and accurately extracted under the condition of grid vol...

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Problems solved by technology

Many existing literatures have proposed different solutions, which can be summarized into three types: ① The second harmonic filtering method uses the second harmonic filter to filter out the second harmonic in the dq coordinate system, but the parameters of the harmonic The design and digital implementation are complicated, and the dynamic performance of the system is affected; ②Dual coordinate system decoupling and sequence method, the asymmetric grid voltage is transformed through double dq, and the positive and negative sequence decoupling is realized in the positive and negative sequence synchronous reference coordinate system The separation of the positive and negative sequence components of the fundamental wave has a complex structure and a large amount of calculation. In order to ensure system stability, the system bandwidth must also be reduced; A second-order generalized integrator is used, but the instantaneous symmetric component operation increases the amount of calculation of the system and the complexity of the system structure

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