Abstract
The phase-locked accuracy of conventional phase-locked method is reduced when the grid voltage contains fundamental frequency negative sequence(FFNS) component, harmonic component, and DC offset component. Aiming at this problem, a novel adaptive notch filter (NANF) is proposed, and a dual NANF (DNANF) structure is designed to eliminate the FFNS component and extract the fundamental frequency positive sequence(FFPS) component based on NANF. Furthermore, dc DNANF with DC offset rejection capability is proposed by adopting DNANF. Then a novel hybrid filter in dq -frame is designed by combining dc DNANF and the cascaded delay signal cancellation operator filter whose delay parameters are 4 and 24 in dq -frame ( dq CDSC4,24). Meanwhile, a new SRF-PLL design method is proposed based on the novel hybrid filter. This proposed method employs dq CDSC4,24 to separate the positive and negative sequences of the voltage and eliminate the high frequency harmonics in the grid voltage, and uses dc DNANF to reject the DC offset, so as to achieve the accurate acquisition of the fundamental voltage information under distortion and unbalanced grid. Simulation and experimental results show that compared with the conventional SRF-PLL methods, the proposed method can obtain faster phase tracking speed, better phase-locked effect, faster dynamic response, and better stability.
Highlights
With the development of new renewable energy generation technologies such as photovoltaic, wind power, etc., distributed generation is increasingly becoming an effective way for meeting the requirement for load growth, reducing environmental pollution, improving the comprehensive utilization efficiency of energy, and improving the reliability of power supply, so it is widely used in the distribution networks[1]
In order to connect the renewable energy generated by distributed generation to the utility grid through grid-connected power converters, and realize continuous and stable operation of the system especially under medium and high voltage conditions, appropriate grid synchronization method is required to realize operation and control on grid-connected converter, and ensures that the output voltage is synchronized with the grid voltage[2]
To improve the filtering performance and dynamic response speed of SRF-Phase-locked loop (PLL), this paper proposes a threephase grid-connected phase-locked loop based on a hybrid filter composed of dual NANF (DNANF) with DC offset rejection capability and dqCDSC4,24
Summary
With the development of new renewable energy generation technologies such as photovoltaic, wind power, etc., distributed generation is increasingly becoming an effective way for meeting the requirement for load growth, reducing environmental pollution, improving the comprehensive utilization efficiency of energy, and improving the reliability of power supply, so it is widely used in the distribution networks[1]. The disadvantage of this approach is that when the power grid is distorted and the frequency is greatly changed, the filtering ability of the approach is deteriorated, and the large estimation error will occur Notch filter is another advanced method used in SRF-PLL [20]–[22]. [31] proposed a HIDHO-PLL composed of a novel DC offset compensation cell (DOCC) and a harmonics and / or interharmonics compensation network (HIH-CN) in the dq-frame This approach can effectively eliminate harmonics, interharmonics and DC offsets in the power grid, but its structure is more complex and difficult to implement. To improve the filtering performance and dynamic response speed of SRF-PLL, this paper proposes a threephase grid-connected phase-locked loop based on a hybrid filter composed of DNANF with DC offset rejection capability and dqCDSC4,24. The model accuracy of the proposed PLL is verified by simulation, and the validity of the proposed PLL is verified by simulation and experiments
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