synchronous reference frame phase-locked loop (SRF-PLL) is a classical method to achieve grid synchronization in three-phase systems. And SRF-PLL has important inflnence on weak grids. Many linearized models have been...
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ISBN:
(纸本)9781665422482
synchronous reference frame phase-locked loop (SRF-PLL) is a classical method to achieve grid synchronization in three-phase systems. And SRF-PLL has important inflnence on weak grids. Many linearized models have been addressed to describe PLLs. However. they have low dynamic accuracy at the case of frequency jump. To fill this gap. an accurate linearized model of SRF-PLL is proposed and the proposed model has good dynamic accuracy in cases of frequency jump and phase angle jump. In details, a nonlinear model of SRF-PLI. is established Then, a simplified model is obtained according to the accurate linearization technology. Compared with the traditional model of SRF-PLL, the proposed model has better dynamic accuracy, especially in the case of frequency jump.
The synchronous reference frame phase-locked loop (SRF-PLL) is widely utilized for grid synchronization in voltage-source converter (VSC) system. However, it fails to eliminate the effect of high grid impedance leadin...
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The synchronous reference frame phase-locked loop (SRF-PLL) is widely utilized for grid synchronization in voltage-source converter (VSC) system. However, it fails to eliminate the effect of high grid impedance leading to instability in weak grids. To address this issue, this paper introduces the back-electromotive-force observer (BEMF observer), commonly being utilized in DC motor, to modify the input of the SRF-PLL. To be specific, the equivalent internal electromotive force calculated by the BEMF observer rather than the PCC voltage is used to capture the phase information. Since the BEMF observer is designed in alpha beta$\alpha \beta$-frame while the SRF-PLL is in dq$dq$-frame, the conventional stability analysis method suffers from complicated process. Thus, this paper further reconstructs the SRF-PLL with the BEMF observer to be symmetrical for simplification. Apart from the symmetrical structure, the stability criterion is accordingly modified. As a result, the proposed back electromotive force based symmetrical PLL (BEFS-PLL) offers the following advantages: (i) it effectively enhances the grid synchronization stability and simplifies the stability analysis process simultaneously, (ii) it exhibits a strong robustness even with the calculation error up to 50%, and (iii) it is characteristic of clear physical meanings. Finally, the effectiveness of the BEFS-PLL is verified by simulation.
Aiming at the problems of grid frequency oscillation and phase distortion in the traditional synchronous reference frame phase-locked loop(SRF-PLL) method for detecting three-phase asymmetric power grid fault signals,...
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ISBN:
(数字)9789887581536
ISBN:
(纸本)9781665482561
Aiming at the problems of grid frequency oscillation and phase distortion in the traditional synchronous reference frame phase-locked loop(SRF-PLL) method for detecting three-phase asymmetric power grid fault signals,an improved PLL method based on a novel dual second-order generalized integratoris *** fundamental voltage component and its 90 degree phase shift component can be extracted by using the novel dual second-order generalized integrator(DSOGI),and then the two orthogonal voltage components are *** the positive sequence calculator(PSC),the positive sequence voltage component is obtained and the disturbance influence caused by the negative sequence component can also be ***,in order to eliminate the AC component of the positive voltage component,the low pass filter(LPF) module is used before the positive sequence voltage component enters the phaselockedloop(PLL) *** simulation and experimental verification,the proposed improved PLL detection method based on the novel DSOGI has proven to perform better than the traditional SRF-PLL both for rapidity and accuracy on detecting the frequency and phase of imbalanced power grid.
Rotor angle is essential in permanent-magnet (PM) brushless machines. Recently, an embedded magnetic encoder (EME) scheme, consisted of linear Hall sensors installing inside of the PM machines, has been proposed to se...
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Rotor angle is essential in permanent-magnet (PM) brushless machines. Recently, an embedded magnetic encoder (EME) scheme, consisted of linear Hall sensors installing inside of the PM machines, has been proposed to sense the flux density and consequently provides rotor position. Compared with traditional optical encoder and resolver, the linear Hall sensor prevails over in both space and cost. The aforementioned scheme is employed successfully in rotor-PM machines, where a PM-excited field rotates at the synchronous speed. In this article, the feasibility of EME in stator-PM flux-switching machine is validated, where PMs are located in stator, resulting in a stationary PM field. The stator slots are selected as installation position of linear Hall sensors to avoid changing the existing structure of machines. The variation of linear Hall signal is due to the changing reluctance of rotor rather than rotating PMs. Then, a decoding algorithm is designed based on an add-up operation, a complex coefficient filter, and a synchronous reference frame phase-locked loop. Finally, experiments on a prototype machine are conducted to validate the effectiveness of EME scheme under both speed-varying and load-varying conditions.
In this Letter, a demodulation based pre-filtering technique is proposed for fast detection of the single-phase grid variables. The estimation of grid voltage parameters is achieved through a Type-I synchronous refere...
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In this Letter, a demodulation based pre-filtering technique is proposed for fast detection of the single-phase grid variables. The estimation of grid voltage parameters is achieved through a Type-I synchronous reference frame phase-locked loop (PLL). The modified bandpass filter in the pre-filtering stage ensure a better rejection of the DC-offset and harmonics. Thus, the grid variables are estimated rapidly with the help of a simple proportional controller. Consequently, in-loop filtering burden and the effort required to tune the PLL is minimal. However, steady errors are witnessed in the fundamental amplitude and the phase information which are mitigated by a curve fitting technique. Importantly, the proposed PLL scheme has improved the dynamic performance under off-nominal frequency conditions with immunity against grid disturbances. The robustness of the proposed algorithm is experimentally verified vis-a-vis existing literature.
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