A Fast Positive-Sequence Component Extraction Method With Multiple Disturbances in Unbalanced Conditions

Abstract

Fast and accurate acquisition of current components is a key factor for an active power filter to realize transient control under unbalanced conditions. In this letter, a robust real-time algorithm, which rapidly separates the positivesequence component (PSC) from multiple decaying dc (DDC) components, dc bias component, negative-sequence component, and harmonics, is proposed. To this end, first, the multiple DDC components are detected in the multiple disturbance and unbalanced grid context, by making use of the periodicity of remaining components. The dc bias can be obtained accordingly, followed by the detection of a compound signal encompassing the positive-sequence component, negative-sequence component, and harmonics. Specifically, the compound signal can be extracted precisely, based on the detected DDC and dc bias components, with one grid cycle response time, or approximately, within half grid cycle. A switching logic of the two approaches is designed to shorten the overall convergence time and improve steady-state accuracy. The PSC is then effectively extracted by constructing the virtual orthogonal signal of the compound signal and using dq-frame filtering. Compared with the existing transient control techniques, the proposed scheme guarantees one grid cycle response time and simultaneously suppresses multiple disturbances. Finally, experimental results verify the effectiveness of the proposed method.

Phase locked-loop with decaying DC transient removal for three-phase grids

“…Though the SRF-PLL scheme is used in this paper as an example, more advanced closed-loop PLL schemes with better performance can be used, as long as the switching logic and initial conditions are properly designed. Besides, the DC offset can also be considered during the transient process by using alternative DDC detection approaches, e.g., the method in [19], at the expense of a slight increase in dynamic response time.…”

“…[16,17] use analysis of empirical formula to derive detection methods based on highorder time-derivatives, which are highly susceptible to random noise. [18] and [19] designed an active power filter to eliminate the DDC current from the source based on detection results, realizing a response time of roughly one grid cycle. Based on mathematical analysis and time integrals, [20] realized DDC component detection within half grid cycle.…”

“…Indeed, this consideration is more practical in the high-voltage transmission and distribution networks, where the X/R ratio is large to produce a significant DDC component, yet the harmonics are usually negligible. In a recent work [19], an open-loop detection scheme is developed to address the DDC transient with the possible presence of a DC offset. Since the addition of the DC offset will invalidate the half-wave symmetry of the DDC-free signal component, the developed algorithm requires slightly increased detection time.…”

Power optimization control of VSC-HVDC system for electromechanical oscillation suppression and grid frequency control

“…The basic structure of the VSC-HVDC is shown in Figure 1 e abc and i sabc are the voltage and line current at the sending-end grid, respectively; θs is the grid voltage phase angle; v d1 and v d2 are the DC voltages at the rectifier end and the inverter end, respectively; i d is the DC line current; V gabc and i gabc are the voltage and current at the receiving-end grid, respectively, and U N and f N are the rated voltage and frequency, respectively; P D , P J , P PD , and P C are the regulated power provided by the droop control, the inertia control, the PD control, and the RPC control, respectively; P 0 and Q are the steady-state active-and reactivepower provided by VSC-HVDC to the receiving-end grid, respectively. Through the phase-locked loop, Liu et al (2022a); Liu et al (2022b), V gabc provides the frequency f, phase θ, and voltage amplitude U at the receiving-end grid, and…”

Research on optimum extended phase-shift control with minimum peak-to-peak current of DAB converter applied to small DC power grid

“…Simple equipment structure and strong ability to connect different distributed generations (Marquardt, 2010;Lin et al, 2016;Liu et al, 2020). In DC distributed energy generation system, DC/ DC converters connect different DC voltage buses and renewable resources (Xiong et al, 2015;Zhao et al, 2015;Liu et al, 2022a). Therefore, its performance determines the economy, reliability and stability of the whole DC distribution system (Cornea et al, 2017;Pannala et al, 2020;Xiong et al, 2022).…”