Ahmad Afif Nazib
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Preferred name
Ahmad Afif Nazib
Official Name
Ahmad Afif, Nazib
Alternative Name
Nazib, Ahmad Afif
Nazib, A. A.
Nazib, Ahmad A.
Main Affiliation
Scopus Author ID
56125536300
Researcher ID
DLD-1667-2022

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High bandwidth sensorless synchronisation strategies for current regulated grid connected converters

2018-02-05 , Ahmad Afif Nazib , Grahame Holmes , Brendan Mcgrath

Distributed generation (DG) sources are commonly interfaced to the grid using a current regulated converter, which must be synchronized to the grid. Typically this is achieved using a phase locked loop (PLL), which must reject any harmonic distortion in the grid voltage. Conventionally this necessitates a PLL design with a low bandwidth, which then degrades the PLL's dynamic capability. In this paper an indirect or sensorless synchronization strategy is presented whereby the PLL is fed instead from the output of a stationary frame Proportional Resonant (PR) current regulator. It is shown that this structure allows for an arbitrary increase in the PLL bandwidth, with the harmonic disturbance rejection properties of the strategy further enhanced by using multiple harmonic resonators in the PR current regulator. Simulation results are presented to validate the theoretical development.

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Phase Angle Compensation-based Highly Accurate Self-Synchronising Inverter

2020-11-29 , Zhu, Rongwu , Kwon Y.D. , Liserre M. , Ahmad Afif Nazib , Holmes D.G. , McGrath B.

Grid voltage measurement-based phase-locked loop (PLL), is one of the most widely used synchronisation techniques for grid-interfaced inverters. However, this PLL easily propagates the harmonics from the ac grid voltage into the control loops of inverters, due to the direct voltage measurement, potentially leading to stability issues, particularly at weak grid conditions. The self-synchronising inverter can synchronise with ac grids without ac grid voltage measurement, avoiding harmonic propagation and increasing stable margin. However, due to no grid voltage measurement, the ac grid angle tracking accuracy of the self-synchronisation becomes a concern. Thus, this paper proposes an improved self-synchronising strategy, taking into account the impacts of ac filter and unbalanced three-phase ac grid voltage. The simulation results carried out in Matlab/Plecs and experimental results based on a 4kW self-synchronising inverter both clearly validate the correctness and effectiveness of the proposed solutions.

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Impedance-based Stability Assessment of Self-Synchronising Power Electronics Converter

2020-11-29 , Kwon Y.D. , Zhu R. , Liserre M. , McGrath B. , Ahmad Afif Nazib , Holmes D.G. , Mu P.

Self-synchronization, which is an unconventional control framework for grid-tied power electronics converters (PECs), uses the internal signals of current regulators instead of direct measurement of ac grid voltages, to obtain ac grid phase information and synchronization with the ac grid. Consequently, the self-synchronization provides various benefits including immunity to grid voltage harmonics and disturbances, and no need of ac voltage sensors. On the other hand, the different synchronization mechanism between the self-synchronization and conventional grid voltage measurement-based synchronization, leads to different harmonic interaction and coupling behaviours. Thus, the impedance-based stability criterion is used to comparatively assess the stability characteristics of the PEC based on the self-synchronization and conventional grid voltage measurement-based synchronization. The simulation and experimental results are clearly validate the effectiveness and feasibility of the theoretical analysis.

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Autonomous Current Sharing Control with Integrated Virtual Impedance and Self Synchronisation for Unbalanced Islanded Microgrids

2020-10-11 , Ahmad Afif Nazib , Holmes D.G. , McGrath B.P.

This paper proposes a new autonomous current sharing control strategy for islanded microgrids that is simple and robust under unbalanced load conditions. The strategy estimates the distributed generator output voltage and current positive sequence components from the internal variables of a resonant current and resonant voltage regulator, and then uses them to create an integrated virtual impedance sharing mechanism. This avoids control complexity and the need for output current measurements, while maintaining a balanced voltage and accurate current sharing. The approach has been verified using a detailed switched simulation.

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Enhanced Transient Performance of a Self-Synchronising Inverter during Start up and Severe Grid Fault Conditions

2020-11-29 , Ahmad Afif Nazib , Holmes D.G. , McGrath B.P.

This paper explores the process of transient inrush current associated with inverters during grid connection startup and grid fault events. The analysis presented identifies the equivalence between both scenarios and investigates the influence of the filter impedance and current controller bandwidth on these current transients. A novel strategy is then proposed to minimise the impact of such transient events, which achieves both a seamless start up, and is capable of riding through a solid short circuit (i.e. zero voltage or crowbar) grid fault. The strategy has been verified via detailed switched simulation and experimental investigations.

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Virtual flux-based grid-forming current controller for flexible operation of voltage source converters

2022-01-01 , Ahmad Afif Nazib , Holmes D.G. , McGrath B.P.

This paper presents a novel approach to incorporate a grid forming capability into a grid-following voltage source converter, while maintaining the high-bandwidth current control capability that is typical of such a converter. The approach uses the resonator outputs of a stationary frame current regulator as a virtual flux estimation of the converter output voltage, and integrates this estimation into an electrical model of a virtual synchronous generator without requiring integration and derivative operations. The generator and converter models are then combined to achieve a robust grid-forming response under grid islanding conditions, without requiring direct grid-side voltage measurements. The proposed strategy is validated using a detailed switching simulation model of the converter and its control processes.

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Accurate Simplified SPWM Control Strategy for Single-Phase Voltage Source Inverter under Varying Grid Conditions

2023-01-01 , Ahmad N.S. , Madzlan N.A. , Ahmad Afif Nazib , Leong Jenn Hwai , Jenn

A single-phase Voltage Source Inverter (VSI) controller with minimal complexity and computational burden is considered attractive. However, the accuracy of its power injection should not be compromised. The simplified sinusoid pulse width modulation (SSPWM) control strategy achieves this simplicity, but the accuracy of its power demands under varying grid conditions is yet addressed. This paper now investigates the power demand accuracy of the SSPWM control strategy. An improved strategy is then proposed by incorporating an optimised Proportional Integral (PI) current regulator within the simplified control strategy to achieve accurate power demands under varying grid conditions. The strategy has been verified via detailed simulation investigations of a single-phase VSI under varying grid conditions. The simulation shows the proposed control structure is 5.1% better than the SSPWM for the injected real power.

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Self-synchronizing stationary frame inverter-current-feedback control for lcl grid-connected inverters

2022-04-01 , Ahmad Afif Nazib , Holmes D.G. , McGrath B.P.

Current regulation of inductive-capacitive-inductive (LCL) grid-connected inverters usually requires multiple current sensors to actively damp the filter resonance. Inverter-side current regulation avoids this issue because of its inherent LCL filter damping properties but does not accurately control the grid-side current, particularly with distorted grids. Furthermore, both strategies typically require high-quality voltage sensors to maintain precise grid synchronization. This article proposes a novel current control strategy for LCL grid-connected inverters that only requires inverter-side current sensors. The strategy uses the resonator output states of a stationary reference frame (SRF) proportional resonant (PR) current regulator to estimate the grid voltage phase and filter capacitor current and, thus, achieve self-synchronized indirect regulation of the grid-side current. The effectiveness of the approach has been verified using simulation and matching experimental investigations.

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