# Saeed GolestanAalborg University · Department of Energy Technology

Saeed Golestan

Phd

## About

87

Publications

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## Publications

Publications (87)

In quantum computing, calculations are achieved using quantum mechanics. Typically, two main phenomena of quantum mechanics (i.e., superposition and entanglement) allow quantum computing to solve some problems more efficiently than classical algorithms. The most well-known advantage of quantum computing is the speedup of some of the calculations, w...

Power quality (PQ) problems, including voltage sag, flicker, and harmonics, are the main concerns for the grid operator. Among these disturbances, voltage sag, which affects the sensitive loads in the interconnected system, is a crucial problem in the transmission and distribution systems. The determination of the voltage sag relative location as a...

Generally speaking, a phase-locked loop (PLL) is a feedback circuit/algorithm that constantly adjusts its output to match in phase and frequency with a reference signal. In power/energy applications , the base for developing the vast majority of available PLLs is the synchronous reference frame PLL (SRF-PLL) that is known to have a limited ability...

With the increased installation of voltage source converters (VSCs) into the power grid, concerns about resonance/stability issues associated with interactions among converters , and between them and the AC grid is growing. The prevailing method for investigating these issues is the impedance modeling of VSCs, which involves linearizing all their c...

Primitive grid synchronization systems of power converters were based on a zero-crossing detection (ZCD) algorithm, which is an open-loop synchronization (OLS) system. A ZCD algorithm, however, could cause some stability problems for power converters. Therefore, they were gradually replaced by some closed-loop synchronization systems. Recently, in...

A SOGI is a resonant regulator with a pair of complex-conjugate poles, and therefore, with infinite magnitude at its center frequency. Thanks to this property, one can put together a set of m SOGIs in an elegant way and decompose a single-phase signal into its constituent frequency components and detect their amplitude and phase angle. Such a confi...

Citation: Hussain, N.; Khayat, Y.; Golestan, S.; Nasir, M.; Vasquez, J.C.; Guerrero, J.M.; Kauhaniemi, K. AC Microgrids Protection: A Digital Coordinated Adaptive Scheme. Appl. Sci. 2021, 11, 7066. https://doi.

The enhanced PLL (EPLL) is one of the most famous PLLs in single-phase applications, and a versatile tool for different signal processing applications, especially for the grid synchronization of power converters. Recently, it has been proved that the EPLL has a quite narrow stable zone (compared to its unstable zone) in the positive parameter space...

With growing environmental concerns, the installation of distributed generation systems forming microgrids in power systems has received much attention recently. This panacea, however, has always some challenges with itself. The delay in digital control systems, grid impedance variations in weak grids, and the interaction between paralleled convert...

With ever-increasing power quality problems in power systems, which are mainly attributable to the proliferation of nonlinear power electronics-based loads and also the high penetration of renewable energy sources in the utility grid, more advanced phase-locked loops (PLLs) for the synchronization of power converters and/or extraction of fundamenta...

Under weak grid conditions and in microgrids, the gird impedance is often large and has a highly varying nature. In such a scenario, stabilizing grid-connected inverters with an LCL output filter could be a challenging task. The control delay that comes from sampling and PWM may contribute to worsen this condition. Especially, the mentioned delay c...

Keeping the synchronization of a grid feeding converter (GFC) with a weak grid during deep voltage sags has been introduced as a serious challenge in converter-interfaced renewable energy sources dominated weak grids. To deal with this challenge, a simple yet effective solution based on the virtual inertia concept is proposed in this paper. This me...

The synchronization dynamics of grid-connected power converters are known to have a tremendous impact on transient stability and fault ride-through performance under grid faults. Up till now, the modeling of converter synchronization stability, which has paved the way for numerous enhanced control methods, is developed around the assumption that th...

In practice, the supply voltage almost always has some degrees of unbalance and harmonic pollution. With increasing the level of these power quality issues in recent years, their monitoring and compensation have received much attention. These tasks often involve using a signal processing tool for the online detection of the fundamental and harmonic...

Due to the rapid adoption of power electronics technology in shipboard microgrids (SMGs) in recent years, harmonic contamination has become now a crucial topic for these power systems. In order to sustain the safety of the electrical power systems standards for power quality have imposed strict limits on the harmonic distortion allowed. In these st...

A large number of single-phase phase-locked loops (PLLs) require generating a 90° phase-shifted version of their single-phase input signal. Among the wide variety of options, using a quarter-cycle transfer delay is particularly popular. In recent years, several single-phase transfer delay-based PLLs (TD-PLLs) have been proposed in the literature. T...

The dc component, which may be caused by different factors in the grid voltage, is one of the disturbances that may severely affect the performance of grid synchronization systems and, therefore, grid-tied power converters. In the phase-locked loop (PLL) and frequency-locked loop (FLL) based grid synchronization systems, which this paper focuses on...

With the increased prevalence of power converters in power systems, especially three-phase voltage source converters (VSCs), the stability analysis of power electronics-based power systems has received much attention recently. To this end, different impedance models for three-phase VSCs, such as the dq-domain, sequence-domain, and phasor-domain imp...

In recent years, single-phase frequency-locked loops (FLLs) are gaining more popularity as a signal processing and synchronization tool in a wide variety of engineering applications. In the power and energy area, a basic structure in designing the most of available single-phase FLLs is the second-order generalized integrator-based FLL (SOGI-FLL), w...

This paper proposes a cost-effective compensator to suppress harmonics and compensate the power factor of all-electric shipboard power systems (SPSs). This compensator, which is based on a fixed capacitor-thyristor controlled reactor (FC-TCR), behaves as a low-pass filter and therefore can reject both low and high-order harmonics. Moreover, the FC-...

Synchronization techniques can be classified into open-loop and closed-loop methods. In power and energy applications, which are the focus here, the latter type is more popular.
Phase-locked loops (PLLs) and frequency-locked loops (FLLs) are two broad categories of closed-loop synchronization techniques. The aim of this paper is providing a review...

All-pass filter (APF) passes all frequency components of a signal without altering their amplitude, but changes their phase. This feature has made the APF a versatile building block in different signal processing applications. The focus of this article is on APF-based phase-locked loops (PLLs), where the APF is required for creating a
$\text{90}^\...

To suppress the most dominant harmonic currents and compensate for the power factor (PF) of electric generators (EGs), a technique based on passive power filters (PPFs) is presented here. The key feature of the proposed method is the implementation of only a set of PPFs for compensating the power‐quality issues of two EGs. This characteristic makes...

This paper proposes a novel method to locate faults in an AC-meshed microgrid. To this end, a set of features is first extracted and selected from the measured signals and fed to a Support Vector Machine (SVM) to detect the occurrence of fault. Then, the Distributed Generator (DG) with the lowest amount of fundamental voltage, which is the closest...

Frequency-locked loops (FLLs) create a rather large category of closed-loop synchronization techniques, which have received considerable attention in different engineering applications, particularly for synchronization, signal processing, and control purposes. Focusing on single-phase grid applications, designing FLLs is often based on a second-ord...

A frequency-locked loop (FLL) is a stationary reference frame adaptive recursive filter with a high popularity in different engineering applications, particularly for extracting the grid voltage parameters and synchronization of power converters. In three-phase applications, the reduced-order generalized integrator-based FLL (ROGI-FLL) is a standar...

The introduction of virtual-synchronous machine (VSM) and generator (VSG) as well as synchronous inverter (synchronverter), in recent years, has facilitated the integration of inverter-interfaced distributed energy resources (IIDERs) into the synchronous generator (SG) dominant microgrids and power grid. In this concept, the voltage source inverter...

In three-phase systems, using the delayed signal cancellation (DSC) operators is one of the most popular approaches for designing advanced phase-locked loops (PLLs), particularly for applications where a high disturbance rejection ability is demanded. In single-phase systems, however, they have not received a considerable attention. The aim of this...

Fault Current Limiters (FCLs) are one of the main solutions to upcoming challenges in microgrid protection. Regarding the high penetration of distributed generations (DGs) in future power system, designing cheap and effective FCL is a necessity. The present study addresses this issue by proposing an embedded FCL operating based on modifying the sec...

The grid synchronization unit, which is often based on a frequency-locked loop (FLL) or a phase-locked loop (PLL), highly affects the power converter performance and stability, particularly under weak grid conditions. It implies that a careful stability assessment of grid synchronization techniques (GSTs) is of vital importance. This task is most o...

Contrary to the phase-locked loop (PLL), which has almost reached a mature stage of development in power and energy applications (particularly in three-phase systems), the frequency-locked loop (FLL) is not a mature technique yet. This is probably because of the implementation of FLLs in the stationary reference frame which makes their modeling, tu...

In three-phase power and energy applications, the synchronous reference frame phase-locked loop (SRF-PLL) is a popular tool for the synchronization purposes. The SRF-PLL can be easily and effectively customized for different scenarios by changing its loop filter. Recently, some supposedly different PLLs using the steady-state linear Kalman filter (...

The second-order generalized integrator-based frequency-locked loop (briefly called the SOGI-FLL) is a well-known tool for filtering and synchronization purposes in the power and energy applications. The SOGI-FLL, nevertheless, has a limited ability in rejecting the grid voltage disturbances. To deal with this problem, two advanced SOGI-FLLs have b...

In this paper, a voltage modulated direct power control for three-phase pulse-width modulated rectifier is proposed. With the suggested method, the differential equations describing the rectifier dynamics are changing from a linear time-varying system into a linear time-invariant one. In this way, the conventional feedback and feedforward controlle...

In power and energy applications, implementing a large number of phase-locked loops (PLLs) involves using transfer delays. These delays are employed for different control and filtering purposes, such as creating a fictitious orthogonal signal (which is required for the frame transformation in singlephase PLLs) and filtering harmonics, dc offset, an...

From the control point of view, synchronization techniques are divided into two major categories: Open-loop and closed-loop methods. Roughly speaking, open-loop synchronization (OLS) approaches are not as popular as closed-loop ones, probably because they suffer from a poor performance in the presence of frequency drifts. This is particularly true...

In recent years, a large number of three-phase phase-locked loops (PLLs) have been developed. One of the most popular ones is the complex coefficient filterbased PLL (CCF-PLL). The CCFs benefit from a sequence selective filtering ability and, hence, enable the CCF-PLL to selectively reject/extract disturbances before the PLL control loop while main...

In recent years, the shunt active power filters (SAPFs) have received much attention for compensating the harmonic pollution and also providing the reactive content. A crucial issue in controlling the SAPF is generating the reference compensating current (RCC). Typical approaches for this purpose are using the discrete Fourier transform (DFT) in th...

In this paper, a DC-link voltage protection (DCVP) control method is proposed to address the DC-link overvoltage issue due to power back-feeding in parallel Uninterruptible Power Supply (UPS) system. The proposed control method is able to protect the inverter against the excessive DC-link voltage, which increases the system reliability and robustne...

The proportional-resonant (PR) controller is highly popular for controlling grid-connected voltage source converters. The resonant part of this controller provides an infinite gain at the nominal frequency and, in this way, ensures a zero steady-state tracking error when the grid frequency is at its nominal value. In the presence of frequency drift...

To regulate the DC-link voltage of three-phase AC/DC converters, an enhanced state observer (ESO)-based controller is presented in this letter. The proposed controller, contrary to the traditional ones, does not require the DC-link current measurement and offers a “plug and play” capability, a rather high disturbance rejection ability and robustnes...

The current control of grid-connected converters is typically carried out by using the proportional-resonant controllers or the synchronous reference frame proportional-integral regulators. The implementation of these controllers requires knowledge of the grid voltage frequency/phase angle, which is often provided by a synchronization unit. It impl...

The rectangular window filter, typically known as the moving average filter (MAF), is a quasi-ideal low-pass filter that has found wide application in designing advanced single-phase phase-locked loops (PLLs). Most often, the MAF is employed as an in-loop filter within the control loop of the single-phase PLL. The in-loop MAF, however, causes a lar...

Using multiple notch filters (NFs) inside the control loop of a standard PLL is a basic strategy to improve its filtering capability. Often, adaptive NFs (ANFs) are employed for this purpose as they can block the disturbance components even under off-nominal grid frequencies. This advantage is at the cost of a rather considerable increase in the PL...

The implementation of a large number of single-phase phase-locked loops (PLLs) involves creating a fictitious quadrature signal. A popular approach for this purpose is using a second-order generalized integrator-based quadrature signal generator (SOGIQSG) because it results in an acceptable speed/accuracy tradeoff. The SOGI-QSG based PLL (or briefl...

Single-phase phase-locked loops (PLLs) are popular for the synchronization and control of single-phase gridconnected converters. They are also widely used for monitoring and diagnostic purposes in the power and energy areas. In recent years, a large number of single-phase PLLs with different structures and properties have been proposed in the liter...

In very recent years, some attempts for designing high-order frequency-locked loops (FLLs) have been made. Nevertheless, the advantages and disadvantages of these structures, particularly in comparison with a standard FLL and high-order PLLs, are rather unclear. This lack of knowledge is attributable to the difficulty of small-signal modeling of th...

All grid-connected power converters require a device/algorithm for the synchronization with the utility grid. Among different synchronization techniques that have been proposed in recent years, the phase-locked loop (PLL) is high probably the most popular one. The PLL, however, in its standard structure, has a limited filtering capability. A simple...

Phase-locked loops (PLLs) are undoubtedly the most popular synchronization technique in the power and energy applications. A challenging problem of designing PLLs is the presence of dc offset in their input, which causes fundamental-frequency oscillatory errors in their estimated quantities. In this paper, a novel method to tackle this problem is p...

In three-phase applications, the synchronous-
reference frame phase-locked loop (SRF-PLL) is a standard PLL,
which benefits from a simple structure and satisfactory perfor-
mance under symmetrical and undistorted grid conditions. Under
unbalanced and harmonically distorted conditions, however, it
suffers from a very poor performance in the detectio...

Generally speaking, designing single-phase phaselocked loops (PLLs) is more complicated than three-phase ones, as their implementation often involves the generation of a fictitious orthogonal signal for the frame transformation. In recent years, many approaches to generate the orthogonal signal have been proposed, the simplest perhaps being the tra...

The phase, frequency, and amplitude of the fundamental-frequency positive-sequence component of the grid voltage are crucial information in control of most grid-connected power electronic based equipment. Often, a standard phaselocked loop (PLL) with a prefiltering stage is employed for the extraction of them. Inspired by the concept of delayed sig...

The quadrature signal generation-based phase-locked loops (QSG-PLLs) are highly popular for synchronization purposes in single-phase systems. The main difference among these PLLs often lies in the technique they use for creating the fictitious quadrature signal. One of the most popular QSG approaches is delaying the original single-phase signal by...

A phase-locked loop (PLL) is a nonlinear negative-feedback control system that synchronizes its output in frequency as well as in phase with its input. PLLs are now widely used for the synchronization of power electronics-based converters and also for monitoring and control purposes in different engineering fields. In recent years, there have been...

To improve the disturbance rejection capability of phase-locked loops (PLLs), which are undoubtedly the most common synchronization tool in power and energy applications, using different filtering techniques have been suggested in the literature. Among these filtering strategies, the delayed signal cancellation (DSC) operator is highly popular prob...

Without any doubt, phase-locked loops (PLLs) are the most popular and widely used technique for the synchronization purposes in the power and energy areas. They are also popular for the selective extraction of fundamental and harmonic/disturbance components of the grid voltage and current. Like most of the control algorithms, designing PLLs involve...

The estimation of the grid voltage fundamental parameters, i.e., the phase, frequency, and amplitude, is required for a wide variety of applications, particularly for synchronization and control of grid-connected converters and for monitoring and protection purposes in power systems. To accomplish this task, many approaches have been proposed in th...

Inspired by induction machines working principles, this paper presents the idea of phase-locked-loop-less (PLL-less) operation of grid-connected voltage source converters (VSCs) under new concept of inducverter. The proposed controller eliminates the need for a dedicated synchronization process and the related PLL, and therefore it offers a simpler...

Designing an effective phase-locked loop (PLL) for three-phase applications is the objective of this paper. The designed PLL structure is able to provide an accurate estimation of grid voltage frequency and phase even in the presence of all harmonic components of both positive and negative sequences and dc offset in its input. It addition to offer...

A basic approach to improve the performance of phase-locked loop (PLL) under adverse grid condition is to incorporate a first-order low-pass filter (LPF) into its control loop. The first-order LPF, however, has a limited ability to suppress the grid disturbances. A natural thought to further improve the disturbance rejection capability of PLL is to...

This study presents a simple and efficient approach for grid voltage estimation based on the converter equations in the stationary reference frame. The proposed technique is adopted for the sensorless operation of the voltage source converter-based power conditioners. In this study, the effectiveness of the proposed estimation method when it is com...

Despite the wide acceptance and use of the conventional synchronous reference frame phase-locked loop (SRF-PLL), no transfer function describing its actual input-output relationship has been developed so far. Arguably, the absence of such transfer function has hampered the application of SRF-PLL as a filter or controller inside the closed-loop cont...

The presence of the dc component in the phase-locked loop (PLL) input results in fundamental frequency oscillations in the phase and frequency estimated by the PLL. The removal of these oscillations is a challenging task because of their low frequency. The aim of this paper is to provide a detailed analysis of several approaches that little work ha...

The grid voltage phase and frequency are crucial information in control of most grid-connected power electronic-based equipment. Most often, a phase-locked loop (PLL) is employed for this purpose. A PLL is a closed-loop feedback control system that the phase of its output signal is related to the phase of its input signal. Arguably, the simplest PL...

The phase-locked loops (PLLs) are widely used in different areas of applications particularly for synchronization and control purposes in grid connected applications. A major challenge associated with the PLLs is how to improve their dynamic performance without jeopardizing their stability and filtering capability. Recently, some approaches based o...