Hossein Dehghani Tafti

• Doctor of Philosophy
• Research Associate at The University of Western Australia

Flexible power point tracking (FPPT) is incorporated in photovoltaic (PV) systems to enhance the quality and reliability of electricity generation while minimizing grid disruptions and overloads. Grid-friendly systems that contribute to grid control can be developed by modifying maximum power point tracking (MPPT) algorithms. However, the widely us...

Flexible power point tracking (FPPT)-based photo- voltaic (PV) controls are widely applied to mitigate PV power fluctuations due to intermittent irradiance changes. In dc mi- crogrid (dcMG) systems, the utilization of a battery energy storage system (BESS) can be alleviated by adjusting the PV power generation to meet the demand. However, conventio...

To maximize conversion efficiency, photovoltaic (PV) systems generally operate in the maximum power point tracking (MPPT) mode. However, due to the increasing penetration level of PV systems, there is a need for more developed control functions in terms of frequency support services and voltage control to maintain the reliability and stability of t...

Using energy storage (ES) in grid-connected photovoltaic (PV) generators is an efficient solution to deliver regulated power to the grid despite fluctuations in solar irradiance. The article analyses a single-phase grid-connected PV generators with ES, where the ES has a low voltage, namely without too many series-connected storing cells. The PV ge...

Grid-connected photovoltaic (PV) systems enhance grid stability during frequency fluctuations by adopting power reserve control (PRC) and contributing to frequency regulation. The cascaded H-bridge (CHB) converter is a suitable choice for large-scale photovoltaic systems. This paper introduces a distributed PRC strategy designed for CHB-based PV sy...

Flexible power point tracking (FPPT) is incorporated in photovoltaic (PV) systems to enhance the quality and reliability of electricity generation while minimizing grid disruptions and overloads. Grid-friendly systems that contribute to grid control can be developed by modifying maximum power point tracking (MPPT) algorithms. However, the widely us...

Flexible power point tracking (FPPT) control algorithms have been introduced in the literature to provide frequency support in low-inertia grid-connected photovoltaic (PV) systems. This is achieved by regulating the PV output power to a power reference obtained from the energy management system. Partial shading of PV arrays is a frequent phenomena...

This article introduces a dynamic power reserve control methodology called reserve power point tracking (RPPT) for grid-connected photovoltaic (PV) plants. The proposed RPPT methodology is employed to ensure availability of the required power reserve to support the grid and accordingly facilitate high penetration of PV generation in the grid. Imple...

An extensive experimental analysis of the behavior of thirty-one off-the-shelf distributed photovoltaic (DPV) inverters to voltage phase angle jump (VPAJ) disturbance is done in this paper. Classification of undesirable behavior from DPV inverters is carried out based on the responses to voltage phase angle jump and identified the cause of such beh...

In stand-alone dc microgrids, battery energy storage systems (BESSs) are conventionally used for regulating the dclink voltage, causing a continuous battery operation. Though operating the photovoltaic (PV) system at its maximum power point yields minimum battery discharge current, the opposite is true for battery charging current. Therefore, reduc...

Flexible power point tracking (FPPT) aims to regulate the output power of photovoltaic (PV) systems to a predefined value to enable grid support functionalities, such as virtual-inertia provision. Even though partial shading is a common condition in PV systems, especially in small-scale residential PV systems, the current literature, only investiga...

High penetration of renewable energy resources in the power system results in various new challenges for power system operators. One of the promising solutions to sustain the quality and reliability of the power system is the integration of energy storage systems (ESSs). This article investigates the current and emerging trends and technologies for...

Photovoltaic (PV) power fluctuations, caused by fast irradiance changes, because of passing clouds, may pose challenges to the stability and reliability of power systems with high penetration of PV inverters. In this regard, new standards impose power ramp rate control (PRRC) on grid-connected PV systems. Available solutions in the literature lack...

In a battery energy storage system (BESS) based on the cascaded H-bridge (CHB) converter or modular multilevel converter (MMC), the active power distribution among the submodules (SMs) can be highly unbalanced, especially when batteries with different power ratings are used. Meanwhile, there are certain limits for the unbalanced power distribution...

Implementing voltage boost multilevel inverter topologies for PV and fuel cell energy sources is highly advantageous. Switched-capacitor multilevel inverters (SCMLI) have a step-up feature with low device requirements and can remove the need for high gain dc-dc converters leading to reduced overall system bulk. This work proposes a dual input SCMLI...

The rapid increase in the installation of distributed photovoltaic (DPV) systems has led to an increased interest in modeling and analyzing residential inverters to understand their behavior and thereby understand the corresponding challenges to the distribution system. This article provides extensive experimental evidence on the behavior of 31 off...

High penetrations of rooftop photovoltaic (PV) systems are creating several challenges for distribution network operators, most critically overvoltage during periods of peak solar generation. To assist with voltage regulation across distribution networks, grid-supporting functions, such as Volt–Watt ( $P(V)$ ) and Volt–VAr ( $Q(V)$ ) response mod...

Replacing conventional synchronous generator-based power plants with inverter-based renewable energy resources results in a reduction of the inertia in power systems. To sustain the security and reliability of these low-inertia power systems, frequency support is increasingly required in new standards for grid-connected renewable energy resources,...

Battery energy storage systems (BESSs) are often integrated into stand-alone dc microgrids (dcMGs) with photovoltaic (PV) system to enhance the microgrid reliability and prevent the dc bus voltage instability arising from PV power generation intermittency and load demand transients. The battery degradation rate is critically influenced by its utili...

DC microgrids with photovoltaic (PV) systems often incorporate a battery energy storage system (BESS) to regulate the dc bus voltage fluctuations due to the intermittent irradiance changes and load transients. Traditional control schemes do not consider the battery charging rate, leading to high current stress and shortening the battery lifetime. I...

https://www.mdpi.com/journal/energies/special_issues/reliability_power_converters ______________________________________________________________________ Regular and review papers, technical reports, and Letters are the acceptable types of your possible manuscripts. If you have an original idea and want to record it as soon as possible (even more ra...

Conventionally, a flexible photovoltaic (PV) power control strategy is used to reduce battery utilization in stand-alone dc microgrids (dcMGs). However, conventional control schemes deploy multiple voltage controllers to regulate the dc-link voltage, causing mode transitions during the transients and complicating the controller design. This paper p...

In the operation of cascaded H-bridge (CHB) converters and modular multilevel converters (MMCs) with energy storage or renewable power resources, unbalanced active power distribution among the submodules (SMs) is unavoidable. Depending on the operating conditions, there are certain upper and lower limits on the active power that can be processed by...

Abstract--- This paper presents a constrained model predictive control (MPC) strategy for a three-phase low-capacitance static compensator (LC-StatCom) with delta configuration. The controller consists of an outer loop that provides dynamic references for the active grid current component and the circulating current; whereas the inner predictive lo...

DC microgrids (dcMGs) are gaining popularity for photovoltaic (PV) applications as the demand for PV generation continues to grow exponentially. A hybrid control strategy for a PV and battery energy storage system (BESS) in a stand-alone dcMG is proposed in this paper. In contrast to the conventional control strategies that regulate the dc-link vol...

This paper presents a control strategy for a dual-input neutral-point-clamped (NPC) inverter-based grid-connected photovoltaic (PV) system to asymmetrically control the PV arrays without incorporating any additional external circuit. This is achieved by employing an analytically developed linearization block, which helps in generating the required...

Dual active bridge (DAB) is one of the most popular high power isolated bidirectional dc–dc converter. It offers high power density, a low number of passive components, high efficiency. It is essential to model the converter so that it can be used in applications such as solid‐state transformer, micro‐grids, and dc distribution systems. Moreover, m...

Grid-connected photovoltaic (PV) systems impose challenges like voltage fluctuations, low system inertia and power quality issues. The need to tackle these challenges led to the introduction of flexible power point tracking (FPPT), where the PV power output is controlled by an energy management system (EMS), rather than solely operating the PV syst...

This paper presents a novel hybrid approach based on fuzzy logic controller and gravity search algorithm to track the global maximum pow er point of a netw ork-connected photovoltaic system in partially shaded conditions. One of the most critical issues in this context, w hich has been neglected in previous studies, is the consideration of speed an...

This paper proposes sectional theory and binary search-based maximum power point tracking (MPPT) algorithms for solar photovoltaic (PV) systems. The maximum power of the solar PV under various environmental conditions are obtained by employing these algorithms. The corresponding voltage of the maximum power is computed in every step with the propos...

This paper presents a dual-mode modulation technique which aims to control the average current flow into the neutral point (NP) of the neutral-point-clamped (NPC) converter without the need for any additional hardware. The two modes of operation are normal mode and compensating mode. In the normal operation mode, all the three phases switch between...

A hybrid control strategy for photovoltaic (PV) system and energy storage system (ESS) in a dc microgrid is proposed in this paper. The proposed control strategy minimizes the utilization of ESS in order to prolong the battery lifetime, reduce the total system power losses, and maintain the state of- charge (SoC) of the battery within a desired ran...

Due to a dramatic increase in grid-connected renewable energy resources, energy storage systems (ESSs) are believed to be a must in future power systems, among which the modular multilevel converter (MMC)-based battery energy storage systems (BESSs) are one of the most modular, efficient and flexible topologies. Uneven active power distribution amo...

Grid-connected photovoltaic (PV) systems can provide grid support features by implementing flexible power point tracking (FPPT) strategies. Conventionally, the FPPT algorithms are based on linear search algorithms, like perturb and observe (P&O). These solutions offer good practical results but usually lead to oscillations around the steady state o...

The continuous increase in the demanded power capacity has made the two-level converter impractical in many applications. In order to increase the power rating, two main approaches are usually adopted: i) the use of multilevel power converters and/or ii) the combination of several converters with simpler structure to achieve higher power levels. Th...

In this paper, the effect of large double frequency capacitor voltage ripple (CVR) on harmonic performance, efficiency and capacitor lifetime in the cascaded H-bridge low capacitance StatCom (LC-StatCom) is analytically determined. With insight provided by the analysis, an LC-StatCom with modular switched capacitors is proposed that provides a degr...

Converters are playing an ever increasing role in electric power grids. To help facilitate a design of power grids that ensures stable and efficient transfer of power, the harmonic pollution injected by converters must be quantified. At present, analytic expressions used to describe modulated converter waveforms have been derived while assuming tha...

High power rated modern wind generators are demanding immaculate performance and greater reliability from the power electronics interface. In order to keep up to the challenges, advanced multilevel front‐end rectifiers and parallel operation of rectifiers are researched. A higher number of semiconductor switches make reliability estimation and feas...

The power system is experiencing an ever-increasing integration of photovoltaic power plants (PVPPs), which leads demand on the power system operators to force new requirements to sustain with quality and reliability of the grid. Subsequently, a significant quantity of flexible power point tracking (FPPT) algorithms have been proposed in the litera...

In this paper, a band-limited three-level modulation scheme is proposed for a three-phase NPC converter with an aim to balance the average capacitor voltages under all operating conditions. When conventional CBPWM is applied, the amplitude of NP voltage ripple tends to increase under linear imbalances, while the NP voltage can shift leading to inst...

This paper presents a novel hybrid approach based on fuzzy logic controller and gravity search algorithm to track the global maximum power point of a network-connected photovoltaic system in partially shaded conditions. One of the most critical issues in this context, which has been neglected in previous studies, is the consideration of speed and a...

This paper proposes a closed-loop analytic filtering scheme for capacitor voltage ripple in cascaded H-bridge converters. Although the technique can be applied to many cascaded converter applications, this paper focuses on the low-capacitance cascaded H-bridge static compensator. Filtering of capacitor voltage signals is particularly important in t...

A low-capacitance static compensator (LC-StatCom) based on a cascaded H-bridge (CHB) multilevel converter can be an efficient and low-cost solution for reactive power compensation in power grids. However, the reduced capacitance, and therefore faster capacitor voltage dynamics, makes it challenging to control it. Classical cascade control schemes,...

This paper proposes a multi-input linear time-variant control law based on the incremental passivity theory for cascaded H-bridge (CHB) low-capacitance static compensators (LC-StatComs). The proposed control law guarantees global asymptotic stability of the system and controls the capacitor voltages and inductor current without assuming fast dynami...

This paper presents a new modulation technique with feedforward compensation for the three-phase three-level neutral-point-clamped converter. With the proposed technique, the capacitor voltage ripples are allowed to vary within certain limits. This enables an optimised design of the converter since the maximum capacitor voltages are predefined. Fur...

This paper proposes a dc-link voltage shaping method for cascaded H-bridge (CHB) static synchronous compensators (StatCom). Recently proposed low capacitance-StatCom systems are able to significantly reduce dc-link capacitor values, by more than 50%, StatCom by operating with large voltage ripples on the dc-link capacitors. This offers the advantag...

Flexible power point tracking (FPPT) is the control of active power generated by grid-connected photovoltaic power plants (GCPVPPs) to provide grid-support functionality. An FPPT algorithm for the reduction of the extracted power from photovoltaic (PV) strings during voltage sags was previously proposed by the authors. An advantage of this algorith...

Power electronic converters are classified mainly based on the current or voltage source. Multilevel power converters, a new breed of power electronic converters, are being developed and evolved since the 1980s. This chapter explores the existing multilevel topologies such as multilevel cascaded H‐bridge inverter, modular multilevel inverter, and a...

Renewable energy sources are occupying an increasing share in the global power generation market. Among various renewable energy sources, photovoltaic (PV) technology has been in the focus of many governments, and the supported substantial subsidies have resulted a steep increase in the installed capacity. This chapter analyses the operation of gri...

The design and implementation of modulation techniques are relevant and important with the growth of multilevel converter topologies. Modulation schemes are applied to synthesize a good output voltage quality while allowing better control over both the magnitude and frequency of the output voltage. Multilevel modulation methods are basically classi...

This chapter analyses the different voltage balancing schemes for dc‐link capacitors used in three‐level inverters. The major unbalanced voltage condition across dc capacitors is caused as a series of connected diodes are clamped to the neutral point of both the series of connected capacitors. The chapter introduces the dc voltage balancing method...

This chapter presents an active balancing circuit for seven‐level (7L) inverter topologies. The seven‐level balancing circuit is known as the single‐input multiple‐output (SIMO) balancing circuit, which maintains six identical voltage levels in the dc bus. The chapter discusses the basic operating principle of the new seven‐level inverter topologie...

This chapter introduces a three‐phase three‐level unity power factor control rectifier with the power‐balanced control strategy based on decoupling hysteresis current control. Such decoupling current control is the new reference current generated by the grid current control and zero sequence current control. The control algorithm is divided into tw...

Offshore wind power has inspired the fields of high voltage direct current (HVDC) for advantages of high power transmission in long distance. Hefty wind generators are making advanced multilevel rectifier and parallel operation of rectifiers popular choice of research with the aim to accommodate higher power. Issues of reliability and complexity of...

One of the major concerns associated with the increasing penetration of grid-connected photovoltaic (PV) power plants is the operational challenges (e.g., overloading and overvoltage), imposed due to the variability of PV power generation. A flexible power point tracking (FPPT), which can limit the PV output power to a specific value, has thus been...

This paper proposes an analytical expression for the calculation of active and reactive power references of a grid-tied inverter, which limits the peak current of the inverter during voltage sags. The key novelty is that the active/reactive power references are analytically calculated based on the dc-link voltage and grid codes, while they do not d...

Multilevel cascade H-bridge (CHB) converters are one of the promising solutions for medium- and largescale grid-connected photovoltaic power plants. However, there is a lack of a complete study about their operation during voltage sags. This paper proposes a flexible control strategy for the operation of photovoltaic grid-connected CHB inverters du...