Vassilios Georgios Agelidis

• Professor at Technical University of Denmark

The grid frequency estimation using a recursive signal or an integrator-based method may suffer from a stability issue due to an accumulation or discretization error. To avoid these shortcomings and also to obtain a robust estimation of three-phase grid frequency under unbalanced and distorted conditions, this letter proposes a demodulation-based m...

This paper proposes a fast and robust technique for instantaneous phase angle estimation of three-phase voltage systems under unbalanced and distorted conditions. It mainly relies on the Clarke transformation, Teager energy operator and delayed signal cancellation (DSC) approach. Unlike an adaptive DSC-based synchronous-reference frame phase-locked...

This paper discusses the control of large-scale grid-connected photovoltaic power plants (GCPPPs) operating under unbalanced grid voltage sags. The positive and negative sequences of the output currents are controlled to achieve different targets: injecting constant power (i) to the grid, or (ii) to the ac side of the converter, i.e., including the...

This study proposes a frequency estimation technique for single‐phase systems in the presence of harmonic pollution. The technique is based on three consecutive samples and has an infinite‐impulse response, thus being a relatively simple one. It is immune to harmonic distortion at both nominal and off‐nominal frequencies. In addition, it offers fre...

Harmonic resonances in traction power supply systems (TPSSs) have attracted great attention due to their potentially destructive impact on the safe and stable operation of railways. Based on operation data acquired from Chinese railways, this paper presents a comprehensive review of this issue considering both academic and engineering requirements....

A frequency adaptive technique relying on a linear Kalman filter (KF) is presented here for robust estimation of voltage harmonics under variable frequency conditions in a single‐phase system. A relatively simple frequency‐locked loop (FLL) is combined with the linear KF (LKF‐FLL) to achieve frequency adaptive ability and avoid the use of a non‐lin...

This paper proposes a technique for accurate phase estimation of distorted three-phase grid voltages including unbalanced amplitudes and/or phase angles. An adaptive cascaded delayed signal cancellation (CDSC) strategy is used for the generation of the amplitude balanced three-phase voltages. The CDSC strategy also eliminates both odd and even harm...

Information is the pathway to smart electricity distribution grids. Current trends point at phase measurement units (PMUs) becoming the gateway to getting distribution grid information to increase its observability, controllability and monitoring and deliver more advanced grid services and other functionalities. Grid-connected power electronics con...

Modeling of battery energy storage systems (BESS) used for applications, such as electric vehicles and smart grids, emerged as a necessity over the last decade and depends heavily on the accurate estimation of battery states and parameters. Depending on the battery-cell type and operation, a combination of algorithms is used to identify battery par...

In the last two decades, emerging use of renewable and distributed energy sources in electricity grid has created new challenges for the utility regarding the power quality, voltage stabilization and efficient energy utilization. Power electronic converters are extensively utilized to interface the emerging energy systems (without and with energy s...

This paper proposes a framework to develop an optimal power dispatch strategy for grid-connected wind power plants containing a Battery Energy Storage System (BESS). Considering the intermittent nature of wind power and rapidly varying electricity market price, short-term forecasting of these variables is used for efficient energy management. The p...

In this paper, an adaptive dispatch strategy is presented to maximize the revenue for grid-tied wind power plant coupled with a battery energy storage system (BESS). The proposed idea is mainly based on time-varying market-price thresholds, which are varied according to the proposed algorithm in an adaptive manner. The variable nature of wind power...

Testing and verification of high-level and low-level control, modulation, fault handling and converter coordination for modular multilevel converters (MMCs) requires development of experimental prototype converters. In this paper, we provide a a complete overview of the MMC-based experimental prototype at UNSW Sydney (The University of New South Wa...

Estimation-based indirect dc-voltage control in MMCs interacts with circulating current control methods. This paper proposes an estimation-based indirect dc-voltage control method for MMC-HVDC systems and analyzes its performance compared to alternative estimations. The interactions between estimation-based indirect dc-voltage control and circulati...

In order to compensate multiple time scales power fluctuation resulted from distributed energy resources and loads, hybrid energy storage systems are employed as the buffer unit in DC microgrid. In this paper, a wireless hierarchical control strategy is proposed to realize power sharing between energy density storage unit and power density storage...

Reliability worth analysis is of great importance in the area of distribution network planning and operation. The reliability worth’s precision can be affected greatly by the customer interruption cost model used. The choice of the cost models can change system and load point reliability indices. In this study, a cascade correlation neural network...

Vehicle to grid (V2G) reactive power compensation using electric vehicle (EV) onboard chargers helps to ensure grid power quality by achieving unity power factor operation. However, the use of EVs for V2G reactive power compensation increases the second-order harmonic ripple current component at the DC-side of the charger. For single-phase, single-...

In this work, a Model Predictive Control (MPC) strategy that combines Finite-Control-Set MPC (FCS-MPC) with Selective Harmonic Elimination (SHE) modulation pattern in its formulation is proposed to govern multilevel power converters. Based on a desired operating point for the system state (converter current reference), an associated predefined SHE...

Operational data from Chinese railways indicate a number of challenges for traction four-quadrant converter (4QC) control including low-order voltage and current harmonics and reference tracking. A control strategy for a single-phase three-level neutral-point-clamped 4QC employed in the electric multiple unit traction system is proposed in this stu...

This paper proposes a new convex model predictive control strategy for dynamic optimal power flow between battery energy storage systems distributed in an AC microgrid. The proposed control strategy uses a new problem formulation, based on a linear d-q reference frame voltage-current model and linearised power flow approximations. This allows the o...

This paper proposes a new convex model predictive control strategy for dynamic optimal power flow between battery energy storage systems distributed in an AC microgrid. The proposed control strategy uses a new problem formulation, based on a linear d-q reference frame voltage-current model and linearised power flow approximations. This allows the o...

This paper proposes the novel use of multi-agent sliding mode control for state of charge balancing between distributed DC microgrid battery energy storage systems. Unlike existing control strategies based on linear multi-agent consensus protocols, the proposed nonlinear state of charge balancing strategy (i) ensures the battery energy storage syst...

A decentralised control method that deals with current sharing issues in dc microgrids (MGs) is proposed in thisstudy. The proposed method is formulated in terms of 'modified global indicator' concept, which was originally proposedto improve reactive power sharing in ac MGs. In this work, the 'modified global indicator' concept is extended tocoordi...

This paper investigates the optimal operation and management of micro-grids (MGs) considering the high penetration of different types of renewable energy sources (RESs) and plug-in electric vehicles (PEVs). Optimal operation of MG is a precious and economic strategy for improving the situation of MG from different aspects such as reducing power los...

In a conventional finite control set model predictive control (FCS-MPC) formulation, active and reactive power control loops rely on the predictive controller, whereas the dc-bus voltage is usually governed by a PI-based control loop. This originates from fact that the dynamic equations for describing the predictions of these variables are heavily...

This work presents a predictive control strategy for grid-connected Cascaded H-Bridge (CHB) converters under unbalanced power generation among each converter phase. The proposed controller belongs to the Finite-Control-Set Model Predictive Control (FCS-MPC) family and is designed to extract unbalanced power from each CHB converter phase while provi...

In this paper, a model predictive control (MPC) based on optimal switching sequences (OSSs) for a single-phase grid-connected full-bridge neutral-point-clamped (NPC) power converter is presented. The predictive control algorithm is formulated in terms of OSSs, which was originally proposed to govern three-phase power converters. In this work, the O...

The cascaded H-bridge (CHB) converter is becoming a promising candidate for use in next generation large-scale photovoltaic (PV) power plants. However, solar power generation in the three converter phaselegs can be significantly unbalanced, especially in a large geographically-dispersed plant. The power imbalance between the three phases defines a...

Research on dc-fault tolerant multilevel converters has gained noticeable attention over recent years. The arm converter (AAC) is one of such emerging multilevel converter topologies, and a hybrid topology of the two-level converter and the modular multilevel converter (MMC). Bipolar sub-modules (SMs) that can produce both positive and negative vol...

The alternate arm converter (AAC) is a multilevel converter of the same family as the modular multilevel converter (MMC). Contrary to the MMC, the AAC offers dc-fault tolerant capabilities but requires complex submodule (SM) capacitor voltage/energy regulation and circulating current control. Such control is also limited due to the small overlap pe...

The cascaded H-bridge (CHB) low-capacitance StatCom (LC-StatCom) has a limited operating area in the inductive region compared to a conventional StatCom’s V-I characteristic. This limitation for operation in the inductive region is considered to be the biggest disadvantage of CHB LC-StatCom. In this paper, the effect of adding parallel and series r...

This paper presents an overview of the state of the art control strategies specifically designed to coordinate distributed energy storage systems in microgrids. Power networks are undergoing a transition from the traditional model of centralised generation towards a smart decentralised network of renewable sources and energy storage systems, organi...

AC electric locomotives that use a number of interleaved four-quadrant converters (4QCs) generate high frequency switching harmonics which may stimulate certain resonances in traction power supply systems (TPSSs). A windowed selective harmonic elimination pulse-width modulation (SHE-PWM) method is proposed to suppress such resonances. Owing to the...

Photovoltaic (PV) power generation levels in the three phases of a multilevel cascaded H-bridge (CHB) converter can be significantly unbalanced owing to different irradiance levels and ambient temperatures over a large-scale solar PV power plant Injection of a zero-sequence voltage is required to maintain three-phase balanced grid currents with unb...

The need for continuous temperature monitoring and thermal management is unquestionable as operating temperature is a critical factor affecting many electrical/electronic components and devices, including energy storage such as batteries and supercapacitors (SCs). On the other hand, many applications require the battery or SC cells to be stacked up...

In conventional parallel hybrid energy storage systems (HESSs), there are usually two cascaded converters active when transferring energy between its energy storage systems (ESSs) that result in the overall efficiency drop. Moreover, the dc-link capacitor has to be oversized to limit the voltage ripple during simultaneous energy exchange between th...

This paper proposes a new method for measuring capacitor voltages in multilevel flying capacitor (FC) converters that requires only one voltage sensor per phase-leg. Multiple dc voltage sensors traditionally used to measure the capacitor voltages are replaced with a single voltage sensor at the ac-side of the phase-leg. The proposed method is subse...

The matlab code allows you to model the i-v and p-v charateristic of photovoltaic modules as a 3D look-up table that can be used in Matalb, Simulink or other software like PLECS. The model generated is according to the single-diode, 5 parameters equivalent circuit. The ideal application of this research would be to model the PV input source in powe...

This paper proposes a multi-agent dynamic optimal power flow strategy for microgrids with distributed energy storage systems. The proposed control strategy uses a convex formulation of the AC dynamic optimal power flow problem developed from a d-q reference frame voltage-current model and linear power flow approximations. The convex dynamic optimal...

Chaotic sinusoidal pulse-width modulation (SPWM) can be used to suppress electromagnetic interference in power converters. In this paper, a mathematical method for estimating power losses in insulated-gate bipolar transistors (IGBTs) and freewheeling diodes occurring under chaotic frequency modulation SPWM (CFM-SPWM) switching is proposed. The meth...

Amongst the main control targets in a modular multilevel converter (MMC) is the control of the circulating currents within the phase-legs of the topology. This paper presents a controller for the circulating current of the MMC that utilises the available redundancies of the multilevel waveform in 2N + 1 modulated MMCs in order to regulate the circu...

This paper presents a methodology to minimize the total cost of buying power from different energy producers including renewable energy generations particularly within the context of a microgrid. The proposed idea is primarily based on the controlled operation of a battery energy storage system (BESS) in the presence of practical system constraints...

The three-phase boost inverter is a differential inverter topology which can provide both boosting and inversion functions in a single power processing stage. If the switching frequency ripple current component is ignored, the DC side current of the three-phase boost inverter contains only a DC component when all three converter legs are identical....

The non-inverting four switches buck-boost (FSBB) converter is a topology which has recently attracted considerable attention in the area of Photovoltaic (PV) module-integrated power electronics. Due to limitations in the switching speed of MOSFETs and delays introduced to avoid current shoot-through, the gain function of such converter exhibits a...

Due to the high penetration of the installed distributed generation units in the power system, the injection of reactive power is required for the medium-scale and large-scale grid-connected photovoltaic power plants (PVPPs). Because of the current limitation of the grid-connected inverter, the injected active power should be reduced during voltage...

High-voltage direct-current (HVDC) based power distribution networks have become an attractive alternative to classical ac distribution networks in more electric aircrafts (MEAs). This paper proposes a power flow management system for an isolated multiport power converter (MPC), which includes a high-frequency transformer, that controls the power f...

Distribution automation systems in terms of automatic and remote-controlled sectionalizing switches allows distribution utilities to implement flexible control of distribution networks, which is a successful strategy to enhance efficiency, reliability and quality of service. The sectionalizing switches play a significant role in an automated distri...

This paper reports the performance of a linear Kalman filter (KF) based technique to estimate the singlephase grid voltage fundamental amplitude and frequency under distorted grid conditions. An enhanced frequencylocked loop is combined with the linear KF to obtain the frequency adaptive capability of the technique. A frequency domain analysis is p...

We present EWNN, a new approach for forecasting the hourly electricity load profile for the next day, from a time series of previous electricity loads. EWNN extends the well-known and successful weighed nearest neighbor method WNN by operating at hourly level and by incorporating feature selection. In contrast to WNN, EWNN builds a separate predict...

Model predictive control (MPC) technologies could deliver numerous competitive advantages for power electronics converters and systems with varying impact and benefits. However, assessing the benefits of such advanced and relatively complex control methods at both converter and system level for specific industrial applications is a serious challeng...

Creating a meaningful photovoltaic (PV) model for circuit simulation software is a task that designers of PV interfacing converters usually deal with during the early stage of a project. The electrical behavior of a PV module can be represented by a 3D lookup table storing values of the PV current for different values of voltage, solar irradiation...

This paper presents a hierarchical control strategy for a multi-module battery energy storage system, with distributed sliding mode controllers for state of charge balancing between modules. Under the proposed control strategy, a central controller generates a nominal module output power reference to regulate the total battery energy storage system...

Permanent Magnet Synchronous Generators (PMSGs) are increasingly considered for large, direct-drive MW level wind energy conversion systems. High-efficiency, high-power density, low maintenance, and high reliability are some cited benefits of PMSGs making them attractive for onshore and offshore wind systems. However, as the PMSG's power level incr...

The bulky electrolytic capacitors that are typically used at the dc-bus of back-to-back topologies limit the reliability of the system and their elimination can benefit the reliability and operational life of a power electronics converter. This paper presents the interconnection of two ac systems through a dc-bus capacitor-less back-to-back convert...

This letter proposes a phase-shifted pulse-width modulation (PS-PWM) technique for the flying capacitor (FC) multilevel converter that improves the quality of the line-to-line voltages. In traditional PS-PWM, the line-to-line voltages include intervals that switch between nonadjacent voltage levels, which deteriorates the harmonic performance. The...

Phase-shifted carrier modulation is an industry standard in its application to multilevel H-bridge converters. The major advantage of this scheme over level-shifted and space vector modulation schemes is its inherent ability to evenly distribute losses between semiconductor devices. However, phase-shifted schemes suffer from harmonic degradation wh...

We consider the task of forecasting the electricity power generated by a solar PhotoVoltaic (PV) system for forecasting horizons from 5 to 60 min ahead, from previous PV power and meteorological data. We present a new method based on advanced machine learning algorithms for variable selection and prediction. The correlation based variable selection...

Reliable prediction of solar power is very important to increase the penetration of this renewable energy source into the electricity grid. In this paper, we consider the task of forecasting solar power output from Photovoltaic (PV) systems at half-hourly intervals. We propose a new approach based on recurrent neural networks trained with cooperati...

We consider the task of forecasting the electricity power generated by a photovoltaic solar system, for the next day at half-hourly intervals. The forecasts are based on previous power output and weather data, and weather prediction for the next day. We present a new approach that forecasts all the power outputs for the next day simultaneously. It...

In the integrated reconfigurable converter (IRC) topology for high-voltage series-connected battery module systems, the converter can be reconfigured into a range of operating modes: 'feeding a load' mode, 'battery modules balancing' mode, 'regenerative' mode, 'charging' mode, and 'backup' mode. In most battery applications, a battery-balancing sys...

In this paper, a cascaded H-Bridge (CHB)-multilevel converter (MC)-based photovoltaic (PV) system with no voltage or current sensors at the dc-side is proposed. Eliminating the dc-side sensors simplifies the hardware, leading to lower cost and higher reliability of the PV system. A novel scheme estimating the capacitors' voltages from the ac output...

A novel monotonic strategy following a consistent charging/discharging direction for each individual battery connected in parallel to form a large-scale battery energy storage system (BESS) is proposed in this paper. The BESS is coordinated with a large wind farm to smooth out the intermittent nature of the farm's output fed to an electricity grid....

The increasing penetration of renewable energy sources (RES) poses a major challenge to the operation of the electricity grid owing to the intermittent nature of their power output. The ability of utility-scale battery energy storage systems (BESS) to provide grid support and smooth the output of RES in combination with their decrease in cost has f...

Model-based temperature estimation has been widely studied and applied in many applications, including for power/energy storage applications such as batteries or supercapacitors (SCs). In this paper, sensors placement for a temperature monitoring and diagnostic system is studied, with respect not only to the state estimation during normal condition...

This paper proposes an active damping technique for grid-connected converters using inductor-capacitor-inductor (LCL) filters. The technique relies on a discrete-time adaptive notch filter (NF) which is able to adapt its resonance frequency and bandwidth in real-time. The tuning function of this filter can be used in the case when the resonance fre...

Interleaving of voltage-source converter (VSC) legs enables higher output currents per phase, effectively increasing the power rating without increasing semiconductor ratings. However, the interleaved operation results in circulating currents between each phase converter legs as well as a zero-sequence circulating current (ZSCC), which become quite...

This paper presents a Proportional Resonant (PR) based circulating current controller for four parallel interleaved Voltage Source Converters (VSCs). Interleaving the carrier signals will cause a switching frequency circulating current to flow between the VSCs. Therefore, to suppress these circulating currents the VSCs are interconnected through Co...

This study proposes a MHz gate driving solution for silicon carbide (SiC) metal oxide semiconductor field effect transistor (MOSFET), which enables multiplication of the switching frequency by using the n-type eGaN FET technology and by connecting half-bridges in parallel. Phase-shifted pulse width modulation is used to multiple the output frequenc...

In this paper, the optimal energy management of MGs (micro grids) including RESs (renewable energy sources), PHEVs (plug-in hybrid electric vehicles) and storage devices is studied by a new stochastic framework that considers the uncertainties in modelling of PHEVs and RESs using the well-known Monte Carlo simulation. In order to see the influence...

This study presents the experimental verification of an interleaved high-gain (IHG) DC-DC converter using series and parallel configurations. The interleaved configurations allow the converter to achieve high voltage gain and high current rating, thus increasing the power rating of the converter. Analytical expressions for the design of these inter...

The study presents experimental verification of a zero-current-switching (ZCS) bidirectional interleaved switched-capacitor (BISC) DC-DC converter that features bidirectional power flow capability and a high-voltage conversion ratio. In addition, the interleaved configuration of the converter and its modular design enable both its current rating an...

This paper discusses the control of large-scale grid-connected photovoltaic power plant (GCPPP) operating under unbalanced grid voltages. The positive and negative sequences of the grid currents need to be controlled to regulate the power injected into the grid during unbalanced grid voltages. This paper shows that the use of conventional proportio...

The increasing installation capacity of large-scale photovoltaic (PV) systems requires higher power-rated converters and connection at a higher voltage level at the point of common coupling (PCC). Additionally, the inherent intermittency of the solar irradiation affects both transient- and steady-state operation of these PV systems. This paper prop...

This paper proposes a novel method based on information gap decision theory to evaluate a profitable operation strategy for combined heat and power units in a liberalized electricity market. Risk levels can be assessed using this technique, taking into consideration whether the generation company is either risk-taking or risk averse. The test syste...

The boost inverter based battery-supercapacitor hybrid energy storage systems (HESSs) are a popular choice for the battery lifetime extension and system power enhancement. Various sliding mode (SM) controllers have been used to control the boost inverter topology in literature. However, the traditional SM controllers for the boost inverter topology...

Multilevel cascaded H-bridge converters are promising candidates for next generation photovoltaic power converters. They feature reduced switching losses and higher conversion efficiency with modular structure; characteristics vital for large-scale photovoltaic power plants. However, the stochastically-variable nature of irradiance levels and ambie...

In this study, the calculations of flexible AC transmission system (FACTS) devices energy function and corrected transient energy function (CTEF) in presence of FACTS are formulated. The most versatile FACTS devices are modelled for transient-stability assessment using CTEF. Furthermore, the effects of FACTS devices on the corrected transient margi...

Multilevel cascaded H-bridge converters are promising candidates for large-scale photovoltaic power plants. They allow direct connection to medium-voltage distribution networks without the presence of bulky line-frequency power transformers. Owing to the stochastically-variable nature of irradiance level, ambient temperature and other factors, powe...

A cascaded H-bridge (CHB) converter is one of the viable options for next-generation large-scale photovoltaic (PV) power conversion. Owing to the increased number of components involved, converter reliability and fault-tolerant control are important issues. A CHB converter must also manage unequal power generation among bridges, which is inherent i...

This paper introduces a modulation method for the stacked multicell converters (SMCs). The proposed method is implemented using phase-disposition pulse width modulation and is capable of balancing and regulating the voltages of all the capacitors in the topology, i.e., the flying capacitors and the dc-link capacitors. The proposed method is also ab...

Filter-based battery-supercapacitor hybrid energy storage systems (HESSs) are popular as a way of extending battery lifetime by diverging the high-frequency power variations to the supercapacitor. However, when a traditional supercapacitor voltage controller (SCVC) is employed in the filter-based HESS, precise sizing of the supercapacitor as well a...

This paper introduces a cascaded H-bridge multilevel converter (CHB-MC)-based StatCom system that is able to operate with extremely low dc capacitance values. The theoretical limit is calculated for the maximum capacitor voltage ripple, and hence minimum dc capacitance values that can be used in the converter. The proposed low-capacitance StatCom (...

In the paper, an electromagnetic interference (EMI) model for a two-stage cascaded boost converter is presented to distinguish its noise sources. To illustrate the effects of switching speeds on EMI generation potential, the relationships between the time domain and the frequency domain with all-SiC and SiC-Si device combinations are provided. It i...

This paper reports the performance of a technique for the estimation of single-phase grid voltage fundamental frequency under distorted grid conditions. The technique combines a Teager energy operator (TEO) with a frequency adaptive bandpass filter (BPF). The TEO is based on three consecutive samples and is used to estimate the fundamental frequenc...

Pollutant gas emission concern is one of the most challenging issues in electric power systems putting excessive pressure on different participants of electricity markets. Integrating renewable energy sources and application of Combined Heat-and-Power to thermal power plants which are applied by system operators have many advantages, such as reduci...

This paper reports a frequency-adaptive robust technique for the accurate estimation of the single-phase grid voltage fundamental and harmonic parameters. The technique is based on the discrete Fourier transform and a cascaded delayed signal cancellation strategy. There is no stability issue in the technique, since it does not contain any type of f...

This paper presents a methodology to evaluate and estimate the dispatch performance of a 30 MW PV power plant including a hybrid energy storage system (HESS) of various capacities. The HESS, consisting of a vanadium redox battery (VRB) and a supercapacitor bank (SCB) with a power rating ratio between the two energy storage technologies of 5:1, is c...

The application and research interest over utility-scale battery energy storage systems have grown significantly over the last years. To achieve utility-scale, series and/or parallel connection of many battery packs with power rating of a few hundreds kilowatts each is the most viable technology at present. The major challenge regarding the connect...

Battery-supercapacitor hybrid energy storage systems (HESSs) are popular as a way of extending the battery lifetime by reducing the battery current fluctuations. In conventional single phase HESSs, both the second-order harmonic power component and the fast power fluctuations are allocated to the supercapacitor. However, the ripple current componen...

To cope with power from large-scale renewable systems, more and more power electronic converters are used in parallel. Typically, carrier interleaving is used, thus leading to a decrease in filtering requirements. However, this causes additional circulating current to flow between the modules of the converter. The modules of the parallel converters...

With large-scale photovoltaic power generation system implementing grid-connected operation, it is essential for the accurate and reliable power forecasting of the photovoltaic generation to reduce the impact of uncertainty on the power network. A method of power forecasting of the photovoltaic generation based on wavelet neural network and residua...

Active distribution network plays an important role in increasing the utilization level of the renewable energy and realizing the flexible intelligent distribution network management. In this paper, aiming to improve the economy and reliability of the active distribution network, the energy dispatch strategy is designed by the method of the chance-...