Jef Beerten

KU Leuven | ku leuven · Department of Electrical Engineering (ESAT)

In order to combat global warming, a detailed knowledge of the greenhouse gas (GHG) emissions associated with different energy conversion technologies is important. For nuclear energy, GHG emissions result from different process stages of the whole fuel cycle. A life-cycle assessment offers the possibility to properly calculate these emissions. In...

This paper analyzes the influence of the converter droop settings and the dc grid network topology on the power sharing in a dc grid based on voltage source converter high voltage direct current technology. The paper presents an analytical tool to study the effect of the droop control settings on the steady-state voltage deviations and power sharin...

This paper discusses the extension of electromechanical stability models of voltage source converter high voltage direct current (VSC HVDC) to multi-terminal (MTDC) systems. The paper introduces a control model with a cascaded DC voltage control at every converter that allows a two-terminal VSC HVDC system to cope with converter outages. When exten...

In this paper, a steady-state multi-terminal voltage source converter high voltage direct current (VSC MTDC) model is introduced. The proposed approach is extended to include multiple AC and DC grids with arbitrary topologies. The DC grids can thereby interconnect arbitrary buses in one or more non-synchronized AC systems. The converter equations a...

In this paper, a prediction scheme is presented to diminish both the torque and flux ripples in a direct torque control (DTC) induction motor drive. In a discrete implementation of the classical DTC scheme, the time delay associated with data processing results in additional torque and flux ripples. This part of the ripples can amount to a signific...

Numerous High‐Voltage Direct Current (HVDC) interconnections in a bipolar configuration are currently in the design phase and set to become operational in the next decade. In the meantime, the shift from Synchronous Generators (SGs) to converter‐interfaced units is raising concerns over the stability of power systems. Grid‐Forming (GFM) control in...

Conventional state-space-based stability assessment method of voltage-source converters (VSCs) can be hindered by the black-box feature. Black box-based state-space model identification method using the terminal admittance/impedance frequency responses has thus been drawing increasing research attentions recently. However, the estimation of out-of-...

Due to the capability to perform participation factor analysis and oscillation origin location, the state-space model (SSM)-based eigenvalue method has been widely used for stability assessment of inverterpenetrated power systems. However, possible internal confidentiality of inverters impedes the derivation of their SSMs. In addition, conventional...

p>Due to the capability to perform participation factor analysis and oscillation origin location, the state-space model (SSM)-based eigenvalue method has been widely used for stability assessment of inverter-penetrated power systems. However, possible internal confidentiality of inverters impedes the derivation of their SSMs. In addition, conventio...

p>Due to the capability to perform participation factor analysis and oscillation origin location, the state-space model (SSM)-based eigenvalue method has been widely used for stability assessment of inverter-penetrated power systems. However, possible internal confidentiality of inverters impedes the derivation of their SSMs. In addition, conventio...

This paper presents a generalized impedance-based modeling framework for harmonic stability assessment due to converter interactions in hybrid AC/DC power systems, relying on detailed analytical frequency-dependent component models. The methodology proposed and derived in this paper enables the stability analysis of complete hybrid AC/DC power syst...

This paper analyzes the harmonic content of the arm currents and voltages of the modular multilevel converter (MMC) by using the dynamic phasor (DP) theory. DP modeling of the MMC facilitates a study without relying on simplifying assumptions on the harmonic content of the currents and voltages. In doing so, the DP-MMC model used in this paper reve...

High-voltage direct current (HVDC) transmission system based on modular multilevel converter (MMC) technology is considered as an attractive solution for the interconnection of two AC grids to enhance the security of supply. Several studies have concluded that the AC grid impedance is a key parameter for the control system design of the MMC. Such i...

Type-IV wind turbines can experience torsional vibrations in the drivetrain structure. This can lead to additional stress on turbine components. Vibrations are mostly induced by fast variations of the electromagnetic torque depending on the control of a back-to-back converter. A number of studies have presented methods to mitigate drivetrain vibrat...

The bandwidth of the measured or simulated frequency responses is sometimes relatively narrow, resulting in that some out-of-band modes of interest cannot be directly observed from the band-limited frequency responses. Although various kinds of curve fitting algorithms aim at generating linear or nonlinear transfer functions for these frequency sam...

One of the popular applications of the high-voltage direct current (HVDC) transmission systems based on modular multilevel converter (MMC) technology is the interconnection of two AC grids to enhance the security of supply. The recent studies have revealed that the AC grid impedance is a key parameter for the control system design of the MMC. Howev...

Time-averaged electromagnetic (EMT) power electronics models can comprise tens of state variables, and in upcoming converter-dominated power systems, this can cause a substantial computational burden. The level of detail in their modeling, however, is typically much greater than what is typically necessary for transient stability (RMS) tools. Hence...

Many efforts have been made in order to identify state-space models of the black-box devices from their terminal admittance/impedance frequency responses. However, the band of the available admittance/impedance frequency responses is sometimes relatively narrow, from which some out-of-band critical modes of interest can thus not be intuitively obse...

Stability analysis of the modular multilevel converter (MMC) requires accurate models over wide frequency ranges, accounting for both the time-periodic nature of internal dynamics and non-passive behavior resulting from time delays. Frequency-lifting techniques such as harmonic state-space (HSS) can be used to tackle the time-periodicity and obtain...

This paper introduces a Type-IV wind turbine interfaced to a grid-forming converter. In order to retain the stable operation of a wind turbine in the presence of a grid-forming control, the classical control of a back-to-back converter has to be modified. The modification of this control creates a strong link between a wind turbine and grid dynamic...

Type-IV wind turbines can experience torsional vibrations in the drivetrain structure. This can lead to additional stress on turbine components and a quality reduction of the power delivered to the grid. The vibrations are mostly induced by fast variations of the electromagnetic torque, which depends on the control of a back-to-back converter. A nu...

This paper introduces a Type-IV wind turbine interfaced to a grid-forming converter. In order to retain the stable operation of a wind turbine in the presence of a grid-forming control, the classical control of a back-to-back converter has to be modified. The modification of this control creates a strong link between a wind turbine and grid dynamic...

The modular multilevel converter (MMC) has emerged as the preferred choice for voltage source converter (VSC)-based high voltage direct current (HVDC) systems due to its low losses, low harmonic distortion, modularity, and redundancy. These advantages come at the expense of a complex control system with the strong coupling among its control variabl...

Multi-vendor interoperable HVDC grid protection is key to build large-scale HVDC grids in a step-by-step manner. On the one hand, various protection strategies and technologies have been developed in the past decade to address the challenges associated with HVDC grid protection. On the other hand, state-of-the-art HVDC technologies are often vend...

This article presents a vector fitting (VF) algorithm-based robust circuit and controller parameters’ identification method for grid-connected voltage-source converters (VSCs). The $dq$ -domain impedance frequency responses (IFRs) of the VSCs are first measured using the frequency scanning method, based on which the corresponding measured phasor-...

In High Voltage Direct Current (HVDC) grids, system parameter and/or topology changes following HVDC grid protection actions affect system dynamics and in combination with the existence of line inductors in series with HVDC circuit breakers (DCCB), pose a challenge to designing converter con- trols that satisfy desired performance and stability req...

HVDC grid protection with adequate speed and reliability is required to minimise the impact of DC faults. In particular, fast breaker failure backup protection algorithms are needed to meet the expected reliability requirements of HVDC grids. In this paper, existing breaker failure backup protection algorithms are shown inadequate to detect partial...

This paper conducts a comparison of two promising frequency-lifted representations used in the state-space modeling of power-electronic converters: dynamic phasors and harmonic state-space. These methods originate from similar hypotheses and aim to tackle the time-periodicity problem observed in systems with multiple harmonic components in steady s...

This paper introduces a complete modeling framework for harmonic stability assessment starting from ABCD parameters. It does so by presenting the theoretical foundations for modeling power system components in the ABCD domain, developing adequate interconnection methods for the components, as well as determining the ABCD parameters from any port in...

This paper presents a small-signal dynamic phasor model of the modular multilevel converter including phase-locked loop (PLL) dynamics. A simple PLL model including a low-pass filter at its input and accounting for the harmonic content of the voltage at the point of common coupling is developed to assess the impact of the PLL on small-signal stabil...

This paper analyzes high-frequency interactions between a Modular Multilevel Converter (MMC) and High Voltage Direct Current (HVDC) grid resonances by studying their effect on the system stability. The recent appearance of converter-related instabilities due to high-frequency oscillations at the converter's ac side raises concerns about whether sim...

This paper proposes the analysis of the frequency support from a Type-IV wind turbine interfaced to the grid via a grid-forming converter. The frequency support including the inertial response and the fast primary frequency support is implemented by integrating a grid-forming control to the control a back-to-back converter. Knowing that the inertia...

This study presents the initialisation of a hybrid alternating current/direct current (AC/DC) power system to determine the operation point around which the system is linearised as a starting point for an electromagnetic or harmonic stability analysis. To this end, each AC or DC power system component is modelled in the Fourier transform domain and...

This article introduces an equivalent multiple $dq$ -frame model of the modular multilevel converter (MMC) that is derived from a dynamic phasor based small-signal state-space MMC model in the stationary $\alpha \beta z$ frame. When compared to a model in the stationary ABC frame, the order of the model in the $\alpha \beta z$ frame can be re...

This paper introduces a complete modeling framework for harmonic stability assessment starting from ABCD parameters. It does so by presenting the theoretical foundations for modeling power system components in the ABCD domain, developing adequate interconnection methods for the components , as well as determining the ABCD parameters from any port i...

Eigenvalue-based analysis of small-signal dynamics in High Voltage Direct Current (HVDC) transmission systems requires cable models that are compatible with a state-space representation. While distributed parameter models accounting for frequency-dependent effects are inherently incompatible with a state-space representation, a conventional π-model...

The increasing number of flexible ac transmission systems (FACTS) and high voltage direct current (HVDC) systems is changing perspectives on small-signal stability in ac grids, as traditional steady-state modeling does not allow representing higher-frequency interactions between synchronous generators, ac grid and power electronic-based devices. Si...

Modern power systems face several problems at frequencies above the range of traditional stability studies due to the increasing penetration of power electronic devices. This phenomenon has been recently referred to as electromagnetic transient stability and is a common issue in systems with power electronic converters at any power and voltage leve...

To date, numerous concepts for converter station designs for use in voltage source converter (VSC)‐based high‐voltage direct current (HVDC) systems have been proposed. These differ not only in converter circuit topology, sub‐module design, and control scheme but also in AC‐or‐DC switchgear and other auxiliary equipment. In the main, the existing li...

Voltage Source Converter based High Voltage Direct Current (VSC HVDC) technology is used more and more in modern power systems. Consequently, in the ac network, an increasing number of converters are appearing in mutual electrical proximity, thus forming Multi-Infeed (MI)-HVDC systems. For VSC technology, several aspects of MI-HVDC system operation...

This paper presents a grid frequency responsive inertial control for the modular multilevel converter–high voltage DC (MMC–HVDC) using the MMC design attribute, i.e. submodule redundancy for high reliability. This control does not rely on the external energy sources in providing the inertial response. With an increase in the number of levels of MMC...

As compared to two‐wire, unipolar DC microgrids (DCμGs), bipolar DCμGs apply a positive, neutral and negative conductor to increase the power transfer capability while retaining two voltage levels for supplying low‐ and high‐power devices at an appropriate voltage. However, connecting devices between the positive or negative pole and the neutral co...

Maintaining balanced voltage during normal operation and rebalancing pole voltages after a pole-to-ground fault are both necessary to prevent high insulation stresses on the DC cable in a HVDC system. The state-of-the-art solution requires two separate devices to deal with normal and post-fault operation separately. This paper proposes pole rebala...

Pole rebalancing in symmetrical monopolar HVDC grids is necessary to remove pole imbalances resulting from pole-to-ground faults. For selective protection employing DC circuit breakers, pole rebalancing considering backup protection operation in case of breaker failure has until now not been studied. This paper proposes fault clearing and post-faul...

This paper introduces a dynamic phasor model of a half-bridge modular multilevel converter (HB-MMC) based on variables in the stationary ABC frame. The application of the dynamic phasor theory makes it possible to use converter eigenvalues to study the effect of steady-state harmonics present in the MMC on its small-signal stability, since the mode...

Pole rebalancing in symmetrical monopolar HVDC grids is necessary to remove pole imbalances resulting from pole-to-ground faults. For selective protection employing DC breakers, the interaction between DC breakers and pole rebalancing methods have not been studied. This paper proposes new strategies for pole rebalancing methods to deal with DC brea...

Fast DC breakers are essential components to realise future high voltage DC grids. Recent development in the industry shows great feasibility in achieving such DC breakers using various technologies. In particular, hybrid DC breakers with modular design have the potential to operate in fault current limiting (FCL) mode, which can provide added func...

This paper proposes a frequency domain based methodology to analyse the influence of High Voltage Direct Current (HVDC) configurations and system parameters on the travelling wave behaviour during a DC fault. The method allows us to gain deeper understanding of these influencing parameters. In the literature, the majority of DC protection algorithm...

To ensure a reliable fault clearing, a backup protection scheme is required for selective HVDC grid protection. One way to achieve this is to use both voltage and current measurements to distinguish uncleared faults from cleared ones during the fault clearing process of the primary protection. This paper studies the applicability of such a backup p...

System stability can be affected by the interaction between the converter control and the network resonances. Current installations of VSC-HVDC converters have experienced instability issues due to this interaction and have triggered questions in industry and research such as the suitable methods to evaluate the interferences, the necessary models...

This paper presents a structured approach for analysing the effect of HVDC transmission system expansion on the small signal dynamics. The methodology decomposes the expansion of the system into a sequence of steps and aims especially at identifying the eigenvalues associated with interactions between the initial system and an added converter termi...

In order to reliably and safely operate future multi-terminal HVDC grids, different protection strategies are currently being developed and presented in the literature. Especially for large DC grids, it is important to investigate how the choice of the protection strategy influences AC system stability during DC fault clearance and system restorati...

In this paper, a methodology is presented to identify and analyse interaction modes between converters in Voltage Source Converter Multi-Terminal High Voltage Direct Current (VSC MTDC) systems. The absence of a substantial level of energy stored in such power electronics based systems results in fast system dynamics, governed by electromagnetic phe...

Accurate eigenvalue analysis of High Voltage Direct Current (HVDC) transmission systems depends on state-space models that are accounting for the frequency-dependent characteristics of the dc cables. A classical simplified model with cascaded pi-sections can be enhanced to capture the frequency dependency of cable parameters by adding parallel RL b...

The modular multilevel converter (MMC) is currently the preferred converter topology for HVDC point-to-point links and the likely choice for future meshed HVDC grids. For breaker dimensioning or protection system design, thorough knowledge of the dc fault currents supplied by these converters is required. In this paper, the dc fault current supplie...

Small-signal stability studies of power systems including Voltage Source Converter (VSC) HVDC transmission schemes are commonly based on state-space models representing two-level converters and their related control loops. However, an increasing share of HVDC links are based on Modular Multilevel Converters (MMCs), which present additional dynamics...

This paper deals with nonunit protection of HVDC grids by proposing a set of parameters that characterizes the open protection zones together with an efficient method to determine the thresholds on these parameters. Selective HVDC grid protection schemes must detect and discriminate faults within the first milliseconds of the fault transient and co...

In this paper, a methodology is presented to identify and analyze interaction modes between converters in voltage-source converter multiterminal high-voltage direct current (VSC MTDC) systems. The absence of a substantial level of energy stored in such power-electronics-based systems results in fast system dynamics, governed by electromagnetic phen...

The number of voltage-source converters connected to the power system is increasing. This has led to concerns about the impact of control interactions between converters and their influence on the system stability. Recent grid codes consider such interactions as low-frequency disturbances between the converters and neglect network dynamics. This pa...

The DC node voltage can be influenced by controlling the current/power of the high-voltage direct current (HVDC) converter at that node. This chapter classifies the different node voltage control methods, which have been proposed in the literature in recent years. It introduces three overall converter control strategies namely, constant voltage con...

This chapter discusses the power flow of a combined AC/DC system. In its most simple form, the converters can be modeled as power injections to the AC system with coupled active power injections and independent reactive power setpoints. The detailed models described in the chapter include the converter losses and limits and allow for various repres...

This chapter highlights the need for different models within power system analysis and indicates the specifics of high-voltage direct current (HVDC) grids with respect to modeling. Next to a reduction in the temporal description of the mathematical model, it is also commonplace to reduce the system model by focusing on a particular area or subsyste...

State-of-the-art time-domain models of power cables account for the frequency dependency of physical parameters to enable accurate transient simulations of high-voltage transmission schemes. Owing to their formulation, these models cannot be directly converted into a state-space form as required for small-signal eigenvalue analysis. Thus, dc cables...

This paper presents a comprehensive modeling framework to analyze and compare the performance of different voltage droop control characteristics in an HVDC grid. All models are fully derived mathematically, both for dynamic simulations and for steady-state power flow analysis. The main contribution lies in the development of a common modeling and c...

Terms of use and extra information: https://www.esat.kuleuven.be/electa/hvdcresearch/hvdc- test-grid. The four-bus test system related to the paper: "A new HVDC grid test system for HVDC grid dynamics and protection studies in EMT-type software".

In a droop-controlled High Voltage Direct Current (HVDC) grid, the line voltage drops throughout the system influence the voltage control. This paper introduces and compares five distinct methods for establishing droop setpoints in order to restore the voltage profile after a contingency and evaluates the ability of these methods to track the setpo...

The large-scale integration of renewable energy sources in the power system, combined with the need for an increased transmission capacity has led to a growing interest in multi-terminal high voltage dc (MTDC) grids. In the future, these grids will be integrated with different existing asynchronous ac grids, eventually resulting in hybrid AC/DC pow...

Abstract This article introduces a hierarchical power control structure for Multi-terminal High Voltage Direct Current (MT-HVDC) systems. The presented hierarchy is similar to the control structure used in classical AC transmission systems and is divided in primary, secondary and tertiary control actions. The voltage control in the MT-HVDC scheme a...

This study presents the creation of a new simulation tool,MATACDC. It is the first open source program for power flow analysis of high voltage direct current (HVDC) grids and hybrid AC/DC systems and uses state-of-the-art developments in the field of HVDC grids research. MATACDC is based on MATLAB and has been fully integrated with the AC system po...

This study focuses on the the reliability of HVDC grids, analysing the secure and optimal operation of transmission systems consisting of both HVDC (High Voltage Direct Current) and HVAC (High Voltage Alternating Current) interconnections, with high penetration of offshore wind, taking into account the system spinning reserves. While AC systems are...

This study presents a tool for solving the Optimal Power Flow (OPF) problem in mixed Direct Current (DC) and Alternating Current (AC) systems. It allows to analyse the optimal operation of multiple independent systems, DC connected and linked to the AC system, from a steady state point of view and for several objective functions. The tool, implemen...

With the increased interest in HVDC grids and their steady-state interactions with existing AC systems, there is a growing need for the development of tools to study the power flows in these systems. In this paper, we present MATACDC, an open source software for the analysis of hybrid AC/DC systems. The tool is available for everyone to download an...