Recently proposed as a viable alternative for connecting offshore wind farms (OWFs) to HVDC netwo... more Recently proposed as a viable alternative for connecting offshore wind farms (OWFs) to HVDC networks, diode rectifiers have prompted increasing interest from both industry and academia. However, before technical connection requirements for such solutions can be determined, more studies are needed to assess their capabilities to contribute to the secure operation of the networks connected to them.
Recently put forward as a feasible alternative for connecting OWFs to HVdc networks, diode rectif... more Recently put forward as a feasible alternative for connecting OWFs to HVdc networks, diode rectifiers (DRs) have elicited growing interest from both academia and industry. Energisation of such OWFs is, however, not straightforward. The present study constitutes a proof of concept for the application of a novel energisation method to the case of an OWF connected to HVdc via DRs. The proposed method provides a robust and reliable alternative with minimal additional hardware, i.e. short additional dc cables connecting the dc bus bar of the energising WT to the HVdc link, and corresponding dc disconnectors at the cable terminals and at the DR dc terminals. This can be easily extended to more WTs in the OWF, increasing reliability by providing redundancy. The simulation results indicate that the proposed method is a suitable alternative for energising OWFs connected to HVdc via DRs.
Before diode rectifier (DR) technology for connecting offshore wind farms (OWFs) to HVdc is deplo... more Before diode rectifier (DR) technology for connecting offshore wind farms (OWFs) to HVdc is deployed, indepth studies are needed to assess the actual capabilities of DRconnected OWFs to contribute to the secure operation of the networks linked to them. This study assesses the capability of such an OWF to provide communication-less frequency support (CLFS) to an onshore ac network. It is shown that the HVdc link's offshore terminal direct voltage can be estimated from measurements at the OWF's point of connection with the DR platform. Two different methods are proposed for implementing CLFS in the OWF active power controls. In Method 1, the estimated offshore terminal direct voltage is used for estimating the onshore frequency deviation. In Method 2, the actual offshore terminal direct voltage measurement is used instead. Unique features of the provision of CLFS from OWFs connected to HVdc via DRs are highlighted, and the dynamic and static performance of the CLFS control scheme is compared to that of the communication-based frequency support scheme. To assess the impact of parameter estimation errors on the provision of CLFS, a parametric sensitivity study is presented as well, and recommendations are given to increase accuracy.
Diode rectifiers (DRs) have been recently suggested as a viable alternative for connecting offsho... more Diode rectifiers (DRs) have been recently suggested as a viable alternative for connecting offshore wind farms (OWFs) to HVdc, eliciting growing interest from both industry and academia. However, energisation of DR-connected OWFs is not straightforward. The present study constitutes a proof of concept of a novel energisation method for DR-connected OWFs, in which auxiliary power is provided from the shore through the HVdc link and the dc bus bar of one or more WTs. The proposed method provides an alternative with minimal additional hardware, which can be easily extended to more WTs in the OWF, increasing reliability by providing redundancy. The study includes coinciding auxiliary loads with active and reactive power components and a semi-aggregated OWF model, in which every WT is individually represented in the string containing the energising WT. An additional sequence of simulation events is considered following the initial energisation sequence. Such sequence comprises wind power taking over the provision of the auxiliary power. The simulation results indicate that the proposed method is a suitable alternative for energising OWFs connected to HVdc via DRs.
Contribution to the power systems' frequency support is expected to be one of the essential ancil... more Contribution to the power systems' frequency support is expected to be one of the essential ancillary services that wind power plants (WPPs) shall provide. The high-voltage DC (HVDC) connected offshore WPPs may provide this service with and without using fast communication links between onshore and offshore. In the case of offshore HVDC grid, implementing the communication-less frequency support is challenging. Although it increases the reliability of the frequency control, among other challenges, it is not straightforward to comply with relevant grid code requirements. In this paper, this issue is mathematically described and a static model is developed to calculate the deviation of various electrical parameters of an HVDC grid in case of frequency drop on the land ac systems. A solution for the aforementioned problem is presented and its associated concerns are addressed. The study is verified by simulations of a four terminals dc grid with two offshore WPPs and two inland ac systems.
IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society, 2019
The current practice of power system restoration mainly relies on conventional power plants, whic... more The current practice of power system restoration mainly relies on conventional power plants, which can provide black start in case of a black out using fossil fuels. HVdcconnected offshore wind power plants can, on the other hand, provide fast and environmentally friendly solutions for power system restoration, once their state of the art wind turbines are equipped with the grid-forming capability. In this paper, the background and existing solutions for wind turbine and wind power plant self-energization and onshore grid black start are presented, together with simulation results of an offshore wind power plant sequentially energizing the offshore ac network, offshore HVdc terminal, HVdc link, onshore HVdc terminal, and onshore ac terminal and load. Black start, energization, grid-forming wind turbine control, HVdc transmission, offshore wind energy integration I.
This repository is used to provide documentation related to the model and data development proces... more This repository is used to provide documentation related to the model and data development process, provide source (raw) data for the model in different forms (i.e. Modelica, CIM 14, and PSS/E) for an equivalent Nordic grid model that has been matched to historical power flow data. The repository is documented in the paper below, see [Ref00]. <strong>Using this model, data or related software = cite our publications!</strong> We are happy to contribute with this dataset, however, if you use any of the data or software provided, we will appreciate if you cite the following publications, as follows: A) Cite that "the raw and processed data files corresponding to the model are available as an open data set and documented in [Ref00]." B) Cite that the first appearance of the model, i.e. "the model is first presented in [Ref01]" [Ref00] L. Vanfretti, S.H. Olsen, V. S. Narasimham Arava, G. Laera, A. Bibadafar, T. Rabuzin, H. Jackobsen, J. Lavenius, and M. B...
Dynamics of distribution grids are becoming more and more complex to analyze due to their transit... more Dynamics of distribution grids are becoming more and more complex to analyze due to their transition from passive networks to active ones. This has necessitated the increase of observability between Transmission and Distribution (T&D) grids for operational security and real-time security assessment. This paper presents an overview of the IDE4L project, funded by the European Commission, where a system of PMU data-based monitoring applications has been developed to facilitate TSO-DSO interactions.
Abstract: This paper proposes a nonlinear control strategy for pulse-width modulated voltage sour... more Abstract: This paper proposes a nonlinear control strategy for pulse-width modulated voltage source converters (VSCs). A passivity-based approach, resulting from the Lyapunov direct method, is presented for designing an effective nonlinear VSC controller to improve their dynamic behaviors under perturbed conditions. The differential equations of the converters are obtained and then transformed into a d − q frame. Considering the nonlinearity of the transformed equations, the Lyapunov direct method is utilized to find a solution to improve the transient response. The time derivative of the Lyapunov function guarantees that increasing its dissipative term will result in the trajectory of the VSC system returning to the equilibrium point more quickly. The proposed control strategy can be simultaneously applied to multiVSC devices, such as a unified power flow controller (UPFC). Moreover, it is shown that the proposed strategy meets the steady-state requirements without using any other ...
Diode rectifiers (DRs) have been recently suggested as a viable alternative for connecting offsho... more Diode rectifiers (DRs) have been recently suggested as a viable alternative for connecting offshore wind farms (OWFs) to HVdc, eliciting growing interest from both industry and academia. However, energisation of DR-connected OWFs is not straightforward. The present study constitutes a proof of concept of a novel energisation method for DR-connected OWFs, in which auxiliary power is provided from the shore through the HVdc link and the dc bus bar of one or more WTs. The proposed method provides an alternative with minimal additional hardware, which can be easily extended to more WTs in the OWF, increasing reliability by providing redundancy. The study includes coinciding auxiliary loads with active and reactive power components and a semi-aggregated OWF model, in which every WT is individually represented in the string containing the energising WT. Two additional sequences of simulation events are considered following the initial energisation sequence. Such sequences comprise wind po...
Synchrophasor applications for distribution networks enhancing T&D operation and information exch... more Synchrophasor applications for distribution networks enhancing T&D operation and information exchange
This paper presents a study assessing the actual capability of an offshore wind power plant (offs... more This paper presents a study assessing the actual capability of an offshore wind power plant (offshore WPP, OWPP) to provide frequency support (FS) to an onshore network, when connected through a high-voltage direct-current (HVDC) link having a diode rectifier (DR) offshore terminal and a voltage source converter (VSC) onshore terminal. Both primary and fast frequency response (PFR and FFR, respectively) are studied, and both the power reserves from preventive curtailment and the kinetic energy stored in the rotating masses of the wind turbines (WTs) are considered as sources of additional power during onshore under-frequency events. Three methods are considered for overloading the WTs, including the proposed External Reference method, in which the base active power reference can be set externally. The performance of the controls is studied by means of electromagnetic transient (EMT) simulations, for which an aggregated model of the OWPP is used. The results suggest that such OWPPs c...
This paper provides an overview of two technologies for connecting offshore wind power plants (of... more This paper provides an overview of two technologies for connecting offshore wind power plants (offshore WPPs, OWPPs) to high-voltage direct current (HVDC) networks: voltage source converters (VSCs) and diode rectifiers (DRs). Current grid code requirements for the connection of such power plants are also addressed, and their implications when using such technologies are discussed.
In this paper a comprehensive approach is presented to improve power swings damping based on dire... more In this paper a comprehensive approach is presented to improve power swings damping based on direct Lyapunov method. The approach combines superconducting magnetic energy storage (SMES) system with static synchronous compensator (STATCOM). Considering the energy absorption/injection ability of SMES, in transient states the combination exchanges both active and reactive powers with power system. Since direct Lyapunov method relies on time derivative of both active and reactive powers, it can offer an effective control strategy for the integrated STATCOM-SMES system to decrease power swings damping time. Line current is proposed as synchronous reference frame for d-q transformation which satisfies the direct Lyapunov method application as optimized approach and also provides decentralized control strategy. Steady state control strategy with respect to proposed reference frame and also SMES existence is given. PSCAD/EMTDC simulation results for a typical multi-area system are presented.
Offshore HVDC grids are envisaged to render more reliable and economical solutions for transferri... more Offshore HVDC grids are envisaged to render more reliable and economical solutions for transferring more offshore wind energy to onshore power systems. From the reliability point of view, the most promising operational/control strategy of HVDC grids is the dc voltage droop control. This control provides autonomous power-sharing among converters and promotes the frequency support to onshore power systems from other ends of HVDC grids without using fast communication links. The simultaneous use of frequency and dc voltage droops in an HVDC converter can transform frequency deviations into dc voltage changes. Other converters with dc voltage droop can react to the changes by regulating their power flow. Therefore, autonomous frequency support can be established through an HVDC grid. Although this method is reliable, fast, and economical, it gives rise to interactions between different droops, which can result in a reduction in the HVDC power that system operators can expect during freq...
Lower costs and higher reliability make diode rectifiers (DRs) a promising alternative for connec... more Lower costs and higher reliability make diode rectifiers (DRs) a promising alternative for connecting offshore wind power plants to HVdc networks. However, such offshore substations lack the grid-forming capability provided by voltage source converters. Hence, the grid-side converters of type-4 (fullconverter) wind turbines (WTs) have been proposed as viable candidates to take over such responsibility, apart from controlling the WT output power. In this work, a common synchronization reference (CSR) is proposed for the synchronization of such converters. Such reference is generated in the offshore HVdc substation and transmitted to the converters through the optical fibers embedded in the power cables. The proposed CSR enables the use of conventional current control for grid-forming WTs. Additionally, a scheme which combines communication-less and communication-based onshore frequency support is proposed and implemented. The proposed controls are validated by simulations under diffe...
The low impedance characteristics of DC transmission lines cause the voltage source converter (VS... more The low impedance characteristics of DC transmission lines cause the voltage source converter (VSC) in HVDC networks to become electrically closer together and increase the risk of severe interactions between the converters. Such interactions, in turn, intensify the implementation of the grid control schemes and may lead the entire system to instability. Assessing the stability and adopting complex coordinated control schemes in an HVDC grid and wind farm turbines are challenging and require a precise model of the HVDC grid, wind farm, and the controllers. In this paper, a linear multivariable feedback control system (FCS) model is proposed to represent the dynamic characteristics of HVDC grids and their controllers. The FCS model can be used for different dynamic analyses in time and frequency domains. Moreover, using the FCS model the system stability is analyzed in both openand closed-loop forms. The standard eigenanalysis identifies the modes of only the closed-loop system and d...
2017 IEEE Power & Energy Society General Meeting, Jul 1, 2017
Distribution grid dynamics are becoming increasingly complex to analyze due to their transition f... more Distribution grid dynamics are becoming increasingly complex to analyze due to their transition from passive to active networks. This transition requires to increase the observability and awareness of the interactions between Transmission and Distribution (T&D) grids, particularly to guarantee adequate operational security. As part of the work carried out in the EU-funded IDE4L project, a specific use case, containing PMU-based monitoring functions, has been defined to support the architecture design of a distribution grid automation system. As a result, the architecture can accommodate for key dynamic information extraction and exchange between Distribution System Operator (DSO) and Transmission System Operator (TSO). This paper presents the use case and focuses on the technical aspects related to the development and implementation of the PMU-based monitoring functionalities.
Diode rectifiers (DRs) have elicited increasing interest from both industry and academiaas a feas... more Diode rectifiers (DRs) have elicited increasing interest from both industry and academiaas a feasible alternative for connecting offshore wind farms (OWFs) to HVDC networks. However,before such technology is deployed, more studies are needed to assess the actual capabilities ofDR-connected OWFs to contribute to the secure operation of the networks linked to them. This studyassessed the capability of such an OWF to provide support to an onshore AC network by means of(active) power oscillation damping (POD). A semi-aggregated OWF representation was considered inorder to examine the dynamics of each grid-forming wind turbine (WT) within a string whenproviding POD, while achieving reasonable simulation times. Simulation results corroboratethat such an OWF can provide POD by means of OWF active power controls similar to thosedeveloped for OWFs connected to HVDC via voltage source converters, while its grid-forming WTsshare the reactive power consumption/production and keep the offshore v...
Due to the increase of generation sources in distribution networks, it is becoming very complex t... more Due to the increase of generation sources in distribution networks, it is becoming very complex to develop and maintain models of these networks. Network operators need to determine reduced models of distribution networks to be used in grid management functions. This paper presents a novel method that synthesizes steady-state models of unbalanced active distribution networks with the use of dynamic measurements (time series) from phasor measurement units (PMUs). Since phasor measurement unit (PMU) measurements may contain errors and bad data, this paper presents the application of a Kalman filter technique for realtime data processing. In addition, PMU data capture the power system's response at different timescales , which are generated by different types of power system events; the presented Kalman filter has been improved to extract the steady-state component of the PMU measurements to be fed to the steady-state model synthesis application. Performance of the proposed methods has been assessed by real-time hardware-in-the-loop simulations on a sample distribution network.
Recently proposed as a viable alternative for connecting offshore wind farms (OWFs) to HVDC netwo... more Recently proposed as a viable alternative for connecting offshore wind farms (OWFs) to HVDC networks, diode rectifiers have prompted increasing interest from both industry and academia. However, before technical connection requirements for such solutions can be determined, more studies are needed to assess their capabilities to contribute to the secure operation of the networks connected to them.
Recently put forward as a feasible alternative for connecting OWFs to HVdc networks, diode rectif... more Recently put forward as a feasible alternative for connecting OWFs to HVdc networks, diode rectifiers (DRs) have elicited growing interest from both academia and industry. Energisation of such OWFs is, however, not straightforward. The present study constitutes a proof of concept for the application of a novel energisation method to the case of an OWF connected to HVdc via DRs. The proposed method provides a robust and reliable alternative with minimal additional hardware, i.e. short additional dc cables connecting the dc bus bar of the energising WT to the HVdc link, and corresponding dc disconnectors at the cable terminals and at the DR dc terminals. This can be easily extended to more WTs in the OWF, increasing reliability by providing redundancy. The simulation results indicate that the proposed method is a suitable alternative for energising OWFs connected to HVdc via DRs.
Before diode rectifier (DR) technology for connecting offshore wind farms (OWFs) to HVdc is deplo... more Before diode rectifier (DR) technology for connecting offshore wind farms (OWFs) to HVdc is deployed, indepth studies are needed to assess the actual capabilities of DRconnected OWFs to contribute to the secure operation of the networks linked to them. This study assesses the capability of such an OWF to provide communication-less frequency support (CLFS) to an onshore ac network. It is shown that the HVdc link's offshore terminal direct voltage can be estimated from measurements at the OWF's point of connection with the DR platform. Two different methods are proposed for implementing CLFS in the OWF active power controls. In Method 1, the estimated offshore terminal direct voltage is used for estimating the onshore frequency deviation. In Method 2, the actual offshore terminal direct voltage measurement is used instead. Unique features of the provision of CLFS from OWFs connected to HVdc via DRs are highlighted, and the dynamic and static performance of the CLFS control scheme is compared to that of the communication-based frequency support scheme. To assess the impact of parameter estimation errors on the provision of CLFS, a parametric sensitivity study is presented as well, and recommendations are given to increase accuracy.
Diode rectifiers (DRs) have been recently suggested as a viable alternative for connecting offsho... more Diode rectifiers (DRs) have been recently suggested as a viable alternative for connecting offshore wind farms (OWFs) to HVdc, eliciting growing interest from both industry and academia. However, energisation of DR-connected OWFs is not straightforward. The present study constitutes a proof of concept of a novel energisation method for DR-connected OWFs, in which auxiliary power is provided from the shore through the HVdc link and the dc bus bar of one or more WTs. The proposed method provides an alternative with minimal additional hardware, which can be easily extended to more WTs in the OWF, increasing reliability by providing redundancy. The study includes coinciding auxiliary loads with active and reactive power components and a semi-aggregated OWF model, in which every WT is individually represented in the string containing the energising WT. An additional sequence of simulation events is considered following the initial energisation sequence. Such sequence comprises wind power taking over the provision of the auxiliary power. The simulation results indicate that the proposed method is a suitable alternative for energising OWFs connected to HVdc via DRs.
Contribution to the power systems' frequency support is expected to be one of the essential ancil... more Contribution to the power systems' frequency support is expected to be one of the essential ancillary services that wind power plants (WPPs) shall provide. The high-voltage DC (HVDC) connected offshore WPPs may provide this service with and without using fast communication links between onshore and offshore. In the case of offshore HVDC grid, implementing the communication-less frequency support is challenging. Although it increases the reliability of the frequency control, among other challenges, it is not straightforward to comply with relevant grid code requirements. In this paper, this issue is mathematically described and a static model is developed to calculate the deviation of various electrical parameters of an HVDC grid in case of frequency drop on the land ac systems. A solution for the aforementioned problem is presented and its associated concerns are addressed. The study is verified by simulations of a four terminals dc grid with two offshore WPPs and two inland ac systems.
IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society, 2019
The current practice of power system restoration mainly relies on conventional power plants, whic... more The current practice of power system restoration mainly relies on conventional power plants, which can provide black start in case of a black out using fossil fuels. HVdcconnected offshore wind power plants can, on the other hand, provide fast and environmentally friendly solutions for power system restoration, once their state of the art wind turbines are equipped with the grid-forming capability. In this paper, the background and existing solutions for wind turbine and wind power plant self-energization and onshore grid black start are presented, together with simulation results of an offshore wind power plant sequentially energizing the offshore ac network, offshore HVdc terminal, HVdc link, onshore HVdc terminal, and onshore ac terminal and load. Black start, energization, grid-forming wind turbine control, HVdc transmission, offshore wind energy integration I.
This repository is used to provide documentation related to the model and data development proces... more This repository is used to provide documentation related to the model and data development process, provide source (raw) data for the model in different forms (i.e. Modelica, CIM 14, and PSS/E) for an equivalent Nordic grid model that has been matched to historical power flow data. The repository is documented in the paper below, see [Ref00]. <strong>Using this model, data or related software = cite our publications!</strong> We are happy to contribute with this dataset, however, if you use any of the data or software provided, we will appreciate if you cite the following publications, as follows: A) Cite that "the raw and processed data files corresponding to the model are available as an open data set and documented in [Ref00]." B) Cite that the first appearance of the model, i.e. "the model is first presented in [Ref01]" [Ref00] L. Vanfretti, S.H. Olsen, V. S. Narasimham Arava, G. Laera, A. Bibadafar, T. Rabuzin, H. Jackobsen, J. Lavenius, and M. B...
Dynamics of distribution grids are becoming more and more complex to analyze due to their transit... more Dynamics of distribution grids are becoming more and more complex to analyze due to their transition from passive networks to active ones. This has necessitated the increase of observability between Transmission and Distribution (T&D) grids for operational security and real-time security assessment. This paper presents an overview of the IDE4L project, funded by the European Commission, where a system of PMU data-based monitoring applications has been developed to facilitate TSO-DSO interactions.
Abstract: This paper proposes a nonlinear control strategy for pulse-width modulated voltage sour... more Abstract: This paper proposes a nonlinear control strategy for pulse-width modulated voltage source converters (VSCs). A passivity-based approach, resulting from the Lyapunov direct method, is presented for designing an effective nonlinear VSC controller to improve their dynamic behaviors under perturbed conditions. The differential equations of the converters are obtained and then transformed into a d − q frame. Considering the nonlinearity of the transformed equations, the Lyapunov direct method is utilized to find a solution to improve the transient response. The time derivative of the Lyapunov function guarantees that increasing its dissipative term will result in the trajectory of the VSC system returning to the equilibrium point more quickly. The proposed control strategy can be simultaneously applied to multiVSC devices, such as a unified power flow controller (UPFC). Moreover, it is shown that the proposed strategy meets the steady-state requirements without using any other ...
Diode rectifiers (DRs) have been recently suggested as a viable alternative for connecting offsho... more Diode rectifiers (DRs) have been recently suggested as a viable alternative for connecting offshore wind farms (OWFs) to HVdc, eliciting growing interest from both industry and academia. However, energisation of DR-connected OWFs is not straightforward. The present study constitutes a proof of concept of a novel energisation method for DR-connected OWFs, in which auxiliary power is provided from the shore through the HVdc link and the dc bus bar of one or more WTs. The proposed method provides an alternative with minimal additional hardware, which can be easily extended to more WTs in the OWF, increasing reliability by providing redundancy. The study includes coinciding auxiliary loads with active and reactive power components and a semi-aggregated OWF model, in which every WT is individually represented in the string containing the energising WT. Two additional sequences of simulation events are considered following the initial energisation sequence. Such sequences comprise wind po...
Synchrophasor applications for distribution networks enhancing T&D operation and information exch... more Synchrophasor applications for distribution networks enhancing T&D operation and information exchange
This paper presents a study assessing the actual capability of an offshore wind power plant (offs... more This paper presents a study assessing the actual capability of an offshore wind power plant (offshore WPP, OWPP) to provide frequency support (FS) to an onshore network, when connected through a high-voltage direct-current (HVDC) link having a diode rectifier (DR) offshore terminal and a voltage source converter (VSC) onshore terminal. Both primary and fast frequency response (PFR and FFR, respectively) are studied, and both the power reserves from preventive curtailment and the kinetic energy stored in the rotating masses of the wind turbines (WTs) are considered as sources of additional power during onshore under-frequency events. Three methods are considered for overloading the WTs, including the proposed External Reference method, in which the base active power reference can be set externally. The performance of the controls is studied by means of electromagnetic transient (EMT) simulations, for which an aggregated model of the OWPP is used. The results suggest that such OWPPs c...
This paper provides an overview of two technologies for connecting offshore wind power plants (of... more This paper provides an overview of two technologies for connecting offshore wind power plants (offshore WPPs, OWPPs) to high-voltage direct current (HVDC) networks: voltage source converters (VSCs) and diode rectifiers (DRs). Current grid code requirements for the connection of such power plants are also addressed, and their implications when using such technologies are discussed.
In this paper a comprehensive approach is presented to improve power swings damping based on dire... more In this paper a comprehensive approach is presented to improve power swings damping based on direct Lyapunov method. The approach combines superconducting magnetic energy storage (SMES) system with static synchronous compensator (STATCOM). Considering the energy absorption/injection ability of SMES, in transient states the combination exchanges both active and reactive powers with power system. Since direct Lyapunov method relies on time derivative of both active and reactive powers, it can offer an effective control strategy for the integrated STATCOM-SMES system to decrease power swings damping time. Line current is proposed as synchronous reference frame for d-q transformation which satisfies the direct Lyapunov method application as optimized approach and also provides decentralized control strategy. Steady state control strategy with respect to proposed reference frame and also SMES existence is given. PSCAD/EMTDC simulation results for a typical multi-area system are presented.
Offshore HVDC grids are envisaged to render more reliable and economical solutions for transferri... more Offshore HVDC grids are envisaged to render more reliable and economical solutions for transferring more offshore wind energy to onshore power systems. From the reliability point of view, the most promising operational/control strategy of HVDC grids is the dc voltage droop control. This control provides autonomous power-sharing among converters and promotes the frequency support to onshore power systems from other ends of HVDC grids without using fast communication links. The simultaneous use of frequency and dc voltage droops in an HVDC converter can transform frequency deviations into dc voltage changes. Other converters with dc voltage droop can react to the changes by regulating their power flow. Therefore, autonomous frequency support can be established through an HVDC grid. Although this method is reliable, fast, and economical, it gives rise to interactions between different droops, which can result in a reduction in the HVDC power that system operators can expect during freq...
Lower costs and higher reliability make diode rectifiers (DRs) a promising alternative for connec... more Lower costs and higher reliability make diode rectifiers (DRs) a promising alternative for connecting offshore wind power plants to HVdc networks. However, such offshore substations lack the grid-forming capability provided by voltage source converters. Hence, the grid-side converters of type-4 (fullconverter) wind turbines (WTs) have been proposed as viable candidates to take over such responsibility, apart from controlling the WT output power. In this work, a common synchronization reference (CSR) is proposed for the synchronization of such converters. Such reference is generated in the offshore HVdc substation and transmitted to the converters through the optical fibers embedded in the power cables. The proposed CSR enables the use of conventional current control for grid-forming WTs. Additionally, a scheme which combines communication-less and communication-based onshore frequency support is proposed and implemented. The proposed controls are validated by simulations under diffe...
The low impedance characteristics of DC transmission lines cause the voltage source converter (VS... more The low impedance characteristics of DC transmission lines cause the voltage source converter (VSC) in HVDC networks to become electrically closer together and increase the risk of severe interactions between the converters. Such interactions, in turn, intensify the implementation of the grid control schemes and may lead the entire system to instability. Assessing the stability and adopting complex coordinated control schemes in an HVDC grid and wind farm turbines are challenging and require a precise model of the HVDC grid, wind farm, and the controllers. In this paper, a linear multivariable feedback control system (FCS) model is proposed to represent the dynamic characteristics of HVDC grids and their controllers. The FCS model can be used for different dynamic analyses in time and frequency domains. Moreover, using the FCS model the system stability is analyzed in both openand closed-loop forms. The standard eigenanalysis identifies the modes of only the closed-loop system and d...
2017 IEEE Power & Energy Society General Meeting, Jul 1, 2017
Distribution grid dynamics are becoming increasingly complex to analyze due to their transition f... more Distribution grid dynamics are becoming increasingly complex to analyze due to their transition from passive to active networks. This transition requires to increase the observability and awareness of the interactions between Transmission and Distribution (T&D) grids, particularly to guarantee adequate operational security. As part of the work carried out in the EU-funded IDE4L project, a specific use case, containing PMU-based monitoring functions, has been defined to support the architecture design of a distribution grid automation system. As a result, the architecture can accommodate for key dynamic information extraction and exchange between Distribution System Operator (DSO) and Transmission System Operator (TSO). This paper presents the use case and focuses on the technical aspects related to the development and implementation of the PMU-based monitoring functionalities.
Diode rectifiers (DRs) have elicited increasing interest from both industry and academiaas a feas... more Diode rectifiers (DRs) have elicited increasing interest from both industry and academiaas a feasible alternative for connecting offshore wind farms (OWFs) to HVDC networks. However,before such technology is deployed, more studies are needed to assess the actual capabilities ofDR-connected OWFs to contribute to the secure operation of the networks linked to them. This studyassessed the capability of such an OWF to provide support to an onshore AC network by means of(active) power oscillation damping (POD). A semi-aggregated OWF representation was considered inorder to examine the dynamics of each grid-forming wind turbine (WT) within a string whenproviding POD, while achieving reasonable simulation times. Simulation results corroboratethat such an OWF can provide POD by means of OWF active power controls similar to thosedeveloped for OWFs connected to HVDC via voltage source converters, while its grid-forming WTsshare the reactive power consumption/production and keep the offshore v...
Due to the increase of generation sources in distribution networks, it is becoming very complex t... more Due to the increase of generation sources in distribution networks, it is becoming very complex to develop and maintain models of these networks. Network operators need to determine reduced models of distribution networks to be used in grid management functions. This paper presents a novel method that synthesizes steady-state models of unbalanced active distribution networks with the use of dynamic measurements (time series) from phasor measurement units (PMUs). Since phasor measurement unit (PMU) measurements may contain errors and bad data, this paper presents the application of a Kalman filter technique for realtime data processing. In addition, PMU data capture the power system's response at different timescales , which are generated by different types of power system events; the presented Kalman filter has been improved to extract the steady-state component of the PMU measurements to be fed to the steady-state model synthesis application. Performance of the proposed methods has been assessed by real-time hardware-in-the-loop simulations on a sample distribution network.
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Papers by Ali Bidadfar