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To mitigate the resonance between the full converter-based wind generation (FCWG) and the grids, their modal interaction is usually coordinated off-line and requires the full system model. In this paper, an on-line coordination strategy is proposed to achieve appropriate modal coordination in a model-free manner. Firstly, the dynamic interaction mechanism is examined to quantify the modal interaction impact, which provides theoretical foundation of how FCWG controller parameter tuning contributes to modal coordination. With phasor measurement unit (PMU) equipped in the power grid, the essential oscillation information (e.g. the critical mode that relates to modal resonance) is acquired without detailed modeling of the power grid. According to the frequency range of critical mode, the proper controller in FCWG is selected for parameter tuning. On this basis, we employ an on-line coordination strategy by adjusting relevant controller parameters to accommodate corresponding changes of system operational conditions and thus mitigate the potential risk of modal resonance. Case studies are carried out to demonstrate how FCWG adjusts the controller parameters timely to improve the oscillatory stability under various operating conditions, and thus in turn substantiate the robustness and adaptability of the proposed strategy.

Droop control has been well adopted for multi-source multi-load DC microgrids (MGs) due to its inherent modularity and reliability by only using local measurements, especially with the most commonly-used voltage-current droop (V-I) mode. While another implementation named current-voltage droop (I-V) mode also can be adopted. With the same value of droop gain in these two modes, a DC MG will have the same steady-state feature, but its dynamic performance of DC voltage control may be different. Our primary motivation is to investigate this phenomenon from the perspective of equivalent RLC circuits. This paper proposes a generic reduced-order modeling method suitable for exploring the dynamic stability of DC voltage control with these two modes. By ignoring fast inner current control dynamic, each droop based DC voltage control unit can be modeled as a RLC parallel circuit in these two modes, which is convenient for modular modeling and extension. In addition, if the inner current control with slow dynamic cannot be ignored in some specific scenarios, a modified RLC model can be still obtained to analyze its influence. Tthe effectiveness of the proposed reduced-order modeling method has been verified by detailed simulation and experiment results.

Increasing penetration level of renewable energy results in unprecedented operational challenges of AC grids due to generation uncertainty and reduced inertia. In grid emergencies, Fast active Power output Reduction (FPR) is demanded to drop wind turbine generator (WTG) power outputs faster than usual. However, the power mismatch between WTG mechanical power input and reduced electrical power output resulted from FPR can lead to rotor overspeed, which cannot be timely nullified by slow‐responding pitch control. Therefore, this paper proposes a novel FPR scheme for doubly‐fed induction generator (DFIG)‐based WTG through coordinated control of DC chopper and pitch angle. Specifically, the FPR command is executed by DFIG rotor‐side converter control, while rotor overspeed is restricted by triggering the DC chopper to dissipate the mismatched power. The pitch angle is actuated at a maximal rate to eliminate the mismatched power and switch off the DC chopper. The effectiveness of the proposed FPR scheme is verified through comparative simulation studies under FPR command execution and a grid fault. It shows the proposed scheme can achieve FPR in tens of milliseconds, avoid rotor overspeed and provide low‐voltage ride‐through capability in a fully‐controlled manner.

This paper presents a flexible model and testing arrangement that can be used to mimic the fault infeed characteristics of power electronics converters and evaluate the performance of transmission protection schemes to faults when the system is “converter-dominated”. That is, sources (e.g. renewables) and infeeds (e.g. HVDC interconnectors) that are interfaced to the main power system via converters. Actual protection relays are injected, in real time, using the outputs of the various fault simulations. A range of potential protection issues, including slow tripping, erroneous discrimination and non-operation, are illustrated for particular scenarios. The main contributions of the paper include knowledge of how different protection schemes may be affected by converter-interfaced sources and guidance on possible solutions to the observed problems. Two solution options are highlighted: changes to the fault detection methods used within relays, and/or defining the fault-response elements of future grid codes (and therefore future converter fault responses) to ensure that existing protection schemes will not be adversely affected in future low-carbon, converter-dominated systems.

With the increasing penetration of renewable distributed generations (DGs), large numbers of “energy prosumers” are emerging rapidly. There will be severe impacts on the utility grid if these renewable DGs are not managed properly. Smart electrical power devices which enable high flexibility in energy management, alleviation in harmonic pollutions and friendly interactions with the utility grid are needed urgently. To meet all these requirements, a novel energy router which enables a unique parallel operation mode to the energy prosumer is presented. Facilitated with a bi-directional DC/AC converter, a switch array module and a fuzzy logic based hierarchical control strategy, the presented energy router enables plug-and-play connections and reliable energy management for the energy prosumer. The switch array and the parallel mode enable the loads to be flexibly scheduled to reduce energy cost and improve system performance. MATLAB/Simulink model of the energy prosumer is set up and a fuzzy logic based hierarchical control strategy is implemented for transient power balance control in various operation modes. Simulation results have demonstrated high flexibility, stability and feasibility of the proposed energy router in energy management of the prosumer, which will contribute to the better utilization of the ever-growing renewable energies.

Uncertainties, which are introduced by environmental conditions in renewable systems, result in unstable energy supply and demand. For a solar heating system, the seasonal variation in the ambient temperature and radiation critically influence system performance. Meanwhile, the current design parameters for improving robustness, based on the empirical tolerance, are unreasonable, which can lead to an overestimation of the facility’s capacity. In addition, the effects of system control parameters, always assumed in the design stage, on the uncertainties of the system are not given more attention. In this study, a theoretical model was chosen to indicate the uncertainties of the design parameters in a complementary heating system by integrating solar energy and an air-source heat pump (ASHP), and a method was proposed to determine the design radiation by considering the uncertainties of the system. First, a Monte Carlo simulation was applied to propagate the input uncertainties of the solar fraction and system efficiency. Then, the input parameters were ordered by significance to the system performance based on sensitivity analysis, to improve the economic dependability of the design. Finally, the economic design radiation values of each district are decided under local calculated outdoor temperature of the enclosure structures in winter. Moreover, the proposed methodology could also be a guide for using uncertainties to determine the optimal design parameters for other renewable systems.

A cluster with multiple AC or DC microgrids (MGs) based on flexible DC interlinking and distributed energy storage systems is studied in this paper, which has been identified to have the following issues in terms of its primary control scheme: coordinated power control among slack terminals in the MG cluster, seamless operation mode transition for the interlinking converters and the common DC bus voltage control. A novel flexible control scheme that unifies the control of all the MGs only using local measured signals without further communications is proposed in this paper, which aims to improve control stability, and operation reliability and flexibility. Theoretical introduction and analysis are presented to explain the proposed control. The detailed average value model and small-signal model of an MG cluster with two AC MGs and two DC MGs are simulated, respectively, with the proposed control in power systems computer-aided design/electro-magnetic transient design and control to verify the effectiveness in control stability and flexibility enhancement, and the impact of control parameters on the small-signal stability of the considered cluster is analysed through root locus.

Hybrid ac/dc microgrids (MGs) integrated with traditional diesel generators, distributed energy storage systems (ESSs), and high penetration of renewable energy sources (RESs)-based distributed generators (DGs) have become an attractive power supply solution for isolated remote areas and islands, which can effectively reduce environmental protection pressure and improve power supply reliability. However, in such inherent low-inertia systems, randomness and fluctuation of the output power of RESs and uncertain load consumption can easily incur dynamic stability issues, such as transient power impact, unacceptable frequency deviations, and operation mode transitions for security. To solve the above problems and enhance the dynamic stability of the system, an enhanced dynamic stability control (EDSC) scheme with locally measured signals only is proposed in this paper. In this control scheme, the bi-directional interlinking dc-ac converter uses the ac frequency in ac MG as the reference value of dc voltage and adopts the current feedforward control to control the dc voltage in the dc MG to be consistent with the ac frequency. By electrically coupling dc voltage and ac frequency, power disturbances in ac or dc sides will cause almost identical variation degrees in both ac frequency and dc voltage. Under the proposed EDSC scheme, the distributed ESSs in both ac and dc sides are then automatically coordinated and controlled by the unified droop control to balance transient power disturbances and smooth output of diesel generator under normal condition, which can effectively improve stability and controllability of such low-inertia systems. Furthermore, in an emergency such as failure of diesel generator, the operation mode can be switched seamlessly with the proposed EDSC scheme. The detailed theoretical analysis including control system design, small signal model analysis of key parameter influence on system dynamics, and simulation verifications in the PSCAD/EMTDC environment is presented to verify the effectiveness and practicality of the proposed EDSC scheme.

As one key content of future grid development, the methodological rationality of power grid planning has crucial impact on the operational security and stability for the power grid. With rapid development of wind power and photovoltaics, the wind-solar-coal bundled transmission pattern is becoming an inevitable trend in order to balance the mismatch between renewable energy generation and load demand in China, which has caused great challenges to power gird planning. In order to address the uncertainty of wind power generation, a two-level planning model considering N-1 security constraint is established in this paper which divides the grid planning problems into four typical scenarios considering the seasonal characteristics of wind power outputs. The high-level model, comprehensively considering the operational efficiency, aims to minimize the costs of wind-solar-coal bundled power transmission under various operating conditions while the low-level model aims to minimize the load shedding based on N-1 security analysis. Both the high-level and low-level models take N-1 constraint as the primary constraint and the best planning scheme can be obtained through iterations. According to the given planning scheme and the actual operation scenarios, the final scheme can be optimized and selected.

With the rapid development of ultra-high voltage direct current (U-HVDC) transmission systems, the security and stability control system (SSCS) plays an increasingly important role in ensuring the reliable operation of the power grid as the second line of defense for power system protection. To analyze the impact of SSCS overall architecture on the system reliability, firstly, a reliability analysis method for the SSCS is proposed to correlate the hardware, software and communication channel of the U-HVDC's SSCS under different U-HVDC's SSCS operation modes by establishing a fault tree model of the SSCS. Secondly, the sequential Monte Carlo method is employed to analyze the reliability of the U-HVDC's SSCC model considering the failure rate and maintenance time for each part of the SSCS. The proposed fault tree model and reliability analysis method is used to simulate a real case of the U-HVDC's SSCS commissioned in China. The result compares the reliability of the system architecture under different operation modes and provides significant insights on the selection rules of the U-HVDC's SSCS operation mode for system reliability improvement.

Physical review accelerators and beams 23(3), 031301 (2020). doi:10.1103/PhysRevAccelBeams.23.031301, From plasma-wakefield acceleration as a physics experiment toward a plasma-based accelerator as a user facility, the beam physics issues remaining to be solved are still numerous. Providing beams with high energy, charge, and quality simultaneously, not only within the plasma but also at the user doorstep itself, is the main concern. Despite its tremendous efficiency in particle acceleration, the wakefield displays a complex 3D profile which, associated to the beam-loading field induced by the accelerated beam itself, makes the acceleration of high charge to high energy often incompatible with high beam quality. Beam extraction from the plasma without quality degradation for a transfer either to the next plasma stage or to the user application is another difficulty to consider. This article presents the substantial studies carried out and the different innovative methods employed for tackling all these different issues. Efforts focused on achieving the challenging beam parameters targeted by the EuPRAXIA accelerator facility project. The lessons learned at the end of these in-depth simulations and optimizations are highlighted. The sensitivity to different error sources is also estimated to point out the critical components of such an accelerator. Finally, the needs in terms of laser and plasma parameters are provided., Published by American Physical Society, College Park, MD

Following the decarbonisation and decentralisation of energy industry, wind energy is becoming a promising generation source to reduce greenhouse emission, and meet future energy demand. Unlike traditional generation using synchronous generators, many wind turbines use induction generators, e.g., doubly-fed induction generators, due to the cost effective design of adjustable-speed operation and flexibility in reactive power control. However, a growing number of doubly-fed induction generator-based wind farms has significantly increased the complexity of system dynamic model, and hence increased the computational burden of power system dynamic study. This becomes a serious concern in the electricity system operation, where a fast power system stability assessment is required to assure the real-time system security during high levels of wind power penetration. In this paper, a novel model reduction strategy of doubly-fed induction generators is derived to improve the efficiency of power system dynamic study, while the study accuracy is still maintained to an acceptable level. To achieve this, a method to assess the modeling adequacy of doubly-fed induction generators for small-signal rotor angle stability analysis is firstly introduced. By evaluating the damping torque contribution to stability margin from different dynamic model components of doubly-fed induction generators, the proposed method provides a quantitative index (i.e., participation level) to show the involvement of each dynamic model component of doubly-fed induction generators in affecting power system damping, and thus can instruct how to reduce the model of doubly-fed induction generators in an efficient and accurate manner. On this basis, five model reduction plans and a model reduction strategy have been proposed according to the previously defined participation levels. The effectiveness of the proposed strategy is demonstrated in the New England test system and a real large power grid in Eastern China respectively. It has been proved that the proposed the model reduction strategy of doubly-fed induction generators for power system dynamic study is undoubtedly useful to the electricity system operator, with a key benefit in reducing model complexity and improving computational efficiency of a large-scale power system with an increasing number of wind power generation.

To address the system operability challenges due to the continuous reduction of system inertia by increasing penetration of renewable power generation, this paper proposes a new synthetic inertia control (SIC) strategy for doubly fed induction generator (DFIG)-based wind turbine generators. The proposed SIC scheme enables individual DFIG generators to contribute an effective inertial response which helps to stabilise the rate of change of frequency and minimize the maximum frequency deviations in particular under severe disturbance conditions. To achieve the proposed SIC, lithium-ion supercapacitors are required in the dc link of the DFIG power electronic conversion system to increase extra energy storage capability. The DFIG's dc voltage operates at various levels following the derived SIC algorithms for energy exchange with the connected ac grid, and the conventional control system for DFIG is modified to implement the algorithms. The functions and system benefits of SIC scheme are verified using a DFIG model connected to a power system and compared with the simulations of conventional DFIG control scheme. Practical issues such as size, cost, weight, connection configuration, and charging/discharging rate of lithium-ion capacitors for the SIC are discussed and relevant recommendations are presented.

Applications of electric heating, which can improve carbon emission reduction and renewable energy utilization, have brought new challenges to the safe operation of energy systems around the world. Regenerative electric heating with load aggregators and demand response is an effective means to mitigate the wind curtailment and grid operational risks caused by electric heating. However, there is still a lack of models related to demand response, which results in participants not being able to obtain maximum benefits through dynamic subsidy prices. This study uses the Weber–Fechner law and a clustering algorithm to construct quantitative response characteristics models. The deep Q network was used to build a dynamic subsidy price generation framework for load aggregators. Through simulation analysis based on the evolutionary game model of a project in a rural area in Tianjin, China, the following conclusions were drawn: compared with the benchmark model, regenerative electric heating users can save up to 8.7% of costs, power grid companies can save 56.6% of their investment, and wind power plants can increase wind power consumption by 17.6%. The framework proposed in this study considers user behavior quantification of demand response participants and the differences among users. Therefore, the framework can provide a more reasonable, applicable, and intelligent system for regenerative electric heating.

With increasing reliance on information technology by modern society, the scale and energy consumption of data centers (DCs) are rising rapidly. Approximately 40% of the energy consumed by DCs is associated with refrigeration systems used to maintain optimal operation temperatures. Such systems produce large amounts of waste heat; therefore, the utilization of the waste heat is essential for the optimization of the energy efficiency of DCs, especially with regard to DC prosumers (producers and consumers). However, the low temperature of the waste heat and variation in load demand are two factors limiting the exploitation of waste heat from DCs. In this study, a prosumer DC energy system based on a ground source heat pump (GSHP) is proposed for the recycling of waste heat from DCs for the heating of surrounding buildings. The heat generated in the non-heating period is stored in the soil and made available for building heating using a carbon dioxide (CO2) direct-expansion GSHP. Furthermore, the cooling power consumption, total power consumption, exergy efficiency, and net profit of the prosumer DC waste heat energy recovery system are evaluated. Compared to conventional cooling systems that use air source heat pumps (ASHPs) for building heating, the energy, exergy, and economic (3E) performance of the prosumer DC have the following advantages: 1) the prosumer DC waste heat energy recovery system yields a heat-power ratio of 5.70, with a total power consumption approximately half (52.86%) that of the conventional system; 2) the matching thermodynamic properties are greatly improved; specifically, the exergy efficiency of the prosumer DC waste heat energy recovery system is 3.87 fold that of the conventional system; 3) better economic revenue of the prosumer DC waste heat energy recovery system generates more economic revenue, with an annual net profit approximately 190.34% of that generated by the conventional system. In general, the prosumer system facilitates flexible and effective utilization of the low-temperature waste heat, by coupling the upstream power supplier and downstream thermal users through a GSHP.

The energy performance of building energy systems usually deviates from expectations, largely due to the differences in information interactions between supply and demand. In this study, mutual information (MI) was used as a tool to quantitatively analyze energy consumption fluctuations due to information interaction differences. First, a building energy system to cool an office building was constructed as a planning model. Meanwhile, three control strategies were developed to control the heat pump and the room temperature. Subsequently, uniform distribution error was used to simulate information interaction deviation during the control phase. Finally, the robustness of the three control strategies was quantified using MI. When MI reached 88.6% of the design phase, the energy consumption and renewable energy usage of the second control strategy were closest to the design phase. Moreover, out of 100 simulation sets with added errors, the second strategy exhibited 10% greater acceptable simulation sets than the other two strategies. The proposed analysis method can effectively identify the best strategy to reduce information differences.

A high-speed railway train control system plays a key role in ensuring the safe operation of the trains. To ensure the safety of high-speed railway train control systems, it is vital to perform hazard analysis on them. In this context, this paper proposes a novel hazard analysis method which extends a previously reported system-theoretic hazard analysis method “system-theoretic process analysis.” The proposed method improves the standard system-theoretic process analysis to capture the temporal relations between inadequate control actions leading to hazards. These temporal relations are crucial for investigating the causes of hazards. To depict the temporal relations of control actions of high-speed railway train control systems, a new temporal logic called “control action temporal logic” is proposed first. Then based on this temporal logic, a new control action relation model is added into the process of system-theoretic process analysis. This model depicts the relations (including temporal relations) between control actions. In order to identify both the inadequate control actions and their temporal relations, an algorithm is designed and used. Finally, the effectiveness of the proposed method is verified through the hazard analysis on the Chinese Train Control System level 3.

According to the entropy theory, the increase in the thermodynamic entropy of energy is reduced under the control of the information entropy. However, the quantitative analysis of this process remains difficult. In this study, energy properties are conferred upon information to enable an uncertain event to be measured. First, the entropy theory was adopted to describe the uncertainty of the energy in a distributed energy system. Further, a method was devised to optimize the configurations of the distributed energy system based on minimize total entropy generation. Finally, using the example of load forecasting, the impact of introducing information in the form of negative entropy on the ability of the system to improve the alignment between supply and demand is quantitatively elucidated. The negative entropy caused by information utilization increased from 356.14 to 638.68 kWh/K, with the load forecasting errors decreased from 30% to 10%. The information entropy was also applied to describe the uncertainty of the On-site energy fraction, by increasing the capacity of energy storage, the uncertainty decreased from 1.81 to 1.80 nat, while the load forecasting could decreased it to 1.71 nat, 1.54 nat, 1.29 nat with the load forecasting errors at 30%, 20% and 10%, respectively.

9th International Particle Accelerator Conference, IPAC18, Vancouver, Canada, 29 Apr 2018 - 4 May 2018; Journal of physics / Conference Series Conference Series 1067, 042011 (2018). doi:10.1088/1742-6596/1067/4/042011, The EuPRAXIA (European Particle Research Accelerator with eXcellence In Applications) project aims at producing a conceptual design for the worldwide plasma-based accelerator facility, capable of delivering multi-GeV electron beams with high quality. This accelerator facility will be used for various user applications such as compact X-ray sources for medical imaging and high-energy physics detector tests. EuPRAXIA explores different approaches to plasma acceleration techniques. Laser-driven plasma wakefield acceleration with external injection of an RF-generated electron beam is one of the basic research directions of EuPRAXIA. We present studies of electron beam acceleration to GeV energies by a two-stage laser wakefield acceleration with external injection from an RF accelerator. Electron beam injection, acceleration and extraction from the plasma, using particle-in-cell simulations, are investigated., Published by IOP Publ., Bristol

The rotor structure varies with different types of wind power induction generator (WPIG), which leads to their different dynamic behaviors during power system disturbances. This paper proposes a generic implementation framework of explicit damping torque analysis to investigate the damping mechanisms of power system integrated with induction generator based wind power generation, so that the essential difference and inner connection between two main types of WPIG (i.e., DFIG and FSIG) in damping power system oscillation can be revealed. The linearized models which can represent DFIG and FSIG as well as three transitional wound rotor generators are established to facilitate the analytical comparison analysis. Phillips-Heffron system linearized model is employed to derive an explicit expression of damping torque contribution from main dynamic components of WPIGs. In the paper, 16-machine 5-area NYPS-NETS example system is used for the demonstration of proposed framework and comparison analysis. Both damping effectiveness and robustness of different WPIGs are extensively examined under multiple operating status, in order to provide useful guidance to system planner for the real-time operation of induction generator based wind generation.

The drive towards renewable energy sources (RES) is dramatically changing the dynamic electrical characteristics of Generators, which are traditionally the dominant dynamic component in Power Systems. Non-synchronous generation (NSG) approaching or even exceeding control area demand is now happening on a rapidly expanding scale. The study identifies from National Grid's perspective as Great Britain transmission system operator, the key challenges during periods of operation with high proportion of RES relative to demand. It raises some major questions. What determines system strength in an HVAC system largely without synchronous generators and what is adequate for stability? What levels of %NSG can be expected in the future energy scenarios? What are the financial consequences of constraining RES production if the technical capabilities create an upper limit of %NSG which the system can be operated at? The study finally proposes closer collaboration across the industry to find the optimal missing solutions.

There is concern that the levels of inertia in power systems may decrease in the future, due to increased levels of energy being provided from renewable sources, which typically have little or no inertia. Voltage source converters (VSC) used in high voltage direct current (HVDC) transmission applications are often deliberately controlled in order to de-couple transients to prevent propagation of instability between interconnected systems. However, this can deny much needed support during transients that would otherwise be available from system inertia provided by rotating plant.

The installed capacity of non-synchronous devices (NSD), including renewable energy generation and other converter-interfaced equipment such as energy storage, bi-directional transfer links, electric vehicles, etc., is expected to increase and contribute a large proportion of total generation capacity in future power systems. Concerns have been expressed relating to operability and stability of systems with high penetrations of NSD, since NSD are typically decoupled from the grid via power electronic devices and consequently reduce the “natural” inertia, short-circuit levels and damping effects which are inherently provided by synchronous machines. It is therefore crucial to ensure secure and stable operation of power systems with high penetrations of NSD. This paper will show and quantify the instantaneous penetration level (IPL) limits of NSD connected to a simple example power system in terms of steady-state stability beyond which the system can become unstable or unacceptable, defined as “unviable”. The NSD used in this example will be a conventional dq-axis current injection (DQCI) convertor model. The paper will introduce a set of criteria relating to locking signal in converter phase-locked loop, frequency, rate of change of frequency and voltage magnitude, which will be used to determine the system viability and the IPL limit. It will also be shown that there are several factors that can potentially affect the IPL limits. Frequency and voltage droop slopes and filter time-constant for DQCI converter are varied and it is shown how these settings influence the IPL limits. Finally, to provide additional insight into network viability under high penetrations of NSD, a visualisation method referred here as “network frequency perturbation” is introduced to investigate responses of individual generators to a change in network frequency.

Conventional converter models for wind turbines and Voltage Source HVDC links, as submitted to System Operators, typically use dq-axis controllers with current injection (DQCI). Recent work carried out by the authors has proven that for DQCI converter-interfaced sources there are overall penetration limits, i.e. the ‘tipping points’ beyond which the system will become unstable. Initial investigations of this “tipping point”, based on a reduced model of the transmission system of Great Britain using phasor simulation within DIgSILENT PowerFactory, are reviewed briefly in this paper. The ‘tipping points’ relating to maximum penetration of DQCI converter-interfaced sources are subsequently investigated in this paper using a higher fidelity three-phase dynamic power system model in Matlab Simulink. Additionally, a new converter controller, termed here as Virtual Synchronous Machine Zero Inertia (VSM0H), is described and implemented in the model. It is shown that, in principle, it is possible to significantly increase the penetration of converter based generation (up to 100% of installed capacity) without reaching a stability constraint.

This paper illustrates how converter interfaces, used to connect renewable energy sources, HVDC links and infeeds to the power system, may bring significant changes to the behaviour of protection systems in the future. A converter model, capable of providing adjustable fault responses, is used to investigate the response of power system protection to a range of fault conditions. Different scenarios have been simulated by applying different types of faults at different location of the transmission system with a variety of different converter response types. A dynamic, verified, relay model and a hardware relay device have been injected with the simulated results to ascertain network protection performance.

This paper investigates the limits to penetration levels of non-synchronous generation (NSG) in a power system and how this may be increased. Reduced system inertia, arising from high penetrations of NSG, is one of the main issues that may increase the risk of system instability in various guises. Swing equation - based inertial response (SEBIR) control, often referred to using a variety of terms, is considered to be a potential solution that can enable converter - interfaced generation to support the system during and after disturbances. However, the effects of SEBIR on system operability and its ability to increase the NSG penetration limits and improve system strength under high NSG scenarios has not been fully investigated. The paper presents the implementation of SEBIR control within a simplified model of the future Great Britain (GB) transmission model, created using DIgSILENT PowerFactory. Using the model, the instantaneous penetration level limits of NSG in terms of both transient and steady - state stability are investigated with and without SEBIR control applied to the NSG. The capability of SEBIR in enabling additional active power output from NSG and improving system frequency response under a loss of infeed event is investigated and it is shown how SEBIR can assist in increasing NSG penetration levels, but that further work is required to understand certain phenomena that have been observed.

The level of inertia in modern power systems is reducing drastically due to the increasing penetration of renewables to the power grid. In the near future the grid will face high penetration of renewable resources because of countries policies. However, renewables provides no inertia. On the other hand, voltage source converter (VSC) based multi terminal HVDC system is a promising solution for connection of offshore wind farms to transmit huge amount of harvested energy to ac grids. This paper proposes a complete VSC-HVDC control structure which enables candidate converter station to mimic the inertia of a synchronous machine considering generalized voltage droop strategy. The emulated inertia comes from the capacitor of the dc link. The proposed strategy enables a VSC station with a fixed dc link capacitor to mimic inertia constant in a considerable range, by configuring a range of dc-link dc voltage variation. Sudden load changes in weak ac grid will be compensated by the emulated inertia that is provided by the candidate grid side VSC station.

With the ultimate aim to remove/reduce constraints on the amount of non-synchronous generators that may be connected to power systems, this paper identifies potential problems associated with system dynamics under high penetrations of converter-interfaced sources, especially from the perspective of inertia and responses to disturbances. The configuration of VSC-HVDC transmission systems and their controllers is introduced and analysed. Methods that have been proposed to enable VSC-HVDC systems to provide frequency response are reviewed, and a typical VSC-HVDC system with an associated control system is built and validated in Matlab Simulink. These models will form a key part of a modelling toolkit that is being developed to investigate optimal methods for reducing (or removing) future Non-Synchronous Generation (NSG) penetration constraints in the power system in the UK, which represents further work that will be conducted in this project.

A generic Inertia Emulation Controller (INEC) scheme for Multi-Terminal Voltage-Source-Converter based HVDC (VSC-MTDC) systems is proposed and presented in this paper. The proposed INEC can be incorporated in any Grid-side Voltage-Source-Converter (GVSC) station, allowing the MTDC terminal to contribute an inertial response to connected AC systems during system disturbances, in a fashion similar to synchronous generators. The DC link capacitors within the MTDC are utilised by the INEC scheme to exchange stored energy with the AC system by varying the overall DC voltage level of the MTDC network within a safe and pre-defined range. A theoretical treatment of the INEC algorithm and its implementation and integration within a conventional VSC control system are presented, and the impact on the total DC capacitance required within the MTDC network to ensure that DC voltages vary within an acceptable range are discussed. The proposed INEC scheme is validated using a Matlab/Simulink model under various changes in demand and in response to AC network faults. The model incorporates a multi-machine AC power system connected to a MTDC transmission system with multiple converter-interfaced nodes. The effectiveness of the INEC in damping post-fault oscillations and in enhancing AC system frequency stability is also investigated. The system is shown to perform well and is attractive for providing a stable MTDC system that is capable of providing valuable support to the connected AC systems.

As the utilization of renewable energy sources (RES) and HVDC links is growing rapidly, many characteristics of the resulting power system can be seriously changed. HVDC links, as well as RES using converters as an interface with the main grid, can be all treated as non-synchronous sources. These sources are different from the traditional synchronous generators in many ways and bring significant challenges to the existing protection systems. Therefore, the aim of this paper is to explore power system protection performance issues under the context of the main characteristics of future power networks. In this paper the operating principles of converters is investigated. Initial equivalent models of Voltage Source Converters (VSC) in response to both symmetrical and unsymmetrical faults in the AC power systems are introduced and developed. Such models explain the characteristics of the future power networks with focuses on protection system performance. The VSC models will investigate system performance under fault conditions taking into account of European HVDC Grid Code requirements proposed by the European Network of Transmission System Operators for Electricity (ENTSO-E)[1].

A generic Inertia Emulation Controller (INEC) for Multi-Terminal Voltage-source-converter based HVDC (VSC-MTDC) is proposed in this paper. The proposed INEC can be incorporated in any grid-side-voltage-source-converter (GVSC) station, allowing the MTDC terminal to contribute an inertial response during system disturbances, in a similar fashion with a synchronous generator. The DC link capacitors of MTDC are utilized by INEC to exchange the stored energy with the AC grid by varying the overall DC voltage level of the MTDC network. The derivation process of the INEC algorithm and its implementation to the conventional VSC control system are presented, and the impact of total DC capacitance of the MTDC network on DC voltage variations is discussed. The proposed INEC for MTDC systems are validated by Matlab/Simulink under demand changes in a simulated multi-machine power system with a MTDC transmission system, and the effectiveness of damping post-fault oscillations is also investigated.

With the deployments of smart grid technologies and communication networks in modern power systems, frequency relays, which are used for the purpose of power system protection, are to achieve more advanced and reliable performance. Load shedding strategies, which prevent power systems from suffering frequency instability based on the real time data frequency relays, are facing a challenge to adequately and accurately take shedding actions, as power system loads are varying all the time. On the generation side, increasingly non-dispatch able and inflexible renewable power generations being integrated to the system complicates generation predictions and results in frequent power imbalance. This paper proposes a load shedding scheme with different magnitudes and load shedding orders for distribution networks, with its effect on power system frequency stability verified in a benchmark IEEE 33-bus distribution system, which is simulated in Dig SILENT Power Factory package.

The increasing penetration of power electronics interfaced renewable generation (e.g. offshore wind) has been leading to a reduction in conventional synchronous-machine based generation. Most converter-interfaced energy sources do not contribute to the overall power system inertia; and therefore cannot support the system during system transients and disturbances. It is therefore desirable that voltage-source-converter (VSC) based high voltage direct current (HVDC) interfaces, which play an important role in delivery of renewable power to AC systems, could contribute a virtual inertia and provide AC grid frequency support. In this paper, an inertia emulation control (IEC) system is proposed that allows VSC-HVDC system to perform an inertial response in a similar fashion to synchronous machines (SM), by exercising the electro-static energy stored in DC shunt capacitors of the HVDC system. The proposed IEC scheme has been implemented in simulations and its performance is evaluated using Matlab/Simulink.

The inherent features of Voltage Source Converters (VSCs) are attractive for practical implementation of Multi-Terminal HVDC transmission systems (MTDC). MTDC can be used for large-scale integration of offshore wind power with onshore grids. However, many of the control strategies for MTDC that have been proposed previously for offshore wind farm integration depend on local control of the wind turbine generators. This paper proposes a new control strategy, termed Current Matching Control (CMC), which can be used with any number of converter terminals, and is independent of the types of wind turbines used within each wind farm. The proposed CMC matches the current reference of the grid side converter to that of the wind farm side converters. In order to achieve such current matching, a telecommunication system will be required to facilitate calculations of the grid side current references to be carried out in real time. To validate the performance of the proposed control strategy, a generic four-terminal MTDC network, which integrates two offshore wind farms with two mainland grids, is simulated and results relating to several steady state and transient scenarios are presented.

A new direct current matching control (DCMC) scheme is proposed in this paper. The scheme is ideally suited for the integration of a large number of wind farms with AC grid systems via a multi-terminal HVDC (MTDC) network incorporating several grid-side converters. The proposed DCMC, which matches, in a near-instantaneous fashion, the cumulative injected DC currents from all wind farms with the total of the output DC currents to the AC grids (via inverters) by communicating real-time data between all terminals, is an improvement upon and potential replacement for conventional DC voltage droop and master–slave control strategies. Through the utilization of a wide-area supervisory control and data acquisition (WA-SCADA) system, the proposed DCMC aims to enhance MTDC network voltage stability and facilitate flexible power dispatch to the supplied AC grids, while maximizing the total amount of generated wind power and offering more flexibility in terms of the ability for wind farms to independently control and maximize their outputs without any requirement for output to be constrained. A six-terminal MTDC system connecting three wind farms to three independent mainland AC grids is used to validate the proposed DCMC and compare its performance with conventional control strategies, three simulation studies are carried out to test and verify the DCMC.

A model of a converter source capable of providing a controllable fault response is introduced to analyse the performance of protection in future power system scenarios. Using a reduced power system model of the National Grid transmission system in Great Britain, a comprehensive set of tests of protection performance are performed to verify how protection systems may be impacted by the introduction of converter-interfaced energy sources and infeeds. Converters with a range of different types of fault response are modelled, as grid codes defining converter response to AC system fault are not completely specific at the present time. The simulated data are injected into an actual protection relay through secondary injection equipment and also to a dynamic protection relay model through simulation, and the results are analysed and compared. The initial results show that there can be a degree of negative influence on protection system performance in converter-dominated scenarios where the power system is relatively “weak”, primarily in the form of longer operating times in certain scenarios. The paper concludes with analysis of results and an overview of on-going and future work to broaden the investigations.