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The increasing amount of renewable power generation systems is a challenging issue for the control and operation of the electrical networks. One of the main issues is their lack of inertia, which is becoming a greater problem as much as the share of the power plants based on traditional synchronous generators gets reduced. In this regard, the new grid codes ask these plants to provide new functionalities such as the frequency support and inertia emulation. In this paper, a synchronous power controller for grid-connected converters is proposed as a good solution for the renewable generation systems with energy storage. It provides inertia, damping, and flexible droop characteristics. Different from the faithful replication of the swing equation of synchronous machines, an alternative control structure is proposed, by which the damping and inherent droop slope can be configured independently to meet the requirements in both dynamics and frequency regulations. Analysis and experimental results are both shown to validate the proposed controller.

The penetration of renewable power plants in the global electricity mix is reaching significant levels, and power system operators are adapting their grid codes, so that renewable generators do not alter the operation of the grid, preventing the introduction of additional disturbances and contributing to the control of the power system. In this context, hybrid solar plants arise as a tradeoff solution that combines the ability of solar thermal energy plants to smooth the solar resource variations and to generate a certain amount of power when there is no sun, with cheaper and easier to build and control solar photovoltaics, with the aim of providing grid-friendly, clean, renewable energy at a minimum cost. This paper analyzes the impact that a hybrid solar plant has on a power system when its PV conversion system employs advanced controllers that further contribute to a harmonious interaction between the solar resource and the grid. The analysis compares the results obtained by the hybrid plant in different operating conditions with the performance of a purely solar thermal energy plant of a similar size, and the results prove that the utilization of PV is beneficial for the power system, increasing the damping of oscillations, mitigating frequency excursions, and reducing the effort done by other generating units in the system when severe disturbances take place.

The utilisation of renewable sources brings many benefits to electric power systems, but also some challenges such as the impact that renewable power plants employing power electronics have on the grid, which is gaining importance as the penetration of this type of generating stations increases, driven by the construction of large wind or solar photovoltaic (PV) power plants. This study analyses the impact of large-scale PV power plants on a transmission grid for different penetration levels. The analysis considers power plants formed by a number of power converters employing synchronous power controllers (SPCs), that allow them to have a harmonious interaction with the grid, and compares their performance with that of conventional power converter controllers, assuming in both cases that the power plants participate in frequency and voltage regulation. The study addresses both the small-signal stability of the system and its response to large disturbances that alter the active power balance and frequency stability. The results of the analysis show that PV power plants using SPCs are able to limit frequency deviations, improve the oscillation damping, and reduce the stress of other generating units, thus having a beneficial impact on the power system.

This paper presents a novel hierarchical control solution and real-time controller for distributed power plants aimed for achieving full control capabilities and increased benefits from direct market participation, grid interaction and plant automation. The hierarchical control structure is introduced in detail, as well as the main functionalities inherent to each control layer. In addition, this paper, introduces a novel power sharing strategy based on the implementation of pricesignal references, to achieve real-time control capabilities by optimally allocating the available resources in active distributed power plants. This power sharing strategy arise as an alternative to the transactive energy concept, being capable of providing real-time control capabilities while reducing information transmission and processing requirements. The proposed plant control strategy provides multi-objective real-time control capabilities.

Distributed renewable energy sources progressively gain importance in power systems, with which new challenges, but also new opportunities, arise. Therefore, it is necessary to analyze the interaction between this type of generators and the grid, and to study adequate control methods that allow small generating units to operate harmoniously within power systems and contribute to their control, stability, and reliability. In this paper, the stability of a distribution system with several renewable energy generators is studied, focusing on its ability to maintain power supply during a transmission blackout. The response of the distribution system after a sudden disconnection from the main network is simulated and analyzed, comparing the results obtained using a conventional control for the renewable generators with those of controllers that enable a synchronous interaction between these generators and the power system.

Recent trend of research is oriented in different methods of emulating the inertia to increase the sustainability of the system. In the case of dynamic performance of power systems especially in frequency control of interconnected system, there are concerns considering the matter of virtual inertia. This paper proposes a new approach on modeling and analyzing the dynamic performance of the system with derivative based virtual inertia capability. As an important part of this paper the dynamic effects of PLL estimations on system performance are discussed and analyzed. The effects of PLL are considered by introducing a second-order function. Simulations performed by Matlab software demonstrate the effectiveness of virtual inertia on the system performance.

The impact that power plants employing renewable energy sources have on power systems is no longer negligible due to the ever-increasing portion of the power share that these generation systems represent. Therefore, the static and dynamic effects of these power plants on the grid must be analyzed in at least the same degree of detail as conventional generating units. For this purpose, it is necessary to develop models that are accurate and able to capture the dynamics of interest for the analysis, but also taking into account that they should be manageable and have a good computational performance. In the case of power plants based on photovoltaic (PV) or wind energy, formed by many power converters, an equivalent plant model that reduces the number of devices offers a good tradeoff between accuracy and complexity. Motivated by the analysis of an actual 100 MW PV power plant formed by 100 converters, each of them governed by a synchronous power controller, this paper presents a general method to derive a dynamic equivalent model of a group of converters that use this type of controller. The method is applied to this power plant in order to obtain several equivalent models with different degrees of detail that are compared through simulation. The results prove the accuracy of the equivalent aggregated models under different conditions and allow measuring the reduction in computation time that they achieve.

Virtual inertia is known as an inevitable part of the modern power systems, especially considering the increasing level of power electronic-based component and HVDC interconnection in the future gird. To cope with this challenging issue, a novel approach for modeling and analysis the effect of virtual inertia on frequency stability of multi area interconnected system is proposed. The proposed method is based on Virtual Synchronous Power (VSP) control strategy of HVDC interconnected systems. The presented work is focused on modeling and detailed sensitivity analysis of VSP-based HVDC concept in frequency control and automatic generation control task of interconnected power systems. In order to understand the influence of virtual inertia parameters, a set of sensitivity analysis is performed to identify the proper range of critical control parameters on the stability of the system. The effectiveness of the proposed concept on dynamic improvements is also validated through Matlab simulation of multi-area (two-area and three-area) test systems. The three-area test system is based on complex model of 39-bus, 10 generator test system.

This paper proposes a novel wave energy converter (WEC) control technique based on an adaptive vector controller for maximum power absorption of the wave energy resource. The proposed controller arises as a suitable solution for a realistic wave energy converter deployment, as it serves from its own wave energy converter velocity to instantaneously determine the required power-take-off force needed for maximizing the power extraction from the waves. The adaptive characteristic of the wave energy controller is achieved thanks to the implementation of advanced signal monitoring and synchronization processes along with vector control algorithms. As a result, maximum power absorption can be instantaneously achieved regardless of the dominant characteristics of the irregular waves

New trends in electricity production, that involve generating power locally at the distribution voltage level by using renewable energy sources, are changing the paradigm of the distribution network, giving it an active role with the integration of Distributed Generators (DG), which leads to the concept of active distribution networks. A key element that connects the distribution system to the rest of the power system is the medium to low voltage transformer substation, which requires further research and development in order to develop active distribution networks. This document presents an overview about the components and functions that an intelligent substation automation system may have

Power plants employing renewable energy sources connected to large power systems continue increasing their number and size. PV and wind farms are a clear example of this trend. They employ power electronics in order to inject power in the grid and in most cases the interaction does not take into account the power system needs. However, as their size increases, these plants should support the grid with ancillary services and it is necessary to analyze their impact on the grid. Despite large conventional power plants usually comprise a small amount of synchronous generators in the range of 100 MW, large power plants using power electronics are formed by a relevant number of individual generating units in the 1 MW range, which introduces additional complexity in the analysis of power systems. Therefore, it is necessary to develop aggregated models of distributed power plants. This paper presents the control of a 20 MW PV power plant and an equivalent model, which is validated through simulation.

The continuous integration of renewable energy sources into power systems has led to the construction of large power plants based on power electronics, with power ratings up to hundreds of megawatts, in order to accomodate technologies like solar PV and wind energy. Due to the size of these plants, they must provide support services for the grid and it is necessary to analyze the impact they have on power systems. Opposing to conventional power plants formed by a reduced number of synchronous generators in the range of several hundreds of megawatts, large power plants based on PV and wind energy are usually composed of a high number of individual generating units with power ratings of a few megawatts. Therefore, it is of great importance to develop aggregated models of power plants formed by multiple power converters to be used in the dynamic analysis of large power systems. This paper presents the control system of a 20 MW PV plant, derives an equivalent aggregated model and studies the performance of this model through simulation.

Three-phase power converters are largely employed in power generation facilities based on renewable energy sources, and these converters commonly working in grid connection mode are frequently connected to the grid through passive filters. Nowadays the need for larger power converter-based generation plants increases continuously, and LCL+trap filter arises as a solution when switching frequency is reduced due to the power increase. However, the tuning of current controllers becomes more complex as the LCL+trap filter lead to a considerably high order system. In this work a method for tuning the gains of proportional resonant current controllers for three-phase high power converters linked to the grid through a LCL+trap filter is proposed and analyzed. Simulation and experimental results taken in different cases are shown to validate the proposed method.

This paper proposes a modified model for active power/ frequency support of multi-area power system analysis that takes into account the effects of AC/DC systems under deregulated environment of the power market. The AC part of studied system is comprised of conventional generators and HVAC lines, while DC systems are related to the parts with converter station models and HVDC interconnection. Simulations performed by Matlab software demonstrate how renewable power plants can serve as conventional generators in AGC control loops under constraints determined by the market rules. This scenery is considered one of the most promising evolutions of the future electrical power systems.

The increasing penetration of renewable energy sources in power systems requires new control systems that provide services similar to those of conventional generators. This paper proposes an active power controller that is able to automatically achieve synchronization with the grid and to control the DC link voltage. Through this controller, the converter can be identified with a virtual synchronous generator whose kinetic energy is stored in the DC link. Moreover, the active power loop becomes a second order system whose damping can be programmed freely.

Power generation facilities based on renewable energy sources, such as PV or wind, are frequently connected to the grid through three-phase power converters. As the power of the plant increases, the design of the grid connection filters becomes critical, as a fast dynamic performance is needed while the injection of current harmonics to the network should be prevented. LCL filters, together with trap filters tuned at the switching frequency, provide a good trade-off between both needs. However, the tuning of the controllers becomes more complex as the LCL+trap filter lead to a considerably higher order system. In this paper a tuning method for determining the parameters of proportional resonant current controllers for three-phase high power converters linked to the grid through a LCL+trap filter is proposed and analyzed. In order to validate the proposed solution, different results taken in different scenarios are shown.

Renewable energy sources are increasing their penetration in power systems, making necessary new control systems that offer services usually provided only by conventional generators. In this paper, an active power controller able to achieve synchronization with the grid and to control the DC link voltage is proposed. This controller allows identifying the converter with a virtual synchronous generator whose inertia can be modified online, considering that its virtual kinetic energy is stored in the DC link. Additionally, the resulting active power loop is a second order system whose damping factor can be defined freely.

A new application of LQR controller with the ability of reference tracking for a multi modular converter with several cells is proposed. First, the mathematical model for the grid connected MMC is presented and then, the small signal state space model is obtained. MMC is a very complex MIMO system with several state variables and global control for this system is very important issue. Optimal advanced controller based on linear quadratic regulator with integral action is a very good candidate for controlling the AC signals and energy balancing in multi cells MMC system. The performance and validity of obtained model and designed linear controller are evaluated with non-linear model of MMC in SimPower System toolbox/Matlab. Simulation results are verified the excellent performance of the proposed approach in the transient and steady state operational conditions.

This paper presents a methodology for designing the link passive filter of the power converters installed in a multi-megawatt wave power plant. Such filter is based on the superposition of both LCL and trap filter configurations with the purpose of achieving enhanced grid interaction of a two-level voltage source converter. The LCL+Trap filter design is highly dependent on the electrical network characteristics; hence the distribution system of the plant is introduced in the paper to take into account its effects on the tuning parameters. The proposed LCL+trap filter topology arises as a successful alternative solution for the conventional LCL filter topology, thanks to its improved filtering capability while ensuring a reduced filter size. The validation of the proposed filter performance is evaluated in simulation by performing a comparative analysis between the LCL+trap and the LCL filters when operate in a wave farm application.

This paper proposes a passive filter design method and validation analysis based on a Trap-LCL filter topology for implementation in grid connected two-level converters for high power applications. The proposed topology appears as an alternative to the conventional LCL filter, since reduced filter parameters can be obtained while still ensuring high filtering capability for switching frequency harmonics. Furthermore, a step-by-step filter design method will be introduced in order to provide a clear scope on the tuning procedure, as well as on the main requirements that the filter should satisfy. Finally, a comparative study between a conventional LCL and a LCL-Trap filter will be performed in simulation with the goal of finding a meaningful evaluation of the advantages and disadvantages provided from the LCL-Trap configuration.

This paper presents a filter design methodology and control design strategy for LCL+Trap filters deployed in large scale wave power plants. This filter topology appears as an alternative for the widely used LCL filters, since effective harmonic mitigation can be achieved while reducing the overall passive filter components size. As a result, the use of LCL+Trap filters for two-level power converters arise as a suitable power processing solution to match the requirements of large scale wave energy applications, since such well-known power converter technology is very robust, reliable and very cost effective. The designed LCL+Trap filter is validated through simulation by performing a comparative analysis between LCL and LCL+Trap filters, and finally, the control of the converter is introduced with the purpose of validating the grid connection compliance of the entire power processing system.

In this paper a new application of PSO technique for optimizing the controller parameters of multi modular converters is presented. PSO based LQR controller is designed for averaged model of modular converter and to obtain better control parameters though the minimizing a quadraticperformance index. In this method in order to have more accuracy and better design for controller parameters, PSO algorithm is added to find the gain matrix of the controller. Simulation results show that with using this method better dynamic responses are accessible.

This paper presents a method for improving the design procedure of AC-DC power converters for power generation applications. The proposed methodology is based on selection of the most convenient configuration, in terms of switching frequency and design of the line filter, in order to minimize the overall losses in the system. In this work two types of semiconductor devices are considered: silicon IGBT and silicon carbide MOSFET for the design of a 100 kVA system, and they performance is compared. The AC-DC converter parameters, the design methodology and preliminary simulation results for representatives of Si IGBT and SiC MOSFET modules are presented.

In the wave energy sector, an increasing concern regarding the grid connection of wave energy converters is recently being experienced, as well as in the main challenges resulting from the grid integration of large scale wave power plants. This increasing interest arise due to the near-commercial developments of several wave energy converter devices, which have already proved its hydrodynamic and power take-off performance. Therefore, this paper proposes a suitable power processing system configuration and its suitable control design used for interfacing the grid connection of such high power wave energy converters while ensuring acceptable grid connection standards compliance. An advanced filter topology will be introduced based on the superposition of LCL+Trap filters as an alternative solution to the conventional LCL filters, as it allows for smaller filter size, while ensuring a reliable and cost-effective power processing solution. Finally, the evaluation of the filter design as well as the power converter control will be introduced in simulation with the purpose of validating the grid connection of wave energy converters.

The integration of AC-DC power converters to manage the connection of generation to the grid has increased exponentially over the last years. PV or wind generation plants are one of the main applications showing this trend. High power converters are increasingly installed for integrating the renewables in a larger scale. The control design for these converters becomes more challenging due to the reduced control bandwidth and increased complexity in the grid connection filter. A generalized and optimized control tuning approach for converters becomes more favored. This paper proposes an algorithm for estimating the dynamic performance of the stationary frame current controllers, and based on it a generalized and optimized tuning approach is developed. The experience-based specifications of the tuning inputs are not necessary through the tuning approach. Simulation and experimental results in different scenarios are shown to evaluate the proposal.

Due to increasing level of power converter-based component and consequently the lack of inertia, automatic generation control (AGC) of interconnected systems is experiencing different challenges. To cope with this challenging issue, a derivative control-based virtual inertia for simulating the dynamic effects of inertia emulations by HVDC (high-voltage direct current) interconnected systems is introduced and reflected in the multi-area AGC system. Derivative control technique is used for higher level applications of inertia emulation. The virtual inertia will add an additional degree of freedom to the system dynamics which makes a considerable improvement on first overshoot responses in addition to damping characteristics of HVDC links. Complete trajectory sensitivities are used to analyse the effects of virtual inertia and derivative control gains on the system stability. The effectiveness of the proposed concept on dynamic improvements is tested through Matlab simulation of two-area test system for different contingencies.

This paper proposes an new approach for modeling and analysis the dynamic effects of virtual inertia on two-area AC/DC interconnected AGC power systems. Inertia emulation is known as key factor for modern power systems. In this paper, the higher level application of derivative control for emulating the inertia is investigated. This method of inertia emulation is developed for two-area AGC system which is connected by two parallel AC/DC transmission systems. Based on proposed technique, the dynamic effects of virtual inertia emulation on frequency and active power control could be evaluated. Simulations results, demonstrate how virtual inertia emulation can effectively improves the performance of the power system. Eigenvalue analyses are also added to support the positive effects of proposed method.

Automatic Generation Control (AGC) in multi-area interconnected power systems is experiencing several adaptions due to increasing level of power converter based components in the system. The concept of Virtual Synchronous Power (VSP) to simulate the dynamic effects of virtual inertia emulations by HVDC links for higher level control applications is introduced and reflected in the multi-area AGC model. By using this proposed combination in AGC model, the dynamic performance of the studied system shows a significant improvement. The proposed formulation is generalized for Multi-areas with multiple HVDC links. The active power loop control in VSP based HVDC link has a second-order characteristic which makes a simultaneous enabling of damping and inertia emulations into the system. Trajectory sensitivities are also used to analyze the effects of VSP’s parameters on the system stability. The effectiveness of the proposed concept on dynamic improvements is tested through Matlab simulation of a four-area system.

There is a growing interest in electrical grid connection of single unit Wave Energy Converters (WECs), as well as the multiple units based Wave Power Plant (WPP) applications. Due to the increasing integration of high power converters in WPP, additional concerns on the harmonic current mitigation of WEC device arise which requires the grid filter installation. Furthermore, the identification and appropriate mitigation of additional harmonics at the WPP level is needed, as any inductances and capacitors of the WPP can interact with the resonant frequency of the entire system and lead to detrimental effects on equipment. The present paper focuses on the potential harmonic studies of a realistic proposed WPP layout, in which the system resonances are identified by performing the frequency scan and modal analysis (HRMA) methods. The later technique has the ability of determining the participation factor of each bus, finding in this way the nodes in the system that have more influence on the obtained results. In this way, the most suitable nodes in which additional filtering solutions should be implemented can be identified.