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Abstract When a severe fault occurs in the distribution network, all or parts of it may be disconnected from the upstream network. Partitioning of these islanded areas is a solution to supplying the affected loads. Due to the variable nature of loads and renewable distributed generation (DG), the static model of partitioning with a fixed nature during island operation cannot be suitable. Therefore, in this article, considering the variable nature of loads and renewable distributed generation, a dynamic model is presented for the island partitioning to restore more valuable loads, which is suitable for quick decision‐making in emergencies. Also, a method for deciding on the mode of charging and discharging storage systems in emergencies is proposed. This model considers time limitation, uncontrollable DGs, controllable DGs and their control, controllability, and priority of loads, tie‐switches, storage systems, simultaneous faults, different situations of unintentional islanding of the distribution network, position of switches, and variable nature of loads and distributed generations. So, it is more comprehensive than the previous methods. Applying the proposed model to the modified IEEE 69‐bus system with controllable and uncontrollable generation and storage systems assuming different scenarios shows the effectiveness of the proposed scheme.

Abstract A systematic definition of an aircraft generator's “available power” (used to supply loads on its DC bus) is given, which is defined in the context of constraints on transient and steady‐state performance. Using a geometric, data‐driven approach, such a characterisation has been achieved, and a new method, called Power availablE Estimation Tool (PEET), has been developed to determine in real‐time whether a given load can be fulfilled at a given time while maintaining power quality. This is an important problem, especially for safety critical electrical systems such as more electric aircraft, for which it is imperative to know a priori whether an added load will result in voltage variations outside of allowed values. PEET is introduced and its conceptual framework is formalised. Lastly, it provides simulation results that illustrate its performance. The results show that the PEET method produces reliable a priori estimates of power availability, and that this can be achieved within time frames that make it applicable in a real‐time implementation.

Abstract As the ratio of newly installed power generation utilizing power electronic converters increases, it results in a decrease in the overall inertia and damping of the power system, as well as the decrease in its ability to resist interference. Aiming to address this issue, the authors propose an adaptive optimal control approach for the parameter in the virtual synchronous generator (VSG). This strategy considers the power angle curve and analyzes the principles of inertia and damping within the oscillation period and its range of values. By coordinating the values of parameters, it achieves the optimization of these parameters. At the same time, in order to take into account the demand for fast regulation response under normal operation control conditions and the demand for synchronization support under disturbance fault conditions, a multi‐mode switching control strategy including virtual synchronization control and conventional PQ control is further proposed. Based on MATLAB/Simulink software, the strategies mentioned above have been proven through simulation. The findings testify the proposed method can significantly enhance the regulation response characteristics of the VSG by optimizing its parameters. Additionally, it enables smooth switching of the control mode independently, based on the specific requirements of different control scenarios. This approach fully leverages the virtual synchronous support and fast regulation characteristics of the power electronic converter, and has practical engineering value.

Abstract Frequency security is the premise of realizing the net‐zero transition. A novel assessment scheme is proposed to quantify the frequency security levels of transmission systems under different inverter‐based resources (IBRs) and their control parameter combinations. A novel system frequency dynamic model is proposed as a parametric optimization method, where the saturation of generators, energy storage systems, and renewable energy sources is incorporated as differential algebra equations. This problem is further reformulated as a mixed‐integer linear programming problem to generate a sufficient amount of data under different IBR integration and control parameters. The frequency security assessment problem is formulated as a data‐driven multivariate classification problem, which is solved by the optimal classification tree (OCT) algorithm with better interptretionability. Simulations are conducted on a transmission system. Numerical results indicate that the proposed system frequency dynamic model can capture the frequency dynamic under different IBR reinforcement plans and the OCT can realize accurate classification of the synthetic data regarding frequency security.

Abstract The transition to renewable energy‐based power systems is fast progressing. One of the main challenges in keeping a power system with high operational reliability is to maintain the system frequency. As synchronous generator units are being replaced with power‐electronic converters, the rotating mass and the system inertia are decreasing. Virtual synchronous machine (VSM) control is a modern control technique that aims to compensate for the reduction in inertia. The usage of power electronic‐based converter units equipped with VSM control has to be managed and scheduled by system operators. An assessment of the operational frequency reliability is used to evaluate different service usages. A method is proposed that allows the comparison of different frequency management strategies. The proposed method uses fuzzy logic to evaluate the system risk for abnormal frequency and the system effort in the form of frequency control usage. This allows to quickly compare different frequency management strategies whilst keeping in mind many different reliability indices. The proposed method is validated with a modified IEEE Reliability Test System with integrated wind power capacity.

DC microgrid provides the horizontal infrastructures to integrate distributed generation (DG) and loads. Unlike traditional AC systems, DC systems cannot survive or sustain high magnitude fault currents. It makes locating faults very difficult. The conventional protection techniques completely de-energies the DC link in the DC microgrid. A new protection scheme for multi-terminal DC microgrid against line-to-line fault and the low resistance earth fault is presented in this study. The scheme isolates the faulted section from the DC microgrid. Healthy sections are operated without any disturbance and supply continuity is maintained in a ring main DC bus system. The current sensors are mounted at DC bus segments to monitor the entering and outgoing current at different nodes. Further, the current sensors are also mounted at both ends of service mains to monitor their current difference at both ends of the service mains. The controller detects this current difference and opens circuit breakers. To meet the requirement of fast interrupting time and high short-circuit current withstanding capability, insulated-gate bipolar transistors used as circuit breakers. The fault location scheme gives the fault location in various sections (service mains) and faults resistance in the microgrid. The proposed concepts have been verified by computer simulation.

With the large-scale configuration of distribution automation and the widespread implementation of distributed generation (DG) and flexible load (FL), the distribution network can achieve active regulation, which makes the traditional fault restoration strategy and distribution network reliability evaluation more complicated. Given this background, a method of reliability evaluation for the active distribution network considering ‘supply-grid-load’ is proposed. On the supply side, a distribution network islanding model considering DG is established, with the objective of supplying power to the maximised amount of equivalent power load. On the grid side, the influence of distribution network automation on the distribution network reliability is elaborately analysed and the time-varying failure rate model of equipment which considers the life cycle characteristics is presented. On the load side, an incentive-based FL model is proposed based on the elastic coefficient matrix. Finally, simulation results of RBTS-BUS6 system demonstrate the effectiveness of the proposed model and method.

In view of the stability and safe service of the transmission system of the wind turbine, the trend early warning method for the stability deterioration of the electromechanical system is proposed and the level of the predictive maintenance of the complex electromechanical system is improved. It includes: establishing the dynamic model of wind power transmission system, revealing the evolution law of the system stability deterioration, putting forward the signal processing method of the weak detection information, extracting the fault features decoupling with energy and constructing the early warning methods of the system stability deterioration trend. The research results can be applied to the safety monitoring and fault warning of the wind turbine. It is beneficial to ensure the safe and reliable operation of the equipment and realise the prediction maintenance, improve the operation and management level of the equipment, reduce the economic loss caused by the failure and promote the utilisation and development of green energy.

Wind energy conversion systems (WECSs) require a suitable control to maximise the power generated by wind turbines independently on the wind conditions. Variable-speed fixed-pitch wind turbines with doubly-fed induction generators (DGIG) are used in WECSs for their higher reliability and efficiency compared to variable-pitch wind turbine systems. This study proposes an effective control algorithm to maximise the efficiency of fixed-pitch wind turbines with DFIGs using particle swarm optimisation control to compensate for the errors in the estimation of the circuit parameters of the generator. The proposed control algorithm generates an optimal speed reference to optimise the mechanical power extracted from the wind and the optimal d-axis rotor current through stator reactive power management to minimise the electrical losses of the doubly-fed generator. The optimal speed reference is provided by a maximum power point tracking control below the rated wind speed and a soft-stalling control above the rated wind speed, while the optimal d-axis rotor current is searched by a particle swarm optimisation algorithm. The proposed control system has been verified by numerical simulations and it has been demonstrated that the energy generated for typical wind speed profiles is greater than that of a traditional control based on a model-based loss minimisation.

DC microgrids are expected to play an important role in maximising the benefits of distributed energy resources in future low carbon smart power systems. One of the remaining complex challenges is the requirement for effective DC protection solutions. The advancement of DC protection is hindered by the lack of good understanding and development of reliable and effective earthing schemes which can enable safe and secure operation of DC microgrids in both on-grid and off-grid modes. Therefore, this study discusses different DC microgrid earthing opportunities, and comprehensively evaluates through detailed simulation studies the influence of different earthing methods on the fault behaviour of DC microgrid. A transient model of an active DC microgrid is developed in PSCAD/EMTDC and used for the paper studies.

A method is proposed for the economic optimisation of offshore wind cable connections through utilising the thermal inertia of the cable system. Taking account of expected wind yields, turbine reliability, and the dynamic thermal environment, the method determines the economically optimal number of turbines for a given export cable system. Analysis has shown that, providing means to actively curtail generation output so as to thermally protect the cable are in place, it is possible to reduce the cost of energy delivered to shore by up to £1/MWhr through the use of ‘over-planting’, i.e. building a wind farm that is larger than the continuous rating of its export cables.

Coordinated control and power management of distributed energy resources, such as diesel generators (DGs), photovoltaics (PVs) and battery energy storage systems (BESSs), is vital for secure, reliable and economical operation of a stand-alone microgrid system. This paper proposes a coordinated control and power management approach for a hybrid stand-alone microgrid system containing DGs and PVs and also BESSs, which commonly servers as a power supply solution for remote areas such as islands. The proposed approach takes into account the maximum utilisation of PV power, economical operation condition of diesel generators, status of battery energy storage system and their operation constraints to share the load among them. Efficacy of the proposed approach is validated through a RTDS-based simulation test and an actual project practice.

Energy management system (EMS) is able to coordinate the generation and load to ensure economic and reliable operation and improve performance metrics of microgrids (MGs). However, most the previous studies have focused mainly on the optimal dispatch of the gas turbines and/or energy storage systems inside a normal MG. Very few works have been carried out to address the potential power outage in MGs. In this study, a novel optimal approach in the EMS based on online forecasts is proposed to minimise the system-wide outages of MG, specifically through pre-emptive load shedding. Online distributed generations' output forecasts are updated to predict the state of system and characterise potential upcoming outages. Proper control strategies based on receding horizon methods are introduced in this study. Outage mitigation actions using pre-emptive load shedding are then performed to avoid power outages or minimise the duration of unavoidable outages. The effectiveness of proposed approach can be demonstrated in the presence of various fluctuations, which can be easily integrated in the EMS for both islanded and grid-connected MGs.

Nowadays, the existing hierarchical, centrally controlled power grid faces new challenges due to the increase penetration of renewable sources, the need of implementing demand-side management and the 2020 and 2050 environmental targets. A promising concept which can successfully contribute to addressing the environmental concerns and energy challenges of the twenty-first century is the grid-connected decentralised energy systems that embed significant amount of renewable generation and allow reverse power flow from distribution grids into the transmission network. Despite their benefits, decentralised energy storage systems are not yet widely spread due to several implementation and designing barriers. The design obstacle which is being addressed in this study includes the determination of the optimal size of the energy storage system components in terms of battery size and rating of the power converter for a single house application. In order to generalise the findings, nine different real houses were considered. Thus, the most financially beneficial battery and power converter combination for nine existing UK houses with installed PV roof-top system were identified in this study.

In recent years, with the increasing of wind power development, the demand for low voltage ride-through (LVRT) technology was proposed to ensure the safe and reliable operation of the power system. The key issue of LVRT strategy for doubly-fed induction generator (DFIG) varies according to the network synchronisation modes. Firstly, the existed LVRT technologies when DFIG is connected to AC network are surveyed. Then relevant literatures about LVRT are summarised and analysed in regard to power surplus of two-terminal system and DC voltage control of multi-terminal system, respectively, when the wind farm is integrated with VSC-high-voltage direct current (HVDC). In the end, the coordinated control strategy of multi-terminal VSC–HVDC system and LVRT technology for islanded system are prospected in this study.

The purpose of this research is to present an innovative load frequency control in the presence of wind turbines in islanded micro-grid (MG). As islanded MG suffers from low inertia and insufficient primary frequency response (PFR), utilising the variable wind turbines in de-loaded area can be considered as an alternative solution to deal with frequency control problems. In this context, the de-load area is referred to a region where wind turbines release their stored kinetic energy in rotational masses following frequency disturbances. For effective utilisation of wind turbines, a self-tuning, adaptive fuzzy droop is proposed, whose membership function parameters are optimised through artificial bee colony algorithm based on a multi-objective decision making process. A comparison is made between the obtained results of the self-tuning, adaptive fuzzy droop with conventional proportional integral derivative droop control in order to assess the proposed method performance in different disturbances.

In the background of the energy Internet, the number of data centres is increasing, aiming at the shortcomings of power supply and reliability in power supply system of traditional data centre and the development trend of green data centres. This article proposes an AC & DC hybrid power supply system with high-proportion renewable energy. The system includes photovoltaic generation, wind power generation, photothermal power generation, thermal utilisation system, power storage system, and different types of loads. Therein, a multi-port power electronic transformer is used to realise AC & DC multi-level mixing system with high proportion of variety of distributed renewable energy. Thereafter, the power supply, power grid, and the load can efficiently complement each other by using the integrated energy storage system such as electricity storage and heat storage. In detail, the rationality and functionality of the AC & DC hybrid power system are analysed through the system simulation and power supply reliability calculation. Moreover, the results show that the proposed hybrid power supply can effectively improve the impact of high-proportion renewable energy access to the grid and provide a new design scheme for the green data centre.

As the environmental problems caused by the consumption of the non-renewable fossil energy are getting increasingly serious, the new energy power generation has received wide attentions. Multi-terminal high voltage DC (HVDC) transmission is one of the key technologies for improving the reliability and stability of new energy power generations. Besides, HVDC circuit breakers (CBs) become the bottleneck of the development and application for multi-terminal HVDC transmission power systems. Here, the active DC vacuum circuit breaker (VCB) is taken as the research object. Meanwhile, the optimisation design of the commutation circuit for the DC VCB is realised. According to Kirchhoff's law, the genetic algorithm is used to calculate the commutation parameters under different optimisation objectives, to obtain the lowest cost and the shortest sheath development time. Based on the software package MATLAB, the simulations and analyses of different optimisation objectives and parameters are carried out. Through the comparative analyses of the two optimisation objectives, the relationships between the development time of the sheath gap and the cost have been obtained.

Forecasting the output power of large wind farms is helpful for planning reserve capacity in a mixed-generation power supply system. After classifying the reserves needed in a power system, this research focuses on the reserve components that are affected by wind–power fluctuations, the regulating, and load-following reserves. Considering the uncertainties in system load forecasts and wind–power forecasts, a general model for calculating the reserve requirements of a power system is proposed. Then, ultra-short-term forecasts of wind–power output 1 h into the future were studied, and a practical method that uses 10-min data to forecast wind output with a rolling average was proposed to predict the amount of power generation in the next hour. Then, using the RTS-96 dataset from the IEEE as an example, the reserve capacity requirement for the power system is determined according to the forecast uncertainty. Accurate predictive models for wind forecasting can reduce the needed reserve capacity of the system while guaranteeing the reliability and safety of the grid.

This study presents a tool to study the cyber-physical resiliency (CyPhyR) of critical energy infrastructure system, in particular the effect of cyber attacks on the microgrid's resiliency. The developed tool enables measuring resiliency using data from cyber and physical systems and suggests control decisions for resilient planning and operation of the microgrid. The microgrid resiliency is formulated based on graph theory based indices and cyber-power system characteristics. A Common Vulnerability Scoring System based metric called the Cyber Asset Impact Potential is developed and used in the planning phase, and another metric, Cyber Impact Severity is introduced to study the system performance in the operational phase. The information from these two phases is provided to the operator to make informed and proactive decisions to ensure the resilient operation of the microgrid. The performance of the developed tool has been tested using comprehensive real-time cyber-power testbed for a Consortium for Electric Reliability Technology Solutions microgrid test system.

With the integration of the ultra-high-voltage direct-current (UHVDC) of large capacity, the scheduled outputs of the power plants are limited, and the direct power purchase (DPP) by large consumers is influenced. The negative impact caused by the failure modes of the UHVDC on the economic dispatch (ED) and the security of the power system is to be studied. Here, the derated capacities of the UHVDC are described together with their state probabilities. To maximise the profit of power plants, an ED model with the DPP is proposed. The relationship between the amount of the DPP and the power transmission by the UHVDC is decided based on two contract strategies for the DPP. The interior-point method is applied to solve the ED problem. The simulation results validate the feasibility and accuracy of the proposed model, which is beneficial to the development of the power market and the UHVDC in China.

The continuing growth of an offshore wind farm integrated into a power grid via high-voltage DC has posed great challenges for automatic generation control (AGC) of the power system. To address these challenges, a new concept of ‘dynamic dispatch of AGC units (DDA)’ under control performance standards from the view of economic dispatch (ED) has been proposed in the previous work, and proved to be an effective technique to co-operate the AGC units with different ramping rates and to fill the gap between ED and AGC. However, the existing DDA model is deterministic in nature, which can hardly deal with the uncertain forecasting error of the offshore wind power output. A novel stochastic DDA model based on chance-constrained programming is proposed considering a random offshore wind power forecasting error, and a hybrid algorithm combining the evolutionary programming algorithm and point estimate method is then developed to solve the stochastic model. Numerical results from a two-area test system with additional offshore wind power generation demonstrate the accuracy and computation efficiency of the hybrid algorithm and the benefits offered by the stochastic AGC dispatch method.

The hybrid AC/DC microgrid is considered to be the more and more popular in power systems as increasing DC loads. In this study, it is presented that a hybrid AC/DC microgrid is modelled with some renewable energy sources (e.g. solar energy, wind energy), typical storage facilities (e.g. batteries), and AC, DC load, and also the power could be transformed smoothly between the AC and DC sub-grids by the bidirectional AC/DC converter. Meanwhile, coordination control strategies are proposed for power balance under various operations. In grid-connected mode, the U–Q (DC bus voltage and reactive) or PQ method is adopted for the bidirectional AC/DC converter according to the amount of exchange power between AC and DC system in order to improve the DG utilisation efficiency, protecting the converter and maintain the stable operation of the system. In islanded mode, V/F control is applied to stabilising the entire system voltage and frequency, achieving the power balance between the AC and DC systems. Finally, these control strategies are verified by simulation with the results showing that the control scheme would maintain stable operation of the hybrid AC/DC microgrid.

Generation maintenance scheduling (GMS) is one of the most important scheduling problems in the restructured power systems. The maintenance time interval of generation units is the crucial factor of GMS for an operation lifespan of generation units, particularly within the smart grid which needs high reliability. Accordingly, this study proposes a multi-objective-GMS (MO-GMS) optimisation model for maintenance scheduling of generation units based on the global criterion approach, adopting a suitable compromise function. The proposed MO-GMS model determines the maintenance intervals, aims to maximise both the generation company's (GenCo's) financial returns from selling electricity and the system reserve at every time interval from the independent system operator (ISO) standpoint. This method searches the optimal maintenance weeks for each generation unit, considering the objectives of both GenCo and ISO, simultaneously. The proposed MO-GMS model is formulated as a mixed-integer non-linear programming problem and examined on the IEEE 24-bus and IEEE 118-bus test systems. The success of the proposed multi-objective model is validated by comparing the obtained results with intelligent optimisation algorithms.

Distribution Asset Management is an important task performed by utility companies to prolong the lifetime of the critical distribution assets and to accordingly ensure grid reliability by preventing unplanned outages. This study focuses on microgrid applications for distribution asset management as a viable and less expensive alternative to traditional utility practices in this area. A microgrid is as an emerging distribution technology that encompasses a variety of distribution technologies including distributed generation, demand response, and energy storage. Moreover, the substation transformer, as the most critical component in a distribution grid, is selected as the component of the choice for asset management studies. The resulting model is a microgrid-based distribution transformer asset management model in which microgrid exchanged power with the utility grid is reshaped in such a way that the distribution transformer lifetime is maximised. Numerical simulations on a test utility-owned microgrid demonstrate the effectiveness of the proposed model to reshape the loading of the distribution transformer at the point of interconnection in order to increase its lifetime.

The main cause for cascading failure is large-scale overload caused by localised abnormal flows. With the increase of wind power penetration, the complexity of flow distribution is strengthened. Therefore, it is necessary to study influences of site selection and permeability of wind power generation on cascading failure. An analysis method based on electric betweenness of nodes was put forward, and influences of permeability change on cascading failure on different location selection for wind power generation were researched. According to the study, it was found that when the electric betweenness was low, the overload of wind power led to declining uniformity of power flow distribution, resulting in transfer of flows to other lines. As a result, the heavy load of lines was further aggravated to promote the development of cascading failure. Simulation results of the IEEE30 system showed that with the increase of wind power penetration, the cascading failure was aggravated; and under the same permeability, the lower the electric betweenness of location selection was, the severer cascading failure would be.

The remarkable benefits of wind power as an environmentally friendly renewable energy resource have led to an increasing penetration of offshore wind energy in modern power systems. Since the DC series–parallel connection system does not need large capacity DC/DC converters, it can reduce the construction costs of wind farms to some extent. In this study, the models of wind speed, wind direction and the wind turbine output power characteristic are developed. Based on this, the output power of each turbine considering the wake effect can be estimated. Then, the reliability block diagrams are drawn according to component relationships in reliability. Moreover, indexes like the probability of all wind turbine string failure, system unavailability and the average available output power of the power system are proposed to assess the reliability of the DC series–parallel offshore wind farm. A case study is presented to calculate the reliability indexes of different situations, where the amount of wind turbines remains the same while the number of turbine strings varies. It can be concluded that the DC series–parallel offshore wind farm is more reliable when increasing turbine string number, and reference is provided for DC series–parallel wind farm structure optimisation.

Modular multilevel converter (MMC)-based high-voltage DC (HVDC) transmission technology has become an ideal solution for large and remote wind farms integration. Oscillation or instability phenomena might occur due to the rapid control of power electronic converters in both wind farms and MMC-based HVDC system. In order to reveal oscillation characteristics of wind farms and MMC-based HVDC interconnected system, the system equivalent damping stability criterion is deduced theoretically, and a system damping analysis platform is built in this study. On this base, the impact on 1–1000 Hz oscillation characteristics from many factors including controller parameters of wind turbines and MMC-based HVDC, wind turbines power and wind turbines number is analysed, and mechanism of instability under different conditions is explained physically in terms of system damping characteristics. Time-domain simulations in RT-LAB are presented to validate the stability study.

Offshore wind power resource, which is relatively stable, abundant, and with modest impact on the environment, is a kind of clean and renewable energy suitable for large-scale development. Offshore wind farms have different topological structures of the collection system, such as AC parallel type, DC parallel type, DC series type, single-ring type, and double-ring type. The purpose of this paper is to analyse reliability and economy for various topologies and provide an insight into wind farm construction. In this study, the topology structure of various offshore wind farms is introduced firstly. Then, the reliability assessment methods are proposed. The reliability of the chain wind farm is analysed with the reliability block diagrams, while the reliability of the ring wind farm is analysed by using the classification method. In addition, the economy is evaluated considering investment costs. The investment cost for each type of component is calculated separately, which contributes to assessing the investment cost of the whole offshore wind farm. Detailed results from a case study, which includes 96 wind turbines, demonstrate that the DC series–parallel wind farm has superiority in reliability and economy, as well as in terms of its potential applications.

Reliability enhancement of power distribution system has attained much significance in the present competitive electricity market. Accordingly, methodologies to assess and improve distribution system reliability are also gaining much importance. This study proposes oppositional differential search (ODS) algorithm to solve reliability optimisation problem of radial distribution system. The objective of this study is to obtain the optimum number, size and location of distributed generation as well as optimal number and location of remote control switch simultaneously in radial distribution system in order to improve system reliability at a compromised cost. A multi-objective function has been formulated here. Differential search (DS) algorithm imitates the seasonal migration behaviour of an organism in search of efficiency of food areas. Opposition-based DS (ODS) algorithm has been used here to improve the quality of solution in minimum time. The proposed opposition-based DS (ODS) algorithm utilises opposition-based learning for Superorganism initialisation and also for iteration wise update operation. Simulation results obtained by ODS algorithm have been compared with that of DS algorithm and differential evolutionary algorithm. Simulation results reveal that ODS algorithm provides considerably superior performance, in terms of quality of solution obtained and computational efficiency.

Transmission system operators have an increased interest in the active participation of wind power plants (WPP) in the power balance control of power systems with large wind power penetration. The emphasis in this study is on the integration of WPPs into the automatic generation control (AGC) of the power system. The present paper proposes a coordinated control strategy for the AGC between combined heat and power plants (CHPs) and WPPs to enhance the security and the reliability of a power system operation in the case of a large wind power penetration. The proposed strategy, described and exemplified for the future Danish power system, takes the hour-ahead regulating power plan for generation and power exchange with neighbouring power systems into account. The performance of the proposed strategy for coordinated secondary control is assessed and discussed by means of simulations for different possible future scenarios, when wind power production in the power system is high and conventional production from CHPs is at a minimum level. The investigation results of the proposed control strategy have shown that the WPPs can actively help the AGC, and reduce the real-time power imbalance in the power system, by down regulating their production when CHPs are unable to provide the required response.