The virtual inductor is widely used in the virtual synchronous generator (VSG) control to attain predominantly inductive impedance and reduce the power coupling. In fact, ‘predominantly inductive impedance’ is a misleading indicator of decoupling performance. In this study, a comprehensive perspective on virtual inductor is given for the improved decoupling performance of VSG control. A small-signal model is proposed to make a thorough inquiry into the effects of virtual inductor on power decoupling. With the proposed model, the optimal value of virtual inductor is obtained, the physical interpretation of the optimal decoupling is revealed, and the necessity of using virtual inductor is discussed. First, with optimisation of the value of virtual inductor, some negative effects of excessively large virtual inductor on power decoupling can be avoided. The excessively large value of virtual inductor will deteriorate the performance of power decoupling, aggravate the reactive power shortage of the grid and increase the capacity demand of voltage-source converter. Additionally, when the grid inductance is larger than the threshold value, virtual inductor is not needed. After that, the external physical characteristics of VSG when the grid inductance is under that critical condition are analysed. Finally, the theoretical analysis is validated by simulation and experiments.

In recent years, the integration of renewable energy resources (RESs) into the power system is growing rapidly, and it is necessary to analyse and evaluate the effect of RES on transient stability of the power system. In this study, centre of inertia (COI) concept is implemented to analyse and evaluate the integration effects of an auxiliary damping control-based virtual synchronous generator (VSG) consisting an improved governor. The impact of VSG integration is divided into synchronous generator (SG) linked parts and COI associated parts. Due to VSG integration into the power system, the significant elements which disturb the COI dynamic motion and rotor dynamics of SG are examined in detail. Different cases are considered to evaluate the effectiveness of the proposed method, i.e. VSG's different integrating location and different power capacities. It is observed in simulation results that COI dynamic motion and rotor dynamics of SG are positively affected by VSG integration, and transient stability improves significantly.

The cost of producing electricity with solar photovoltaic (PV) has decreased drastically in the past 10 years, so much that the installed PV capacity has increased exponentially between 2010 and 2018. South Africa is endowed with a technical potential of 72 GW for PV rooftop systems, but the economic potential is largely unknown. As a result, the integrated resource plan assumes that an annual installation of 200 MW of distributed generation will be made between 2018 and 2030. This study evaluates the economic potential of rooftop PV systems in the residential sector within metropolitan cities in South Africa using financial metrics. The important financial metrics used to qualify an investment are net present value, internal rate of return (IRR) and payback period. An investment is expected to pay itself back in less than 10 years with a high rate of return (IRR). Households are classified into living standards measure so that it is easier to map customers to related tariffs. Using this method, the eight metropolitan municipalities will have PV economic potential of 11 GW in 2019 and 22.7 GW by 2030 if the current tariff grows at 5% and the tariff structure does not change.

In distribution networks, different methods are used to reduce power loss, improve voltage profile, and release the capacity of lines. Among them, methods related to capacitor placement and conductor selection have common objectives and can result in significant improvements in distribution networks if implemented simultaneously. By using these methods, in addition to achieving the abovementioned objectives, the load supply capability of distribution networks, which indicates the amount of allowable increase in load, can also be improved. In this study, optimisation algorithms are implemented to solve optimal capacitor placement and conductor selection in a radial distribution network including renewable power generations. These algorithms consider different goals such as improving load supply capability. Furthermore, due to the existence of uncertainties such as load variations and fluctuations in output power, a probabilistic evaluation needs to be performed on the distribution network. To do so, the probabilistic and efficient approach of spherical unscented transformation is used. The most important feature of this approach is that it takes the correlation between the random input variables of the problem into consideration. The results of this probabilistic evaluation are used for conductor selection and capacitor placement by means of a radial 30-bus distribution network.

In this study, the real-time energy management system (RT-EMS) of a microgrid (MG) is proposed to deal with different uncertainties due to the errors in the prediction of renewable generation, load and market price. In the day-ahead EMS, the error in prediction of data; thus, the uncertainties in the scheduling are dealt with using different scheduling methods. Nonetheless, utilising the online RT measurements is an advanced solution to eliminate the uncertainties because there would be no prediction error in employing the RT information. In this study, a RT-EMS of a MG is designed using the Lyapunov optimisation method. In RT-EMS, satisfying the time-coupled constraints such as the battery energy limit and provision of load quality of service is a demanding challenge. This problem is addressed in Lyapunov optimisation by defining distinct virtual queues for satisfaction of time-coupled constraints. Moreover, the variable V algorithm is employed to provide a better compromise between stabilising the virtual queues and the total operation cost. A test MG system consisting of combined heat and power units, renewable energy sources, energy storage systems and flexible loads is used for evaluation. The underlying distribution network and power distribution loss are further considered satisfying the voltage limits.

In this study, a new market model is proposed to enable the smooth integration of distributed energy resources (DERs) in day-ahead (DA) and balancing (BL) markets. The DA market is a joint energy and reserve market. DERs participate in the local market operated by the distribution market operator (DMO) which is coordinated with the wholesale market. During local market clearing, the DMO considers the technical constraints of the distribution grid to keep the operation of the distribution grid within limits. Moreover, the DMO, through preliminary scheduling, estimates preliminary prices for energy, reserve and balancing services. These can be seen as offer prices by which the DMO will bid into the TMO DA and BL market. The uncertainty of renewable-based DERs is considered through the use of stochastic programming. The proposed market model is compared with a centralised market model. Results show that adding the distribution network constraints to the proposed market model is capable of alleviating overloading and appropriately accounting this effect in terms of increasing the operational cost. Moreover, it has been shown that the scalability of the proposed market model is higher compared to the currently applied centralised market models.

Aiming at improving the effectiveness and real-time performance of the fault detection of the photovoltaic (PV) array under different outdoor conditions, a novel method based on Grubbs criterion and local outlier factor (G-LOF) method is proposed in this study. The simulation model of the PV array is built to obtain the reference current of each PV string. The local outlier factor (LOF) is a ratio of the average local reachability density of sample neighbourhoods relative to its local reachability density. In this study, the LOF is used to quantify the abnormality by comparing the measured current and the simulated reference current. To reduce the false alarm probability of LOF, the Grubbs criterion is utilised as the test criterion to detect the abnormality of PV strings and it is merged with the LOF to derivate the G-LOF. The experiments of partial shading, open-circuit fault and short-circuit fault of PV modules are implemented in sunny and cloudy days. Experimental results verify that the proposed G-LOF method can sensitively detect above abnormalities, especially can detect the slight performance reduction caused by the partial shading or faults.

From the electrical energy point of view, the smart community (SC) concept is meant to be as a sustainable and environmentally friendly alternative to the classical configuration. The SC includes small-scale renewable energy sources (RES) and small-scale energy storage system (ESS). The SC energy management system acts as an aggregator, aiming to assure benefits for community stakeholders. These trends led to the energy routers (ERs) concept. This study proposes and describes the control strategies for these ERs to contribute to the SC goals. The approach of these strategies increases the RES adjustability, contributing to maintain the ESS state of health. The ER is able to operate simultaneously with active and reactive power control, besides compensating SC grid voltage imbalances, and providing ancillary services to the SC. The proposed control strategies are validated by simulations and experiments.

Fast dc fault detection method is required in medium-voltage dc (MVDC) microgrids to avoid severe damage to the interfacing converters. Ensuring selectivity and sensitivity of the protection system within a few milliseconds is a major challenge. This study proposes a new technique based on fault launched travelling-waves (TWs) to detect, classify, and locate different dc fault types in MVDC microgrids. Unlike the existing TW-based protection and fault location methods, the proposed technique utilises the frequency of TW reflections, rather than their arrival time. Moreover, the fault initiated voltage TW is contained within the faulted line by adding smoothing inductors on line terminals, which (i) prevents relays on adjacent lines from detecting the TW and (ii) results in higher reflected TW magnitudes. Therefore, the proposed method's selectivity and sensitivity are enhanced compared to existing methods. Other salient features of the proposed scheme include a moderate sampling frequency of 2 MHz, detection speed of 128 μs, fault location accuracy of ±25 m, no communication requirement, and independence from system configuration. The proposed scheme's performance has been assessed using a ±2.5 kV TN-S grounded MVDC microgrid under various conditions. The fault location accuracy of the proposed technique is compared to the conventional single-terminal TW-based method.

When open-loop modal resonance (OLMR) happens, a grid-connected PMSG may induce torsional sub-synchronous oscillations (SSOs) in a power system. This study examines the magnifying effect of a weak grid connection for the PMSG to induce torsional SSOs under the condition of OLMR. Theoretical analysis is carried out in this study to indicate that the weak grid connection magnifies the impact of OLMR, when the resonant mode of PMSG is dominated by the dynamics of a phase-locked loop (PLL) or the DC voltage control of the grid side converter. The magnifying effect of weak grid connection is analytically proved to have two aspects. First, the magnitude of the real part of the open-loop residue of the PMSG increases when the grid connection weakens. Second, the magnitude of the real part of the resonant open-loop oscillation mode of PMSG decreases under the condition of weak grid connection. According to the OLMR theory, the weakly connected PMSG is more likely to cause growing torsional SSOs when the grid connection is weak. This study helps to understand the mechanism of recent SSO incidents in a practical Chinese power system is analysed. Study cases are presented to demonstrate and evaluate the analysis and conclusions made in this study.

Contribution of Photovoltaic (PV) systems is rapidly growing and great attention is given to the design of PV controllers to enhance both the performance of PV systems and the low voltage ride through (LVRT) capability during abnormal operational conditions. This article presents a novel application of the salp swarm algorithm (SSA) in order to optimally tune the PV controllers to enhance the LVRT of grid-connected PV systems. Enhancement of LVRT is indicated in percentage undershoots or overshoots, settling time and steady-state error of voltage response. A control strategy is applied to the DC-DC converter to obtain a maximum power point tracking operation through a proportional-integral (PI)-based open fractional voltage control. The grid side inverter controls both the point of common coupling voltage and the DC-link voltage through PI-based cascaded-voltage control. To get PI controller parameters that guarantee the optimum design of the controllers, the fitness function is optimized by using the SSA. The proposed optimal control scheme is tested under various fault scenarios and compared with other conventional optimization-based PI controllers to examine its validity under PSCAD environment. The effectiveness of the optimal control scheme is verified by comparing the simulation results with the practical results of the PV system.

In this study, an intuitive control technique based on ‘fifth-order generalised-integrator (FOGI)’ is proposed for grid-connected solar photovoltaic (PV) energy conversions system (SECS). In the grid-tied SECS, a single-phase single-stage topology is considered. Moreover, on solar PV array, partially shaded condition is considered, where for global maximum power point tracking, the human psychology optimisation is utilised. The prime intention of the control technique is, feed all the generated solar power at the unity power factor into the grid, which is successfully achieved by the FOGI-based control method. During the evaluation of the performance of control based on FOGI, different adverse conditions related to the grid and dynamic change of solar insolation are considered, where the proposed control technique's performance illustrates the fulfilment of the motive of the work.

Ocean wave energy is a developing industry that provides many attractive qualities for utilities to meet future energy demand. Therefore, it is important to investigate and understand the impact that ocean wave energy has on power system reliability. Reliability assessment techniques have been applied to systems with variable amounts of wind penetration, but as of yet, no study has explored the impacts that ocean wave energy may have on the reliability of power grids. The authors’ approach to this problem applies a sequential Monte Carlo technique coupled with a Well-Being analysis approach to capture the seasonal variations associated with the ocean and then calculate key loss-of-load indices. The authors benchmark this method on the IEEE Reliability Test System 1996 and integrate synthesised ocean wave energy farms throughout the system. Their results suggest that wave energy results in a small decrease on the reliability of the power system, however, this change does not result in additional failure states as compared to the base system. Additionally, they are able to mitigate marginal system states with a relatively small increase in system capacity.

In this study, an improved method of optimal sizing method for a hybrid-energy microgrid (HEM) is proposed, simultaneously considering the impact of correlation and randomness of the wind power and photovoltaic (PV) power on HEM's sizing. The proposed optimal sizing method is based on the following steps: firstly, in order to obtain a large amount of data for the wind power and PV power in the planned area, a combined method which includes Kendall rank correlation coefficient, non-parametric estimation, Copula theory and Monte Carlo is proposed to generate the joint probability density function of the wind power and PV power and to generate an amount of data. Then, while guaranteeing reliable system operation of energy supply, the optimal sizing objective function with a minimum of operation cost, investment cost and pollution gas treatment cost is established based on the scenario-based approach. Finally, a case study of HEM is presented to verify the advantages of the proposed optimal sizing method.

This study analyses the dynamic behaviour of a doubly fed induction generator (DFIG)-based wind integrated power system (WIPS) resulting from a major disturbance. The effects of transient disturbance on WIPS are examined without and with a controller in terms of performance and stability of the system. To enhance the performance of WIPS after a sudden disturbance, an optimally designed linear quadratic regulator (LQR) controller is applied to the system. The wind energy system is described in state-space representation, whose states and outputs are taken as feedback to the controller for improving their dynamic response. An artificial bee colony (ABC)-based swarm optimisation technique is used to evaluate the optimal weighting matrices of the LQR controller in parallel with minimising the performance index and dynamic response characteristics of the system. The effectiveness of the proposed ABC–LQR controller in WIPS is verified by comparing their simulation and numerical results with standard proportional–integral and LQR controllers. It indicates that the proposed controller provides better enhancement of dynamic response as compared with other controllers in terms of performance index and dynamic response characteristics. Moreover, the robustness and stability of various system configurations are tested by the eigenvalue analysis.

The widespread deployment of autonomous inverter-based solutions for mitigating voltage and frequency excursions caused by high-penetration photovoltaic (PV) systems has drawn increased attention due to their potential impact on PV production. It is now important to quantify the amount of solar energy curtailed as a result of the activation of inverter-based grid support functions (GSFs). This study proposes a methodology for estimating the impact of volt–watt on customer PV energy curtailment using smart meter voltage data. This method estimates maximum possible curtailment for a given volt–watt curve based on the customer smart meter voltage during the time period of interest. This study compares the proposed methodology with field measurements using irradiance and customer inverter data from Hawaii as well as with results from a previous simulation-driven study on the impact of advanced inverter GSF activation on PV energy curtailment. Results show that the proposed method for estimating lost PV production caused by volt–watt control aligns reasonably well with field measurements and computer simulations for hundreds of customers. The proposed method could be used to estimate customer energy curtailment, which could inform future compensation mechanisms for utilities leveraging customer-sited resources to mitigate high voltage and defer infrastructure upgrades.

This study presents a new control scheme to provide both voltage regulation and power sharing within a DC microgrid. It includes both primary and secondary levels as well as the proposed auxiliary feedback. The secondary control distributes and uses the consensus algorithm to share power. First, the auxiliary feedback is formulated. Then the features of the feedback are analytically extracted to provide both voltage regulation and power sharing. Next, the particle swarm optimisation algorithm determines the parameters of the controller optimally. Following that, a series of simulations is carried out to show the performance of the proposed scheme in comparison with the conventional methods. Hence, to validate the advantages of the proposed scheme, a four distributed energy resource (DER) DC microgrid is considered, and the proposed approach is applied. Afterwards, the eigenvalue and sensitivity analysis show the effect of the parameters variation on microgrid stability. The results show that the applied method can regulate the voltage well and shares the power in the presence of the load demand as a disturbance besides the long-time delay associated with the secondary control as an uncertainty.

This paper analyses the contribution of non-conventional pumped-storage hydropower plant (PSHP) configurations like variable-speed pumping and hydraulic short-circuit, to reducing the scheduling cost and wind curtailment of an isolated power system with a high penetration of renewable energy. Their impact on the system's CO₂ emissions and generation mix is analysed as well. For this purpose, the next-day generation scheduling of the power system of the Great Canary island is computed on a rolling horizon basis for an entire year, considering conventional and non-conventional PSHP configurations and an increasing installed wind power. Different types of start-ups of the thermal generating units and the opportunity cost of water (water value) are considered in the day-ahead generation scheduling. The water value is daily updated by using a two-stage stochastic optimisation model with a two-week planning horizon. The results obtained show how these non-conventional pumped-storage hydropower plant configurations help not only to reduce the power system scheduling cost but also to integrate more wind energy.