This study discusses synthetic inertia from the perspective of a transmission system operator and compares it to fast frequency response based on frequency deviation. A clear distinction of the meanings between these concepts is discussed, the basis of which is a description of their characteristics. A contribution and the purpose is the clarification of these concepts in addition to share the perspectives of a transmission system operator. The frequency response of a power system based on the Nordic system is examined for future scenarios with large amounts of wind power. Conclusions are drawn regarding the benefit of synthetic inertia compared with fast frequency response based on frequency deviation.

To better assess the contribution of wind power plants (WPPs) during disturbances, Hydro-Québec TransÉnergie (HQT), the main transmission system operator in the Quebec Interconnection, uses on-line monitoring to record data at the point of common coupling of each WPP. This data is used to analyse their performance during voltage and frequency disturbances. Until recently, very few WPPs were able to provide an inertial response (IR) for under-frequency events. On 28 December 2015, a generation loss of 1700 MW caused a frequency nadir of 59.08 Hz on the system, to which most WPPs required to provide IR contributed significantly. The analysis of the event showed that the behaviour of the WPPs had a significant effect on the recovery of the system frequency. This study presents the performance analysis of WPPs during this under-frequency event. The analysis is based on data collected from 25 large-scale WPPs in operation and equipped with the IR feature as required by HQT. Field measurements and simulation results are used to emphasise the effect of the active power reduction during the recovery phase. Impacts of the IR from the WPPs as used on the Hydro-Quebec system are discussed.

Renewable generation is mainly connected through converters. Even if they provide more and more ancillary services to the grid, these may not be sufficient for extremely high penetrations. As the share of such generating units is growing rapidly, some synchronous areas could in the future occasionally be operated without synchronous machines. In such conditions, system behaviour will dramatically change, but stability will still have to be ensured with the same level of reliability as today. To reach this ambitious goal, the control of inverters will have to be changed radically. Inverters will need to move from following the grid to leading the grid behaviour, both in steady state and during transients. This new type of control brings additional issues on converters that are addressed in this study. A solution is proposed to allow a stable operation of the system together with a limited solicitation of inverters during transients.

Network integration studies try to assess the impact of future developments, such as the increase of Renewable Energy Sources or the introduction of Smart Grid Technologies, on large-scale network areas. Goals can be to support strategic alignment in the regulatory framework or to adapt the network planning principles of Distribution System Operators. This study outlines an approach for the automated distribution system planning that can calculate network reconfiguration, reinforcement and extension plans in a fully automated fashion. This allows the estimation of the expected cost in massive probabilistic simulations of large numbers of real networks and constitutes a core component of a framework for large-scale network integration studies. Exemplary case study results are presented that were performed in cooperation with different major distribution system operators. The case studies cover the estimation of expected network reinforcement costs, technical and economical assessment of smart grid technologies and structural network optimisation.

Integration of wind power plants (WPPs) into weak electric grids has gained a lot of interest in recent years due to an increase in sites with low short-circuit power at the point of connection. In response to this reality, wind turbine (WT) manufacturers have been working on developing suitable technical functionalities. However, it can be argued that technology is not the only challenge faced during the interconnection of WPP to a weak grid. This study aims at proposing and demonstrating the application of a process that can be applied to optimise many aspects of such projects and outlines the tools needed to do so. Outcomes and experiences from applying this process and its tools to a real project including steady-state and time-domain simulation results are also presented. It is shown that, in order to successfully interconnect WPPs into weak grids without putting power system safety and reliability at risk, strong collaboration between project developers, network operators, consultants and WT manufacturers is crucial. The proposed process will greatly support all stake holders involved in developing the market of WPPs connected to weak grids.

For safety purposes, many photovoltaic (PV) systems are designed using galvanic isolation and transformers. The main problem in the existing topologies is that transformers are expensive, heavy and large. Another problem is that at conversion stage, the overall frequency is reduced. The efficiency of a PV inverter which is equipped with a transformer is usually between 91 and 94%. To tackle this issue, a transformerless (TL) PV system is proposed which has high efficiency and is lighter and cheaper. Due to stray capacitance, harmful leakage current will flow to the grid and PV array. H5, HERIC, H6 and oH5 are different types of existing TL inverter, and may be used to solve this problem. Each configuration has its drawbacks like shoot-through issues of switches, high conduction losses, metal-oxide-semiconductor field-effect transistor reverse recovery issues, or to avoid shoot-through fault when dead time requirements and grid voltage are nearly zero. The efficiency of the proposed TL inverter presented in this study is compared with other existing configurations. It shows that the proposed inverter efficiency is better than the conventional hard switching inverters. Moreover, to increase reliability, the inverters do not contain any shoot-through issues.

Modern PV arrays are generally designed with bypass diodes to avoid damage. However, such arrays exhibit multiple peaks in their P–V characteristics under partial shading conditions. Owing to the limitation in the abilities of conventional maximum power point tracking algorithms in such cases, the application of other optimisation algorithms has been explored. This study proposes a modified particle velocity-based particle swarm optimisation (MPV-PSO) algorithm for tracking the global power peak of the multiple peak P–V characteristics. The MPV-PSO algorithm is both adaptive and deterministic in nature. It eliminates the inherent randomness in the conventional PSO algorithm by excluding the use of random numbers in the velocity equation. The proposed algorithm also eliminates the need for tuning the weight factor, the cognitive and social acceleration coefficients by introducing adaptive values for them which adjust themselves based on the particle position. These adaptive values also solve problems like oscillations about the global best position during steady-state operation and particles getting trapped in local minima. The effectiveness of the proposed MPV-PSO algorithm is validated through MATLAB/Simulink simulations and hardware experiments.

This study presents an improved under-frequency load shedding (UFLS) scheme that can detect power deficit during the shedding process and accordingly adjust the amount of load shedding. This is achieved by continuous monitoring of the overshooting signal of the second frequency derivative of the centre of inertia. Once detected, an equivalent system inertia constant is estimated in order to quantify the new power deficit. The scheme is also equipped with an optimisation algorithm to determine the best combination of loads that is close to the amount of power deficit, which minimises frequency overshoot/undershoot. The optimisation technique selected for this work is based on particle swarm optimisation. The performance of the proposed UFLS scheme was validated using a modified IEEE 33 bus with two mini-hydro generators and one full converter wind turbine. The system and the proposed UFLS was modelled and simulated in PSCAD/EMTDC software. The results confirmed that the proposed scheme is capable of shedding loads with minimum undershoot/overshoot, and detect and estimate a new power deficit during load shedding. The results reported by the proposed scheme proved to be significantly better than those reported by conventional and adaptive load shedding schemes.

This study presents an analysis of the energy curtailment caused by the DC series–parallel collection systems of HVDC connected offshore wind farms. Wind speed differences between the series connected wind turbines cause unequal voltages at the DC output of the wind turbines. This can lead to unacceptable over-voltage or under-voltage conditions. The over-voltage and under-voltage conditions on the turbine DC outputs can be avoided by curtailing the power outputs of the wind turbines, which will result in loss of wind power. The annual energy curtailment due to the over-voltage limits of turbine DC–DC converters is analysed for a 200 MW DC series–parallel wind farm. The impact of wake effects on the energy curtailment losses is quantified and demonstrated with a case study.

The present study highlights an attempt of integrating the geothermal power plant (GTPP) in automatic generation control of an interconnected system comprising of dish-Stirling solar–thermal system (DSTS) and the conventional thermal system (TS). Generation rate constraints of 3%/min are considered for the TSs. A new fractional-order (FO) cascade controller named as FO proportional (P)–integral (I)–FOP–derivative (D) (FOPI–FOPD) is proposed as secondary controller and performance is compared with commonly used classical controllers. Controller gains and other parameters are optimised using a novel stochastic algorithm called sine–cosine algorithm. The analysis reveals the superiority of FOPI–FOPD over others. The effect of inclusion of GTPP and DSTS is also analysed on the conventional TS, both in a combined manner and separately. Sensitivity analysis reflects the robustness of optimum FOPI–FOPD controller gains and other parameters obtained at nominal and recommend that the optimised parameters do not suffer much deviations and are able to withstand wide fluctuations in system operating conditions, system loading and inertia constant. The dynamic behaviour of the system is studied with 1% step load perturbation in area1.

This study presents a modified proportional–resonant (M-PR) control topology for single-stage photovoltaic (PV) system, operating both in grid-connected and stand-alone modes. Dual two-level voltage source inverter fed three-phase open-end winding transformer is used to supply the load in this scheme. The M-PR controller is developed for the inner current control loop of the system. The M-PR controller has the ability to track ac current with zero steady-state error. The outer dc-link voltage control loop is developed through the indirect vector control method at synchronously rotating reference frame. The control scheme ensures improved performance of the system at variable solar irradiance and load disturbances. The performance analysis of the dual two-level PV inverter is carried out for different operating conditions. The control scheme is implemented in MATLAB–SIMULINK environment. The theoretical results are verified through experiments in a laboratory prototype. The experimental results show close match with their theoretical counterparts.

The study presents the modelling and allocation strategy for open unified power quality conditioner (UPQC-O) integrated photovoltaic (PV) generation system in radial distribution networks to improve the energy efficiency and PQ. An UPQC is a custom power device, which consists of series and shunt inverters. In UPQC-O, these inverters are placed in different locations in a network. There is a communication channel to share the information among these inverters to select the respective set point. Two models proposed are: (i) UPQC-O with battery and PV array (UPQC-O-WB) and (ii) UPQC-O with only PV array (UPQC-O-WOB). In UPQC-O-WB, the energy generated by PV array is stored during its operation hour to utilise it during peak hour. However, in UPQC-O-WOB, the energy generated by PV array is directly injected to the network. The proposed models are incorporated in the forward–backward sweep load flow to determine the operational parameters such as bus voltage. An optimisation problem is formulated to determine the optimal placement of UPQC-O with PV array in distribution networks. The objective function includes the investment and operational costs of inverters, battery and PV array, and the cost of energy loss. The particle swarm optimisation is used as the solution strategy.