Grid codes are now requesting grid forming capability to renewable energy sources. The provision of this service is being thoroughly investigated for type-IV wind turbines (full electronic interface) ...with the virtual synchronous machine (VSM) control technique. However, this issue has been barely addressed for type-III wind turbines. In this turbine topology, it is of special interest to keep the current controller of the rotor-side converter (RSC) unaltered since many functions that are required for the safe operation of the machine and to comply with grid codes depend on it. In this article, two control alternatives to implement a VSM without modifying the structure of the inner current controller of type-III wind turbines are proposed. The first one is based on a current controller plus a novel flux-based virtual inductance, while the second one has a more traditional structure based on a current controller, a voltage controller, and a virtual impedance. Results show that a vector voltage controller is not an essential requirement to provide grid-forming capability. In addition, the operation of a wind farm consisting of six parallel-connected type-III wind turbines is studied analytically for both alternatives. The parallel operation of the wind turbines is verified by using real-time simulations performed in OPAL-RT. Finally, the control alternatives were experimentally validated in a real doubly fed induction generator rated at 28 kVA.
With the high penetration of renewable energy, its intermittency and volatility also bring challenges to traditional power system such as maintaining reliable operation of system and improving the ...utilization of renewable energy. Under the background of Energy Internet (EI), energy router (ER) emerges as the times require. Aiming to improve the ability of support of energy storage units to DC buses and suppressing power shocks both inside and outside the ER, in this paper, an ER based on multi-hybrid energy storage system (MHESS) is proposed. As the principle of maximizing the utilization of renewable energy, a corresponding energy coordinated management strategy is proposed. Charging/discharging timespan optimization model is established to ensure MHESS as available as possible. The reference power of MHESS is allocated based on the proposed optimization model. Simulation analysis of different working conditions in 4 operation scenarios are carried out and the results show that the power oscillation on different buses of ER can be dampened within 0.1s and the bus voltages fluctuate within 2% while operation scenarios are switched, which verifies the feasibility and effectiveness of the proposed energy coordinated management strategy.
•The ancillary service of islanded operation capability in presented to increase reliability and resilience.•A proposal for the implementation of the IOC ancillary service in the Colombian electrical ...system is made.•The modernization of the distribution grid is important to make the IOC ancillary service feasible.
The Island Operation Capability service allows operators to split the system (in case of an accident, for instance) and operate as an integral isolated subsystem. This, in turn, increases reliability, resilience, efficiency, and reduces restoration times after a blackout in the islands power systems. The provision of this kind of service from distributed energy resources has recently been introduced in different power systems. This paper outlines a proposal for the implementation of Island Operation Capability in the Colombian electricity market. The proposal considers technical variables, namely, energy not supplied, generation not delivered, and electrical losses. We developed a behavioral simulation model to test the impact of the implementation and an upgrade of the grid. Simulation results show technical benefits for the distribution system operator and economic benefits for investors and project promoters of distributed energy resources. Finally, the simulation’s results show that modernizing the distribution grid is important in order to increase Island Operation Capability and the security of the electrical system.
•For modeling and simulation purposes, a new frequency computation method based on the bus voltage phasor data in rectangular form is proposed in this article.•An integrated control system ...architecture is proposed without replacing the existing generator control structure. Within this control architecture, a control scheme for controlled islanding, islanded operation and autonomous re-synchronization is proposed herein.•Taking advantage of PMU measurements, an angle difference control function is proposed to influence the phase angle difference during the grid re-connection process.•The use of advanced object-oriented equation-based modeling language features from Modelica are exploited and illustrated, giving an example of how such advanced language features can facilitate design and analysis of new control functionalities, i.e. controlled islanding, islanded operation and re-sychronization.•The performance of the control system is evaluated considering both deterministic and stochastic load models
This article proposes a novel synchrophasor-based control scheme enabling controlled islanding, islanded operation and automatic re-synchronization of a distributed energy resource (DER) in a distribution network. The performance of the proposed control system is studied using a test power system model. The DER controller uses a centralized architecture, receiving phasor measurement unit (PMU) measurements from both the transmission and distribution grids. In simulation, the frequency control function inside the proposed controller uses frequency estimates calculated using a new formula that exploits the bus voltage in rectangular form (real and imaginary values). The performance of the proposed frequency computation method is studied and compared with the conventional washout filter (WF) approach used by most power system software tools. The study also discusses why unwrapped bus angles are necessary to perform the automatic re-synchronization process. The performance of the proposed controller is evaluated using both deterministic and stochastic load models, allowing the assessment of variability in distribution grids. The implementation of the proposed control scheme and the simulation of the test system is carried out leveraging rich features of Modelica language and the Open-Instance Power System Library (OpenIPSL).
•DGUI (DG Unavailability Index) and composite indexes CISAIDI-DG, CISAIFI-DG.•Optimization of equipment type, number and location on a MV network.•NSGA-II algorithm applied real MV network with ...no-Island operation.•Pareto optimal front solutions with respect to the three objective functions.
With the growth of Distributed Energy Resources (DER) in electrical systems, an increase in the benefits with the reconfiguration of radial networks related to the use of renewable energy is expected. However, in some countries the reconfiguration of radial networks has some limitations like the impossibility of island operation. Also, many of them have contracts with Distributed Generation (DG) operators that force them to buy all the available generation of electricity. After a fault these limitations increase DG unavailability resulting in a waste of resources in the form of payments of available electricity generation not used. In this paper we propose a multiobjective optimal placement of switching devices considering DG unavailability, network reliability and equipment cost, with no island network operation. Two approaches are proposed in this multiobjective problem. In the first approach, besides the minimization of the equipment cost and the reliability indices, it is proposed an extra objective function that considers the minimization of the Distributed Generation Unavailability Index (DGUI). In the second approach two new composite indices comprising DG, interruption duration and interruption frequency are presented. Results obtained from a case study using a real utility distribution network are presented and discussed.
The challenges of contingent island operation of hydropower plants are addressed by proposing an enhanced frequency control with advanced control algorithms. The study is based on a real power plant ...and considers the relevant power system in its entirety along with the load and transmission lines. Integrated transfer functions between the guide vane opening of a hydro turbine and the frequency of the associated generator were determined by in-situ identification. A model predictive controller, a fractional order PID controller, and a PID controller utilizing integral absolute error and integral time absolute error criteria were designed and developed. The performance of the proposed algorithms with the identified plant model was tested on a NI-cRIO 9049 FPGA platform. Improved frequency control in terms of setpoint change was achieved with the MPC and FOPID controllers. The MPC controller also features betters disturbance rejection compared to conventional PID controllers, which are tuned according to integral error criteria. The considered algorithms have been simulated in different operating scenarios, such as variations of active power load and transmission length. The proposed approach enhances stability and consequently avoids operational failures of hydropower plants in contingent islanding mode.
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•Modeling of plant in conjunction with transmission lines and load.•Advanced plant control in island operation with enhanced stability.•Fault avoidance of plant with the use of predictive control.•Thorough algorithm evaluation and assessment of stable operating conditions.•Outlined algorithms are transferrable to other plants with various turbine types.
Power systems are currently experiencing a transition towards decarbonisation through the large‐scale deployment of renewable energy sources. These are gradually replacing conventional thermal power ...plants which today are the main providers of black start services. Consequently, in case of a total/partial blackout, conventional black‐start resources may not be ready for operation. Offshore wind farms (OWFs), with their large capacity and fast controllers, have potential as innovative black‐start units, thus, the need for a new design for OWFs. Here, challenges and possible solutions in integrating black start services into offshore wind farms will be presented. The first challenge is represented by the self‐start capability. The self‐start unit should be capable of forming the wind farm power island and withstanding transient phenomena due to the equipment energisation. The investigated solution comprises grid‐forming (GFM) converters in the wind farm design, which could be battery energy storage systems (BESSs) to also increase the service availability. The challenges are analysed using simulations on a wind farm, and the proposed solutions are discussed. It can be concluded that a hybrid system comprised of a BESS and an OWF, with GFM control, applying soft‐charging, etc., represents a good proposal to provide black start services by OWFs.
This paper presents the integration of black start capabilities into offshore wind farms by grid‐forming battery energy storage systems, and discusses related challenges and solutions for a real life implementation. Electromagnetic transients analysis in PSCAD is used to simulate the black start procedure of the hybrid generation system. Overall results show the feasibility of offshore wind farms delivering a resilient black start procedure.
Battery Energy Storage Systems (BESS) based on Li-Ion technology are considered to be one of the providers of services in the future power system. Although prices for Li-Ion batteries are falling ...continuously, it is still difficult to achieve profitability from a single service today. Multi-use operation of BESS in order to reach a so-called “value-stacking” of services therefore is a hotly debated topic in literature, since such an operation holds the potential to increase profitability dramatically. The multi-use operation of a BESS can be divided into two parts: the operational planning phase and the real-time operation. While the operational planning phase has been examined in many studies, there seems to be a lack of discussion for the real-time operation. This paper therefore tries to address the topic of the real-time operation in more detail. For this reason, this paper discusses concepts for implementing a real-time multi-use operation and introduces the novel concept of dynamic prioritization, which allows resolving conflicts of services. Besides the ability to cope with abnormal grid conditions, this concept also holds potential for a better utilization of resources during normal grid conditions. A mathematical framework is used to describe several services and their interaction, taking into account the concept of dynamic prioritization. Several applications are presented in order to demonstrate the behavior of the concept during normal and abnormal grid conditions. These applications are simulated in Matlab/Simulink for specific events and in the form of long-time simulations.
When the microgrid is in the islanding operation mode, affected by the line impedance difference between the distributed power sources (DGs), the traditional droop control strategy will lead to the ...fact that the reactive power of the system cannot be reasonably distributed according to the droop gain, which makes the power grid prone to failure. To solve this problem, an improved sag control strategy based on adaptive virtual impedance is proposed in this paper. The central controller calculates the given power according to the capacity of each inverter and the total load capacity of the line, and then sends it to each inverter, and the inverter determines the value range of the virtual impedance according to the given reactive power. A voltage compensation link is added to the control strategy to compensate for the voltage drop difference caused by the line impedance difference, thereby ensuring the stability of the output power and realizing the power control of the microgrid. The MATLAB/Simulink simulation platform was built to establish the microgrid simulation model in island mode. The simulation results show that when the inverters with the same capacity are connected in parallel, the output active power is the most stable, and the reactive power maintains an equalized state; When inverters of different capacities are connected in parallel, the output active power takes the shortest time to stabilize, and the reactive power basically matches the rated capacity ratio. Therefore, it is fully demonstrated that this method has a good control effect on the power control and operation of the islanded microgrid.
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