Ashish P Agalgaonkar

Distribution System Planning With Incorporating DG Reactive Capability and System Uncertainties

Distributed generation (DG) systems are considered an integral part in future distribution system planning. The active and reactive power injections from DG units, typically installed close to the load centers, are seen as a cost-effective solution for distribution system voltage support, energy saving, and reliability improvement. This paper proposes a novel distribution system expansion planning strategy encompassing renewable DG systems with schedulable and intermittent power generation patterns. The reactive capability limits of different renewable DG systems covering wind, solar photovoltaic, and biomass-based generation units are included in the planning model and the system uncertainties such as load demand, wind speed, and solar radiation are also accounted using probabilistic models. The problem of distribution system planning with renewable DG is formulated as constrained mixed integer nonlinear programming, wherein the total cost will be minimized with optimal allocation of various renewable DG systems. A solution algorithm integrating TRIBE particle swarm optimization (TRIBE PSO) and ordinal optimization (OO) is developed to effectively obtain optimal and near-optimal solutions for system planners. TRIBE PSO, OO, and the proposed algorithm are applied to a practical test system and results are compared and presented.

Online Voltage Control in Distribution Systems With Multiple Voltage Regulating Devices

Voltage regulation in distribution systems is typically performed with the aid of multiple voltage regulating devices, such as on-load tap changer and step voltage regulators. These devices are conventionally tuned and locally coordinated using Volt/VAR optimization strategies in accordance with the time-graded operation. However, in case of distribution systems with distributed generation (DG), there could be a possibility of simultaneous responses of DG and multiple voltage regulators for correcting the target bus voltage, thereby resulting in operational conflicts. This paper proposes an online voltage control strategy for a realistic distribution system containing a synchronous machine-based renewable DG unit and other voltage regulating devices. The proposed strategy minimizes the operational conflicts by prioritizing the operations of different regulating devices while maximizing the voltage regulation support by the DG. It is tested on an interconnected medium voltage distribution system, present in New South Wales, Australia, through time-domain simulation studies. The results have demonstrated that voltage control for a distribution feeder can effectively be achieved on a real-time basis through the application of the proposed control strategy.

Placement and Penetration of Distributed Generation under Standard Market Design

Distributed Generation (DG) can help in reducing the cost of electricity to the costumer, relieve network congestion and provide environmentally friendly energy close to load centers. Its capacity is also scalable and it provides voltage support at distribution level. Hence, DG placement and penetration level is an important problem for both the utility and DG owner. The cost of electricity as a commodity depends upon market model. The restructured power markets are slowly maturing with standardizations like Standard Market Design (SMD). The key feature of SMD is the Locational Marginal Pricing (LMP) scheme. This paper examines placement and penetration level of the DGs under the SMD framework. The proposed approach is illustrated by case studies on MATPOWER 30 bus and IEEE 118 bus systems.

Optimal sizing of distributed generators in microgrid

Hybrid optimization model for electric renewables (HOMER), developed by National Renewable Energy Laboratory (NREL), enables economic analysis for single source and hybrid distributed energy resources (DERs). However, current version of HOMER does not support microgrid analysis. In this paper, economic analyzer for distributed energy resources (EADER) is developed. It finds minimum cost of energy (COE) and optimal mix of DERs with multiple sources and sinks. In addition to single source distributed generator (DG) and hybrid DG, EADER is also capable to analyze microgrid. EADER results are validated for single source DG and hybrid DG with results obtained from HOMER for the same systems. Further, a sample practical system from Western Maharashtra, India, is analyzed using EADER. The results which consider all practical constraints are presented and discussed

Microgrids of Commercial Buildings: Strategies to Manage Mode Transfer From Grid Connected to Islanded Mode

Microgrid systems located within commercial premises are becoming increasingly popular and their dynamic behavior is still uncharted territory in modern power networks. Improved understanding in design and operation is required for the electricity utility and building services design sectors. This paper evaluates the design requirements for a commercial building microgrid system to facilitate seamless mode transition considering an actual commercial building microgrid system. A dynamic simulation model of the proposed microgrid system is established (utilizing DIgSILENT Power Factory) to aid the development of planning and operational philosophy for the practical system. An economic operational criterion is developed for the microgrid to incorporate selective mode transition in different time intervals and demand scenarios. In addition, a multi-droop control strategy has been developed to mitigate voltage and frequency variations during mode transition. Different system conditions considering variability in load and generation are analyzed to examine the responses of associated microgrid network parameters (i.e., voltage and frequency) with the proposed mode transition strategy during planned and unplanned islanding conditions. It has been demonstrated that despite having a rigorous mode transition strategy, control of certain loads such as direct online (DOL) and variable-speed-drive (VSD) driven motor loads is vital for ensuring seamless mode-transition, in particular for unplanned islanding conditions.

An Effective Power Dispatch Control Strategy to Improve Generation Schedulability and Supply Reliability of a Wind Farm Using a Battery Energy Storage System

The uncertainty in the availability of wind generation and the lack of coincidence between wind generation and system peak demand make wind farms (WFs) to be nondispatchable energy resources and impose limits on the potential penetration of wind generation in the generation mix. Battery energy storage systems (BESSs) integrated with WFs can reduce the variability of wind generation output allowing them to be dispatched for the network support, especially under peak load conditions. This paper proposes an effective power dispatch control strategy of WFs with the aid of BESSs to improve the supply reliability taking into account the uncertainties in wind generation output and load demand. A stochastic programming model is formulated considering uncertainty in wind generation and energy price to schedule WF dispatch. A novel rank-based BESS dispatch control algorithm is developed to achieve the assured WF power output levels for dispatch. Also, the application of the power dispatch control strategy is presented with the simulation study. Simulation results suggest that the implementation of the proposed strategy will improve supply reliability and revenue stream of the WFs.

Voltage support by distributed generation units and shunt capacitors in distribution systems

Integration of distributed generation (DG) units and shunt capacitors in the radial distribution networks is one of the effective options that can be used to improve the system voltage and reduce system losses. Optimal sizing and siting of DG units and shunt capacitors need to be ensured for strengthening the supply quality and reliability of distribution systems. In this regard, new analytical strategies need to be devised to minimise the computational burden and improve the overall accuracy of the solution. In this paper, a numerical method for the identification of the target voltage support zones is proposed by reducing the large search space. The strategic placement of DG units and shunt capacitors is proposed for overall voltage support and power loss reduction in a distribution feeder. The investment cost for DG units and shunt capacitors is minimised by using particle swarm optimisation (PSO) technique.

Intelligent load management in Microgrids

The increased levels of distributed generator (DG) penetration and the customer demand for high levels of reliability have attributed to the formation of the Microgrid concept. The Microgrid concept contains a variety of technical challenges, including load management and anti-islanding protection discrimination strategies. This paper provides a novel scheme in which loads and DG are able to detect the conditions where the load of the island cannot be sufficiently supplied. In these instances, a load shedding algorithm systematically removes loads from the system until an island can be maintained within satisfactory operating limits utilising the local DG. The concept of an Intelligent Load Shedder (ILS) module is proposed in this paper. This module is connected in series with non-critical loads in order to detect the conditions where that non-essential load should be isolated from an island. This module must be capable of communicating with the static transfer switch (STS), which is the intelligent isolator associated with the island. The STS will also be capable of sending and receiving data with each DGs islanding protection device. The combined algorithmic control of the STS, ILS module and DG islanding protection device forms the Intelligent Load Management algorithm. This algorithm is capable of islanding protection and load shedding irrespective of the use of communications. The algorithms within this paper are simulated using MATLAB script. The results show that, on a theoretical level, the intelligent load management scheme described in this paper can be used to detect the conditions where an insufficient load is available using local parameters. Load shedding coordination is also shown to be possible with and without the use of communications between the STS, ILS module and DG islanding protection module.

Subsynchronous torsional interaction behaviour of wind turbine-generator unit connected to an HVDC system

Utilisation of wind energy to generate electricity has attracted considerable attention worldwide, and is rapidly-growing. The integration of large wind farms with high voltage direct current (HVDC) transmission network could be one of the preferred options for supplying bulk power over a long distance. Since HVDC rectifier stations with constant current control may introduce negative damping on the nearby generating units, it is important to identify the torsional interaction characteristics between turbine-generator units and the HVDC systems over a frequency range of interest. However, very little related information exists in regard to wind turbine-generators. This paper presents the electromagnetic transient time domain analysis to investigate the possible subsynchronous torsional interaction (SSTI) phenomenon of fixed-speed (induction machine based) wind turbine-generator (WTG) unit interconnected to a CIGRE first HVDC benchmark system. Electrical disturbances, such as three-phase short circuit fault at the inverter station and DC power flow change are simulated to examine the possible dynamic interactions of the WTG unit. Simulation studies are conducted using PSCAD®/EMTDC®.

An Analytical Approach for Reliability Evaluation of Distribution Systems Containing Dispatchable and Nondispatchable Renewable DG Units

With ever increasing penetration of renewable distributed generation (DG) in distribution systems, power restoration of remote distribution feeders under emergency conditions tends to be carried out with the support of renewable DG units. The available power from the renewable DG units ensures restoration of more number of affected customers, thus, improving overall system reliability. In this paper, a probabilistic based analytical method is developed to assess system reliability in terms of system average interruption duration index and system average interruption frequency index for distribution feeders containing dispatchable and nondispatchable renewable DG units. The proposed method has been developed by implementing DG side restoration with comprehensive technical considerations, including possible failures of DG units, time-dependent patterns of load demand and DG power output, and single-stage and two-stage restoration. The proposed analytical method is validated by comparing with the Monte Carlo simulation and results are presented.