Enhanced frequency response strategy for PMSG based wind energy conversion system using ultracapacitor in remote area power supply systems

The high penetration level of wind energy, and non-responsive nature of power electronic interfaced wind energy conversion system (WECS) during frequency variations may create significant stress on conventional generators in a wind-diesel hybrid remote area power supply (RAPS) system. Hence, it is a necessity for WECS to provide frequency support. However, conventional frequency control strategies being used for WECS may impose a severe stress to wind turbines. In this paper, an enhanced frequency response strategy is proposed for the permanent magnet synchronous generator (PMSG) based WECS to regulate RAPS system frequency jointly with its integrated ultracapacitors. The proposed frequency response strategy utilizes the droop control and virtual inertial techniques while suboptimal power point tracking (SOPPT) is implemented in WECS. It can effectively regulate RAPS system frequency while alleviating high rate of change of power (ROCOP) and thus torque stress on both the conventional generators and wind turbines under frequency disturbances

Recent Advances of Wind-Solar Hybrid Renewable Energy Systems for Power Generation: A Review

A hybrid renewable energy source (HRES) consists of two or more renewable energy sources, such as wind turbines and photovoltaic systems, utilized together to provide increased system efficiency and improved stability in energy supply to a certain degree. The objective of this study is to present a comprehensive review of wind-solar HRES from the perspectives of power architectures, mathematical modeling, power electronic converter topologies, and design optimization algorithms. Since the uncertainty of HRES can be reduced further by including an energy storage system, this paper presents several hybrid energy storage system coupling technologies, highlighting their major advantages and disadvantages. Various HRES power converters and control strategies from the state-of-the-art have been discussed. Different types of energy source combinations, modeling, power converter architectures, sizing, and optimization techniques used in the existing HRES are reviewed in this work, which intends to serve as a comprehensive reference for researchers, engineers, and policymakers in this field. This article also discusses the technical challenges associated with HRES as well as the scope of future advances and research on HRES

A Modified Carrier-Based Advanced Modulation Technique for Improved Switching Performance of Magnetic-Linked Medium-Voltage Converters

© 1972-2012 IEEE. The high-frequency magnetic link is gaining popularity due to its lightweight, small volume, and inherent voltage balancing capability. Those features can simplify the utilization of a multilevel converter (MLC) for the integration of renewable energy sources to the grid with compact size and exert economic feasibility. The modulation and control of the MLC are crucial issues, especially for grid-connected applications. To support the grid, the converter may need to operate in an overmodulation (OVM) region for short periods depending upon the loading conditions. This OVM operation of the converter causes increased harmonic losses and adverse effects on the overall system efficiency. On top of that, the size and cost of filtering circuitry become critical to eliminate the unwanted harmonics. In this regard, a modified OVM scheme with phase-disposed carriers for a grid-connected high-frequency magnetic-link-based cascaded H-bridge (CHB) MLC is proposed for the suppression of harmonics and the reduction of converter loss. Furthermore, with the proposed OVM technique, the voltage gain with the modulation index can be increased up to the range which is unlikely to be achieved using the classical ones. Extensive simulations are carried out with a 2.24 MVA permanent magnet synchronous generator based wind energy conversion system, which is connected to the 11 kV ac grid through a high-frequency magnetic-link and a five-level CHB MLC. A scaled down laboratory prototype is implemented to validate the performance of the converter

Modeling and Control of Diesel-Hydrokinetic Microgrids

A large number of decentralized communities in Canada and particularly in Québec rely on diesel power generation. The cost of electricity and environmental concerns suggest that hydrokinetic energy is a potential for power generation. Hydrokinetic energy conversion systems (HKECSs) are clean, reliable alternatives, and more beneficial than other renewable energy sources and conventional hydropower generation. However, due to the stochastic nature of river speed and variable load patterns of decentralized communities, the use of a hybrid diesel- hydrokinetic (D-HK) microgrid system has advantages. A large or medium penetration level has a negative effect on the short-term (transient) and long-term (steady-state) performance of such a hybrid system if the HKECS is controlled based on conventional control schemes. The conventional control scheme of the HKECS is the maximum power point tracking (MPPT). In the long-term conditions, the diesel generator set (genset) can operate at a reduced load where the role of the HKECS is to reduce the electrical load on the diesel genset (light loading). In the short-term, the frequency of the microgrid can vary due to the variable nature of water speed and load patterns. This can lead to power quality problems like a high rate of change of frequency or power, frequency fluctuations, etc. Moreover, these problems are magnified in storage-less DHK microgrids where a conventional energy storage system is not available to mitigate power as well as frequency deviations by controlling active power. Therefore, developing sophisticated control strategies for the HKECS to mitigate problems as mentioned above are necessary. Another challenging issue is a hardware-in-the-loop (HIL) platform for testing and developing a D-HK microgrid. A dispatchable power controller for a fixed-pitch cross-flow turbine-based HKECS operating in the low rotational speed (stall) region is presented in this thesis. It delivers a given power requested by an operator provided that the water speed is high enough. If not, it delivers as much as possible, operating with an MPPT algorithm while meeting the basic operating limits (i.e., generator voltage and rotor speed, rated power, and maximum water speed), shutting down automatically if necessary. A supervisory control scheme provides a smooth transition between modes of operation as the water speed and reference power from the operator vary. The performance of the proposed dispatchable power controller and supervisory control algorithm is verified experimentally with an electromechanical-based hydrokinetic turbine (HKT) emulator. The permanent magnet synchronous generator (PMSG) is preferred in small HKECSs. So, a converter-based PMSG emulator as a testbed for designing, analyzing, and testing of the generator’s power electronic interface and its control system is developed. A 6-switch voltage source converter (VSC) is used as a power amplifier to mimic the behaviour of the PMSG supplying linear and non-linear loads. Technical challenges of the PMSG emulator are considered, and proper solutions are suggested. Finally, an active power sharing control strategy for a storage-less D-HK microgrid with medium and high penetration of hydrokinetic power to mitigate: 1) the effect of the grid frequency fluctuation due to instantaneous variation in the water speed/load, and 2) light loading operation of the diesel engine is proposed. A supplementary control loop that includes virtual inertia and frequency droop control is added to the conventional control system of HKECS in order to provide load power sharing and frequency support control. The proposed strategy is experimentally verified with diesel engine and HKT emulators controlled via a dSPACE® rapid control prototyping system. The transient and steady-state performance of the system including grid frequency and power balancing control are presented

Hourly Dispatching Wind-Solar Hybrid Power System with Battery-Supercapacitor Hybrid Energy Storage

This dissertation demonstrates a dispatching scheme of wind-solar hybrid power system (WSHPS) for a specific dispatching horizon for an entire day utilizing a hybrid energy storage system (HESS) configured by batteries and supercapacitors. Here, wind speed and solar irradiance are predicted one hour ahead of time using a multilayer perceptron Artificial Neural Network (ANN), which exhibits satisfactory performance with good convergence mapping between input and target output data. Furthermore, multiple state of charge (SOC) controllers as a function of energy storage system (ESS) SOC are developed to accurately estimate the grid reference power (PGrid,ref) for each dispatching period. A low pass filter (LPF) is employed to decouple the power between a battery and a supercapacitor (SC), and the cost optimization of the HESS is computed based on the time constant of the LPF through extensive simulations. Besides, the optimum value of depth of discharge for ESS considering both cycling and calendar expenses has been investigated to optimize the life cycle cost of the ESS, which is vital for minimizing the cost of a dispatchable wind-solar power scheme. Finally, the proposed ESS control algorithm is verified by conducting control hardware-in-the loop (CHIL) experiments in a real-time digital simulator (RTDS) platform

Electrical performance and economic feasibility analyses of hybrid and battery storage devices used in remote area islanded renewable energy systems

South Africa has the fifth largest coal based utility grid in the world, unfortunately many regions in the country are simply too remote for connection with this grid thus have no electricity access [1]. Many remote areas possess high wind speeds and solar irradiance exposure, which makes them ideal for Renewable Energy Systems (RES) but the electrical and economic viability of this deployment, is still in question. Based on these observations, an electrical performance analysis and economic feasibility study based on islanded RES deployment in remote areas of SA is conducted. RES growth is restricted to the effectiveness of its energy management strategy. Pumped Hydro Storage (PHS) is the cheapest islanded large scale storage option but its assignment is restricted to applicable an landscape and terrain [2], [3]. After conducting a critical review, the Lead Acid Battery Storage System (BSS) and Hybrid Battery Supercapacitor Storage (HBS) were over the PHS. A theory development study on established generations systems and storage models was used to compare software designs which resulted in the selection of Matlab software for electric performance analysis and HOMER for the economic feasibility study. The electric performance analysis was divided into three case studies based on the input power supply, viz. ideal voltage source, Solar Photo Voltaic (PV) and Wind Energy Conversion System (WECS), with each case being connected to a BSS and HBS. A load profile and solar and wind resource investigation was conducted using the NASA, Wind Atlas of South Africa (WASA) and Solar GIS database. Electrical cases were modelled in Matlab and evaluated in terms of power security, load matching, power response and charge algorithm accuracy. The results showed that deploying an islanded RES in South Africa is indeed electrically feasible based on the high power security, load matching accuracy, and disturbance response seen in the solar-RES cases. The wind-RES maintained an uninterruptable power supply but failed to match the load as accurately. Cases which used the HBS showed improvements in power stability; load fluctuation response and an extension of storage device lifespan when compared to the BSS connected cases. This was due to the supercapacitor high power density which made it ideal for the compensation of RES and load fluctuations. Three new cases were established for the economic study as follows; solar, wind and hybrid solar-wind generation all tested under BSS and HBS conditions once again. A socio economic study established the region of deployment, natural resources, terrain, landscape as well as the price of WECS, PV, storage, and converter components. These findings were used in HOMER to construct an optimised combination of components required for the supply of a 5MWh/d average load. This was followed by a sensitivity analysis which conducted 14 different optimisations at loads ranging from 1-10MWh/d. Economic benefits of the supercapacitor power density was uncovered through a reduction of the required RES Peak Operating Reserve (POR) capacity. This is especially significant in islanded RES, as they demand large POR in order to maintain autonomous power supply. This amounted to substantial NPC savings ranging from $1 -$7.5 million for the 25 year project. What was more interesting was the hybrid wind-solar generation results of the last case which extended total NPC savings, by up to $10 million. The hybrid-HBS does show some POR reductions which brought the COE to 0.3$/kWh on average, with the hybrid-BSS at 0.35$/kWh. The hybrid-BSS is slightly more expensive but has a reduced complexity which can be more inviting to project engineers therefore both hybrid cases are exceptionally feasible for local RES deployment. Single source RES is indeed electrically and economically feasible and shows extended sizing and performance benefits when implementing HBS. However, the cost reductions and performance benefits of hybrid generation make it the most practical solution to islanded RES in South Africa