Browsing by Author "Kazerani, Mehrdad"

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A Centralized Energy Management System for Isolated Microgrids
(Institute of Electrical and Electronics Engineers (IEEE), 2014-04-25) Olivares, Daniel E.; Canizares, Claudio A.; Kazerani, Mehrdad
This paper presents the mathematical formulation of the microgrid's energy management problem and its implementation in a centralized Energy Management System (EMS) for isolated microgrids. Using the model predictive control technique, the optimal operation of the microgrid is determined using an extended horizon of evaluation and recourse, which allows a proper dispatch of the energy storage units. The energy management problem is decomposed into Unit Commitment (UC) and Optimal Power Flow (OPF) problems in order to avoid a mixed-integer non-linear formulation. The microgrid is modeled as a three-phase unbalanced system with presence of both dispatchable and non-dispatchable distributed generation. The proposed EMS is tested in an isolated microgrid based on a CIGRE medium-voltage benchmark system. Results justify the need for detailed three-phase models of the microgrid in order to properly account for voltage limits and procure reactive power support.
Assessment of Battery Capacity Fading in Partially-Decoupled Battery-Supercapacitor Hybrid Energy Storage System Topologies for Electric Vehicles
(University of Waterloo, 2016-08-16) Abuaish, Ahmad; Kazerani, Mehrdad
Battery energy storage system (ESS) is a major component of an electric vehicle (EV), as it supplies the entire propulsion power, constitutes a significant share of the EV’s cost and weight, and plays a key role in EV performance. Consequently, extending the battery lifetime is vital, given that batteries in EV propulsion applications experience accelerated capacity fading due to aggressive traction demand and regenerative braking power spikes. Subsequently, it is beneficial to relieve the battery stress by adopting a hybrid energy storage scheme that combines the battery pack with an auxiliary energy storage device of high specific power such as supercapacitor (SC). The SC is used as a power buffer to process the high-frequency component of the traction demand and regenerative braking power. There are many topologies through which the battery and SC can be interfaced with the DC bus. Two partially-decoupled topologies have proved to be the most promising candidate topologies for a hybrid energy storage system (HESS). In the first HESS topology, the battery is connected directly to the DC bus and the SC is interfaced with the DC bus through a DC/DC converter, whereas in the second topology, the SC is connected directly to the DC bus and the battery is interfaced with the DC bus through a DC/DC converter with a bypass diode. Comparative assessment of these topologies in terms of battery capacity fading based on a qualitative analysis is unclear and inconclusive. Therefore, a quantitative analysis is necessary to assess the pros and cons of these HESS topologies in comparison with one another. Generally, HESS is most effective in urban drive cycles rather than highway drive cycles, due to the more frequent occurrence and higher intensity of regenerative braking in urban drive cycles, as the SC is dedicated to processing the generative braking energy. From the study reported in this thesis, it is observed that the second topology is superior to the first topology in extending the battery lifetime. For the same battery pack size in the second HESS topology and battery-only ESS, the battery lifetime in HESS is extended by 18, 4.5, and 8.7% for urban, highway, and urban-highway hybrid drive cycles, respectively, with respect to battery-only ESS. However, for battery-only ESS with an extended battery pack with a monetary value equivalent to that of the second HESS topology, the battery pack lifetime of the former is longer than the latter. In this thesis, an onboard integrated charger scheme is proposed, which eliminates the active rectifier in the original onboard charger, yielding significant cost savings. In the integrated charger scheme, the traction inverter and HESS DC/DC converter are used to realize the two-stage charger topology. Also, two single- pole-double-throw (SPDT) switches are added between the traction inverter and motor, which connect the inverter to the motor during propulsion and to the charger outlet during charging. Further, it is observed that HESS lifetime is about 4% higher compared to that of the battery-only ESS with and extended battery pack, where the monetary value of battery pack extension is equal to the cost of the SC minus the cost of the original active rectifier.
Design and Implementation of a Modular Test Bed Platform for Hardware-In-the-Loop Simulation of Electric Vehicles
(University of Waterloo, 2019-06-20) Kardasz, Martin; Kazerani, Mehrdad
Over the course of the last decade, electric vehicles have seen explosive growth and interest with public adoption and shifting research and development priorities by original equipment manufacturers towards these new powertrains. However, the development of electric vehicles remain costly due to new technologies being implemented in the vehicle with the ﬁnal cost ultimately being passed down to consumers. This method of developing new products where the price does not justify the product in the eyes of consumers hinders the adoption of the next generation of environmentally friendly vehicles. To verify electric vehicle drivetrain platforms and software models, test beds with speciﬁc capability to simulate the entire vehicle are required. Currently, an abundance of valuable engineering resources are dedicated to creating full-scale test beds and full- sized vehicles for testing. Only then, at this stage in the development cycle, are drivetrain tests conducted outside of simulation models. Getting to this ﬁrst level of functional testing requires using valuable time waiting for components to be designed, manufactured, validated, and installed before the system can be tested. The full-scale vehicle test bed becomes expensive, consumes a lot of space, and cannot be reconﬁgured easily without changing key components. Therefore, this thesis presents a systematic approach to down-scaling full-size electric vehicles’ parameters and environmental conditions to a level that can be handled by a small-scale hardware-in-the-loop simulation test bed. The method for taking the results obtained from the test bed and scaling them back up to the full-size vehicle level are also examined for completion. The hardware-in-the-loop test bed is realized using a twoelectric machine system. The electric machine responsible for the electric vehicle propulsion is the traction motor and is tasked with maintaining the vehicle speed. The other electric machine, directly coupled to the ﬁrst machine, is controlled by the simulation environment. This machine is the load motor which emulates the vehicle operating environment including the forces acting on the vehicle. This motor also compensates for all losses experienced by the actual hardware setup. A detailed explanation of the entire hardware-in-the-loop setup is discussed with speciﬁc details relevant to the system design. The modularity of the system, allowing each block of the setup to be easily replaced, and making the test bed highly re-conﬁgurable, is also discussed in detail.
Design and Performance Evaluation of a Battery Simulator
(University of Waterloo, 2016-05-12) Wang, Haoduo; Kazerani, Mehrdad
The increasing demand on alternative fuel vehicles, especially electric vehicles (EVs), has created an enormous market, as well as great opportunities for further improvements, for battery industry. However, using battery packs as the energy source in the design/development process of new electric vehicles, is not an optimal choice, due to high cost and cycle life reduction of battery cells. Utilizing a battery simulator, with bidirectional power transactions with the grid, which can emulate different battery cell chemistries and battery pack sizes, is a viable solution to the problem. In this work, a battery simulator is proposed which has the potential of providing a high power DC supply, while emulating multiple types of battery cell chemistries, including Li-ion, lead-acid, NiCd, NiMH, and polymer-lithium. The proposed battery simulator consists of two main parts. The first part is the battery model that generates the reference signal for the DC terminal voltage of the battery simulator according to the present value of the load current. The second part is a voltage-source converter (VSC) that controls its DC-side voltage according to the reference signal provided by the battery model. Different battery modelling approaches are introduced and compared to select the most appropriate model to be realized. The control strategy and controller tuning method are also discussed following a systematic approach. Simulations under various loading conditions are carried out and extended simulation results are presented to verify the expected capabilities of the proposed battery simulator.
Distributed Secondary Control of Hybrid ac/dc Microgrids
(University of Waterloo, 2021-10-25) Espina González, Enrique; Kazerani, Mehrdad; Simpson-Porco, John
This thesis focuses on studying hybrid ac/dc-microgrids, composed of an ac-microgrid and a dc-microgrid, connected by Interlinking Converters (ICs). Specifically, this work is focused on developing distributed secondary controllers that consider the hybrid microgrid as a single entity and not as three independent systems interacting with each other. The main goal of the secondary controller is augmented with one of the following objectives: (i) achieving active power consensus between ac-DGs and dc-DGs (and ICs), or (ii) minimizing the operation cost of the microgrid. The additional control task is performed with information from the nearest neighbours from both sides of the microgrid. Two analytical closed-loop models for a hybrid microgrid are obtained in this thesis. The first one considers the consensus-based distributed control strategy proposed for active power consensus. In contrast, the second one considers the strategy proposed for minimizing the operation cost of the microgrid. The closed-loop models are used to perform several analyses of the control systems proposed. Several tests are carried out to validate the performance of the proposed control strategies in two different topologies: a 24kW prototype with a single IC and a 33kW prototype with multiple ICs.
Fast DC Fault Current Suppression and Fault Ride Through in Full-Bridge MMCs via Regulation of Submodule Capacitor Discharge
(University of Waterloo, 2022-05-16) Sakib, Munif Nazmus; Azad, Sahar; Kazerani, Mehrdad
High Voltage Direct Current (HVDC) is more cost-effective than High Voltage Alternating Current (HVAC) for transmitting power over long distances, and therefore is ideal for bulk power transfer from wind, solar, hydroelectric, and tidal power plants located in offshore or remote locations to load centers. The use of Voltage-Sourced Converters (VSCs) in HVDC transmission systems offers greater flexibility when compared to their counterpart, Line Commutated Converters (LCCs), due to their smaller footprint, improved power quality, as well as decoupled active and reactive power control, voltage support, and black start capabilities. The most recent advancements in VSC technology have led to the emergence of a new converter topology known as the Modular Multilevel Converter (MMC). The simplest and most economical MMC cell structure is the Half-Bridge Submodule (HBSM), which is unable to prevent AC side contribution to DC side faults in HVDC systems. Therefore, DC fault protection in the HB-MMC requires either installation of expensive DC Circuit Breakers (DCCBs) or the opening of AC side breakers that are not adequately fast. Adding two extra switches to the HBSM results in the Full-Bridge Submodule (FBSM) configuration which ensures that, in the event of a DC side fault, there is a reverse voltage in the path of AC side current feeding the DC side fault through the antiparallel diodes in the SM switches. In addition, such fault blocking SMs capable of bipolar voltage generation equip the MMCs with Fault Ride Through (FRT) ability, thus allowing them to remain connected to both AC and DC networks during DC faults while operating as Static Compensators (STATCOMs) and exchanging reactive power with the AC network. A comprehensive review of notable fault blocking SM configurations and fault ride through techniques is presented in this thesis. In the event of a DC side fault, the fault current contributions are initially made by SM capacitor discharge, which occurs before the fault is detected, followed by the AC side contribution to the DC side fault. While the AC side currents can be regulated using fault blocking SMs with bipolar voltage generation capability, the initial discharge of the SM capacitors results in high DC fault currents, which can take several milliseconds to be brought under control. A method to actively influence the rate of rise of the DC fault current by regulating the discharge of SM capacitors in an HB-MMC system has been presented in the literature. In this thesis, the approach has been modified and adapted to a FB-MMC system. The discharge direction of the FBSM capacitors is inverted following the detection of a DC side fault which leads to a reversal in the fault current direction and a fast drop-off towards zero. The conventional FRT procedure where the DC fault is cleared by making adjustments to the MMC arm reference voltages followed by STATCOM operation of the MMC is initiated after the detection of zero-crossing of the DC fault current. The proposed control scheme provides significantly faster DC fault current suppression compared to the case where the conventional FRT procedure is initiated immediately upon DC fault detection. Simulations performed on a point-to-point FB-MMC test system are used to verify the theoretical analysis and to evaluate the DC-FRT performance of the proposed scheme.
A Generalized Optimal Planning Platform for Microgrids of Remote Communities Considering Frequency and Voltage Regulation Constraints
(University of Waterloo, 2017-10-24) Karimi, Elham; Kazerani, Mehrdad
Access to electricity is a key factor behind development and expansion of modern societies, and electric power systems are the backbone infrastructure for economic growth of nations and communities. However, more than a billion people all over the world have no or limited access to electricity and are deprived of basic services. Furthermore, there are many communities that rely on small-scale isolated microgrids to supply their electric power demands, and many challenges exist in keeping those microgrids operating. The cost of operating isolated microgrids is a major issue which impacts the availability of a proper power network in remote communities. Hence, many organizations, communities and governments around the world are looking into alternative options for electrification of remote communities by considering Renewable Energy (RE) resources, such as wind and solar power, and utilization of Energy Storage Systems (ESS). This thesis investigates the feasibility of RE deployment in remote communities, by proposing a generalized optimal planning platform and conducting comprehensive simulation studies based on real measured data, and evaluates the impact of economic, technical and operation constraints on the planning of an isolated microgrid involving conventional generation, RE resources and ESS. This work suggests that further investigation should be made on the potential impacts of the integration of RE resource on systems operation constraints, such as frequency and voltage regulation, and the results justify the importance of such investigations. Detailed studies on the impact of operation constraints on the planning and sizing of the microgrid are performed. The impact of ESS on planning studies and its potential role in system operation are analyzed. Furthermore, the impact of RE integration on reduction of diesel generation and thus carbon footprint in remote communities is evaluated. The inclusion of a demand response management strategy in microgrid planning problem is considered and its impact on the integration of RE and ESS in remote communities is analyzed. The proposed planning platform is applied to the microgrid of Kasabonika Lake First Nation (KLFN), a northern Ontario remote community. The results indicate that RE and ESS integration projects are achievable considering alternative incentives and funding resources. It is also shown that frequency regulation constraints have remarkable impact on the sizing of the RE units and ESS. A sensitivity analysis is also performed in order to study the effect of variable parameters on the optimal design of the microgrid at KLFN.
Integration of Green Ammonia into Smart Grids: Neural Network-Based Modeling and Control for Direct Ammonia Synthesis and Fuel Cells
(University of Waterloo, 2024-09-18) Syed, Miswar; Kazerani, Mehrdad
The current green ammonia production method involves generating green hydrogen via an electrolyzer and combining it with nitrogen through the Haber Bosch (HB) process to produce ammonia. A newer method, Direct Ammonia Synthesis (DAS), is gaining attention as it can produce green ammonia directly using an Electrochemical Ammonia Synthesizer (EAS) without the electrolyzer and HB system, significantly reducing costs and energy consumption. The produced ammonia can be directly converted to electricity using Direct Ammonia Fuel Cells (DAFC). Additionally, ammonia addresses hydrogen-related issues such as high flammability, poor volumetric density, and high storage costs. First, the thesis focuses on the DAS approach. It explores the integration of EAS and DAFC into the grid as a means to provide stable power through the utilization of various power smoothing filters. The EAS converts excess wind/solar power into green ammonia, which is then used by DAFC to produce electricity during power deficits. Second, a novel neural network (NN) model for EAS is developed to simplify the traditionally complex and sensor-intensive modeling of electrochemical systems. This NN model accurately predicts ammonia production based on solar power, nitrogen, and water inputs. Third, an NN model for DAFC is created to output electrical power from ammonia. Both EAS and DAFC NN models can be integrated into the existing microgrid system models in MATLAB-Simulink and Python. Finally, the thesis introduces a Neural Network-based Model Predictive Control (NNMPC) approach for regulating EAS output and meeting the ammonia demand, which demonstrates superior accuracy and efficiency compared to the traditional fuzzy logic control method. Unlike a traditional MPC, which uses a mathematical plant model for predictive optimization, an NN model demonstrates superior accuracy in encapsulating plant dynamics. The NNMPC addresses mathematical intricacies in MPC models, especially as plant complexities increase. Simulation results confirm the effectiveness of the NN models and NNMPC in practical applications. The research conducted in this thesis has resulted in journal and conference research publications as well as a collaborative project with a Waterloo-based company.
Long-Term Renewable Energy Planning Model for Remote Communities
(Institute of Electrical and Electronics Engineers (IEEE), 2015-10-27) Arriaga, Mariano; Canizares, Claudio A.; Kazerani, Mehrdad
This paper presents a novel long-term renewable energy (RE) planning model for remote communities (RCs), considering the characteristics of diesel-based RCs in Canada and other parts of the world such as Alaska and northern Chile. Over the past few years, there has been a significant increase in assessing and deploying RE projects in northern remote locations. The model proposed in this paper adds to such efforts by creating a multiple-year community planning tool that can be used to determine economic and technically feasible RE solutions, considering the current operating structures, electricity pricing systems, subsidy frameworks, and project funding alternatives under which RE can be deployed in RCs. The proposed model is implemented in a case study for the Kasabonika Lake First Nation community in northern Ontario. The case study shows that RE projects can be feasible under current operating conditions, for a set of funding alternatives that share the economic risks.
Modeling and Testing of a Bidirectional Smart Charger for Distribution System EV Integration
(Institute of Electrical and Electronics Engineers (IEEE), 2016-03-25) Restrepo, Mauricio; Morris, Jordan; Kazerani, Mehrdad; Canizares, Claudio A.
This paper proposes a model of a single-phase bidirectional electric vehicle (EV) charger with capability of operating in all four quadrants of the P-Q plane. The steady-state and step responses of the proposed model are used to validate it based on the actual responses of a bidirectional charger prototype for different P-Q requests. The model can be used efficiently in time-domain simulations that require models of a number of EV chargers, such as EV integration studies in low-voltage (LV) distribution networks. A practical case study is presented to demonstrate and test the proposed smart charger and model, investigating the provision of vehicle-to-grid (V2G) for active and reactive power in an LV residential distribution network. These results demonstrate the advantages of the presented charger model for developing V2G strategies in distribution networks.
Northern Lights: Access to Electricity in Canada's Northern and Remote Communities
(Institute of Electrical and Electronics Engineers (IEEE), 2014-06-12) Arriaga, Mariano; Canizares, Claudio A.; Kazerani, Mehrdad
Access to energy in many of the world's remote communities is still restricted; these locations only have access to simple and inexpensive local energy sources, such as biomass for cooking and kerosene lamps or candles for lighting. The World Bank and the International Energy Agency (IEA) perceive this energy deficit as a major obstacle to achieving community economic development as well as to obtaining adequate access to health services and clean water. Electricity is a flexible, modern source of energy that is considered to be one of the principal driving forces that stimulate community development and access to basic services in remote locations. Governments, private institutions, and nongovernmental organizations have gradually recognized these energy needs and have established electrification programs at the national and regional levels that aim at the gradual electrification of remote locations. The main objective is to give the reader a better understanding of the challenges and opportunities with regard to electricity generation in Canada's N&RCs beased on their use of renewable energy (RE) alternatives.
An Offshore Wind Farm Featuring Differential Power Processing
(University of Waterloo, 2021-12-22) Pape, Marten; Kazerani, Mehrdad
Offshore wind farms are a rapidly growing technology used to harvest wind energy on the open seas where wind speeds are significantly higher and steadier than onshore. Current wind farms located far away from shore (e.g., 50 km or more) require a large amount of equipment to be deployed in order to transport generated energy to shore most cost-effectively. In these cases, energy is transmitted to shore using High-Voltage DC (HVDC) transmission connected to wind turbines with AC voltage output. During the past decade, research has studied alternate arrangements to reduce the amount of equipment deployed offshore and increase conversion efficiency. The redesign of offshore collection systems between wind turbines from AC to DC voltages is seen as a key tool to achieve the research objectives. The presented research is focused on the design of offshore wind farms with DC collection system and series-connected wind turbines based on partial power processing converters (PPPCs). This wind farm configuration significantly improves conversion efficiency compared to AC wind farms with HVDC link, since PPPCs are only required to process output power differences among wind turbines in a wind farm to achieve maximum power point (MPP) operation, and other wind farm components are operated at variable operating points, improving low-load efficiency. Furthermore, PPPCs can be of reduced size to realize MPP operation. To find the best variable operating points, a loss minimizing HVDC link current scheduling scheme has been derived and a comprehensive sizing framework was developed to inform the best choice of PPPC ratings. The presented work addresses major design considerations at wind farm, wind turbine, and PPPC levels. An efficiency, size and economic evaluation has been conducted for a 450 MW wind farm located 100km from shore, confirming significant annual loss reductions and economic advantages compared to a conventional AC wind farm with HVDC link, as well as two other series-connected DC wind farm configurations. A generic converter sizing framework for single-string series-connected DC wind farms has been developed and applied to the 450 MW wind farm. Challenges in wind turbine startup with this configuration have been identified and schemes were developed to enable successful wind turbine startup without the need of significant adidtional hardware.
Planning, Operation and Control of Battery Energy Storage Systems based on Repurposed Electric Vehicle Batteries
(University of Waterloo, 2020-09-25) Alharbi, Talal; Bhattacharya, Kankar; Kazerani, Mehrdad
Battery Energy Storage Systems (BESSs) play a pivotal role in facilitating the grid integration of renewable energy resources and mitigating the impact of high penetration of Electric Vehicles (EVs). The increasing number of EVs, however, would lead to stockpiling of used Electric Vehicle Batteries (EVBs) after their vehicular End-of-Life (EoL). Since high installation and capital costs of new BESS pose a barrier to their large-scale deployment, utilization of the used EVBs after repurposing can play a significant role in power systems by helping defer capacity addition in the long-term. This would also alleviate the adverse environmental impacts of manufacturing more batteries and delay the recycling process of used EVBs. There are significant benefits for the utilities, EV customers, and governments in utilizing the used EVBs, as they offer a cheaper option for energy storage applications. In this context, BESS has emerged as a promising and viable solution for utilities such as microgrids and Local Distribution Companies (LDCs) for balancing their supply and demand and implementing efficient control and operation. The thesis aims at developing models for planning, operation, and control of BESS and Repurposed Electric Vehicle Battery (REVB) in isolated microgrids and distribution systems. The thesis first presents a comprehensive and novel framework for planning and operation of BESS based on REVBs. A systematic procedure is proposed to model and simulate the degradation of EVBs during their first life in vehicles to capture the impact on their State of Health (SoH) and hence on the number of years to reach their EoL, which are used to estimate the expected cost of installing REVBs. A generic microgrid planning model is developed to determine the optimal energy and power ratings, and year of installation and replacement of new BESSs and REVBs considering the impact of calendar and cycling degradations. The proposed planning model introduces a novel set of mathematical relations for BESS degradation and optimal year of replacement, thereby avoiding premature replacements and additional costs. The EVB degradation model is arrived at by using a real EVs drive cycle database and the microgrid planning model is validated using the CIGRE isolated microgrid test system. The thesis then extends the earlier proposed microgrid planning model to include system adequacy requirement using a novel backward-forward propagation approach with an embedded energy sharing strategy for multiple REVB units. A novel concept of measuring the adequacy level of the microgrid in terms of REVB energy to power ratio (E/P) is presented. The novel, heuristic, adequacy check module starts from the terminal year of the planning horizon, and propagates to the initial year, to ensure that the microgrid's capacity adequacy requirements are met in all years. To accommodate multiple installations and replacements of REVBs over the planning horizon, an energy sharing strategy among various installed REVB units is proposed to enhance the battery useful life and delay their replacements so as to minimize the total cost. The proposed models are validated on the CIGRE isolated microgrid test system. The third part of the thesis introduces an interactive real-time Community Energy Management System (CEMS) for an REVB-based Community Energy Storage System (CESS) in a practical Low-Voltage (LV) distribution system. This is an extension (in terms of operation and control) to the first research problem, where economic viability of installing REVBs is assessed. A rule-based controller for the four-quadrant REVB-based CESS is embedded in the CEMS to reduce the loading of the distribution transformer and slow down battery degradation. The proposed controller structure can be modified based on the specific characteristics of the battery. A Hardware-in-the-Loop (HIL) simulation is carried out to validate the simulation results and illustrate the effectiveness of the proposed CEMS and its rule-based control algorithm, using actual signals from the Battery Management System (BMS) and the bidirectional charger setup.
Renewable Energy Alternatives for Remote Communities in Northern Ontario, Canada
(Institute of Electrical and Electronics Engineers (IEEE), 2013-02-12) Arriaga, Mariano; Canizares, Claudio A.; Kazerani, Mehrdad
The paper investigates renewable energy alternatives to reduce diesel fuel dependency on electricity generation in Ontario's remote northern communities; currently, these communities use diesel fuel as the sole energy source to produce electricity. The current operation is complex, involving several stakeholders, high operating costs, and a considerable CO2 footprint. Several of these communities have electric load restrictions that limit further building construction and economic growth. This preliminary work discusses the barriers for renewable energy (RE) projects in northern Ontario communities by analyzing the current economic structure, the high capital costs, the available natural resources, and the installation and operation complexity. Also, a detailed analysis of six scenarios is presented; three scenarios consider a solar and/or wind-diesel system with a low RE penetration of 7% without any excess energy, whereas other three scenarios increase the RE penetration to 18%, requiring a dump load, an additional small diesel engine, or a battery storage system. The proposed systems reduce fuel consumption, operating costs and CO2 emissions, considering the investment, operation and maintenance costs and constraints in remote regions.
A Small-Scale Standalone Wind Energy Conversion System Featuring SCIG, CSI and a Novel Storage Integration Scheme
(University of Waterloo, 2016-08-12) Alnasir, Zuher; Kazerani, Mehrdad
Small-scale standalone wind turbines provide a very attractive renewable energy source for off-grid remote communities. Taking advantage of variable-speed turbine technology, which requires a partial- or full-scale power converter, and through integrating an energy storage system, smooth and fast power flow control, maximum power point tracking, and a high-quality power is ensured. Due to high reliability and efficiency, permanent magnet synchronous generator seems to be the dominating generator type in gearless wind turbines, employed for off-grid applications. However, wind turbines using geared squirrel-cage induction generator (SCIG) are still widely accepted due to their robustness, simplicity, light weight and low cost. Permanent magnet induction generator, a relatively new induction-based machine, has recently been recognized in the wind energy market as an alternative for permanent magnet synchronous generator. A thorough comparative study, among these three generator types, is conducted in this research in order to enable selection of the most appropriate generator for off-grid wind energy conversion system (WECS), subject to a set of given conditions. The system based on geared SCIG has been shown to be the most appropriate scheme for a small-scale standalone WECS, supplying a remote area. Different topologies of power electronic converters, employed in WECSs, are overviewed. Among the converters considered, current source converter is identified to have a great potential for off-grid wind turbines. Three current-source inverter-based topologies, validated in the literature for on-grid WECS, are compared for off-grid WECS application. Feasibility study and performance evaluation are conducted through analysis and simulation. Among all, the topology composed of three-phase diode bridge rectifier, DC/DC buck converter, and pulse-width-modulated current-source inverter (PWM-CSI) is identified as a simple and low-cost configuration, offering satisfactory performance for a low-power off-grid WECS. A small-scale standalone wind energy conversion system featuring SCIG, CSI and a novel energy storage integration scheme is proposed and a systematic approach for the dc-link inductor design is presented. In developing the overall dynamic model of the proposed wind turbine system, detailed models of the system components are derived. A reduced-order generic load model, that is suitable for both balanced and unbalanced load conditions, is developed and combined with the system components in order to enable steady-state and transient simulations of the overall system. A linear small-signal model of the system is developed around three operating points to investigate stability, controllability, and observability of the system. The eigenvalue analysis of the small-signal model shows that the open-loop system is locally stable around operating points 1 and 3, but not 2. Gramian matrices of the linearized system show that the system is completely controllable at the three operating points and completely observable at operating points 1 and 3, but not 2. The closed-loop control system for the proposed wind turbine system is developed. An effective power management algorithm is employed to maintain the supply-demand power balance through direct control of dc-link current. The generator’s shaft speed is controlled by the buck converter to extract maximum available wind power in normal mode of operation. The excess wind power is dumped when it is not possible to absorb maximum available power by the storage system and the load. The current source inverter is used to control positive- and negative-sequence voltage components separately. The feasibility of the proposed WECS and performance of the control system under variable wind and balanced/unbalanced load conditions are analyzed and demonstrated through simulation. Finally, the proposed WECS is modified by removing the dump load and avoiding the surplus power generation by curtailment of wind power. The operation of the modified system is investigated and verified under variable wind and load conditions.
Smart Operation of Electric Vehicles With Four-Quadrant Chargers Considering Uncertainties
(Institute of Electrical and Electronics Engineers (IEEE), 2018-03-15) Mehboob, Nafeesa; Restrepo, Mauricio; Canizares, Claudio A.; Rosenberg, Catherine; Kazerani, Mehrdad
Given the expected impact of electric vehicle (EV) charging on power grids, this paper presents a novel two-step approach for the smart operation of EVs with four-quadrant chargers in a primary distribution feeder, accounting for the uncertainties associated with EVs, and considering the perspectives of both the utility and the EV owners. In the first step of the proposed approach, the mean daily feeder peak demand and corresponding hourly feeder control schedules, such as taps and switched capacitor setpoints, considering the bidirectional active and reactive power transactions between EVs and the grid, are determined. A nonparametric bootstrap technique is used, in conjunction with a genetic algorithm-based optimization model, to account for EV uncertainties and discrete variables. In the second step, the maximum possible power that can be given to connected EVs at each node, while providing active and/or reactive power to maintain the peak demand value and corresponding feeder dispatch schedules defined in the first step, is computed every few minutes in a way which is fair to the EVs. The proposed approach is validated using the distribution feeder model of a real primary feeder in Ontario, Canada, considering significant EV penetration levels. The results show that the proposed approach could be implemented in practice to properly operate EVs, satisfying feeder, and peak demand constraints, which would be better than the business-as-usual practice or a popular heuristic method in terms of number of tap operations, system peak demand, and voltage regulation.
Smart Operation of Four-Quadrant Electric Vehicle Chargers in Distribution Grids
(University of Waterloo, 2017-05-10) Restrepo Restrepo, Mauricio; Canizares, Claudio; Kazerani, Mehrdad
Many policies and programs adopted in the context of climate change mitigation and substitution of fossil fuels are contributing to the continuous development and growth of Electric Vehicles (EVs) in urban mobility systems, reaching 1.26 million units on the roads through the end of 2015. Even though the increasing number of EVs will create problems in distribution systems, which can be mitigated using smart charging strategies, there will also be economic opportunities for EV owners to provide services to the grid while their vehicle are parked and plugged in, a concept known as Vehicle-to-Grid (V2G). Most of the studies on V2G have concentrated on the provision of services such as frequency regulation or spinning reserves, which may reduce the battery life because of the required extra charging/discharging cycles, and little attention has been paid to the possibility of providing reactive power control services to the grid by using the ac/dc converter and the dc link capacitor available in most advanced chargers, a practice that does not compromise the vehicle battery life. These kinds of chargers, which are known as four-quadrant EV chargers due to the capability of being operated in all quadrants of the P-Q plane, can be used in distribution networks to improve the power factor and help regulate voltage, thus facilitating larger EV penetrations, as discussed in this thesis. In the first part of this thesis, a new average model of a single-phase, four-quadrant EV charger is developed. The steady-state and step responses of the proposed model for different P-Q requests, corresponding to the operation in the four quadrants of the P-Q plane, are used to validate its performance against a four-quadrant EV charger prototype. The model is shown to be useful for efficient time-domain simulations and studies that include a number of EV chargers, such as EV integration studies in Low-Voltage (LV) distribution networks. A practical case study is presented to demonstrate and test the performances of the four-quadrant charger and its model, investigating the voltage interactions of several chargers in an LV residential network during the provision of three vehicle-to-grid (V2G) strategies for active and reactive power. In the second part, a novel three-stage algorithm to coordinate the operation of four-quadrant EV chargers with other volt/var control devices in Medium-Voltage (MV) and LV distribution feeders is proposed. The first stage of the algorithm is operated on a day-ahead basis and defines the Load Tap Changer (LTC) and capacitor schedules while minimizing the peak load associated with EVs in the distribution system. The second and third stages update their operation every five minutes, to fairly allocate the aggregated and individual EV loads in the MV and LV feeders, respectively, while minimizing active power losses and voltage deviations. The proposed technique is applied to CIGRE's North-American MV and LV benchmark systems to demonstrate its ability to properly allocate EV loads, and improve distribution system performance in terms of losses and voltage profiles.
Steady-State Analysis and Optimal Power Routing of Standalone Unbalanced Hybrid AC/DC Microgrids
(University of Waterloo, 2018-08-03) Alsanbawy, Mahmoud Ahmed Allam Sayed; Kazerani, Mehrdad
The concept of ac microgrids was introduced to integrate distributed generators (DGs) and loads within one entity that can operate autonomously or connected to a utility grid. Furthermore, dc microgrids have received increasing attention as a potential solution to deliver power from DGs to modern dc loads with reduced conversion stages. Moreover, hybrid ac/dc microgrids have been introduced as a paradigm combining the benefits of the two types of microgrids by interconnecting them through interlinking converters (ICs). Steady-state analysis is essential for planning and operation studies of electrical power systems. However, conventional analysis approaches cannot be applied to hybrid ac/dc microgrids due to their distinctive features, such as droop characteristics, lack of a slack bus, and coupling between the ac and dc variables. Additionally, the unbalanced nature of ac microgrids adds to the complexity of modeling and analysis in such networks. Therefore, this thesis is focused on developing steady-state modeling and analysis framework for standalone unbalanced hybrid ac/dc microgrids. First, a steady-state analysis tool for unbalanced hybrid ac/dc microgrids is developed. The ac subgrid's components are modeled in phase coordinates. Furthermore, the dc subgrid's components are modeled and the coupling between the ac and dc variables is formulated. The models of the various system elements are incorporated into a unified power flow formulation, which is solved using a Newton-Trust Region (NTR) method. The developed power flow algorithm is verified through comparisons with time-domain simulations of test microgrids. The analysis tool is used to analyze a larger hybrid ac/dc microgrid through case studies. The case studies shed light on some challenges of these microgrids, namely, imposed limitations on microgrid loadability due to unbalanced ac subgrid's loading, effect of IC settings on microgrid operation, and trade-off between proportional loading of the ac and dc subgrids and proportional power-transfer sharing among ICs. Second, based on the identified microgrid loadability limitation of unbalanced microgrids, a novel adaptive power routing (APR) scheme is proposed to maximize the microgrid loadability. The proposed scheme allows independent control of active and reactive powers flowing through IC phases, so that power can be routed among the ac subgrid's phases. The DPR scheme is integrated into an optimal power flow (OPF) formulation with the objective of minimizing load shedding. A supervisory controller is proposed to solve the OPF problem by adjusting the DG and IC settings. Several case studies are conducted to show the ineffectiveness of conventional supervisory controllers in resolving the loadability issue, and to verify the success of the proposed controller in solving the problem. Third, a power flow approach based on sequence component analysis of the ac microgrid's elements is adopted for faster convergence and improved modeling accuracy as compared to conventional approaches in phase coordinates. This approach breaks down the system model into positive-, negative-, and zero-sequence subsystems that can be solved in parallel for enhanced performance. The positive-sequence power flow is solved using a Newton-Raphson (NR) method, while the negative- and zero-sequence voltages are obtained by solving linear complex equations. The approach is verified through comparisons with time-domain simulations. In addition, the algorithm is utilized to investigate the operation of droop-controlled DGs in larger-scale isochronous unbalanced ac microgrids, and to examine its limit-enforcement abilities at the same time. The algorithm demonstrates significant improvements in terms of accuracy and convergence time when compared against the conventional NTR-based approach in phase coordinates. Finally, the power flow approach developed in the third part is extended to include the IC's and dc subgrid's models so that it can be applied to hybrid ac/dc microgrids. A power flow algorithm is proposed to solve the ac and dc power flows independently in a sequential manner, while maintaining the correlation between the two. The algorithm is verified through comparisons with time-domain models of test hybrid microgrids. Case studies are introduced to test the algorithm's effectiveness in enforcing the DG and IC limits in the power flow solution under various conditions. The algorithm also shows enhanced accuracy and solution speed with respect to the tool developed in the first stage.
Stochastic-Predictive Energy Management System for Isolated Microgrids
(Institute of Electrical and Electronics Engineers (IEEE), 2015-09-14) Olivares, Daniel E.; Lara, Jose D.; Canizares, Claudio A.; Kazerani, Mehrdad
This paper presents the mathematical formulation and control architecture of a stochastic-predictive energy management system for isolated microgrids. The proposed strategy addresses uncertainty using a two-stage decision process combined with a receding horizon approach. The first stage decision variables (unit commitment) are determined using a stochastic mixed-integer linear programming formulation, whereas the second stage variables (optimal power flow) are refined using a nonlinear programming formulation. This novel approach was tested on a modified CIGRE test system under different configurations comparing the results with respect to a deterministic approach. The results show the appropriateness of the method to account for uncertainty in the power forecast.
The Canadian Renewable Energy Laboratory: A testbed for microgrids
(Institute of Electrical and Electronics Engineers (IEEE), 2020-03-04) Nasr-Azadani, Ehsan; Su, Peter; Zheng, Wenda; Rajda, Janos; Canizares, Claudio; Kazerani, Mehrdad; Veneman, Erik; Cress, Stephen; Wittemund, Michael; Manjunath, Manoj Rao; Wrathall, Nicolas; Carter, Mike
This article presents a test facility for design validation of microgrids with high penetration of renewable energy, developed as a joint effort with industry, government, and academia. The Canadian Renewable Energy Laboratory (CANREL) described here is a physical simulation tool for the design, development, and performance testing of islanded and grid-connected microgrid projects. CANREL is equipped with a diesel generator, different renewable energy sources, various renewable energy generation simulators and physical systems, a bidirectional power-flow grid simulator, a battery- based energy-storage system, and controllable resistive?inductive?capacitive and electronic test loads for the design and testing of a variety of microgrid solutions. The test facility provides project performance demonstration and validation services at each stage of a microgrid project development to help utilities and project developers reduce risks. It is also a physical simulation tool for benchmarking microgrid equipment and controllers for research and development purposes. Some facility test results are presented in this article to demonstrate the capabilities of CANREL for simulating a wide range of scenarios.