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Recent developments in the renewable energy sector have seen an unprecedented growth in residential photovoltaic (PV) installations. However, high PV penetration levels often lead to overvoltage problems in low-voltage (LV) distribution feeders. Smart inverter control such as active power curtailment (APC)-based overvoltage control can be implemented to overcome these challenges. The APC technique utilizes a constant droop-based approach which curtails power rigidly, which can lead to significant energy curtailment in the LV distribution feeders. In this paper, different variations of the APC technique with linear, quadratic, and exponential droops have been analyzed from the point-of-view of energy curtailment for a LV distribution network in North America. Further, a combinatorial approach using various droop-based APC methods in conjunction with adaptive dynamic programming (ADP) as a supplementary control scheme has also been proposed. The proposed approach minimizes energy curtailment in the LV distribution network by adjusting the droop gains. Simulation results depict that ADP in conjunction with exponential droop reduces the energy curtailment to approximately 50% compared to using the standard linear droop.
Manisha Maharjan; Ujjwol Tamrakar; Zhen Ni; Bishnu Bhattarai; Reinaldo Tonkoski. Overvoltage Prevention and Curtailment Reduction Using Adaptive Droop-Based Supplementary Control in Smart Inverters. Applied Sciences 2021, 11, 7900 .
AMA StyleManisha Maharjan, Ujjwol Tamrakar, Zhen Ni, Bishnu Bhattarai, Reinaldo Tonkoski. Overvoltage Prevention and Curtailment Reduction Using Adaptive Droop-Based Supplementary Control in Smart Inverters. Applied Sciences. 2021; 11 (17):7900.
Chicago/Turabian StyleManisha Maharjan; Ujjwol Tamrakar; Zhen Ni; Bishnu Bhattarai; Reinaldo Tonkoski. 2021. "Overvoltage Prevention and Curtailment Reduction Using Adaptive Droop-Based Supplementary Control in Smart Inverters." Applied Sciences 11, no. 17: 7900.
The displacement of rotational generation and the consequent reduction in system inertia is expected to have major stability and reliability impacts on modern power systems. Fast-frequency support strategies using energy storage systems (ESSs) can be deployed to maintain the inertial response of the system, but information regarding the inertial response of the system is critical for the effective implementation of such control strategies. In this paper, a moving horizon estimation (MHE)-based approach for online estimation of inertia constant of low inertia microgrids is presented. Based on the frequency measurements obtained in response to a non-intrusive excitation signal from an ESS, the inertia constant was estimated using local measurements from the ESS’s phase-locked loop. The proposed MHE formulation was first tested in a linearized power system model, followed by tests in a modified microgrid benchmark from Cordova, Alaska. Even under moderate measurement noise, the technique was able to estimate the inertia constant of the system well within ±20% of the true value. Estimates provided by the proposed method could be utilized for applications such as fast-frequency support, adaptive protection schemes, and planning and procurement of spinning reserves.
Ujjwol Tamrakar; David A. Copp; Tu A. Nguyen; Timothy M. Hansen; Reinaldo Tonkoski. Real-Time Estimation of Microgrid Inertia and Damping Constant. IEEE Access 2021, 9, 114523 -114534.
AMA StyleUjjwol Tamrakar, David A. Copp, Tu A. Nguyen, Timothy M. Hansen, Reinaldo Tonkoski. Real-Time Estimation of Microgrid Inertia and Damping Constant. IEEE Access. 2021; 9 ():114523-114534.
Chicago/Turabian StyleUjjwol Tamrakar; David A. Copp; Tu A. Nguyen; Timothy M. Hansen; Reinaldo Tonkoski. 2021. "Real-Time Estimation of Microgrid Inertia and Damping Constant." IEEE Access 9, no. : 114523-114534.
The lack of inertial response from non-synchronous, inverter-based generation in microgrids makes the power system vulnerable to a large rate of change of frequency (ROCOF) and frequency excursions. Energy storage systems (ESSs) can be utilized to provide fast-frequency support to prevent such large excursions in the system. However, fast-frequency support is a power-intensive application that has a significant impact on the ESS lifetime. In this paper, a framework that allows the ESS operator to provide fast-frequency support as a service is proposed. The framework maintains the desired quality-of-service (limiting the ROCOF and frequency) while taking into account the ESS lifetime and physical limits. The framework utilizes moving horizon estimation (MHE) to estimate the frequency deviation and ROCOF from noisy phase-locked loop (PLL) measurements. These estimates are employed by a model predictive control (MPC) algorithm that computes control actions by solving a finite-horizon, online optimization problem. Additionally, this approach avoids oscillatory behavior induced by delays that are common when using low-pass filters as with traditional derivative-based (virtual inertia) controllers. MATLAB/Simulink simulations on a test system from Cordova, Alaska, show the effectiveness of the MHE-MPC approach to reduce frequency deviations and ROCOF of a low-inertia microgrid.
Ujjwol Tamrakar; David A. Copp; Tu Anh Nguyen; Timothy M. Hansen; Reinaldo Tonkoski. Optimization-Based Fast-Frequency Estimation and Control of Low-Inertia Microgrids. IEEE Transactions on Energy Conversion 2020, 36, 1459 -1468.
AMA StyleUjjwol Tamrakar, David A. Copp, Tu Anh Nguyen, Timothy M. Hansen, Reinaldo Tonkoski. Optimization-Based Fast-Frequency Estimation and Control of Low-Inertia Microgrids. IEEE Transactions on Energy Conversion. 2020; 36 (2):1459-1468.
Chicago/Turabian StyleUjjwol Tamrakar; David A. Copp; Tu Anh Nguyen; Timothy M. Hansen; Reinaldo Tonkoski. 2020. "Optimization-Based Fast-Frequency Estimation and Control of Low-Inertia Microgrids." IEEE Transactions on Energy Conversion 36, no. 2: 1459-1468.
This document is a summary of a report prepared by the IEEE PES Task Force (TF) on Microgrid Stability Definitions, Analysis, and Modeling \cite{task}, which defines concepts and identifies relevant issues related to stability in microgrids. In this paper, definitions and classification of microgrid stability are presented and discussed, considering pertinent microgrid features such as voltage-frequency dependency, unbalancing, low inertia, and generation intermittency. A few examples are also presented, highlighting some of the stability classes defined in the paper. Further examples, along with discussions on microgrid components modeling and stability analysis tools can be found in the TF report.
Mostafa Farrokhabadi; Claudio A. Canizares; John William Simpson-Porco; Ehsan Nasr; Lingling Fan; Patricio A. Mendoza-Araya; Reinaldo Tonkoski; Ujjwol Tamrakar; Nikos D. Hatziargyriou; Dimitris Lagos; Richard W. Wies; Mario Paolone; Marco Liserre; Lasantha Meegahapola; Mahmoud Kabalan; Amir H. Hajimiragha; Dario Peralta; Marcelo A. Elizondo; Kevin Paul Schneider; Francis K. Tuffner; James T. Reilly. Microgrid Stability Definitions, Analysis, and Examples. IEEE Transactions on Power Systems 2019, 35, 13 -29.
AMA StyleMostafa Farrokhabadi, Claudio A. Canizares, John William Simpson-Porco, Ehsan Nasr, Lingling Fan, Patricio A. Mendoza-Araya, Reinaldo Tonkoski, Ujjwol Tamrakar, Nikos D. Hatziargyriou, Dimitris Lagos, Richard W. Wies, Mario Paolone, Marco Liserre, Lasantha Meegahapola, Mahmoud Kabalan, Amir H. Hajimiragha, Dario Peralta, Marcelo A. Elizondo, Kevin Paul Schneider, Francis K. Tuffner, James T. Reilly. Microgrid Stability Definitions, Analysis, and Examples. IEEE Transactions on Power Systems. 2019; 35 (1):13-29.
Chicago/Turabian StyleMostafa Farrokhabadi; Claudio A. Canizares; John William Simpson-Porco; Ehsan Nasr; Lingling Fan; Patricio A. Mendoza-Araya; Reinaldo Tonkoski; Ujjwol Tamrakar; Nikos D. Hatziargyriou; Dimitris Lagos; Richard W. Wies; Mario Paolone; Marco Liserre; Lasantha Meegahapola; Mahmoud Kabalan; Amir H. Hajimiragha; Dario Peralta; Marcelo A. Elizondo; Kevin Paul Schneider; Francis K. Tuffner; James T. Reilly. 2019. "Microgrid Stability Definitions, Analysis, and Examples." IEEE Transactions on Power Systems 35, no. 1: 13-29.
HongBin Sun; Qinglai Guo; Junjian Qi; Venkataramana Ajjarapu; Richard Bravo; Joe Chow; Zhengshuo Li; Rohit Moghe; Ehsan Nasr-Azadani; Ujjwol Tamrakar; Glauco N. Taranto; Reinaldo Tonkoski; Gustavo Valverde; Qiuwei Wu; Guangya Yang. Review of Challenges and Research Opportunities for Voltage Control in Smart Grids. IEEE Transactions on Power Systems 2019, 34, 2790 -2801.
AMA StyleHongBin Sun, Qinglai Guo, Junjian Qi, Venkataramana Ajjarapu, Richard Bravo, Joe Chow, Zhengshuo Li, Rohit Moghe, Ehsan Nasr-Azadani, Ujjwol Tamrakar, Glauco N. Taranto, Reinaldo Tonkoski, Gustavo Valverde, Qiuwei Wu, Guangya Yang. Review of Challenges and Research Opportunities for Voltage Control in Smart Grids. IEEE Transactions on Power Systems. 2019; 34 (4):2790-2801.
Chicago/Turabian StyleHongBin Sun; Qinglai Guo; Junjian Qi; Venkataramana Ajjarapu; Richard Bravo; Joe Chow; Zhengshuo Li; Rohit Moghe; Ehsan Nasr-Azadani; Ujjwol Tamrakar; Glauco N. Taranto; Reinaldo Tonkoski; Gustavo Valverde; Qiuwei Wu; Guangya Yang. 2019. "Review of Challenges and Research Opportunities for Voltage Control in Smart Grids." IEEE Transactions on Power Systems 34, no. 4: 2790-2801.
The rapid transition towards an inverter-dominated power system has reduced the inertial response capability of modern power systems. As a solution, inverters are equipped with control strategies, which can emulate inertia by exchanging power with the grid based on frequency changes. This paper discusses the various current control techniques for application in these systems, known as virtual inertia systems. Some classic control techniques like the proportional-integral, the proportional-resonant, and the hysteresis control are presented first, followed by the design and discussion of two more advanced control techniques based on model prediction and machine learning, respectively. MATLAB/Simulink-based simulations are performed, and results are presented to compare these control techniques in terms of harmonic performance, switching frequency, and transient response.
Ujjwol Tamrakar; Dipesh Shrestha; Naresh Malla; Zhen Ni; Timothy M. Hansen; Indraman Tamrakar; Reinaldo Tonkoski. Comparative Analysis of Current Control Techniques to Support Virtual Inertia Applications. Applied Sciences 2018, 8, 2695 .
AMA StyleUjjwol Tamrakar, Dipesh Shrestha, Naresh Malla, Zhen Ni, Timothy M. Hansen, Indraman Tamrakar, Reinaldo Tonkoski. Comparative Analysis of Current Control Techniques to Support Virtual Inertia Applications. Applied Sciences. 2018; 8 (12):2695.
Chicago/Turabian StyleUjjwol Tamrakar; Dipesh Shrestha; Naresh Malla; Zhen Ni; Timothy M. Hansen; Indraman Tamrakar; Reinaldo Tonkoski. 2018. "Comparative Analysis of Current Control Techniques to Support Virtual Inertia Applications." Applied Sciences 8, no. 12: 2695.
Modern data centers consume large amounts of electricity, resulting in high operational costs. The efficiency of a data center power distribution system can be increased, and the operational cost reduced, if the number of power conversion stages can be minimized and more efficient converters, such as wide bandgap (WBG) converters, are used. This can be achieved by using DC distribution voltage at the rack level by eliminating extra conversion stages. In this paper, benchmarks for both AC and 380V DC data centers were developed and efficiency analyses were performed for an entire year. The impact of integrating photovoltaic (PV) systems into the data centers has also been analyzed in both cases in terms of efficiency. The results show that 380V DC data centers are more efficient than AC data centers with and without PV integration. Furthermore, the reliability of an AC system was compared to a 380V DC architecture with Tier-IV standard. Monte-Carlo simulations were used to perform reliability analyses for different levels of redundancy in the Uninterruptible Power Supply (UPS) system for both cases. The simulation results showed that the 380V DC distribution system had a higher level of reliability than the AC distribution system in data centers.
Bijen R. Shrestha; Ujjwol Tamrakar; Timothy M. Hansen; Bishnu P. Bhattarai; Sean James; Reinaldo Tonkoski. Efficiency and Reliability Analyses of AC and 380 V DC Distribution in Data Centers. IEEE Access 2018, 6, 63305 -63315.
AMA StyleBijen R. Shrestha, Ujjwol Tamrakar, Timothy M. Hansen, Bishnu P. Bhattarai, Sean James, Reinaldo Tonkoski. Efficiency and Reliability Analyses of AC and 380 V DC Distribution in Data Centers. IEEE Access. 2018; 6 (99):63305-63315.
Chicago/Turabian StyleBijen R. Shrestha; Ujjwol Tamrakar; Timothy M. Hansen; Bishnu P. Bhattarai; Sean James; Reinaldo Tonkoski. 2018. "Efficiency and Reliability Analyses of AC and 380 V DC Distribution in Data Centers." IEEE Access 6, no. 99: 63305-63315.
Virtual inertia based control of renewable energy sources (RESs) helps to enhance the frequency stability of power systems. In this paper, a Control Area Network (CAN) communication-based method is demonstrated to emulate virtual inertia using commercial off-the-shelf inverters. This allows the currently installed systems to be retrofitted with virtual inertia in a cost-effective manner which would allow for higher RES penetration in power systems. The proof-of-concept is demonstrated using a Xantrex XW6048 hybrid inverter/charger and OPAL-RT real-time digital simulator. Results show that CAN-based communication can be an effective way to reduce frequency variations in the power system.
Ujjwol Tamrakar; Fernando B. Dos Reis; Andre Luna; Dipesh Shrestha; Robert Fourney; Reinaldo Tonkoski. Virtual Inertia Emulation using Commercial Off-The-Shelf Inverters. 2018 IEEE Energy Conversion Congress and Exposition (ECCE) 2018, 1111 -1116.
AMA StyleUjjwol Tamrakar, Fernando B. Dos Reis, Andre Luna, Dipesh Shrestha, Robert Fourney, Reinaldo Tonkoski. Virtual Inertia Emulation using Commercial Off-The-Shelf Inverters. 2018 IEEE Energy Conversion Congress and Exposition (ECCE). 2018; ():1111-1116.
Chicago/Turabian StyleUjjwol Tamrakar; Fernando B. Dos Reis; Andre Luna; Dipesh Shrestha; Robert Fourney; Reinaldo Tonkoski. 2018. "Virtual Inertia Emulation using Commercial Off-The-Shelf Inverters." 2018 IEEE Energy Conversion Congress and Exposition (ECCE) , no. : 1111-1116.
The increase in the penetration of photovoltaics (PVs) and wind energy resources has decreased the inertia of power systems and made them inverter-based. This makes the modern grid susceptible to frequency instability when facing generation-load imbalances. In this paper, we provide an overview of the changing trends in frequency response and frequency control strategies in the modern power grid under high renewable penetrations. Virtual inertia emulation through Energy Storage Systems (ESSs), which have fast-ramping capabilities, is reviewed as a potential solution to the frequency instability issue. Recent grid codes and rules related to fast frequency services in the power system are discussed. A case study of the PJM interconnection, which was one of the first ISOs/RTOs to introduce the use of ESSs for frequency response, is then presented. The challenges faced to properly procure and reward such fast frequency response services in the PJM interconnection is analyzed in detail.
Andre Luna; Ujjwol Tamrakar; Timothy M. Hansen; Reinaldo Tonkoski. Frequency Response in Grids with High Penetration of Renewable Energy Sources. 2018 North American Power Symposium (NAPS) 2018, 1 -5.
AMA StyleAndre Luna, Ujjwol Tamrakar, Timothy M. Hansen, Reinaldo Tonkoski. Frequency Response in Grids with High Penetration of Renewable Energy Sources. 2018 North American Power Symposium (NAPS). 2018; ():1-5.
Chicago/Turabian StyleAndre Luna; Ujjwol Tamrakar; Timothy M. Hansen; Reinaldo Tonkoski. 2018. "Frequency Response in Grids with High Penetration of Renewable Energy Sources." 2018 North American Power Symposium (NAPS) , no. : 1-5.
Energy storage systems (ESSs) play a significant role in a remote microgrid's energy management system (EMS) by improving its reliability and energy efficiency. Lead-acid batteries are commonly used as ESS in remote microgrids due to comparatively low investment costs. However, the real-time operating conditions of lead-acid (PbA) batteries are quite severe than the standard test conditions which impacts the performance of an EMS and degrades the battery faster. The Schiffer weighted Ah-throughput model was considered in this paper, introducing different weight factors to analyze the operating conditions of PbA batteries. This paper presents the economical aspects of weekly, bi-weekly, monthly, and threshold crossing battery cycling strategies on PbA battery operating conditions. Its impact on the yearly operational costs of a remote microgrid and the battery lifetime are analyzed. Results showed that, effective battery cycling strategy can reduce the yearly operational cost by about 1.2% ($1,275) and increase the battery lifetime by 3.47 years. Hence, in the long run, it will reduce the expensive battery replacement cost and will maximize the profit of the system.
Habib Ullah; Santosh Chalise; Ujjwol Tamrakar; Reinaldo Tonkoski. Impact of Battery Operating Conditions on Remote Microgrid’s Energy Management System. 2018 IEEE Power & Energy Society General Meeting (PESGM) 2018, 1 -5.
AMA StyleHabib Ullah, Santosh Chalise, Ujjwol Tamrakar, Reinaldo Tonkoski. Impact of Battery Operating Conditions on Remote Microgrid’s Energy Management System. 2018 IEEE Power & Energy Society General Meeting (PESGM). 2018; ():1-5.
Chicago/Turabian StyleHabib Ullah; Santosh Chalise; Ujjwol Tamrakar; Reinaldo Tonkoski. 2018. "Impact of Battery Operating Conditions on Remote Microgrid’s Energy Management System." 2018 IEEE Power & Energy Society General Meeting (PESGM) , no. : 1-5.
Data centers have significant capital investments in large underutilized energy resources in the form of backup generators and batteries. In this paper, we propose to use these energy resources in demand response (DR) by operating a data center as a virtual power plant (VPP). An optimization model is designed which schedules the energy resources on a day-ahead basis using forecasted values of both renewable energy sources and the data center load for participation of the data center in DR. This optimization model also incorporates realtime dispatch of units to handle variations during operation. An improved battery cost model is designed and implemented as a soft constraint in the VPP energy management system (EMS) model, ensuring that the batteries' use in DR does not affect their float life. A case study is conducted in which the data center is connected to bus 8 of the modified IEEE 30-bus system. The results show that real-time operation of a data center participating in DR significantly reduces the operational cost, especially during network congestion, without causing battery degradation.
Prajina Tandukar; Labi Bajracharya; Timothy M. Hansen; Robert Fourney; Ujjwol Tamrakar; Reinaldo Tonkoski. Real-time Operation of a Data Center as Virtual Power Plant Considering Battery Lifetime. 2018 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM) 2018, 81 -86.
AMA StylePrajina Tandukar, Labi Bajracharya, Timothy M. Hansen, Robert Fourney, Ujjwol Tamrakar, Reinaldo Tonkoski. Real-time Operation of a Data Center as Virtual Power Plant Considering Battery Lifetime. 2018 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM). 2018; ():81-86.
Chicago/Turabian StylePrajina Tandukar; Labi Bajracharya; Timothy M. Hansen; Robert Fourney; Ujjwol Tamrakar; Reinaldo Tonkoski. 2018. "Real-time Operation of a Data Center as Virtual Power Plant Considering Battery Lifetime." 2018 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM) , no. : 81-86.
Studies had shown that the transient stability of a PV-Hydro micro-grid could be improved using a virtual synchronous machine (VSM), by injecting virtual inertia into the system. In the case of an interconnected system with multiple numbers of PV-Hydro micro-grid, a number of VSMs need to be operated in parallel. The parallel operated VSMs shall share the transient load in proportion to their respective capacities. Otherwise, the storage battery of one VSM will discharge more and other storage battery will be less discharged. This paper presents a control logic for parallel operated VSMs so that they share the transient load in proportion to the capacity of respective VSMs. Frequency droop control approach is used in the control logic to ensure proper load sharing. The control logic is simulated in MATLAB\ Simulink and results show that the frequency droop control approach is good enough for parallel operation of VSMs.
Prabin Adhikari; Suresh Prajapati; Indraman Tamrakar; Ujjwol Tamrakar; Reinaldo Tonkoski. Parallel operation of virtual synchronous machines with frequency droop control. 2017 7th International Conference on Power Systems (ICPS) 2017, 116 -120.
AMA StylePrabin Adhikari, Suresh Prajapati, Indraman Tamrakar, Ujjwol Tamrakar, Reinaldo Tonkoski. Parallel operation of virtual synchronous machines with frequency droop control. 2017 7th International Conference on Power Systems (ICPS). 2017; ():116-120.
Chicago/Turabian StylePrabin Adhikari; Suresh Prajapati; Indraman Tamrakar; Ujjwol Tamrakar; Reinaldo Tonkoski. 2017. "Parallel operation of virtual synchronous machines with frequency droop control." 2017 7th International Conference on Power Systems (ICPS) , no. : 116-120.
Photovoltaic (PV) charger systems are implemented in power electronic converters for battery charging applications. In order to achieve high efficiency, the choice of the component plays a major role. At the same time, such systems require high performance in terms of faster switching, high-power, and high-temperature operation capability. Converters with conventional silicon-based power switching devices may not accomplish all these requirements effectively. This paper presents the design of a single-ended primary inductance converter (SEPIC) using silicon carbide (SiC) and conventional silicon power switching devices to compare the performance in terms of the efficiency. The designed converter was first validated in PSIM simulation software to assess the effectiveness of using SiC power devices to charge a 48 V battery from a 250 Wp PV panel with a voltage of 30.7 V. Furthermore, a hardware prototype of the converter was developed and tested on a resistive load. The use of SiC-based switches increased the efficiency of the SEPIC converter by 3.6% at full load and at a switching frequency of 100 kHz.
Manisha Maharjan; Prajina Tandukar; Abhilasha Bajracharya; Fernando B. Dos Reis; Ujjwol Tamrakar; Dipesh Shrestha; Fernando S. Dos Reis; Reinaldo Tonkoski. SEPIC converter with wide bandgap semiconductor for PV battery charger. 2017 Brazilian Power Electronics Conference (COBEP) 2017, 1 -5.
AMA StyleManisha Maharjan, Prajina Tandukar, Abhilasha Bajracharya, Fernando B. Dos Reis, Ujjwol Tamrakar, Dipesh Shrestha, Fernando S. Dos Reis, Reinaldo Tonkoski. SEPIC converter with wide bandgap semiconductor for PV battery charger. 2017 Brazilian Power Electronics Conference (COBEP). 2017; ():1-5.
Chicago/Turabian StyleManisha Maharjan; Prajina Tandukar; Abhilasha Bajracharya; Fernando B. Dos Reis; Ujjwol Tamrakar; Dipesh Shrestha; Fernando S. Dos Reis; Reinaldo Tonkoski. 2017. "SEPIC converter with wide bandgap semiconductor for PV battery charger." 2017 Brazilian Power Electronics Conference (COBEP) , no. : 1-5.
Large-scale penetration of power electronic based systems demands the need for sophisticated control algorithms. Conventional current control techniques may not give the required dynamic performance for modern power electronic systems. This paper designs an online supplementary adaptive dynamic programming (ADP) controller based on neural networks which improves the dynamic performance of a conventional proportional-integral (PI) current controller. A case study with a 1 kW shunt active filter (SAF) was developed and simulated in MATLAB/Simulink environment to verify the investigated controller. Compared to an SAF with a conventional PI controller, the proposed approach obtained a better dynamic response for the current control loop, and thus showed a reduced total harmonic distortion (THD) of the source current from 4.24% to 3.64%.
Ujjwol Tamrakar; Naresh Malla; Dipesh Shrestha; Zhen Ni; Reinaldo Tonkoski. Design of online supplementary adaptive dynamic programming for current control in power electronic systems. 2017 IEEE Energy Conversion Congress and Exposition (ECCE) 2017, 3038 -3043.
AMA StyleUjjwol Tamrakar, Naresh Malla, Dipesh Shrestha, Zhen Ni, Reinaldo Tonkoski. Design of online supplementary adaptive dynamic programming for current control in power electronic systems. 2017 IEEE Energy Conversion Congress and Exposition (ECCE). 2017; ():3038-3043.
Chicago/Turabian StyleUjjwol Tamrakar; Naresh Malla; Dipesh Shrestha; Zhen Ni; Reinaldo Tonkoski. 2017. "Design of online supplementary adaptive dynamic programming for current control in power electronic systems." 2017 IEEE Energy Conversion Congress and Exposition (ECCE) , no. : 3038-3043.
Nonlinear loads in the power distribution system cause non-sinusoidal currents and voltages with harmonic components. Shunt active filters U+0028 SAF U+0029 with current controlled voltage source inverters U+0028 CCVSI U+0029 are usually used to obtain balanced and sinusoidal source currents by injecting compensation currents. However, CCVSI with traditional controllers have a limited transient and steady state performance. In this paper, we propose an adaptive dynamic programming U+0028 ADP U+0029 controller with online learning capability to improve transient response and harmonics. The proposed controller works alongside existing proportional integral U+0028 PI U+0029 controllers to efficiently track the reference currents in the d-q domain. It can generate adaptive control actions to compensate the PI controller. The proposed system was simulated under different nonlinear U+0028 three-phase full wave rectifier U+0029 load conditions. The performance of the proposed approach was compared with the traditional approach. We have also included the simulation results without connecting the traditional PI control based power inverter for reference comparison. The online learning based ADP controller not only reduced average total harmonic distortion by 18.41 U+0025, but also outperformed traditional PI controllers during transients.
Naresh Malla; Ujjwol Tamrakar; Dipesh Shrestha; Zhen Ni; Reinaldo Tonkoski. Online learning control for harmonics reduction based on current controlled voltage source power inverters. IEEE/CAA Journal of Automatica Sinica 2017, 4, 447 -457.
AMA StyleNaresh Malla, Ujjwol Tamrakar, Dipesh Shrestha, Zhen Ni, Reinaldo Tonkoski. Online learning control for harmonics reduction based on current controlled voltage source power inverters. IEEE/CAA Journal of Automatica Sinica. 2017; 4 (3):447-457.
Chicago/Turabian StyleNaresh Malla; Ujjwol Tamrakar; Dipesh Shrestha; Zhen Ni; Reinaldo Tonkoski. 2017. "Online learning control for harmonics reduction based on current controlled voltage source power inverters." IEEE/CAA Journal of Automatica Sinica 4, no. 3: 447-457.
Solid State Transformers (SSTs) are power electronic-based transformers that will be a vital component of the future smart grid with high amount of renewable energy integration and the need for improved controllability. Among its various unique features, the reactive power compensating capabilities of SSTs can be exploited in future smart distribution systems for voltage regulation under high renewable energy penetrations. SSTs are power electronic devices that show fast and non-linear dynamics which means the simulation models are often complicated and need small time steps for accurate solutions. This prevents real-time and long-term simulation of large distribution systems as the simulations become computationally prohibitive. This paper designs a simplified equivalent model of an SST using simple current and voltage sources along with simple modeling equations. These simplified models can be used to perform long-term voltage regulation studies of distribution systems where traditional transformers are replaced with SSTs.
Manisha Maharjan; Ujjwol Tamrakar; Surendra Bajagain; Timothy M. Hansen; Reinaldo Tonkoski. A steady-state equivalent model of solid state transformers for voltage regulation studies. 2017 IEEE Power & Energy Society General Meeting 2017, 1 -5.
AMA StyleManisha Maharjan, Ujjwol Tamrakar, Surendra Bajagain, Timothy M. Hansen, Reinaldo Tonkoski. A steady-state equivalent model of solid state transformers for voltage regulation studies. 2017 IEEE Power & Energy Society General Meeting. 2017; ():1-5.
Chicago/Turabian StyleManisha Maharjan; Ujjwol Tamrakar; Surendra Bajagain; Timothy M. Hansen; Reinaldo Tonkoski. 2017. "A steady-state equivalent model of solid state transformers for voltage regulation studies." 2017 IEEE Power & Energy Society General Meeting , no. : 1-5.
The modern power system is progressing from a synchronous machine-based system towards an inverter-dominated system, with large-scale penetration of renewable energy sources (RESs) like wind and photovoltaics. RES units today represent a major share of the generation, and the traditional approach of integrating them as grid following units can lead to frequency instability. Many researchers have pointed towards using inverters with virtual inertia control algorithms so that they appear as synchronous generators to the grid, maintaining and enhancing system stability. This paper presents a literature review of the current state-of-the-art of virtual inertia implementation techniques, and explores potential research directions and challenges. The major virtual inertia topologies are compared and classified. Through literature review and simulations of some selected topologies it has been shown that similar inertial response can be achieved by relating the parameters of these topologies through time constants and inertia constants, although the exact frequency dynamics may vary slightly. The suitability of a topology depends on system control architecture and desired level of detail in replication of the dynamics of synchronous generators. A discussion on the challenges and research directions points out several research needs, especially for systems level integration of virtual inertia systems.
Ujjwol Tamrakar; Dipesh Shrestha; Manisha Maharjan; Bishnu P. Bhattarai; Timothy M. Hansen; Reinaldo Tonkoski. Virtual Inertia: Current Trends and Future Directions. Applied Sciences 2017, 7, 654 .
AMA StyleUjjwol Tamrakar, Dipesh Shrestha, Manisha Maharjan, Bishnu P. Bhattarai, Timothy M. Hansen, Reinaldo Tonkoski. Virtual Inertia: Current Trends and Future Directions. Applied Sciences. 2017; 7 (7):654.
Chicago/Turabian StyleUjjwol Tamrakar; Dipesh Shrestha; Manisha Maharjan; Bishnu P. Bhattarai; Timothy M. Hansen; Reinaldo Tonkoski. 2017. "Virtual Inertia: Current Trends and Future Directions." Applied Sciences 7, no. 7: 654.
Clean energy incentives and the continuous fall in the cost of photovoltaic (PV) installations have led to a steady growth in residential PV systems. One of the main consequences of this high PV penetration in low voltage (LV) distribution networks is the overvoltage issue. Active power curtailment of PV inverters has been previously used to curtail the output power of the inverters below its operating point to prevent such overvoltages. This technique, however, uses a constant droop-based approach to curtail the power, based on the difference between the measured voltage and a critical voltage level. In this paper, this technique is implemented in a typical LV distribution network in North America with high PV penetration level. The simulation results show that the system undergoes excessive curtailment resulting in unnecessary energy loss. An adaptive droop-based approach using adaptive dynamic programming (ADP) is proposed as a possible solution to minimize the total energy loss in the system while keeping the system voltage under the critical operating limits. The energy loss due to curtailment has decreased by 25% after implementing the adaptive-droop based approach using ADP.
Manisha Maharjan; Ujjwol Tamrakar; Naresh Malla; Fernando B. Dos Reis; Zhen Ni; Timothy M. Hansen; Reinaldo Tonkoski. Adaptive droop-based active power curtailment method for overvoltage prevention in low voltage distribution network. 2017 IEEE International Conference on Electro Information Technology (EIT) 2017, 1 -6.
AMA StyleManisha Maharjan, Ujjwol Tamrakar, Naresh Malla, Fernando B. Dos Reis, Zhen Ni, Timothy M. Hansen, Reinaldo Tonkoski. Adaptive droop-based active power curtailment method for overvoltage prevention in low voltage distribution network. 2017 IEEE International Conference on Electro Information Technology (EIT). 2017; ():1-6.
Chicago/Turabian StyleManisha Maharjan; Ujjwol Tamrakar; Naresh Malla; Fernando B. Dos Reis; Zhen Ni; Timothy M. Hansen; Reinaldo Tonkoski. 2017. "Adaptive droop-based active power curtailment method for overvoltage prevention in low voltage distribution network." 2017 IEEE International Conference on Electro Information Technology (EIT) , no. : 1-6.
The dynamic frequency stability issues in microgrids with large penetration of low inertia and intermittent photovoltaic (PV) systems can be improved by using virtual inertia (VI). A VI is the combination of energy storage system, power electronics converter and a proper control algorithm. This paper presents design and experimental verification of the VI in a PV-diesel generator based remote microgrid system. Firstly, the VI was designed and tested in simulation using MATLAB/Simulink. Later, a hardware prototype of 1 kW inverter for the VI was designed and tested with a 13 kW diesel generator test system. The VI unit was able to reduce the frequency variations from a minimum value of 57.39 Hz to 58.03 Hz for a step change in the system load. The frequency deviations can be further reduced with a larger VI unit or multiple VI units in a real microgrid scenario.
Dipesh Shrestha; Ujjwol Tamrakar; Zhen Ni; Reinaldo Tonkoski. Experimental verification of virtual inertia in diesel generator based microgrids. 2017 IEEE International Conference on Industrial Technology (ICIT) 2017, 95 -100.
AMA StyleDipesh Shrestha, Ujjwol Tamrakar, Zhen Ni, Reinaldo Tonkoski. Experimental verification of virtual inertia in diesel generator based microgrids. 2017 IEEE International Conference on Industrial Technology (ICIT). 2017; ():95-100.
Chicago/Turabian StyleDipesh Shrestha; Ujjwol Tamrakar; Zhen Ni; Reinaldo Tonkoski. 2017. "Experimental verification of virtual inertia in diesel generator based microgrids." 2017 IEEE International Conference on Industrial Technology (ICIT) , no. : 95-100.
Various current control techniques for implementation in virtual synchronous machines (VSM) are compared. MATLAB\Simulink simulations are performed for different control approaches like the proportional-integral control, the proportional-resonant control and the hysteresis control to control the output current of a grid connected inverter. The techniques are compared on the basis of the steady state error produced, transient performance, harmonics content and hardware implementation aspects. The steady state error was found to be zero in all the techniques. Proportional-integral control technique showed good harmonic rejection with a low total harmonic distortion of 0.40%, but the transient performance had an overshoot of about 30%. The proportional resonant control technique and the hysteresis control technique had slightly higher total harmonic distortion of 1.31% and 0.89%, respectively, but the overshoot was low compared to the proportional-integral control. The simulation results indicate that the PR controller is the suitable technique for current control in virtual synchronous machines, both from the point of view of the ease of implementation and performance.
Ujjwol Tamrakar; Reinaldo Tonkoski; Zhen Ni; Timothy M. Hansen; Indraman Tamrakar. Current control techniques for applications in virtual synchronous machines. 2016 IEEE 6th International Conference on Power Systems (ICPS) 2016, 1 -6.
AMA StyleUjjwol Tamrakar, Reinaldo Tonkoski, Zhen Ni, Timothy M. Hansen, Indraman Tamrakar. Current control techniques for applications in virtual synchronous machines. 2016 IEEE 6th International Conference on Power Systems (ICPS). 2016; ():1-6.
Chicago/Turabian StyleUjjwol Tamrakar; Reinaldo Tonkoski; Zhen Ni; Timothy M. Hansen; Indraman Tamrakar. 2016. "Current control techniques for applications in virtual synchronous machines." 2016 IEEE 6th International Conference on Power Systems (ICPS) , no. : 1-6.