Abstract— The potential to harness offshore wind power and transmit that energy to shore is of widespread interest in the electric power and energy industry sector, as well as within U.S. government agencies such as the Department of Energy. Studies are currently being conducted to find optimal placement of offshore wind turbines along the perimeter of the United States coast lines, and evaluations of current technology solutions for transmitting the electrical energy onshore are being investigated. Transmitting high capacities of energy from sea to shore presents a significant challenge due to the need for a very efficient, robust, and reliable technical solution that must be cost effective. High Voltage AC (HVAC) and two forms of High Voltage DC (HVDC), Voltage Source Converter (VSC) based and Line Commutated-Converter (LCC) based, are possible transmission solutions to these challenges. Therefore, we present herein the applicability of these topologies for offshore wind power transmission and present the necessary procedures to select the most cost effective solution for a given application.

Index Terms— economics, HVDC, offshore transmission, offshore wind farms, power electronics, renewable energy.

I. INTRODUCTION

he energy challenges of the 21st century have led to a shift toward more sustainable energy solutions, such as wind

and other renewable resources. Wind resource potentials are particularly abundant far offshore in the oceans. Thus, many offshore wind projects have been built in Europe and are planned to be built in the U.S. to take advantage of thistremendous energy resource potential. When wind farms are being built very far from the coast lines, delivering that energy to shore is a challenge due to the need for very efficient and cost effective transmission solutions.

Various types of transmission solutions will be investigated in this paper, and a s ystematic procedure for aneconomic analysis will be presented in order to provide a guide to engineers responsible for selecting the optimal systemconfiguration for a specific project. High voltage AC (HVAC) transmission, as well as two forms of high voltage DC (HVDC) configurations - voltage source converter (VSC) andline commutated converter (LCC) - will be investigated. Transmission distance and average output-power both play a

This work was supported by funding from the United States Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE), and the Commonwealth of Pennsylvania, Ben Franklin Technology Development Authority (BFTDA).

The authors are with the Center for Energy's Electric Power Initiative and the Department of Electrical & Computer Engineering, in the Swanson School of Engineering at the University of Pittsburgh, Pittsburgh, PA 15261 USA. (e-mails: gfr3@pitt.edu, haa20@pitt.edu, mjk40@pitt.edu, ptl7@pitt.edu,bmg10@pitt.edu)

critical role in choosing the most efficient and cost effective solution for a given application.

II. TRANSMISSION SYSTEMS TOPOLOGIES

In this section, descriptions of system configurations,advantages, and limitations of the three main transmission system topologies for offshore wind applications will be presented. T he systems to be compared include traditional HVAC systems with both types of HVDC systems described in the previous section.

A. Offshore HVAC Transmission SolutionMany offshore wind farm interconnections use HVAC

transmission systems. However, the use of such a system has decreased over recent years due to their high losses and costassociated with AC for long distance transmission. This is mainly due to the reactive power generated in the cables, which increases with the cable length and the square of the AC voltage [1]. This limits the active power that can be transmitted through the cables, and thus limits the cable length in offshore applications, mainly due to the high cost and the difficulty associated with installing reactive power compensation units along submarine cables. C ompensation units can only be installed at the ends of the line in offshore transmission applications and have a very limited effect [2].

Research has been conducted to maximize the transmission distance. One of the solutions presented by [1] is operating the electrical s ystem at a lo wer frequency. This requires extra frequency conversion equipment and larger transformers and reactors, which is difficult to i mplement offshore mainly due to the large platforms needed and the high costs associated with such an approach. Another solution that has been presented by [3] is using more than three phases, which also is impractical in offshore applications since the amount of cable used is o f critical importance. Fig. 1 shows cable losses against the total transmitted power for various distances. Cable losses increase significantly with increasing transmission distance for HVAC systems.

Fig. 2 shows the basic configuration of a HVAC system for offshore wind farms. T he HVAC transmission system consists of HVAC submarine cables (XPLE cables), offshore transformers, FACTS compensation units like the SVC or TCR both onshore and offshore, and onshore transformers, depending on the grid voltage, [4].

Comparison of HVAC and HVDC Solutions for Offshore Wind Farms with a Procedure for System Economic Evaluation

Gregory F. Reed, Member, IEEE; Hashim A. Al Hassan, Student Member, IEEE;Matthew J. Korytowski, Student Member, IEEE; Patrick T. Lewis, Student Member, IEEE; and

Brandon M. Grainger, Student Member, IEEE

T

978-1-4673-4444-9/13/$31.00 ©2013 IEEE

Fig. 1. Cable losses against the total transmitted power. VLL=132kV [10].

A step-up offshore transformer is necessary because the voltage level in the offshore wind farm is usually in the range of 30kV-36kV, [4], and the transmission level is usually in the range of 132kV to 400kV. Also, an onshore transformer might be necessary if the rated voltage in the interconnectingonshore grid is different than the offshore transmission systemrated voltage.

Fig. 2. Basic configuration of HVAC solution [11].

B. HVDC Line Commutated Converter Based SolutionThe HVDC Line Commutated Converter (LCC) design has

been used for power transmission for many years, but it has never been used for offshore power transmission due to its large size and poor performance when connected to weak AC grids, which is u sually the case in offshore wind farm applications. This weak performance is because this system is based on power electronics with turn-on capability (thyristors) that require a s trong network voltage to commutate against [1]. Also, one of this system’s limitations is t hat it can not energize the system from shore (black start). This problem is solved by combining the LCC-interface with an auxiliary source of reactive power [1]. Fig . 3 shows the basic configuration for HVDC LCC used in offshore wind farms.

The main components of the system include AC and DC filters, converter transformer, converter based on thyristor valves, smoothing reactor, capacitor banks or STATCOM, DC cable, auxiliary power set, protection and control devices, [4].

Fig. 3. Basic configuration of HVDC LCC solution [2]

A hypothetical offshore system has been studied in [2], [4], and [5] in order to com pare it with the other types of systems. The HVDC LCC s ystem needs AC and DC f ilters because it produces a great deal of harmonic content. The AC filters are u sed in order to absorb the harmonic currents generated by the converter station in order to reduce the impact these harmonics have on the connected AC grid, [5]. DC filters are n ecessary in order to filter out the AC harmonics in the DC transmission line, [5]. Also as stated in [5], smoothing reactors are u sed in order t o prevent current interruption at minimum load, limit the DC fault current, and prevent resonances in the DC circuit and reduce the harmonic current caused by interferences from the overhead lines. LCC requires STATCOMs or ca pacitor banks in the converter station in order to provide control over the reactive power, [5]. The large amount of equipment used in this system makes the offshore platform very large, and therefore impractical for offshore applications. The performance of a LCC system is also poor with the presence of a weak AC connection.

C. HVDC Voltage Source Converter Based SolutionHVDC VSC is the most attractive technology for offshore

wind farms, especially when considering long distance transmission. HVDC VSC is designed by ABB under the commercial name HVDC Light, by Siemens Energy under the commercial name HVDC Plus, and by Alstom Grid under the commercial name HVDC MaxSine. HVD C VSC has only two main system components, including two converter stations (one offshore and one on shore); and a pai r of polymeric extruded cables. One of the converters operates as a rectifier and the other as an inverter at v ariable frequency, and they can both absorb or deliver reactive power to the AC grid, [6]. This four quadrant operation of the system makes bidirectional power flow possible. Also, HVDC is not limited by distance as opposed to the HVAC system because there are no reactive power losses along the line. This system also provides independent control of reactive and active power, providing voltage and frequency stability as opposed to t he HVDC LCC system, [6].

HVDC VSC uses IGBT semiconductor technology which provides high frequency switching (commutation) of up to 2 kHz. This high switching frequency reduces the number of harmonics in the system, thus reducing the amount of filtering needed as co mpared to VSC LCC systems, [6]. HVDC VSC

transmission systems do not require as much overall infrastructure as compared to HVDC LCC systems. Thus, the converter stations can be i mplemented in a very compact form, making this approach a v ery attractive solution for offshore applications.

Fig. 4 shows a basic HVDC VSC system configuration for offshore wind farms. This technology consists of a V SC converter station circuit breaker, system side harmonic filter, interface transformer, converter side harmonic filter, VSC unit, VSC DC capacitor, DC harmonic filter, DC reactor, DC cable of overhead transmission line and auxiliary power set.

Fig. 4. Basic configuration of HVDC VSC solution [2]

III. PROCEDURE FOR OPTIMAL TRANSMISSION SYSTEM SELECTION FOR OFFSHORE WIND FARMS

It is clear from the overview presented that the HVDC VSC system technology is t he most attractive solution for offshore wind farms that are located at very long distances from the interconnecting onshore grid. Some vendors suggest using HVDC VSC for distances beyond a certain length (e.g, 80 km). H owever, the most appropriate engineering solution for any project requires a com plete study of the specific application in order to select the optimal system configuration.Therefore, this section presents an economical approach to be used as a gu ideline, in order to determ ine the optimal transmission solution for any project. Specific project parameters such as power output of the wind farm, distance to shore, and onshore AC grid specifications need to be known. Also, certain parameters such as average output power, losses, availability, initial investment cost and the total energy transmission cost must be calculated for each system, in order to determine the most economical transmission system solution. Due to the lack of data, only a generalized procedure will be presented and results from other researchers will be used for discussion at the end. The procedure is mainly a compilation of the literature found in [2, 3, 4, 5, 7, 8, 10, 11,12].

A. Calculating Average Output Power from the Wind Farm The average output power of the wind farm has to be

determined in order to calculate the losses of the system. The method that is widely used for determining the average wind power will briefly be presented.

An aggregate wind farm power model and wind speed distribution model are required to determine the power curve of the wind farm. Norgaard and Holttinen in [7] used an

aggregate power curve model and Rayleigh wind speed distribution to calculate the power output of the wind farm for varying wind speeds. The average wind power of the wind farm can be calcu lated is the wind speed, f( ) is the Rayleigh probability distribution, P( ) is the power output from the wind farm according to the aggregate model,

sin is the cut in speed, sout is the cut out speed. For further details see reference [7].

sout

dfPPAvg

sin

)()( (1)

B. Calculation of LossesThe next step for the cost analysis is the loss evaluation,

which is a critical ly important factor in the determination of the reliability and the overall cost of the transmission system. A loss calculation method for each transmission system is briefly presented here.

1) HVAC Transmission System Losses

Losses are calc ulated based on [8] which takes into account the current distribution along cable lin es and temperature dependence, and pr ovides accurate results of cable losses. According to [8], the total cable losses per unit length can be calculated with (2). Note that P’max,I is the nominal total cable losses, P’D is the dielectric losses, I is the load current, IN is the nominal current, v is the temperature correction coefficient which can be calculated with (3), where

T is the temperature coefficient of the conductor resistivity,)20(1 ambT Cc , amb is the ambient temperature,

and max is the maximal temperature rise.

D

N

I PvII

PP '2max,

'' )( (2)

])(1[ 2max

NT I

Ic

cv

(3)

The current for a s pecific load alon g the cable rou te depends on its p osition. Therefore, the integral found in (4)has to be solved in order to calculate cable losses, [4].

0

0

'22

0

max'

' )()(l

x

D

N

lo PdxxvxIIl

PP (4)

The cable losses per unit length are attained by solving (4) for a cable length of l0. The total losses are o btained by multiplying the integral with l0. It is clear from (4) that cable losses of HVAC systems increase with distance. Thus this imposes a distance limit on the AC system approach.

In order to calculate transformer losses, certain parameters such as winding resistance, iron resistance, leakage and magnetizing inductances are needed. Lundberg in [9] presents details for transformer loss calculations. The data of the transformer can be obtained from the manufacturer. The totalHVAC transmission system losses can be calculated with (5), [4].

N

iiigen

N

iiilost

ahpP

ahpPl

)(

)(

,

,

% (5)

Note that Plost, i is the power lost by the transmission system at wind speed i, Pgen,i is the power generated by the wind farm at wind speed i, N is the number of wind speed class considered in the model, pi is the probability to have acertain wind speed i and it is obtained by the Rayleigh distribution, h is the number of hours in a year, and a is the availability of the wind farm. A brief review of the availability analysis will be presented in a future section of this article.

2) HVDC LCC Transmission System Losses

In [2], the author used Brakelmann theory, [8], to calculate losses for AC systems and assumed that the calculation is approximately the same for HVDC LCC. Several other authors have also made the same assumption such as S harma in [10]. The relationships describingBrakelmann’s method can be described with (6) through (10).

vII

PPN

Lcable2

max'' )( (6)

cableNmL lIcRP 20max' (7)

)20(1 max20 Cc ambLm (8)

)20(1 ambT Cc (9)

])(1[ 2max

NLT I

Ic

cv

(10)

R0 is the DC resistance of the conductor at 20oC per unit length, 20 is the constant mass temperature coefficient at 20oC, P’max,I is the lost power in the cable at it s maximum operating temperature, Lmax = 55OC is the maximum operating temperature of the insulator, I is the current flowing into the cable, IN is the nominal current of the cable, lcable is the length of the cable. The results of Ackerman’s calculations will be presented later and his procedure applicability will also be discussed.

3) HVDC VSC Transmission System Losses

Data from existing projects could be used for an estimate of the total power losses for HVDC VSC system. In [4] the authors divided the total system losses into three components (2 stations and a DC cable) in order to facilitate the calculations. Also, assuming the percent losses is equal in both converters, the following relationships listed as (11) through (13) are attained, [4]. xs is percent losses, Pin is the inputpower into rectifier station, P1 is the output power from therectifier station, P2 is the input power into inverter station, Pout

is the output power from the inverter station, VC is rated voltage of the cable, I is current flowing in the cable. xs is calculated from (14) and the temperature dependent resistance is calculated with (15).

ins PxP )1(1 (11)

21221 )(

CC V

PRIRPPP (12)

2)1( PxP sout (13)

0)1()1( 2232 outinsins

C

PPxPxVR

(14)

2max'N

L Iv

PR (15)

Equations (7), (10), (14), (15) are so lved iteratively in order to obtain the value of current flowing into the cable andcalculate the value of the resistance, [4]. T he calculation process is terminated when the difference between (k-1)th and (k)th iterations is less than a specified error value. The above method is an experimental method for the converter loss calculations, and generally data f or losses can be obtain ed from the manufacturer. However, in order to theoretically calculate converter losses, many parameters have to be taken into account such as the semiconductor switching losses and modulation index, cooling system losses, building system HVAC and other auxiliary load losses, etc. In [14], the authors present details of the theory behind loss calculations.

C. Energy Unavailability CalculationsThe energy unavailability of each transmission system has

to be calcu lated in order to determine energy cost of each system for finding the most economical system. As stated in [5] and shown by (16), the energy unavailability is defined as the percentage of the energy produced by the wind farm that could not be transmitted as a resu lt of failures in the transmission system (forced outages). In (16), UN is the energy unavailability ratio, ENT is the energy not transmitted, and ET is the energy that could have been transmitted.

The authors in [5] pro posed a v ery applicable assumption for the unavailability calculations. They made the assumption that maintenance outages will have no effect on the calculations, as maintenance is assumed to tak e place during periods of low wind speeds, and thus having very small contribution to the availability of the system. T he energy produced by the wind farm does not follow load but depends on the wind speed. Thus, using the Rayleigh distribution and the aggregate model for the wind farm developed in [5], an algorithm that takes into consideration the special characteristics of the wind farms has been developed in [5].Statistical failure data are used to determine the unavailability of the systems. More details of unavailability calculations can be found in [2] and [5].

T

NTn E

EU (16)

D. Total Investment Cost and Energy Transmission CostThe last step of this analysis is calculating the energy

transmission cost of each transmission system. First, the cost of the components in each transmission system must be determined in order to calculate the investment cost and hence the energy transmission cost. Companies do n ot provide investment costs of their components as they treat this kind of information as co nfidential. However, the total investment cost can be calculated with (17). Cinvest is the total investment paid off in dollars, r is the interest rate, N is the life time of the project in years, Invest is the investment paid today in dollars.

Investr

NrrC

N

N

invest 1)1()1(

(17)

The annual installment for the loan in dollars can be calculated with (18).

Investr

rrR

N

N

1)1()1(

(18)

The amount of the annual energy delivered to the onshoregrid can be calculated with (19). ED is the amount of energy delivered in kWh, Pout.AVG is the average output power from the wind farm (kW), L is the average power losses in the transmission system, T is the operational time of the wind farm, under one year, in hours.

)100

1()100

1(.n

AVGoutD

UT

LPE (19)

The energy transmission cost can be calcu lated with (20). Note that p is the annual profit the company has to make as a percentage. Equations (17) – (20) are found in [5].

pER

CD

trans 100100

(20)

IV. TRANSMISSION TOPOLOGY COST COMPARISONS

The cost estimate results that were obtained by [5] for a 400 MW wind farm are shown in Fig. 5 and 6. Fig. 5 shows that the HVAC cost for a 400 MW w ind farm increases significantly for distances over 150 km, which is expected due to the reactive power losses and the cost associated with reactive power compensation units. The figure also shows that the energy transmission cost of HVDC LCC is less than that of HVAC for distances over 52 k m. HVDC VSC energy transmission cost is s hown to be less th an HVAC for distances over 85km. HVDC LCC transmission cost results obtained by [5] were lower than HVDC VSC for distances from 0 to 300 km.

Fig. 5 Energy transmission cost for 400 MW wind farm and 11m/s wind speed for distances 50-300 km [5]

Fig. 6. Energy transmission cost from Fig. 5 magnified for 50-100 km [5]

V. CONCLUSIONS

The main objective of this article was to summarize the advantages and disadvantages for the three main transmission system topologies for offshore wind applications and to summarize a method for estimating system losses, which ultimately impact the economics of the system. The loss calculation method presented for an HVDC LCC system was approximate, as it is deemed the same as the HVAC method.

The results of the model presented shows that the HVDC LCC system has the lowest energy transmission cost compared to the other transmission systems. However, that model does not take into account the installation cost and the onshore upgrade requirements. The HVDC LCC offshore platform is much larger in size than the HVDC VSC platform. Thus, the installation cost for HVDC LCC platform infrastructure would be significantly higher than the HVDC VSC platform.

Also, integrating large amounts of wind power into the onshore grid would result in stability issues that are u sually solved with adding components onshore to stabilize the system, such as SVCs or STATCOMs. The characteristics of independent active and reactive power control in the HVDC VSC system contributes to a better system stability, thus requiring very small onshore upgrades as oppos ed to the HVDC LCC system where it req uires large amounts of onshore upgrades. Therefore, the expected cost of the onshoreupgrade will be higher in the HVDC LCC system than the HVDC VSC system.

The calculation of the upgrades necessary is a dif ficult task, such that any specific offshore transmission project must be studied in detail, including the onshore grid interconnection considerations. T hese extra costs added to the HVDC LCC system would ultimately make the HVDC LCC energy transmission cost more expensive than the HVDC VSC, which explains the current trend in HVDC VSC systems.

VI. REFERENCES

[1] Kling, W.L.; Hendriks, R.L.; den Boon, J.H.; , "Advanced transmission solutions for offshore wind farms," Power and Energy Society General Meeting - Conversion and Delivery of Electrical Energy in the 21st Century, 2008 IEEE , vol., no., pp.1-6, 20-24 July 2008.

[2] T. Ackermann, N. Barberis Negra, J. Todorovic, and L. Lazaridis, “Evaluation of electrical transmission concepts for large offshore wind farms,” Copenhagen Offshore Wind-Int. Conf. Exhib., Copenhagen, Denmark, October 2005.

[3] Burges, K et al. “Bipolar offshore networks of high capacity for collective wind farm connections” The European Offshore Wind Conference and Exhibition Berlin Germany. January 10th, 2007.

[4] N. Barberis Negra, J. Todorovic, T. Ackermann,” Loss evaluation of HVAC and HVDC transmission solutions for large offshore wind farms”, Electric Power Systems Research, vol.76, no.11, pp. 916-927, July 2006

[5] Lazaridis, Lazaros P.; “Economic Comparison of HVAC and HVDC Solutions for Large Offshore Wind Farms Under Special Consideration of Reliability” Master’s Thesis, Royal Institute of Technology, department of Electrical Engineering, Stockholm, 2005.

[6] Agap, Adelina.; Madalina Dragan, Cristina.; “Multiterminal DC connection for offshore wind farms” Master’s Thesis, Aalborg University, Denmark, 2009

[7] Holttinen H., Norg aard P.,“A Multi-Machine Power Curve Approach”, Nordic Wind Power Conference 1-2, Chalmers University of Technology, Göteborg, March 2004.

[8] Brakelmann H., “Loss determination for long three-phase high-voltage submarine cables”, European Transactions on Electrical Power, vol.13, no. 3, pp 193-198, 2003.

[9] Lundberg, Stefan “Performance Comparison of Wind Park Configuration”, Technical report, Chalmers University of

Technology, Department of Electric Power Engineering,Goteborg, Sweden 2003.

[10] Sharma, R.; Rasmussen, T.W.; Jensen, K.H.; Akamatov, V.; , "Modular VSC converter based HVDC power transmission from offshore wind power plant: Compared to the conventional HVAC system," Electric Power and Energy Conference (EPEC), 2010 IEEE , vol., no., pp.1-6, 25-27 Aug. 2010.

[11] Kong Xiangyu; Jia Hongjie; , " Techno-Economic Analysis of SVC-HVDC Transmission System for Offshore Wind," Power and Energy Engineering Conference (APPEEC), 2011 Asia-Pacific , vol., no., pp.1-5, 25-28 March 2011.

[12] Foster, S.; Lie Xu; Fox, B.; , "Control of an LCC HVDC system for connecting large offshore wind farms with special consideration of grid fault," Power and Energy Society General Meeting - Conversion and Delivery of Electrical Energy in the 21st Century, 2008 IEEE , vol., no., pp.1-8, 20-24 July 2008.

[13] Press releases found at www.siemens.com (last visit April 2012)[14] Liu Yang; Chengyong Zhao; Xiaodong Yang; , "L oss

calculation method of modular multilevel HVDC converters," Electrical Power and Energy Conference (EPEC), 2011 IEEE , vol., no., pp.97-101, 3-5 Oct. 2011.

VII. ACKNOWLEDGEMENTS

The authors would like to extend sincere thanks to the U.S. Department of Energy, Energy Efficiency and Renewable Energy Laboratory (EERE) for their support of this work under the National Offshore Wind Energy Grid Integration Study (NOWEGIS) project, as well as to ABB Inc. and in particular John Daniel of ABB – lead organization and lead investigator of the NOWEGIS program. T hanks also to the other NOWEGIS project partners, including Duke Energy, the U.S. DOE National Renewable Energy Lab (NREL), and AWS Truepower, for all of t heir efforts and contributions to the project.

VIII. BIOGRAPHIES

Gregory F. Reed (M’1985) is the Director of the Electric Power Initiative in the Swanson School of Engineering at the University of Pittsburgh, Associate Director of the University’s Center for Energy, and Associate Professor of Electric Power E ngineering in the S wanson School’s Electrical & Computer Engineering Department. He i s also the Director of the newly established Grid Technologies Collaborative of the DOE National Energy Technology Laboratory's Regional University Alliance; and an inaugural member of the National Academies of

Science and Engineering's Energy Ambassador Program. His research interests, teaching activities, and related pursuits include advanced electric power and e nergy generation, transmission, and distribution system technologies; power electronics and c ontrol technologies (FACTS, HVDC, and MVDC systems); renewable energy systems and in tegration; smart grid technologies and applications; and energy storage. Dr. Reed has over 27 years of combined industry and academic experience in the electric power and energy arena, including engineering, research & development, and executive management positions throughout his career with the Consolidated Edison of New York, ABB Inc., Mitsubishi Electric Corp., and DNV-KEMA. He is an active member of the IEEE Power & Energy Society and the American Society of Engineering Education. Dr. Reed earned his Ph.D, in electric power engineering from the University of Pittsburgh (1997), M.Eng. from Rensselaer Polytechnic Institute (1986), and B.S. from Gannon University (1985).

Hashim Al Hassan (M’2012) was born in Ras Tanura, Saudi Arabia, on July 16, 1987. He graduated from the University of Pittsburgh with a bachelor of science in electrical engineering, concentrating in power systems, and a m inor in m athematics. His work experience included ANSYS Inc. where he worked as a co-op testing engineer for two rotations. He is currently pursuing his master’s degree in electric power engineering at the University of Pittsburgh. His research interest include,

power quality, protection, and control, power system state estimation , HVDC, renewable energy integration, power transmission and distribution systems,and smart grids.

Matthew J. Korytowski (M’2006) was born in E rie, Pennsylvania. Attending the University of Pittsburgh in Pittsburgh, Pennsylvania, he received a Bachelor's degree and MS degree in Electrical Engineering with a Concentration in Electric Power in 2009. He is pursuing a PhD in e lectrical engineering also at the University of Pittsburgh. Matthew is currently focused on research in power electronics and renewable energy integration. He

has interned at ABB performing work in PSCAD on power system simulations and modeling of renewable generation and control. Mr. Korytowski is a student member of the IEEE Power & Energy Society and the Power Electronics Society.

Patrick T. Lewis (S’2011) was born in Pittsburgh, Pennsylvania, in 1989. I n the spring of 2012, he graduated Cum Laude with a Bachelor of Science degree in electrical engineering from the University of Pittsburgh. H e is now currently pursuing his master’s degree also at the University of Pittsburgh, in electrical engineering concentrating in electric power engineering. From fall 2012 through spring 2013, he has been a Graduate Student Researcher with Dr. Gregory Reed as his academic advisor. From January 2010 through

August 2011, he worked three CO-OP rotations within three different departments at Curtiss Wright Flow Control Company. For the summer of 2012, he interned at Mitsubishi Electric Power Products Inc. within their Power System Engineering Studies group (PSES). Hi s research interests include the integration of renewables to the grid, power electronic applications, converter design, HVDC technologies, and power system fault and transient studies. Mr. Lewis is a student member of IEEE Power and Energy Society.

Brandon M. Grainger (S’2006) was born in Pittsburgh, Pennsylvania. Currently, he is pursuing his Ph.D. concentrating in power electronics, microgrids, and medium voltage DC systems at the University of Pittsburgh. Mr. Grainger has a master’s degree in electrical engineering from the University of Pittsburgh with a concentration in electric power engineering and in 2007 graduated Magna Cum Laude

with a bachelor’s degree in mechanical engineering from Pitt. From August 2004 through August 2006, Brandon performed four work rotations with ANSYS. From April 2008 to April 2009, Mr. Grainger interned for Mitsubishi Electric Power Products, Inc, during the summer of 2010 and 2011, with ABB Corporate Research Center in Raleigh, NC, and during the summer of 2012 with Siemens-Robicon in New Kensington, PA. Brandon’s research interests are in power electronic technologies and electric machines,specifically, power electronic converter design, power electronic applications suitable for renewable integration, and FACTS devices. H e is a s tudent member of the IEEE Power & Energy Society, Power Electronics Society, and Industrial Electronics Society.