1 Analysis of an Offshore Medium Voltage DC Microgrid Environment – Part I: Power Sharing Controller Design Brandon M. Grainger, Velin Kounev, Gregory F. Reed, Thomas E. McDermott, David Tipper and Zhi-Hong Mao University of Pittsburgh Pittsburgh, PA USA 2 Background and Motivation • The U.S. Department of Energy has found great interest in exploring the integration of offshore wind and has funded a team (including ABB Grid Consulting & Pitt) to determine the optimal location for placing large wind turbines around the U.S. perimeter. • The directions that many manufacturers are exploring with offshore technologies to harness and transmit electric power provides further encouragement that the direction towards offshore is viable. 3 Coupled Renewable Generation and Industrial Environment through DC Backbone Wind Generation (Off-Shore) 5 MW Supply AC / DC Three Level Multilevel Rectifier (NPC) PMSG Based MVDC Collection Platform + DC Cable 5 MW Supply PMSG Based ~ ~ -~ ~ ~ ~ DC / DC Converter DC Cable MPPT Enabled AC / DC Three Level Multilevel Rectifier (NPC) - DC Cable 5 MW Supply PMSG Based + Breakers MPPT Enabled AC / DC Three Level Multilevel Rectifier (NPC) Off-Shore Oil Drilling Platform - DC Cable DC / DC Converter DC Cable MPPT Enabled 5 MW Supply AC / DC Three Level Multilevel Rectifier (NPC) PMSG Based MPPT Enabled DC Cable DC / AC Three Level Multilevel Inverter (NPC) Voltage Regulator AC Cable #1 #2 M M M M M M Diesel Generator 4 Microgrid Challenges Fundamental Requirements of Microgrids (1) Capability of operating in islanding and/or grid connected modes with high stability (2) Mode switching with minimum load disruption and shedding during transitions (3) After a transition, stabilize in a certain amount of time Technical Challenges of Microgrids (1) Operation modes and transitions that comply with IEEE1547 (2) Control architecture and communication Research Challenges of Microgrids (1) Operational inverter improvements (harsh environment design, robust operation during fault conditions, improved overload, volume and weight reduction, etc). (2) Integrated storage inverter & direct medium voltage inverter design (3) These components are extremely important but protection is also one of the most important challenges facing the deployment of microgrids. 5 Power Management Strategy Off-Shore Oil Drilling Platform + I1 DC Cable DC / DC Converter ɸ1 DC I2 DC Cable DC / DC Converter ~ ~ -~ ~ ~ ~ Primary Control on Each of the Units M M M M M M Diesel Generator Power flow adjustment for DC/DC Converters ɸ2 (Imeasured)=0 DC/DC Converter Power Sharing and Power Management Scheme Islanded Condition Imeasured,1 Pmeasured,1 (X1,X2,X3) Σ kα OR Grid Connected N-Motors OPEN LOOP Poptimal,1 (X1,X2,X3) Imeasured>0 Equation (2a) P kβ (Imeasured)=0 Imeasured,N ɸ2 PI ɸ1 PI ɸ2 PRef,1 kα CLOSED LOOP kβ kα Pmeasured,total PRef,2 + Grid Connected Pmeasured,N (X1,X2,X3) OR Poptimal,N (X1,X2,X3) Equation (2a) + Islanded Condition ɸ1 nVLVH d h (1 d h ) 2 fL - Grid Connected / Islanded Condition For this case, red breakers resemble a mode transition occurrence - Machine Line Current Entering - Imeasured>0 kβ Pmeasured,total 6 Representative Results as System Transition Occurs 3 Lm Te 2 1 r 0.14 X: 29.51 Y: 0.147 X: 38.4 Y: 0.1101 0.12 0.1 0.08 0 Mechanical Power (W) DC/DC Duty Cycle 0.16 2 x 10 10 20 30 Time (seconds) 40 50 6 X: 30.46 Y: 5.458e+05 1 X: 37.55 Y: 4.265e+05 0 -1 0 10 20 30 Time (seconds) 40 50 Magnetization Current (A) nV1V2 d h (1 d h ) 2 fL Quadrature Axis Current (A) P imr isq 500 Imr Imrref 250 0 -250 -500 0 10 20 30 Time (seconds) 40 50 3000 I sq 2000 I sqref 1000 0 -1000 0 10 20 30 Time (seconds) 40 50 7 Concluding Remarks • Microgrid challenges and opportunities were addressed with practical scenario described. • Preliminary controller design for managing power within the microgrid was evaluated. • This work primarily focused on the electrical engineering analysis. Part II focuses on the communication framework (coming next!) • Thanks to our corporate sponsor, ABB Corporate Research, for funding these efforts. • See those who are interested at the poster session. 8 Contact Information Dr. Gregory Reed Professor of Electric Power Engineering, ECE Dept. Director, Electric Power & Energy Initiative Associate Director, Center for Energy Swanson School of Engineering University of Pittsburgh E-mail: [email protected] Brandon M. Grainger Richard K. Mellon Graduate Student Fellow PhD Candidate Swanson School of Engineering University of Pittsburgh E-mail: [email protected]
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