Overview of Actuation Thrust

Transcription

1 Overview of Actuation Thrust Fred Wang Thrust Leader, UTK Professor ECE 620 CURENT Course September 13, 2017

2 Actuation in CURENT Wide Area Control of Power Power Grid Grid Measurement &Monitoring HVDC Storage PMU FDR WAMS Communication Communication Solar Farm Actuation Wind Farm PSS Responsive Load FACTS Generator 2

3 Actuation Technology Linkages Engineered Systems Hardware Testbed Testbeds Monitoring Modeling Large Scale Testbed Control Actuation Enabling Technologies Situational Awareness & Visualization Estimation Communication & Cybersecurity Control Design & Implementation System-level Actuation Functions Fundamental Knowledge Wide-area Measurements Modeling Methodology Control Architecture Economics & Social Impact Actuator & Transmission Architecture 3

4 Basic Actuation Functions in Power Systems Power flow control Voltage and var support Stability Protection Separation Fault current limiting Overvoltage suppression Energy source and load grid interface 4

5 Power Flow Control Power flow is determined by Kirchhoff's Laws, e.g. G1 G2 P V V = X ( δ ) sin 1 δ 2 12 V 1 P D1 P G1 P 1 P G2 P 2 V 2 P D2 V 3 P G3 P D3 G3 5

6 Non Power Electronics Power Flow Actuators Voltage Generators (exciter control - PE) Switched shunt capacitor banks Transformer tap changer Impedance Switched lines Series compensation (switched series capacitors) Angle Phase-shifting transformers 6

7 Example of Phase-shifting Transformers A direct, symmetrical PST with limited range and voltage magnitude change. There are also other types (e.g. indirect PST) 7

8 Non Power Electronics Voltage & Var Actuators Generator (exciter) Condenser Switched capacitor banks Transformer tap changer Load management 8

9 Non Power Electronics Actuator for Stability Generator Governor Power system stabilizer (excitation) Switchgear Line switching Source and load switching Switched compensators Reactors Capacitors 9

10 Protection - Breakers Live-tank breakers Dead-tank breakers 10

11 Breaker with Switching Resistors Switching resistors Must absorb energy during switching => shorted after several ms! 11

12 Overvoltage Protection Spark Gaps Metallic electrodes providing a gas insulated gap to flash over Very robust, but large variance in protection level Magnetically blown Surge Arresters Same basic principle as spark gaps, adopt SiC varistors but can handle much higher energy dissipation Metal Oxide Varistor (MOV) Ceramic composites based on zinc, bismuth, and cobalt Highly non-linear current-voltage characteristic Very precise and stable protection level Limited overload capability I = V α α > 20 12

13 Metal Oxide Varistor (MOV) peak voltage continuous operating voltage 13

14 Power Electronics Based Power Flow Control V 1 /δ 1 P V 2 /δ 2 Power flow ~ = = ~ P = V 1 X V 12 2 δ δ sin ( 1 2 ) + P HVDC Static Var Compensation (SVC) Series Compensation (SC) Phase Shifting Transformers 14 FACTS = Flexible AC Transmission System HVDC and HVDC Light

15 Power Electronics Power Flow Actuator Voltage SVC (Static Var Compensator) STATCOM (Static Synchronous Compensator) Impedance TCSC (Thyristor Controlled Series Compensator) SSSC (Static Series Synchronous Compensator) Angle All TCPFT (Thyristor Controlled Phase-shifting Transformers or Angle Regulator) HVDC UPFC (Unified power flow controller) 15

16 Thyristor Controlled Series Capacitor (TCSC) A capacitive reactance compensator which consists of a series capacitor bank shunted by a thyristor-controlled reactor in order to provide a smoothly variable series capacitive reactance. Can be one large unit or several small ones. Limits fault current when reactor is fully on. AC Capacitor Line Reactor Thyristor valve 16

17 STATCOM and SSSC A static synchronous generator operated without an external electric energy source Can be shunt or series connected As a shunt compensator, can inject reactive power As a series compensator, its voltage is in quadrature with, and controllable independently of, the line current for the purpose of increasing or decreasing the overall reactive voltage drop across the line and thereby controlling the transmitted electric power. Line Interface Energy storage Transformer Converter 17

18 Unified Power Flow Controller The UPFC, by means of angularly unconstrained series voltage injection, is able to control, concurrently or selectively, the transmission line voltage, impedance, and angle or, alternatively, the real and reactive power flow in the line. The UPFC may also provide independently controllable shunt reactive compensation. AC line Coupling Xfmr Coupling Xfmr DC link Shunt VSI STATCOM SSSC Series VSI 18

19 HVDC Technology Development Mercury Arc Valve HVDC (Phased out) Thyristor Valve HVDC Classic IGBT (Transistor) Valve HVDC Light Year Pros: Low losses Cons: Reliability Maintenance Environment Pros: Reliable Scalable Cons: Footprint Pros: Controllability Footprint DC Grids Cons: Losses 19

20 800 kv DC for long distance bulk power transmission Tranmission of 6000 MW over 2000 km. Total evaluated costs in MUSD Number of lines: MUSD kv AC 500 kv DC 800 kv DC Losses Line cost Station cost Right of way ~300 ~ 120 ~ 90 (meter) 20

21 Power Electronics Actuator for Stability 1 st Thyristor-Controlled Series Compensation (TCSC) Project 21

22 Power Electronics Actuator for Protection 22

23 VSC HVDC DC Fault Protection Solution Fast fault clearance solution (<5 ms) ABB method: Hybrid DC breaker Fast disconnector Auxiliary DC breaker Disconnect switch Main DC breaker 23

24 Summary of Actuation Technologies Traditional non power electronics based actuators have limited actuation capability. The system is generally not very flexible PE based actuators (FACTS, HVDC) can be very effective for Power flow control Voltage and var control System stability Protection Interface of source and load Issues: cost, reliability Solutions: new PE technology, modular approach, hybrid approach, different architecture 24

25 Modular Approach - Distributed FACTS Distributed Series Static Compensator 25

26 Modular Converters for Multi-Terminal HVDC Systems Modular multilevel converter (MMC) P C sub + L arm L arm L arm A B C L arm L arm L arm N 26

27 Hybrid Approach - Thin AC Converter 27

28 Actuation Thrust Objectives and Challenges Objectives Develop actuation methodology and system architecture that will enable wide-area control in a transmission grid with high penetration of renewable energy sources Challenges 1) Lack of cost effective wide-area system-level actuators 2) Lack of global actuation functions for the existing actuators or lack of knowledge how to use these actuators for global functions 3) System architecture not best suited for wide-area coordinated actuation and control for network with high penetration of renewable energy sources 4) Lack of design and control methodologies for systems with power electronics converters interfacing a high percentage of sources and loads 28

29 Technical Approaches and Research Focus Multifunctional actuators to exploit full capabilities of existing or future actuators Renewable energy sources supporting system control FACTS, HVDC Flexible and controllable transmission architecture Hybrid AC/DC Multi-terminal HVDC 29

30 Renewable Energy Sources for Grid Support Objective: Demonstrate grid supporting capability of renewable energy sources and energy storage in systems with >50% of renewables Accomplishments: Renewable energy sources and energy storage working modes implemented in simulation & HTB 30

31 Frequency Support Function Test in HTB Scenario 80% renewable by onshore wind & offshore wind through HVDC Event triggered by a HVDC converter failure. Frequency and voltage support from onshore wind farm and the HVDC converters Curtailment and voltage mode control when necessary Integration of energy storage to further enable grid support controls Wind Turbine Active Power (p.u.) Area Frequency (Hz) Time (s)

32 Design of Renewable Interface Converters Considering Stability Objective: Develop stability criterion and design methodology of renewable interface converters to ensure stable operation of multi-bus systems with renewable energy sources. Grid-Connected Radial-line Renewable System Stability PV Grid V g + Check at PCC Z g Z g i g (v PCC ) PCC Check at Bus 2 Y PCCR Check at Bus 3 i L1 Wind turbine Check at Bus 1 Z 1 Y B1R Z 1 Y oc1 i 1 (v 1 ) G I * clc1 1 Z 2 Z 2 Y oc2 Y B2R i 2 (v 2 ) G I * clc2 2 Z 3 Y oc3 Z 3 Bus 1 Bus 2 Bus 3 i L2 i L3 Checking sequence Y oc3 i 3 (v 3 ) Inverter 1 Inverter 2 Inverter 3 G I * clc3 3 Phase margin ϕm [deg] Bus 3, λ 1 (T m_b3 ) Bus 2, λ 1 (T m_b2 ) Stable case Unstable Stable Bus 1, λ 1 (T m_b1 ) PCC, λ 1 (T m_pcc ) Unstable case Voltage-feedforward ω ff [Hz] 32

33 Hybrid AC/DC Transmission Objective: Upgrade existing AC lines to hybrid AC and DC lines, to expand the power transmission capability HVAC HVDC Hybrid AC/DC V(t) AC AC V DC AC AC Neutral AC 2V g 0 t I(t) I DC V DC I DC DC A DC 2I g 0 t 33

34 Basic Concept of Hybrid AC/DC System System topology: AC Bus CB1 Transmission Line CBx L X CBy AC Bus CB2 CB3 I dc V dc CB4 LCC Station LCC Station CB5 I dc V dc CB6 DC injection link: zigzag transformer A 1 L X CB7 CBx CBy CB8 AC Bus Transmission Line AC Bus a 2 a N a 1 B 1 b 2 b b 1 C 1 c 2 c c 1 34

35 Benefits and Issues Benefits: A lower cost solution for increased power transfer and improved stability Cost of H ybrid AC/ DC over H VDC Balance 1% Unbalance 2% Unbalance 3% Unbalance 4% Unbalance Cost of H ybrid AC/ DC over H VDC Balance 1% Unbalance 2% Unbalance 3% Unbalance 4% Unbalance Cost Ratio 1 Cost Ratio The Same power angle limit Power angle limit increase from 30 to Power Increasing (Base:P H VAC ) Issues: Zigzag transformer may be saturated with unbalanced AC line resistance, due to the uncanceled DC flux within zigzag windings. Neutral point of zigzag transformer needs extra insulation to withstand dc bias voltage Power Increasing (Base:P H VAC )

36 Active Unbalance Mitigation Method 3: Hybrid line balance control Immunity to unbalance Low voltage rating, no insulation issue Active impedance with low loss With extra converter cost, but low compared to main HVDC converters Hybrid line impedance conditioner: L f C L Hybrid line C i a Adjust the line resistance by phase. Can be enabled or bypassed I dc Same core L f L f C C L L C C i b i c R V I AC / DC = AC / DC VDC I DC 3 Bidirectional Active Hybrid Line Impedance Conditioners (Two conditioners are active, at the most) 36

37 Line Length Impedance Conditioner Design and Simulation System Parameters 650km L f C L C i a Impedance Unbalance 5% Line voltage (phase) Line current Transmission Power Inverter AC voltage DC link voltage DC link Capacitance Rectifier AC voltage Zigzag transformer windings 0.035Ohm/km mH/km AC: 115 kv; DC 180 kv AC: 612A, DC: 1000A 729 MW (189 AC and 540 DC) 3.183kV(peak) 3.617kV 3300uF kv(peak) balance design + conditioner winding (170/138/138/3) 5K 4K 3K 2K Vdc Ia Ib Ic Ia_dc Ib_dc Ic_dc Ia Vxa Time (s) 37 I dc Conditioner enabled at 0.6s. Control reference goes from zero to the desired impedance.

38 Magnetic Amplifier Controller 38

39 Magnetic Amplifier Controller 39

40 Magnetic Amplifier Controller AC Winding Reactance (Ω) ac 1500A ac 1000A ac 750A ac 500A ac 250A

41 Multi-terminal HVDC Modeling & Control Area 1 (NYISO) G Area 2 (ISO-NE) G3 L7 C7 C9 L9 2 G2 4 G4 L12 L13 Area 3 (Load Center) VSC 4 VSC 3 DC cable VSC 2 VSC 1 Area 3 (MTDC) Wind 41 Farm II Wind Farm I

42 Multi-Terminal HVDC Testbed Objective: Build a hardware platform for MT-HVDC system operation/control/protection development and demonstration System Structure Onshore I Cable 1 Offshore I PCC 1 Wind emulator I MTDC Testbed Hardware Cable 4 Cable 3 PCC 2 Cable 2 Onshore II Offshore II Wind emulator II Testbed Capability on Scenario Emulation: System start-up Station online recommission Wind farm power variation Station outage Transmission line trip Station online mode transition 42

43 MT-HVDC Testbed Interface 43

44 VSC HVDC DC Fault Protection A CURENT Proposed Solution P L arm L arm L arm Proposed + + C sub C sub In case of DC short circuit fault + + C sub C sub AC grid (a) L arm L arm L arm + + C sub C sub N Normal operation (b) + + C sub C sub Two half-bridge sub-modules + + C sub C sub (c) 44

45 Smart and Flexible Microgrid System control Local protective devices Local controllers Normal open smart switch Normal closed smart switch PCC Microgrid central controller PCC PCC Electrical network Communication and control network 45

46 Conclusions Actuation thrust provides essential technology for wide-area coordinated control, and directly supports the CURENT systems. Thrust research focuses on multifunctional actuators and flexible architecture. 46