FACTS & Power Quality Issues

MANJULA NAIR & SINDHU.M.RDEPT OF EEEAMRITA SCHOOL OF ENGINEERING, COIMBATORE

OUTLINE

� PART I – FLEXIBLE AC TRANSMISSION SYSTEMS [FACTS][FACTS]

� PART II – POWER QUALITY ISSUES AND IMPROVEMENT TECHNIQUES

Introduction – Energy Scenario

� Electrical Energy is one of the major building blocks of modern societyof modern society

� Continued depletion of fossil fuels turned attention to renewable energy resources

� Energy, like money, is never ‘sufficient’� World’s energy consumption as on 1998 [1]

– 80% fossil, oil, natural gas, coal– 14% renewable energy– 6% nuclear

Introduction – Energy Scenario

� Global renewable energy resources [1]– Solar = 12,000 – 40,000 TW h / year– Solar = 12,000 – 40,000 TW h / year– Wind = 20,000 – 40,000 TW h / year– Wave, Tidal = 2000 – 4000 TW h / year– Geothermal = 4,000 – 40,000 TW h / year– Biomass = 8000 – 25,000 TW h / year

� Energy scenario in India as in 2005 [1]– World’s 6th largest energy consumer– Major source of electrical energy is coal and petroleum

products– Next comes hydroelectric and nuclear– 4% renewable energy of total grid capacity

OUTLINE – PART I - FACTS

� Why FACTS ?� Why FACTS ?� What is FACTS ?� FACTS Devices

� TSC & TSR� TCSC & TCR� TCPAR & TCBR� STATCOM & DVR� UPFC

OUTLINE – PART I - FACTS

� Digital Controllers for fast operation of FACTSDSP Controller – DSP Controller � Fuzzy Controller� Artificial Neural Network (ANN) Controller

� Lab Models of FACTS Devices (TSC & TCR)� CONCLUSIONS – Part I

Why FACTS ?

� Why we need transmission interconnections? Within Utility, inter-utility, inter-regional, international interconnections? interconnections?

� To pool power plants and load centers so as to minimize total power generation capacity and fuel cost

� Cost and difficulties in building new transmission lines, difficulty to get right-of-way

� Existing transmission grid capacity to be tapped to the brim!

� Most appropriate solution is FACTS technology

What is FACTS ?

� Flexible AC Transmission Systems (FACTS) makes transmission lines ‘ Flexible’ - N.G. Hingorani

� Insertion of controllable L and C elements make the net impedance of transmission line controllable to suit any operating condition

� With fast switching series, shunt, series-shunt compensators

– Real/reactive power control with energy backup– Voltage regulation, PF correction– Phase angle regulation– Maintain power system stability

FACTS DEVICES [2,3]

� Shunt compensator, Series voltage regulator, switched capacitor banks, phase shifter, controlled capacitor / reactor reactor

� Realized using fast acting power semiconductor switches of suitable power rating – thyristors, IGBTs, GTOs

� TSC, TSR, TCSC, TCR� TCPAR, TCBR� STATCOM, DVR, UPFC

Thyristor Switched Capacitor (TSC) & Thyristor Switched Reactor (TSR)

� Fixed value of C switched in/out of system using thyristor switchesthyristor switches

� Fast &reliable switching� PF correction capacitors

and C banks for reactive power compensation

� Thyristor switching selects appropriate Inductor tappings in TSR

Thyristor Controlled Series Capacitor (TCSC)

� Fixed value of C made controllable by varying inductive reactance inductive reactance through firing angle control

� Rapid impedance control� Enhancement of

transmission line capability

Thyristor Controlled Reactor (TCR)

� Variable inductive reactance through firing angle controlfiring angle control

� Variable shunt compensator

Thyristor Controlled Phase Angle Regulator (TCPAR)

� Voltage or Phase angle control using tap changing transformerschanging transformers

� Delay angle controlled thyristor tap changers used

� Fast and smooth control of phase angle achieved for power flow control

Thyristor Controlled Braking Resistor (TCBR) / Dynamic Brake

� Thyristor controlled resistor connected in shunt with line� Prevents transient instability by taking away power

which otherwise accelerates generator� Prevents dynamic instability involving low frequency

oscillations

STATCOM

� PWM Voltage Source Inverter (VSI) using GTOs / IGBTsGTOs / IGBTs

� Shunt compensator –in shunt with line

� Reactive power exchange

� Power Factor improvement

� Voltage regulation� Real power exchange

with battery support

DVR

� PWM Voltage Source Inverter (VSI) using GTOs / IGBTsGTOs / IGBTs

� Series compensator –in series with line

� Reduction of voltage sags, swells, transients

� Fault current limitation� Voltage regulation� Real power exchange

with battery support

UPFC

� STATCOM and DVR connected back-to-back through common back through common DC link capacitor

� Series compensation as well as shunt compensation achieved

� Enhances power transmission capability

� Higher cost

Digital Controllers for fast control of FACTS DEVICES

� Application specific control schemes can be developed and implemented using digital controllersand implemented using digital controllers

� Fuzzy controller is an ideal choice due to its adaptive nature

� Artificial Neural Networks (ANN) based controllers also very effective, adaptive

� DSP controllers or Micro-controllers can implement scheme of control for fast and precise operation of the FACTS devices

Laboratory Models of FACTS Devices developed at AMRITA

� Thyristor Switched Capacitors (TSC)� Thyristor Controlled Reactor (TCR)� Thyristor Controlled Reactor (TCR)� Reactive power Compensation� Voltage Regulation � TSC-TCR combination for smooth control of net

reactance of transmission line� Transmission line model with TSC-TCR

Conclusions – Part I

� How effective are FACTS devices in wind power- grid interconnected systemspower- grid interconnected systems– in maintaining power system stability– for voltage regulation – PF correction – reactive power compensation– Phase angle regulation– Fast operating Shunt / Series/ combined

Compensators

OUTLINE – PART II- POWERQUALITY

� What is Power Quality?Power Quality issues in power systems� Power Quality issues in power systems

� Power Quality issues specific to Wind farms coupled to Grid Power

� Effects of poor Power Quality� Sources of Power Quality problems� Power Quality Standards –IEEE STD 519 1992, 1995

and IEC Standards

OUTLINE – PART II - POWERQUALITY

� Power Quality Improvement TechniquesRetrofit systems– Retrofit systems

– New installations

� Conventional Passive Filtering – merits & demerits� Active Filtering – Shunt & Series Active Filters

� Digital/ Analog Controllers– IRPT, SD, DC Bus, I.CosΦ

OUTLINE – PART II - POWERQUALITY

� Hybrid Filtering – Shunt, Series, UPFCImproved Power Quality Converters [IPQCs]� Improved Power Quality Converters [IPQCs]

� Custom Power Parks� Custom Power Devices [CPDs]� CONCLUSIONS – Part II

What is Power Quality?

� Delivery of High grade Electrical service to Customers� Sinusoidal load bus voltage and current – at stipulated � Sinusoidal load bus voltage and current – at stipulated

magnitude and frequency� Voltage Quality� Current Quality� Involvement – Utility, Equipment Manufacturer and

Customer of Electrical Power

Power Quality Issues

� Voltage Sags and Swells� Voltage TransientsVoltage Transients� Harmonic Distortion� Poor Power Factor� Voltage Spikes, Flicker� Brownouts, Blackouts� EMI, RFI

Power Quality Issues – Specific to Wind Farms coupled to Grid Power [4,5]

� Poor Voltage Regulation� Voltage Spikes� Voltage Spikes� Harmonic Distortion in Line Currents � Harmonic Distortion in Bus Voltages� Poor Power Factor

Effects of poor Power Quality

Effects of poor Power Quality

Effects of poor Power Quality

� Customer Side– Sensitive Loads become susceptible to harmonics– Sensitive Loads become susceptible to harmonics– Computers, Communication devices – malfunctioning, loss of

critical data– Increased losses – de-rating of motors, transformers– Automated processes adversely affected – paper making, chip

making– Malfunction of relays, circuit-breakers– Home electrical and electronics affected – TV, Telephones,

VCRs

Effects of poor Power Quality

� Utility Side– Failure of Power Factor correction capacitors – due to – Failure of Power Factor correction capacitors – due to

resonance– Increased Losses in cables, transformers– Erroneous operation of Energy Meters – calibrated to 50 Hz– Malfunction of Protection Systems – relays, circuit breakers– Malfunction of Remote switching and load control systems

Sources of Power Quality Problems

� Major sources– Static Power Converters – AC/DC, DC/DC, DC/ACStatic Power Converters – AC/DC, DC/DC, DC/AC– Uncontrolled Rectifiers, Phase-angle controlled Rectifiers/

Inverters– Large power converters (metal reduction industry, HVDC)– Medium power converters (DC/AC drives in railways,

manufacturing industry)– Low power converters (single-phase supply in television sets,

battery chargers)– AC Voltage Regulators, Cyclo-converters– Imperfect system conditions (imperfect AC source, firing

asymmetry, control system imperfections)

Sources of Power Quality Problems

� Minor sources– Transformer Magnetization non-linearities– Transformer Magnetization non-linearities– Rotating Machines– Fluorescent Lighting– Arc-furnace

Power Quality Standards –IEEE & IEC Standards

� IEEE Standards for Power Quality Limits– IEEE STD 519 - 1992– IEEE STD 519 - 1992– IEEE STD 519 – 1995– Recommended practices for Utility and Customers

� IEC and other standards– IEC 61000– EN 50160

Power Quality Improvement Techniques

� Retrofit Systems (Existing installations)– Conventional passive Filters– Conventional passive Filters– Active Filters– Hybrid Filters

� New Installations– Improved Power Quality converters (IPQCs)– Single-phase and Three-phase IPQCs

Conventional Passive Filtering

� Tuned LC filters– Single-tuned filters– Double-tuned filters– Auto-tuned filters– Damped filters

� Functions– Reactive power compensation– Elimination of low-order harmonic frequency currents

(to which each filter is tuned)– Power factor correction

Conventional Passive Filtering

� Merits and Demerits– Comparatively low cost– Comparatively low cost– simple design

– Resonance with system impedance, de-tuning– Fixed compensation– Large size– High no-load losses

Active Filtering

� Active Filters– PWM based VSI / CSI– PWM based VSI / CSI– Shunt Active Filters– Series Active Filters

Shunt Active Filter

� Functions– Reactive power

compensationcompensation– Current

harmonic compensation

– Power factor correction

– Unbalanced current compensation

– Voltage regulation

Series Active Filter

� Functions– Reactive power

compensationcompensation– Voltage

harmonic compensation

– Power factor correction

– Voltage regulation

– High Impedance path to harmonic currents

Digital / Analog Controllers

� Control Algorithms – Time domain– Instantaneous PQ Theory (IRPT) by Dr. Akagi– Synchronous Detection (SD) algorithm by C.L.Chen et.al– Synchronous Reference Frame (SRF) Theory by Divan et.al– DC Bus Voltage algorithm by H.L.Jou– I.CosΦalgorithm by the author& Dr. G. Bhuvaneswari IITD

� Control Algorithms – Frequency domain– Using Fourier transformation

� DSP, micro-controller, simple analog circuits– to realize the control scheme

Hybrid Filtering

� Hybrid Filters– Combination of Passive tuned Filters & Active Filters– Combination of Passive tuned Filters & Active Filters– Shunt Hybrid Filters– Series Hybrid Filters– Other configurations

� Low-order voltage / current harmonics eliminated by passive elements

� Rating, Size and Cost of Active filter element thereby reduced

Shunt Hybrid Filter

� Shunt passive + Shunt active

Shunt passive – Shunt passive filter eliminates low order current harmonics

– Shunt active filter does rest of compensation

– Rating, Size & Cost of Active filter reduced

Series Hybrid Filter

� Shunt passive + Series active

Shunt passive – Shunt passive filter eliminates low order current harmonics

– Series active filter does voltage harmonic compensation

– Combined voltage and current harmonic compensation

Other Hybrid Filter Configurations

� Active filter in series with shunt series with shunt passive filter

– Shunt passive filter reduces voltage stress on active filter switches

– Higher voltage applications

Unified Power Flow Conditioner (UPFC)/ Unified Power Quality Conditioner (UPQC)

� Series Active + Shunt Active

– Shunt active filter for current for current harmonic compensation and reactive power compensation

– Series active filter for voltage harmonic compensation and voltage regulation

Unified Power Flow Conditioner (UPFC)/ Unified Power Quality Conditioner (UPQC)

Improved Power Quality Converters (IPQCs)

� Rating of active filters close to rating of loadActive filtering made inherent part of improved AC-DC � Active filtering made inherent part of improved AC-DC converters

� Improved converters (IPQC) used in new installations � Single-phase IPQCs� Three-phase IPQCs

Single -phase IPQCs

� Unidirectional converters� Bi-directional convertersBi-directional converters� Buck converters� Boost converters� Buck-Boost converters� Multi-level converters� Matrix converters� Fly-back, Forward, Push-pull, Half-bridge, Bridge,

SEPIC, CUK, Zeta

Three-phase IPQCs

� Unidirectional & Bi-directional converters� Buck & Boost converters� Buck & Boost converters� Buck-Boost converters� Multi-level converters� Multi-pulse converters� Matrix converters� Fly-back, Forward, Push-pull, Half-bridge, Bridge,

SEPIC, CUK, Zeta

Custom Power Parks

� Commercial power companies/ power industrial parks� Buy Grid quality power, install various FACTS devices

such as STATCOM, DVR, UPQC, SSTS, SSB, SSCLsuch as STATCOM, DVR, UPQC, SSTS, SSB, SSCL� Provide high quality, regulated, uninterrupted, steady

and clean electrical power to customers at higher costs

� Customers of Custom Power Parks– High precision process industry – DVR with energy backup to

overcome voltage sags/swells/transients– Large industrial installations/ computer firms need

uninterrupted, regulated, PF compensated power – STATCOM with energy storage, SSB to isolate loads from network faults

Custom Power Devices - CPDs

� Static Compensator (STATCOM)– Voltage regulation through reactive power compensation– Current harmonic compensation– Current harmonic compensation– Uninterrupted power supply with energy storage– Reactive power control

� Dynamic Voltage regulator (DVR)– Voltage regulation through reactive power compensation– Voltage harmonic compensation– Fault current limiting– Overcome voltage sags/swells/transients with energy storage

� Unified Power Quality conditioner (UPQC)– Combines functions of STATCOM and DVR

Custom Power Devices - CPDs

� Solid State Breaker (SSB)– Instantaneous current limiting– Fault current limiting– Fault current limiting

� Solid State Transfer Switch (SSTS)– Protects loads of the park from dynamic over-voltages and

voltage dips– Rapid load transfer

� Solid State Current Limiter (SSCL)– Limits fault current by injecting high impedance to flow of

current

Conclusions – Part II

� Power Quality limits / standards to be strictly followed in wind power- grid interconnected systems

– Voltage harmonic limits, Current harmonic limits, %THD limits within IEEE/IEC standards

– Strict Voltage regulation and control over voltage transients– Active Filters and Hybrid Filters with fast digital control is an

appropriate solution to existing installations– IPQC AC-DC converters are a better choice for new

installations– Research going on in the area of power quality improvement in

wind power-grid interconnected systems

Reference

[1] G.N. Tiwari & M.K. Ghosal, Renewable Energy Resources, Narosa Publishing house, New delhi, India,2005.(Book)

[2] N.G. Hingorani & L. Gyugyi, Understanding FACTS, IEEE Press, [2] N.G. Hingorani & L. Gyugyi, Understanding FACTS, IEEE Press, 2000.(Book)

[3] C.M. Bhatia, Power Quality, Study material from site- www.e-shikshalaya.com.

[4] L.H. Hansen et.al, Conceptual survey of generators and power electronics for wind turbines, Riso National laboratory, Denmark, Dec.2001.

[5] Papathanassiou S.A.,& Papadopoulos M.P, Harmonic analysis in a power system with wind generation, IEEE Tran. on Power Delivery, vol.21(4), Oct.2006, pp.2006-2016.

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