Modern Trends in Power Electronics & Electric Drives Prof. Sujit K. Biswas Dept. of Electrical Engg. Jadavpur University Kolkata 700032, INDIA

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“Power Electronics” can be considered as : “The technology associated with the conversion, control and conditioning of electric power from its available form to the desired electrical form, by the application of electronics”

Dept. of Electrical Engg, Jadavpur University, Kolkata

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Why Power Electronics ? • Power Electronics is one of the fastest changing technology today, having gone through dynamic changes in the last several decades • The solid state era, which has accelerated automation in industry, has led to increased R&D in Power Electronics, in order to meet the demands of increased productivity and improved product quality • The technologies involved have been going through constant change, depending on the demands of its diverse and ever-expanding application area • Today, significant developments in non-power-electronics areas are catalyzing spontaneous development in power electronic converters for those specific areas • The future of Power Electronics is truly multi-disciplined and multi-solutioned in nature Dept. of Electrical Engg, Jadavpur University, Kolkata

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Importance of Power Electronics • Conversion of electrical energy from one form to another of choice. • Smooth control of electrical power flow. • High efficiency involved in the above processes. • High speed of response • Permits controlled storage of energy for use when required • High reliability of the controlling system. • Compact size of the controlling system. Dept. of Electrical Engg, Jadavpur University, Kolkata

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Power Control Methods • Control through Electro-Mechanical Power Components. • Control through Magnetic Power Components. • Control through Magnetic and ElectroMechanical Power Components. • Linear Control through Semiconductor Power Components. • Phase Control through Semiconductor Power Components. • Switching Control through Semiconductor Power Components. Dept. of Electrical Engg, Jadavpur University, Kolkata

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Power Control Elements • • • • •

Gas-filled Tubes Mercury-arc Tubes Magnetic Amplifiers Electro-mechanical Elements Solid State Devices

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Solid State Semiconductor Era • 1948 - Invention of the ‘Transistor’ • 1956 - Commercial availability of the Silicon Diode • 1958 - Commercial availability of the Silicon Controlled Rectifier (SCR) (a member of ‘thyristor’ family). The term ‘Thyristor Technology’ introduced • 1960’s – ‘High frequency’ (about a kHz) switching techniques using forcedcommutation introduces PWM Dept. of Electrical Engg, Jadavpur University, Kolkata

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Modern Power Semiconductor Devices • Early 1970’s - Toshiba Corporation of Japan introduced high power rated ‘Giant Transistors’ • Late 1970’s - ‘Power MOSFET’s’ was released in by International Rectifier of USA • Early 1980’s - Gate Turn Off Thyristor (GTO) was released by Japanese companies • Mid 1980’s - Insulated Gate Bipolar Transistor (IGBT) released by General Electric of USA • Mid 1990’s - Integrated Gate Commutated Thyristor (IGCT) from ABB, Sweden Dept. of Electrical Engg, Jadavpur University, Kolkata

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Developments in High Power Semiconductors • Insulated Gate Bipolar Transistors (IGBT): 1.2kV, 1400A to 6.5kV, 750A • Integrated Gate Commutated Thyristors (IGCT): 4.5kV, 2100A to 6.5kV, 1290A • Gate Turn Off Thyristors (GTO): 2.5kV, 3000A to 4.5kV, 4000A

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Power Converters • High frequency (above 20 kHz) Switching Power converters developed since 1970’s • Awareness of line harmonics and power factor due to converters. • Static VAr compensators used • Active Power Filters developed • Power converters to meet ‘Power Quality’ standards • ‘Soft’ switching technique introduced Dept. of Electrical Engg, Jadavpur University, Kolkata

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Developments in High Power Converters • High efficiency inverters with sinusoidal output voltages and currents • High performance Bi-directional power converters with capability for connection to the AC grid • High efficiency, Bi-directional DC to DC power converters for controlled energy storage and retrieval • FACTS devices with low THD current and smooth operation Dept. of Electrical Engg, Jadavpur University, Kolkata

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Active Power Factor Technology 1

2

Vs DC Bus to Converter

AC Supply

is

Control

• Permits control of ac side current waveshape • DC bus voltage is higher that peak line voltage • Short circuit protection on dc side is not possible Dept. of Electrical Engg, Jadavpur University, Kolkata

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Bidirectional Active Power Factor Corrected Converter

• • • • •

Permits control of ac side current waveshape Permits power flow in both directions Permits control of the VAr flow DC bus voltage is higher that peak line voltage Short circuit protection on dc side is not possible Dept. of Electrical Engg, Jadavpur University, Kolkata

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3-phase Bidirectional Power Converter

• • • • •

AC side voltage is PWM with a fundamental content of same frequency as the supply AC side current waveshape is nearly sinusoidal Permits power flow in both directions Permits control of the VAr flow DC bus voltage is higher that peak line voltage Dept. of Electrical Engg, Jadavpur University, Kolkata

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Control of Bidirectional Converter

CONVERTER

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PWM Output Waveform Generation & Control +Vd/2

S3

S1

Vd/2

+

Vd

N S4

 VO

S2

- Vd/2

•

• •

Vd/2

Each limb mid-point (or pole) is to be either connected to the top bus or the bottom bus and cannot be left free Pulse width modulation is generated by shifting the operation of the limbs in time (phase shifting) Zero voltage durations are ensured by short circuiting the load through the switches Dept. of Electrical Engg, Jadavpur University, Kolkata

Vd

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Single Phase Output +Vdc

+Vdc

O

a

0V

Phase shift between the outputs is 180deg for maximum fundamental voltage

b

O

0V

+Vdc

a

VaO O

a

b

O

VL

VbO 0V

b

Dept. of Electrical Engg, Jadavpur University, Kolkata

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Three-Phase Output +Vdc

+Vdc

O

a

0V

+Vdc

b

O

0V

c

O

Phase shift between the outputs is 120deg for balanced fundamental voltage

0V

+Vdc R

O

a

b

VaO

c

VcO O VbO

B 0V

Y

VLL

Dept. of Electrical Engg, Jadavpur University, Kolkata

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Conditions when Bidirectional Converter does not Exchange Average Power on DC side • When ac supply voltage is sinusoidal and current is also sinusoidal of same frequency, but displaced by 90 deg • When ac supply voltage is sinusoidal and current is also sinusoidal but at harmonic frequency This implies that there is no need of energy source or energy receiver on dc side and a capacitor, charged up to the requisite dc voltage will be sufficient for the operation, neglecting circuit losses Dept. of Electrical Engg, Jadavpur University, Kolkata

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Principle of Operation of Grid Connected Bidirectional Converter X V

E

I

E

I.X V

I

V

I E

Rectification

I.X

Inversion

Dept. of Electrical Engg, Jadavpur University, Kolkata

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Grid Connected Wind Turbine using Doubly Fed Induction Generator

Dept. of Electrical Engg, Jadavpur University, Kolkata

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Wind Turbine

Grid

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Photo Voltaic Cell fed Solar Power Generation System with Storage

SPV

BiInverter directional Converter

MPPT Converter

Grid Switch

Battery

Dept. of Electrical Engg, Jadavpur University, Kolkata

Load

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Active Power Filter Fundamental Current

Distorted Current

SUPPLY Source Impedance

Sinusoidal Distorted Voltage

LOAD (Generating Harmonics)

Harmonic Current

ACTIVE POWER FILTER (Static Power Converter)

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Example of Active Power Filter

~ ~ ~ 4-Wire 3-Phase AC Mains

isa

iLa

isb

iLb

isc

iLc iLn

isn

icn icc

Non-Linear Four-Wire Unbalanced Loads

icb

ica

a

b

c

Cdc n

AF

Dept. of Electrical Engg, Jadavpur University, Kolkata

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Static VAr Compensators using Thyristors

Load

TCR

TSC

TSC

TSC

TSC = Thyristor Switched Capacitor  Provides leading VAr adjustment in steps TCR = Thyristor Controlled Reactor  Provides lagging VAr adjustment smoothly Capacitors may be replaced by tuned LC circuits for filtering of current harmonics also. Dept. of Electrical Engg, Jadavpur University, Kolkata

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Principle of Thyristor Controlled Reactor Line voltage Inductor Current

α = Conduction angle β = Extinction angle Cosα = Cosβ or β = 2π - α Current waveform is continuous only when α = π/2 Dept. of Electrical Engg, Jadavpur University, Kolkata

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Basic Principle of STATCOM

• A 3-ph inverter can supply reactive power • Output voltage is PWM with a fundamental content of same frequency as the supply • Required to provide energy for the losses only, thus dc bus can have capacitor only Dept. of Electrical Engg, Jadavpur University, Kolkata

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Example of DSTATCOM isa 3-Phase 4-Wire AC Mains

isb isc

ila ilb ilc

iln

iln

icc

icb

ica Lf,Rf

S1

S3

ila ilb ilc

Linear/ Non-Linear Loads

iln

S5

Cdc +

-

icn

Vdc S4

S6

S2

+ -

DSTATCOM

Dept. of Electrical Engg, Jadavpur University, Kolkata

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Multi-Level Inverters and Converters Van vx1



2

vx2



3 2

2

V x5

Vx4

Vx3 Vx2 vxn

Vx1

Dept. of Electrical Engg, Jadavpur University, Kolkata

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• • • •

Power Electronically Controlled Storage of Energy

Battery Storage System Hydrogen Storage System for Fuel Cells Super Capacitor Storage System Superconducting Magnetic Energy Storage System

Dept. of Electrical Engg, Jadavpur University, Kolkata

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Technology Development for Adjustable Speed Drives • Mechanical and Electro-mechanical speed variation methods were popular as motors were considered as fixed speed devices. • DC motors and Brush shifting motors bring in the era of mechanically adjustable speed motors. • The DC motor becomes the first electrically controlled drive since 1920’s using Phase Controlled Rectifier. • The Synchronous motor is an alternative since 1930’s using Phase Controlled Cyclo-converters. • The Squirrel Cage Induction motor, the known rugged alternative since 1930’s, becomes the preferred option only since the late 1960’s. Dept. of Electrical Engg, Jadavpur University, Kolkata

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Reasons for Induction Motor being the Preferred Alternative • Rugged and maintenance-free. • Lesser size, weight and cost for same hp. • Superior operating characteristics. • Can be operated in inflammable environment. • Can be made to be totally enclosed for hazardous and corrosive environments. • No need for separate dc power supply to field. Dept. of Electrical Engg, Jadavpur University, Kolkata

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Reasons for Induction Motor Drives being the Preferred Alternative • The solid state era, which had accelerated automation in industry, had led to increased R&D in order to meet its dual demands of increased productivity and improved product quality. • ‘High frequency’ (about a kHz) switching techniques using forced-commutated SCR’s introduces PWM for easy power control in 1960’s. • New methods of motor analysis and control brings in high performance induction motor drives in 1970’s. Dept. of Electrical Engg, Jadavpur University, Kolkata

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Landmark Large Power Equipment • 1930 - The New York subway installed a 3MW grid-controlled mercury arc rectifier for dc drive • 1931 - German Railways introduce mercury-arc grid-controlled Cycloconverters for traction drive of Universal motors • 1934 - The first variable frequency ac drive was installed at Logan Power Station, USA, for a 400hp synchronous motor used in ID fan drive, using thyratrons Dept. of Electrical Engg, Jadavpur University, Kolkata

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The Induction Motor as an Adjustable Speed Drive

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Rotational Movement from Linear Movement Magnet being attracted

Magnet being attracted

Magnet being moved

LINEAR MOTION

Magnet being moved

Dept. of Electrical Engg, Jadavpur University, Kolkata

CIRCULAR MOTION

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The Equivalent Circuit of an Induction Motor R1

V1

Ns = 60*f1/p

X1

X2

Xm

E1

Ro

R2/s

V2

Im = E1/Xm = (E1/f1)/(2*pi*Lm)

Dept. of Electrical Engg, Jadavpur University, Kolkata

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Induction Motor Characteristics under Adjustable Speed

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Principle of Space Vectors

Dept. of Electrical Engg, Jadavpur University, Kolkata

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3-phase Components of Space Vector

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Projection on Multiple Reference Frames

X = Xd + jXq in synchronously rotating d-q reference frame. = X.e jθd in fixed stator axes = X.e j(θd-θr) in reference frame fixed to rotor Dept. of Electrical Engg, Jadavpur University, Kolkata

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Induction Motor Drive System

Dept. of Electrical Engg, Jadavpur University, Kolkata

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Vector Controlled Induction Motor Drive

Dept. of Electrical Engg, Jadavpur University, Kolkata

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PWM Waveform fed to Motor Drives

• • •

Problem of harmonics that cause additional loss and hence thermal de-rating of motor. Problem of Travelling wave in cable, that generates higher voltages at motor that damage its insulation. Problem of Common-mode current flow through the motor bearings that damage them. Dept. of Electrical Engg, Jadavpur University, Kolkata

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The Harmonic Equivalent Circuit of an Induction Motor Rn1

V1n

nX1

nX2

nXm E1n

Ron

Dept. of Electrical Engg, Jadavpur University, Kolkata

Rn2/sn

V2n

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Multi-level Inverter Drive System IM

P hase A

H-Bridge cell -I

T11

Phase C

Phase B

T31

T41

T21

T32

T12

T42

T22

N

H-Bridge cell -II

Stator Voltages (V)

500

0

Stator Currents (A)

-500 0.24

0.245

0.25

0.255

0.26

0.265

0.27

0.275

0.28

0.285

0.29

0.28

0.29

20 0 -20 0.21

0.22

0.23

0.24 0.25 Time (Sec)

0.26

Dept. of Electrical Engg, Jadavpur University, Kolkata

0.27

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Multi Phase Induction Motor Drives

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Space Vector Modulation • Considers the distinct switching states of the inverter switches for the exact magnitude and position of the Space Vector. • Eliminates fluctuations in the isolated neutral voltage of motor. • Can generate highest fundamental voltage. • Can provide various types of optimization of motor performance. Dept. of Electrical Engg, Jadavpur University, Kolkata

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Efficiency Optimized Induction Motor Drives

At rated speed

At 20% rated load

Dept. of Electrical Engg, Jadavpur University, Kolkata

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Future Trends in Motors and Drives • Increased use of the Induction and Synchronous Machines in various forms • Several application areas that used constant speed drives (like air-conditioning) are opting for variable speed drives • Motor drive converters based on phase control will become obsolete and will be replaced by ones with excellent input power factor • Very little change is expected in the design of the motors, but new applications will demand the motors to be built in new shapes • New Motors such as Switched Reluctance Motor & Brush Less DC Motors will occupy some areas, but are dependant on Power Converters Dept. of Electrical Engg, Jadavpur University, Kolkata

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Future Trends in the Technology of Drives • Concepts of Space Vector PWM are applied to get better performance. • Multilevel Inverters are used for higher voltage applications. • Multi-phase motor drives are becoming popular for ship propulsion due to inherent redundancy of the drive system. • Artificial Intelligence (Expert System, Fuzzy Logic, Artificial Neural Network and Genetic Algorithm) are the control algorithms of the future. Dept. of Electrical Engg, Jadavpur University, Kolkata

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Future Trends in Simulation & Control of Drives • More analytical and simulation tools • Control through digital technology based on high speed computing • Sensor-less control will be the demand of the future. • Single package microcontrollers are fast becoming an integral part of the drive controller in simple systems • DSP Controllers are taking over the more complex ones due to their better computational power • Future prediction is that digital controllers for drives will be mostly based upon gate array technology, involving LD and FPGA technology Dept. of Electrical Engg, Jadavpur University, Kolkata

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Future Trends (device related) • Higher switching frequencies • IGBT to dominate, with MOSFET and SCR in restricted application areas • No new Power semiconductor device expected to be evolved in near future • New materials like Silicon Carbide expected to play significant role • Improved packaging technology • Increased ‘Soft Switching’ applications Dept. of Electrical Engg, Jadavpur University, Kolkata

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Future Trends (application related) Power generation, transmission and distribution will become the application area of the largest power rating of an individual converter, instead of the earlier dominance of industrial and traction application : • Power electronics is finding increasing application in the power area, being termed as ‘FACTS’ or Flexible AC Transmission System, ‘Power Quality’ and ‘Custom Power’ • With the growing interest in Renewable Energy sources like wind & solar power as well as the concepts of Distributed Generation, its interconnection to the grid has to depend upon power electronic converters Dept. of Electrical Engg, Jadavpur University, Kolkata

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Power Electronics Application Thrust Areas for Future

☞ Main Grids:  HVDC & FACTS Devices for Improved operation  Transmit Electricity than Fossil Fuel over Long Distance  HVDC is a good solution for sending power through cables also  Maintain good power factor for reduced losses

 Smart Grids  Power Electronic Interfaces for Bi-directional energy flow  Power Electronic converters permit Distributed Generation of power Dept. of Electrical Engg, Jadavpur University, Kolkata

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Power Electronics Application Thrust Areas for Future

☞ Mini & Micro Grids: Inverters for Mini & Micro Grids DC Grids for Lighting in Rural Areas Wind & Solar based Energy storage systems for remote locations Solar & Wind based Load leveling

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Power Electronics Application Thrust Areas for Future ☞ Renewable Energy Harvesting:  Solar Power  MW Grid Export  Roof Top Systems:  Central Inverters, String Inverters, Micro Inverters  Bi-directional Inverters

 MPPT Chargers  Solar Pumps

 Wind Power  10’s of kW range Inverters  MW range Inverters

 Hydro Power  Small Inverters Dept. of Electrical Engg, Jadavpur University, Kolkata

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Future Trends (application related) Increased application in lighting control : • Various types of lamps are having efficient electronic ballasts with dimming control • Development in LED technology has triggered the development of specifically designed power converters for use with LED lamps Dept. of Electrical Engg, Jadavpur University, Kolkata

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Future Trends (application related) ‘More Electric’ Aircrafts, Ships and Electric Vehicles : • Traditional hydraulic systems are expected to be replaced by electrical actuators with power electronic control • Alternators connected to the driving shafts directly need power electronic converters to control its output voltage and frequency inspite of shaft speed variations • Hybrid Electric Vehicles are expected to be popular, with the need for increased power electronic control. Dept. of Electrical Engg, Jadavpur University, Kolkata

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Future Trends (simulation & control) • More analytical and simulation tools • Control through digital technology based on high speed computing • Single package microcontrollers are fast becoming an integral part of the power electronic controller in simple systems • DSP Controllers are taking over the more complex ones due to their better computational power • Future prediction is that digital controllers for power electronics will be mostly based upon gate array technology, involving FPGA technology Dept. of Electrical Engg, Jadavpur University, Kolkata

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