Lecture-3 : More Applications of Power Electronics

More Applications of Power Electronics(Lecture-3)

R S Ananda Murthy

Associate Professor and HeadDepartment of Electrical & Electronics Engineering,

Sri Jayachamarajendra College of Engineering,Mysore 570 006

R S Ananda Murthy More Applications of Power Electronics

Problems in Present Day Power Systems

Growing consumer’s demand for power.Increasing system complexity due to inter-connectionsbetween different grids.Constraints on installation of new generators andtransmission lines due to economic and environmentalissues.Loss of system stability due to unregulated active andreactive power flow in transmission lines.Higher transmission power losses.Loop power flow in large integrated power systems.Voltage instability.Inability to utilize power transmission capability of thetransmission line up to its thermal limit.


Inflexible Power Flow in Transmission Lines

S RT

The power flow in a transmission line is entirely governedby the voltage across the line and the line impedance.If the impedances of lines are not similar then, atransmission line operating in parallel with others may notbe loaded up to its thermal capacity.


FACTS Controller Controls Power Flow in Lines

S RT

FACTSController

Using FACTS controllers – which are power electroniccontrollers – we can utilize the full capacity of thetransmission lines.Using FACTS controllers we can also route power flow inthe desired path of transmission lines in a complex powersystem network.


Steady-state Stability Limit of a Line

S R

Theoretical steady-state stability limit of a line isPm = |VS| · |VR|/X corresponding to δ = 90◦.But in practice, δ is kept in the range 30◦-40◦ as otherwisethe synchronous machines will become unstable and losesynchronism, especially when there is a fault on thetransmission line.


STATCOM Increases Steady-state Stability Limit

STATCOM

WithCompensation

WithoutCompensation

With STATCOM – which is a power electronic controllerthat supplies only reactive power – at the middle of the line,more power can be transmitted over existing line for agiven δ without instability problems.


Reactive Power Compensation using Capacitor

InductiveLoad

Inductive load, which is very common, causes drop in VR.To improve VR, traditionally, a capacitor – which suppliesreactive power – is connected in parallel with the load.But if the inductive load increases further, then, VR dropsagain causing a decrease in the reactive power Q.Then, we need to change C in order to increase Q toimprove VR. But C can be varied only in steps and notsmoothly.


SVC Delivers Q Independent of VR

InductiveLoad

SVC

Static VAR Compensator (SVC) is a power electroniccompensator.When VR drops, SVC can be made to deliver reactivepower to improve VR.Under very light load conditions, when VR tends to riseabove rated value, SVC can be made to absorb reactivepower to bring down VR to the rated value.With SVC, smooth variation of Q is possible.


Problems of Long Transmission Lines

Typically very long transmission lines carry power fromremote generating stations to the urban areas where userloads are concentrated.But very long lines have high inductive reactance due towhich the maximum power transmission capacity of theline decreases which may lead to instability.High impedance of long lines also causes low voltage atthe receiving end due to higher voltage drop in the line.


HVDC Transmission

Converter 1

A B

50 Hz 60 Hz

Load

Load

Load

Load

Converter 2

Requires only two conductors.No voltage drop due to inductance of line due to D.C.flowing through the lines.Bidirectional power flow is possible. For example, to makepower flow from A to B, we should make Converter 1 workas rectifier and Converter 2 as an inverter.No instability problem as in the case of a long A.C.transmission line.


Typical Stand-alone PV System

PVModule

ChargeController

Inverter LoadsBatteries

Charge controller is a power electronic interface whichfeeds energy captured from PV module into the batteries.Inverter is a power electronic interface which converts D.C.power stored in battery to A.C. power required by the load.


Typical Grid Connected PV System

PVModule

D.C-to-D.C.Converter

Inverter

A.C. Grid

D.C.-to-D.C. converter is used to boost the PV arrayvoltage and extract maximum solar power from the PVmodule.The inverter takes D.C. power from D.C.-to-D.C. converterand converts it to A.C. power that is fed to the utility grid.


Power Electronics in Wind Energy Systems

Rectifier

GearBox

Inverter

Rectifier

Transformer

SynchronousGenerator

Grid

WindTurbine

Frequency and magnitude of voltage generated bysynchronous generator varies due to changes in windspeed.The grid supply is rectified to supply D.C. to the field coilson the rotor of the alternator.The inverter produces A.C. from D.C. link voltage andfeeds to the grid through a step-up transformer.


Power Electronics in Fuel Cell Energy Systems

D.C-to-D.C.Converter

A.C. Grid

Stack ofFuel Cells

Inverter Filter

In a fuel cell energy is produced when hydrogen reactswith oxygen to form water.Typically a stack of hydrogen fuel cells produces D.C.power at low voltage.D.C.-to-D.C. converter boosts up the D.C. voltage to thelevel required by the inverter.The inverter converts D.C. power to A.C. and feeds it to thegrid at the voltage and frequency required by the grid.Filter is an L-C circuit which removes unwanted harmonicsfrom the inverter output.


Power Electronics Tries to Achieve These

In power electronics we always strive to achieve these —High energy efficiency.Compactness and light weight of hardware.High reliability.Economy.


Power Electronics is Enabling Technology

“In the highly automated industrial environment strugglingfor high quality products with low cost, it appears that twotechnologies will be most dominating: computers andpower electronics ...” – Bimal K. Bose, “Energy,Environment and Advances in Power Electronics”, IEEETransactions on Power Electronics, Vol. 15, No. 4, July2000, p. 680.“Modern computers, communication and electronicsystems get life blood from power electronics. Modernindustrial processes, transportation and energy systemsbenefit tremendously in productivity and qualityenhancement with the help of power electronics.”, ibid,p. 693.


Next Lecture...

In the next lecture we will discuss semiconductor switchingdevices used in power electronics.

Thank You.


Lecture-3 : More Applications of Power Electronics

Technology

Transcript of Lecture-3 : More Applications of Power Electronics