EE 6904 Ad d P El i EE 6904: Advanced Power Electronics

EE 6904 Ad d P El iEE 6904: Advanced Power Electronics

Lecture 08

Switched Mode Power Supply and UPSPWM based 1‐φ and 3‐φ Voltage Source ConverterPWM based 1 φ and 3 φ Voltage Source Converter

(VSC)

Dr. Md. HabibullahAssociate Professor, EEE, KUET

Power SuppliesPower Suppliesa power supply is a device that converts the output from an ac power line to a t d d t t lti l t tsteady dc output or multiple outputs.

Block diagram of a dc power supply.

Department of EEE, KUET 2

Classification (based on dc/dc transistor regulator)regulator)

lPower supply

SMPS LPSSMPS LPS

Series regulator

Shunt regulator

When the transistor operates at any point in its active region, the regulator isreferred to as a linear voltage regulator.

When the transistor operates only at cutoff and at saturation, the circuit is referredto as a switching regulator.


A linear series voltage regulator.

A li h t lt l t


A linear shunt voltage regulator.

i hswitch

A simplified form of a switching regulator.

Regulation is achieved by adjusting the on‐time of the control transistor. In this mode ofoperation, the control transistor does not dissipate as much power as that in the lineartypes Therefore switching voltage regulators have a much higher efficiency and cantypes. Therefore, switching voltage regulators have a much higher efficiency and canprovide greater load currents at low voltage than linear regulators.


Factors to be Considered for Power supply selection Is input‐to‐output dielectric isolation required for the application?

Are multiple outputs required?

h l l bl l h l Does the prospective topology place a reasonable voltage stress across the voltage

semiconductors?

D th ti t l l bl t t th lt Does the prospective topology place a reasonable current stress across the voltage

semiconductors?

How much of the input voltage is placed across the primary transformer winding or How much of the input voltage is placed across the primary transformer winding or

inductor?


A simplified isolated flyback regulator: (A) circuit and (B)regulator: (A) circuit and (B) the associated waveforms.

A Practical Fly Back Converter


The primary and secondary winding currents of a flyback regulator operated in the continuous mode.


A simplified peak current‐mode controlled flyback regulator: (A) circuit and (B) the y g ( ) ( )associated waveforms.


Some of the popular A simplified average current‐mode controlled flyback regulator: (A) circuit and (B) the associated waveforms.

p pcurrent‐mode control ICs are UC3840/2, UC3825, MC34129,


and MC34065

A simplified voltage‐mode controlled forward regulator: (A) circuit and (B) the associated driving signal waveform.

Some of the popular voltage‐mode control ICs areSG1524/25/26/27, TL494/5, and MC34060/63


Circuit topology of a practical forward converter

QuizFind maximum voltage stress of the switch in the primary winding and diode in the tertiary winding if the converter‐transformer has 10 primary turns and 15 tertiary turns and the maximum input dc voltage is 300 volts.


p g

Uninterruptible power supply (UPS)Uninterruptible power supply (UPS)

Configuration of a typical standby UPS system.


Block diagram of an online UPS system.


PWM based 1‐φ and 3‐φV lt S C tVoltage Source Converter

(VSC)(VSC)

5.5kW 380V Inverter


To produce an ac output waveform from a dc power supply is the main objective of a

Inverter BasicTo produce an ac output waveform from a dc power supply is the main objective of a voltage source converter (VSC) which is also known as inverter.

Some applications of VSC:

ASDUPS SVC


FACTSPV systemAPF

Classification of the invertersClassification of the inverters


Basic Elements of an Inverter

Diode

Switch (IGBT/MOSFET/SCR etc.)

Fig Inverter legCapacitor

The output waveforms are made up of a fundamental component that behaves as a pure

Fig. Inverter legCapacitor

sinusoidal and an infinite number of harmonics. This behavior should be ensured by amodulating technique that controls the amount of time and the sequence used to switch thepower semiconductors on and off.

The modulating techniques mostly used are the carrier‐based technique (e.g., sinusoidal pulsewidth modulation, SPWM), the space‐vector (SV) technique, and the selective harmonicelimination (SHE) technique


elimination (SHE) technique.

In order to operate properly the voltage‐p p p y gsource inverter, the following rules are compulsory:p y

1. Switches of the same leg cannot be on simultaneously, because a

short circuit across the dc link voltage source vi would be produced.

2. Diode in antiparallel to each switch must be placed, in order to

provide a current path for inductive loads. If the commercial switch

includes this diode, then the circuit

is already complete.

3 In practical implementation a dead time also known as blanking3. In practical implementation, a dead time, also known as blanking

time, must be considered in the control signals of the leg switches, to

avoid breaking rule 1.


gIsolated gate signal is also required

Effect of dead Time

Fig. PWM block per phase including dead time

R lt i li it• Results in nonlinearity


Effect of dead Time (contd…)

Fig. Effect of dead time on sinusoidal output voltage


Need for isolated gate‐control signals for the switches

Boosted switching signal

A schematic opto‐isolator circuit

Two isolated grounds


g

General Structure of VSI

A dc link capacitor Cdc is placed in parallel with the dc supply

Th di t b t C d it h h ld b l ibl


The distance between Cdc and switch should be as close as possible

Single‐phase VSI

Fig. Single‐phase half bridge VSI

Table: Switch states for a half‐bridge single‐phase VSI


Pulse Width Modulation (PWM)( )

PWM is a modulation technique that controls the amount of time and the sequence d t it h th i d t d ff d th t l th t tused to switch the power semiconductors on and off, and thus controls the output

voltage amplitude, phase and frequency.

Commonly used PWM techniques are:

1. Single‐pulse‐width modulation2 multiple pulse width modulation2. multiple‐pulse‐width modulation3. SPWM4. Modified SPWM5 Phase‐displacement control5. Phase displacement control


SPWM based half‐bridge VSI

ic VvV

sinˆ2ˆ

1

1

cc

ico

tVv

VV

2

sinˆˆsin

11

1

ico

cc

VtVVV

tVv

Fig The half bridge VSI Ideal waveforms for the SPWM: (A) carrier and modulating

2V


Fig. The half‐bridge VSI. Ideal waveforms for the SPWM: (A) carrier and modulatingsignals, (B) switch S + state, (C) switch S state, and (D) bipolar ac output voltage.

ˆˆ

VVm

tri

controla Harmonic spectrum for spwm

1ffm s

f

tri

based half bridge inverter

1f


Overmodulation

Fig. Normalized fundamental acgcomponent of the output voltage in ahalf‐bridge VSI SPWMmodulated.

In the overmodulation region (ma>1), some intersections between the carrier and thed l i i l i d hi h l d h i f l d h i bmodulating signal are missed, which leads to the generation of low‐order harmonics, but a

higher fundamental ac output voltage is obtained.

h i i d i h d l i i l d h i i hWhen an inverter is operated in the overmodulation region, low‐order harmonics appear in theac output voltage. Very large values of the modulation index (ma>3.24) lead to a totally squareac output voltage.


Fig. Single‐phase full bridge VSI

Table: Switch states for a full‐bridge single‐phase VSI


c VvV

cc

ic

o

tVv

VV

V

1

1

sinˆ

ˆ

ic

o

cc

tVVVV

tVv

11

1

sinˆˆs

Fig. Ideal waveforms for the unipolarSPWM: (A) carrier and modulating signals (B) switch S1+ state (C) switch

V

signals, (B) switch S1+ state, (C) switch S2+ state, and (D) unipolar ac output voltage.


Full‐Bridge DC‐AC InvertergUnipolar Voltage Switching

1

• Harmonic components around the switching frequency are absent

Copyright © 2008 by Jose Bastos

Chapter 8 Switch‐Mode DC‐Sinusoidal AC Inverters

Fig. Output filter for a VSI: (A) inductor, (B) second‐order filter, and (C) LCL filter.

Filter is required in order to provide the fundamental component of the outputFilter is required in order to provide the fundamental component of the output.

The first and the last one are used to provide a current output, such as in VSIs connected to thegrid, where a current‐like performance is required. The second‐order filter is used for voltage


output, such as stand‐alone applications or ASDs.

Three‐phase VSI

Fig Three phase VSI topologyFig. Three‐phase VSI topology.

Table: Valid switch states for a three‐phase VSI


Fig. The three‐phaseFig. The three phase VSI. Ideal waveforms for the SPWM (ma=0.8, mf =9): (A) ( a , f ) ( )carrier and modulating signals, (B) switch S1 state, (C) switch S3 state, (D) ac output voltage, (E) ac output voltage spectrum, (F) ac output current, (G) d ( ) ddc current, (H) dc current spectrum, (I) switch S1 current, d (J) di d D1and (J) diode D1

current.


References1. Power Electronics Handbook, Fourth Edition‐‐‐‐‐‐‐‐‐‐‐ by M. H. Rashid2. Modeling, Simulation and Control of Electrical Drives……. By M. F. Rahman and S. K. Dwivedi3 https://nptel ac in/course html3. https://nptel.ac.in/course.html4. Switch‐Mode DC‐AC Inverters ppt prepared by Jose Bastos


Lecture 09

PWM based 3‐φ Voltage Source Converter (VSC)

37Department of EEE, KUET

EE 6904 Ad d P El i EE 6904: Advanced Power Electronics

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