APPLICATION OF SVPWM TECHNIQUE TO THREE …iet-journals.org/archive/2011/oct_vol_1_no_1/427351318579516.pdfAPPLICATION OF SVPWM TECHNIQUE TO THREE LEVEL VOLTAGE SOURCE INVERTER

International Journal of Engineering and Technology Volume 1 No. 1, October, 2011

Copyright IJET © 2011 - IJET Publications UK

APPLICATION OF SVPWM TECHNIQUE TO THREE LEVEL

VOLTAGE SOURCE INVERTER

1JBV Subrahmanyam,

2Sankar

1Electrical & Electronics Engineering Dept.,Bharat Institute of Engineering &Technology, mangalpally, ibrahimpatnam,

RR district, Hyderabad,AP,INDIA 501 510 2Electrical & Electronics Engineering Dept Holymary institute of technology&science,kesara, RR district,

Hyderabad,AP,INDIA Email: [email protected], [email protected]

ABSTRACT

The purpose of the study is to compute the Total Harmonic Distortion (THD) with the proposed latest Space Vector Pulse

Width Modulation(SVPWM) technique and prove that the proposed technique gives lesser THD compared to that of

Sinusoidal PWM.Multilevel inversion is a power conversion strategy in which the output voltage is obtained in steps thus

bringing the output closer to a sine wave and reduces the Total Harmonic Distortion (THD). Multilevel inverter structures have

been developed to overcome shortcomings in solid-state switching device ratings so that they can be applied to higher voltage

systems. The multilevel Voltage Source Inverter (VSI) unique structure allows them to reach high voltages with low harmonics

without the use of transformers. The general function of the multilevel inverter is to synthesize a desired ac voltage from

several levels of dc voltages. In recent years, the multilevel inverters have drawn tremendous interest in the area of high-power

medium-voltage energy control. Three different topologies have been proposed for multilevel inverters like Diode-Clamped

Inverter (DCI), Capacitor Clamped Inverter (CCI) and Cascaded Multicell Inverter (CMI). The DCI is also called the Neutral-

Point Clamped (NPC) inverter, when it was first used in a three-level inverter in

which the mid-voltage level was defined as the neutral point. CCI is also called Flying Capacitor Inverter (FCI) and cascaded

multicell is combination of individual small voltage sources, with separated dc sources. In addition, several modulation and

control strategies have been developed or adopted for multilevel inverters including multilevel Sinusoidal

Pulse Width Modulation (SPWM), and Space Vector Modulation (SVM).

Key words: Total Harmonic Distortion, Sinusoidal PWM, Space Vector Pulse Width Modulation(SVPWM), Voltage Source Inverter (VSI)

1. INTRODUCTION

Inversion is the conversion of DC power to AC

power at a desired output voltage or current and frequency.

A static semiconductor inverter circuit performs this

electrical energy inverting transformation. The terms

voltage-fed and current-fed are used in connection with the

output from inverter circuits. A Voltage Source Inverter

(VSI) is the one in which DC input voltage is essentially

constant and independent of the load current drawn. The

inverter specifies the load voltage while the drawn current

shape is dictated by the load.

The DC power input to the inverter is obtained

from an existing power supply network (or) from a

rotating alternator through a rectifier (or) a battery, fuel

cell, photo voltage array (or) Magneto Hydro Dynamic

(MHD) generator.

Inverters are mainly classified as Voltage Source

Inverters (VSI) and Current Source Inverters (CSI). A VSI

is the one in which the DC source has small or negligible

impedance. In other words, a VSI has stiff DC voltage

source at its terminals. Because of low internal impedance,

the terminal voltage of a VSI remains substantially

constant with variations in load. It is therefore equally

suitable to single motor and multi-motor drives. Any short

circuit across its terminals causes current to rise very fast,

due to the low time constant of its internal impedance. The

fault current cannot be regulated by current control and

must be cleared by fast acting fused links.

On the other hand, the CSI is supplied with a

control current from a DC source of high impedance.

Typically a phase control thyristor rectifier feeds the

inverter with a regulated current through a large series

inductor. Thus load current rather than load voltage is

controlled and the inverter output voltage is dependent

upon the load impedance. Because of large internal

impedance, the terminal voltage of a CSI changes

substantially with a change in load. Therefore, if used in a

multi-motor drive, a change in load on any motor affects

other motors. Hence, CSIs are not suitable for multi-motor

drives.

MATERIALS AND METHODS

This study was conducted in 2011 in the Electrical

&Electronics Engineering Department of Bharat Institute

of Engineering & Technology, Mangalpally,

Hyderabad,AP, India

mailto:[email protected]

mailto:[email protected]



2. MULTILEVEL INVERTERS AND

MODULATING TECHNIQUES

2.1 Pulse Width Modulation(PWM) Techniques

A power electronic inverter is essentially a device

for creating a variable AC magnitude and frequency output

from a DC input. The frequency of the output voltage or

current is readily established by simply switching for equal

time periods to the positive and negative DC bus and

appropriately adjusting the half cycle period. However the

variable frequency ability is accompanied by a

corresponding need to adjust the amplitude of fundamental

component of the output waveform as the frequency

changes i.e., voltage control. One of the widely utilized

strategies for controlling the AC output of power

electronic converters is the PWM [4] Technique. This

varies the duty cycle of the inverter switches at a high

frequency to achieve a target average low-frequency

output voltage or current.

Modulation theory has been a major research area

in power electronics for over three decades and continues

to attract considerable attention and interest. On the other

hand, there have been a number of clear trends in the

development of PWM concepts and strategies since 1970s,

addressing the main objectives of reduced harmonic

distortion and increased output magnitudes for a given

switching frequency and the development of modulation

strategies to suit different converter topologies.

Principle of PWM

Fig. 2.1 illustrates the circuit model of a single-

phase inverter with a center-tapped grounded DC bus and

Fig. 2.2 illustrates the principle of PWM.

Fig. 2.1 Circuit Model of Single - Phase Inverter

Fig. 2.2 Pulse Width Modulation(PWM)

From Fig. 2.2 the inverter output voltage is determined in

the following

1. When , = /2

2. When , = /2

M= , ………(1)

……..(2)

3. MODULATION TECHNIQUES FOR

DIODE CLAMPED MULTILEVEL

INVERTER

3.1 Third Harmonic Injected PWM

The reference ac waveform is not sinusoidal as

illustrated in Fig. 3.1 but consists of both fundamental

component and a third harmonic component. As a result,

the resulting peak to peak amplitude of the resulting

reference function does not exceed the dc supply voltage

, but the fundamental component is higher than the

available supply . The presence of exactly the same

third harmonic component in each phase results in an

effective cancellation of the third harmonic component at

the neutral terminal and all sinusoidals with peak

amplitude. This is approximately 15.5% higher in

amplitude than that achieved by the sinusoidal PWM.

Therefore, the third harmonic PWM provides better

utilization of the dc supply voltage.



Fig. 3.1 Third Harmonic Injected PWM with Triangular

Carriers for Multilevel Inverter

4. SPACE VECTOR MODULATION

(SVM)

4.1 INTRODUCTION

The space vector constituted by the pole voltages ,

and is defined as:

= + .exp [j (2π/3)] + .exp [j (4π/3)]…(3)

The relationship between the phase voltages , ,

and pole , and is given by:

= + ;…..(4)

= + ;…….(5)

= + ;……(6)

Since + + =0;

= ( )/3 …..(7)

Where is the common mode voltage

From Eqns. (4), (5) and (6) it is evident that phase voltages

, , also result in the same space vector .

The space vector can also be resolved into two

rectangular components namely and as in Eqn. (7).

It is customary to place the α-axis along the A-phase axis

of the motor.

Hence:

= +j …….(8)

4.2 PRINCIPLE OF SPACE VECTOR

MODULATION

An inverter is now-a-days commonly used in

variable speed ac motor drives to produce a variable, three

phase ac output voltage from a DC voltage. Since AC

voltage is defined by two characteristics, amplitude and

frequency, it is essential to work out a strategy that permits

control over both these quantities. PWM controls the

average output voltage in a sufficiently small period,

called switching period, by producing pulses of variable

duty-cycles [3]. Here, sufficiently small means the

switching is small compared to the desired output voltage

which may be considered as equal to desired.

Fig. 4.1 Three-phase two-level PWM inverter

= …(9)

Also, the relationship between switching variable

vector [a b c] t and line-line voltage vector [ ]

t

can be expressed in Eqn. (10)

= ……(10)

As illustrated in Fig. 4.2 there are eight possible

combinations of on and off patterns for the three upper

power switches [11]. The on and off states of the lower

power devices are opposite to the upper one and so are

easily determined once the states of the upper power

transistors are determined. According to Eqns.(4),(5),(6),

the switching vectors, output line to neutral voltage, and



output line-line voltages in terms of DC link are given

in table 4.1 and Fig. 4.2 shows the eight inverter voltage

vectors ( to )

Table 4.1 Switching vectors, line to neutral

voltages and line to line voltages

Voltage

Vector

Switching

Vectors

Line to neutral

voltage

Line to line

voltage

a b c

0 0 0 0 0 0 0 0 0

1 0 0 2/3 -1/3 -1/3 1 0 -1

1 1 0 1/3 1/3 -2/3 0 1 -1

0 1 0 -1/3 2/3 -1/3 -1 1 0

0 1 1 -2/3 1/3 1/3 -1 0 1

0 0 1 -1/3 2/3 2/3 0 -1 1

1 0 1 -2/3 1/3 1/3 1 -1 0

1 1 1 0 0 0 0 0 0

Fig. 4.2 Inverter voltages vectors ( to )

4.3 OPERATION OF THREE-PHASE

THREE-LEVEL INVERTER

Fig. 4.3 Power circuit for Three-phase three-level inverter

Fig. 4.3 illustrates the basic circuit for the three-level

DC3LI. The circuit employs 12 power switching devices

and 6 clamping diodes (D1-D6)and the DC bus voltage is

split into three-levels(+Vdc/2, 0,-Vdc/2). Thus, the voltage

stress of the switching device is greatly reduced. The

output phase voltage Vao has three different states: +Vdc/2,

0, -Vdc/2. Here take phase A as an e.g., for voltage. For

voltage +Vdc/2, Sa1 and Sa2 need to be turned on. We can

define these states as 2, 1, and 0, respectively [12].The

switching variable Sa in table 4.4 ,is similar to three-phase

two-level inverter, the switching states of each bridge leg

of three-phase three-level inverter is described by using

switching variables Sa, Sb and Sc.The difference is that, in

three-level inverter, each bridge leg has three different

switching states.

Table 4.4 Switching variables of phase A

Vao Sa1 Sa2 S'a2 S'a1 Sa

+Vdc/2 ON ON OFF OFF 2

0 OFF ON ON OFF 1

-Vdc/2 OFF OFF ON ON 0

Using switching variable Sa and DC bus voltage

Vdc, the output phase voltage Vao is obtained as follows:

Van=(Sa-1)*Vdc/2 ………(11)

And the output line voltage of phase A and B can be

expressed as follows:

Vab = Vao - Vbo = 1/2*Vdc (Sa-Sb).....(12)

4.4 SPACE VECTOR PWM FOR THREE

LEVEL INVERTER

There are altogether 27 switching states in a

DC3LI. They correspond to 19 voltage vectors whose

positions are fixed. These space voltage vectors can be

classified into four groups, where the first group

corresponds to 3 zero vectors or null vectors (V0, V7,

V14), the second group consists of large voltage vectors

(V15-V20), the third group consists of medium voltage

vectors (V8-V13) and finally the fourth group consists of

small voltage vectors (V1-V6). The last three groups can

be distinguished into three hexagons illustrated in Fig. 4.6.

Fig. 4.4 Space Vector hexagon



The plane can be divided into 6 major triangular

sectors (1-6). Each major section represents pi/3 of the

fundamental cycle. Within each major sector, there are 4

minor triangular sectors. There are totally 24 minor sectors

in the plane and the vertices of these sectors represent the

voltage vectors.

Fig. 4.5 Space Vector hexagon displaying switching states

Fig. 4.6 Three-level inverters hexagons

(a) Small hexagon (b) Medium hexagon (c) Big hexagon

In three-phase three-level inverter, when the rotating

voltage vector falls into one certain sector, adjacent

voltage vectors are selected to synthesize the desired

rotating voltage vector based on the vector synthesis

principle, resulting in three-phase PWM waveforms. By

the examination of the phase angle and the magnitude of a

rotating reference voltage vector V*, the sector wherein

V* resides can be easily located.

From table 4.5, each small voltage vector and zero voltage

vector have 2 and 3 redundant switching states,

respectively. This will be analyzed in the later section.

X = Tx/Ts ; Y = Ty/Ts ; Z = Tz/Ts …..(13)

Based on the principle of vector synthesis, the following

equations can be written:

X+Y+Z=1 ... (13.1)

Vx *X +Vy *Y+ Vz *Z = …….(14)

The modulation ratio of three-phase three-level inverter is

represented as follows:

M= / (2/3Vd) = 3 /2Vd ……(15)

Table 4.5 The switching states (27 states) for a three-

level inverter

THE

SWITCHIN

G STATES

Sa

Sb

Sc

V

S1 0 0 0 V0

S2 1 1 1 V7

S3 2 2 2 V14

S4 1 0 0 V1

S5 1 1 0 V2

S6 0 1 0 V3

S7 0 1 1 V4

S8 0 0 1 V5

S9 1 0 1 V6

S10 2 1 1 V1

S11 2 2 1 V2

S12 1 2 1 V3

S13 1 2 2 V4

S14 1 1 2 V5

S15 2 1 2 V6

S16 2 1 0 V8

S17 1 2 0 V9

S18 0 2 1 V10

S19 0 1 2 V11

S20 1 0 2 V12

S21 2 0 1 V13

S22 2 0 0 V15

S23 2 2 0 V16

S24 0 2 0 V17

S25 0 2 2 V18

S26 0 0 2 V19

S27 2 0 2 V20



Where is the magnitude of the reference

voltage vector , which rotates with an angular speed of

ω=2f in d-q coordinate plane and 2/3 Vdc is magnitude of

the large voltage vector, e.g., V13.states: + Vdc /2, 0, and -

Vdc /2

5. SIMULATION RESULTS AND

DISCUSSION

5.1 FOR A DIODE CLAMPED THREE-LEVEL

INVERTER

5.1.1. Sinusoidal Pulse Width Modulation (SPWM)

Fig. 5.1 Line Voltage of DC3LI with SPWM

Fig. 5.2 THD spectrum of DC3LI with SPWM

Fig. 5.1 illustrates the Line Voltage of DC3LI with

SPWM and Fig. 5.2 illustrates the THD spectrum of

DC3LI with SPWM.In this modulation technique the

fundamental voltage is 233.3 V and THD is 29.89%.

5.1.2 Space Vector Pulse Width Modulation

(SVPWM)

Fig. 5.3 Line Voltage of DC3LI with SVPWM

Fig. 5.4 THD spectrum of DC3LI with SVPWM

MODULTION

TECHNIQUES

DC3LI

THD Fundamental

Component

Sinusoidal PWM 29.95% 200.1 V

SVPWM 20.31% 173.1.7 V



Fig. 5.4 illustrates the Line Voltage of DC3LI with

SVPWM and the THD spectrum of DC3LI with SVPWM.

In this modulation technique, the fundamental voltage is

312.7 V and THD is 23.20%.

6. CONCLUSIONS AND FUTURE SCOPE

6.1 Conclusions

Diode Clamped Multi-Level Inverter topologies are

developed with 3-levels for various modulation techniques

i.e., Sinusoidal PWM, Space Vector PWM and DC3LI

topology. Space Vector PWM technique gives lesser THD

compared to that of Sinusoidal PWM.

6.2 Scope For Future Work

The presented simulink model can be setup

experimentally using semi conductor devices like

Transistor, Thyristor, MOSFET etc., and controlling

strategies by using any of the following devices like

microprocessor, microcontroller, digital signal processor

and FPGA. The controlling strategies can be implemented

using m-file programming with FPGA for better

processing speed and performance.

ACKNOWLEDGEMENT

Authors acknowledge the support, encouragement

and facilities provided by the Electrical&Electronics

Engineering Department and management of Bharat

Institute of Engineering & Technology

(BIET),Mangalpally, ibrahimpatnam,Hyderabad,AP, India

in carryout the presented study/research work.

REFERENCES

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AUTHOR’S BIOGRAPHY

Dr. JBV Subrahmanyam is a Doctorate in Electrical

Engineering from JNTU-Hyderabad, India, with two

decades of rich experience in teaching, training, research,

industry, projects and consultancy. He published 15

research papers in reputed international journals and 20

papers in international and national conferences.His

research interest is in automation of power systems. He is

an expert in condition monitoring of industrial equipment

through modern diagnostic techniques. He implemented



the latest GPS and GIS technologies in many power

utilities in India successfully. He executed many

international and national level technical projects

effectively funded by Power Finance Corporation,

Ministry of Power, Government of India, APDRP, DRUM,

USAID and DFID-UK.

Mr. Sankar is a faculty in electrical engineering

department of HITS, Hyderabad, India, with many years of

rich experience in teaching, training, research. His

research interest is in automation of power systems.

Documents

APPLICATION OF SVPWM TECHNIQUE TO THREE …iet-journals.org/archive/2011/oct_vol_1_no_1/427351318579516.pdfAPPLICATION OF SVPWM TECHNIQUE TO THREE LEVEL VOLTAGE SOURCE INVERTER