an e cient approachonsingle phase cascaded …an e cient method for a single-phase cascaded...

An Efficient ApproachonSingle PhaseCascaded Multilevel Inverter with Space

Vector Modulation

P.E.Robinson1 and Dr.G. T. Sundar Rajan2

1P.G Scholar, Sathyabama [email protected]

2Professor,Department of Electrical and Electronics Engineering,

Sathyabama University, Chennai 600 [email protected]

December 30, 2017

Abstract

Research on MultiLevel Inverter (MLI) isemerging asa new breed on power electronics inthe high power appli-cations, Especially for FACTS controllers, Medium-voltagedrives, HVDC applications etc. In this paper we proposean efficient method for A Single-Phase Cascaded MultilevelInverter, based on the Space Vector Modulation techniques(SVM) with Reduced Number of Power Switches. Due tothe reduction of switches it will reduce the complication indriver circuits, space, cost and when MLI‘s working oper-ation the heat generation will be in as required level. Oursystem reveals that Total Harmonic Distortion (THD)willbe put under control less as per the recommendations inIEEE standards. As the output will be of modified sinewave which in turn will be beneficial to rotating machinesand magneto coupled electrical equipments, since the TotalHarmonic Distortion is reduced from the conventional sys-tem. Inclusion of SVPWM results in smoother AC outputs

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International Journal of Pure and Applied MathematicsVolume 118 No. 16 2018, 999-1013ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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and less Total Harmonic Distortion from Multilevel inverter.With the above all the information provided it is well ev-ident and the ability to produce the output by using 13thlevel Multi level inverter.

Key Words : THD (Total Harmonics Distortion), CMLI(Cascaded Multi Level Inverter), SVM (Space Vector Mod-ulation), developed cascaded multilevel inverter, (FACTS).

1 Introduction

Now a days ,the usage of High voltage or high power is an increasingfactor in the electrical field .It is difficult to connect a power semi-conductor switch directly, so we need multilevel inverters to solvethis problem, in order to generate AC output in a smoother way weneed power switches diodes DC voltage. If the number of DC volt-age sources gets increased, the sinusoidal like waveform can be gen-erated at the output, in multilevel inverter the harmonic distortiondecreases and the output quality of the wave form gets increases,the other important advantages of multilevel inverters are high ef-ficiency and better electromagnetic interference [1-6].Inverters aregenerally categorized into 3 types: cascaded multilevel inverter andneutral point (NPC) clamped multilevel inverter, flying capacitor(FC) multilevel inverter [7-10]. There is no diode clamped or fly-ing capacitors in cascaded multilevel inverters.Multilevel inverterhas the features of modularity, easeof control, consistency and re-quire less number ofsemiconductor devices to achievethe desiredoutput [11-15]. The loses and cost of the inverters decreases andthe efficiency will increase, there are two types cascaded multilevelinverter, cascaded and symmetric multilevel inverter. The instal-lation space and total cost of an asymmetric cascaded multilevelinverter is lower than symmetric one [16-19].In paper [19-23] dif-ferent types of symmetric cascaded multilevel inverters has beendiscussed.In this paper,first convert DC into multi level AC usingreduced number of power switches.Multiple 3level inverter is con-nected in series and fed to inverter to form 13level inverter.

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International Journal of Pure and Applied Mathematics Special Issue

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2 Space Vector Pulse Width Modula-

tion

The main objectives of space vector pulse width modulation gener-ated gate pulse are the following.

• Wide linear modulation range

• Less switching loss

• Less total harmonic distortion in the spectrum of switchingwaveform

• Easy implementation and less computational calculations

With the emerging technology in microprocessor the SVPWMhas been playing a pivotal and viable role in power conversion(Jenni and Wueest 1993). It uses a space vector concept to calculatethe duty cycle of the switch which is imperative implementation ofdigital control theory of PWM modulators. With the applicationof Fourier analysis the harmonic content of any waveform can bedetermined. This study is with a view to measure total harmonicdistortion which will indicate the probable losses in the output.

This following fig.1 shows the square wave to explain aboutharmonics.

Figure 1: Typical Inverter Output Voltage

Switching Time Calculation of Each Section switch (VoltageSource Inverter)

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The following table shows the upper switch and the lower switchtrigger pattern.

Sector Upper switch Lower switch1 S1 = T1 + T2 + T0/2 S4 = T0/2

S3 = T2 + T0/2 S6 = T1 + T0/2S5 = T0/2 S2 = T1 + T2 + T0/2

2 S1 = T1 + T0/2 S4 = T2 + T0/2S3 = T1 + T2 + T0/2 S6 = T0/2S5 = T0/2 S2 = T1 + T2 + T0/2

3 S1 = T0/2 S4 = T1 + T2 + T0/2S3 = T1 + T2 + T0/2 S6 = T0/2S5 = T2 + T0/2 S2 = T1 + T0/2

4 S1 = T0/2 S4 = T1 + T2 + T0/2S3 = T1 + T0/2 S6 = T2 + T0/2S5 = T1 + T2 + T0/2 S2 = T0/2

5 S1 = T2 + T0/2 S4 = T1 + T0/2S3 = T0/2 S6 = T1 + T2 + T0/2S5 = T1 + T2 + T0/2 S2 = T0/2

6 S1 = T1 + T2 + T0/2 S4 = T0/2S3 = T0/2 S6 = T1 + T2 + T0/2S1 = T1 + T0/2 S2 = T2 + T0/2

Table 1: Switching Time Calculation of Each Section switch (Volt-age Source Inverter)

Any periodic function can be represented by fundamental sineand cosine waves and their harmonics are illustrated by the follow-ing equation 1.

∂2V∂x2

+ ∂2V∂y2

= 0 (1)

A real-valued function is considered harmonic in a domain D ifall of its second-order partial derivatives are continuous in D, andif at each point in D the function satisfies Laplace’s equation [1].Such functions come from the real and imaginary parts of complexanalytical functions.

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Consider the function:

f(z) = u(x, y) + iv(x, y) (2)

We assume the derivative of this function exists at zo = xo+iyo.We let ∆z = ∆x + i∆y → 0 along the x and y axis independently,which is to say,

df(zo)dx

= lim∆z=∆z→0

(u(xo+∆x,yo)+iυ(xo+∆x,yo)

∆x− u(xo,yo)+iυ(xo,yo)

∆x

)

Likewise for ∆z = i∆y, such that we have the set of equations,

df(zo)z

= ∂u∂x

+i∂υ∂x

= −i∂u∂y

+∂υ∂y

(3)

These are better known as the Cauchy-Riemann equations,

∂u∂x

= ∂υ∂y, ∂υ∂x

= −∂u∂y

(4)

The demand that∂∂y

∂u∂x

= ∂∂x

∂u∂y

∂2υ∂y2

= −∂2υ∂x2

givesFrom Equation (2), it is known that the output voltage contains

odd harmonics. To eliminate the third harmonic and its multiplespresent in the inverter output, third harmonic injection techniqueis followed which can be done using space vector pulse width mod-ulation. Different types of harmonics are illustrated in Figure.2.

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Figure 2: Theoretical Harmonic Identification of Inverter Output

3 Existing System

In the existing system, there are more switches other than the basic15 numbers of switches like ‘H‘ Bridge which is less efficient andoccupies more space and switching losses. The following fig 3 showsthe single phase multilevel inverter and its base unit.

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Figure 3: Single phase Multilevel Inverter with Hbridgeand its BaseUnit

4 Proposed System

In the proposed System, with the available 15 numbers of powerswitches the space vector PWM is introduced, the simplified onelimb is mentioned as in the following fig 4.

Figure 4: Switch (Power Devices)

Space Vector implemented circuit diagramWith the available base switches, Space vector algorithm is be-

ing implemented.

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Figure 5: Space Vector Modulation Implemented Model

MODE OF OPERATIONMODE 1: Switch S1 S2 S3 S4 OFF state, S5 ONstate

Figure 6: Mode 1

As an initial phase of operation on the mode 1 except S5 otherall switches are kept open and the voltage from that level is avail-able as an output on the connected scope or load.

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MODE 2: Switch S1 S2 S3 S5 OFF state, S4ONstate

Figure 7: Mode 2

As an second phase of operation on the mode 2, switches S1,S2,S3,S5are on OFF State except S4 will be on ON state the voltage fromthat level is available as an output on the connected scope or load.

. MODE 3: S1 S2 S3 ON state, S4 S5 OFF state

Figure 8: Mode 3

As an third phase of operation on the mode 3, switches S1, S2,S3 are on ON State except S4, S5 will be on OFF state the voltagefrom that level is available as an output on the connected scope orload.

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5 Experimental Results

An experimental model is constructed in the MATLAB Simulinkmodel in order to analyze the theoretical model. A proposed con-verter prototype element is shown in the fig.9.

From the complete 13 level of switching is extracted from theexperimental results.

Figure 9: Output of mulitilevel inverter from the simulation model

Table 2: The following table Table 2 shows that output achievedby using the SPVM.Sl.No. PERFORAMNCE EXISITING PROPOSED SYSTEM

DETAILS SYSTEM OPEN CLOSED

1. INPUT VOLATAGE 20V 20V 20V

2. OUTPUT VOLTAGE 200V 0V/40V/60V 250V

3. OUTPUT P-P VOLTAGE 400V - 500V

4. OUTPUT FREQUENCY 50HZ 50HZ 50HZ

5. NO.OF.LEVELS 5 3 13

6 Conclusion

This manuscript presented a new efficient approach on single phasecascaded multilevel inverter with space vector modulation, whose

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main feature is its capacity to provide an output waveform withbetter Harmonics THD. Based on experimental results the followingconclusion can be drawn as the maximum THD has been capturedless than the traditional method.

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an e cient approachonsingle phase cascaded …an e cient method for a single-phase cascaded...

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