fpga based variable frequency ac to ac power conversion

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Electric Power Systems Research 90 (2012) 67– 78

Contents lists available at SciVerse ScienceDirect

Electric Power Systems Research

jou rn al h om epage: www.elsev ier .com/ locate /epsr

PGA based variable frequency AC to AC power conversion

nshul Agarwal, Vineeta Agarwal ∗

epartment of Electrical Engineering, Motilal Nehru National Institute of Technology, Allahabad 211004, India

r t i c l e i n f o

rticle history:eceived 6 October 2011eceived in revised form 29 March 2012ccepted 4 April 2012vailable online 10 May 2012

eywords:ield-programmable gate array (FPGA)ycloinverterycloconverterrapezoidal modulation (TM)requency converter

a b s t r a c t

AC/AC variable frequency power conversion system is proposed which makes use of a cycloconverter innewer form, ac–ac matrix converter. An attempt has been made to operate this matrix converter bothin conventional low frequency ac–ac converter, cycloconverter and new high frequency ac–ac converter,cycloinverter. The ability to directly affect the frequency conversion of power without any intermediatestage involving DC power is a huge advantage of the system. The undesirable harmonic componentsin the output of the matrix converter have been minimized using an advanced modulation techniquecalled as trapezoidal modulation technique. The technique offers several advantages compared to othermodulation techniques in terms of easy and fast real-time waveform generation with higher fundamentaloutput voltage. The converter is simulated using well known software package MATLAB. Simulationsresults are presented for both cycloconverter as well as for cycloinverter. It has been found that forcycloinverter operation the total harmonic distortion (THD) is more as compared to cycloconverter mode

otal harmonic distortion (THD) of operation. The simulated results are also validated with experimental results by implementing thetrigger controller circuit to generate trapezoidal modulated trigger signal for matrix converter on fieldprogrammable gate array (FPGA). Peripheral input–output and FPGA interfacing has been developedthrough Xilinx 9.2i using very high speed integrated circuit hardware description language (VHDL). Thecircuit has been tested qualitatively by observing various waveforms on digital storage oscilloscope (DSO).The operation of proposed system has been found satisfactory.

© 2012 Elsevier B.V. All rights reserved.

. Introduction

Traditionally ac–ac power conversion using semiconductorwitches is done in two different ways: (1) in two stages (ac–dcnd then dc–ac) as in dc link converters or (2) in one stage (ac–ac)ycloconverters. Majority of the cycloconverters are naturally com-utated and the maximum output frequency is limited to a value

hat is only a fraction of source frequency [1]. As a result theajor applications of cycloconverter are low speed AC motor drivesith frequency from 0 to 20 Hz [2]. With recent device advance-ent, newer forms of cycloconverters are being developed and

rawing more research interest. These new cycloconverters useelf-controlled switches and are known as ac–ac matrix convert-rs. These converters may also be used for high frequency ac–aconversion and known as cycloinverter. Cycloinverters are ideal in
nduction heating and in aircraft for use in the ground power unito power the airplane while it is on the ground [3]. The outputf the matrix converter is however rich in harmonics [4]. Various
∗ Corresponding author.E-mail addresses: [email protected] (A. Agarwal), [email protected]

V. Agarwal).

378-7796/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.epsr.2012.04.003

modulation techniques employed to reduce the harmonics aresinusoidal pulse width modulation (SPWM) [5], space vectorpulse width modulation (SVPWM) [6,7], staircase case pulsewidth modulation (SCPWM) [8] and delta modulation [9]. Anadvanced modulation technique, named as trapezoidal modulationtechnique, has been proposed in this paper where sinusoidal mod-ulating signal is replaced by a trapezoidal wave. The trapezoidalwave is suitable for on line computation and its waveform variesfrom a rectangular wave to a triangular wave. The technique offersseveral advantages compared to other modulation techniques interms of easy and fast real-time waveform generation with higherfundamental output voltage [10–14].

Many digital and transistor logic circuit (such as microproces-sor and microcontroller) can develop PWM [15]. The performanceof these devices is however limited because these are made withgeneric hardware, leaving software as the only method to createapplication-specific functions by the designer [16]. In comparison,FPGAs [17] give designers the freedom to create custom functions,completely adapted to their specific application requirements, by
enabling customization of both hardware and software at very lowcost [18]. In this paper a digital controller has been designed andimplemented on FPGA to generate the trigger pulses for a fre-quency conversion system using hardware description language
dx.doi.org/10.1016/j.epsr.2012.04.003

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68 A. Agarwal, V. Agarwal / Electric Power Systems Research 90 (2012) 67– 78

S1a

S4a

S2a

S3a

S2bS1b

S3b S4b

LOAD

V i(t)

IGBT

IGBT

DIODE

DIODE

CurrentFlowCurrent

Flow

S1bS1a

(b) Common emitter configuration. (a) Power circuit.

uency

Vcc

2

ratg

Fig. 1. Freq

HDL. Trigger requirements are obtained for single-phase matrixonverter which is operated both as cycloconverter as well asycloinverter [19].

. Principle of operation

Fig. 1(a) shows the proposed frequency power converter that
equires four bi-directional switches capable of blocking voltagend conducting current in both directions. In the absence of bidirec-ional switch module, the common emitter anti-parallel insulatedate bipolar transistor (IGBT), with diode pair as shown in Fig. 1(b)
S4b

S2b

S4a

S1a S2aS1b

S3bS3a

LOAD

(a) Positiv

S4a

S1a S2aS1b

S3bS3a

LOAD

(b) NegatiFig. 2. Cycloconver

converter.

is used. The diodes provide reverse blocking capability to the switchmodule. The IGBT is used due to its high switching capability andhigh current carrying capacity desirable for high-power applica-tions [20]. The output can be synthesized by suitable toggling ofthe switches subject to the conditions that ensures the switches donot short-circuit the voltage sources, and do not open-circuit thecurrent sources [21].

The converter will operate in cycloconverter mode to producepositive output when switches S1a and S4a conduct for positiveinput cycle while for negative input cycle switches S3b and S2bwill conduct as shown in Fig. 2(a). The negative half output of

S4bS4a

S1a S2bS1b S2a

S3bS3a

LOAD

e output.

S4bS4a

S1a S1b S2bS2a

S3bS3a

LOAD

ve output. ter operation.

A. Agarwal, V. Agarwal / Electric Power Systems Research 90 (2012) 67– 78 69

S4b

S2b

S4a

S1a S2aS1b

S3bS3a

LOAD

S4a

S1a S2aS1b

S3bS3a

LOAD

(a) Positive input cycle.

S4bS4a

S1a S1b S2bS2a

S3bS3a

LOAD

S4bS4a

S1a S2bS1b S2a

S3bS3a

LOAD

tivenverte

cS

mi

f

Fg

f

H

(b) NegaFig. 3. Cycloi

ycloconverter is obtained by conduction of the switches S2a and3a and switches S4b and S1b (Fig. 2(b)).

The operation of cycloinverter may be explained in a similaranner, with Fig. 3(a) and (b). In general, the output of converter

n cycloinverter mode will have a frequency given by (1),

o = fi × Nr (1)

or cycloconverter mode of operation, the output frequency will beiven as,

o = fiNr

(2)

ere fi is the source frequency and Nr may be any real number.

Fig. 4. Ideal wa

input cycle. r operation.

Fig. 4(a) and (b) shows the ideal waveforms of frequency con-verter for cycloconverter operation and cycloinverter operation atan output frequency of 25 Hz and 100 Hz respectively.

The mechanism to generate the triggering pulses for Nr = 3, usingtwo set of pulses having frequency, 50 Hz (input supply frequency)and 150 Hz (Nr times the input supply frequency that is desiredoutput frequency) is shown in Fig. 5. Let X1 represents the pulsesat a frequency of 50 Hz and X2 of 150 Hz. Then ANDing of X1 and X2will result the pulses required by the switches (S1a, S4a). Furtherif this X2 is inverted by a NOT gate, then the ANDing of X1 and X2′

will result the pulses required by the switches (S2a, S3a). Similarly,ANDing of X1′ and X2 results the pulses required by switches (S2b,S3b) and then ANDing the X1′ and X2′ finally generates the requiredpulses for switches (S1b, S4b).

veforms.


X1

X2

X1X2

X2'

X1X2'

X1'

X1'X2'

X1'X240 ms30 ms20 ms10 ms

Fig. 5. Gate pulses for different IGBTs switches.

Table 1Truth table logical expression of triggering pulse for converter operation.

Converter (Conducting switches) Logical operation

Cycloinverter

Sla, S4a Yl, (X1, X2)S2a, S3a Y1, (X1′ , X2)S2b, S3b Y1, (X1′ , X2′)Slb, S4b Y1, (X1, X2′)

CycloSla, S4a Y2, (X1, X2)

′

esltOao

3

aosfittitsbo

c

con-verter

S2b, S3b Y2, (X1 , X2)S2a, S3a Y2, (X1, X2′)Slb, S4b Y2, (X1′ , X2′)

The cycloconverter or cycloinverter may be realized using anxclusive OR gate by taking a 2 bit input word AB from user ashown in Fig. 6. If both A = 1and B = 1 or A = 0 and B = 0, the outputine Y2 will high while Y1 will be low. So the cycloconverter func-ion connected to Y2 output line will be enabled else vice versa.nce the converter is selected, the trigger signals for cycloconverternd cycloinverter operation are generated by operating the logicalperators on these signals as shown in Table 1.

. Trapezoidal modulation technique

Trapezoidal modulation is a technique to advance the controlbility by using on-line computation of PWM patterns. This is basedn the classical uni-polar PWM switching. The uni-polar PWMwitching method uses multiple trapezoidal modulation wave-orms with a single triangular wave as shown in Fig. 7. Trapezoidaltself comprises of two linear segments, namely the slope line andhe horizontal line. The waveform of the trapezoidal depends onhe location of its slope angle, ˛. Different locations of ̨ will resultn different shape of trapezoidal waveforms and harmonic con-ents. As compared to bipolar PWM switching, the uni-polar voltagewitching results in a better output voltage waveform and in the
etter frequency response since the effective switching frequencyf the output voltage waveform is doubled and the ripple is reduced.
The intersection between modulating trapezoidal signal andarrier signal defines the switching instant of the PWM pulses. The

A

B

Y2

Y1

Fig. 6. Converter selector.

Fig. 7. Trapezoidal modulation technique.

gating signals are generated by comparing the modulating trape-zoidal signal Vm(t) with an amplitude, Ar and the frequency fs with acarrier triangular signal Vtri(t) which is a train waveform with a fre-quency fc and amplitude Ac. The output frequency of the converteris decided with the frequency of the modulating wave.

Since the modulation is symmetric, the modulation signals aresampled once in every carrier cycle. The modulation index m isgiven as

m = Ar

ACfor 0 < m < 1 (3)

The magnitude of harmonics for the trapezoidal waveformhaving ̨ within 0–90◦, can be calculated using Fourier analysis.Assuming quarter-wave symmetry, only the odd sine terms are tobe considered. Thus the sine-term Fourier coefficients can be givenby (4)

An = 4�

∫ �/2

0

V(�) sin(n�) d� (4)

where n is the harmonic order while V(�) represents trapezoidalwaveform.

V(�) ={

1˛

0 < � < ˛

1 ̨ < � < 90◦

}(5)

Now (4) can be rewritten as

An= 4˛�

[(−� cos(n�)

n

)˛

0

+ 1n

∫ ˛

0

cos(n�) d�

]

+ 4�

∫ �/2

0

sin(n�) d� (6)

Eq. (6) can be simplified into the general equation as given below:

An = 4n2�

× sin(n˛)˛

(7)

In order to use the proposed trapezoidal modulation in motordrives, it is desirable to increase the fundamental magnitude ofoutput. Clearly each value of ̨ yields different harmonic content of
the trapezoidal. However, it should be noted that the fundamentalcomponent magnitude will also be reduced if ̨ is selected towards90◦. Therefore, to gain high fundamental magnitude, ̨ should beplaced nearby 0◦. Harmonics can be eliminated by selecting the

ower Systems Research 90 (2012) 67– 78 71

choewb

qogvfta

4

Fgserhr

arprls

4

cfsnbiwd

f

Fig. 8. Digitized triangular carrier waveform.

A. Agarwal, V. Agarwal / Electric P

orrect value of ˛. For example if ̨ = 76◦, the 5th, 7th, 11th, and 13tharmonics can be eliminated. Thus by carefully selecting ˛, the lowrder of harmonic content of trapezoidal signal can be reduced. Byliminating a number of dominant harmonics, an output voltageith high fundamental magnitude and low harmonic content can

e obtained [22].The logical gating pulses generated in Fig. 5, for a particular fre-

uency of the converter are ANDed with the logical trapezoidalutput and the resulting pulses, after amplification to the requiredating power level, are fed to the respective IGBTs. The outputoltage produced by the frequency power converter contains theundamental component of which the sine wave is a replica. In addi-ion, it contains harmonic components which are located in bandsround multiples of the triangle frequency [23].

. Realization of trapezoidal modulation in FPGA

The principle of trapezoidal modulation is implemented onPGA using Xilinx. Initially, for a particular value of Nr the logicalating signals are generated by VHDL programming in Xilinx ISE9.2ioftware. After this the triangular carrier wave and trapezoidal ref-rence waveform are also generated by programming. The digitizedeference signal and sampled triangular wave is then compared atigh repetition rates in a comparator to obtain the required timeesolution [24].

The whole behavioural model is synthesized in ISE simulatornd test bench waveform is generated for all different signals. Theesulting coding is then downloaded in Spartan-3E FPGA kit. Theulses from the output port of FPGA kit are fed to the gates ofespective IGBTs after amplifying them to required gating powerevel. Generations of different waves are described in followingubsections:

.1. Basic signal generation

For successful firing of IGBT the trigger signals must be syn-hronized with input supply. Hence the signal X1 at 50 Hz inputrequency is obtained by converting sinusoidal input wave as aquare wave with zero crossing detector (ZCD) output while sig-al X2 is generated from input clock of FPGA kit, which is 50 MHz,y counting N clocks at the rising edge of ZCD output. After count-

ng these numbers of clock, the output pulse is reset. The outputave is set after counting N number of clocks again. This gives the
esired frequency output. The formula used in the code is given as
out = fclk

2N(8)

Fig. 10. Switching i

Fig. 9. Digitized trapezoidal reference waveform stored in ROM.

where fout = desired output frequency pulse. fclk = main clock ofFPGA. N = no. of clocks to be counted.

4.2. Digitized triangular waveform generation

One 8 bit up/down counter is used to generate the ‘M’ shape tri-angular waveform. The counter digitally increments its value from0 to 255 and then subsequently decrements it back to 0 over aperiod of time. Good accuracy requires high bit number. The car-rier frequency of triangular wave is determined by the followingformula [25].

fc = fclk

2(2n − 1)(9)

Fig. 8 shows the generated triangular carrier wave of frequency1800 Hz when the clock frequency of the counter is taken as918 kHz.

nstant pulses.


4

msas

4

zwIsaacfg

5

qofu

v

reduction in THD is found for this case as compared to Fig. 12.Now it is approximately equal to 8%. When output frequency, f0 isincreased to 500 Hz while modulation index and carrier frequency

Fig. 11. Output voltage of unmodulated cycloinverter (fo = 150 Hz).

.3. Digitized trapezoidal signal generation

A standard trapezoidal signal is generated by using look-up tableethod. Fig. 9 shows the digitized trapezoidal reference waveform

tored in the ROM at sequential addresses. Binary counter whichcts as memory counter addressees the ROM and the trapezoidalamples are updated by clocking the counter [26].

.4. Gating signal generation

The gating signals are generated by comparing the scaled trape-oidal signals obtained from the look-up table with the triangularave generated from the up/down counter as shown in Fig. 10.

n order to have different modulation index the maximum valuetored for trapezoidal wave is modified. The modulation index maylso be changed by changing the maximum number of steps in tri-ngular waveform or modifying the number of counts in up/downounter. The gating pulses generated are then multiplied with theour basic switching pulses obtained in Fig. 5 and then fed to theate of respective IGBTs.

. Simulation results

SIMULINK software and its facilities are used to model the fre-uency converter loaded with resistive-inductive load. The resultsf simulation are reported for different output frequency first
or cycloinverter operation and then for cycloconverter operationsing trapezoidal modulation technique.
The output voltage waveform and THD of unmodulated cycloin-erter for an output frequency of 150 Hz is shown in Figs. 11 and 12.

Fig. 12. THD of unmodulated cycloinverter.

Fig. 13. Output voltage and THD of trapezoidal modulated frequency converter atfo = 150 Hz, m = 1, and fc = 2 kHz.

It is clearly seen that the output is rich in harmonics and THD isapproximately 60%, which is undesirable.

Fig. 13 shows the output voltage waveform of cycloinverteralong with its THD for an output frequency of 150 Hz when modu-lation index, m = 1 and carrier frequency, fc = 2 kHz. A significant

Fig. 14. Output voltage and THD of trapezoidal modulated frequency converter atfo = 500 Hz, m = 1, and fc = 2 kHz.


Ff

atar

ofd

ovTqs

u

Ff

Fig. 17. Performance analysis of frequency converter with variation of modulationindex (m).

ig. 15. Output voltage and THD of trapezoidal modulated frequency converter ato = 25 Hz, m = 1, and fc = 2 kHz.

re same, THD is reduced to 4.8% as shown in Fig. 14. With fur-her increase in output frequency, THD again increases and aftern output frequency of 1 kHz, the THD attains a value of 12% whichemains constant afterwards.

If the modulation index is decreased the THD increases in theutput. It has also been observed that with an increase in carrierrequency, switching frequency increases, but the total harmonicistortion does not reduce significantly.

Fig. 15 shows the output voltage waveform of cycloconverterperation along with THD for an output frequency of 25 Hz for samealue of modulation index, m = 1 and carrier frequency fc = 2 kHz.HD for this case has been found to only 2.2%. When output fre-
uency is further reduced, say equal to 10 Hz, the THD increaseslightly to 3.2% as shown in Fig. 16.
A number of observations have been made for different mod-lation index (m). Fig. 17 shows the performance of frequency

ig. 16. Output voltage and THD of trapezoidal modulated frequency converter ato = 10 Hz, m = 1, and fc = 2 kHz.

Fig. 18. Performance with different frequency for cycloinverter operation.

Fig. 19. Performance with different frequency for cycloconverter operation.

Fig. 20. Experimental set-up.


am of TPWM generator in Xilinx FPGA.

cflAMm2

cascTiCts

Fig. 21. Top level schematic diagr

onverter for both cycloinverter and cycloconverter mode for dif-erent modulation index (m). It has been observed that THD isowest for modulation index around 1 for any output frequency.ny decrease in modulation index increases the THD in the output.inimum THD comes out to be 4.8% for cycloinverter operation at

= 1, whereas for cycloconverter mode the minimum THD is only.2% again at m = 1.

Figs. 18 and 19 show the comparative performance of differentarrier based modulation techniques for cycloinverter operationnd cycloconverter operation at various frequencies. There is nopecific pattern for the value of THD for different value of frequen-ies. It is observed that for trapezoidal modulation (TM) techniqueHD decreases up to output frequency of 500 Hz and after that THDncreases sharply and finally remains constant at a value of 10.2%.ompared to sin PWM (SPWM) and staircase modulation (SCM),
he THD is minimum for trapezoidal modulation (TM) technique ashown in Fig. 18.
Fig. 22. Synchronization of 50 Hz and 500 Hz signal.

Fig. 23. Synchronization of 50 Hz and 25 Hz signal.

Fig. 24. Triangular wave generation at fc = 500 Hz.


Fig. 25. Generation of trapezoidal waveform for fc = 500 Hz.

ooFb

6

twso

Fig. 26. Generation of gating signals for fo = 500 Hz.

For cycloconverter operation minimum THD in SPWM comesut to be 3.5% whereas for trapezoidal modulation it is equal to 2.2%nly. For staircase modulation minimum THD is 5.3% as shown inig. 19. Thus, it may be concluded that trapezoidal modulation isetter for both cycloinverter and cycloconverter operation.

. Experimental results

Experimental results are obtained qualitatively by testing the
rigger circuit on Xilinx 9.2i ISE Simulator and by observing theaveforms on DSO at salient points of the control circuit. Fig. 20
hows the photograph of the experimental set-up. It consistsf power circuit made up of four IGBTs with common emitter

Fig. 28. Harmonic spectra of unmodula

Fig. 27. Output voltage of unmodulated cycloinverter for fo = 200 Hz.

configuration, FPGA SPARTAN-3E kit, input interfacing circuit,driver circuit using opto-couplers for isolation and resistive-inductive load. FPGA kit provides flexibility with circuit designwithout any hardwired modifications making it a favorable choicefor Application Specific Integrated Circuits (ASIC) prototyping.The input interfacing circuit consists of a step down transformer(220 V/6 V), connected to the main source operating at a frequencyfi. The transformer provides the desired input frequency referenceto the control circuit. The secondary voltage Vr of the transformeris fed to the zero crossing detector (ZCD) that compares input volt-age Vr with a reference voltage kept at zero. The output is driveninto positive saturation when Vr passes zero in positive direction.When Vr changes its direction the output switches and becomeszero. Fig. 21 shows the top level schematic view of the proposedscheme.

The synchronization of input frequency signal with 500 Hz andwith 25 Hz signal for cycloinverter and cycloconverter operation isshown in Figs. 22 and 23 respectively. Figs. 24 and 25 show the gen-eration of triangular carrier wave and trapezoidal reference wave ata carrier frequency of 2 kHz and output frequency of 500 Hz. Differ-ent trigger signals are generated by applying logical operation onthese two sets of pulses as shown in Fig. 26 for an output frequencyof 500 Hz.

The output voltage and harmonic spectra for an output fre-quency of 200 Hz is depicted in Figs. 27 and 28 for an unmodulatedcycloinverter. The harmonics components are quite high for this
case which is undesirable.
Fig. 29 shows the output voltage along with input voltageand Fig. 30 shows the THD spectra of frequency converter oper-ating as a cycloinverter for an output frequency of 150 Hz at a

ted cycloinverter for fo = 200 Hz.


Fig. 29. Input voltage (upper trace: 100 V/div) and output voltage (lower trace:50 V/div) of frequency converter at Nr = 3, m = 0.8 and fc = 2 kHz.

mowmfaoqca

F5

Fig. 32. Harmonic spectra for output frequency of. of 500 Hz.

Fig. 30. Harmonic spectra for output frequency of 150 Hz.

odulation index, m = 0.8. The output voltage and THD spectra atutput frequency, fo = 500 Hz and m = 1 is shown in Figs. 31 and 32ith a carrier frequency, fc = 2 kHz. A significant reduction in har-onics content has been observed. The magnitude of fundamental

requency component is higher as desired. The largest harmonicmplitude in the output voltage is associated with harmonics ofrder of the carrier frequency i.e. at 2 kHz. When the output fre-
uency is further increased, fo = 750 Hz, the output voltage andorresponding THD spectra is shown in Figs. 33 and 34 at m = 1nd fc = 2 kHz.
ig. 31. Input voltage (upper trace: 100 V/div) and output voltage (lower trace:0 V/div) frequency converter at Nr = 10, m = 1 and fc = 2 kHz.

Fig. 33. Input voltage (upper trace: 100 V/div) and output voltage (lower trace:50 V/div of frequency converter at Nr = 15, m = 1 and fc = 2 kHz.

Fig. 35 shows the output voltage and output current at an outputfrequency of 150 Hz with a carrier frequency of 6 kHz and modula-tion index, m = 1.

Figs. 36 and 37 show the output voltage and harmonic spectra offrequency converter operating as a cycloconverter for an output fre-quency of 10 Hz at m = 1 and carrier frequency of 2 kHz. It has been
observed that the harmonics in the output are reduced if the slopeangle is closer to 90◦. If ̨ is selected approaching towards 0◦ theharmonics start to increase. By eliminating a number of dominant


Fig. 35. Input voltage (upper trace: 100 V/div), output current(middle trace) and output voof 6 kHz with R–L load having supply voltage 220 V.

Fig. 36. Input voltage (upper trace: 50 V/div) and output voltage (lower trace:50 V/div) of cycloconverter at fo = 10 Hz, m = 1 and fc = 2 kHz.

ha

7

bauoSctvs

[

[

[

[

[

[


armonics, an output voltage with high fundamental magnitudend low harmonic content can be obtained.

. Conclusion

A new version of cycloconverter, in matrix converter form, haseen designed that can work both in step-up mode of operationnd step-down mode of operation. An advanced trapezoidal mod-lation technique is used to reduce the harmonics in the outputf converter. A very convenient and to used software packageIMULINK is used to determine the harmonics in the output and to
alculate total harmonic distortion factor (THD). It has been foundhat the minimum THD is equal to 4.8% when frequency of con-erter is increased from 50 Hz to 1 MHz (step-up operation). Duringtep-down operation when frequency of converter is decreased
[

ltage (lower trace: 100 V/div) for output frequency of 150 Hz with carrier frequency

from 50 Hz to 1 Hz, the minimum THD has been found to be 2.2%only. Simulated results are validated with experimental results.XILINX 9.2i Web Pack software is used and implemented on FPGASpartan-3E kit. The trigger pulses obtained from the FPGA boardare fed to the driver circuit of frequency converter with the helpof the connector pins to get the required output voltage wave-forms. Experimental results are shown by interfacing DSO withSpartan-3E. They are found in close agreement to the simulatedresults. FPGA enables to make easy, fast and flexible design andimplementation.

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fpga based variable frequency ac to ac power conversion

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