An Improved Conventional Diode-Clamped Multilevel Inverter Using

Non-Zero Triangular- Based Unipolar Modulation Scheme

CANDIDUS U. EYA1,2,a, UGWUANYI OLIVER O.3,b, OMEJE CRESCENT O.4,c

four triangular waves and one modulating sinewave for the same inverter type. The proposed system also used

microcontroller in the combinational of its wave signals in order to generate the appropriate triggering signals

for switching the power semiconductor switches. The proposed system has the following features: (i) It

produces two distinct triggering trains (W1 and W2) meant to reduce the low and high harmonics unlike

conventional modulation techniques (ii) All its carrier waves operate in continuous current mode which makes

it unique from other multicarrier and other related modulation schemes (iii) it has low component counts. The

proposed scheme on the conventional diode-clamped inverter produced the following results: voltage and

current with total harmonic distortions of 0.4547%, stabilized 400V output voltage and 20A output current,

probability results at each level of voltage and current occurrences are 0.10, 0.25, 0.25, 0.75 and 0.90; power

output of 80kW, low component counts of modulation circuit scheme and experimental prototype.

input supply voltage/s depending on the stability of

the system and the kind of circuit configurations.

Under stabilized operating conditions, the output

voltages of the multilevel inverter (MLI) share the

input voltage equally and vice versa. A lot of

researches have been ongoing on multilevel inverter

due to its attractive features of high power

eminence, great voltage handling capability, little

switching power losses and reduced EMI

Multilevel inverters have various types ranging

[18]. The three conventional multilevel inverters

have intrinsic imbalance voltage levels which is

observable in the waveforms of the input capacitors

and the loads beyond 0.1second [already seen in 2]

without adding any extra circuitries for removing

the imbalances. The concept of additional circuits

on the conventional types is to compensate those

voltage drops so as to improve the quality of the

output waveforms as can be seen in [19]. Multilevel

inverters (MLIs) have many applications such as in

Some of those schemes are: in-phase disposition

pulse width modulation (IPDPWM), phase

opposition disposition PWM (PODPWM), alternate

phase disposition PWM(APDPWM), phase shift

PWM, space vector modulation scheme, modified

space vector modulation techniques, optimized

(NZTBUMS). NZTBUMS is a modified class of

multicarrier PWM scheme. It is different from

multicarrier PWM scheme in the sense that (i) the

carrier waveforms are not touching zero axis

therefore operating in continuous current mode, (ii)

it has reduced number of carrier waveforms, (iii) it

has reduced total harmonic distortions (iv) It has

lower signal component counts (v) It produces two

distinct trains of firing signals unlike conventional

multicarrier modulation techniques.

connecting wires and DC source for power circuit.

These materials are used to build the power circuit

topology as shown in Fig.1. MatLab modelling and

implementation methods are adopted in this

research. Fig.1 consists of single source, Vs, two

input capacitors, four clamping diodes, eight IGBTs,

thirteen defined nodes with thirty two branches

(b11….b32) and load point. In furtherance to that, it

has two legs that are phase shifted at 180 degrees.

from positive half cycle to negative half cycle and

vice versa. This shows that five output voltage

levels (i.e Vs , Vs/2, 0, Vs , Vs/2) are generated in

illustrated from eq.5 to eq.12. During the positive

half cycle, eq.5 to eq.8 are carried out.

Consequently, after processing eq.5, the next line of

action is eq.6

(8)

(10)

Vc.2 and Vc.2 is illustrated Fig.2. It consists of

triangular generator, level shifter, sinewave

generator, microcontroller (ATmega328p) and

drivers. The carriers and modulating signals in Fig.2

are generated using one TL084 and resistor-

capacitor-zener diode combination.

Fig. 2: Non-zero triangular- based unipolar

modulation scheme topology

(13)

Amp, 1, Vo2, output voltage of the Op Amp.2.

But the output voltage of the operational amplifier

1, Vo1 with respect to resistances R2 and R3 and

Besides, taking into consideration, the second

Op.Amp.2 of Fig.2, the transfer function of the

integrator becomes:

(16)

Assuming R2=R3, the face of eq. 16 becomes:

Fig.3 displayed the MatLab/ Simulink model of the

power circuit and the proposed modulation

technique. In addition that, it showed that under

resistive load, the total distortions of both output

Fig.7b have equal 200V across C1 and C2

throughout the span of 5 seconds without changing.

Fig.7c also showed where the V.C1 and V.C2 are

The output voltage waveform across the resistive

load of Fig. 1 is shown in Fig.8. It has stabilized

five line-to-line output voltage levels with peak

voltage of 400V at 4.85≤ 𝑡 ≤ 5𝑠𝑒𝑐𝑜𝑛𝑑𝑠. It is

noticed that there is no voltage drops beyond

0.1second using NZTBUMS, which cannot be

released with other convention scheme without

using extra compensating circuitries. Even beyond

The spectral characteristics of output voltage is

shown in Fig.9. It indicated that at fundamental

frequency of 50Hz and maximum voltage of 400V,

the system output voltage has the total harmonic

Fig. 9: Spectral analysis of total harmonic distortion

of output voltage of the diode-clamped MLI

Fig.10 represented the output current wave shape of

the MLI under resistive load. It mimics Fig.8 except

that it has lower amplitude. The peak current value

is 20A. The power output of the MLI in this

research when the peak value of Fig.8 is multiplied

by the maximum value of Fig.10 is 8kW.

Fig.11 depicted the spectral analysis of total

of the multilevel inverter

Fig. 11: Spectral analysis of total harmonic

distortion of output current of the MLI

The statistical probabilistic analysis of both current

and voltage excursions are displayed in Fig.12. The

levels that spanned from -20A to +20A along the

horizontal axes represent the current output

statistical analysis. In Fig.12, the level 1, 2, 3, 4 and

level 5, counting from the negative half cycle to

positive half cycle, have the same probabilities of

0.1, 0.25, 0.25, 0.75 and 0.9. This implies that the

current and voltage under restive load are in phase

Fig. 12: Statistical analysis of voltage and current waveforms of the diode clamped multilevel inverter based on

the proposed scheme

maximum voltage of the MLI across the load are -

scheme and its experimental set-up are shown in

Fig.14-21. The experimented analog oscilloscopic

display of the two modulating sinewaves in Fig.14

has already been expressed in eq. 3 and eq.4 and

simulated in Fig.4. This implies that they resemble

each other

Fig. 14: Experimented waveforms of two

modulating reference voltages

Vc.2 as well as the practical comparison with the

reference signals, Fig.16 and 17 emerged.

Fig. 15: Experimented waveforms of carrier

voltages

In Fig.16, the positive zero-free carrier wave was

compared with the modulating sinewave to generate

the triggering pulses. The comparison between the

signals has been shown in eq.5, simulated as part of

Fig.4 and shown in experimented form in analog

oscilloscope in Fig.16. It is observed that the zero-

A zero-free negative carrier wave was compared

with the 180o phase shifted reference signal in

Fig.17. The MatLab/Simulink simulated form of it,

has been shown in part of Fig.4 and its arithmetic

expression was deduced in eq.9

Fig. 17: Experimented waveforms of modulating

The triggering pulses were generated when the

comparative results of Fig.16 and 17 were further

processed by Atmega328p and drivers (TLP 250

and VO3120). Fig.18 showed generated triggering

there is no voltage drop at each level of excursion.

This show that there is a stabilized output voltage

using NZTBUMS. It is noticed that it resembles the

wave form in Fig.7

Fig. 19: Experimented waveforms of 5-level line-to-

line Output voltage of the MLI

Fig.20 illustrated an experimented un-energized

Complete experimented and energized prototype of

the proposed scheme and diode-clamped MLI power

circuits were practically shown in in Fig.21. It can

be observed that it consists of power supply unit for

used in generation five level line-to-line output

voltage.

Fig. 21: Experimented energized prototype of the

proposed scheme and power circuit

An improved conventional diode-clamped

multilevel inverter using non-zero triangular-based

MLI have been showed on two channel analog

oscilloscope. It was observed that the simulation

results and the practical waveforms resembled one

another very closely. Therefore, the experimental

prototype validates the simulated results of the

proposed system.

It was also noticed that the NZTBUMS occupied

small space and has less number of carrier signals

unlike the conventional modulation schemes, hence,

leading to low component counts and better

current with total harmonic distortions of 0.4547%,

stabilized 400V output voltage and 20A output

current, probability results at each five levels of

voltage and current occurrences corresponded to

higher diode-clamped multilevel inverters and other

hybrid multilevel inverters to determine their

performance characteristics.

The authors acknowledge TETFUND for

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https://doi.org/10.1109/APEC.2016.7467951

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