This paper proposes pulse width modulation
technique to get balanenced line to line out put voltage. in
linearly modulation range maximize the modulation indeex
,linearly varying out put voltage occurs. In the cascaded
multilevel inverter(MLCI) operating under unbalanced dc
link the linear modulation is reduced caused to voltage
imbalance as voltage references increses. In order to analyze
these effects, the voltage vector space for MLCI is evaluated
in detail. From this analysis, the theory behind the output
voltage imbalance is explained, and the maximum linear
modulation range considering an unbalanced dc-link
condition is evaluated. After that, a neutral voltage
modulation strategy is proposed to achieve output voltage
balancing as well as to extend the linear modulation range up
to the maximum reachable point in theory. In the proposed
method, too large of a dc-link imbalance precludes the
balancing simulations and the experiments for a seven-level
phase-shifted modulated MLCI for electric vehicle traction
motor drive show that the proposed method is able to balance
line-to-line output voltages as well as to maximize the linear
modulation range under the unbalanced dc-link conditions.

V. Gireesh : M.Tech Student, Lenora College of Engineering- Rampachodavaram

M. Chandra Sekhar : Asst. Professor, Lenora College of Engineering- Rampachodavaram

Harmonic Injection

Multilevel Cascaded
Inverters (MLCIs)

Neutral Voltage Modulation (NVM)

Phase-Shifted (PS) Modulation

Space Vector Pulsewidth
Modulation (PWM) (SVPWM)

The NVM technique for MLCIs under unbalanced dc-link
conditions has been proposed in this paper. In order to
analyze the maximum synthesizable voltage of MLCIs, the
voltage vector space has been analyzed using the
switching function. From the analysis, the maximum linear
modulation range was derived. The proposed NVM
technique is applied to achieve the maximum modulation
index in the linear modulation range under an unbalanced
dc-link condition as well as to balance the output phase
voltages. Compared to the previous methods, the proposed
technique is easily implemented and improves the output
voltage quality under unbalanced dc-link conditions. Both
simulations and experimental results based on the IPM
motor drive application verify the effectiveness of the
proposed method.

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