Page 55 - IJEEE-2022-Vol18-ISSUE-1

Al-Jrew, Mahmood & Ali
The third form of multilevel inverter is the capacitor
clamped multilevel inverter illustrated in Fig. 3, also known
as a fly-wheel capacitor inverter .The primary distinction
between the two topologies, capacitor clamped and a diode
clamped multilevel inverter is that the diode is replaced with
a capacitor in the capacitor clamped multilevel inverter. To
generate an n-level staircase output voltage, the number of
capacitors needed is (n-1). A number of supplemental
capacitors are added and clamped across switches in a ladder
construction, so that each capacitor branch carries a distinct
voltage value, which allows mathematical exploitation of the
output voltage [20]. The major disadvantage in this topology
is large number of capacitors is required when output voltage
level is high also the complexity in the inverter control [21]. modulation [23].
In general, the only drawback of a multilevel inverter is
the need for a large number of switches to produce a variety
of voltage levels number. This increment in the number of
switches leads to increase the complexity of controlling
method and high cost. The suggested topology employs a
low number of power switches, which not only reduces the
number of driving circuits but also results in excellent
efficiency.
Fig.3: Structure of flying capacitor multilevel inverter
III. TYPES OF MODULATION TECHNIQUE
The modulation techniques play an important rule for
multilevel inverter since they are directly related to the
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overall efficiency of the system. Many modulation methods
have been introduced for multilevel inverter. For multilevel
inverters, modulation methods and control paradigms like
sine PWM, selective harmonic elimination and space vector
modulation have been developed [22].
Controlling the output voltage and current may be
accomplished using modulation methods. The modulation
signal's primary aim in MLI is to generate a stepped
waveform that is closely similar to the reference signal,
which is typically sinusoidal. To achieve a sinusoidal
waveform, modulation techniques are categorize into three
types: amplitude, frequency, and fundamental component
The multicarrier PWM methods has been utilized in this
present work. These methods can be divide in to two types,
phase shift and level shift. Phase Shift modulation is a
multicarrier modulation method in which all carrier waves
are phase shifted from one another. The number of voltage
level relates to the number of carriers. All carriers must have
similar frequency and peak-to-peak amplitude.
The level shift multicarrier modulation method have the
same relation between voltage levels and carriers number as
phase shift. This technique differs from phase shift in the
disposition of the triangular carriers [24].
The level shift can be subdivide into three subcategories
according to the carriers’ phase disposition, Inverted phase
disposition, phase opposition disposition and alternative
phase opposition disposition. In this paper, we focused on
these techniques and compared among them for the proposed
five level inverter and the two conventional MLI topologies.
IV. PROPOSED TOPOLOGY
The suggested five-level inverter topology is a combined
of two conventional topologies, the cascade H-bridge and
neutral point clamped multilevel inverter. The suggested
five-level inverter's circuit schematic is illustrated in Fig. 4.
It is made up of six MOSFET switching devices designated
as (SW1, SW2... SW6) and two power diodes designated as
(D1 and D2). Two identical capacitors (C1 and C2) has been
used to divide the input DC voltage source by connecting
them in parallel with the source. Through the two MOSFET
switches (SW1 and SW2) and the two power diodes (D1 and
D2), the divided voltage transferred to the H-bridge.
Fig.4: Proposed five level inverter