Design and Implementation of a New Multilevel Inverter Topology
Design and Implementation.pdf (Size: 1,019.85 KB / Downloads: 177)
Multilevel inverters have been widely accepted for
high-power high-voltage applications. Their performance is highly
superior to that of conventional two-level inverters due to reduced
harmonic distortion, lower electromagnetic interference,
and higher dc link voltages. However, it has some disadvantages
such as increased number of components, complex pulsewidth
modulation control method, and voltage-balancing problem. In
this paper, a new topology with a reversing-voltage component
is proposed to improve the multilevel performance by compensating
the disadvantages mentioned. This topology requires fewer
components compared to existing inverters (particularly in higher
levels) and requires fewer carrier signals and gate drives. Therefore,
the overall cost and complexity are greatly reduced particularly
for higher output voltage levels. Finally, a prototype of
the seven-level proposed topology is built and tested to show the
performance of the inverter by experimental results.
MULTILEVEL power conversion was first introduced
more than two decades ago. The general concept involves
utilizing a higher number of active semiconductor
switches to perform the power conversion in small voltage
steps. There are several advantages to this approach when
compared with the conventional power conversion approach.
The smaller voltage steps lead to the production of higher power
quality waveforms and also reduce voltage (dv/dt) stress on
the load and the electromagnetic compatibility concerns .
Another important feature of multilevel converters is that the
semiconductors are wired in a series-type connection, which
allows operation at higher voltages. However, the series connection
is typically made with clamping diodes, which eliminates
overvoltage concerns. Furthermore, since the switches are not
truly series connected, their switching can be staggered, which
reduces the switching frequency and thus the switching losses.
NEW MULTILEVEL TOPOLOGY
A. General Description
In conventional multilevel inverters, the power semiconductor
switches are combined to produce a high-frequency waveform
in positive and negative polarities. However, there is no
need to utilize all the switches for generating bipolar levels.
This idea has been put into practice by the new topology.
This topology is a hybrid multilevel topology which separates
the output voltage into two parts. One part is named
level generation part and is responsible for level generating in
positive polarity. This part requires high-frequency switches to
generate the required levels. The switches in this part should
have high-switching-frequency capability.
Switching sequences in this converter are easier than its
counter parts. According to its inherent advantages, it does not
need to generate negative pulses for negative cycle control.
Thus, there is no need for extra conditions for controlling the
negative voltage. Instead, the reversing full-bridge converter
performs this task, and the required level is produced by the
high-switching-frequency component of the inverter. Then, this
level is translated to negative or positive according to output
This topology is redundant and flexible in the switching
sequence. Different switching modes in generating the required
levels for a seven-level RV inverter are shown in Table I.
In Table I, the numbers show the switch according to Fig. 1
which should be turned on to generate the required voltage
level. According to the table, there are six possible switching
patterns to control the inverter. It shows the great redundancy
of the topology. However, as the dc sources are externally
adjustable sources (dc power supplies), there is no need for
voltage balancing for this work.
In this paper, a new inverter topology has been proposed
which has superior features over conventional topologies in
terms of the required power switches and isolated dc supplies,
control requirements, cost, and reliability. It is shown that this
topology can be a good candidate for converters used in power
applications such as FACTS, HVDC, PV systems, UPS, etc. In
the mentioned topology, the switching operation is separated
into high- and low-frequency parts. This will add up to the
efficiency of the converter as well as reducing the size and cost
of the final prototype.
The PD-SPWM control method is used to drive the inverter.
The PWMfor this topology has fewer complexities since it only
generates positive carriers for PWM control.