ABSTRACT:
This paper presents a
switched-capacitor multilevel inverter (SCMLI) combined with multiple
asymmetric DC sources. The main advantage of proposed inverter with similar
cascaded MLIs is reducing the number of isolated DC sources and replacing them
with capacitors. A self-balanced asymmetrical charging pattern is introduced in
order to boost the voltage and create more voltage levels. Number of circuit
components such as active switches, diodes, capacitors, drivers and DC sources
reduces in proposed structure. This multi-stage hybrid MLI increases the total
voltage of used DC sources by multiple charging of the capacitors stage by
stage. A bipolar output voltage can be inherently achieved in this structure
without using single phase H-bridge inverter which was used in traditional
SCMLIs to generate negative voltage levels. This eliminates requirements of
high voltage rating elements to achieve negative voltage levels. A 55-level
step-up output voltage (27 positive levels, a zero level and 27 negative
levels) are achieved by a 3-stage system which uses only 3 asymmetrical DC
sources (with amplitude of 1Vin, 2Vin and 3Vin) and 7 capacitors (self-balanced
as multiples of 1Vin). MATLAB/SIMULINK simulation results and experimental
tests are given to validate the performance of proposed circuit.
KEYWORDS:
1. Multi-level inverter
2. Switched-capacitor
3. Bipolar converter
4. Asymmetrical
5. Self-balancing
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig
(1) Three stage structure of the proposed inverter
EXPECTED SIMULATION RESULTS
Fig
(2) Waveform of the output voltage in (a) 50Hz and pure resistive load (b)
the
inset graphs of voltage and current
Fig
(3) waveform of the output voltage in 50Hz with resistive-inductive load
Fig
(4) Capacitor’s voltage in 50Hz (a) middle stage (b) last stage
CONCLUSION:
In this paper, a multilevel inverter based on
combination of multiple DC sources and switched-capacitors is presented. Unlike
traditional converters which used H-bridge cell to produce negative voltage
that the switches should withstand maximum output AC voltage, the suggested
structure has the ability of generating bipolar voltage (positive, zero and
negative), inherently. Operating principle of the proposed SCMLI in charging
and discharging is carried out. Also, evaluation of reliability has been done
and because of high number of redundancy, there has been many alternative
switching states which help the proposed structure operate correctly even in
fault conditions. For confirming the superiority than others, a comprehensive
comparison in case of number of devices and efficiency is carried out and shows
that the proposed topology has better performance than others. For validating
the performance, simulation and experimental results are brought under
introduced offline PWM control method.
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