ABSTRACT:
In this paper a
new cascaded nonlinear controller has been designed and implemented on the
packed U-Cell (PUC) seven-level inverter. Proposed controller has been designed
based on a simplified model of PUC inverter and consists of a voltage
controller as outer loop and a current controller as inner loop. The outer loop
regulates the PUC inverter capacitor voltage as the second DC bus. The inner
loop is in charge of controlling the flowing current which is also used to
charge and discharge that capacitor. The main goal of the whole system is to
keep the DC capacitor voltage at a certain level results in generating a smooth
and quasi-sine-wave 7-level voltage waveform at the output of the inverter with
low switching frequency. The proposed controller performance is verified
through experimental tests. Practical results prove the good dynamic
performance of the controller in fixing the PUC capacitor voltage for various
and variable load conditions and yet generating low harmonic 7-level voltage
waveform to deliver power to the loads. Operation as an uninterruptible power
supply (UPS) or AC loads interface for photovoltaic energy conversion
applications is targeted.
KEYWORDS:
1. Packed
U-Cell
2. Multilevel
Inverter
3. Voltage
Balancing
4. Nonlinear
Controller
5. Renewable
energy conversion
CONCLUSION:
In this paper a new cascaded nonlinear
controller has been designed for 7-level PUC inverter based on the simple model
derived by multilevel inverter topology concept. Experimental results showed
appropriate dynamic performance of the proposed controller in stand-alone mode
as UPS, renewable energy conversion system or motor drive applications.
Different changes in the load and DC bus voltage have been made intentionally
during the tests to challenge the controller
reaction in tracking the voltage and
current references. Proposed controller demonstrated satisfying performance in
fixing the capacitor voltage of the PUC inverter, generating seven-level
voltage with low harmonic content at the output of the PUC inverter and ensures
low switching frequency operation of those switches. By applying the designed
controller on the 7-level PUC inverter it can be promised to have a multilevel
converter with maximum voltage levels while using less active switches and DC
sources aims at manufacturing a low-cost converter with high efficiency, low
switching frequency, low power losses and also low harmonic contents without
using any additional bulky filters
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