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
SOFTWARE:
MATLAB/SIMULINK
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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