Cascaded Multilevel Inverters: off grid and grid-tied applications
Dr. Leon M. Tolbert
Tiago H. A. Mateus
Helder Z. Maia
Joao O. P. Pinto
In the off grid application a new approach for selective harmonic elimination in
a 11-level cascaded multilevel inverter with separate DC sources are being studied.
The DC sources feeding the multilevel inverter are considered to be varying in time.
This method uses genetic algorithms to obtain switching angles offline for different
DC source values and uses neural networks to determine the switching angles that
correspond to the real-time values of the DC sources for each phase. This implies
that each one of the DC sources of this topology can have different values at any
time but the output fundamental voltage will stay constant and the harmonic content
will still meet the specifications. The switching angles are updated at each cycle
of the output fundamental voltage.
A grid tied application is being studied with focus on a single-phase 11-level (5 H-bridges)
cascade multilevel DC-AC grid-tied inverter. Each inverter bridge is connected to a
200W solar panel. OPAL-RT lab was used as the real-time control system platform where
a Maximum Power Point Tracking (MPPT) algorithm was implemented based on the inverter
output power to assure optimal operation of the inverter when connected to the power
grid as well as a Phase Locked Loop (PLL) for phase and frequency match. A novel SPWM
scheme is proposed to be used with the solar panels that can account for voltage profile
fluctuations among the panels during the day. Simulation and experimental results are
shown for voltage and current during synchronization mode and power transferring mode
to validate the methodology for grid connection of renewable resources.
Fig. 1. 11-Level Cascade multilevel inverter: (a) topology and (b) voltage output waveform generation
Fig. 2. 11 Level cascade multilevel Inverter and Control System
Related publications and presentations
1. Filho, F.J.T.; Mateus, T.H.A.; Maia, H.Z.; Ozpineci, B.; Pinto, J.O.P.; Tolbert, L.M.,
"Real-time selective harmonic minimization in cascaded multilevel inverters with varying
DC sources," Power Electronics Specialists Conference, 2008. PESC 2008. IEEE , vol.,
no., pp.4302-4306, 15-19 June 2008.