MULTILEVEL INVERTER & CONVERTER
|PEML1||Optimal Low Switching Frequency Pulse width Modulation of Nine-Level Cascade Inverter||Synchronous optimal pulse width modulation (SOP) permits low switching frequency modulation of multilevel inverter for medium-voltage high-power industrial ac drives without compromising on total harmonic distortion (THD). An aim of our experiment was to operate a nine-level cascade inverter of an induction motor drive at an average device switching frequency limited to rated fundamental frequency by using SOP technique. To reduce the number of separate dc sources, a three-level diode clamped converter was used as a cell in the nine-level cascade inverter. Using SOP technique, optimal nine-level waveforms were obtained by offline optimization assuming steady-state operation of the induction machine. The switching angles for each semiconductor switch are then obtained from optimal nine-level waveforms based on the criteria to minimize the switching frequency as well as unbalance in dc-link capacitor voltages. experimental results obtained
from the 1.5-kW induction motor drive show THD < 5% for stator currents. The results indicate that SOP technique reduces the switching frequency of operation without compromising on THD.
|PEML2||Modular Multilevel Converter With an Adaptive Observer of Capacitor Voltages||A modular multilevel converter (MMC) is an attractive solution for power conversion without informers. The MMC consists of cascade connections of floating dc capacitors. In this paper,
an adaptive observer design has been proposed to estimate the capacitor voltages from the measurement of arm currents. This work introduces the capacitance value of the cell capacitors as a parameter uncertainty for making the system performance robust with unknown constant parameters. It may be used for predictive control, condition monitoring for capacitors, and diagnosis check for capacitor health. In addition, a pulse width modulation (PWM) technique for MMChas been explored. The PWM technique is performed
Using a carrier-based level-shifted PWM strategy. It does not necessitate the calculation of duty cycles, and can be easily implemented in a DSP. By using the PWM technique, harmonics in the phase voltage is shifted to twice the switching frequency. Theoretical analysis is included in this paper for showing stability and convergence of the proposed observer. Analytical expressions are verified by simulation and experimental results.
|PEML3||Hybrid Multicarrier Modulation to Reduce Leakage Current in a Transformer less Cascaded Multilevel Inverter for Photovoltaic Systems||This letter proposes a hybrid multicarrier pulse width modulation (H-MCPWM) technique to reduce leakage current in a
Transformer less cascaded multilevel inverter for photovoltaic (PV) systems. The transformer less PV inverter topology has the advantages of simple structure, low weight and provides higher efficiency. However, the topology makes a path for leakage current to flow through parasitic capacitance formed between the PV module and the ground. A modulation technique has significant impact to reduce the leakage current without adding any extra component. The propose DH- MCPWM technique ensures low leakage current in the transformer less PV inverter system with simplicity in implementation of the modulation technique using lesser number of carriers. Experimental prototype developed in the laboratory demonstrates the performance of the proposed modulation technique in reducing the leakage current.