In
this paper, a novel cascaded seven-level inverter topology with a single input
source integrating switched capacitor techniques is presented. Compared with
the traditional cascade multilevel inverter (CMI), the proposed topology
replaces all the separate dc sources with capacitors, leaving only one H-bridge
cell with a real dc voltage source and only adds two charging switches. The
capacitor charging circuit contains only power switches, so that the capacitor
charging time is independent of the load. The capacitor voltage can be
controlled at a desired level without complex voltage control algorithm and
only use the most common carrier phase-shifted sinusoidal pulse width
modulation (CPS-SPWM) strategy. The operation principle and the
charging-discharging characteristic analysis are discussed in detail. A 1kW
experimental prototype is built and tested to verify the feasibility and
effectiveness of the proposed topology.
KEYWORDS:
1. Cascaded seven-level inverter
2. Switched capacitor techniques
3. Carrier
phase-shifted sinusoidal pulse width modulation
4. Charging
and discharging characteristic
SOFTWARE: MATLAB/SIMULINK
Fig.
1. Topologies of the proposed inverter. (a) The novel single dc source cascaded
seven-level inverter. (b) Three-input cascaded seven-level inverter for PV
systems.
Fig.
2. Output voltage and current waveforms. (a) At resistive load. (b) At
inductive load. (c) THD value of the output voltage
Fig.
3. Voltage waveforms of the charging-switch. (a) SC1. (b) SC3.
Fig.
4. The capacitor voltage and the charging current waveforms of capacitors C1.
(a) RESR=5mΩ. (b) RESR=200mΩ.
CONCLUSION:
A
novel single DC source cascaded seven-level inverter integrating switched
capacitor techniques is developed in this paper. In the proposed topology, the
transformerless charging circuit only contains power switches and capacitors,
and the charging time is independent of the load. The operation principle and
the charging-discharging characteristic analysis are investigated in depth.
With the common CPS-SPWM strategy, the sinusoidal output voltage can be well
obtained. Moreover, the capacitors are properly charged without complex voltage
balancing control algorithm. The peak charging current and the charging loss
can be reduced with appropriate circuit parameters. The proposed topology has
the features of modularity, low cost and simplicity of control and makes it
attractive in DC-AC power applications. A 1Kw experimental prototype verifies
the feasibility of the proposed inverter. The proposed inverter is also
suitable for photovoltaic-battery multi-input application with high redundancy.
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