ABSTRACT
State-of-the-art low-power-level metal–oxide–semiconductor field-effect
transistor (MOSFET)-based transformerless photovoltaic (PV) inverters can
achieve high efficiency by using latest super junction MOSFETs. However, these MOSFET-based
inverter topologies suffer from one or more of these drawbacks: MOSFET failure
risk from body diode reverse recovery, increased conduction losses due to more
devices, or low magnetics utilization. By splitting the conventional MOSFET based
phase leg with an optimized inductor, this paper proposes a novel MOSFET-based
phase leg configuration to minimize these drawbacks. Based on the proposed
phase leg configuration, a high efficiency single-phase MOSFET transformerless
inverter is presented for the PV microinverter applications. The pulsewidth modulation
(PWM) modulation and circuit operation principle are then described. The
common-mode and differential-mode voltage model is then presented and analyzed
for circuit design. Experimental results of a 250W hardware prototype are shown
to demonstrate the merits of the proposed transformerless inverter on non-isolated
two-stage PV microinverter application.
KEYWORDS: Microinverter,
MOSFET inverters, photovoltaic (PV) inverter, transformerless inverter.
SOFTWARE:
MATLAB/SIMULINK
BLOCK
DIAGRAM:
CIRCUIT
DIAGRAM:
Fig. 2.
Proposed transformerless inverter topology with (a) separated magnetic and (b)
integrated magnetics.
EXPERIMENTAL
RESULTS:
Fig. 3.
Output voltage and current waveforms.
Fig. 4. PWM
gate signals waveforms.
Fig. 5.
Inverter splitting inductor current waveform.
Fig. 6.
Waveforms of voltage between grid ground and DC ground (VEG ).
CONCLUSION
This paper
proposes a MOSFET transformerless inverter with a novel MOSFET-based phase leg,
which achieves:
1) high efficiency
by using super junction MOSFETs and SiC diodes;
2)
minimized risks from the MOSFET phase leg by splitting the MOSFET phase leg
with optimized inductor and minimizing the di/dt from MOSFET body
diode reverse recovery;
3) high
magnetics utilization compared with previous high efficiency MOSFET
transformerless inverters in [21], [22], [25], which only have 50% magnetics
utilization.
The
proposed transformerless inverter has no dead-time requirement, simple PWM
modulation for implementation, and minimized high-frequency CMissue. A
250Whardware prototype has been designed, fabricated, and tested in two-stage
nonisolated microinverter application. Experimental results demonstrate that
the proposed MOSFET transformerless inverter achieves 99.01% peak efficiency at
full load condition and 98.8% CEC efficiency and also achieves around 98%
magnetic utilization. Due to the advantages of high efficiency, low CM voltage,
and improved magnetic utilization, the proposed topology is attractive for
two-stage nonisolated PV microinverter applications and transformerless string
inverter applications.
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