ABSTRACT
High
efficiency and compact single-phase inverters are desirable in many
applications such as solar energy harvesting and electric vehicle chargers.
This paper presents a 2 kW, 60 Hz, 450 VDC to 240 VAC power inverter, designed and
tested subject to the specifications of the Google/IEEE Little Box Challenge.
The inverter features a 7-level flying capacitor multilevel converter, with
low-voltage GaN switches operating at 120 kHz. The inverter also includes an
active buffer for twice-line-frequency power pulsation decoupling, which
reduces the required capacitance by a factor of eight compared to conventional
passive decoupling capacitors, while maintaining an efficiency above 99%. The
inverter prototype is a self-contained box that achieves a high power density
of 216 W/in3 and a peak overall efficiency of 97.6% while meeting the
constraints including input current ripple, load transient, thermal and FCC Class
B EMC specifications.
KEYWORDS:
1. Single-phase
2. Inverter
3. Flying-capacitor
multilevel
4. GaN.
SOFTWARE: MATLAB/SIMULINK
BLOCK
DIAGRAM:
Fig. 1. Full system overview of the
single-phase inverter.
EXPECTED EXPERIMENTAL RESULTS:
Fig.
2. Waveforms showing active energy buffer operation at 2kW. Voltage
ripple
on VC3 counters the ripple on VC1 so that the bus voltage is constant.
Fig.
3. Waveforms showing the output voltage, output current and the
switching node voltage (VSW) of the
7-level inverter at full load.
Fig.
4. Capacitor voltages of the 7-level inverter during full load operation,
obtained using National Instruments
data acquisition system (PXIe-1073).
Fig.
5. Energy buffer operation during a load step-down from 100% to 75%.
The input current ripple becomes
within specifications after 80 ms.
Fig. 6. Inverter operation during a
load step-down from 100% to 75%.
Fig.
7. Conducted EMI measurement at full power (2kW) from 150 kHz to
30 MHz, obtained using Tektronix
RSA5126A real-time signal analyzer.
CONCLUSION
This
paper has presented a 2 kW, 450 VDC to 240 VRMS single-phase inverter. The dc
to ac conversion is accomplished through a 7-level flying-capacitor multilevel
converter, with GaN transistors switching at 120 kHz, which is the highest switching
frequency achieved to date for a 7-level implementation. The commutation loop
in the FCML converter is identified, and a switching cell design is used to
minimize loop inductance and reduce the drain-source voltage ringing. In
addition, the multilevel inverter is complemented by a series stacked buffer
converter for twice-line-frequency ripple compensation. The active energy
buffer achieves a high efficiency of 99% while reducing the required capacitor
volume by a factor of eight.
The combined inverter prototype successfully demonstrated a 216 W/in3 power
density with a rectangular volume of 9.26 in3. A peak overall efficiency of
97.6% is achieved, including the power losses from control and cooling fan. The
prototype meets all the specifications of the Google/IEEE Little Box Challenge,
such as the current ripple, the load transient, the EMC and case temperature
requirement, showcasing the capability of the multilevel converter design and
the series stacked active energy buffer.
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