ABSTRACT
Single-phase
two-stage inverters generally use an intermediate capacitor to buffer the power
imbalance between DC input and AC output. However, the resultant low-frequency voltage
ripple on this intermediate capacitor may produce low frequency ripple at the
source side, especially when the front-end dc/dc converter operates in
continuous conduction mode (CCM). Some common solutions to reducing this ripple
are feed forward control and power decoupling circuits. Alternatively, this
paper analyzes a two-stage inverter where the front-end is a dc/dc converter operating
in discontinuous conduction mode (DCM). In general dc/dc converters operating
in DCM have inherent natural capability to reduce this low-frequency input
current ripple, without needing a sophisticated control or complex circuitry as
compared with its CCM operation. Analysis with simulation verification is
reported to demonstrate such capability.
KEYWORDS
1. Dc/ac
2. Low-frequency
ripple
3. Single-phase
4. Two
stage
SOFTWARE:
MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.
1. A simplified power-stage diagram of a single-phase two-stage inverter.
EXPECTED SIMULATION RESULTS
(a)
CCM operation: _vin = 3:3V
(b)
DCM operation: _vin = 0:88V
Fig.
2. DCM boost front-end converter has lower voltage ripple than CCM.
Fig.
3. DCM buck-boost front-end converter does not contain low-frequency
ripple
but only high-frequency ripple.
Fig.
4. SEPIC front-end converter operating in DCM+CCM contains negligible
low-frequency
ripple but only high-frequency ripple.
Fig.
5. High-gain front-end converter operating in DCM does contains
significant
low-frequency ripple.
CONCLUSION
This
paper analyzes basic and several higher-order front-end dc/dc converters for
single-phase two-stage inverter design. Through inspecting the instantaneous
average input current of those converters in discontinuous conduction mode
(DCM), it has confirmed that buck-boost converter and buck-boost derived
converters such as ZETA are free of low-frequency (mainly double ac line
frequency) input current ripple due to the lack of direct connection between
input and output during switching actions. For boost converter based converters
such as SEPIC and C´ uk converters, their input currents contain lower
low-frequency content thanks to the cascaded design. For boost converter based
high voltage gain converters, its input current may not necessarily reduce the
low-frequency content effectively. It depends on how the high-gain sub circuit is
constructed and interacts with the input inductor. Further research is
necessary to identify suitable converter topologies which have both smooth
input current and low frequency content.
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