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A NON-ISOLATED BIDIRECTIONAL SOFT SWITCHING CURRENT FED LCL
RESONANT DC/DC CONVERTER TO INTERFACE ENERGY STORAGE IN DC
MICROGRID
ABSTRACT:
This project proposes a non-isolated soft-switching bidirectional dc/dc converter for interfacing
energy storage in DC Microgrid. The proposed converter employs a half-bridge boost converter
at input port followed by a LCL resonant circuit to assist in soft-switching of switches and
diodes, and finally a voltage doubler circuit at output port to enhance the voltage gain by 2x. The
LCL resonant circuit may also add a suitable voltage gain to the converter. Therefore, overall
high voltage gain of the converter is obtained without transformer or large number of multiplier
circuit. For buck operation, the high side voltage is first divided by half with capacitive divider to
gain higher step down ratio.
Converter is operated at high frequency to obtain low output voltage ripple and reduced
magnetic and filters. Zero voltage turn-on is achieved for all switches and zero current turn -on
and turn-off is achieved for all diodes for both buck/boost operation. Voltage stress across
switches and diode is clamped naturally without external snubber circuit. At front end proposed
converter has a half bridge boost LCL resonant circuit, purpose of it is to increase the voltage
gain and provide ZVS soft switching for switches. For boost operation, front-end half-bridge
boost converter provides a voltage gain of and LCL resonant circuit provides an additional gain.
The LCL resonant circuit may also add a suitable voltage gain to the converter. Therefore,
overall high voltage gain of the converter is obtained without transformer or large number of
multiplier circuit. For buck operation, the high side voltage is first divided by half with
capacitive divider to gain higher step down ratio. Converter is operated at high frequency to
obtain low output voltage ripple and reduced magnetics and filters. Zero voltage turn-on is
achieved for all switches and zero current turn on and turn-off is achieved for all diodes for both
buck/boost operation. Voltage stress across switches and diode is clamped naturally without
external snubber circuit.
LCL resonance circuit also provides ZVS for switch M1 and M2 and ZCS for D3 and D4. At the
output side, a half-bridge voltage doubler circuit is adopted to give additional gain of 2x. In buck
operation, the high side voltage is divided by capacitor divider to half. Further, switches M3 and
M4 are modulated to give high step down ratio.
The LCL resonant circuit provides ZVS for switches M3 and M4 and ZCS for rectifier diodes D1
and D2. Gating signals of switch pair M1 and M2 are complementary with each other with
appropriate dead band between them for boost operation. M3 and M4 are in turn-off state for
boost operation. Switch pair M3 and M4 is operated complementary with each other with dead
time for buck operation. M1 and M2 are in off state for buck operation.