Derivation of Boost-Buck Converter Based High-Efficiency PV InverterZheng Zhao, Jih-Sheng Lai and Younghoon Cho

Future Energy Electronics Center, Virginia Tech, Blacksburg, VA 24060 USA

Boost-Buck Converter Based High-Efficiency Robust PV Inverter

Each mode operates separately based on instantaneous grid voltage.

A universal control could be realized for both modes.

PROPOSED PV INVERTER

MODELING of BUCK MODE

EXPERIMENTAL RESULTS

PV LightingBIPV

OPERATION MODES

Boost Mode Transfer FunctionDouble-pole position Q

Buck Mode Transfer FunctionDouble-pole position Double-zero position Q

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Experiment Results of PWM Signals

Photograph of Prototype

Small L1 leads to high frequency double-pole, high gain and small Q, which are all critical to controller design.

Interleaved boost is proposed for smaller inductance of L1 to achieve the same current ripple.

Efficiency of the Boost-Buck Stage

PWM MODULATOR

An offset of the sawtooth ramp right on the top of the buck mode PWM modulator

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MODELING of BOOST MODE

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Where:

INDUCTANCE’S IMPACT ON BOOST MODEExperiment Results

SUMMARY Efficiency peaks at 98.5%. High efficiency is achieved because of single-

stage PWM operation. Ultra high control loop bandwidth with a

multiphase interleaved boost stage, which allows a high resonant pole frequency.

The proposed circuit along with its controller has been designed, simulated, and tested with a hardware prototype.

Buckmode

BoostMode

VPV(t)

Vgrid(t)BoostMode

Buckmode

Buckmode

0

Rated power: 2.5 kWInput voltage: 200 – 500 VOutput voltage: 208/240 VrmsOutput frequency: 60 Hz