Derivation of Boost-Buck Converter Based High-Efficiency PV Inverter Zheng 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 Lighting BIPV OPERATION MODES Boost Mode Transfer Function Double-pole position Q Buck Mode Transfer Function Double-pole position Double-zero position Q j L L C L D L s 2 1 1 1 2 2 ' j L L C D L L s 2 1 1 2 1 2 1 1 1 1 1 1 1 1 2 2 4 ) ( L C j L C DCR ESR C V L D I s in 1 2 1 4 1 1 2 2 ' ' ESR L C D L L D L Q 1 1 2 1 2 1 2 1 2 DCR ESR L C D L L L Q Experiment Results of PWM Signals Photograph of Prototype Small L 1 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 L 1 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 d D V c ˆ d I ˆ 1 2 L2 2 1 1 1 1 d I c ˆ d D V ap ˆ e 1 1 1 1 2 2 2 2 2 2 2 2 1 1 1 1 ) ( ) 1 ( ) ( ESR DCR r ESR DCR D D D DCR D L s r D D D DCR D L s Z ESR sC DCR sL Z e e Le LC 2 2 2 ˆ ˆ ) ˆ ˆ ( i D Z d D V i D d I Z Le in LC MODELING of BOOST MODE e L L C L C L C L C L c C L L L Z i Z i Z i d D V D i i d I D i 1 1 2 2 2 2 2 1 1 1 ˆ ˆ ) ˆ ˆ ( ˆ ˆ ˆ ˆ o c L C L L C C L C L C C L L V V I I Z Z Z Z Z Z Z Z i i , , ˆ ˆ 1 1 2 2 2 2 2 2 1 2 ESR DCR r e Where: INDUCTANCE’S IMPACT ON BOOST MODE Experiment 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. Buck mode Boost Mode V PV (t) V grid (t) Boost Mode Buck mode Buck mode 0 Rated power: 2.5 kW Input voltage: 200 – 500 V Output voltage: 208/240 V rms Output frequency: 60 Hz