Title :
Loss-model based interleave technique to improve the efficiency of micro-inverter
Author :
Zhang, Zhe ; Gao, Mingzhi ; Mo, Qiong ; Chen, Min ; Qian, Zhaoming
Author_Institution :
Coll. of Electr. Eng., Zhejiang Univ., Hangzhou, China
Abstract :
Micro-inverters convert direct current (DC) from a single solar panel to alternating current (AC). They have several advantages over conventional string inverters like higher maximum power point tracking (MPPT) efficiency, easier installation and longer lifetime. Interleave technique could be used in micro-inverter to reduce the power devices´ conduction loss at full load, enlarge the power capacity and reduce the input/output current ripple. However, if the PV modules´ output power decreases, the efficiency of the interleaved micro-inverter will drop sharply due to the increasing switching loss. Besides, the variation of PV modules´ voltage and grid voltage will make the maximum efficiency point fluctuated. Therefore, a power loss model which is a function of the input/output voltage and the output power is proposed in this paper to optimize the efficiency of the interleaved micro-inverter at various input/output conditions. A 200W prototype was setup to verify the loss-model and the control strategies.
Keywords :
invertors; losses; maximum power point trackers; optimisation; photovoltaic power systems; power grids; solar cells; switching convertors; PV module voltage; control strategy; direct current conversion; grid voltage; input-output condition; input-output current ripple; input-output voltage function; interleaved microinverter; maximum efficiency point fluctuation; maximum power point tracking; power 200 W; power capacity; power device reduction; power loss model based interleave technique; solar panel; string inverter; switching loss; Core loss; Equations; Inverters; Mathematical model; Power generation; Switches; Switching frequency; ƒL Grid voltage frequency; ƒe Equivalent switching frequency; Δn Skin depth in the conductor at the nth harmonic frequency; α, β Coefficients to evaluate the core loss; Bac Alternative magnetic field intensity; Coss Equivalent capacitance across the switch SA; Davg Proposed average duty ratio; Iref_A Current reference of phase A; Irms_A RMS value of output current of phase A; Lleak Leakage inductance of the primary; Np Number of layers of the primary winding; Nrm Turns ratio of the transformer; QMOS Gate charge of the switch SA; Ron On state resistance of the switch SA; Rp DC resistance of the primary winding; UGrid Grid voltage; UPV PV modules´ voltage; VD Forward voltage of the diode; VDS_A Turn on voltage across the switch SA; Vdrive Drive voltage of switch SA; tƒ Overlap time during the turn-off of the switch; toff_A Off time of the switch SA; ton_A On time of the switch SA;
Conference_Titel :
IECON 2011 - 37th Annual Conference on IEEE Industrial Electronics Society
Conference_Location :
Melbourne, VIC
Print_ISBN :
978-1-61284-969-0
DOI :
10.1109/IECON.2011.6119944
