Abstract
This paper proposes a three-phase isolated flyback inverter (IFBI) for single-stage grid-tied solar PV applications, considering a simple sinusoidal pulse-width modulation (SPWM) scheme. The proposed single-stage inverter employs a reduced passive elements count by considering three input-parallel output-differential (IPOD) flyback converter modules. Additionally, a single small size LC-input low-pass filter is utilized at the input paralleling point for ripple-free input current operation, which is essential in grid-connected renewable energy applications. In addition, a mathematical model of the IFBI is presented to confirm the existence of its low-order harmonic components. A simple PI controller-based control scheme, considering only two loops and five sensors, is used to control the proposed grid-tied IFBI. Continuous modulation scheme (CMS) combined with SPWM is used to diminish the low-frequency harmonic components. Moreover, a simple selective harmonic elimination (SHE) loop is used for second-order harmonic components (SOHC) elimination from grid-injected currents. The SHE has decreased the SOHC from 43% to 0.96%, which improves the grid current THD from 39% to 3.65%, to follow the IEEE harmonic standard limits. Additionally, the harmonic elimination technique decreases the circulating power between the inverter paralleled modules, which enhances the grid currents power factor. The proposed inverter is verified through a grid-connected 200 V, 1.6 kW, 60 Hz experimental prototype, and the switching frequency is 50 kHz. TMS-based DSP controller is used to control the grid-injected power to follow the reference power set-point.
Highlights
Renewable energy has maintained its expeditious expansion in many countries, which has paved the way for power electronics evolution.Many three-phase inverter topologies have been recommended in the literature [1,2,3].Transformer-less inverter topologies have been extensively recommended [4,5,6,7], which require a boost converter on the input side to grasp the required voltage-gain [8]
isolated flyback inverter (IFBI), a mathematical model is presented in order to confirm the negative sequence low-order harmonic components in the ment number due to the usage of a single LC filter at the input DC side compared to other grid current waveforms, which requires a harmonic elimination control loop in order to inverter structures that need individual LC filters at the input side of each module
The proposed inverter performs voltage boosting of the input DC voltage as well as DC-AC voltage conversion through a single-stage operation, which improves the inverter power density and decreases its cost
Summary
Renewable energy (especially photovoltaics) has maintained its expeditious expansion in many countries, which has paved the way for power electronics evolution. In [43], a boost/flyback based two-stage micro-inverter for solar PV systems was presented in order to enhance the transformer utilization It loses the isolation property and requires the unfolding circuit for DC-AC conversion. The proposed IFBI offers a number of merits such as: reduced number of passive and switching components, voltage boosting/bucking capability in a single-stage operation, and control design simplicity. The proposed IFBI provides a galvanic isolation property for grid-tied applications due to the existence of HFTs. the HFT winding turns ratio offers a wide flexibility for voltage boosting and bucking operations. IFBI, a mathematical model is presented in order to confirm the negative sequence low-order harmonic components in the ment number due to the usage of a single LC filter at the input DC side compared to other grid current waveforms, which requires a harmonic elimination control loop in order to inverter structures that need individual LC filters at the input side of each module.
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