# Flyback Photovoltaic Micro-Inverter with a Low Cost and Simple Digital-Analog Control Scheme

^{1}

^{2}

^{3}

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## Abstract

**:**

## 1. Introduction

#### 1.1. Background and Motivation

#### 1.2. Literature Review and Research Gap

#### 1.3. Aims and Contributions

## 2. Flyback Micro-Inverter and Its Analysis

_{in}, HFT with one primary and center-tapped two secondary windings, and one switch in the PV side module, two switches in the grid side with two diodes, and an output filter. Moreover, the main switch S

_{PV}is operated with high switching frequency (about 30 kHz), while the secondary switches, S

_{AC1}and S

_{AC2}are operated with a grid frequency (50 Hz). The simulation and practical implementation of the proposed work depend on the following main specifications:

- ✓
- Input voltage from PV module is 25–33 V;
- ✓
- RMS grid voltage is 220 V;
- ✓
- Grid frequency is 50 Hz, and;
- ✓
- Maximum transferred power to the grid is 120 W.

#### 2.1. Analysis of Duty Cycle and Turns-Ratio

_{s}is the switching frequency. By substituting Equation (5) into Equation (3) we reach the following expression:

#### 2.2. Analysis of Magnetizing Inductance

## 3. Design of Transformer and System Parameters

## 4. Proposed Digital-Analog Control Scheme

#### 4.1. Simple Analog Control Circuit

#### 4.2. Digital Control Circuit

## 5. Simulation and Experimental Results

^{2}and temperature $\mathrm{T}=20\text{}\xb0\mathrm{C}$. From this figure, it is clear that the output current is in phase with the utility voltage, so the maximum real output power of $120\text{}\mathrm{W}$ is delivered to the grid with a power factor $\mathrm{PF}=0.988$ and $\mathrm{THD}=3\%$. Also, the PWM pulses for the control of the IGBTs are shown in Figure 9. As shown in this figure, these pulses are obtained to turn on the first IGBT ${\mathrm{S}}_{\mathrm{AC}1}$ in the positive cycle and the second IGBT ${\mathrm{S}}_{\mathrm{AC}2}$ in the negative cycle.

## 6. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 4.**Simulation results (${\mathrm{V}}_{\mathrm{pv}}=33\text{}\mathrm{V},{\text{}\mathrm{P}}_{\mathrm{o}}=120\text{}\mathrm{W}$). Top to bottom: the primary current, the output current with grid voltage, and PWM pulses of the IGBTs.

**Figure 6.**Experimental waveforms of the switching control signals. Top to bottom: primary current reference signal with S(t) signal, and HF pulses of ${\mathrm{S}}_{\mathrm{PV}}$.

**Figure 8.**Experimental waveform for the primary current in the proposed flyback micro-inverter (5A/div.).

**Figure 9.**Experimental waveforms for the output current with the grid voltage, and the PWM signals of the IGBTs.

**Figure 10.**Experimental waveforms for the output current with the grid voltage at 10% of the rated power.

Component | Quantity | Price (USD) |
---|---|---|

Arduino Uno | 1 | 4.2 |

Quad op. amps LM324N | 2 | 1.24 |

Quad comparator LM339 | 1 | 0.95 |

Signal transformer (220/6 V) | 1 | 2.8 |

10 k (1/4 w) resistor | 8 | 0.5 |

Diode 1N4007 | 2 | 0.1 |

Hall current sensor (20 A) | 1 | 1.68 |

Total cost | 11.47 |

Parameter | Symbol | Value |
---|---|---|

Rated output power | ${\mathrm{P}}_{\mathrm{o}}$ | 120W |

PV module voltage | ${\mathrm{V}}_{\mathrm{pv}}$ | 33V-38V |

Grid voltage | ${\mathrm{V}}_{\mathrm{grms}}$ | 220V, 50Hz |

Switching frequency | ${\mathrm{f}}_{\mathrm{s}}$ | 30kHz |

Total input capacitance | ${\mathrm{C}}_{\mathrm{in}}$ | $7\mathrm{mf}$ |

Main MOSFET | ${\mathrm{S}}_{\mathrm{PV}}$ | FDH50N50 |

IGBTs | ${\mathrm{S}}_{\mathrm{AC}1}$,${\mathrm{S}}_{\mathrm{AC}2}$ | FGL40N120 |

Power diode | ${\mathrm{D}}_{\mathrm{AC}1}$,${\mathrm{D}}_{\mathrm{AC}2}$ | RHRG75120 |

Flyback transformer | ||

Core type | - | E55/28/2-3C90 |

Effective length | ${\mathrm{l}}_{\mathrm{e}}$ | $12.4\text{}\mathrm{cm}$ |

Turn’s ratio | $\mathrm{N}$ | 10 |

Magnetizing inductance | ${\mathrm{L}}_{\mathrm{m}}$ | $18.8\text{}\mathsf{\mu}\mathrm{H}$ |

Maximum flux density | B_{m} | 0.2 T |

Output power | 12 W | 50 W | 100 W | 120 W |

Proposed THD | 6% | 4.6% | 3.5% | 3% |

Zhang Z.et al. [20] | 7.8% | 6.6% | 5.4% | 4.2% |

Paper | Type of Micro-Inverter | Controller Used | Maximum Efficiency | Cost |
---|---|---|---|---|

Z. Zhang et al. [20] | Interleaved flyback, 200 W | FPGA EP3C10E | 94% | 29$ |

H. Hu et al. [33] | Single-stage flyback, 120 W | Microprocessor STM32F103 | 89.7% | 7.77$ |

Y.H. Kim et al. [18] | Interleaved flyback, 100 W | TMS320F28035 | 94.5% | 17$ |

H. Hu et al. [32] | Single-stage flyback,100 W | Microprocessor STM32F103 | 90% | 7.77$ |

Proposed | Single-stage flyback, 120 W | Arduino Uno microcontroller | 91% | 4.2$ |

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**MDPI and ACS Style**

Yaqoob, S.J.; Obed, A.; Zubo, R.; Al-Yasir, Y.I.A.; Fadhel, H.; Mokryani, G.; Abd-Alhameed, R.A.
Flyback Photovoltaic Micro-Inverter with a Low Cost and Simple Digital-Analog Control Scheme. *Energies* **2021**, *14*, 4239.
https://doi.org/10.3390/en14144239

**AMA Style**

Yaqoob SJ, Obed A, Zubo R, Al-Yasir YIA, Fadhel H, Mokryani G, Abd-Alhameed RA.
Flyback Photovoltaic Micro-Inverter with a Low Cost and Simple Digital-Analog Control Scheme. *Energies*. 2021; 14(14):4239.
https://doi.org/10.3390/en14144239

**Chicago/Turabian Style**

Yaqoob, Salam J., Adel Obed, Rana Zubo, Yasir I. A. Al-Yasir, Hussein Fadhel, Geev Mokryani, and Raed A. Abd-Alhameed.
2021. "Flyback Photovoltaic Micro-Inverter with a Low Cost and Simple Digital-Analog Control Scheme" *Energies* 14, no. 14: 4239.
https://doi.org/10.3390/en14144239