# Induction Heating for Variably Sized Ferrous and Non-Ferrous Materials through Load Modulation

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## Abstract

**:**

## 1. Introduction

## 2. Design of Induction Heating System

#### 2.1. System Description

#### 2.2. System Topology

#### 2.3. Modes of Operation

#### 2.3.1. Ferrous Heating Mode

_{r}, R

_{pot}, C

_{r1}, and S3. After that, switch S1 was turned off, and S2 was turned on; the power flow was in the direction through S3, C

_{r1}, R

_{pot}, L

_{r}, and S2. The maximum power supplied to the load at resonance frequency is given by Equation (1).

_{f}is the maximum power in the ferrous heating mode, V

_{in}is the input voltage to the inverter, and R

_{pot}is the resistance of the metal at the load. The operating frequency of the series resonant inverter in this mode remained the same as the switching frequency. Equation (2) provides the resonance frequency for an LC circuit.

_{s}is the resonance frequency, L

_{r}is the coil inductance, and C

_{r}is the resonant capacitance. The ferrous heating mode can be used to heat ferromagnetic materials such as iron, stainless steel, etc. Equation (2) can also be rewritten by including the Q factor as

_{0}is the natural frequency without any losses, and α is the damping attenuation in nepers per second, which can be expressed as Equation (6).

#### 2.3.2. Non-Ferrous Heating Mode

_{r}, R

_{pot}, C

_{r2}, and S4, and for when S2 was in the ON state, the energy flow was in the direction through S4, C

_{r2}, R

_{pot}, L

_{r}, and S2. The maximum power available in this mode is given by Equation (7).

_{nf}is the maximum power in the non-ferrous heating mode, V

_{in}is the input voltage to the inverter, and R

_{pot}is the resistance of the metal at the load. This mode of operation is generally used to heat non-ferromagnetic materials such as aluminium; since the resistance of these materials is low, the increased operating frequency was used to increase the resistance of the material to help heat it to the same degree as the ferromagnetic materials.

#### 2.4. Selection of the Operational Mode

_{2}is given by Equation (12).

_{pot}(Equation (14)) and the imaginary part as L

_{r}(Equation (15)).

_{pot}and L

_{r}), and the determined values were used in the simulation.

## 3. Results and Discussion

#### 3.1. Simulation Results of Heating Different Metals

#### 3.1.1. Analysis of Results with Ferrous Heating Mode

_{r}and C

_{r}values selected for this mode were 160 uH and 253 nF, respectively. From Figure 12, it could be inferred that the equivalent input voltage (220 V) in ferrous heating mode was twice the input voltage (±110 V). The magnitude of the output voltage was nearly half of the input voltage. Therefore, the series resonant inverter transmitted the power of 1 kW in the resonant frequency of 25 kHz.

#### 3.1.2. Analysis of Results with Non-Ferrous Heating Mode

#### 3.2. Experimental Results of Heating Different Metals

#### 3.2.1. Hardware Implementation

#### 3.2.2. Practical Results of Ferrous Heating Mode

#### 3.2.3. Practical Results of Non-Ferrous Heating Mode

#### 3.3. General Discussion

## 4. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Correction Statement

## Nomenclature

V_{DC} | Input DC voltage for the system |

L_{r} | Resonant tank inductor |

C_{r} | Resonant tank capacitor |

t_{s} | Time period of PWM pulses |

G_{m} | Maximum voltage gain |

P_{f} | Maximum power in ferrous heating mode |

P_{nf} | Maximum power in non-ferrous heating mode |

FLM | Flexible load modulation |

IH | Induction heating |

R_{pot} | Resistance of the material to be heated |

F_{s} | Resonance frequency |

F_{sw} | Switching frequency |

PWM | Pulse width modulation |

P_{r} | Rated power |

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**Figure 12.**Power and voltage waveforms (input and output) for ferrous heating mode during simulation.

**Figure 14.**Power and voltage waveforms (input and output) for non-ferrous heating mode during simulation.

**Figure 17.**Thermal image of heating different metals: (

**a**) stainless steel; (

**b**) aluminium; (

**c**) copper (power rating: 2 kW and time period: 100 s).

Parameters | Ferrous Heating Mode | Non-Ferrous Heating Mode |
---|---|---|

V_{in} (Volts) | 220 | 220 |

Capacitance (C1) (mF) | 1.0 | 1.0 |

Capacitance (C2) (mF) | 1.0 | 1.0 |

Pot resistance (ohms) | 15.2 | 9.8 |

Inductance (Lr) (uH) | 160 | 160 |

Capacitance (Cr) (nF) | 253 | 63.3 |

Resonant frequency (kHz) | 25 | 50 |

Type of Metal | Dimension (cm) | Weight (gm) | Calculated Temperature, T (°C) | Time Taken to Attain Calculated Temperature (s) |
---|---|---|---|---|

ALUMINIUM | ||||

Aluminium bowl | Diameter = 16 | 155 | 367 °C | 656 |

Thickness = 3.2 | ||||

Aluminium rod | Diameter = 2.6 | 47 | 369 °C | 700 |

Length = 3.2 | ||||

COPPER | ||||

Copper bowl | Diameter = 8 | 166 | 377 °C | 965 |

Thickness = 3.7 | ||||

Copper round bar | Diameter = 1.16 | 35.1 | 401 °C | 1000 |

Length = 3.7 | ||||

STAINLESS STEEL (S4) | ||||

Stainless steel bowl | Diameter = 8 | 144 | 889 °C | 333 |

Thickness = 3.7 | ||||

Stainless steel round bar | Diameter = 1.72 | 68 | 906 °C | 591 |

Length = 3.7 | ||||

CAST IRON | ||||

Iron pan | Diameter = 16 | 152 | 315 °C | 765 |

Thickness = 3.2 | ||||

Iron rod | Diameter = 1.7 | 53 | 400 °C | 768 |

Length = 3.2 |

Types of Metal | Switching Frequency (kHz) | Simulation Results | Experimental Results | ||||
---|---|---|---|---|---|---|---|

Output Voltage, Vo (V) | Output Current, Io (A) | Output Power, Po (W) | Output Voltage, Vo (V) | Output Current, Io (A) | Output Power, Po (W) | ||

Ferrous | 25 | ±110 V | 9 A | 990 | ±108.9 V | 8.59 A | 935.5 |

Non-ferrous | 50 | ±110 V | 14 A | 1540 | ±108.3 V | 13.2 A | 1429.6 |

Study | Key Technology | Scheme Topology | Remarks |
---|---|---|---|

Millan et al. [11] | Selective harmonic scheme | Modified half-bridge series resonant inverter. | The authors proposed a modified topology of half-bridge inverter with two operation modes of selective harmonics. |

Park and Jung [12] | Load adaptive modulation (LAM) | Full bridge series resonant converter. | LAM was proposed by the authors to vary the input voltage magnitude of IH coil and series resonant inverter’s operating frequency based on the pot resistance. |

Tanaka [15] | - | Half-bridge series resonant inverter. | Examined the input resistance of different metals and determined the finest condition for a high-frequency inverter. |

Shoji et al. [20] | - | Buck–boostfull-bridge inverter. | The authors applied this method for induction cookers with left and right sides to heat all metals. |

Proposed system | Flexible load modulation (FLM) | Half-bridge resonant converter | Here, FLM was proposed to heat various loads with variable sizes by using a half-bridge resonant converter without any rectification stage. |

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**MDPI and ACS Style**

Ramalingam, S.R.; Boopthi, C.S.; Ramasamy, S.; Ahsan, M.; Haider, J.
Induction Heating for Variably Sized Ferrous and Non-Ferrous Materials through Load Modulation. *Energies* **2021**, *14*, 8354.
https://doi.org/10.3390/en14248354

**AMA Style**

Ramalingam SR, Boopthi CS, Ramasamy S, Ahsan M, Haider J.
Induction Heating for Variably Sized Ferrous and Non-Ferrous Materials through Load Modulation. *Energies*. 2021; 14(24):8354.
https://doi.org/10.3390/en14248354

**Chicago/Turabian Style**

Ramalingam, Senthil Rajan, C. S. Boopthi, Sridhar Ramasamy, Mominul Ahsan, and Julfikar Haider.
2021. "Induction Heating for Variably Sized Ferrous and Non-Ferrous Materials through Load Modulation" *Energies* 14, no. 24: 8354.
https://doi.org/10.3390/en14248354