**A New Adaptive Control Scheme for**

Induction Heating System

Induction Heating System

**M’Hamed HELAIMI*, Djilali BENYOUCEF,
Rachid TALEB, Bachir BELMADANI **

Laboratoire de Génie Electrique et Energies Renouvelables,

Université Hassiba Benbouali,

Hay Salem, route nationale N° 19, 02000 Chlef, Algérie

halimi1976@yahoo.fr

^{*} *Corresponding author*

**Abstract: **This paper proposes the design of a new adaptive power control scheme for full bridge series-parallel resonant inverter with AVC control strategy. This scheme is used to control the heating process by adjusting the output power of the inverter irrespective of load and line variations. Two independent control loops are used in this technique: power control loop and frequency control loop (PLL). In the first, an adaptive PID controller with parallel structure is used to force the output power to track the desired trajectory. The adaptive PI controller of the PLL varies the DC input of the VCO in order to generate the required output frequency to maintain ZVS operating during the heating process. The desired performances of the closed loop control are given by two independent reference models. The design of the adaptive mechanism is based on MIT rule and the small signal model of the inverter around the operating point. Compared with other works, the adaptive mechanism redesigns the parameter gains of the PID and the PI controllers in order to avoid the disturbance. Simulation results confirm the effectiveness of the proposed system.

**Keywords: **H Bridge Resonant Inverter, Induction Heating, PLL, PI, PID, MIT rule, Design, Simulation.

**>Full text**

**CITE THIS PAPER AS**:

M’Hamed HELAIMI, Djilali BENYOUCEF, Rachid TALEB, Bachir BELMADANI, **A New Adaptive Control Scheme for Induction Heating System**, *Studies in Informatics and Control*, ISSN 1220-1766, vol. 24 (2), pp. 181-190, 2015.

**Introduction**

Induction heating is a very complex process that involves multi-physics couplings such as electromagnetic, thermal and mechanical. Its application permits to heat a ferromagnetic work piece with better heat distribution, more accuracy and low power consumption [1]-[2].

Recently, a full bridge series-parallel resonant inverter with AVC control strategies is the most widely used topology due to its high reliability. This structure can deliver three level output voltage from DC input voltage [3]-[8].

Induction heating systems are known as complex non linear multivariable problems in which a time-varying structure and parameters variation during the heating phase entail an additional difficulty for modeling and control purposes [9]. Generally, Extending Describing Function methods are used to establish a small signal model of the overall system from any desired input to any desired output [9]-[13].

In control practice, the closed control diagram of induction heating system consists of two control loops: power control loop and frequency control loop (PLL) [9]-[11]. A PID controller with parallel structure is the most popular algorithm used in power control loop [14]-[15]. The conventional PLL with a phase comparator, a low pass filter and linear voltage controlled oscillator (VCO) is the most used [16]. Performance of these control loops with constant gain of PID and PLL diminishes under disturbance and load variations. This problem can be solved by using adaptive control techniques.

Compared with other papers [17]-[20], the basic idea of this work is to propose a new power control scheme based on two adaptive control loops. In the frequency control loop, an adaptive PI controller is introduced between the phase detector and the VCO. This controller is used to adjust the DC input voltage of the VCO for tracking the resonant frequency of the system in order to maintain the ZVS operation during the heating process. In the power control loop, an adaptive PID controller with a parallel structure is used to adjust the shifted angle of the switches to control the output power of the inverter. The required performances of two control loops are expressed by two reference models. An adaptive mechanism based on MRAC and MIT rule [21]-[28] is used to redesigns the gains parameters of PI and PID controllers in accordance to the change in the induction heating system and the rectifier.

This paper is organized as follows: the resonant inverter configuration and the complete closed loop diagram of the proposed control are given in Section 2 and 3, respectively. A Generalized small signal model of the overall system is developed in Section 4. The adaptive power control scheme controller design is introduced in Section 5. Some simulation results are given in Section 6. Finally, Section 7 concludes this paper.

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