An Improved PIλ Controller for Resonant Inverter Induction Heating Systems under Load and Line Variations

Abstract

This paper presents the description, analysis and control of an LLC resonant inverter suitable for induction heating applications. The output power of the proposed inverter has to be controlled by adjusting the duty cycle of the switches using a power loop circuit based on fractional order PI λ controller. A phased locked loop (PLL) is used as frequency tracking control circuit. The complete closed loop control model is obtained using small signal analysis. The validity of the proposed control is verified by simulation results. Results of this simulation are compared to those obtained by using a PI controller. They show that the improved PI λ controller exhibits a much better behaviour.

A New Adaptive Control Scheme for Induction Heating System

“…The oscillating circuit given in Figure 1 [3] is composed of a series inductor L s with a parallel resonant capacitor C . The induction heating load (copper coil and workpiece) can be modeled by means of a series combination of its equivalent resistance R and equivalent inductance L transferred to the primary side of the matching transformer [9], [30]. The converter is operated at frequency above the natural one for the LLC load given by [3]:…”

“…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].…”

Current predictive controller for high frequency resonant inverter in induction heating

“…In induction heating, the control of current and consequently the power needs more and more of an advanced control technique to ensure a good regulation with precision, quickness and efficiency. Several classical methods of control have been adopted to control the frequency, current and power transmitted into the piece to be heated, whose [1][2][3][4] have successively proposed the use of PI and I regulators for induction heating applications.But these conventional control laws may be insufficient because they are not robust, especially when the accuracy requirements and other dynamic features of the system are stringent. An optimal regulator (LQR) has been proposed by [5] and [6], this method is not robust to the uncertainties of the models (uncertainties about the parameters, disturbances ....) [5], and [7] has also proposed the application of sliding mode control in serie-parallel LCC resonators for induction heating.…”