Source: https://sic.ici.ro/past-issues/volume21-issue4-2012/helaimi/
Timestamp: 2019-04-26 07:41:50+00:00

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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? 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? controller exhibits a much better behaviour.
Keywords: Robustness, LLC resonant inverter, small signal model, improved PI? controller, induction heating system.
Nowadays, resonant topologies are used in a number of industrial applications, including power supplies for induction heating systems. LLC is being a more popular topology because it has the desirable characteristics of the series and parallel ones -.
In control practice, fractional order PIλ controllers have been successfully applied to a wide variety of engineering problems -, including DC-DC converters .
Several research works on control theory reveal that the design of the PIλ controller is not easy when the system is difficult to model due to complexity, non linearity, or when the resource of information are inexact. LLC resonant inverters fall into this category because they have a time varying structure and contain elements that are non linear.
In this paper, we propose an effective control system for LLC resonant inverter which uses variable frequency and variable duty cycle. The output power of the proposed inverter has to be controlled by adjusting the duty cycle of the switches using power loop circuit based on fractional order PIλ controller. A PLL is used as frequency tracking control. In this case, a stability and small signal dynamic performance can be assessed using linear control techniques and the small signal model of the LLC resonant inverter.
The organization of this paper is as follows: he proposed inverter circuit configuration and the detailed control system architecture are given in Sections II and III. Closed loop system design and parameter tuning of the proposed PIλ controller are presented in Sections IV. Conclusion is given in Section V.
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