Abstract
The nonferromagnetic pans with a low equivalent resistance are desired to generate sufficient power for heating by larger eddy current. First, Maxwell 3D is used to estimate the equivalent heating resistance of a copper pan and select the optimal number of turns for a induction coil by Litz wire according to its size limitations and efficiency. Furthermore, the optimal resonant frequency is determined by maximizing the heating efficiency. Finally, the electric parameters are obtained to construct a simulation environment for the design of control strategies. A full-wave rectifier, buck converter, and half-bridge resonant converter are cascaded to construct the converter. Because of low equivalent resistance and high quality factor of the copper pan, a high slope ratio of the resonant current to the frequency is obtained. Therefore, the resonant converter is operated at a fixed switching frequency to reduce low-frequency oscillations of the resonant current. The buck converter is used to control the DC link voltage with third-harmonic injection, which enables heating power control, increases heating power and satisfies the standard, IEC-61000-3-2 Class A. Moreover, a resonant frequency estimator is developed to detect the resonant frequency for various positions of the pan on the induction coil to determine the optimal heating frequency. Finally, TMS320F28075-based converter with 100 A of peak resonant current is built. The heating effect and power loss on a copper pan is then measured, and the maximum heating efficiency is 69%. The measurement results verify the effectiveness of the proposed induction cooker and exhibits excellent agreement with the simulated results.
Highlights
Induction heating (IH) has become popular in domestic cooking because of its high efficiency, fast heating, accurate power control, and safety [1], [2]
Conventional induction cookers consist of an AC–DC rectifier, a resonant converter, and an induction coil so that they can generate high-frequency magnetic flux and the coil with a pan acts as the resonant inductor of the resonant circuit [4]–[6]
RESONANT CAPACITOR AND CURRENT 1) RESONANT CAPACITANCE According to the specifications in Table 2, the induction coil made of a 21-turn and 3200-strain Litz wire exhibits its maximum efficiency at 130 kHz
Summary
Induction heating (IH) has become popular in domestic cooking because of its high efficiency, fast heating, accurate power control, and safety [1], [2]. Because current converters for IH are voltage sources in principle, adjusting the impedance of the resonant tank by changing the operating frequency with 50% duty (VF) [12] is a popular method for controlling the heating power. IH operates with low efficiency if the resistances of the induction coil and nonferromagnetic pan become close due to improper design. The resonant inductance and equivalent heating resistance obtained for the proposed induction cooker by using power integration and the impedance analyzer exhibited excellent agreement with the corresponding simulations obtained using Maxwell 3D. The proposed control approaches of resonant frequency estimation and increasing heating power through third-harmonic injection are verified through experimental results. This paper derived the design procedure by using simulated software for self-inductance, coupling factor, misalignment effects, and voltage gain in advance for the converter design to reach needed functions with higher efficiency
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