Optimal Switching Waveform with near Zero-Voltage and Zero-Current turn-onDesigning Induction Cooktop Magnetic Circuit

INDUCTION COOKTOP COIL DESIGN P =Power delivered by induction coil to cooktop.fmains = mains frequencyfsw = Switching frequencyL= Inductance of induction coilVm=Peak supply voltageN=fsw /fmains Nos. of pulses in one mains cycle

For P = 2000W and fsw = 20KHz; L = 165uH. so Im = 12.36Amps, Irms = 8.71Amps and P= Vrms*Irms =230*8.71 = 2000WThe flux density is maximum at the starting edge of ferrite core that is near centre of coil and linearly reduces to zero at the outer edge.Assuming total flux linking through the ferrite core where average flux density is Bm/2, we get total flux =(BmWLP/2), where P is no of ferrite bars and

W = ? ML = ? MLg = ? MP = 6LC = ? uHFrom the Wheelers formula (Wheeler, 1928), inductance of the flat spiral coil asshown in Fig. 5.4 with out feromagnet is obtained using the expression mentioned below.

where, N = total number of turns, R = mean radius of the spiral coil (in inches) = 0 0.5(R0 - c) , W = depth of the spiral coil (in inches) = outer radius inner radius = (Ro - c)

Calculate coil inductance of Prestige Cooktop without pot and measure with meterCalculate coil inductance of Prestige Cooktop

ELECTROMAGNETIC FIELDS ANALYSIS OF INDUCTION COOKER BY FINITE ELEMENT SOFTWARE SUCH AS COMSOL/ANSOFT

Model of induction cooker is established by American finite element electromagnetic field computation software Ansoft. The model is 2D and axis symmetric. By numerical calculation, the distribution of eddy current induced in the pan and the distribution of magnetic field intensity are as shown in Fig. 1 and Fig. 2EQUIVALENT CIRCUIT OF INDUCTION COOKERThe coupling between the coil and the pan is modeled as the series connection of an inductor and a resistor, based on the transformer analogy. Fig. 4 shows the equivalent circuit of induction cooker. The coil of induction cooker is equivalent to the source side of transformer, and the pan is equivalent to the vice side of transformer. In Fig. 3(a), R1 is resistance of the coil, L1 is inductance of the coil, R2 is resistance of the pan, L2 is inductance of the pan, M is mutual inductance between the pan and the coil.The equivalent circuit from the power source end looked is showed in Fig. 3(b). Z11 is impedance of the coil, Z12 is the pan's impedance converted into to the source side, their expressions are as follows: Z11 = R1 + L1, Z12 = R12+jL12, R12 = 2M2R2/(R22+X22), X12 = 2M2X2/(R22+X22).

Although the voltage of power source will be different against the pan's parameters, in the analysis andcalculation of power, the source should be regarded as a constant voltage source or a voltage source withsmall interface resistance and not as constant current source. That is because the current has a very bigchange along with the pan's parameter and the operating frequency. By the analysis of the circuit, we cansee that at a certain voltage U, P=U2R/(R2+X2), Q=U2X/(R2+X2), where, R=R11+R12, X=X11+X12, P is the total active power and Q is the total reactive power. Peddy = U2R12=(R2 + X2), eff = R12=(R12 + R1), where Peddy is power of the pan, eff is efficiency.

Table 1 is about the results along with the change of frequency. From Table 1, we can see that:efficiency has a maximum value when the frequency is about 28 kHz, but the change is very small, only differs 0.2% between 15 kHz and 40 kHz, when voltage is a constant, Peddy and Q reduce monotonously and quickly.

Table 2 is about the results along with the change of pan's permeability. When conductivity is decided as 1.389e6, permeability is changed. Permeability has a direct impact on the value of inductance and the reactance. In the following table permeability is relative permeability. From Table 2, we can see that: efficiency has a maximum value when permeability is about 800, and the maximum efficiency and minimum efficiency has a difference about 1%. (2) Peddy and Q reduce monotonously and quickly along with the increase of permeability.

Table 3 is about the results along with the change of pan's conductivity. The relative permeability is decided as 1 (except the case of iron pan with relative permeability 800 noted in the table 3). From Table 3, we can see that: efficiency has a maximum value when conductivity is about 500000, and has a obvious variation along with the change of conductivity, Stainless steel pan's efficiency is high above 30% than aluminium pan's, and lower 0.7% than iron pan's, (2) power also has a maximum value when conductivity is about 5e5 S/m.

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