In the past year or two, a number of customers engaged in the production/sale of household induction cookers have provided feedback. For household induction cookers sold in India, the percentage of abnormal quality of the whole appliance after a few months of use is much higher than in other sales regions. The problems of the whole machine with abnormal quality are mainly concentrated in high temperature protection, (fuse/rectifier bridge/IGBT/filter capacitor/resonant capacitor) burnout, etc. Based on the analysis results provided by multiple customers, the main problem lies in supporting use On the pots and pans. India mainly uses J4 pots, while other regions mainly use 430/304 pots.

The company's 5μF filter capacitors and 0.3μF resonant capacitors are used by many customers. We have also collected that the failure ratio of the complete machine sold in India is much higher than the overall failure ratio. In view of this, the company also analyzed the failure reasons of the capacitor by itself, and cooperated with customers to make a series of improvement measures. After many cooperation and rectifications with many customers, we can basically implement the problems that need attention in the use of film capacitors in India. The specific conditions are as follows:

One: Analysis of the causes of heating of film capacitors

The ideal film capacitor is a purely capacitive electronic component. As long as the capacitor is charged, the electrical energy can be stored in the capacitor forever. But in fact, due to the influence of factors such as structure, material and production process, film capacitors will have certain stray inductance (ESL), equivalent series resistance (ESR), parallel resistance, etc., which will cause heat generation inside the film capacitor itself loss. The formula for calculating the heat loss of the film capacitor is P(heating)=2*Pi*F*C*U*U*tgθ From this formula, we can know that the heating of the film capacitor follows the frequency F passing through the capacitor, and the working voltage U at both ends of the capacitor, The capacitance C of the capacitor itself is proportional to the loss tangent of the capacitor. The larger these parameters are, the more the capacitor heats itself.

For filter capacitors, the most important factors affecting their heating are ripple voltage and ripple current. The ripple voltage is generally only 30-50Vpp, and high-order ripples exist in the range from above 100HZ to 1MHZ, with complex waveforms and rich frequencies. At present, there is no reliable calculation formula and measurement method to detect ripple current.

Two: The influence of Indian J4 cookware on the electrical performance parameters of the whole machine when used in household induction cookers:

A 2000W model sold to India by a certain company, the same induction cooker, replaced with different pots 430, 304, J4, the measured voltage waveform data of the 0.33μF resonant capacitor actually working are as follows:

It can be seen from the above data that the Qn (reactive power) of the resonant capacitor is the largest when the J4 cookware is used on the same machine, which is nearly 30% higher than the other two cookware. Qn is the reactive power that the resonant capacitor needs to carry when it works.

Three: The influence of Indian J4 cookware on household induction cooker

According to the measured data, when using India J4 cookware, the actual working resonance frequency of the household induction cooker will increase. After the resonance frequency increases, it will have a certain impact on the internal electronic components of the machine, such as PCB copper foil, rectifier bridge, The temperature rise of chokes, filter capacitors, resonant capacitors, IGBTs, coil disks, etc. will increase, and in serious cases, explosions will occur.

For a resonant capacitor, the resonant frequency increases, and the reactive power that the capacitor needs to bear will increase, causing the resonant capacitor to increase its own heating, which is reflected in the increase in temperature of the resonant capacitor. For the filter capacitor, the resonance frequency increases, the ripple voltage generated by the IGBT due to high-speed switching will increase, the number of high-order ripples will increase, and the ripple current flowing through the filter capacitor will increase, which is finally reflected in the temperature rise of the filter capacitor. high.

4: Recommendations for household induction cookers sold to India

A. Improve the electrical performance margin of key components and materials such as rectifier bridges, filter capacitors, resonance capacitors, coil plates, IGBTs, radiators, fans, and PCB copper foils. For example, increase the current value and improve the heat dissipation conditions.

B. The chip control scheme of the whole machine is adjusted to suppress the abnormal temperature rise of key components by limiting the power. For example, when it is detected that the pot is made of J4 and other materials, the power and temperature rise protection are set on the software.

Five: Improvement direction of filter capacitor and resonance capacitor

Household induction cookers sold in India are used with J4 cookware. If there is no change in software control, only the heat generated by the filter capacitor and the resonant capacitor can be reduced, thereby reducing the temperature rise of the capacitor.

For filter capacitors, there are several ways to improve:

A Increase the capacity of the filter capacitor. (Increase from 5μF to 6μF, 7μF, 8μF, etc.)

B Due to the relatively small size of the fourth-generation small-volume capacitors, the gold-sprayed end face bearing capacity of the capacitor appears to be slightly insufficient when used in harsh electrical parameters and environments, so it is recommended to change to the third-generation large-volume capacitor.

C The most ideal effect is to adopt the third-generation large-volume structure, keep the capacity of the filter capacitor unchanged, and shorten the pitch of the capacitor (from P=30.5MM to P=26.5MM). This can shorten the width of the film and increase the winding. Increase the area of the gold-sprayed end surface to reduce the self-heating of the filter capacitor.

For resonant capacitors, there are the following directions for improvement:

A. Because the fourth-generation small-volume capacitors are relatively small, and when used in harsh electrical parameters and environments, the gold-sprayed end surface bearing capacity of the capacitor appears to be slightly insufficient, so it is recommended to change to the third-generation large-volume capacitor.

The most ideal effect of B is to adopt the third-generation large-volume structure, keep the capacity of the filter capacitor unchanged, and shorten the pitch of the capacitor (from P=30.5MM to P=26.5MM). This can shorten the width of the film and increase the winding. Increase the area of the gold-sprayed end face to reduce the self-heating of the resonant capacitor.

C can consider appropriately increasing the capacitance of the resonant capacitor and adjusting the reel parameters appropriately to reduce the LC resonant frequency, so that the temperature rise of related electronic components is reduced as a whole, and finally reliable use is guaranteed.

Through the improvement and test evaluation of the film capacitor scheme with many customers, the above schemes can solve the problem of excessive temperature rise and burnout of filter capacitors and resonant capacitors when used in the complete household induction cooker in India. Since each company's household induction cooker scheme and structural cooperation are different, it will eventually require actual installation evaluation to be finalized.