Application and solution of IGBT in induction cooker

Discrete IGBTs are the power switch of choice for modern inverter-based induction cooking products. As energy costs continue to rise and consumer demand for smaller cooking solutions increases, IGBT technology must evolve to meet these demands.

The basic principle of induction heating was discovered by Michael Faraday in 1831 and further developed by Heinrich Lenz. In experiments with magnetism and electromotive force, they found that heat is generated in the core during the switching of the magnetic field.

Based on this basic principle, induction cookers use a magnetic field to directly heat the cookware, and therefore the food. This method of cooking is becoming increasingly popular because it is more energy-efficient than a gas stove, as it only heats the cookware. It is also fast and highly controllable, as the heat level can be varied simply by changing the strength of the magnetic field.

The same induction technology is now used in rice cookers, which spreads heat better than standard heating elements and allows for instantaneous and precise temperature changes. A major advantage of induction cooking is that the cooking surface is completely sealed and therefore easier to clean, making the cooking process more hygienic than other methods.

As induction cooking devices become more popular, consumer expectations are rising, creating greater challenges for designers. Efficiency is a major concern for many consumers due to rising global energy costs and stricter regulations. Designers must also focus on safety and reliability, ensuring that the product does not fail, leaving consumers without a place to cook and damaging the supplier’s reputation.

To differentiate their product portfolios, many manufacturers are offering advanced features, such as Wi-Fi-enabled control. As consumers evaluate these additional features, value and price become increasingly important criteria in selecting induction cooking equipment.

At the heart of an induction cooker is an insulated gate bipolar transistor (IGBT) that controls the critical power switching function. As such, the IGBT is a key factor affecting the efficiency, size, reliability and cost of the end product.

Obviously, choosing the best IGBT solution is critical for induction cooker designers. In most cases, designers will focus on key parameters such as maximum collector current (IC) and maximum collector-emitter voltage (VCE) to ensure that the IGBT can control the required power (typically up to 2100 W for cooking applications) as well as VCEsat and Eoff, which are critical to the operating efficiency of the device.

Choosing the best topology for the circuit is also important, as the design needs to be simple, reliable, and energy efficient. One of the most popular topologies for induction cooking is the single-ended parallel resonant inverter (SEPR), although its power levels are relatively limited.

The topology consists primarily of a shunt inductor and capacitor resonant tank network with a combined IGBT and diode and a small capacitor that improves EMI performance and, along with the diode, provides a path for the inductor's resonant current. The inverter is typically powered from a rectified but unfiltered mains line voltage, achieving near unity power factor correction.

Typical operating frequencies are in the 20 to 60 kHz range, well outside the audible range. The switching frequency is controlled, with soft-start running at the higher frequency and maximum power delivered toward the lower part of the range. In general, the requirements for induction cooking applications are simpler than motor drives, as hard switching capabilities, high short-circuit ratings, or special package types are not required.

Soft switching topologies significantly reduce the switching losses of the IGBTs by using zero voltage switching (ZVS) or zero current switching (ZCS) operating modes. In hard switching applications, the voltage drop across the IGBT switches can result in considerable power losses. However, in soft switching applications, these losses are almost negligible, thereby improving the overall efficiency of the system.

The Reverse Conducting IGBT (RC-IGBT) integrates an IGBT and a freewheeling diode (FWD) on a single chip. It has lower losses than a normal IGBT, and lower losses mean less energy is consumed when cooking, which reduces operating costs for consumers. With less waste heat, the RC-E will run cooler, improving reliability. Since less cooling is required for a given power level, the end product immediately becomes smaller as the heat sink size is reduced, reducing costs. In addition, this helps to improve the efficiency of the IGBT and extend its service life.

Combining the field stop layer with the trench gate structure, the saturation voltage of the RC-E is greatly improved, and very little energy is consumed when turned off. Compared with the early NPT technology, the thinner substrate improves the conduction and switching performance. Compared with the co-packaged diode solution, the RC-E provides higher power density. The use of RC-IGBT is already the first choice in today's induction cooker solutions.

Fusit induction cooker application solution