First, IGBT
Normal IGBTs operate at 10-20 kHz and have a much faster switching speed than GTO and IGCT. In the AC motor frequency control, it is a better choice. It has been concluded that the elimination of power bipolar transistors (GTRs) in small and medium capacity devices. IEGT maintains fast switching characteristics in the high voltage field. At the end of the 20th century, IGBTs with special structures and special minority carrier lifetime control (such as proton implantation plus special annealing process specifications) were used to achieve operating frequencies of 150 kHz (hard switching) and 300 kHz (soft switching) at 600-1200 V. It is called a 霹雳-type IGBT. They will compete with power MOSFETs in switching power supplies, with advantages such as low turn-on voltage drop, high current density, high voltage levels, and low cost. For the next ten years of switching power supply, perhaps the market share of this IGBT will expand.
Second, zero voltage IGBT soft switch
1, hard switch and soft switch
(1) Hard switching: The opening and closing of the switch is accompanied by drastic changes in voltage and current, resulting in large switching losses and switching noise.
(2) Soft switch: Add a small inductance or capacitor and other resonant components in the main circuit, so that the switching tube introduces resonance before and after switching, and the switching conditions are improved, thereby reducing switching loss and switching noise.
2, voltage IGBT soft switch
The IGBT is a composite device composed of a power MOSFET and a bipolar transistor. The advantage of the IGBT over the MOSFET is that it can save the area of ​​the silicon wafer and the current characteristics of the bipolar transistor.
3, circuit composition
With the development of the industry, the induction heating power supply is getting bigger and bigger. Thus, MOSFETs that are widely used in small and medium power applications cannot meet the power requirements. On a high-voltage, high-power power supply, the IGBT becomes the main character. But IGBT
There is a large power loss. On the basis of the phase-shifted full-bridge PWM hard switch, we add a resonant inductor to form a PB-ZVS-PWM converter using IGBT.
4, input low voltage limit
The minimum input voltage of the power supply is 320V. When the input voltage is lower than the minimum voltage required for normal operation, the shutdown operation is normally performed under normal conditions. However, this causes the voltage-controlled power supply to enter the "blocking" mode, that is, The duty cycle of the output reaches the maximum value, and the output cannot be adjusted. When the input voltage returns to the normal value, the power supply and load are damaged. In addition, the lower the input voltage, the larger the current through the power switch tube will cause the switch tube to be damaged due to excessive power consumption. For this reason, we have solved this problem with a simple voltage comparator at the input end. This problem.
Third, IGBT drive protection
Use IGBT as the power supply, when working in high-speed and high-power switching state, make it safe and reliable.
Work, we must reasonably design the drive circuit, according to the characteristics of IGBT, we mainly consider the following aspects in the design:
(1) Select the appropriate gate forward drive
Voltage: From the perspective of reducing on-state loss, the higher the gate forward voltage, the better. However, too high forward gate voltage will reduce the short-circuit withstand capability of the IGBT. Therefore, we use a compromise method. A voltage of about 15V has received good results.
(2) Adding a 5V reverse bias voltage for the fast turn-off of IG-BT: This article has been mentioned in 2.2.
(3) In order to improve the leading edge steepness of the control pulse and prevent oscillation, reduce the voltage spike of the IGBT collector, and select the appropriate gate series resistance value according to the IGBT current capacity, voltage rating and switching frequency.
(4) In order to prevent the external voltage from being high when the high voltage is applied between the emitters, the gate voltage is too high, causing the device to be mis-conducted. This problem is solved by connecting a gate resistor between the gates. In addition, in order to prevent high-voltage spikes in the gate drive circuit, we connected two anti-series Zener diodes in parallel between the gates, and the regulation voltage is the same as the positive gate voltage and the negative gate voltage, but in the opposite direction.
(5) IGBT super-audio induction heating frequently starts and stops, and it needs to protect the power device IGBT from overcurrent. IGBT can generally resist short-circuit current of about 10us. By adopting the method of delaying the search for the overcurrent signal, that is, when the overcurrent fault signal comes, the gate voltage is first reduced from +15V to a certain set value, and the delay is about 10 s, and then the detection is performed. When it disappears, the gate voltage automatically recovers to about +15V. If it is still in the overcurrent state, the gate voltage is reduced to zero volts or less to turn off the IGBT.
Fourth, the conclusion
Since the beginning of the 21st century, power electronics, which is the key to strong electricity and weak electrical interfaces and to promote modern advanced manufacturing technology, is developing in the world. The next decade is an important period for Chinese society to move from a well-off to an initial affluence. As a developing country, the development of power electronics is a major measure to complete industrialization and promote informationization. We will see that the new ideas, new theories, new technologies, new materials, new products and new applications related to power electronics in the next decade will continue to emerge under the joint efforts of the government, industry, academia and research community, and will continue to benefit the people. Contribute
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