20 Aug Application of IGBT in induction cooker
Appliance Research of IGBT in Induction Cookers
This article first introduces the application of IGBT in induction cookers, analyzes the various control circuits of induction cookers, and according to the most common application method of IGBT in induction cooker, analyze the possible failure of IGBT.
According to the most common application method of IGBT in induction cooker, this article analyzes the possible failure of IGBT, proposes the matters that should be paid attention to during the application of IGBT in induction cooker, and improves the reliability of IGBT.
In order to achieve the purpose of improving the safety and reliability of induction cooker.
The induction cooker coil generates a high-speed alternating magnetic field, and the high-speed alternating magnetic field acts on the cookware to produce an eddy current, which heats the food with Joule heat. Induction cookers control the generation of high-speed alternating magnetic fields, mainly through the induction power switching device IGBT to achieve, the performance of the IGBT and the control method of induction cookers play a particularly critical role in the quality. In actual use, IGBT breakdown short-circuit accounts for a large proportion of the failures in induction cookers. How to improve the reliability and safety of IGBT? It has become an urgent problem in the development process of induction cooker.
IGBT parameters IGBT is a three-terminal device with gate G, collector C and emitter E. It combines the advantages of GTR and GTO, and has the advantages of fast switching speed, high through-current capability, high transmission and discharge impedance, good thermal stability, low driving power and simple driving circuit. The main parameters of IGBT are: maximum collector voltage, maximum collector current, and maximum collector power consumption.
Driving Circuit of IGBT
IGBT can be driven in the following ways: discrete component drive (direct drive by complementary trident), transformer isolation drive, and dedicated drive chip. The discrete component drive method, which uses complementary strides to form the drive circuit, is generally used in circuits where isolation is not required and the collector current of the IGBT is not too high. If isolation is required, an tocopherol can be added at the front for isolation. This driving method is simple and low-cost, but it is prone to large oscillations during the conduction and shutdown of the IGBT and has low reliability. The transformer isolation drive method uses a transformer to achieve good isolation between the chip output and the drive signal, which can achieve good isolation effect and effectively avoid the interference of high frequency and high current of IGBT to the chip.
Single-tube control circuit
IGBT parameters IGBT is a three-terminal device with gate G, collector C and emitter E. Combining the advantages of GTR and GTO, it has the advantages of fast switching speed, high through-current capability, high transmission and discharge impedance, good thermal stability, low driving power and simple driving circuit. The main parameters of IGBT are: maximum collector voltage, maximum collector current, and maximum collector power consumption.
Driving Circuit of IGBT
IGBT can be driven in the following ways: discrete component drive (direct drive by complementary triode), transformer isolation drive, and dedicated drive chip. The discrete component drive method, which uses complementary strides to form the drive circuit, is generally used in circuits where isolation is not required and the collector current of the IGBT is not too high. If isolation is required, an tocopherol can be added at the front for isolation. This driving method is simple and low-cost, but it is prone to large oscillations during the conduction and shutdown of the IGBT and has low reliability. Transformer isolation drive method, using a transformer to achieve good isolation of the chip output and drive signal, this method can well achieve the effect of isolation, can effectively avoid the IGBT high-frequency high current interference to the chip, but due to the existence of the transformer, belongs to the inductive components, the signal synchronization is not very good. The special driver chip driving method is used to drive the IGBT, because the driver chip has large current driving ability and fast shutdown speed, the oscillation during the IGBT conduction and shutdown process is small, and the reliability is high.
Application of IGBT in induction cooker
The operation of induction cooker needs to generate high-speed alternating magnetic field, mainly through the IGBT to control the charging and discharging of the bobbin to achieve, at the same time, because the bobbin of induction cooker is an conductor, generally used in induction cooker IGBT internal integration of a damping diode for the renewal of current, if the internal integration of damping diode is not required to connect external damping diode, for the IGBT control of the bobbin induction cooker control mode is divided into: single tube circuit, half-bridge circuit, full-bridge circuit several ways, the principle is shown in Figure 1, Figure 2, Figure 3.
Single-tube control circuit
When the IGBT is on, the current is charged to the coil tray through conductor L1, and the coil tray current increases. When the IGBT is turned off, the coil tray current charges the capacitor C1, and the coil tray current decreases and the voltage of C1 increases gradually, and when the coil tray current decreases to 0, the voltage across C1 reaches the maximum. Then C1 discharges to the coil tray, and the coil tray current increases from 0 to 0 until C1 is discharged, then, due to the presence of the IGBT damping diode, the coil tray charges to C2, thus completing one oscillation cycle. Then, due to the presence of the IGBT damping diode, the coil is charged to C2, thus completing one oscillation cycle. By controlling the on/off of the IGBT, a continuous oscillation current is generated for heating purposes.
Half Bridge Control Circuit
The bobbin and capacitor form an LC series resonant circuit. First, the upper bridge IGBT conducts, and when the lower bridge IGBT cuts off, the power supply charges the bobbin, then the upper and lower bridge IGBT cut off at the same time, and the bobbin continues to charge the capacitor. Next, the lower bridge IGBT turns on, the upper bridge IGBT turns off, and the capacitor discharges the bobbin. Next, the upper and lower bridge IGBT cut off at the same time, the bobbin charges the upper bridge capacitor, and the voltage at the lower end of the capacitor drops. This completes an oscillation process. The circuit IGBT drive needs to have the required dead band control to prevent the upper and lower bridges from conducting at the same time, resulting in a short circuit. During the charging process of the bobbin, the voltage at both ends of the bobbin gradually decreases due to the presence of the series capacitor, and the current value rises gradually.
Full Bridge Control Circuit
The bobbin is not connected with series or parallel capacitors alone, but through the IGBT and internal damping diodes and power capacitors to form a charging and discharging process, the oscillation process is as follows: first, one pair of corner IGBT V1 and V3 conduct at the same time, another pair of corner IGBT V2 and V4 cut off at the same time, the power supply charges the bobbin, the voltage across the conductor remains unchanged, the current gradually increases, and the next four IGBT cut off at the same time. The next pair of corner IGBT V2 and V4 conduct at the same time, and the other pair of corner IGBT V1 and V3 cut off at the same time, the bobbin is discharged, and the next four IGBT cut off at the same time. The above cycle will complete an oscillation process. The circuit IGBT drive needs to meet the requirements of the dead band control, to prevent the same position of the upper and lower bridges on at the same time, the phenomenon of short circuit. During the charging process of the bobbin, the voltage at both ends of the bobbin is the supply voltage. The current can theoretically reach infinity.
Analysis of the advantages and disadvantages of various control methods
The single tube control circuit uses only one IGBT, which is low cost, but the LC is parallel resonant, so the capacitor will be charged during the discharging process of the bobbin, which results in high IGBT back voltage and a certain limitation of power, generally the maximum power is below 3000W, and it is necessary to judge whether the collector voltage of the IGBT is already at or below the zero point, if it is not at or below the zero point, due to the existence of the capacitor, when the IGBT conducts, a short circuit will occur. If it is not at or below zero, the IGBT will generate a large inrush current due to the presence of capacitors, which makes the IGBT prone to breakdown and makes its peripheral circuit more complicated. Half-bridge control circuit, using two IGBT, the cost is medium, the IGBT counter voltage is low, can meet the requirements of high-power development, the peripheral circuit is simpler, LC belongs to series resonance, due to the presence of capacitors, the voltage at both ends of the coil in the charging process in the process of falling, the maximum current appears in the charging process capacitor voltage is equal to the supply voltage, the power increase is somewhat limited, but compared to a single tube, the power is still greater. The power increase is limited to a certain extent, but the power is still greatly improved compared to the single tube, and the maximum power can reach several tens of thousands of W.
Half Bridge Control Circuit
Full Bridge Control Circuit
The full-bridge control circuit, which uses four IGBT, has the highest cost, low IGBT reverse voltage, and simple peripheral circuits. Since the current can be very high during charging, it is usually necessary to add a current-limiting circuit to avoid abnormal driving and excessive current, which can cause the IGBT to break down.
Failure of IGBT in single tube induction cooker application analysis
Due to the defects of the single-tube circuit itself and the complexity of the circuit, the controller has a certain unreliability, and the biggest failure occurs during the IGBT operation. The causes of breakdown can be divided into the following scenarios.
IGBT Thermal Destruction
When the temperature of IGBT exceeds 100 degrees, the current resistance of IGBT collector drops sharply, and when its temperature reaches about 200 degrees, IGBT will have thermal breakdown.
IGBT damping diode voltage breakdown
Under normal conditions, the reverse voltage can reach about 1000V when the maximum power of a single tube is about 2000W, and when the coil inductance fluctuates or the power supply fluctuates, the reverse voltage may be even larger. Therefore, the voltage resistance of the IGBT damping diode should be above 1200V.
IGBT Current Breakdown
IGBT are prone to breakdown under over current operation. According to the analysis of the control mode of induction cooker, there are several cases of IGBT over-current: When the power is turned on and the IGBT is on, the voltage across the capacitor C1 cannot change suddenly, so when the IGBT is on, a large current will be generated through C1 to the IGBT, and this current can reach about 100A, and if this current lasts for a long time, the IGBT will have instantaneous current breakdown. Breakdown. When the current value of IGBT is close to the maximum power running current of induction cooker, the temperature rise of IGBT will be larger if it works under such condition for a long time, which will affect the service life of IGBT. Due to the different pots and pans of the induction cooker, the pots and pans will be shifted and turned upside down during the process of shifting and turning, and if the induction cooker does not judge in time, there will be abnormally high current in the process of moving the pots and pans. Synchronous circuit detection error, the current single tube control induction cooker need to have a synchronous circuit to detect whether the voltage of IGBT collector is zero, only when the voltage is close to zero or less than zero, then the IGBT can be turned on, otherwise there will be a voltage difference between the IGBT collector and emitter, resulting in high current through the capacitor when the IGBT is turned on, which leads to current breakdown of the IGBT. Otherwise, there will be a voltage difference between the collector and emitter of the IGBT, resulting in a large current through the capacitor when the IGBT is on, which will lead to current breakdown of the IGBT.
For the thermal breakdown of IGBT, IGBT must dissipate sufficient heat to ensure the normal temperature rise range. For single-tube control induction cookers with high counter voltage, the design phase must ensure that the counter voltage is controlled within the maximum counter voltage of the IGBT, and the over voltage protection circuit is generally required for control. Since the IGBT cannot exceed its collector current under any circumstances, it is also necessary to add a current limiting circuit to avoid abnormal currents. To avoid the high current generated by the voltage across the capacitor C1 when the IGBT starts to conduct, the capacity of C1 should not be too large because it will increase the inrush current when the IGBT starts to conduct, but C1 should not be too small because if it is too small, the IGBT back-voltage will increase during the discharge of the coil. The selection of this capacitor should be considered according to the actual situation. For the abnormally high currents that may occur during pot shifting and pot reversing, we can limit them by adding current-limiting circuits on the one hand, and enhance the speed of current detection and processing in the software design process on the other. The synchronous circuit needs to use high-precision devices, and the devices need to ensure high reliability and accurate zero detection to ensure that the collector voltage is close to zero or less than zero when the IGBT is on. The IGBT selection should ensure sufficient margin, such as collector current, reverse voltage of damping diode, etc., to ensure sufficient design margin. To ensure the reliable operation of the device.
This article analyzes the application of IGBT in induction cookers, analyzes the most common application methods, analyzes the possible situations, and proposes effective solutions, which can effectively reduce the failure rate of IGBT and improve the reliability of induction cookers through a comprehensive assessment of various situations.