IGBT with X-Ray Machine

A 48kW resonated converter involves four power modules, per module contains two paralleled IGBTs and ant parallel diodes. They are arranged in a half-bridge or push-pull configuration depending on the input, at 400Vac or 200Vac. At maximum power, peak load current is 550A at 50 kHz, or 275A per module for 48kW out. The generator is zero-voltage switched to create a continuous series resonant output current that's transformer-isolated stepped up and rectified to the desired output level. The output voltage is regulated by a DSP based frequency modulated controller, with dual loop feedback on resonant current and load kV. For a range of output power, the system operates from 48 kHz up to 68 kHz with a resonant LC shunt across the load transformer. With fundamental series resonance at 48 kHz, the shunt resonates at 68 kHz. At low frequencies, the generator functions near resonance, with high power throughput. As frequency increases, the impedance rises the load being shorted by the resonant shunt. At 68 kHz, power is zero. Minimum size is important for state of the art X-ray equipment. In this version of the converter, the four ZVS modules with their tightly packed IGBT and FRED chips require only ¼ of the surface area formerly used. Integration of drivers, isolation, and ZVS logic circuitry further shrinks the footprint. Control signals have less distance to travel, which improves noise immunity and mechanical.

Different Behaviors of Paralleling IGBTS Published

The paralleling behavior for IGBTs deserves of an special attention that has to be given to the drive circuit, this is due to the variation of the gate threshold voltage of the different chips, simply connecting the gates is not adequate. As they are not just a few of them but several, Instead, each gate has to be driven by its own gate resistor in order to ensure that the chip with the lowest threshold voltage does not clamp the voltage for the others and carry all the current.

The layout of the emitter circuit has to be very symmetrical in order to minimize differences in emitter inductances and resistances. Even minor, unavoidable differences in the emitter inductances and resistances will generate compensation currents between the gate drive emitter connections. It is recommended to use a resistor in the range of at least 0.5 Ohm, but not to exceed approximately 1/3 of the total gate resistance.

The on-state behavior is something more critical when it comes about paralleling igbts. Some devices such as the P700 six-pack suggests a relatively variation in IGBT collector-emitter and diode forward voltage. For the IGBT, the collector-emitter saturation voltage at 25 °C is given as 1.7 V typical and 2.25 V maximum. No value is provided for the minimum voltage. Keeping this in mind, the paralleling of chips cannot be recommended, since the current sharing among the individual IGBTs cannot be ensured. The situation is even worse for the diodes in parallel systems but it can be avoided depending it its final use.

However based in the present times, the actual spread of the devices within one power module is lower than the parallel system users. This is due to the fact that they are picked from locations either exactly next or very close to each other on the same wafer, and will as is stated, feature similar electrical characteristics. Using multiple smaller chips instead of one larger chip improves the thermal behavior, as they doesn`t heat as quickly as a larger one, they tend to devides the heating properties well, This is due to the fact that not only the chip itself, but also a certain area around the chip, will participate in the transfer of heat from the chip to the heatsink. Parallelling systems have improved thermal spreading when using two small chips instead of one large, with in equal total area in both cases.

This case can also be seen when comparing the thermal resistance of the 100 A IGBT in the P569-F module with the 35 A IGBT in the P700-F module. The thermal resistance junction to heatsink for the 100 A the device is 0,57 K/W. The resistance for the single 35 A IGBT is 1,29 K/W, resulting in an resistance of 0,43 K/W, when 3 of them are used in parallel. This provides an improvement of about 25 % in thermal performance,one point for these kind of system, that left behind the more traditional one-module igbt old system,this also compensates for some if not all of the de-rating required due to the non-ideal current sharing.

PARALLELING SYSTEMS FOR IGBTS AND THEIR IMPROVEMENT

Widespread application of IGBTs in the past two decades has resulted in dramatic improvement in performance of power electronic converters, the efficiency of these devices has made its mark, reducing the cost of power electronic systems and  improving their own reliability, making them the first option of the manufacturing industry, Paralleling systems for IGBTS and diodes is one of the best alternatives to achieve a best performance.

The conclusion is that paralleling systems for igbts provides an advantage due to the improved thermal behavior of several small chips rather than fewer big ones. The breakthrough in performance is seen when real life data of parameter variations within one power module are considered, instead of the datasheet values, which suggest a much higher spread than actually seen in real life.

SISTEMA PARALELIZADOR PARA IGTBS Y SUS MEJORAS

La extendida aplicación de IGBT`s en las dos décadas pasadas resultaron   dramáticamente en  mejoras en  la actuación de convertidores electrónicos de potencia, la eficacia de estos aparatos  han dejado marca, reduciendo los costos  del sistema de potencia electrónica y mejoran su propia confianza, haciéndoles  la primera opción de Industria de fabricación, sistema paralelizador  para IGBTS y diodes es una de las mejores alternativas para lograr la mejor actuación.

La conclusión es que sistema  paralelizador  para IGBTS nos brinda  una ventaja gracias  al mejorado comportamiento térmico de varios chips pequeños en vez de grandes. El gran avance en rendimiento se mira cuando   los datos reales de la vida real de las  variaciones de los parámetros cuando el módulo de potencia se considera, en vez de los valores de las  fichas de datos, que sugieren una mayor propagación  que la que hemos visto en la vida real.

Switching Behavior of Paralleling IGBTs

The paralleling behavior for  IGBTs deserves of an special attention that has to be given to the drive circuit, this is due to the variation of the gate threshold voltage of the different chips, simply connecting the gates is not adequate. As they are not just a  few of them but several, Instead, each gate has to be driven by its own gate resistor in order to ensure that the chip with the lowest threshold voltage does not clamp the voltage for the others and carry all the current.

The layout of the emitter circuit has to be very symmetrical in order to minimize differences in emitter inductances and resistances. Even minor, unavoidable differences in the emitter inductances and resistances will generate compensation currents between the gate drive emitter connections. It is recommended to use a resistor in the range of at least 0.5 Ohm, but not to exceed approximately 1/3 of the total gate resistance.

Thermal Behavior of Paralleling IGBTS

Using multiple smaller chips instead of one larger chip improves the thermal behavior, as they doesn`t heat as quickly as a larger one, they tend to devides the heating properties well, This is due to the fact that not only the chip itself, but also a certain area around the chip, will participate in the transfer of heat from the chip to the heatsink. Parallelling systems have improved thermal spreading when using two small chips instead of one large, with in equal total area in both cases.

This case can also be seen when comparing the thermal resistance of the 100 A IGBT in the P569-F module with the 35 A IGBT in the P700-F module. The thermal resistance junction to heatsink for the 100 A the device is 0,57 K/W. The resistance for the single 35 A IGBT is 1,29 K/W, resulting in an  resistance of 0,43 K/W, when 3 of them are used in parallel. This provides an improvement of about 25 % in thermal performance,one point for these kind of system, that left behind the more traditional one-module igbt old system, this also compensates for some if not all of the de-rating required due to the non-ideal current sharing.

Paralleling Systems for IGBTs and their Improvement

Widespread application of IGBTs in the past two decades has resulted in dramatic improvement in performance of power electronic converters, the efficiency of these devices has made its mark, reducing the cost of power electronic systems and  improving their own reliability, making them the first option of the manufacturing industry, Paralleling systems for IGBTS and diodes is one of the best alternatives to achieve a best performance.

The conclusion is that paralleling systems for igbts provides an advantage due to the improved thermal behavior of several small chips rather than fewer big ones. The breakthrough in performance is seen when real life data of parameter variations within one power module are considered, instead of the datasheet values, which suggest a much higher spread than actually seen in real life.