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准确计算IGBT模块死区时间(4)


举例: 这里选用驱动IC HCPL-3120,IGBT驱动器具有一个MOSFET关断输出级,0V/+15V电压下:
td_off 约为1500ns.
td_on约为100ns.
HCPL-3120手册里tpdd_max - tpdd_min为 700ns. 应用这些数据到死区计算公式中可得到死区时间为大约2.5μs.文章来源: http://www.igbt8.com/qd/170.html
2.4.3       死区时间的验证
With the discussion above and the formula (1) given in chapter 2.1 it is now possible to calculate the required dead time based on the measurements above. With the calculated dead time, a worst case measurement can then be performed to verify if the chosen dead time is enough or not. From the measurement it can be seen that the turn off delay time increases with temperature. From this reason it is preferable that the test should be done both at cold and hot condition. The schematic illustration of the test looks like following:
Schematic illustration of test to check calculated dead time value
Figure 13 Schematic illustration of test to check calculated dead time value
下管IGBT被打开和关断,然后上管执行相同动作。在特定的驱动条件下,两个脉冲之间的间隔应该被调整到计算的死区时间。测量负边DC link电流,如果死区时间足够,不应该观察到直通电流。
因为没有电流流过IGBT,所描述的测试是死区时间最坏的情况。从关断延迟时间的讨论已知,死区时间随着集电极电流的减少需要变长,所以如果没有电流流动,关断延迟时间最大,导致了最大死区时间的需求。如果在零集电极电流下没有桥臂直通,则在该特定驱动条件下,选择的死区时间是充足的。
3      如何减少死区时间
For a proper calculation of control dead time the dedicated driving condition should be considered:
l   What is the applied gate voltage to the IGBT?
l  What is the chosen gate resistor value?
l  What type of output stage does the driver have?
Based on these conditions a test should be made, from the test results the control dead time can then be calculated using equition (1).
由于死区时间对逆变器的性能有负面影响,必须最小化,可以采取下面一些措施:
l  选择足够强大的驱动器以吸收或提供IGBT峰值门极电流;
l  使用负电源加速关断;
l  基于更快速的信号传输技术,如无芯变压器技术优于传统光耦技术;
l  如果门极驱动电压使用0V/15V,考虑采用下面描述的独立Rgon/Ggoff。
本文的2.3章中描述了td_off对门极电阻有很强的依赖性,如果Rgoff降低则td_off及死区时间都会减少。英飞凌建议如果施加0V/15V驱动电压,应该降低Rgoff的值至1/3Rgon。下图显示了单独设置Rgon及Rgoff的电路。
Suggested circuit with 0V/15V gate voltage
Figure 14 Suggested circuit with 0V/15V gate voltage.
R1 should be chosen to satisfy the following relation:
R1 should be chosen to satisfy the following relation
From equation (3) it is to be noticed that the requirement Rgon>2Rgint has to be fulfilled to get a positive value of R1. However, with some modules this requirement can not be true. In this case, R1 can be omitted completely.
 The diode should be a schottky type diode.
Another very important issue with 0V/15V gate voltage is the parasitic turn on effect. This issue can be also solved if suggested circuit is used.
4      结论
本文介绍了一种测量IGBT模块开关时间及计算控制死区时间的方法。首先描述了开关时间对门极电阻的依赖性,讨论了门极驱动器及开关集电极电流对开关时间的影响。最后,介绍了可能减少死区时间的方法。转载请注明出处:http://www.igbt8.com/
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