IGBT｜Basic

Selective Use of Power Devices in Motor Applications

2023.08.30

Points of this article

・In rough terms, IGBTs cover the range of lower frequencies and larger output capacities, Si MOSFETs cover the range of higher frequencies and smaller output capacities, and SiC MOSFETs cover the range of higher frequencies and larger output capacities.

・In motor applications, designs based on IGBTs, which are capable of switching driving at low frequencies (up to 20 kHz) and have large output capacities, are generally used.

・SiC MOSFETs are superior with respect to low switching losses and large output capacities, but cost considerations place limits on potential applications.

Different power devices have their various features, and are generally selected according to the application in which they are to be used and the characteristics and performance required. This article provides insights into the selective use of IGBTs, Si MOSFETs, and SiC MOSFETs in motor applications.

Selective Use of Power Devices in Motor Applications

The diagram below is the same as one used in the article on “Range of Application of IGBTs”, and indicates the areas suited for use, with respect to operating frequency and output capacity (VA), given the features of different power devices. On comparing the ranges covered by discrete IGBs, Si MOSFETs, and SiC MOSFETs, the following can be concluded. Of course, individual power devices vary widely; these conclusions are based on general features of the different device types.

  • ① In comparisons of IGBTs and Si MOSFETs, IGBTs cover a lower frequency, higher output capacity range, while Si MOSFETs extend over a higher frequency, lower output capacity range.
  • ② When comparing IGBTs and SiC MOSFETs, SiC MOSFETs cover a higher frequency, higher output capacity range.
  • ③ When comparing Si MOSFETs and SiC MOSFETs, the frequency bands are similar, but Si MOSFETs extend over lower output capacities, while SiC MOSFETs cover a higher output capacity range.

The following table provides somewhat more specific insights into these features and into the selective use of these devices in motor applications. Among perspectives on device selection, differences in losses under different conditions is important. Losses can be considered to consist of conduction losses and switching losses. Below, “IGBTs”, “SiC MOSFETs”, and “Si MOSFETs” all refer to discrete devices, whereas “+SBD” and “+FRD” means the devices provided with external discrete diodes.

With respect to conduction losses, in the region in which the passed current is about 5 A or less, Si MOSFETs are superior to IGBTs, but for currents greater than this, IGBTs have lower losses. This current region is not covered by SiC MOSFETs, and so for this current range, the choice comes down to either IGBTs or Si MOSFETs. In systems that operate on smaller currents, such as the outdoor units of home-use air conditioners and similar systems that run constantly with light loading, Si MOSFETs are preferable. This also applies to the comparison of IGBTs and Si MOSFETs in ① above.

With respect to switching losses, in comparisons of IGBTs+FRDs (fast recovery diodes) versus SiC MOSFETs+SBDs (Schottky barrier diodes), as PWM frequencies (switching frequencies) rise, SiC MOSFETs+SBDs become superior, as per ② above. This is because IGBTs + FRDs increase switching losses due to their characteristic recovery current at turn-on and tail current at turn-off, while SiC-MOSFETs + SBDs have no tail current flow, etc., which can significantly improve switching losses.

However, when considering motor applications, because motors are generally used at comparatively low frequencies below 20 kHz, and because SiC MOSFETs have cost disadvantages, at present SiC MOSFETs are mainly used in special applications. IGBTs currently represent the mainstream for motor applications, owing to the balance they strike between performance, losses, and cost.

Thus, the features as well as the costs of the various power devices must be studied in order to select the product that provides the best balance for a particular application. For inverters and other motor driving uses, in addition to the discrete IGBTs + FRDs as in the examples above, discrete IGBTs with internal FRDs and IGBT IPMs (intelligent power modules) designed for motor applications are widely used.

【Download Documents】 Basics of IGBTs

IGBTs are one of the typical power devices and are used in a wide range of applications including motor drives. This handbook provides a basic understanding of IGBTs, including their application scope and application picture based on their features, their structure and principle of operation, and how they compare with and use other power devices.

Selective Use of Power Devices in Motor Applications
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