Transformers for IGBT/FET

Application Note Motor/Inverter Circuit Configuration Example

Motor/Inverter Circuit Configuration ExampleAs the electrification of the automotive progresses, the demand for motor generators is on the rise. There is also a trend towards integration of electric motors and inverters, and the requirements with regard to compact dimensions and resistance against heat and vibrations are becoming ever more severe, while high reliability is also an important factor. In some cases, wiring inductance can lead to high surge voltages which requires countermeasures such as suitable wiring design and snubber capacitors. At the same time, noise countermeasures are also essential.

Motor/generator circuit configuration example

Inverter circuits that convert direct current to alternating current are used to drive motors and generators. Such circuits incorporate Insulated-Gate Bipolar Transistors (IGBT) and other semiconductor switches. Recently, Silicon Carbide (SiC) and other high-speed devices are also coming into use, operating at higher frequencies while featuring smaller dimensions. Driving a large electric motor requires voltages of 400 volts and higher. A booster circuit therefore is generally placed in front of the inverter circuit, and a configuration with two semiconductor switches is used to increase efficiency. When the motor is driven, a steep current rise occurs which requires the high-voltage line connecting the booster circuit and the inverter to be stabilized. This task is performed by a capacitor called DC LINK.

Figure 1 : System configuration
System configurationSystem configuration

Capacitors for DC Link/Snubber Use

The use of high-speed devices such as SiC, Gan etc. is progressing and the dimensions of inverters are shrinking, but this makes it even more important to effectively control noise. Wiring inductance can lead to high surge voltages which requires countermeasures such as suitable wiring design and snubber capacitors.

Figure 2 : TDK capacitor product map
Capacitors for DC Link/Snubber Use
Figure 3 : Representative Capacitors

■Film capacitors

B3277*H Series

・Compatible with moisture-resistance environmental load test conditions
 (60℃x95%RH+Vrdc 1,000H)
・Supported DC voltage range: 450 to 1,100 V
・Supported capacitance range: 1.5 µF to 120 µF

Film capacitors

■CeraLink®

B58031* Series

・Voltage Rating 500 V DC, 700 V DC
 Up to 900 V DC possible
・Low ESR (Equivalent Series Resistance)
・Low ESL (Equivalent Series Inductance)

CeraLink®

Film Capacitors

Inverter circuit inputs require a stable DC voltage at the input. Because electric motors are driven at low frequencies, a relatively large capacitance is required to absorb ripple components. Film capacitors have high allowable ripple current ratings ,making them suitable for achieving stable voltage.

Table 1 : Film capacitor lineup
  High-Output
B3267x Series
High Density
B3277x Series
High Temperature Resistance
B3277xP Series
High reliability
B3277xM Series
Dielectric Metallized polypropylene (MKP) Metallized polypropylene (MKP) Metallized polypropylene (MKP) Metallized polypropylene (MKP)
Vdc 300, 450, 630, 780, 875 450, 800, 1100, 1300 630, 700, 840 450~1600
Capacitance range [µH] 0.47 to 270 1.5 to 480 1.0 to 50 1.5 to 170
Operating temperature range [℃] 105 Max. 105 Max. 125 Max. 105 Max.
Lead wire spacing [mm] 27.5 to 52.5 27.5 to 52.5 27.5 to 52.5 27.5 to 52.5
10kH current handling [A] 5 to 108 5 to 79.5 3 to 25 5 to 36.5
Ambient environment test conditions 40℃ / 93% RH 40℃ / 93% RH 40℃ / 93% RH rating
60℃ / 93% RH rating
60℃ / 95% RH rating
85℃ / 85% RH rating
56 days 56 days 1000 hrs at 40℃
500 hrs at 60℃
1000 hrs at 60℃
1000 hrs at 60℃
AEC-Q200 compliant - -

CeraLink® Snubber Circuit Application Example

When an electric motor is driven, a steep current rise occurs. This generates a large ringing voltage which results in noise and can lead to withstand voltage degradation in semiconductor devices. Although CeraLink® are SMD products, they realize high withstand voltage and high capacitance. While harnessing the advantages of the SMD format to optimize the pattern layout, parasitic inductance in the wiring can be kept low. Furthermore, the ESL of the devices themselves is low, which makes it possible to reduce ringing voltage generation.

Figure 4 : CeraLink® snubber circuit application example
CeraLink® snubber circuit application example

Required values
●High capacitance density: 2 to 5 µF/cm³
●Low ESL: 2.5 to 4 nH
●By placing the highly heat resistant CeraLink® product near the semiconductor device, operation at temperatures up to 150°C can be realized.
● No dV/dt limitation

Figure 5 : CeraLink® features low losses at high frequencies and high temperatures, providing outstanding allowable ripple current ratings
CeraLink® features low losses at high frequencies and high temperatures, providing outstanding allowable ripple current ratings

Transformers for IGBT/FET Drive

Motor drive inverter circuits and high-power converters use a bridge circuit configuration, which consists of semiconductor switches for the high voltage side and the low voltage side. A stable power supply is required for driving these semiconductor switches. The high side in particular has to be able to handle voltages up to 800 V for electric vehicle motors. A power supply that is insulated from the low side is required, and a compact, transformer with high withstand voltage is used for this purpose. Moreover, since multiple semiconductor switches are used and the gate voltage varies, causing reliability differences between devices, voltage equalization is desirable.

Figure 6 : Features of TDK transformers
Features of TDK transformers
Table 2 : Differences in structure and lineup
Transformer type Distributed transformers Centralized transformers
Circuit diagram Distributed transformers Centralized transformers
Number of outputs 1 ~ 2 3 ~ 6
Advantages Small size increases layout design freedom
Low weight improves vibration resistance
Total cost is lower than distributed type.
Disadvantages Higher cost per output as compared to centralized type Larger size imposes restrictions on layout design
Variations in coupling between NS winding and NF occur more easily than in distributed type
Higher weight reduces vibration resistance
Coplanarity accuracy inferior to distributed type
Product VGT10SEE-200S2A5
VGT12EEM-200S1A4
VGT15SEFD-200S1A4
VGT15EFD-200S3A6
VGT15SEFD-250S4A7
VGT22EPC-200S6A12

Example of IGBT/FET Drive Transformer

IPM (Intelligent Power Modules) are used for high-power inverters, booster circuits, and similar. They are semiconductor components created by combining power devices such as power MOS-FETs or IGBTs with a drive circuit and an integrated self-protection function.
A power supply voltage of 15 V ±10% is required to drive an IPM. Transformers are used to provide insulation from power devices, but poor characteristics of the transformer will degrade voltage stability. The wire material is also crucial in terms of achieving the required insulation reliability. Material that can withstand high temperatures is therefore used. If space and cost are the top considerations, the choice will be an integrated transformer. By contrast, if layout design freedom and voltage stability are given priority, the choice is a distributed transformer.

Figure 7 : Example of IGBT/FET drive transformer
Example of IGBT/FET drive transformer

Required Transformer Characteristics

  • ・High reliability:Insulation between windings on the secondary side is essential
       (there is a constant harsh, high-voltage environment (400 V–800V) for extended periods between the windings)
  • ・High efficiency:Structural and design optimization for low leakage and variation
  • ・Mountability:High-frequency support and miniaturization through optimization of platforms