IGBT DRIVE POWER SUPPLY DESIGN AND USABILITY TEST FOR ELECTR

The electric vehicle inverter is used to control the main motor of the automobile to provide power for the operation of the automobile. The IGBT power module is the core power device of the electric vehicle inverter, and the driving circuit is the key circuit for exerting the performance of the IGBT. The design of the drive circuit and the drive circuit of the industrial general-purpose inverter and the wind energy solar inverter have more severe technical requirements, and the power supply circuit is limited by the small space size and high working temperature, and faces many challenges. This paper designs a drive power supply and proves its availability through actual testing.

 

Common drive power supplies are designed with flyback circuits and transformers with multiple primary and secondary sides. Since the flyback power supply provides the inherent characteristics of the energy output to the load during the off period of the switch, its current output characteristics and transient control characteristics are relatively poor.

 

In the space layout of IGBT modules of the order of 100 kW, the design of a single transformer to produce 4 to 6 isolated positive and negative power supplies has many disadvantages: the power supply is too concentrated, the creepage distance and the clearance are difficult to guarantee, and the power supply distance of the board is Too long and so on.

 

This design uses common non-dedicated chips for circuit design. The SEPIC circuit in the front stage realizes closed loop, and the isolation of the latter half-bridge circuit effectively solves the above problems. The circuit has been successfully applied to the design of international leading new energy vehicle inverters. Applications show that the design has good flexibility, high reliability and transient response.

 

1 Analysis of the requirements of electric vehicle inverter drive power supply

 

The electric vehicle inverter drive power supply is generally 6 isolated +15V/-5V power supplies. The power, electrical isolation, peak current capability, operating temperature, etc. of the power supply have strict requirements. The specific calculation of the power supply specification is carried out with Infineon's automotive-grade IGBT module FS800R07A2E3_B31. The module supports inverter system design up to 150kW.

 

1.1 Drive power calculation

 

The input power of the drive power is calculated as:

 

P=f_sw×Q_g×△V_g/η(1)

 

The f_sw switching frequency is 10 kHz, Q_g is 8.6 nC according to the data sheet, and ΔV_g is 23V for the gate driving voltage. Considering that the power is small, the efficiency is 85%. Also note that the 8.6nC in the data sheet is calculated according to the voltage +/-15V, which needs to be considered for conversion, and the final calculation result is 1.8W. Consider the design margin of 1.1 times, recorded as 2W.

 

1.2 Drive current calculation

 

The average drive current is calculated as:

 

I_av=f_sw×Q_g(2)

 

The average current can be calculated to be 86 mA.

 

The peak current calculation formula is:

 

I_peak=△V_g/(R_gext+R_gint)(3)

 

R_gext is the external sector pole resistance, according to the data sheet to open 1.8 euros off 0.75 ohms. R_gint is the internal gate resistance, which is 0.5 ohm according to the data sheet, and the peak current is 10A, and the peak current is 18.4A. In actual use, the turn-on and turn-off resistors require a compromise between switching speed and short-circuit protection. A good design value is in the range of 2.2 to 5.1 ohms, so the actual switching peak current is in the range of 4 to 10A.

 

2 drive power circuit design

 

2.1 Power Topology Design

 

The input of this power supply is the conventional 12V power supply of the new energy passenger car. The power supply usually has a fluctuation range of 8~16V, and the output of the driving power supply needs to be relatively stable. It is necessary to design multiple sets of isolated power supplies with wide voltage input and constant voltage output. This design divides the power supply into two levels: the front-stage power supply realizes the wide-voltage input and the constant-voltage output function, and the latter stage realizes the isolation function. The structure is shown in Figure 1.

 

IGBT drive power supply design and usability test for electric vehicle inverter

 

Figure 1: Schematic diagram of the power supply topology

 

The benefits of this structure are:

 

First, the pre-stage power supply does not need to solve the isolation problem, and can adopt the conventional SEPIC or buck-boost non-isolated topology, and the output of the pre-stage power supply is a low-voltage constant voltage without isolation, and it is not necessary to consider the creepage between the groups of power sources in the layout and wiring. Distance and clearance problems. Therefore, the preamplifier of the part can be implemented independently as a low voltage weak current circuit without occupying the area of ​​the driving board.

 

Second, the rear-level power supply does not need to solve the feedback problem, and adopts open-loop control to avoid the trouble of isolation signal feedback. Because the working conditions of passenger car equipment are bad, the working temperature varies greatly. The traditional linear optocoupler and other devices are greatly reduced in accuracy due to temperature drift, and the temperature drift compensation device is costly. This method effectively avoids this drawback.

 

2.2 Rear half-bridge switching power supply design

 

The pre-stage power supply is a typical constant voltage design, and there is no need to give a design principle. This article focuses on the latter stage half-bridge circuit. The specific schematic diagram is shown in Figure 2 and Figure 3. Figure 2 shows a 50% duty cycle signal generator designed with an automotive-grade timer circuit to provide control signals to the half-bridge switching power supply. R49 can be used to adjust the switching frequency, typically between 70kHz and 300kHz. The frequency selection is mainly based on the actual space size of the board and the volt-second product of the transformer.

 

The formula for calculating the volt-second product from the transformer is:

 

ET=V*D/f_sw(4)

 

V is the voltage applied to the transformer, D is the duty cycle, and f_sw is the switching frequency. This design selects a transformer with an ET value of 44Vusec, so the switching frequency setting is lower, 120kHz.

 

IGBT drive power supply design and usability test for electric vehicle inverter

 

Figure 2: 50% duty cycle signal generation circuit

 

Figure 3 shows a half-bridge switching power supply circuit. This circuit uses an IR automotive grade half-bridge chip IRS2004S as the drive, paralleling two parallel half-bridge circuits consisting of Infineon BSR302N. A general-purpose transformer with a turns ratio of 1:1.25 is used, and a voltage of +15 V is obtained by voltage doubler rectification, and a voltage of -8 V is obtained by ordinary rectification. Each transformer is used to power an IGBT drive. Connecting the automotive-grade EMC magnetic beads in series on the primary side of the transformer can effectively suppress the voltage spike generated by the switch. For specific device information, see Appendix Table 1. The IGBT gate is a capacitive load. Each switch is accompanied by a higher transient current, which is the peak drive current calculated above. Therefore, a long-life capacitor with a strong ripple current capability is required. Each power supply uses 4.7uF. X7R automotive grade multilayer ceramic capacitor for transient voltage support. X7R multilayer ceramic capacitors have the advantages of small package size, low ESR, large ripple current, and reduced temperature loss.

 

IGBT drive power supply design and usability test for electric vehicle inverter

 

Figure 3: Schematic diagram of the half-bridge switching power supply circuit

 

3 test results

 

The actual test conditions are: the final stage input constant voltage 16.5V, input current 0.67A, IGBT switching frequency 10kHz, signal is SVPWM, switching power supply operating frequency 120kHz, room temperature conditions. According to simple calculations, the power consumption per channel is 1.84W, which is consistent with the theoretical calculation.

 

Select the high duty cycle and low duty cycle two conditions, observe the waveform of the relevant signal, see Figure 4 and Figure 5. The orange 1 channel displays the low side drive input signal, the pink 2 channel displays the -8V power output waveform, the blue 3 channel displays the +15V power output waveform, and the green 4 channel displays the gate output waveform.

 

At the time of IGBT turn-on, the charge of the power supply is quickly transferred to the gate through the gate resistor. The time is usually only 1~3us, which causes the voltage drop on the +15V power supply, but the platform voltage can be quickly recovered. In the same way, when the IGBT is turned off, the voltage of the -8V power supply will drop. This drop is an undesirable reaction that does not cause the IGBT to turn on or off, so it is acceptable. Comparing Fig. 4 and Fig. 5, it can also be found that the duty ratio does not affect the amplitude and duration of the voltage drop because the gate of the IGBT is a capacitive load.

 

It can also be seen in Figures 4 and 5 that the turn-on voltage waveform produces a sharp peak at the turn-off time of the IGBT. Since the turn-on voltage supply is in an instantaneous no-load state at this time, the drive control is not affected. On the whole, the low-voltage weak current signal of the primary side and the low-voltage strong electric signal of the secondary side are not interfered by the switching frequency of the switching power supply itself.

 

IGBT drive power supply design and usability test for electric vehicle inverter

 

Figure 4: High Duty Cycle Waveform

 

IGBT drive power supply design and usability test for electric vehicle inverter

 

Figure 5: Low Duty Cycle Waveform

 

4 Conclusion

 

The design verification shows that the pre-SEPIC non-isolated voltage regulator and the rear-stage half-bridge isolation open-loop topology are superior to the traditional flyback single-primary multi-side concentrated power supply, especially suitable as a new energy source of the order of 100kW. The driving power supply of the passenger car inverter is designed not to use a power-type integrated chip that often does not meet the automotive standard, but to adopt an AEC-certified automotive-grade universal discrete device to meet the demanding requirements of the passenger car electronic design.

Source: https://www.slw-ele.com/igbt-for-electric-vehicle-inverter.html

What is an IGBT?

WHAT IS IGBT?

1. What is an IGBT?

 

One of the most important components in power electronics is the IGBT.

 

The so-called IGBT (Insulated Gate Bipolar Transistor) is a composite full-regulated-voltage-driven-power semiconductor device composed of BJT (Bipolar Junction Transistor) and MOS (Insulated Gate Field Effect Transistor), which has its own The feature of shutdown.

 

To put it simply, it is a non-on-off switch. The IGBT does not have the function of amplifying the voltage. It can be regarded as a wire when it is turned on and an open circuit when it is disconnected. IGBTs combine the advantages of both BJT and MOSFET devices, such as low drive power and reduced saturation voltage.

 

 

 

The IGBT module that we usually use in practice is a modular semiconductor product that is packaged by IGBT and FWD (freewheeling diode chip) through a specific circuit bridge. It has the characteristics of energy saving, convenient installation and maintenance, and stable heat dissipation.

 

 

2, the traditional power MOSFET

 

In order to understand the IGBT, I will first talk about the structure of the Power MOSFET. The so-called power MOS is to withstand high power, in other words, high voltage, high current. We combine the general low-voltage MOSFET to explain how to change the structure to achieve high voltage and high current.

 

 

 

1) High voltage: If the general MOSFET has high voltage of Drain, it will easily lead to breakdown of the device. The general breakdown channel is the other three ends of the device (S/G/B), so to solve the high voltage problem, you must block the three. end. The Gate end can only rely on the field oxygen pad to isolate the drain-to-drain distance (Field-Plate), while the Bulk-side PN junction breakdown can only reduce the concentration on both sides of the PN junction, and the most annoying is to the Source end, which is A long drift region is required as the drain series resistor divider so that the voltage drops across the drift region.

 

2) High current: The channel length of a general MOSFET is determined by Poly CD, and the channel of the power MOSFET is controlled by the difference of the junction depth of the two diffusions, so as long as the process is stable, it can be made small and is not affected by light. The accuracy of the engraving. The current of the device depends on W/L, so if you want to get a large current, you only need to increase W.

 

So the above Power MOSFET is also called LDMOS (Lateral Double diffusion MOS). Although such a device can achieve high power requirements, it still has its inherent disadvantages. Since its source, gate, and drain are all on the surface, the drain and source need to be pulled long, which wastes chip area. And because the device is on the surface, the complexity is increased and isolation is required if the device is to be connected in parallel. So later developed VDMOS (Vertical DMOS), the drain is uniformly placed on the back of the Wafer, so that the drift zone length of the drain and source can be controlled by the backside thinning, and such a structure is more conducive to the between the tubes. The parallel structure achieves high power. However, the LDMOS structure is still used in the BCD process in order to be compatible with CMOS.

 

Let me talk about the development and evolution of VDMOS. The earliest VDMOS is to directly put the LDMOS Drain on the back through the back thinning, Implant, metal evaporation, he is the legendary Planar VDMOS, it and the traditional LDMOS The challenge is the back side process. But its advantage is that the front process is compatible with traditional CMOS processes, so it is still alive. However, this structure has the disadvantage that its channel is transverse to the surface and the area utilization is still not high enough.

 

 

 

Later, in order to overcome the shortcomings of Planar DMOS, VMOS and UMOS structures were developed. Their approach was to dig a groove in the surface of Wafer and change the channel of the tube from the original Planar to the vertical along the wall. It was a clever idea. But a pie always matches a trap (IC manufacturing is always trade-off). The inherent disadvantage of this structure is that the slot is too deep and the electric field is concentrated, resulting in breakdown, and the process is difficult and costly. The bottom of the groove must be absolutely routing, otherwise it will easily break down or create a lattice defect of stress. However, its advantage is that the number of crystal saturation is much larger than the original, so more transistors can be connected in parallel, which is more suitable for applications with low voltage and high current.

 

 

 

There is also a classic thing called CoolMOS, everyone learn google yourself. He should be considered the highest voltage of Power MOS, and can reach 1000V.

 

3. Structure and principle of IGBT

 

The Power MOSFET is described above, and the IGBT is essentially a field effect transistor. It is structurally very close to the Power MOSFET. A P+ layer is added to the drain electrode on the back side, which we call the Injection Layer. The Power MOSFET described above is basically a traditional MOSFET. It is still a single carrier (multi-sub) conductive, so we have not yet exerted its ultimate performance. So later, a new structure was developed. How can we not inject holes from the drain side in addition to the MOSFET's own electrons when the Power MOSFET is turned on? So naturally, a P+ injection layer is introduced at the drain end, and a P+/N-drift PN junction is added from the structure, but it is positively biased, so it does not affect the conduction but increases the null. The hole injection effect, so its characteristics are similar to BJT. There are two kinds of carriers involved in conduction. So the original source becomes Emitter, and Drain becomes Collector.

 

 

From the above structure and the equivalent circuit diagram on the right, it has two equivalent BJTs linked back to back. It is actually a PNPN Thyristor. This thing is not what we deliberately do, but the structure is generated. I wrote an article about Latch-up five months ago. The most terrible thing about this structure is the Latch-up. The key to controlling Latch-up is to control Rs, as long as α1+α2<1 is satisfied.

 

In addition, such a structural advantage is to improve the current drive capability, but the disadvantage is that when the device is turned off, the channel is quickly turned off without multiple sub-currents, but the Collector (Drain) side continues to have minority hole injection. Therefore, the current of the entire device needs to be slowly turned off (tailing current), which affects the turn-off time and operating frequency of the device. This is a taboo for switching devices, so a structure is added to add an N+buffer layer between P+ and N-drift. This layer is used to allow the device to inject holes from the Collector when it is turned off. It is quickly compounded in the N+ buffer layer to increase the turn-off frequency. We call this structure PT-IGBT (Punch Through type), and the original NPT-IGBT without N+buffer.

 

 

In general, NPT-IGBT is higher than Vce(sat) of PT-IGBT, mainly because NPT is a positive temperature coefficient (P+ substrate is thinner and less hole injection), and PT is a negative temperature coefficient (because P substrate is thicker) Therefore, the hole injection is more caused by the triode base region modulation effect, and Vce (sat) determines the switch loss, so if the same Vce (sat) is required, the NPT must increase the thickness of the drift, so Ron has increased.

 

 

 

4, IGBT manufacturing process

 

The process front of the IGBT is not worse than the standard BCD LDMOS, but the back is more difficult:

 

1) Back thinning: generally required 6~8mil, this thickness is difficult to grind and easy to chip.

 

2) Back injection: Both are ground to 6~8mil, and also need to hit High current P+ implant >E14's dose, it is easy to be fragmented, and there must be special equipment dedicate. Even the fourth generation has two Hi-current injections, which is the limit.

 

3) Back cleaning: This general SEZ is fine.

 

4) Back metallization: This can only be done by metal evaporation process, Ti/Ni/Ag standard process.

 

5) Back Alloy: The main consideration is that the wafer is too thin and easy to warp the pieces.

 

5, new technology of IGBT

 

1) Field cut-off FS-IGBT: No matter whether the PT or NPT structure can finally meet the requirements of infinite high power, to achieve high power, it is necessary to lower Vce (sat), that is, reduce Ron. Therefore, it is necessary to reduce the thickness of the N-drift, but this N-drift thickness is again constrained by the electric field of the off state. Therefore, if you want to reduce the thickness of the drift, you must let the cut-off electric field drop before the channel. Therefore, it is necessary to introduce an N+ field stop layer (FS) between the P+ injection layer and the N-drift. When the IGBT is in the off state, the electric field is rapidly reduced to 0 in the cut-off layer to achieve the purpose of termination, so we can Further reducing the N-drift thickness reduces Ron and Vce. Moreover, this structure is very similar to the N+ buffer structure, so it also has the effect of PT-IGBT to suppress the tailing current in the off state to increase the closing speed.

 

 

 

The question is, what is the difference between this and the N+ buffer of the PT-IGBT? In fact, the production process is different. The PT-IGBT is made with two layers of EPI, which is the first layer of ~10um N+ buffer on the P+ substrate, and then the second layer ~100um of N-Drift. This cost is very high! In contrast, the FS-IGBT is based on the NPT-IGBT directly on the back side of the high-concentration N+ cut-off layer, the cost is relatively low, but the challenge is how to achieve no fragmentation under thinner thickness.

 

 

 

2) Anode shorting (SA: Shorted-Anode): Its structure is that the N+ collector is intermittently inserted into the P+ collector, so that the N+ collector directly contacts the field stop layer and serves as the cathode of the PN diode, while P+ continues to do its FS. - The collector of the IGBT, which has enhanced current characteristics and changes the cost structure, since there is no need to co-package the anti-parallel diodes. Experiments have shown that it can increase the saturation current and reduce the saturation pressure drop (~12%).

 

 

 

6, the main I-V characteristics of IGBT

 

IGBT You can use it as a MOSFET in series with a PiN diode, or as a wide base PNP driven by a MOSFET (Darlington structure), the former can be used to understand its characteristics, the latter is his principle. It seems that the IV curve of a MOSFET has moved backwards (>0.7V) because the channel turn-on current must satisfy the drift region current and drift region resistance product multiplied by 0.7V to make the P+ substrate and N-drift The PN junction is conducting, so that it can work, otherwise the channel can not work.

 

 

 

7. Why should we pay attention to IGBT?

 

IGBT is the core device for energy conversion and transmission, and is the "CPU" of power electronic devices. The use of IGBT for power conversion can improve the efficiency and quality of power consumption, and is characterized by high efficiency, energy saving and environmental protection. It is a key supporting technology for solving energy shortage problems and reducing carbon emissions.

 

IGBT Manufacturer

IXYS  Hitachi Infineon Mitsubishi Powerex  FUJI ELECTRIC  Sanyo  Toshiba  Intersil

source: https://www.slw-ele.com/what-is-igbt.html