What are the "three-electric system" and "electric drive system"? IGBT module structure and automotive IGBT module application

IGBT

The current module system of electric vehicles is composed of many parts, such as batteries, VCU, BSM, motors, etc., but these are relatively mature products. Domestic and foreign module manufacturers have developed many, but there is one module that needs to be paid attention to in the industry, that is the motor drive part, and the core component of the motor drive part is IGBT (Insulated Gate Bipolar Transistor insulated gate bipolar transistor chip).

Understanding automotive electronic control IGBT modules from scratch

The role of electric drive system and IGBT module

To understand the IGBT module, we must first understand the electric drive system of new energy vehicles. Let's summarize how the electric drive system works in one sentence: When driving a new energy vehicle, the motor controller converts the direct current (DC) released by the power battery into alternating current (AC) (this process is called inversion), which allows the drive motor to work. The motor converts electrical energy into mechanical energy, and then uses the transmission system (mainly the reducer) to make the wheels of the car run. Conversely, the process of converting the mechanical energy of the wheels into storage in the battery is kinetic energy recovery.

1. What are the “three-electric system” and “electric drive system”?

The three-electric system, namely the power battery (battery for short), drive motor (motor for short), and motor controller (electronic control for short), is also called the three major parts. Together, they account for more than 70% of the total cost of new energy vehicles and are the core components that determine the vehicle's sports performance.

Electric drive system, we generally simply refer to the motor, electronic control, and reducer as the electric drive system.

But strictly speaking, according to Jinjing Electric's prospectus, the electric drive system includes three major assemblies: a drive motor assembly (which converts the electrical energy of the power battery into rotational mechanical energy and is the source of output power), a controller assembly (based on the hardware and software design of power semiconductors, which controls the working status of the drive motor in real time and continuously enriches other control functions), and a transmission assembly (which reduces the output speed and increases the output torque through a gear set to ensure that the electric drive system continues to operate in a high-efficiency range).

Figure: Schematic diagram of electric drive system

Image source: Jinjing Electric's prospectus

2. What is the “all-in-one electric drive system”?

At first, the motor, electronic control, and reducer were all independent components, but with the advancement of technology, we combined these three parts into one component, which became a "three-in-one electric drive." The purpose of integration is mainly to save space, reduce weight, improve performance, and reduce costs.

Currently, the most integrated system on the market is the "eight-in-one electric powertrain" of BYD's Fudi Power. This eight-in-one electric drive system integrates the drive motor, motor controller, reducer, on-board charger, DC converter, distribution box, vehicle controller and battery manager.

Of course, it does not mean that the higher the integration, the better. There are issues that need to be resolved, such as heat dissipation structure design, system stability, and production process maturity. For consumers, the cost of later maintenance is also a big problem. Therefore, how to choose an all-in-one electric drive system requires comprehensive consideration.

3. How does the IGBT module work?

In the electronic control module, the IGBT module is the core component of the inverter. Its working principle is summarized as follows:

Through the semiconductor characteristics of either on or off, without considering the transition process and parasitic effects, we regard a single IGBT chip as an ideal switch. We build a parallel and series structure of several IGBT chip units inside the module. When direct current passes through the module, the outflow direction and frequency of the current are changed by the rapid opening and closing of different switch combinations, so as to output the desired alternating current.

IGBT module structure and automotive IGBT module application

The role of the IGBT module in the electric drive system was mentioned above. Now let’s take a closer look at the structure of the IGBT module.

4. What does the IGBT module actually look like?

The standard package of IGBT modules is a flat rectangular block. The following figure shows the top view of the HP1 module. The outermost white part is the plastic shell, and the bottom is a metal base plate (usually copper material) for heat conduction and heat dissipation. You can see that there are many terminals and pins outside the module, each with its own function:

1 is DC positive, 2 is DC negative; 3, 4, 5 are the U, V, W interfaces of three-phase AC power; 6, 25, 22 are the collector signal terminals, 7, 9, 11, 13, 15, 17 are the gate signal terminals; 8, 10, 12, 14, 16, 18 are the emitter signal terminals; 19 is the DC negative signal terminal; 23, 24 are the NTC thermistor terminals.

Figure: HP1 module equivalent circuit diagram

Figure: HP1 module equivalent circuit diagram

Image source: Cuizhanwei

5. What is the basic topology of IGBT?

Figure: IGBT module basic circuit topology

Image source: Cuizhanwei

As shown in the figure above, in the IGBT module/single tube, one unit is generally referred to as an IGBT single tube, two units are a single bridge arm (half bridge), four units are H bridges (single-phase bridges), six units are three-phase bridges (full bridges), seven units are generally six units + one braking unit, and eight units are generally six units + a braking unit + a pre-charging unit.

One unit consists of 1, 2 or 3 pairs of FRD+IGBT, of which one pair can be 1 FRD+1 IGBT, or 1 FRD+2 IGBTs, etc.

Please refer to the figure below for the specific object. This is a 6-unit IGBT module.

Figure: Infineon Primepack IGBT module

Image source: "Dr. Geng Power Electronics Technology" public account

6. What is the production process of IGBT modules?

Figure: Cross-section of IGBT standard package structure

Image source: Cuizhanwei

As shown in the figure above, we can see the cross-section interface of the IGBT module. The basic structure of the modules currently using the shell sealing process is not much different. The IGBT module packaging process is roughly as follows:

SMT → vacuum reflow soldering → ultrasonic cleaning → X-ray defect detection → wire bonding → static test → secondary soldering → shell glue filling and curing → terminal forming → functional test (dynamic test, insulation test, reverse bias test)

First, each die on the IGBT wafer is mounted on the DBC. DBC is a copper-clad ceramic substrate, with ceramic in the middle and copper on both sides. DBC plays the role of conductivity and electrical isolation similar to PCB. Commonly used ceramic insulating materials are aluminum oxide (Al2O3) and aluminum nitride (AlN);

Vacuum welding: After mounting, the die and DBC are fixed by vacuum welding. The general solder is tin sheet or solder paste.

X-ray void detection needs to detect bubbles that appear during the bonding process, that is, voids. The presence of voids will seriously affect the thermal resistance and heat dissipation efficiency of the device, resulting in problems such as overheating, burning, and explosion. Generally, automotive IGBT modules require a void rate of less than 1%;

Next is the wire bonding process, which uses metal wires to bond the die and DBC. The most commonly used wires are aluminum wires, and other commonly used wires include copper wires, copper tapes, and aluminum tapes.

There will be a series of appearance inspections and static tests during the process, and modules with problems will be scrapped directly;

Repeat the above process to weld and bond the DBC to the copper base plate, followed by glue filling, encapsulation, laser coding and other processes;

A final functional test will be performed before leaving the factory, including dynamic testing of electrical performance, insulation testing, reverse bias testing, etc.

7. What are the common automotive IGBT module packaging types?

Econodual series half-bridge packages are mainly used in commercial vehicles, with main specifications of 1200V/450A, 1200V/600A, etc.

HP1 full-bridge package is mainly used in small and medium-power models, including some A-class cars, most A0 and A00 cars, with peak power generally within 70kW, and the main model is 650V400A, and other specifications include 750V300A, 750V400A, 750V550A, etc.;

HPD full-bridge package, used in medium and large power vehicles, most A-class vehicles and above, with 750V820A specifications occupying the mainstream of the market, and other specifications such as 750V550A, etc.;

DC6 full-bridge package, based on the integrated packaging solution of UVW three-phase full-bridge, has the characteristics of compact packaging, high power density and good heat dissipation performance;

TO247 single tube parallel connection, there are also a small number of electric control system solutions using TO247 single tube packaging on the market. The advantages of using a single tube parallel connection solution are mainly two points: ① The single tube solution can realize flexible line design, and the corresponding single tube can be used in parallel according to the required current, so the cost also has certain advantages; ② The parasitic inductance problem is easier to solve than the IGBT module. However, there are also some difficulties to be solved when using single tubes in parallel: ① It is difficult to share and balance the current between each parallel single tube, and it is difficult to ensure consistency, such as achieving simultaneous disconnection, the same current, temperature, etc.; ② The customer's system design and process are very difficult; ③ There are many interfaces, and the requirements for the production line are very high.