Benchmark Report on Control Boards for Toyota’s Prius (DAA-ZVW51) and Power Control Unit (PCU)

2017/04/17

Summary

Fig.1 Product view
Fig.1 Product view
Source: Toyota Motor Corp.
Fig.2 PCU topological view
Fig.2 PCU topological view
Source: Toyota Motor Corp.

  The 4th-generation Prius launched in December 2015 is equipped with an engine that has a maximum thermal efficiency of 40%. In addition, the system consisting of the motor, transaxle, power control unit, and drive battery has been designed both to reduce size and weight, and lower loss by roughly 20%. The Power Control Unit (PCU), which will be the focus of analysis in this report, is installed adjacent to the engine, and its general functions are as follows: (1) 2-way DC-DC converter, (2) regenerating inverter, and (3) motor driver inverter. The PCU achieves improve loss reduction for the heat radiating system of IGBT-equipped power cards that are conventionally adopted, and also reduces size roughly 30% by unifying the high-side and low-side IGBTs into one card. A control board is positioned on the very top of the PCU, and it is this board as well as the power card that achieve the functionality noted above.

  The gate driver attached to the power card has functions of operating the gate to achieve an appropriate slew rate, as well as detecting the temperature and excess current. Moreover, the controller comprises a custom ASIC that integrates a number of features into 1 chip that include the following: isolated power supply-use oscillation circuit; internal power supply circuit; battery voltage / boosted voltage detection circuit; 2 MCU that perform vector control calculations for the 2 motors and generator; and power source-use error amplifier + CAN + ADC + resolver interface. The control board has 6 layers and through-holes.

  The gate driver connected to the power card is isolated from lower voltage circuits such as the MCU by means of the transformer and photo-coupler, and the circuit patterns are also isolated with each other physically (patters are isolated for individual gate drivers). This design seems to takes breakdown voltage and the reduction of electric field influence into account.



Fig.4 X-ray photo of the board (side view) Fig.3 Board (bottom view)



Fig.5 Individual circuit block functions
Fig.5 Individual circuit block functions
Table 1 Circuit functions
Table 1 Circuit functions

   Power Control Unit board circuits
  The main board has the following blocks (see Fig. 5).

  • Internal Power Supply:
    A circuit generating the internal power supply for the board that is the subject of this report from external supply voltage. An error amplifier for the power supply is integrated into an IC supplied by Denso.
  • Oscillator for Isolated Power Supply:
    A circuit applies alternating voltages to the primary side of the transformer supplying power to the isolation area
  • Gate Driver for Bidirectional DC-DC Converter/for:
    A circuit that regulates the two-way DC-DC converter switching transistors, regenerating inverter, and motor driving inverter.
  • Voltage Detect:
    A circuit for detecting voltages of the nickel-metal hydride battery, and boosted voltage in the two-way DC-DC converter.
  • High-speed CAN:
    A circuit for transmission of CAN protocols from the control board to external boards. Its communication function appears to be integrated in the ASIC.
  • Resolver Interface:
    A circuit connected with the external resolver that seems like it has a function of detecting the angle of the motor.
  • Current Sense:
    This circuit appears to detect the output current of the regenerating inverter and motor-drive inverter.
  • MCU and Peripheral, Communication:
    A circuit that connected the areas around the custom MCU supplied by Renesas with peripheral ICs.

  The 3 main chips mounted on the board are as follows: Custom ASIC (n=1), Gate drive ASIC (n=14) for driving the power card, and the custom MCU (n=1) supplied by Renesas.

  The Denso-made Custom ASIC (n=1) is contained in a QFP-128 package. It has a diffusion process with 3 metal and 1 poly silicon layers and adopts a high voltage SOI process (Fig.6).

  The Gate drive ASIC is also made by Denso and contained in a QFP-36 package.  It has a diffusion process with 4 metal and 1 poly silicon layers and adopts a high voltage BiCMOS process (Fig.7).



Fig.6-1 ASIC chip Fig.7-1 Gate drive ASIC
Fig.6-1 ASIC chip Fig.7-1 Gate drive ASIC
6-2 Chip marking (ASIC) Fig.7-2 Chip marking (Gate driver)
6-2 Chip marking (ASIC) Fig.7-2 Chip marking (Gate driver)


Fig.8 Die-cast removed from the control board
Fig.8 Die-cast removed from the control board
Fig.9 Slots for individual applications (Scale up)
Fig.9 Slots for individual applications (Scale up)
Fig.10 X-ray photo of a power card
Fig.10 X-ray photo of a power card

  The power card is mounted to connectors on the control board, and as it requires no soldering, can be easily removed (areas 3, 4, and 5 in Fig. 5). The system achieves high reliability even for the vibrations that occur during driving. When the control board is removed the die-cast and control pins jutting out of the lower portion can be seen (Fig. 8).

  A total of seven power cards can be inserted into the slots for drive, generation, and boost use (Fig. 9). The IGBTs integrated on power cards are made by different manufacturers depending on the application.

  LTEC Corp. offers the following detailed analysis reports for sale:

  1. Analysis of circuits on control boards
  2. Analysis of the functions of the custom ASIC
  3. Analysis of the functions of the gate drive ASIC
  4. Analysis of the structure of the power cards