Buck Converter Design for Motor Application in Simulink/Simscape

Hello MATLAB Community,

I am facing a challenge with a buck converter design in Simulink and Simscape for a specific motor application. My objective is to achieve a stable output of 200V DC to power a motor, but I am encountering issues with the output voltage. Here are the key specifications and requirements of my design:

Motor Specifications:

• Rated Power: 50 kW
• Rated Voltage: 200V DC
• Rated Current: 250A

Battery Specifications:

• Nominal Voltage: 400V DC
• Capacity: 50 kWh

DC-DC Converter Requirements:

• Input Voltage Range: 300V - 450V DC
• Output Voltage: 200V DC
• Output Current: 250A
• Switching Frequency: 50 kHz

In my initial design, I used a motor, but for troubleshooting, I replaced it with an R-Load, and the output was satisfactory. However, with the motor in place, the desired output voltage is not achieved.

I am seeking insights or advice on the following questions:

1. Are there specific considerations I should take into account in Simulink/Simscape for designing a buck converter for this motor specification?
2. Could the issue be related to the switching frequency? Is 50 kHz appropriate for this application, or should it be adjusted?
3. What are some common best practices or potential pitfalls in designing such a converter for a high-power motor application?

I will attach the relevant Simulink/Simscape file along with this question for a more detailed review. Any guidance, tips, or references to similar projects would be immensely helpful.

Thank you in advance for your time and expertise!

Answer 1

[Darshan Pandit]

Hi Badr Al-Sabri,

I've tried to answer your query below:

1. Are there specific considerations I should take into account in Simulink/Simscape for designing a buck converter for this motor specification?

>> use a large output capacitor to handle voltage dyanmics, reactive power support & reverse power flow. Ideally this can become a capacitor bank. you can also consider bidirectional dc dc converter.

>> dynamic response times of both systems and active/reactive power flow must be considered. The output voltage control of buck converter must be in steady state for motor controller to work satisfactorily; in orther words, the buck converter must respond 10x faster w.r.to dynamics in motor currents from motor controller. A large capacitor bank can help resolve this issue as well.

2. Could the issue be related to the switching frequency? Is 50 kHz appropriate for this application, or should it be adjusted?

>> this depends on switching devices, selection of inductor and capacitor and control system design. It is hard to comment without looking at system engineering.

3. What are some common best practices or potential pitfalls in designing such a converter for a high-power motor application?

>> inductor saturation, overtemperature of inductor and dc-dc converter, control stability, power system & voltage stability, current sensing, start-up and shutdown, etc.

>> revisit systems engineering to avoid using the dc dc converter at all by seeing the possibilities of a 200V DC battery bank, reprogramming motor controller to work with 400V dc with a 2:1 gearbox at motor shaft, etc.

As for the last part of your query, if you wish us to have a detailed look at the model, please contact us and we have a team who would be glad to help you out.

Have a good day.