Regenerative Braking Current Limitation in Myxa A2Z ESC (Telega v0)

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1

We are using a Zubax Myxa A2Z ESC (AmpDrive AD0505A/B, Telega V0) in a regenerative braking configuration. The ESC is operating in RPM control mode (esc_rcm = 1). Our setup involves one motor connected to the Myxa ESC, which is being driven by another motor acting as an “engine.” The goal is to maintain a constant RPM while maximizing regenerative power extraction.

Currently, the regenerative performance appears to be limited by the maximum braking current, which in v0 appears to be hard coded to be a fraction of the rated phase current amplitude.

In the Kucher app, the max_current is set to 200 A (maximum allowed) However, the phase current (I_Q) saturates around 20 A
This suggests an internal limitation at approximately 10% of max_current.

With this configuration, we are able to extract approximately 300 W of power, but our target is 1200 W or as high as practically achievable.
Now, we are wondering if it is possible to increase the maximum allowable phase current (I_Q) or increase the maximum braking current fraction in Telega v0 for the Myxa ESC? If so, could you let us know which parameters control this limit?

2

Sensorless FOC drives tend to lose stability at high braking currents so there is a hard-coded 10% limit in v0. This limit is adjustable in Telega v1 so you might want to try that. Alternatively, we could craft a special build of v0 for you but it might take some time to get around to that.

3

Thanks for the response, Pavel.

Sensorless FOC drives tend to lose stability at high braking currents so there is a hard-coded 10% limit in v0.

I assume the underlying stability concern is tied to sensorless FOC operation, so this issue may still exist in v1, even though the braking-current limit is adjustable. Is that correct?

This limit is adjustable in Telega v1 so you might want to try that

I have updated one ESC to v1 and will test with it to see whether the adjustable limit helps us reach the desired regenerative power level.

Alternatively, we could craft a special build of v0 for you but it might take some time to get around to that.

At the moment, however, the special v0 build is our preferred option. We are using a Simulink-to-PX4 workflow, and I am not yet sure whether Cyphal is supported cleanly in that workflow. We also have other DroneCAN devices, including power management units and servos, that are currently working well with v0. Do you have an estimate of how long it would take to prepare the special v0 build?

Thanks again for your help.

4

Here’s a custom build of Telega v0.6 with the braking current limit removed:

com.zubax.telega-1-0.6.b5bb86c0.application.bin (275.9 KB)
com.zubax.telega-1-0.6.b5bb86c0.compound.bin (323.8 KB)

Use the .application.bin file for software update.

1 Like
5

Thanks, Pavel.

We have upgraded to the special Telega v0.6 firmware with the braking-current limit removed and have tested it with both a Myxa B and a Komar.

We are having an issue with the Komar ESC during regenerative operation. We have been unable to consistently generate more than approximately 100 W of DC power, and more importantly, we have burned two Komar ESCs while attempting to increase the regenerative power.

With the Myxa B, we have had some initial success and can reach approximately 200 W of regenerated DC power without an issue. Our goal with the Komar was to eventually operate closer to its rated capacity (approximately 2500 W).

Test setup and procedure

Our setup consists of two motors mechanically coupled shaft-to-shaft. One motor acts as the engine (setup image attached at the bottom), while the other acts as the generator. The Zubax ESC is connected to the generator motor. A 6S battery is used.

The generator-side ESC is operated in RPM control mode and commanded to a fixed speed around 7000 RPM. Once the commanded RPM is reached, we gradually increase the engine-side throttle in increments. This applies increasing torque to the generator while the Zubax ESC attempts to maintain the commanded RPM.

The regenerated voltage, current, and power are measured on the DC side of the generator ESC.

We tested the same generator motor with each ESC, one at a time, using the same setup and procedure.

Observations

With the Myxa B , we can reach approximately 200 W of regenerated DC power without an issue.

With the Komar , the regenerated DC power reaches approximately 100 W consistently. When we increase the engine-side throttle further to increase the regenerative power, the Komar begins to smoke/burn. We have experienced this failure with two Komar ESCs.

Given that the Komar has a substantially higher current/power rating than the Myxa B, could you please help us understand why it is unable to produce more than approximately 100 W of regenerative DC power and why the ESC fails when the mechanical load is increased further?

Is there a hardware or control limitation specific to the Komar that we should be aware of when using it for regenerative operation with the modified Telega v0.6 firmware?

Also, what parameters or signals would you recommend monitoring, and what should we check before attempting further testing with another Komar?

I have attached the configuration files. I can also provide video of the test with Kucher screen caputre from both ESCs if that would help diagnose the issue.

Thanks again for your help.

TestBench
TestBench1448×1086 1.65 MB

BenchTest_Zubax_MyxaB.yml (2.4 KB)

BenchTest_Zubax_Komar.yml (2.4 KB)

6

This will not work with Telega-based drives. As I mentioned earlier:

More specifically:

image
image1216×1558 341 KB

To be precise, this is not true in general for all sensorless drives, but this is true for the particular class of sensorless observers used in Telega because they are optimized for a different class of applications where strong regenerative currents are uncommon.

If you need to achieve full braking power, it would require a slightly different approach to state estimation. This can be implemented as another firmware change, but this would be not as trivial as simply removing a limit (as I did here earlier). Is this something you might be interested in?

7

Thanks, Pavel, for your response.

Is this something you might be interested in?

Yes, that would be great. We are definitely interested in testing this modified firmware.

Please find attached the schematic showing the intended setup and the operating conditions for the ESC. Our goal is to use the Komar for sustained regenerative operation and eventually operate closer to its rated capacity (~2.5 kW).

ESCOperatingCondition
ESCOperatingCondition1884×1009 51.6 KB

8

Noted. Could you please reach out to me via pavel.kirienko@zubax.com to discuss the terms? Thanks.