Actuator Parameters

Internal Control Loop of Motor Driver

Current Limit and Current Limit Margin

You can understand current limit and current limit margin as:

"Target current limit" + "protective redundancy margin"

Together, they define the safe operating range of the current controller.

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📌 Basic Concepts

Current Limit

👉 The maximum current that the controller is allowed to output under normal operation

Current Limit Margin

👉 A reserved "buffer space" for the controller to handle transient fluctuations / control errors

Actual Hard Limit (Absolute Upper Bound)

current_lim + current_lim_margin

👉 Exceeding this limit will trigger protection (e.g., error / current limit violation)

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Block Diagram (Logical Structure)

🧩 Detailed Explanation

1️⃣ Role of current_lim (Soft Limit)

In the control loop (FOC):

Iq_cmd = clamp(Iq_target, -current_lim, +current_lim)

👉 The Iq setpoint is constrained within ±current_lim

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2️⃣ Role of current_lim_margin

Used to detect whether the "actual measured current" is abnormal

Possible sources of error: - ADC error - PWM delay - Back EMF - Dynamic disturbances

👉 Therefore, short-term exceeding of current_lim is allowed

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3️⃣ Protection Trigger Condition

|Iq_measured| > current_lim + current_lim_margin

👉 This will trigger:

ERROR_CURRENT_LIMIT_VIOLATION

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📊 Example

Assume:

• current_lim = 40 A
• current_lim_margin = 8 A

Range	Meaning
0 ~ 40A	Normal operation
40 ~ 48A	Transient allowed (margin zone)
>48A	❌ Protection triggered

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⚠️ Engineering Significance

current_lim determines

👉 Maximum motor output torque

Torque ∝ Iq

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current_lim_margin determines

👉 System stability / robustness

• Too small: prone to false protection triggers
• Too large: may cause overcurrent damage to MOSFETs or motor

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🧠 Summary

• current_lim → "desired maximum current"
• current_lim_margin → "allowed transient overshoot range"

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🚀 Engineering Recommendations

Applicable for:

• High dynamic motion (jumping / locomotion)
• Strong nonlinear control (RL control)

Recommended configuration:

• Set margin to 20% ~ 30%
• Combine with:
  • Bus current limit
  • Temperature protection
  • Torque limiter