What Is FOC Control and Why Are More Underwater Thrusters Using FOC?

FOC (Field Oriented Control) is an advanced motor control technology for brushless motors. By precisely controlling torque and magnetic field components, FOC delivers low noise, high efficiency, reduced heat generation, and extremely smooth power output.

In underwater propulsion systems—especially for ROVs, AUVs, USVs, and other professional underwater platforms where stability and reliability are critical—FOC control is rapidly becoming the mainstream solution.

When combined with APISQUEEN Beluga 24V 30A / 24V 50A FOC ESCs and the APISQUEEN 24V U92 Pro Underwater Thruster, users can experience significantly improved low-speed control, acoustic performance, and overall energy efficiency in real-world underwater applications.

1. How FOC Control Works and Its Key Advan

FOC control, also known as vector control, is designed for BLDC (Brushless DC Motors) and PMSM (Permanent Magnet Synchronous Motors).

The core principle of FOC is to mathematically decompose the three-phase motor current into two independent components:

1. Torque Component (Iq)
   Directly responsible for producing motor torque.

2. Flux Component (Id)
   Responsible for establishing and maintaining the magnetic field.

By dynamically adjusting the magnitude and phase of these two components in real time, FOC allows the motor to operate close to its ideal electromagnetic state under all conditions.

Key Advantages of FOC Compared to Traditional Square-Wave (Trapezoidal) Control

• Ultra-smooth operation
  Sinusoidal current output greatly reduces torque ripple, vibration, and mechanical shock.

• Excellent low-speed precision
  Stable and linear thrust even at very low RPM, ideal for precise underwater maneuvering and station keeping.

• Higher efficiency
  Better current utilization reduces electrical losses and extends battery endurance.

• Lower heat generation
  Reduced copper and iron losses significantly improve reliability in sealed underwater thrusters.

• Lower acoustic noise
  Sinusoidal drive minimizes electromagnetic noise, making it suitable for scientific research, inspection, and underwater filming.

Control Method Comparison

2. APISQUEEN FOC ESC Solutions for Underwater Thrusters

To meet the demanding requirements of underwater propulsion systems, APISQUEEN offers two high-performance FOC ESCs specifically designed for reliability, efficiency, and smooth control.

1. APISQUEEN Beluga 24V 30A FOC ESC

• Supports PWM control, with optional RS485 / CAN bus customization

• Smooth low-speed startup, ideal for small ROVs, scientific instruments, and lightweight underwater platforms

• Built-in protections: over-current, over-voltage, and thermal protection for enhanced safety

2. APISQUEEN Beluga 24V 50A FOC ESC

• Higher power output for medium to large underwater thrusters

• Fast dynamic response for both precise low-speed control and stable high-thrust operation

• Designed for long-duration continuous operation, helping extend thruster service life

3. Real-World Performance with the APISQUEEN 24V U92 Pro Underwater Thruster

When paired with the APISQUEEN Beluga FOC ESCs, the APISQUEEN 24V U92 Pro underwater thruster delivers noticeable improvements in real underwater environments:

• Lower operational noise
  Users report significantly reduced noise levels at low and medium speeds.

• Smooth and linear thrust output
  FOC control ensures predictable thrust response across the entire speed range, eliminating low-speed jitter and sudden torque steps.

• Higher efficiency with reduced heat
  Lower energy losses increase battery endurance and reduce thermal stress, extending thruster lifespan.

• High reliability in harsh environments
  The U92 Pro features an outer-rotor motor design with anti-sand, anti-mud, and corrosion-resistant housing. When combined with FOC control, it operates reliably in complex underwater conditions.

4. Advantages of FOC Control in Practical Underwater Applications

1. Scientific Research and Exploration

Low noise and stable thrust minimize interference with sonar systems and sensitive underwater instruments.

2. Precision Low-Speed Maneuvering

Multi-thruster systems require accurate low-speed control for attitude adjustment, cruising, and station keeping—FOC provides smooth and predictable response.

3. Long-Term Continuous Operation

High efficiency and reduced heat generation make FOC ideal for long-duration missions and endurance-focused platforms.

4. Operation in Harsh Environments

Sealed underwater thrusters have limited heat dissipation. FOC control reduces thermal buildup, significantly improving overall system reliability.

5. Frequently Asked Questions (FAQ)

Q1: Does FOC control require an encoder?
Not necessarily. Many underwater thrusters use sensorless FOC, where the controller estimates rotor position algorithmically, simplifying system structure and improving reliability.

Q2: Is FOC always better than square-wave control?
In most high-performance applications, yes. However, FOC involves higher hardware and development costs. For low-cost or entry-level use cases, square-wave control may still be sufficient.

Q3: Can the APISQUEEN U92 Pro be used in seawater?
Yes. Its corrosion-resistant design, combined with FOC control, ensures reliable long-term operation in saltwater, sandy, and muddy environments.

6. Conclusion

FOC control is not a new technology, but it is becoming increasingly popular in underwater propulsion systems due to its clear advantages:

• Smooth and precise thrust output, especially at low speeds

• Reduced noise, improved efficiency, and longer endurance

• Enhanced reliability when paired with high-quality thrusters such as the APISQUEEN 24V U92 Pro

By combining APISQUEEN Beluga 24V 30A / 50A FOC ESCs with professional underwater thrusters, users can achieve quieter, smoother, and more efficient propulsion for applications including ROVs, AUVs, research platforms, inspection systems, and electric boats, effectively solving common issues related to low-speed vibration, noise, and heat management.