Electrical machines are often treated as black boxes, and their design and integration remain central to performance, reliability, and mission success. Without electric motors, control electronics, and advanced batteries, today’s autonomous and remotely operated subsea systems would not be possible.
Hydrospace Group specializes in the design and manufacture of high-reliability subsea electric systems, including high-energy batteries, custom permanent-magnet brushless DC motors (1–100 HP), deep-sea motor controllers, and application-specific motion-control software. These vertically integrated capabilities allow system designers to optimize performance from the power source through to final mechanical output.
AN ELECTRICAL SYSTEM VIEW
Every electric machine application can be reduced to four tightly linked elements:
- Power source (battery or surface power)
- Electric motor
- Motor controller and sensors
- Control software
These elements must be considered together. A decision about battery voltage or current limits constrains the motor. The motor’s electrical and thermal characteristics dictate the controller. The controller, in turn, defines the achievable control strategies. The most robust and efficient subsea systems are those designed holistically from the start, rather than assembled from independent components.
DISTINGUISHING ENERGY FROM POWER
Modern lithium battery systems have dramatically expanded the endurance and capability of underwater vehicles over the past 15 years. For designers, a fundamental distinction must be made between ENERGY and POWER. Energy defines how long a system can operate. Power defines how much work it can perform at any moment. A battery may store sufficient energy for a long mission yet be incapable of delivering the instantaneous current required by propulsion or tooling. Both limits must be addressed early in the design phase to avoid later compromises in performance or architecture.
MOTOR SELECTION
Subsea designers most commonly choose between AC induction motors and permanentmagnet brushless DC motors. While induction motors are widespread in industrial applications, they are typically heavier and more difficult to cool in oil-filled, pressurebalanced designs.
Permanent-magnet brushless motors offer superior power density, efficiency, and thermal behavior. Nearly all heat is generated in the stator, where it can be conducted efficiently through the motor housing to the surrounding environment. Their mechanical simplicity— essentially a magnet rotor supported by bearings—also supports long-term reliability.
For low-volume, mission-critical subsea systems, these characteristics often outweigh manufacturing-driven motor innovations developed for automotive or high-volume industrial markets.
THE CONVERSION ENGINE
Motor controllers perform the essential task of converting electrical power into controlled motion. Advances in solid-state electronics have dramatically increased current capacity while reducing size and losses. Modern compact controllers typically fall into three ranges: up to 25 amps, 25–50 amps, and 50–100 amps, across voltage classes extending to 800 VDC and beyond.
Pressure-tolerant controllers further reduce system mass and volume by eliminating heavy housings. The current state of the art includes deep-sea, pressure-tolerant controllers capable of hundreds of volts and tens of kilowatts of output—enabling more powerful and efficient subsea architectures.
SOFTWARE TO DEFINE PERFORMANCE
Control software transforms hardware capability into operational function. At the motion level, embedded code governs torque, speed, and position control. At the system level, higher-order software integrates motors into the broader vehicle or instrument control architecture. Clearly defining the scope between these layers is essential to achieving predictable performance and efficient system integration.
Successful subsea electric machine design is fundamentally a system exercise. Batteries, motors, controllers, and software must be engineered as a unified whole. When this is done well, designers gain higher efficiency, improved reliability, and greater operational flexibility—critical advantages as subsea systems move deeper, operate longer, and perform increasingly complex tasks.
This spotlight appeared in ON&T Magazine’s 2026 February Edition, Exploring the Deep, to read more access the magazine here.
