VideoRay's long or short tether underwater remotely operated vehicles (ROVs) protect ports and waterways with modular and scalable power electronics design, thus enabling precise maneuverability in challenging situations.
There are underwater applications that include port security and search & rescue that represent very specific challenges for system designers. VideoRay’s underwater remotely operated vehicles (ROVs), designed to protect ports and waterways, are constructed with a modular approach to power electronics design so that different ROVs can be configured to support the precise maneuverability requirements of specific underwater situations.
Chris Gibson, vice president, sales, marketing & business development at VideoRay, highlighted the ROVs’ features, pointing out that the VideoRay Defender leverages a high-density power delivery network (PDN) to deliver high voltage power output. This mirrors VideoRay’s proprietary modular design approach that allows the ROVs to be customized for various missions.
Aligning the proper power with each custom system is important. The boost offered by the modular power design must withstand changing ocean currents and provide all operating conditions under different operational loads. The power technology employed consists of Vicor DC-DC DCM converters that provide 48V from the 400V long tether and PRM regulators that provide 48V from a redundant 48V on-board battery source. Low-voltage fixed-ratio BCMs are used in both cases to convert that 48V into voltages needed for electronics and payloads. High-voltage BCM modules are also used with short 72V tethers.
ROVs are equipped with cameras and various sensors to reach difficult-to-access underwater locations at extreme depths for extended periods. They can be deployed for 24/7/365 operation at depths up to 305 meters (2,000m in deep mode), with power supplied by the platform or host ship (Figure 1).
“The main markets where we operate are the defense market, the first responder market, the offshore oil and gas, and renewable energy market, but also in many others including aquaculture, civil inspections, hydro inspections, nuclear industry, science and research,” said Gibson.
Underwater vehicles discover the secrets of the ocean
Increasingly, unmanned underwater vehicles are taking on the most complicated and dangerous jobs such as creating maps, monitoring the environment, collecting water samples, patrolling ports, and detecting sea mines to make the sea a safer space. These remotely operated vehicles (ROV) are managed by a person in a control center or fully autonomous (AUV), true underwater robots.
Underwater drones face substantial challenges, as many navigation and communication technologies we take for granted are ineffective in the water. GPS, cellular (3G, 4G), WiFi, and radar are among the technologies essential to the operation of airborne drones, but they are useless underwater.
ROVs replace (or augment) the use of divers for underwater inspection tasks in hazardous environments. Military, government, and force protection personnel employ these solutions for a variety of underwater inspection tasks such as explosive ordnance disposal (EOD), meteorology, port security, mine countermeasures (MCM), and maritime ISR (Intelligence, Surveillance, Reconnaissance).
Power design for ROVs
VideoRay Defender is a customizable ROV platform that can be adapted to various missions. It is also distinguished by power, tethering lengths, high-resolution video, and interchangeable modular systems. The power architecture must allow the vehicle to operate in extreme conditions while maintaining a form factor that matches the environmental conditions. Among the many design factors involved is the modularity and power density of the on-board power components.
The power electronics management of VideoRay’s solutions leverages Vicor’s high-density modular technology to meet efficiency and low EMI noise requirements while reducing dissipation systems that can limit space.
“Modularity is important so that if something breaks, there’s no need to send it all back; just pull the module out and insert a new one. It’s designed so that an operator in the field can take the equipment apart at the module level, and replace something very quickly,” Gibson said.
The Defender ROVs employ Vicor DCM series converters with peak efficiencies of 93 percent to produce 48VDC low-voltage power to power all main thrusters and control electronics within the underwater vehicle. The DCM series also integrates monitoring and auto-shutoff features and offers large voltage drops on longer tethers with active cooling for easy thermal management in a waterproof enclosure.
Vicor’s Sine Amplitude Converter (SAC) topology extends the voltage range from 48V to 800V input with various K-factors with integrated PMBus control and telemetry, EMI filtering, and transient protection. The tether voltage is isolated and regulated to 48V, which directly powers the thrusters and two BCM DC-DC transformers with 95% efficiency provide 24V and 12V outputs for other onboard electronics (Figures 2 and 3).
For longer tethers, the 400V output from the rectifier directly feeds the tether. On the ROV the tether voltage is isolated and regulated to 48V by DCM DC-DC converters. The design uses DCMs with different inputs depending on the tether voltage. The regulated 48V rail directly powers the thrusters and two BCM DC-DC transformers with 95% efficiency provide the 24V and 12V outputs for other onboard electronics.
For short tethers, the ship’s rectified AC supply is converted to a 72V tether voltage using three high-voltage BCMs with outputs connected in series. Inside the ROV, the 72V is down-converted to 12V.
Vicor’s BCM fixed-ratio bus converter used in VideoRay’s Pro 4 Main Controller unit (Figure 4), converts rectified AC from the host vessel to 72V DC in a compact manner, bringing it to the ROV via the cable to power it. It uses a heat dissipation and active cooling system for easy thermal management.
“We have a very long cable sometimes up to 2,000 feet to bring power into the vehicle that is in the water,” said Gibson. “The cable has its own resistance that is low, with a voltage drop. The high voltage in the range of 200 – 400V will make sure that in the ROV there will be the range available for the DCM to power the equipment.” He also pointed out that in addition to the power supply, there is a control box to support ethernet communication of video and sensor data.
When the ROV is powered by two redundant 48V batteries, an array of PRM regulators stabilize the 48V output of each battery. These outputs are then combined. In both cases, the onboard control electrical system is the same, with only the 48V delivery network changing to accommodate the different power sources.
For longer tethers, the 400V output of the rectifier powers the tether directly. For short tethers, the ship’s rectified AC power supply is converted to a 72V tether voltage using three high-voltage BCMs with outputs connected in series. Inside the ROV, the 72V is converted to 12V. In addition to a long or short tether, the ROV can be powered by on-board battery power using PRM buck-boost converters with constant current and voltage control (figure 5). A zero-voltage switching (ZVS) architecture, PRM buck-boost regulators, accommodate a wide range of input voltages and provide a regulated and adjustable output voltage.
This article was originally published on EE Times.
Maurizio Di Paolo Emilio holds a Ph.D. in Physics and is a telecommunication engineer and journalist. He has worked on various international projects in the field of gravitational wave research. He collaborates with research institutions to design data acquisition and control systems for space applications. He is the author of several books published by Springer, as well as numerous scientific and technical publications on electronics design.