Background
ROVs were developed in the 1960s and used by US Navy to perform deep-sea rescue operations and recover objects, such as lost bombs, from the ocean.
Even though they have been with us for less than half a decade, technological development of ROV vehicles has come a long way. Not only have ROVs matured considerably technologically, but they’ve become an essential tool in a whole array of industries, serving oil & gas, underwater construction, military, scientific and even filmmaking needs.
The Client
Sperre is a company in Norway that specializes in providing customised ROV solutions for inshore and offshore use. Their different models of ROVs and TMSs (Tether Management Systems) are used in initial subsea construction, as well as subsequent repair and maintenance of subsea structures, pipelines, etc. Their products are also utilised in a number of military applications, particularly in mine hunting and mine breaking. Apart from that, ROVs are working for archaeological and scientific purposes and contribute to the discovery of new species of ocean plants and animals.
Since the nature of applications is so vast and varied, ROVs from Sperre As use VSD where speed can be adjusted, based on a specific application need. In other words, VSDs allow locking of the speed or torque of a drive, adjusting it to various environmental conditions, resulting in saving energy and improving the efficiency of a drive. On top of that, controlled speed of the drive helps to regulate fuel input to the engine and, therefore, positively affects the cost of fuel and energy consumption, used by ROVs.
The Challenge
With the rising cost of energy, use of VSD with the ability to control the motor’s speed and torque is growing at an increasing rate. Looking to continuously improve product performance and efficiency for their clients, for the last couple of years, Sperre As was focusing on optimising the design of their VSD. This new design is seeking to benefit from closed-loop sensorless control of the motor. This newly built-in option offers the potential to significantly increase the performance of equipment, simultaneously providing a sophisticated monitoring of the process. Thus, to prove improved control over VSD, verifying that new algorithms are working properly, is of crucial importance and can be done with the help of accurate torque measurement of the drive.
The challenge was to demonstrate that the motor could meet the worst case drive requirements at temperatures over 50°C. With the Datum M425 Torque Sensor, we were able to accurately measure the motor heat generation, do this quickly and be confident in the test data.
Solution
The effectiveness of the algorithm is measured by its ability to provide constant torque across the full speed range and by its speed of response to step changes in the load. To look closely at the algorithms and prove that they can be controlled, Sperre As was in need of a highly accurate torque measurement solution. In addition, the solution had to have an ability to show torque and speed on a digital display and, due to the system compatibility, have a digital RS-232 or Ethernet Interface. As all Datum Series 425 inline torque sensors are compatible with the optional Datum Universal Interface, Sperre As decided to use the Datum Torque Measurement Solution for their trials.
After a full check up and assistance from Datum’s support team, the torque transducer was installed on a test rig for repetitive engine testing. This continuous testing was done to optimize and verify the closed loop sensorless control by maximizing the amount of torque per ampere current drawn from the VSD.
As a result, the Sperre As team was able to tune the open loop U/F curves to work optimally for a given load (torque) for optimizing U/F controls in old drives, increasing their efficiency.
Datum’s service is really good and responsive.
Impact
Even though tests are still in a very early stage, the company was able to significantly improve motor control tuning. Their current progress shows there is a lot of potential for the new VSD system to enter a market as an innovative product, allowing their clients to maximise their competitive advantage.
Even now, as motor output can now be proved and guaranteed, Sperre As is already seeing a higher quality of deliveries and it’s just a matter of time for the new VSD to achieve its full potential through its entire range.
The overall design and all-digital interface of the Datum sensor are great. It avoids introducing errors or noise in analogue signals.
