Providing power on warships to meet the growing demand from ship systems is becoming more of a concern, particularly as legacy warships also need more power to host weapons and sensor upgrades.
Warships are usually built with some future-proofing inherent in their designs. Extra allowances for space, weight and power (SWaP) will allow for future upgrades and the addition of new systems and equipment. However, the ‘P’ in SWaP is becoming much more important as one of the issues being faced is how to manage the electrical loads on a ship’s power systems when future capabilities are integrated.
Warships currently assess power demands through the requirements of the radar/advanced sensors or mission load. The power levels can therefore go from hundreds of kilowatts (kW) up to megawatts (MW) and depend on the technologies being used.
It is expected that the electrical power demand of advanced radar and electrical weapons will grow by 50 percent or more over the coming decade compared to that needed for propulsion.
Back in 2019, U.S. Naval Sea Systems Command (NAVSEA) recognised the need for technological innovations to provide solutions and set out its Naval Power and Energy Systems (NPES) technology development roadmap that year.
The NPES roadmap called the changes in power supply a “revolution” stating that it will be driven by high-power pulsed mission systems.
“These include directed energy weapons such as lasers and electronic warfare (EW) systems, radiated energy systems such as the Air and Missile Defense Radar, and advances in kinetic energy weapons, including electro-magnetic railguns,” the NPES said.
In the future, power can be a limitation for a platform or a discriminator. Whichever ship has the most power can have the most powerful sensors and weapons.
However, the NPES found that legacy power systems found on all existing ships “do not possess the inherent electrical ‘inertia’ to withstand the ramp-up/down (on/off), or ripple (pulsation) effects of complex power profiles of these advanced mission systems.”
High power demands
Until recently it has been common for warships to have separate engine arrangements: one set will provide power for propulsion to turn the propellers, with a second set of generators to provide electricity for the ‘’hotel’ load. The hotel load includes most other systems on the warship from lighting through to the weapons and sensors. But the existing generators providing power for the hotel loads are barely sufficient now and will not be sufficient in future.
Robert Sacca, director, power & control systems, Northrop Grumman told AMR generation capacity “is clearly and area of tension.” But he said that as important as capacity is power quality: “Higher power and more highly dynamic loads wreak havoc on the distribution system and cause stability issues that can damage mission equipment and adversely impact platform performance.”
He explained that attitude is that all mission equipment must be capable of full power operation 100 percent of the time. “We need to examine if that is still the most appropriate path forward with power systems that can manage and allocate power and energy resources based on the specific combat scenario and where energy storage can seamlessly be integrated into the electrical system to provide extended capabilities,” Sacca said.
Some of the more powerful weapons and sensors already being integrated into US warships include the Raytheon AN/SPY-6 Air and Missile Defense Radar (AMDR) and the Northrop Grumman SEWIP Block 3 electronic warfare (EW) system. Both will be fitted to the U.S. Navy’s new Constellation-class frigates, the Arleigh Burke-class Flight III destroyers and retrofitted onto the Flight IIA destroyers when the latter enter their DDG Mod 2.0 modernisation programme.
New equipment
Looking beyond the AMDR and EW systems, future power hungry weapons and sensors will likely include lasers/Directed Energy Weapon (DEW) systems. At the moment lasers and EW systems often comes with their own power system, which is inefficient, costly and there isn’t the space on warships to have additional power and cooling equipment.
“Future warships are expected to continue to employ high powered radars and electronic warfare systems that require power conversion and energy management system to properly decouple their dynamics from the shipboard distribution system while meeting the instantaneous demands of the load. Conditioned high power energy sources,” Sacca said. “In addition, the advancement of Directed Energy Weapon (DEW) technology will bring high energy lasers, high powered microwaves, rail guns, and other technologies that employ stored electrical energy to maximise the resiliency and energy efficiency of the war fighting platform.”
Future systems will have to be integrated into the power structure of the warship. Next generation warships will employ high energy weapon and sensor systems that require harnessing the total ship’s energy and power to meet the mission needs.
“The evolution of DEW requires a fresh look at resource allocation,” Sacca said, “It is no longer practical to size ship service generation to meet the peak demands of the weapons and sensors as the generation plant would remain idle for nearly the life of the platform.”
He stated that electric and hybrid propulsion should be employed on future platforms along with a Multifunction Prime Power System that allows the incorporation of energy storage and the capabilities to manage the power and energy resources in near real-time.
“Electrical or hybrid propulsion provide ultimate flexibility for the platform. It is the best defence against an obsolete platform,” Sacca explained, “By having all the power on the platform in electrical form it affords the opportunity to apply that power to the most critical resources based on the threat and combat scenario.”
He added: “Mechanical propulsion locks up 98 percent of the platform’s power to the shaft. By employing electric or hybrid propulsion and implementing an electrical power conversion system capable of effective energy management, you can produce a platform that is ready to support the mission system of today and tomorrow.”
Integrated power
An integrated power system (IPS) is one solution. Diesel engines can power electric generators that through the IPS can be used to power both the propeller shafts and the ship’s systems. The IPS can also access Energy Storage modules and can distribute power where it is needed through advanced controls and a distribution bus that can serve high demand mission loads and high speeds whilst ensuring the lights do not go out.
IPS are not new and there have been many systems integrated onto commercial ships because electrical loads on commercial ships are relatively stable, rising and falling slowly. The challenge for warships is the electrical loads are not as steady with periods of stability punctuated by massive increases in demand when high speeds are needed and weapons and sensors are activated.
It means that an IPS is needed that can protect the ship’s electrical bus from sudden increases or decreases in power. The best way to achieve this is to provide the IPS in a series of modules or building blocks containing the required components and where additional energy storage or power modules can be added depending on the loads that need managing.
Development challenges
Building a new IPS is not easy. It requires high quality state-of-the-art systems that can move large amounts of power around in real-time. Sacca explained that this includes conversion equipment, a distributed control system and energy management algorithms that can properly utilise power generation, power conversion, and energy storage to meet the load requirements of the platform.
The UK Royal Navy Type 45 destroyer was the first frontline warship to have an all-electric power and propulsion system but has had well-publicised problems with its electrical generation capacity. The innovation that came with developing an all-electric power and propulsion architecture is not without risk. Issues with the Type 45’s Integrated Electric Propulsion system resulted in instances of total electrical failure during its first years of operation.
A new WR-21 advanced cycle gas turbine (ACGT) was selected with two 21MW turbines driving two GE Marine and two Warstila generator sets. High voltage switchboards and transformers distribute power to the ship systems. However, the planned operation of the system using a single GT with the second only used for high-tempo scenarios did not work out and long periods operating at low speeds in high temperature environments made the situation worse. The ship’s two 2MW diesel engines were intended for port manoeuvres and operations and not supposed to be used as a back-up.
These problems are being rectified under an expensive and very invasive Power Improvement Programme (PIP) that has been running since 2016 with the replacement of the two Wartsila W200 diesel generators with three more powerful MTU V-20 series. The PIP is being delivered under a major design and manufacture contract to BAE Systems along with partners BMT Defence and Cammell Laird from the U.K. Ministry of Defence (MoD) worth $204.7 million (£160 million). The additional 5MW of power is being managed by a new high-voltage switchboard, the platform management system has been reconfigured, the GTs are being refurbished with the intercoolers and recuperators replaced.
The result of all this is that the Type 45 destroyers will run its power and propulsion very differently to how it was originally envisaged. Instead of running of its two GTs with the DGs as back-up, the class will now operate in a Combined Diesel-Electric and Gas (CODLAG) arrangement with GTs and DGs employed where required in different modes.
The U.S. Navy pursued its first all-electric ship with the DDG 1000 Zumwalt-class destroyer programme. Although the programme was cancelled after three ships it was successful in developing a new IPS for the vessels. Formerly separate, the ship combined the combat information centre and engineering control room into a single Ship’s Mission Centre (SMC). This allows for direct communications and observation by the weapon’s officers and the engineers. The Zumwalt’s has 80MW of installed power provided by two 36MW Rolls-Royce MT30 and two 3.9MW Rolls-Royce RR4500 gas turbine generator units.
The U.K.’s Queen Elizabeth-class carriers are able to generate 110MW of power from two 36MW Rolls-Royce MT30s and two 9MW and two 11MW Wärtsilä diesel generators, however the capabilities and operational profile of frontline warships is different from supporting vessels.
New IPS efforts
The U.S. Navy is not stopping with the Zumwalts, however. Its next generation destroyer programme, known as DDG(X), aims to deliver a new warship that will replace the Ticonderoga-class cruisers and eventually the Arleigh Burke-class destroyers, starting with the old flight vessels.
DDG(X) will be over 13,000 tonnes and is being designed from scratch with the specific purpose of providing the SWaP to host numerous future weapon systems. It will also have a new IPS and energy architecture that can manage the electrical loads of the destroyer.
A new land-based test site (LBTS) for the DDG(X) was opened in March 2023 by the U.S. Naval Surface Warfare Center (NSWC) that will be used to test technologies for the IPS, which represents one of the high risk elements in the programme. This is designed to ensure that the future destroyer can host the SWaP and Cooling (SWaP-C) requirement of the IPS and that it can meet ship’s power requirements.
The U.S. Navy FY2024 budget states that LBTS will take delivery of IPS hardware in late-2024 with tests to run out to early FY2027 under the preliminary design phase for the DDG(X). Full testing is expected later in FY2027. Work in the IPS will build on the DDG 1000 programme as the NSWC had previously tested the IPS for this programme also.
Power system solution
While predicting the power demands of the future is uncertain, we do know the demand will grow and that it will likely be significant as energy continues to play an increasing role in the kill chain. The question is how best to future proof the next platform.
“Northrop Grumman believes that by employing electric or hybrid propulsion and an advanced electrical architecture that incorporate power conversion equipment, energy storage, and controls to effectively manage power and energy demands is essential to meeting the unknown demands of future platforms,” Sacca said, “Additionally, an electrical architecture that is scalable and flexible is critical to effectively manage the platform well into the future, be it to support upgrades mission packages or completely new future weapons and sensors.”
Northrop Grumman has developed a Multifunction Prime Power System (MPPS) that is designed to support the integration of new sensors and weapons into the DDG(X). But it is also being offered as a way of supporting the addition of both the SPY-6 and SEWIP Block 3 EW system onto the Arleigh Burke-class destroyers.
“Northrop Grumman has invested in modular technology power conversion and control building blocks that can provide power at the levels described (100’s of kilowatts to megawatts) and these building blocks are already in use within deployed radar and electronic warfare systems,” Sacca explained.
“It is scalable to platform requirements but, more importantly, designed to intelligently share power across loads to mitigate the need for individual systems requirement for reserve power,” he added, “With the addition of our energy storage cabinets, we enable platforms to peak shave and therefore reduce overall average energy demand on the generators.”
Using those building blocks, the company has re-architected the prime power system to support a variety of loads and seamlessly incorporate energy storage as needed resulting in the MPPS. It is an enabling technology that can help extend the life of existing hulls with better utilisation of installed hardware and effective utilization of energy storage.
Building blocks
The MPPS includes a bidirectional converter module (BCM), which is a multifunctional software configurable component, several of which comprise a power converter cabinet. A microDSP controls the functionality of the BCM. Energy storage modules can be installed into an Energy Storage cabinet and it means that the number of cabinets and number of components within those cabinets can be scalable as required.
“The challenge is a paradigm shift in how prime power equipment is managed for the platform. We must break down the stove piped solutions where every mission package has its own dedicated EMI filter, power conversion, energy storage, protection, and distribution that is not available to support other mission systems,” Sacca said, “We have also developed an energy storage capability to compliment this power conditioning capability that can help but, energy storage alone will not be sufficient to meet the needs of the next generation warships.”
But during designs for new ships or when finding room on a legacy warship there can only be so much space reserved for power. Therefore, the intention when developing the IPS components is to ensure that more efficient components can be built so more can be fit into each cabinet. In the future more effective power storage components can be added that will increase the power supply in the same space constraint, so more space does not have to be found on the ship.
by Tim Fish
