Mitsubishi Heavy Industries Technical Review Vol. 60 No. 2 (June 2023)
1High-Efficiency Electric Compressor that Improves
Decarbonization Technology and Fuel Cell Performance

Mitsubishi Heavy Industries Engine& Tu r b o c h a r g e r, L t d .
S a l e s D e p a r t m e n t , Tu r b o c h a r g e r
Division+080-42-763-1685

As the global movement accelerates toward the realization of a decarbonized society, themobility industry has a growing need for electrification of vehicle powertrains. In order to expand
the electric vehicle market in the future, it is necessary to solve issues such as higher battery
performance and fast charging technology. In recent years, fuel cell systems that can extractelectric energy directly from clean hydrogen fuel and achieve high power generation efficiency
have attracted attention as the most effective means of zero emissions.
Fuel cell systems can be applied to vehicles, stationary and other industrial applications, and areexpected to become widely used after 2030 with the provision of hydrogen infrastructure. It is also
incorporated into long-term policies of countries around the world, and continuous market
expansion is expected. Mitsubishi Heavy Industries Engine & Turbocharger Co., Ltd. (MHIET) has
developed a highly efficient electric compressor for fuel cell systems to meet the changing businessenvironment of shifting from internal combustion engine vehicles to zero-emission vehicles, andhas begun supplying samples to customers. Widespread use of hydrogen infrastructure takes time,and it is expected that the infrastructure will be developed first for limited applications such astransportation between bases. This report introduces the product specifications and features of thehigh-efficiency electric compressor for commercial vehicles.

|1. Introduction
With the global trend of decarbonization, the volume of electric vehicles is expected toincrease year by year. On the other hand, electric vehicles in the commercial vehicle field have aproblem of load reduction due to larger batteries. The demand for fuel cell systems using hydrogenfuel is expected to increase as one of the countermeasures. Figure 1 is a diagram of a vehicle
system with fuel cells. The electric compressor under development is an important component infuel cell systems that supplies compressed air into the stack and obtains electrical energy bychemical reaction with hydrogen fuel. According to the market analysis of MHI-ET, the size ofelectric compressors for fuel cell vehicles is expected to expand mainly in the 3 regions of China,
Europe and North America, and the motor output of 20~30 kW for pickup trucks and medium-duty
trucks will occupy the majority of the market in 2045. For the fuel cell stack with the highest needof 150 kW, a motor output of 30 kW is required. In addition, for heavy-duty trucks with a fuel cellstack output of 200 kW or more, 2 electric compressors are used in parallel. MHI-ET is being
developed with a view to customer needs that can be met by a single electric compressor. Electriccompressors contribute the most to the overall efficiency of fuel cell systems, and it is necessary todevelop high-efficiency electric compressors that are adapted to the needs required by the products.

Mitsubishi Heavy Industries Technical Review Vol. 60 No. 2 (June 2023)
2

Figure 1 Diagram of vehicle system with fuel cells|2. Product specifications
Figure 2 shows the exterior view of the developed electric compressor, and Table 1 shows thespecifications. Our target fuel cell stack output range for commercial fuel cell vehicles is120-150 kW, which is most needed by the customers. The product has the specificationsof a maximum DC voltage of 850 V, motor output of 25-30 kW, and 100 krpm or more. A
water-cooling system is mainly used in the motor/inverter, while an air-cooling systemusing compressed air is employed in the rotor magnet and the foil air bearing, which
are the heat-generating components in the motor. Moreover, oil-free foil bearings areused to prevent poisoning of fuel cell stacks. Figure 3 shows the outline of thedevelopment of the electric compressor series. Our goal is to contribute toward theachievement of a carbon neutral society by offering a product lineup with a fuel cellstack output range of 100-300 kW, thereby meeting a wide variety of needs from small
commercial vehicles to heavy-duty trucks to marine vessels.
Table 1

Specifications of developed
products

Item
Maximum voltage
Rated motor output
Motor type
Cooling system
Bearing typeFigure 2Exterior view of developed electriccompressor

Figure 3

Outline of development of electric compressor seriesSpecifications
DC850V
25-30 kW
Permanent magnet
Water cooling
Foil bearingMitsubishi Heavy Industries Technical Review Vol. 60 No. 2 (June 2023)
3|3. Product features
Electric compressors developed for fuel cell systems have the following features. MHI-ET has
been developing electric compressors for some time and is currently developing the secondgeneration. Figure 4 shows a comparison of the features and appearance of the developed products.

Figure 4 Comparison of features and appearanceof developed products(1)

Higher efficiency
Electric compressors for fuel cell systems are driven using electric power generated by fuelcells. Therefore, higher efficiency of the electric compressor itself is an important factor directly
linked to higher efficiency, smaller size and lower cost of the entire fuel cell system. In thisstructure, high-pressure compressed air is supplied to the fuel cell stack by supercharging in twostages sequentially with two compressors at each end, thereby realizing high flow rate and highpressure while minimizing the size of electric compressors. In addition, the technology establishedin the turbocharger business has enabled a more advanced aerodynamic design and more efficientcompressor wheels. Furthermore, with a balanced design between the thrust load generated by thetwo compressor wheels of both ends and the foil air bearing, mechanical loss has been reduced toelevate the efficiency of electric compressors. The type of motor used is a permanent magnet motorwith distributed windings suitable for high-speed revolution and high efficiency applications.
(2) Higher output
Electric compressors for vehicles are required to be smaller and lighter due to restrictions on
their loading locations and effects on fuel consumption. On the other hand, our company realized
the design of high-speed rotation, which reduced the required driving torque and enabled smaller
motor designs. Higher output has also been realized with a balance design including the appropriateenhancement of cooling for the motor housing and the inside of the motor, and the minimization ofpressure loss in the bypass of compressed air from the compressor.
(3) Higher durability
When oil leaks from the bearings and reaches the fuel cell stack, poisoning occurs
resulting in declining performance and shortened life of the stack. Oil-free foil airbearings are applied to electric compressors for fuel cell systems, but ensuring the durability of foil
air bearings is also an important point of electric compressor durability. Our company has thedesign, manufacturing and quality control know-how of rotary rotors accumulated in
the production of turbochargers. Therefore, it is possible to design and manufacture astable rotor with less vibration to ensure durability. Especially when the motor isstarted, the foil air bearing rotates in contact with the shaft. However, since it floats incontact up to a certain number of revolutions, a highly abrasion-resistant coating isapplied to achieve both bearing function and durability. In addition, the company has
established an insulation design that can handle high voltage DC of 850 V and anevaluation method for the design, thereby contributing to the improvement of motorreliability.

Mitsubishi Heavy Industries Technical Review Vol. 60 No. 2 (June 2023)
4(4)Lower cost
Fuel cell systems are expected to play an important role in realizing a decarbonized society,but they are also required to be economical. We have already introduced a pilot production
machine and have adopted the design and manufacturing method for the mass production process,so that the cost can be reduced according to the specifications required by automobile
manufacturers. Moreover, in addition to the specification work for cost reduction, the global supply
chain established through the turbocharger business is utilized for cost reduction. Such features arebased on the needs understood through various types of market research/analysis and engagement
in dialogue with customers, as well as our rotor technology cultivated in the turbocharger business.

|4. Future prospect
Our product development is also aimed at making the following options available: asingle-stage type for cost reduction, and an expander type for enhancing the efficiency of the entire
system by recovering energy from the fuel cell exhaust during high load operations. Production of
the high-efficiency electric compressor for commercial vehicles introduced in this report isexpected to begin in 2025. MHI-ET develops products for fuel cell systems according to market
needs, thereby contributing to the achievement of a decarbonized society.