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【Company Summary of Aisin Seiki Co., Ltd.】
Company Name Aisin Seiki Co., Ltd.
Head Office Asahi-machi, Kariya, Aichi 448-8650, Japan
Businesses Manufacture and sales of automotive parts (drivetrain, body, brake and chassis, engine, information technology-related), lifestyle- and energy-related products (sewing machines, beds, gas heat pump products, etc.), and wellness-related products
URL [Japanese]

Designing a long-awaited next-generation cogeneration system
Solving an unexpected problem using Toshiba’s photocoupler incorporating the latest LED

Aisin Seiki, a manufacturer of cutting-edge automotive parts, also leads the world in the development of new energy systems that address the worldwide concern over global warming. Aisin Seiki is known for its unique ideas and high-quality, outstanding "monozukuri"—the art, science and craft of making things.

Among a range of new energy systems, Aisin Seiki has focused on fuel cell-based home cogeneration systems ever since the concept first emerged. Aisin Seiki’s cogeneration systems use solid oxide fuel cells (SOFCs) that provide the highest power generation efficiency among fossil fuel-based cogeneration systems. Its development efforts began in 2009. In that year, Aisin Seiki participated in a multi-party joint development project for a home SOFC cogeneration system. Setting an ambitious goal of commercializing a home SOFC cogeneration system in the early 2010s, Aisin Seiki also played an active role in demonstrations and field tests. Its commitment helped accelerate the R&D of home SOFC cogeneration systems. Consequently, Aisin Seiki released ”ENE·FARM type S,” the first home SOFC cogeneration system, in 2012. Four years later, in 2016, Aisin Seiki released the latest Gen-4 model, the fruit of continuous improvement. The Gen-4 model provides the world’s highest power generation efficiency of 52%, which is 5.5% higher than that of the preceding model. Furthermore, since the Gen-4 model is the world’s smallest home cogeneration system, it became the focus of attention in the industry.


One of the major units of this latest model is a power conditioner, which incorporates Toshiba’s new photocoupler, the TLP383. The power conditioner is an important unit that converts a direct current generated by fuel cells into an alternating current to be used in the home.

Why did Aisin Seiki choose Toshiba’s TLP383 photocoupler from among many options from many manufacturers? The following is a background story, with opinions and testimonials from Aisin Seiki’s engineers involved in the development project.

Challenges that faced Aisin Seiki’s project team

In March 2011, the Great East Japan Earthquake struck. In the wake of the earthquake, the country was under pressure to secure a supply of electricity to homes. In the face of competition with cogeneration systems with different mechanisms and installation costs, Aisin Seiki steadily increased the number of installations of its home SOFC cogeneration systems. But, it was high time Aisin Seiki introduced a new model. For the development of the new 2016 model, Aisin Seiki placed the highest priority on addressing the feedback from its customers and field engineers and considered improving weak points of the previous model significantly.

Challenges that faced Aisin Seiki’s project team

Aisin Seiki’s chief engineer at the Energy Engineering Department of the Life & Energy Product Division said, “We had two prime goals for the new model: a further improvement in power generation efficiency and a reduction in the size of the main unit compared to the previous model. More specifically, we considered integrating a water tank and its control circuitry into the main unit. The purpose of this was to reduce the installation footprint and complexity of the new model in order to make it installable at various locations. Our goal was to combine high efficiency and small footprint to make the new model competitive.” Previously, many households gave up using an SOFC cogeneration system or chose other types of system because of space constraints. The new model would make it possible for them to use a high-efficiency SOFC cogeneration system. Aisin Seiki’s project team was tasked with not only enhancing power generation efficiency but also reducing the size and cost of the main unit. Thus began a formidable challenge for the project team, with more engineers assigned than previously.

Just as the project started, the project team encountered a problem with the redesign of the power conditioner circuit. In an evaluation of service life, the power conditioner failed to exhibit the expected characteristics. The evaluation revealed that, with the new circuit configuration, the current transfer ratio (CTR) of the photocoupler plays a significant role in achieving the target characteristics. It was found that although the power conditioner performs well at an early stage of the life cycle, its characteristics would drop considerably below the target as the current transfer ratio of the photocoupler degrades over time. The project team did not experience this problem during the development of the previous model. Feeling dismayed, team members performed verification repeatedly. Day after day, they sought advice from device manufacturers and checked out the websites of the vendors they had dealt with before in order to collect information. However, they could not elicit any suggestions from the vendors or find any information about photocouplers that could possibly lead to a solution. The previous power conditioner circuit was too costly to be used in the new model. However, the project team would not be able to use the newly developed circuit without solving the aging problem. At one time, it crossed their mind that they should make a drastic change to the circuit design, but that meant they would have to evaluate a new circuit from scratch. Therefore, all the project members wanted to solve the problem without changing the circuit configuration.

Reasons for selecting Toshiba’s TLP383

It was just then that the project members heard some good news. They received information about the TLP383, the latest photocoupler of Toshiba Electronic Devices & Storage Corporation, from its sales representative who was dealing with Aisin Seiki concerning another circuit. According to his explanation, one of the features of the TLP383 is that it incorporates a cutting-edge LED that is much less subject to aging degradation than the LEDs in the other commercially available photocouplers. This LED would be beneficial not only at the early stage of a product life cycle but also at the aging stage. Since the TLP383 was a new product, it took a while to obtain samples, but the project team received samples in time to meet the design schedule. No sooner had the samples arrived than the project team commenced evaluating them.

Reasons for selecting Toshiba’s TLP383

All the project members were surprised at the evaluation results. Under any current and temperature conditions, the TLP383 exhibited stable performance with little output variation and hardly any change in the current transfer ratio. The project team was firmly convinced that the evaluation results and the reliability data of the TLP383 were sufficient to confirm its aging reliability. One of the engineers who evaluated the TLP383 said, "No matter how many times we performed evaluation, the TLP383 always showed stable results. So, we had plenty of time left to verify the potential risk of our circuit design. The TLP383 saved us a lot of trouble since we were under pressure to complete the circuit within the allotted time."

Finally, the 2016 model of ENE·FARM type S was completed and commercialized as originally planned. Integrated into a single unit, the 2016 model became even more compact and sophisticated than the previous model. In addition, the 2016 model is less costly and provides improved power generation efficiency as originally planned. As a result, the market response to the new model has been very positive since its release. Sales of the 2016 model rapidly reached nearly twice the sales volume of the previous model. And the new model is still selling briskly.

Next step

Most of Aisin Seiki’s products are delivered to automakers. In contrast, Aisin Seiki plans, designs, develops, manufactures, and sells ENE·FARM type S and other cogeneration systems on its own. Therefore, the development of the 2016 model was a challenging and rewarding task for the project team.
The chief engineer of the project team commented on his expectations of Toshiba Electronic Devices & Storage Corporation, "The SOFC cogeneration system is one of the products you can use at home to combat global warming. We will continually improve the power generation efficiency and reduce the size and cost of our SOFC cogeneration system. So that we can develop and manufacture products that satisfy our customers, we’d like to ask Toshiba to develop high-performance, high-precision, and high-quality electronic devices like the TLP383, promptly provide a wide range of information and sample devices, and offer technical support in various ways."

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