Engineer Interview

Aim to be a Top Brand for customers! Know-how gained from repeated analysis of trial and error – Development of the Small-Capacity UPS SANUPS A11K Series

In this segment, we introduce the people who support SANYO DENKI’s technologies in a variety of scenes.
On the front line of monozukuri (Japanese for manufacturing), what do you think about daily, and how do you confront any difficulties that arise? Let me share some of the thinking that goes into our products.

UPS is the abbreviation for Uninterruptible Power Supply, which are devices which supply power to devices for a fixed amount of time without stopping, even when problems occur with utility power and other power sources. In our high information society, networks are used in a growing number of fields; network system stoppages have an enormous impact on the community, and as such the importance of UPSs to provide these systems with a stable power supply is increasing.
This time, we talked to the members of the Power Systems Division, Design Dept. 2, who was at the center of the development of the “SANUPS A11K” small capacity UPS.

 

 Mr. Shinichiro Yamagishi/ Power Systems Div.,/ Design Dept #2

 Mr. Yasuhiko OgiharaPower Systems Div.,/ Design Dept #2

 Mr. Yuki Kurashina/ Power Systems Div.,/ Design Dept #2

 Mr. Shota Ozawa/ Power Systems Div.,/ Design Dept #2

 

Can you briefly tell us about the features of the SANUPS A11K small capacity UPS?

 

Mr. Yamagishi
We developed it as the successor model to our current UPS, with expanded output capacities from 1 to 5 kVA. Features include modularization of the inverter and battery sections, high efficiency, compactness, a wide -10°C to +55°C operating temperature range, and a wide input range. We improved performance while keeping the positive aspects of our conventional model’s circuitry, and developed it to be extended to other power supply products in addition to UPSs in the future.

Market competition in the 1 to 5kVA range seems to be fierce, what features did you focus?

 

Mr. Yamagishi
Definitely operating temperature range. Our conventional product had a range of about 0 to 40°C, but in the summer temperatures can exceed 40°C, and in the winter some regions are below freezing. So, by expanding the operating temperature range, the range where it can be installed with no air conditioning is greater. As for the battery chemistry, right now we’re using lead-acid batteries, so there is a limit of temperatures above 40°C, but in the future, we will use lithium-ion batteries which can handle both high and low temperatures.

With the inverter and battery units being modularized, am I correct that two kVA is made with two one kVA units?

Mr. Ogihara
That’s right. We developed 1kVA and 1.5 kVA modules. To get 2kVA we used two 1kVA modules, to get 3kVA we used two 1.5kVA modules, and for 5kVA we used three 1.5kVA modules. We developed two types of inverter module and five UPS capacities. Through modularization, maintenance work such as the replacement of the inverter module has been simplified. We were also able to reduce our development and manufacturing time.

 

 

One feature of the “SANUPS A11K” is the 92% efficiency. With the most recent products having 90% efficiency, how difficult was it to raise the rate by 2%?

Mr. Yamagishi
Inverter circuit technology is a mature technology, and there is not much new. So, we can only use new components with excellent characteristics, or try to reduce losses in the control power supply circuit. Other than that, there is no point where we can substantially increase efficiency, so it is difficult.

How exactly do you reduce loss in the control power supply circuit to achieve high efficiency?

Mr. Yamagishi
The control power supply circuit performs switching, and it inevitably involves some loss in the circuit. To reduce that loss, we used soft switching to reduce the switching loss compared to conventional UPSs. This kind of soft-switching circuit has become mainstream recently. It is called a quasi-resonant type that uses resonance phenomena to reduce power supply noise.

 

Did you have any troubles with downsizing?

Mr. Ogihara
Based on requests from members of our Field Service team, we reduced the width by 5 mm. But, this makes the inside of the device narrow, so making it smaller was a problem. Because we stopped using bare substrate type inverters and instead used modular inverters enclosed in casings, the internal space became very narrow. Since we did not change the battery size, the inside of the inverter was dense. As a result, air could not flow, and we struggled with rising temperatures.

 

What other difficulties did you have?

Mr. Yamagishi
I want to use lithium-ion batteries in the future, so this time we designed a battery charge/discharge circuit utterly different from that in previous models. The charging voltage and current can easily be adjusted so that both lead-acid and lithium-ion batteries can be used. But, redesigning the circuit was quite tricky.

Mr. Kurashina
First, we tried a charge/discharge circuit that we verified using simulation software, but when we tested it, the operation was unstable because of noise, and it did not operate as designed. Also, the downsizing made the air flow path narrower, which increased temperatures. To resolve this, we reviewed the arrangement of parts and changed the number of reactor turns and the shape of the fin. We did a lot of temperature testing, too.

A single temperature test takes hours; first, you turn on the power, then wait for the temperature to rise until you can identify the saturation point at which the heat stops rising. Then you look at that data, judge if it is good or bad, replace it again… It’s not something that can be done many times a day. It is the reason the evaluation took so long. Expanding the operating temperature range was one of the development targets for this product, so we had to work hard on assessments to achieve it. At one point, I remember feeling that taking temperature measurements was all I did (laughs).

Mr. Ogihara
For temperature, I tried to come up with a solution running simulations with thermal analysis software. I had just installed some new thermal analysis software, so I tried using it. However, the simulation data and the actual data didn’t match… We carried out trial and error and built up know-how.

Mr. Yamagishi
Even if the simulation didn’t deliver the same data, it did help us visualize a path for design. Even when I wasn’t fully proficient with the software, I think it was more efficient to design with it than without.

Mr. Ogihara
Components used in the Power Systems Division, like power modules, are relatively easy to model with 3D CAD software. However, there are tips you need to keep in mind when analyzing with simulation software. Heat is generated by electronic components that are only a few mm in size, and if you assume that heat spreads to the surrounding case, the simulation will not match the actual situation at all. We were able to build up this know-how while conducting an analysis. In addition to thermal simulations, we also performed structure, mold flow, and deformation simulations, which were connected to efficient design.
Regarding simulation… Just buying analysis software is not enough. Know-how is essential. Often, when I was analyzing earnest, I would get so into it that I lose all track of time for design. Many companies specialize in the analysis. It’s such a broad field.

Can you tell us about your workplace atmosphere?
 

Mr. Kurashina
We meet every day and share information. My boss tells me what he’s looking for, so I consider how to achieve it and make sure I make progress by quickly consulting with him if there’s anything I don’t understand.

Mr. Ogihara
That’s right, and I ask myself if I’m reporting, contracting, and consulting correctly. I think it’s a good atmosphere. Everyone voluntarily thinks and acts, but it’s by no means disorganized, and veterans often take care of the less experienced members.
We all have areas in which we specialize, so if you are a person on the structure side, you may not fully know details of the electrical parts. But, I stay in communication with the people who design the electrical circuits, so work goes well.

Finally, what are your thoughts on work and your enthusiasm for future UPS development?

Mr. Kurashina
SANYO DENKI’s goal is to be a “Top Brand,” that means “the brand that customers like the most.” To that end, I think that everything must be “top,” including design and evaluation. I always try to keep this in mind so my designs can be worthy of being called “top.”

Mr. Ozawa
Since joining SANYO DENKI, I have wanted my work to be something that I can leave behind as a record in history.

Because we produce complete products and not just components, we in the Power Systems Division, out of all SANYO DENKI design teams, interact directly with the end-user customers so that we can get feedback directly from the customer. So, I am aware that design is what customers come into closest contact with. Also, because we make complete products, we combine the work in many fields. I think that technology which best combines electricity and structure is required. I am proud that I have been doing this for twenty years and I can have confidence in my work every day.

Mr. Yamagishi
In Design, we take care to create stable quality. So, it makes me happy when customers tell me that the product is excellent and durable. Besides that, I think it’s improved operability. I think it was worth it to develop it so that people would come and say that it was easier to operate than before. We also work paying careful attention to fine details that won’t be included in the catalog specification table. In the future, I would like to build a power supply unit that can be deployed in various fields. In our daily work we examine new power supply unit applications, so in addition to meeting customer requests, I strive to increase what we as a company can propose to customers.

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