Technical Library

Capacitors for Power Electronics:
Latest Technology Trends

NICHICON CORPORATION

In the capacitor business, Nichicon is concentrating on power electronics. We are working to expand our sales based on the strengths of our technological expertise and reliability. Nichicon is focusing on solar power generation, wind-power generation, electric and hybrid vehicles, railway cars, and inverter applications for industrial equipment and household electronics. For this market, we are able to develop and mass produce both aluminum electrolytic capacitors and film capacitors, providing technologies and products tailored to meet our clients’ requirements. In this article we will focus recent technological trends in aluminum electrolytic capacitors and film capacitors for the power electronics market.

1.Market Requirements for Aluminum Electrolytic Capacitors

The main application of large can-type aluminum electrolytic capacitors is to smooth the power source input voltage. These capacitors are used in switching power supply circuits and inverter circuits. Within these circuits, aluminum electrolytic capacitors are important and indispensable for providing a stable supply of electricity.
Regardless of where these large can-type alumuinum electrolytic capacitors are used, the expectation is they will make effective use of the limited space available as equipment shrinks in size. As the demand for space saving equipment grows the demand for smaller and lower profile electrolytic capacitors is increasing.

In recent years, the industrial equipment market has moved toward energy conservation and higher efficiency, placing a focus on advances in high-voltage systems. Against this backdrop, demand is growing for the use of aluminum electric capacitors that can handle high voltages in inverter power supplies and other control circuits. In particular, demand has increased for high-voltage products for markets related to renewable energy, such as solar power generation and wind-power generation.
In addition, in regions where power sources are unstable, leading to variable input voltages, equipment design needs to take major voltage fluctuations into account. This situation presents the need for higher-voltage capacitors than in the past.
To meet these market needs, we have developed the LGM Series (the industry’s most compact), and the LGN Series 600V products (the industry’s highest voltage for 105°C snap-in terminal-type products).

(1) LGM Series (Compact Components: the industry’s Smallest)
As the capacitance of aluminum electrolytic capacitors is proportional to the surface area of their aluminum electrode foils, we employ a process called etching to electrochemically create irregularities on the surface of the aluminum foils, thereby increasing their surface area.
A development focus for making components more compact is to use a newly developed etching technologies to increase the effective surface area through the use of high-magnification anode aluminum electrode foils. One method of using etching technologies to increase the surface area is to optimize the diameter of holes (pits) in the foil surface. This approach allows capacitance levels to be increased substantially by increasing the number and length of pits.

In addition, we employed high-voltage electrolysis paper in the element structure and made the electrolysis paper thinner. Thinner electrolysis paper allows component volume to be reduced while maintaining the same level of capacitance. By increasing the capacitance of electrode foils and using high-voltage electrolysis paper, we succeeded in making components that are smaller than series that are currently main stream.
The LGM Series achieves a volume reduction of up to 16% compared to the LGL Series, which had been our most compact product, making it the industry’s smallest.

Figure 1 LGM Series of snap-in terminal-type aluminum electrolytic capacitors, the industry’s smallest

Figure 1.LGM Series snap-in terminal-type aluminum electrolytic capacitors achieve compactness as the smallest such capacitors in the industry

(2) LGN Series 600V Products ( Industry’s Highest Voltage 105°C Snap-in Terminal-Type)
In addition to electrode foils and electrolysis paper as in the compact series, performance of the electrolytic solution is an important point in the development of high-voltage products.
These products use anode aluminum electrode foils formed on high-voltage oxide films and electrolysis paper capable of withstanding high voltages. The new development of an electrolytic solution that ensures long-term stability and enhances oxide film restoring capacity at high voltages led to our development of a product rated at 600V—the highest voltage level in the industry.
The newly developed electrolytic solution offers a more highly optimized component configuration than current electrolytic solutions and a material for increasing withstand voltage that does not impact heat resistance and conductivity. This additive helped to achieve a product with 20–30% higher voltage than current products.

 LGN Series snap-in terminal-type aluminum electrolytic capacitors, with an expanded lineup adding products rated at 600V, the industry’s highest level

Figure 2. LGN Series snap-in terminal-type aluminum electrolytic capacitors,with an expanded lineup adding products rated at 600V, the industry’s highest level

With this LGN Series 600V product, connecting multiple aluminum electrolytic capacitors in series allows for the number of capacitors to be reduced. For example, whereas three 400V products in series would be needed to reach 1,200V, the same effect can be achieved by using two LGN Series 600V components connected in series. This reduction in the number of components should help to save space.

Figure 3 1,200V circuit example

Figure 3.Example of 1,200V high-voltage application

Market Requirements for Film Capacitors

Capacitors for industrial equipment and railway cars have conflicting technical requirements, as they must achieve high voltage and high ripple current as well as compactness. Furthermore, in the interests of better safety and light weight, in recent years demand has grown for dry film capacitors that do not use oil internally.
Primarily targeting applications in the railway car, industrial equipment and environmental equipment fields, we have developed the EJ Series DC dry film capacitors. These capacitors achieve compactness, high ripple current and high reliability.

(1) Capacitors for Industrial Equipment and Railway Cars
By making dielectrics (vapor-deposited film) thinner and increasing element storage capacity, we have made these capacitors 40% more compact than our current products. At the same time, we have adopted an entirely resin-molded structure (caseless structure) that enables use at low temperatures (-40°C) and high temperatures with high humidity (85°C 85% RH 1000h). In addition, the vapor-deposited film employs a security apparatus that both increases safety and extends product life, and employs more environmentally conscious component materials.

Figure 4. EJ Series DC dry film capacitors

Figure 4. EJ Series DC dry film capacitors

 

NICHICON CORPORATION
From the Dempa Shimbun, Jul. 1, 2016

 
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