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Power inverters, batteries and Supercapacitors

A single-phase inverter is able to provide backup during power glitches and outages; however, this architecture is not able to provide a peak load surge at initial startup. If a supercapacitor is integrated into this architecture along with the battery, the battery stress will be lowered and its lifetime extended. As a bonus, the supercapacitor can provide peak currents far more quickly than a battery.

The three common topologies for multilevel inverters are as follows: cascaded H bridge inverters (CHB), diode clamped inverters and flying capacitors invertors. Among this configuration, CHB is referred because of its simplicity, modularity and minimum number of components requirement. Reference 1 found that a sinusoidal pulse width modulation provides a better resulting output with lower harmonic reduction as compared to a single pulse width modulation. See Figure 1.

Figure 1

Block diagram of proposed scheme of single phase inverter with supercapacitor (Image courtesy of Reference 1)

Block diagram of proposed scheme of single phase inverter with supercapacitor (Image courtesy of Reference 1)

Reference 1 chose to use a single-phase full-bridge inverter in which the design uses pairs of controlled switching devices like SCRs, power BJTs, MOSFETs, IGBTs, maybe even GaN and SiC devices could work well here for efficiency and high frequency designs (S1, S2, S3, and S4). Nevertheless, the design consists of MOSFET switches in this paper. Among these, only one pair conducts simultaneously. As a solution, this paper presents a single-phase, three-level PWM inverter whose output voltage has three values: zero, half and full supply dc voltage levels in the positive half cycle. See Figure 2.

Figure 2

A single-phase three-level H bridge inverter (Image courtesy of Reference 1)

A single-phase three-level H bridge inverter (Image courtesy of Reference 1)

Reference 1 determined that the addition of a supercapacitor does indeed show a drastic drop in surge current during switching as well as lower stress on the battery (The battery also gets an opportunity to re-charge when the supercap is performing the surge demand current.

An ultracapacitor, also known as supercapacitor, can also be used in electric vehicles as an excellent partner to Lithium Ion batteries. An ultracapacitor can provide the power needed for acceleration, while a battery provides range and recharges the ultracapacitor between surges. Skeleton Technologies has a really nice design for their supercaps. (See my upcoming article on Formula E racing and my interview with the Venturi Racing team and the intricacies of racing and designing an all-electric race car)

Powerbox S-CAP BOOST

Powerbox, one of Europe’s largest power supply companies, just acquired by Tokyo-based Cosel Co., Ltd —the number one industrial power supply company in Japan, has developed a supercapacitor boost technology called S-CAP BOOST designed for backup and peak power solutions to industrial and medical applications. This technology is based on the latest supercapacitor technology and combined with intelligent control and monitoring.

S-CAP BOOST will provide a solution to equipment manufacturers who require high energy peaks for short periods or emergency backup purposes in applications where due to safety regulations, Lithium Ion or acid batteries are not allowed. Depending on the application, S-CAP BOOST can be configured to charge and monitor supercapacitor banks to work as Uninterrupted Power Supplies (UPS), delivering backup power to allow safety operations to take place before shutdown or delivering high peak power for a short period without disturbing the main source or discharging/damaging the system battery in applications such as laser, electric motor booster or X-ray emission element.

Critical applications operating in hostile or confined environments are strictly regulated in terms of chemical and other hazardous risks, reducing or forbidding certain types of batteries such as Lithium Ion. For safety reasons, those applications must have a power backup long enough to run alarms and safety shutdown processes. In such arduous conditions conventional batteries are replaced by supercapacitor banks whose values could be from few Farads to 200 Farads for general applications, but up to container size in the case of large systems. S-CAP BOOST technology tightly controls vital parameters, from a single 2.8V cell supercapacitor to a wide range of assemblies delivering a specific voltage and energy required for a given application.

One example of a product built using Powerbox’s S-CAP BOOST technology is a 2500W backup unit developed for an industrial process-control computer installed in a very restricted area. The design is housed in a 19-inch 2U chassis. Powerbox’s 29F-54V-60A UPS design integrates 22 supercapacitors totaling 29 Farads and has a capacity of 2500W during 5 seconds at full load and 30 seconds at half-load. To optimize the cells charge, the 29F-54V-60A integrates a DC/DC converter with current control, guaranteeing the supercapacitors are properly charged to deliver full power when required. The unit includes active charging cells control with load balancing, cell health monitoring and alarms. Alarms signals including Vcell-high, Vcell-low, Vcell-zero and temperature are available via a physical interface, with digital control and monitoring being an alternative option. See Figure 3.

Figure 3

The 29F-54V-60A UPS module is housed within a 19' 2U chassis and integrates 22 supercapacitors, totalizing 29 Farad with a capacity of 2500W (Image courtesy of PowerBox)

The 29F-54V-60A UPS module is housed within a 19” 2U chassis and integrates 22 supercapacitors, totalizing 29 Farad with a capacity of 2500W (Image courtesy of PowerBox)

Patrick Le Fèvre, Powerbox’s Chief Marketing and Communication Officer sees that integrating supercapacitors within power supplies is fast becoming an extremely reliable and well-suited option to be considered by system architects. LeFevre forsees their S-CAP BOOST as a powerful platform for the future with many applications applications for supercapacitor energy storage technology and not just in electrical vehicles.

Lithium Ion only has a cyclability (number of recharges) of 500 to 1,000, whereas supercapacitors can sustain from 500,000 to 20,000,000 cycles, making that technology extremely relevant for applications requiring large amounts of charge /discharge cycles with high energy such as in industrial or medical lasers. S-CAP BOOST technology has been developed for very tight control of the supercapacitors’ charge in order to optimize the energy stored between each cycle, with very high levels of safety and reliability.

References

1 Single Phase Residential Multilevel Inverter Using Supercapacitor, A. K. Saonerkar, A. Thakre, A. Podey, A. Chimote, P. Kadao, P. Kadu, R. Satpute, J D College of Engineering and Management; Rajiv Gandhi College of Engineering and Research, India

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