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Energy Harvesting Everywhere

By Yao Chia Yang
Published: Sep 30,2014

As smartwatches, the Internet of Things, and wearable electronics gradually become mainstream applications, their power supply problems will also create major challenges for the development of future applications.

Consequently, although originally only sources from the traditional power industry were looked upon as renewable energy resources, nowadays in everyday life, common forms of energy are also being considered for use in generating electricity.

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Even though in the past, renewable energy resources had enormous importance in the domain of energy harvesting, it is undeniable that vibration, pressure conversion, and thermal energy conversion can also all be looked upon as important methods in this domain in the near future.

Power Management Need to Becomes Smart

The problem is that even if all of the systems have the capability to harvest energy, if dynamic management of power sources is unable to reach the highest efficiency, the amount of power that can finally be attained is unfortunately unknown. If the whole system’s conversion rate is not working, then energy harvesting is just meaningless talk.

Figure 1 :   From the case of lighting for football in Africa, it is apparent that the types of energy harvesting have already become more diverse.
Figure 1 : From the case of lighting for football in Africa, it is apparent that the types of energy harvesting have already become more diverse.

Linear Technology Director of Power Source Products, Tony Armstrong, stated, “low power consumption” is a crucial condition often found in every domain’s wireless sensory network (WSN) in energy harvesting systems. Their specifications must meet the demands for “millimicro” power; therefore, the power ratio needed for the power conversion ICS may be just dozens of mW while the electrical current may reach an nA level.

Currently the most advanced off-the-shelf energy harvesting technologies, such as vibration energy harvesting and indoor or wearable solar power installations, only produce power ratios on the milliwatt scale under regular working conditions.

Furthermore, energy harvesting systems are usually implemented before the battery runs out and must be charged; however, this is still something that the main battery in the system is able to do.

Therefore, currently the majority of systems’ methods involve using certain kinds of energy sources in the environment as their main power sources. However, they will also use batteries to supply supplementary power for the entire system. When the environmental energy sources disappear or are disrupted, it is easy to switch on the battery to supply backup power.

Figure 2 :   In minimum volume electronics systems, finding ways to use extremely low amounts of power to maintain the system’s operations is a major challenge.
Figure 2 : In minimum volume electronics systems, finding ways to use extremely low amounts of power to maintain the system’s operations is a major challenge.

MCU Is Oriented Towards Low Operating Frequencies

The current electronic systems solutions related to energy harvesting resources can be divided into two modules. One is MCU (micro-controllers), and the other is components related to power management. MCU is responsible for controlling systems operations, while the later type is only able to increase the efficiency of power management.

Considering that the work time is easily ten to twelve years in a situation with no external power support, the power ratio that the whole system consumes cannot be too high. It can even be equipped with handle button batteries or super capacitors to act as power sources; however, they have their limits. The biggest problem is finding ways to use the smallest amount of power to complete all of the system’s operations.

In the current MCU product lines, the approximately 8-bit framework for power consumption is better than the 32-bit. However, the key is still that the tasks done by the system itself cannot be overly complex. They can just do the tasks of keeping data records and making transmissions.

Stable Output is Important for Energy Harvesting Circuit Design

As for power source management design, Tony Armstrong has pointed out that in general when there is energy harvesting, the system usually must supply a stable and continuous output of an electrical current (approximately 50mA). At the same time, it does not need to obtain power from the battery itself.

Consequently, it can extend battery life. Of course, if energy harvesting is strongly lacking electrical power, when it is time to output, the battery must supply electricity to the system.

Generally speaking, in a situation without any load, the working current is approximately 950nA. Of course in a situation with under voltage, the need to boost must be considered. Therefore, the DC/DC end boost function is essential.

Another important issue is the problem of unstable conditions of electrical currents or voltage outputs in energy harvesting. In addition to requiring stable output of electrical current or a boost function, power source management systems also must gauge situations when the power output is excessive, and the system must automatically charge the battery in order to avoid waste. At the same time, the energy harvesting end must automatically power batteries in situations when there is no way to output electrical power.

If the energy harvesting end operation time far exceeds the battery end, the life span of not only the battery but the entire system can be extended.

Tony Armstrong further elaborated, saying that if the entire power supply output can be made more stable, the system will be equipped with an ultracapacitors balancer and is a more ideal method of design.

Solar Micro Inverter Technology is Still Progressing

Looking at solar micro inverter technology market development, there have not been many actual changes or breakthroughs.

Even if micro inverters perform well both in terms of convenient installation and energy efficiency, they are only used in the domain of residential homes. If their applications for large-scale power plants are examined, they still are predominantly central inverters. From the viewpoint of unit cost, micro inverters are still more expensive than the central models.

Figure 3 :   Circuit design for micro inverters actually are already considerably fixed. The only more obvious progress is advances in the switching of frequencies.(
Figure 3 : Circuit design for micro inverters actually are already considerably fixed. The only more obvious progress is advances in the switching of frequencies.(

However, even though micro inverters are not a mainstream market, in the technological aspect during the past two years there has been a certain degree of progress.

International Rectifier (IR) Asia Pacific Vice President of Sales, Bo Da-wei has pointed out that if a solar micro inverter system is installed on or behind solar panels, it will be exposed to the environment. Therefore, for each environmental condition, such as high temperature, high humidity, and dust, there must be an extremely high capacity for resilience.

Consequently, they should provide the highest quality components to these systems and have a high degree of reliability and undergo industrial-grade certification to guarantee that they will not fail over long periods of time.

Heat management is another issue that the market is paying attention to. Micro inverter manufacturers can make use of industrial grade advanced thermal packaging technology, which can transfer as much heat as possible out of the micro inverters.

Infineon Solution Day and Diversified Electronics Division Manager Wu Rong-hui stated that the problem with micro inverters is that they have short life spans. There is a bottleneck in the electrolytic capacitors’ excessively short life spans, and replacing them is less convenient than to just replace the entire micro inverter.

However, with the constant development of technology, the systems integration industry has begun to use film capacitors as replacements for electrolytic capacitors. The former’s biggest advantage is perhaps being able to take a step forward in dealing with the problem of electrolyte boiling in electrolytic capacitors.

Another problem is that the switching frequencies used by film capacitors must be increased. Using the old IGBT, it is impossible to meet the frequency requirements, but if silicon carbide (SiC) is used, improvements can be made.

Will SiC Replace IGBT?

However, will IGBT be replaced by SiC? Bo Da-wei evidently has a different viewpoint. He spoke more about high frequency applications, and noted that there are 1200V and 600V IGBT product lines for each IR. As a result, the IGBT chips for IRs can still be supplied in wafer form and be used by engineers to design power modules.

When engineers choose IGBTs they must evaluate a number of parameters, and they cannot be simplified into a single standard. He also stated that IGBT-related system design can be accomplished with the assistance of effective development tools. Effectively selected tools for IGBT will evaluate the application conditions, including bus voltage, switching frequency, and short circuit protection needs.

They should also evaluate wear and tear and supply recommendations for components under different given conditions. These tools still should also provide pricing information for each component to allow designers to consider the cost impact on selecting components for their systems.

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