Conclusions from CAPACON Use Case High efficiency power converters

Conclusions from CAPACON Use Case – High efficiency power converters

Power electronics is one of the main technologies to realize energy conversion with high efficiency. It is known that about 70% of electric energy is converted by power electronics devices before it reaches the consumer.

Solar micro-inverter SMI260

Nowadays, power electronics has become a fundamental technology critical for the development of energy conservation, especially for renewable energy. Especially in the area of renewable energy applications, power electronics converters play a more important role, which enables DC micro-grids to realize highly efficient usage of renewable energy and stable interfaces between energy storage systems and renewable energy resources, as well electrification of distant villages and rural areas. High-voltage direct current (HVDC) systems can also be enabled to replace some long-range transmission AC transmission systems and aircraft power supplies with special requirements can be realized by specific power converters.

The case study shows how modern approaches in design of power converters were applied to improve energy efficiency of a micro-inverter for photovoltaic modules. Case study has been done for the Solar Micro Inverter SMI260 by Letrika Sol.

ABOUT USE CASE DISCUSSION & OUTLOOK STATUS AFTER THE PROJECT FULL REPORT

ABOUT THE USE CASE:

The Case study has been done for the Solar Micro Inverter SMI260 by Letrika Sol.

According to the development of renewal resources technologies, the photovoltaics already is and will be one of the crucial players on the market. Most of the photovoltaic systems are connected to the utility grid, which operates with voltage and current of sinusoidal shape. Due to that, the inveter (DC-AC converter) is one of the most important component in that conversion mission.

The cost reduction of photovoltaic panels is one of the main reasons that there are more and more inverters on the market with different technical solutions which leads to higher conversion efficiency, better MPPT (maximum power point tracking) efficiency of the photovoltaic modules and higher reliability wihout influence to the final costs.

In general, the photovoltaic cells, united into the singular module, string of modules or array of modules generate a DC power.

The generated power depends on solar radiation (strength and angle of sun rays), temperature and terminal voltage. This DC power is converted into the AC power through inverter’s stage and can be transfered to the utility grid with the sinusoidal AC voltage of 230 V and frequency of 50 Hz (in the USA there is a voltage of 120 V and frequency of 60 Hz).

Additional to the inverter’s stage, there are input filter, output filter and isolation transformer. The latest one is an option according to the local regulations, power range and structure of the converter itself.

In case of a single or few photovoltaic modules in series, an additional DC-DC convertion stage is required in order to increase the voltage, decouple DC input and AC output and also to provide galvanic isolation. It also allows the implementation of the algorithm for maximum power point tracking.

DISCUSSION & OUTLOOK:

DC-AC converters for small photovoltaic systems (microinverters) are one of the very popular converters on the photovoltaic market mostly due to the better use of sun power, higher system efficiency, lower mounting costs, plug-n-play operation, modularity and flexibility. However, there are many possible ways to additionaly increase the performance of the microinverter, reduce the components number and production costs and increse the expected lifetime of the whole system.

Microinverter is normally mounted on the back of each photovoltaic module and is therefore well integrated into a single unit. Due to that reason, the same lifetime is expected for both, photovoltaic module and microinverter (25 years). In terms of power conversion efficiency there are of course possible improvements.

With already mentioned solutions which are more and more in common to all power converters on the market, not just microinverters, are implementation of soft switching techniques and usage of Silicone Carbide or Gallium Nitride semicounductor devices. On the other side there are a lot of research and development of different circuit topologies which leads to higher power conversion efficiency, lower costs and more compact designs with higher power density.

At the end there is always a compromise between several aspects which defines the final power converter’s structure and design: the first one and probably the most important is price of the product, the second one is the efficiency of the power conversion, the third one is the size of the converter (which is also in correlation with the price), and last but not least is the reliability. There are also other views (maybe less important but still) which influence to the final design and have to be taken into account: thermal management of the converter, manufacturing and assembly difficulties (additional costs), spare parts availability and alternatives etc.

Annual Energy Outlook 2019 with projections to 2050 provides modeled projections of domestic energy markets through 2050, and it includes cases with different assumptions regarding macroeconomic growth, world oil prices, and technological progress (U.S.). Some predictions can be used as a basis for final conclusions about high efficiency power converters :

Increasing energy efficiency across end-use sectors keeps U.S. energy consumption relatively flat, even as the U.S. economy continues to expand.
In the Reference case, the United States adds 72 gigawatts (GW) of new wind and solar photovoltaic (PV) capacity between 2018 and 2021, motivated by declining capital costs and the availability of tax credits.
Residential solar photovoltaic (PV) capacity increases by an average of 8% annually from 2018 through 2050 in the Reference case compared with the commercial sector’s 5% per year average growth.

Based on above energy consumption projections and economy growth we can conclude, that energy efficiency of the power converters will continue to increase. With increased solar photovoltaic capacity, the number of high efficient inverters will be also higher. Therefore, the development of new topologies, devices and techniques are going to be continued.

STATUS AFTER THE PROJECT:

Power electronics is one of the main technologies to realise energy conversion with high efficiency. It is known that about 70% of electric energy is converted by power electronics devices before it reaches the consumer. Nowadays, power electronics has become a fundamental technology critical for the development of energy conservation, especially for renewable energy.

With the rapid development of modern industry, power electronics is facing severe problems, namely

how to meet the requirements of the load;
how to improve the efficiency and reliability of power-semiconductor devices;
how to design converters with smaller volume, less weight and lower cost;
how to reduce the number of power switches and, thus, the design complexity of converters and how to improve the robustness of entire systems;
and how to minimise negative influences on other equipment in electric power systems and on the electromagnetic environment.

Facing these challenges, some advances have been witnessed with respect to semiconductor switches of power converters, for example, integrated gate-commutated thyristors (IGCT) were invented to have lower conduction loss compared to the traditional high-capacity switches. Accordingly, control strategies were also improved.

To design a new power electronics converter, one can, on one hand, develop a new control strategy; on the other hand, one can design a novel power converter topology, so as to achieve specific outputs, simpler control, higher efficiency, less complexity, lower weight, minimal cost and better robustness. In fact, a control strategy is specified for a certain topology, and the topology determines the control system. Therefore, it is of great significance to coin optimal power-converter topologies to fulfill the requirements of various applications.

Power electronics converters fall into four categories, i.e. AC-DC, AC-AC, DC-DC and DC-AC converters, and they have been invented for and found a wide spectrum of applications in, for instance, transportation (electric/hybrid electric vehicles, electric locomotives, electric trucks), utilities (line transformers, generating systems, grid interfaces for alternative energy resources like solar panels, wind turbines and fuel cells, energy storage), industry/commerce (motor drive systems, electric machinery and tools, process control, factory automation), consumer products (air conditioners/heat pumps, appliances, computers, lighting, telecommunication equipment, un-interruptible power supplies, battery chargers) or medicine.

Especially in the area of renewable energy applications, power electronics converters play a more important role, which enable DC micro-grids to realise high efficient usage of renewable energy, and stable interfaces between energy storage systems and renewable energy resources, as well electrification of distant villages and rural areas; high-voltage direct current (HVDC) systems can be also enabled to replace some long-range transmission AC transmission systems; aircraft power supplies with special requirements can be realised by specific power converters; to list just a few.

In the present project study, we tried to describe all the aspects of power converters. A list of high efficiency converters is provided within electronic devices and systems that can be found in the SI-AT Programme region. In the case study analysis, a detailed technical overview of the microinverter of Letrikasol was provided. The converter has been fully designed and manufactured in the SI-AT region and contains many modern technology approaches, which ensures high efficiency at a low price of the product. An example of the analysis also confirms the use of technology in the latest state of the art technology in the field of power electronics in the CAPACON project region.

The full report is available here: