Innovative PV inverter design reduces cost, increases efficiency
The Freiburg (Germany) based institute worked with partners to investigate how a new generation of PV inverters can look under the aspect of cost optimization. Design, cooling and connection technology have been identified as central parameters to attack this problem.
In the project named “PV-Pack”, the research was focusing on optimized cooling, connection and installation technology for efficient, fast-switching and highly integrated photovoltaic inverters of the power class 10 to 40 kW. SMA Solar Technology AG, the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research IFAM, Phoenix Contact GmbH & Co. KG and the Fraunhofer ISE have joined forces to achieve this goal. At the same time, the partners complement each other ideally in the fields of thermally highly conductive sintered materials, connection technology and power electronics. In view of the rapid development of the market needs, they have extended the target for the development of a highly integrated PV inverter to a nominal output of 70 kW.
At the beginning of the project work stood a cost analysis of the mechanical and electromechanical components, which account for up to 70% in today’s equipment. The mechanical components include the housing, the cooling components and support structures. The electromechanical components include components such as connectors, inductors, and circuit boards. “One approach to cost reduction is to optimize the technologies of the components used in the smaller performance classes in such a way that devices with higher performance can be developed from them,” says research team Sebastian Franz.
The central element of the integrated concept is the so-called “hot core”. Here, the losses occurring in the semiconductors can be dissipated over the heat sink on multiple sides. By decoupling the cooler from the housing, the developers could raise the maximum temperature level by 30% and significantly reduce the amount of material used in conjunction with sintering materials. The design concept includes different temperature zones, which differ by the type of cooling, the maximum temperatures and the IP protection classes. This allows the use of low-cost components with lower temperature requirements in the cooler zones. The use of standard technologies also saved costs for the printed circuit boards. The two-stage power-electronic converter incorporates five step-up controllers and a three-phase inverter topology. Due to the targeted use of silicon carbide (SiC) semiconductors and the associated higher clock frequencies, the researchers succeeded in significantly reducing the dimensioning of the passive elements, which increased the power density and at the same time reduced the bill of material.
The maximum measured efficiency of the developed inverter, including its own consumption, is 98.8%. The reduction of the volume was essentially achieved using smaller mechanical and electromechanical components. This resulted in a total weight of 58.5 kg with at an installation space of 110 liters. “With 1200 watts per kilogram, the power density clearly exceeds the available devices on the market,” claims Sebastian Franz.
The “PV-Pack” project, launched in 2014, lasted three years and was funded by the German Federal Ministry of Education and Research (BMBF) with around 1.9 million euros.
Further information: https://www.ise.fraunhofer.de/