Preventing module degradation Depending on the module type used for an installation, irreversible performance degradation effects have been observed especially on amorphous silicon panels (a-Si) caused by a negative potential relative to the ground. While this so-called TCO (Transparent Conductive Oxide) corrosion effect has been extensively analyzed and shall be prevented by negative grounding, a more recent study shows that wafer-based crystalline silicon technology is also not completely immune to Potential Induced Degradation effects (PID) [1]. In addition, other module technologies display reversible phenomena induced by surface polarization effects, which require a positive-grounded array in order to prevent the performance degradation effect. To allow either positive or negative grounding systems usually require an inverter with galvanic isolation, adding costs and weight to the equipment. Central inverters using the new circuit topology offer a solution for this problem by adding a dedicated control scheme at the grounded terminal without affecting the costs or the system safety. Thus positive or negative grounded systems reach the same performance as traditional ungrounded crystallinebased PV power plants. Furthermore, PV generators can be designed according to the desired schemes with independent PV arrays connected to each inverter to form separate MPPTs. This eliminates the need to combine the arrays of all inverters connected to the same transformer winding in parallel to form a single MPPT.
Modular liquid cooling Even the most efficient and high performance inverter design may fail completely if it does not meet the construction characteristics expected in this professional market segment. An environmental-proof construction using an IP65 enclosure which allows mounting in a free-field installation without additional infrastructures is just one of those requirements. An elaborate cooling concept is even more important. To respond to these requirements, Power-One decided on using a passive liquid cooling construction. Offering much higher heat-extraction capabilities with respect to forced air-cooled heat sinks, the liquidcooled cold plates are ideally suited for large
inverter systems. An additional secondary air/ inverter technology manufacturers in the water exchanger is used to cool the rest of the future. This new inverter concept for utilitymagnetic and electromechanical components grade applications shows that many inverter that cannot be effectively attached to the cold systems still offer a huge savings potential. plate. This method allow to segregate the Besides optimizing the system-level BOS, active parts of the unit in a watertight and lifecycle costs can be significantly reduced pollution-free chamber, further improving the at the same time, for example by simplifying system long-term Images and captions:} immunity against {B aggressive agents in the harshest environments. This also extends the maintenance cycle and reduces the costs of maintenance. To ensure the optim um trade-off between weight, dimensions ((Efficiency vs. input voltage) and the lowest specific costs at maximum efficiencies, the installation, operation and maintenance 350kW single cold-plate IGBT power procedures. modules were selected. The overall weight of the whole power converter assembly has been limited to a maximum of 50kg to ensure {A1} Additional easy maintenance and installation by two operators. To reduce the deployment and installation costs eve n f u r t h e r the inverter system has been assembled in a compact lightweight single cabinet. Thanks to its modular structure which (ULTRA with retractable solar tent) is made of front accessible and extractible subassemblies, installation and Information maintenance procedures are rather easy. [1] J. Berghold, O. Frank, H. Hoehne, S. The inverter system can also be monitored Pingel, B. Richardson, M. Minkler: via Ethernet communication and two Potential Induced Degradation of Solar independent RS-485 communication Cells and Panels ; September 2010. interfaces for inverter and intelligent string The efficiency increases towards the combiner monitoring. upper end of the input operating voltage range.
Outlook
To develop savings opportunities well beyond the mere component-level cost reduction is and will remain the mission for
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Copyright: Power-One Power-One’s liquid-cooled cold plates are ideally suited for large inverter systems.
EQ INTERNATIONAL - April 2013
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