Many components within inverters today suffer failure as a consequence of heat. This is especially an issue in many developing regions of the world where climate controlled buildings are rare and ambient temperatures are high. Although increasing the allowable inverter input voltage would assist in decreasing the heat generation due to high current flow, there are additional measures such as strategic component selection can be taken to minimize failure rates. The components that are most susceptible to heat related failure are typically either the capacitors or the switching components within the inverter.
Heat is generated in switching components as a result of the internal resistance of these components to current flow through them. In order to minimize the failure of these components due to heat, there are two steps that can be taken. First of all, the use of materials that have a low internal resistance and higher temperature tolerance will result in a system that generate less heat and is better capable of dealing with hot environments. By contrast to the low thermal conductivity and relatively low breakdown voltage of conventional silicon based semiconductors, advances in new silicon carbide based semiconductors offer high thermal conductivity, very high breakdown temperatures and voltages, as well as low on-state resistance.
Although silicon based switching components are extremely inexpensive and operate satisfactorily in many inverters, the use of silicon carbide based switching components would lead to a much more robust and long lasting system than that made with the lower performance silicon devices. Additionally the cost of silicon carbide, when compared to other high performing semiconductor materials such as gallium nitride is relatively low. Secondly, using a soft switching scheme at lower frequencies decreases wear on these components thereby increasing their mean time to first failure (MTFF). Since soft switching is the process of resonantly switching the semiconductor when zero current is passing through the semiconductor (occurs as reactive components become charged), there is minimal wear on the semiconducting material and minimal heat generated.
Even more frequent than failures caused by switching components are failures caused by capacitors. According to Russell, the extreme thermal sensitivity of electrolytic capacitors and the tendency of capacitor to lose electrolyte are the two main causes of capacitor failure. In developing parts of the world, ambient temperatures are commonly 30-40 degrees Celsius with extremes exceeding this range. When typical maximum temperatures for electrolytic capacitors are 85-100 degrees Celsius and typical operation temperatures are roughly 25-35 degrees greater than the ambient, there leaves little question as to the cause of their failure. Advances in ceramic type capacitors are providing an attractive and robust alternative to the popular electrolytic capacitor as they can withstand temperatures in the range of 200 degrees Celsius, have a much lower lifetime loss of capacitance than their electrolytic counterpart and are very affordably priced.
Although failure mitigation is ideal, there will always be a certain percentage of components that experience failure. When a component fails on an off-grid inverter, whether a capacitor, switching component or other component, replacement parts and skilled labor to repair the device are often not readily available.
Many renewable energy technologies and components are starting to be distributed locally in “remote and low-income areas”; however there are still many regions where maintenance and replacement parts are inconveniently far away. By moving towards the development of modular component boards in the next generation alternative energy inverter, overall reliability and simplicity of repair can be achieved through color coded plug and play componentry or similar and distributed locally in these remote regions without the requirement of extensive technical training.
In addition to increased reliability and ease of repair, the move towards modular component within an inverter system allows the manufacturer to utilize the same components within multiple product lines (for example both grid tied and off-grid models) which would lead to a decrease in unit cost though increased production volumes.
- Blaabjerg, F. Iov, R. Teodorescu and C. Zhe, “Power Electronics in Renewable Energy Systems,” in PowerElectronics and Mothion Control Conference, Portoroz, 2006.
- Russel, “The Promise of Reliable Inverters for PV Systems: The Microinverter Solution,” Greenray Solar, 18 June 2010.
- Dufo-López, G. Zubi and G. V. Fracastoro, “Tecno-economic assessment of an off-grid PV-powered community kitchen for developing regions,” Applied Energy, vol. 91, pp. 255-262, 2012.
V. A. Sankaran, F. Rees and C. Avant, “Electrolytic Capacitor Life Testing and Prediction,” in BrowseConference Publications > Industry Applications Confere … Help Electrolytic capacitor life testing and prediction This paper appears in: Industry Applications Conference, Dearborn, 1997.