This applies mainly for the grid side filter. If possible, a filterless VFD design is preferred. Of course, there are high performance applications that require speed and/or position encoder. In sensorless variant the speed is calculated in VFD software based on electrical signals that are already available. unbalance), environmental factors (dust, vibration) etc. Performance of an encoder is affected by multiple factors such as physical distance between inverter and motor, type of signal, interfences with other equipment (EMC topic), installation aspects (e.g. Sensorless speed controlĮlimination of a speed encoder can also be seen as a step towards KISS. It reduces the parts count, simplifies the maintenance job throughout the lifetime of equipment and boosts the availability. A fuseless design will be more in line with KISS principles. In the example of a 5 MW, 4.16 kV multi-cell inverter a total amount of 36 fuses is needed (some manufacturers reduce the quantity to 24 pcs using two fuses per cell). And again, there is the topic of quantity. Fuses also naturally age making the maintenance somewhat cumbersome. The fuse needs to have very quick response to provide required protection of semiconductor devices. Use of fuses in medium voltage VFDs is tricky. Thus increasing the probability of leakages. Inverter with high quantity of semiconductors also requires large quantity of plastic pipes distributing the water to the individual heat sinks. Similar situation is for example with cooling pipes in case of a liquid cooled VFD. 5 MW, 4.16 kV neutral point clamped (NPC) inverter:Īnd it does not involve power semiconductors only.Instead of using large quantity of components and engineering complex redundancy concepts the same or even better reliability figures can be achieved with low parts count and no semiconductor redundancy. VFD topology utilizing medium voltage semiconductors with high power density and low parts count is one example. KISS aims to eliminate the root cause of the problem rather than solving the consequences. How to apply the principle in medium voltage drives? There are several areas such as hardware design, protection concept or software architecture.
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