| | April - May 20228IN MY OPINIONELECTRICAL MODELING DURING DEVELOPMENT KEY TO MICROGRID SUCCESSBy MarkVilchuck,Energy Infrastructure Project Operations and Maureen McDonald, Director, Energy Services, Southland IndustriesThe solar industry will play an important role in the emerging microgrid market.Resilency is becoming an increasingly important requirement with the federal government and in states, such as California, where utilities are responding to the wildfire dangers with pre-emptive grid shutdowns.As electrical resiliency needs continue to escalate, potential solutions consisting of large, integrated microgrids with ever increasing islanding capabilities supplemented by renewables and storage are desired. All of these potential solutions will have one thing in common, a very high initial cost, and for those development efforts that get funded and become real-life projects, many will experience additional start-up and retrofit costs from unforeseen electrical issues.The electrical grid is often called the most complex system ever created as it involves millions of individual devices working simultaneously so that every electron generated is continuously balanced to serve every watt of demand. Although microgrids operate on scales orders of magnitude smaller, this balancing act must still be performed properly to ensure these loads are balanced through a wide range of operating and upset conditions. Performing electrical modeling during development allows you to "bench test" your microgrid's responses to these changing conditions to avoid startup delays, additional costs and unwelcome surprises. The two project scenarios below detail typical microgrid control and stability issues that were mitigated during development using electrical modeling.Scenario #1 - Microgrid with Multiple Parallel Units ­ Controlling Circulating CurrentsLarge-scale microgrids capable of extended islanding times typical involve a heterogeneous mix of distributed generation (DG) for generation diversity and to lower costs by using existing DGs. DG equipment include solar panels, battery storage, natural gas generators, wind turbines, solar panels, microturbines and fuel cells. Using a mix of DG sources as part of a microgrid almost always require the need to parallel multiple generators or other DG sources with themselves or the utility supply. Controlling circulating currents when paralleling generators in a microgrid that shares a common neutral can be challenging. When DGs are paralleled, it is critical that voltages produced by the generating equipment are as closely matched as possible. To properly match voltages, not only do the DG RMS values need to be similar but the instantaneous values, which are determined by the voltage waveshapes, should be similar as well. This voltage and waveform mismatch is often experienced with microgrids which attempt to parallel a mix of new and existing isochronous generators with different winding pitch configurations. Circulating currents will likely appear in the common neutral which ties the wye connections of the generating sources. These circulating currents can cause overheating in the generator windings and false tripping of overcurrent protection equipment, particularly ground fault detection schemes. Performing electrical stability modeling during both steady-state and transient conditions allowed the design team to Maureen McDonald
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