Mitigating Negative Sequence Current of Islanded SmallScale Synchronous Generator Using an Inverter-based Resource

The load unbalance is one of inherent features of distribution systems which draws a negative sequence current from islanded synchronous generators. This leads to overheating of the stator and, in particular, the rotor core. In such a case, it is not possible to operate the generator at its associated rated power. Thus, implementing an inverter-based resource in parallel with the synchronous generator is the main strategy proposed in this paper to tackle such a problem. To do so, the negative sequence of the reactive power is measured, and the output voltage of the inverter is regulated using a resonance controller in the αβγ reference frame such that its injected negative sequence current makes the generator voltage balance, as much as possible. Investigations performed in this paper show that based on the proposed method, the inverter can rapidly and effectively compensate the load unbalance in the distribution system. Accordingly, the generator current is also balanced, and thus, there is no need to limit the synchronous generator output power. Moreover, it is not necessary to overdesign the synchronous generator for unbalanced load conditions. As a result, the islanded mode synchronous generator can also be operated in a distribution system with unbalance loads without considerable derating.