Converting a Solar Installation into a Microgrid Using a Residential Synchronous Condenser
Grid-scale synchronous condensers have long been used to stabilize grids. They may soon support disaster or power-outage operations, where they can be used to minimally retrofit a conventional solar array, which turns off during an outage, into a high-surge-capacity microgrid. A synchronous condenser is a motor/generator attached to a flywheel. When the flywheel motion is synchronous with a stable AC waveform, the motor/generator only draws power required to overcome frictional losses. Through the motor/generator, the flywheel’s rotational inertia resists changes in the AC waveform, sourcing or sinking power up to the surge rating of the motor. The condenser can be also be operated to source or sink reactive power.
A household synchronous condenser suitable for emergency or power-outage operations is presented and analyzed. After disconnecting from the grid, a microgrid is created by energizing the synchronous condenser and maintained by power from a conventional photovoltaic grid-tie inverter. The synchronous condenser uses modest battery storage to ‘charge’ the flywheel. When the flywheel stabilizes to the target rotation rate, it is connected to a grid-tied inverter, which detects a healthy ‘grid’ and begins feeding power into it.
The synchronous condenser controller must ensure power production from the inverter balances consumption, but the flywheel inertia provides seconds or more of reaction time to maintain a stable, high-quality AC waveform. The synchronous condenser surge capacity costs much less than comparable battery storage and can avoid exotic or energetic materials for scalability and safe deployment to disaster areas or residences.