Synchronverter

It is standard for electricity generation and demand to not be perfectly balanced, but the imbalance is tightly controlled such that the grid frequency remains within a small band of ±0.05 Hz.

[5] A synchronous generator’s rotating mass acts as a bank of kinetic energy for the grid to counteract changes in frequency – it can either provide or absorb power from the grid – caused by an imbalance of electric power supply and demand – in the form of kinetic energy by speeding up or slowing down.

Because it takes work to speed up or slow down rotating mass, this inertia dampens the effects of active power imbalances and therefore stabilizes the frequency.

Theoretically, inverter-based generation could be controlled to respond to frequency imbalances by altering its electric torque (active power output).

Synthetic inertia is defined as the “controlled contribution of electrical torque from a unit that is proportional to the rate of change of frequency (RoCoF) at the terminals of the unit.”[9] However, in order to have capacity to react to this RoCoF, the participating generators would be required to operate at levels below their maximum output, so that a portion of their output is reserved for this particular response.

This requirement for a reliable and fast-acting power supply makes inverter-based energy storage a better candidate for providing synthetic inertia.

The electronic part refers to measuring and control units, including sensors and digital signal processor (DSP).

The important point in modeling synchronverter is to be sure that it has similar dynamic behavior to Synchronous generator (see figure 3).

[18] Synchronverter also is suggested to be used in microgrids because DC sources can be coordinated together with the frequency of the ac voltage, without any communication network.

Figure 1. A simple diagram of synchronverter operation environment
Figure 2. Power part of a synchronverter
Figure 3. The per-phase model of an SG connected to an infinite bus
Figure 4. Typical control structures for a grid-connected power inverter.(a) When controlled as a voltage supply.(b) When controlled as a current supply.
Figure 5. Compact control structure for a grid-connected inverter.
Figure 6. Power part of three-phase synchronverter.