Electronic – Will a large amount of constant-power loads make an electrical grid unstable

mainspower electronicspower-grid

Over time, a larger proportion of electronics are constant-power loads, while they used to be constant-resistance. Will this lead to an unstable grid? If not, why not?

Constant power loads at home are battery chargers, TVs, many appliances.

In a constant-resistance environment, the grid is self-regulating to a certain extent, as if power generation cannot match power consumption, then a slight drop in voltage would reduce the consumption.

In a constant power environment, this self-regulation would not exist, as a slight drop in generator voltage would just lead to an increased current draw and a constant power consumption. This sounds like it would lead to a run-away process if left unchecked.

Best Answer

Yes, potentially a lot of constant-power loads will destabilize a feedback loop that keeps the grid voltage steady. This is because constant power is symbolized by $$power = V \times I = constant$$ while resistive (like a heater) loads are symbolized by $$power = V \times I = V^2 \times constant$$

The grid must deliver extra power whenever it sees a voltage dip. The heater load makes a V versus I function that has a strong power decrease when V goes low, i.e. it helps the grid feedback control (lower power load is like higher power supply). The constant-power load, however, has a proportional current-load INCREASE when V goes low, which means it requires a larger current increase than the voltage deficiency alone would indicate. It is thus fighting the power-grid voltage regulation mechanism.

Fighting is normal, but you don't want the power-grid to lose that fight.