A method of controlling a plurality of power units in a power distribution network (PDN), comprising: a) receiving one or more requests to increase or decrease the power drawn from, or the power supplied to, the PDN; b) determining, based on aggregated power and/or energy data regarding the plurality of power units, and the one or more requests, one or more parameters defining properties of power units to be controlled in response to the one or more requests; c) receiving status updates from the plurality of power units; d) for each status update, determining whether the properties of the power unit fulfils the determined parameters; and e) if the properties of the power unit fulfils the determined parameters, controlling the power unit to change the amount of power drawn from or supplied to the PDN.