System for controlling the voltage maintenance and/or the frequency maintenance in an energy supply system, comprising a transmission network of a first voltage level and, coupled thereto via a substation device, at least one distribution network of a second voltage level, which is lower than the first voltage level, wherein the distribution network is connected to a number of controllable network participants (5, 6, 7), characterized by - first measuring means (13, 14) for detecting the frequency (f measured) or active power and/or for detecting the voltage (U measured) or reactive power at a node of the transmission network, - second measuring means for detecting values of electrical network state variables (P VN, Q VN, U VN, f VN) at at least one node of the distribution network, and - third measuring means for detecting values of electrical participant state variables (P load, P storeVN, Q storeVN, P DEA, Q DEA, U DEA, f DEA, availability) of the network participants (5, 6, 7), - an evaluation entity for network state evaluation, which is connected to the second and third measuring means (20, 24) at least indirectly via first communication means and which is configured to determine from the detected values of the network and participant state variables the availability of each network participant (5, 6, 7) for an additional power consumption and/or power output and to provide it as a state matrix, and - a control unit comprising at least one difference-forming element for forming a difference (Δf, ΔU) from a predefinable setpoint Variable (f setpoint, U setpoint) and the detected frequency (f measured) or active power and/or voltage (f measured) or reactive power, furthermore comprising at least one control module (16, 17), to which the difference (Δf, ΔU) formed and the state matrix can be forwarded, wherein the control module (16, 17) is configured to identify from the difference (Δf, ΔU) and the state matrix those network participants (5, 6, 7) which can implement a measure for compensation of the difference (Δf, ΔU), and to define for at least one of said network participants (5, 6, 7) a power stipulation, in particular a power change stipulation, in such a way that the difference (Δf, ΔU) can be compensated for to become zero, wherein the control unit is connected to the network participants (5, 6, 7) at least indirectly via a second communication means for the transmission of the power stipulation, in particular the power change stipulation. - first measuring means (13, 14) for detecting the frequency (f measured) or active power and/or for detecting the voltage (U measured) or reactive power at a node of the transmission network, - second measuring means for detecting values of electrical network state variables (P VN, Q VN, U VN, f VN) at at least one node of the distribution network, and - third measuring means for detecting values of electrical participant state variables (P load, P storeVN, Q storeVN, P DEA, Q DEA, U DEA, f DEA, availability) of the network participants (5, 6, 7), - an evaluation entity for network state evaluation, which is connected to the second and third measuring means (20, 24) at least indirectly via first communication means and which is configured to determine from the detected values of the network and participant state variables the availability of each network participant (5, 6, 7) for an additional power consumption and/or power output and to provide it as a state matrix, and - a control unit comprising at least one difference-forming element for forming a difference (Δf, ΔU) from a predefinable setpoint Variable (f setpoint, U setpoint) and the detected frequency (f measured) or active power and/or voltage (f measured) or reactive power, furthermore comprising at least one control module (16, 17), to which the difference (Δf, ΔU) formed and the state matrix can be forwarded, wherein the control module (16, 17) is configured to identify from the difference (Δf, ΔU) and the state matrix those network participants (5, 6, 7) which can implement a measure for compensation of the difference (Δf, ΔU), and to define for at least one of said network participants (5, 6, 7) a power stipulation, in particular a power change stipulation, in such a way that the difference (Δf, ΔU) can be compensated for to become zero, wherein the control unit is connected to the network participants (5, 6, 7) at least indirectly via a second communication means for the transmission of the power stipulation, in particular the power change stipulation.