A conditioning device is described for power supply networks (2) having a network voltage measurement unit (3) which can be connected to a three-phase power supply network (2), having a computation unit (1) which is connected to the network voltage measurement unit (3) and is used to determine conditioning current values (K) and having an inverter unit (4) which is connected to the power supply network (2) and is used to feed in conditioning currents (IK) as a function of the determined conditioning current values (K). The computation unit (1) is designed for modeled simulation of a synchronous machine in order to determine at least one component of the conditioning current values (K) as stator currents of the simulated synchronous machine as a function of freely variable synchronous machine parameters, using the network voltages (UN), measured in three phases, of the power supply network (2) as input variables. In addition, compensation currents are fed into the network (2) via the inverter (4), and are determined by the algorithms for harmonic current compensation (7) and unbalance compensation (8).