Impedance of Inverter Front-ends at the Frequency of Ripple-control Signals

Ripple control is the technique of controlling loads and other devices in the distribution grid by sending lowfrequency signals along the phase conductors or the neutral conductor. The magnitude of the signal is determined by the impedance of the network, loads, capacitor banks, filters and generators. An increase of the amount of electrical equipment connected to the grid, e.g. due to an increasing use of distributed generation, changes the impedance of the power system. This can cause excessive amplification or attenuation of the control signals, resulting in the malfunction of receivers and other equipment. In this paper, the impedance of three-phase inverter front-ends at the frequency of the control signals is discussed. The following elements are taken into account: The AC filter, the switching of the inverter and the DC circuit. Equivalent impedances are calculated, which can be used in analytical calculations.