Modeling of the behavior of power electronic equipment to grid ripple control signal

The paper presents time-domain simulation for power electronic device equivalent impedance computation at ripple control signal frequency.The ripple control used by the grid is a low frequency voltage signal superimposed at MV substation. In France, the frequency used by grid ripple control systems is 175 Hz. It is well known that some customer loads can disturb ripple control signal transmission such as capacitor bank, distributed generator, etc. These equipments can influence or disturb ripple control signal by two main ways: presence of a small impedance or an important interharmonic current injection at ripple control frequency. In transient state, even a symmetrical static converter can produce interharmonic currents.In site studies, some customer power electronic device (variable speed drive for example) is often modeled by an infinite impedance at ripple control frequency. However, site measurements and simulations show that this simplification can cause in some case important error in ripple control signal level assessment.The main purpose of this study is to define ripple control frequency equivalent impedances of typical converters used in industry. The study shows that a voltage source converter (rectifier with dc capacitor structure) gives a relative small impedance at ripple control frequency. It is recommended to integrate this impedance in performing ripple control signal propagation study by means of frequency-domain software.