Common Mode of Inverters: Survey and Study of Filter Placement on Grid and Load Side

Abstract:
Inverters driving motors fed by the grid require PFC stages with a suitable filter. Designing the filter requires knowledge of the noise level. As cm-noise prediction of inverters is quite difficult, this paper studies an inverter’s cm-noise by experiments. It is shown that high levels can be expected from inverters, when no filter is applied. Thus, this paper analyzes the cm-noise paths and derives a filter placed between grid and inverter. An alternative position of the filter is between inverter and motor. This configuration requires a smaller common mode choke to comply with EMI standards.