An embodiment of the present invention comprises a multi-level PWM inverter that is constructed by cascading multi-level H-bridge inverters and providing different voltage inputs to the multi-level H-bridges. The present invention also provides methods for the determination of the relative affinity of a ligand for the biomolecular target it interacts with. Al3\u2003\u2003Formula 2Here, R6 is defined in the specification. A plurality of such movable filter units are movable while suspended from a supporting-rail system, it being possible for all of these filter units, which are each intended for separating off a particular type of powder in particular one powder paint color, to be selectively brought under the extraction opening of the booth.