Minimization of a VSD Multilevel Inverter Output Filter through a Systemic Modeling Approach

Abstract:
High power inverters applied in the oil and gas offshore industry are typically installed in floating platforms, while the driven electric motors are often installed in the seabed. A long power cable in the range of several kilometers is employed and might lead to wave reflection resulting in resonances and overvoltage effects. Thus, an output sine filter is typically used, which is bulky and leads to additional losses in the variable speed drive (VSD) setup. The inverters are typically rated for high power at medium voltage, which strongly limit the achievable switching frequency and, thus, optimal synchronous modulation is often used. The design of the modulation pattern is typically done in a first step and the design of the output sine filter follows, but this procedure does not consider the full setup. Therefore, this work proposes that the design of the filter and the modulation pattern are done in an iterative manner so to minimize the filter volume. This is done through a careful modeling of the complete system and an optimization procedure that includes the model and the possibility to vary modulation and filter components. The results are promising in the sense of reducing filter volume without compromising the overall system performance.