Open Access

This paper presents a new methodology for the design process of DC ripple filters for voltage source converters. It focuses on fast-switching, wide-bandgap-material-based converters. Therefore, a wide frequency range of up to 100 MHz is taken into consideration during the whole process. Different tools like analytic calculations, time-domain modelling, and the finite element method are used for different tasks in order to generate a realistic model in terms of filter effect and reliability. The models are validated by small-signal measurements using a vector network analyser as well as realistic high-power tests. The contribution of this paper is to provide a tool for DC link filter design to estimate the filter efficiency and the current stress on the filter elements with a special focus on WBG hardware.

The paper presents design and modulation strategy for a high bandwidth PWM-based amplifier. It consists of multiple H-bridges connected in parallel and switched sequentially. As the effective switching frequency is a multiple of the switching frequency of each single switch, the bandwidth is scaled by the number of H-bridges in parallel. The prototype presented supports a maximum number of eight H-bridges in parallel.

(English) When using voltage source converters (VSC) to control the load flow between the DC voltage circuit and n-phase AC consumers/generators, distortion currents/voltages occur due to the principle involved. These describe the deviation of the real, measurable signal from its ideal, desired course. The distortion voltages occurring at the AC-side connection points of the VSC correspond to the deviation from the specified set voltage. At the DC-side connection point strong distortion currents are superimposed on the direct current emitted or absorbed by the VSC. Within the scope of this work, the emergence of the DC-side distortion currents, caused by the switching mode of operation of the VSC, based on corresponding literature sources, is discussed. The consideration here is limited to the differential mode components of the currents mentioned, a common mode consideration is not carried out. Criteria for describing the DC-side distortion currents and factors for influencing these criteria are derived from the results of the investigations carried out. For a given system and operating range, the distortion current stress caused by the VSC can be varied by adapting the control method used. For this purpose, different control methods found in the literature are selected and the operating point-dependent distortion current stress caused by them is determined analytically. To verify the results, a simulation model is developed and tests are carried out on an experimental test setup. The VSC is operated with a modulator-based control method as well as with a direct current control method. The results are compared regarding the DC-side distortion current. Namely, the control methods used are Space Vector Modulation (SVM) and Scalar Hysteresis Control (SHC). The latter was developed at the Technical University of Applied Sciences Wuerzburg-Schweinfurt. If the DC-side distortion current stress caused by the VSC is known, a filter can be designed that reduces the interference emission of the VSC to a specified level. As a level for the remaining interference emission, the remaining voltage ripple at the DC-side connection point of the filter is usually used in regulative specifications. Passive filters consisting of one or more capacitors of the same or different type are usually used for this purpose. This filter structure is described below as conventional structure. The different variants are presented accordingly and the filter capacitor is designed analytically/numerically on a concrete example for the DUT operated with SHC as well as SVM. Concepts known from literature for reducing the passive filter effort are presented and their effects on the DC-side distortion current load are described analytically. The concepts presented are divided into the categories of horizontal and vertical extension of the VSC as well as extension by downstream active components. In the second part of the work, a non-linear hybrid filter consisting of an actively controlled four-quadrant controller and two passive filter stages is designed and a methodology for the design of the components is developed. Furthermore, a modulation scheme with superimposed control for the use of the four-quadrant controller as an active filter is developed. The methodology for designing the filter is applied to the DUT used in this work as an example. The verification of the calculated results is carried out using a simulation model and an experimental test setup. Finally, the presented and more detailed passive filter variants as well as the developed non-linear hybrid filter are compared with each other in terms of construction volume and interference immunity. This shows that the presented non-linear hybrid filter has a significantly better interference immunity and a lower tendency to oscillate compared to passive filters. As a result, a more stable filter effect can be expected, especially when used in dynamic systems or systems with unknown dynamic behaviour.