Validation of the Quasi-Two-Level Operation for a Flying Capacitor Converter in Medium-Voltage Applications

Standard medium-voltage converters are operated at low switching frequencies using bulky passive components. One concept to change this involves the quasi-two-level operation (Q2O) of multilevel converters that use fast-switching semiconductors to minimize the need for passive components. The flying capacitor converter (FCC) uses SiC semiconductors and operates with Q2O to minimize passive components. In this paper, two different quasi-two-level algorithms are analyzed. A medium-voltage prototype was built and low-voltage and medium-voltage measurements were used to validate the concept. A particular focus is on the overvoltage, the dv/dt behavior of the converter, as well as the dynamic behavior

A 60 kW Power Hardware-in-the-Loop Test Bench for grid emulation based on a Series Hybrid Cascaded H-Bridge Converter

In this paper the requirements for a Power Hardware-In-the-Loop (PHIL) system for the emulation of grids and grid faults are discussed. Solutions for all parts of the PHIL system – the power electronics, the signal processing system and the software structure – are presented. Subsequently, an analysis of the accuracy, bandwidth and stability of the PHIL testbench is done and the effects of different interface algorithms are shown. Concluding, measurement results of emulated highly dynamic grid faults such as voltage dips and spikes, distorted grids and weak grid situations are shown, which prove the performance of the PHIL system

Portable Generator to Detect Cracks on Large Steel Structures: An Application of Inductive Thermography

The demand of non-destructive methods to detect cracks caused by fatigue or brittle behavior in large steel structures has increased in the last years. Thermography based on electromagnetic induction is a promising method to detect cracks in weld seams and notches. This paper presents a portable experimental setup, which allows to perform in situ crack detection tests on large steel structures. The success of this configuration is based on the use of a highly efficient switched H-Bridge circuit, which can generate a square-wave output voltage with a fundamental frequency up to 100 kHz. Due to the low losses and the low necessary DC-link voltage, the circuit can be supplied by a lithium-ion battery, which allows a small and light setup. The generated square-wave output voltage supplies an air coil resulting in a high frequent triangle current. The induced electromagnetic field caused by the current signal generates eddy currents in the steel structure. Due to an increased current density of the eddy currents in the crack area, there is a measurable temperature increase near the crack. The resulting temperature field is visualized and recorded with an infrared (IR) camera, which shows in real time the occurrence of cracks

A standardized and modular power electronics platform for academic research on advanced grid-connected converter control and microgrids

This paper introduces a multifunctional converter platform rated at 30kW. Individual units allow research on advanced grid-connected converter control, while their interconnection enables isolated microgrid investigations. The standardized and modular design allows simple reconfiguration of the system for different setups, for which multiple measurements are presented

Power Hardware-in-the-Loop Test Bench for Permanent Magnet Synchronous Machines based on a Parallel Hybrid Converter

This paper presents a Power Hardware-in-the-Loop (PHIL) emulation test bench for emulating highly utilized perma-nent magnet synchronous machines (PMSM). The output stage of the PHIL is a Cascaded H-bridge based Parallel Hybrid Converter (PHC) with a 17-level output voltage and an effective switching frequency of 1 MHz. The nonlinear machine is emu-lated with a sampling frequency of 5 MHz and is implemented on a field programmable gate array (FPGA) using Matlab/Simulink\u27s HDL Coder. For this purpose, the time-discretized model equations of a PMSM and the PHIL test bench are derived and their mapping into an HDL code-generable and fully fixed-point transformed model in Simulink is described. To enable the high model sampling rate of 5 MHz, it is optimized for a low clock cycle count and the nonlinear relations between the machine currents and flux linkages are stored in lookup tables (LUT). The measurements are carried out in steady-state operation as well as for highly dynamic current and rotor speed steps. They demonstrate the excellent performance of the presented PHIL test bench, which even perfectly reproduces the current ripple of the modeled PMSM

Cascaded H-Bridge based Parallel Hybrid Converter – A new Voltage Source for Power-Hardware-in-the-Loop Emulation Systems

This paper presents a new 50 kVA Parallel Hybrid Converter (PHC) for Power-Hardware-in-the-Loop (PHIL) emulation systems. The converter combines the high output voltage quality of a low power 17-level Cascaded H-Bridge (CHB) converter in star configuration with the high efficiency and high power density of a 2-level converter. The requirements a converter topology must fulfill in order to be used for PHIL emulation systems are derived and it is shown, that the PHC topology characteristics ideally meet these requirements