Development of a Modular High-Power Test Circuit for Components of Future Direct Current Grids

Abstract

The implementation of high voltage direct current (HVDC) technology poses complex operational requirements for the equipment and components of future energy transmission systems. Technically proven equipment of the alternating current technology (AC) cannot be used for DC applications. This results in an increased necessity for research and development to ensure the functionality of DC systems in nominal operation as well as in the event of faults. In this context, however, the use of conventional synthetic test circuits is only suitable to a limited extent for the reproduction of prospective fault currents in DC systems. Therefore, the Institute for High Voltage Technology at RWTH Aachen University develops and implements a novel high-power test circuit for investigations on DC equipment. Due to different requirements and stresses on the equipment during nominal operation and after a short-circuit fault has occurred, the test circuit consists of two parts in order to guarantee an in-depth investigation. A continuous high-current source (5 kADC, 120 kW) is used to investigate the thermal load capacity of electrical devices under nominal conditions or in overload situations. Investigations of the behavior of equipment during a short-circuit fault are ensured by an innovative high-power source. This source is conceptualized as a modular power electronic buck converter consisting of individual test circuit cells. For each cell, a pre-charged capacitor is discharged by power electronic switching elements (insulated-gate bipolar transistor, IGBT). By using pulse-width modulation for the control of the IGBTs, it is possible to generate high DC fault currents derived from grid simulations or field measurements. Furthermore, it is possible to reproduce arbitrary monopolar current waveforms (e.g. sinusoidal or triangular waveforms). This allows for realistic investigations on DC components. Due to the modular design and flexible control of the high-power test circuit, DC fault currents with an amplitude of up to 30 kA and a maximum energy of 1.92 MJ can be generated with a test voltage of up to 8 kV. This paper derives the requirements for the novel high-power test circuit based on an analysis of exemplary prospective DC fault currents in realistic fault scenarios. Furthermore, it provides an overview of the corresponding development approach as well as the usability of the test circuit for research on equipment of future DC grids.