Considerations on Voltage Ripple Assessment in dc Power Network

Abstract

The main components used for integration in the power system of distributed renewable energy sources, basically work in dc, f.i. batteries, photovoltaic systems and fuel cells. In addition, most common loads already use dc power internally, usually provided by rectifiers. Consequently, the usage of generated energy can be made more effective if directly delivered to load through a dc grid or microgrids, with improvements in efficiency, costs and reliability. The HVDCs are already widely used for their convenience over long-distance bulk power transmission. Despite this wide usage of the dc power network, the Power Quality definition and assessment in dc is still in an unstandardised situation. This paper focuses on a specific PQ phenomenon typical of dc networks: voltage ripple. Observations are made on the sources of this phenomenon and a methodology is proposed for measuring the intensity of this disturbance by introducing synthetic indices, also with reference to the most recent technical standards, with the specific scope to the compatibility level assessment. The proposed measurement techniques are applied to experimental data acquired on the power supply of a dc railway system.

Power Quality Measurements in a Low-Voltage DC Microgrid in an Open Parking Garage

“…The ripple content defined this way is a measure of the total contribution of the spectral content of the signal 𝑥 in each 1-second time window beyond the DC component, i.e., including noise and electromagnetic interference; in fact, it is equivalent to the standard deviation of a random variable x. Different definitions of ripple and time windows have been considered [13] and applied to real measurement data [18] before; for the purpose of this paper, we only consider the RMS-based definition of ripple in (3) and fix the time window to 1 second.…”

“…Initial measurement results are available for DC railway systems [11], but results from other types of DC grids are necessary as well. Pending the measurement results in other DC grids, considerations on the detection of dips, swells, and interruptions [12] and voltage ripple [13] for DC electricity grids were presented already, based on the preliminary analysis of measurements in DC railway systems.…”

Power Quality Measurement Results for a Configurable Urban Low-Voltage DC Microgrid

“…Further details on determining this parameter for different voltage and current signals, as well as alternative approaches, were considered in Ref. [38].…”