Power electronics in SmartGrids - impact on power system reliability

Abstract

The leading themes in the distribution network development are the cost effectiveness and system reliability. Also the requirements for reducing pollution and increasing the service quality are issues, which have led to the introduction of SmartGrids network concepts. These network solutions are mostly dependent on power electronics, applied to connection of loads, generation and storages to the independently operable low-voltage (LV) grids. One of such solutions is the low voltage DC (LVDC) distribution system, which is an interesting challenger to the AC low voltage network solutions. An often-asked question is how the shorter lifetimes of power electronics compared to the traditional network components affect on the reliability of the electricity distribution and also to its total costs. In the this paper the question about the reliability development is approached from two main points of view: The component level focusing on the reliability of power electronics based network components, and the system level concentrating on the power quality experienced by the customers and the effects of converters on the entire distribution system reliability. The question of the reliability impact of large-scale utilization of power electronics in electricity distribution is relevant, when considering the direction of the technical development in electricity distribution. This paper is especially aimed at discussing the modelling of the reliability impacts in the case of the LVDC-system.

Mitigation of Power Quality Problems in Grid-Interactive Distributed Generation System

“…However, the above approach did not consider the unbalance in grid voltages since in practice grid 4 voltages may vary upto 5%. In [12][13], authors considered that each DG is connected to two converters, one in series and other in parallel.…”

“…Usually, DGs are connected near the local load and are connected to the grid through a short/medium transmission line for the low/medium voltage network. To deliver high quality and reliable power, DGs should appear as a controllable unit that responds to changes in the system [4]. DG should preferably tie to the utility grid so that any surplus energy generated within them can be channelled to the grid.…”

Operation and control of a hybrid microgrid containing unbalanced and nonlinear loads

“…. (6) where P Lav and Q Lav are respectively the average active and reactive power demand of nonlinear load and λ P (0 < λ P < 1) and λ Q (0 < λ Q < 1) are respectively fractions of the active and reactive power supplied by compensating DG to the nonlinear load. We can substitute (6) …”

“…To deliver high quality and reliable power, the microgrid should appear as a single controllable unit that responds to changes in the system [6]. The high penetration of DGs, along with different types of loads, always raises concern about coordinated control and power quality issues.…”

Voltage balancing in low voltage distribution networks using Scott transformers

“…Moreover, the conduction and switching losses occurring during the AC-DC-AC conversion would reduce the power delivery efficiency. In addition, the critical components in a converter have a shorter lifetime than traditional network components such as transformers; the switches are mostly IGBT-transistors having an average lifetime of ten years and capacitors often begin to fail after five years [5]. Moreover, the fault rate of these components varies significantly according to the operating conditions, which would further weaken the reliability of the converters.…”