Effect of distributed generation on protection of medium voltage cable grids

ABSTRAC

Adaptable energy systems integration by modular, standardized and scalable system architectures

Energy conversion and distribution of heat and electricity is characterized by long planning horizons, investment periods and depreciation times, and it is thus difficult to plan and tell the technology that optimally fits for decades. Uncertainties include future energy prices, applicable subsidies, regulation, and even the evolution of market designs. To achieve higher adaptability to arbitrary transition paths, a technical concept based on integrated energy systems is envisioned and described. The problem of intermediate steps of evolution is tackled by introducing a novel paradigm in urban infrastructure design. It builds on standardization, modularization and economies of scale for underlying conversion units. Building on conceptual arguments for such a platform, it is then argued how actors like (among others) municipalities and district heating system operators can use this as a practical starting point for a manageable and smooth transition towards more environmental friendly supply technologies, and to commit to their own pace of transition (bearable investment/risk). Merits are not only supported by technical arguments but also by strategical and societal prospects like technology neutrality and availability of real options

Novel inverter topologies for single-phase stand-alone or grid-connected photovoltaic systems

Photovoltaic and battery systems often operate in small stand-alone or grid-connected applications, where the generator voltage is lower than the grid voltage. To boost the voltage up to the grid level a further element, either a DC/DC converter or 50 Hz transformer, is connected in series with a PWM inverter. To reduce the high cost of such low power systems, the costs of the power electronics should be minimized. In this paper, several new low-cost inverters with and without HF-transformers are presented. Simulation and experimental results of their operation and control for stand-alone as well for grid-connected applications are discusse

Influences of a hybrid grid on the network's voltage quality and supply reliability

The electricity is a basic need for functioning of modern society. In the deregulated electricity market, delivering quality power to the clients is a challenge for the utilities. In this paper, a hybrid grid is discussed that consists of centralized generations and localized distributed generations which may be comprised of small-scale conventional and sustainable sources. Energy storage option is also integrated in the hybrid-grid. Simulations are done on a test network, using Power-Factory software. It was found from the analysis that voltage quality and power supply availability of a hybrid-grid can be improved by proper selection of energy storage system along with protective and control devices

Decentralised allocation of generation in autonomous power networks

Due to much larger numbers of small generators it will be more complex to control the balance between supply and demand in future power systems. To deal with this complexity, autonomous power networks could be effective. Autonomous power networks are aggregations of producers and consumers on both physical and economical level and have the capability to control complex systems with simple rules. To demonstrate economic dispatch within an autonomous power network, this paper describes the setup of a model for matching supply and demand within control zones. Next, a method for distributed economic dispatch is incorporated in the model to show how allocation of generators can be executed in a decentralised way

Harmonic distortion and oscillatory voltages and the role of negative impedance

This paper focuses on two power quality effects that are noticed with power electronic appliances. One effect is a harmonic oscillation by inverters of photo voltaic systems because they bring a high parallel capacitance to the grid and negative output impedance. The other effect is a sub-harmonic oscillation due to the negative differential impedance of constant power loads. This paper discusses both effects and proposes counter measures to mitigate these effects. For harmonic oscillations due to photo voltaic inverters, an extra feature for these inverters is discussed. For the sub-harmonic oscillatory voltages due to appliances with negative differential impedances, a solution can be found in the voltage control systems of the power generators connected to the networ

A power system equivalent impedance based voltage control

Abstract--Voltage control is traditionally achieved through reactive power control, mainly because of the inductive nature of the transmission grids. However, when considering distribution networks, reactive power may not be an effective mean for voltage control. This is because of the X/R ratio which determines the controllability of voltage through active and/or reactive power. Therefore, in this paper a voltage control scheme is proposed based on the estimation of the X/R ratio of the grid. The estimated X/R will then be used to determine the active and reactive power to be injected into the grid in order to keep the voltage between permissible limits