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

Classification of reserve capacity in future power systems

In electrical power systems must always be a balance between supply and demand. Any imbalance will result in a frequency deviation. To reduce the imbalance to zero, ancillary services for balancing are in use. Ancillary services are characterised by their deployment time and their capacity. By using Discrete Fourier Transform, the kind of ancillary services as well as the requirements for balance management can be characterised in the frequency domain. Agents, that are responsible for maintaining balance in a network, can use the characterisation in the frequency domain to define their needs for reserve capacity. This paper describes a method for spectral analysis of the required reserve capacity. Based on examples and a model, changes in a future power system are discussed using the frequency domain

Harmonic effects caused by large scale PV installations in LV networks

In the next decade the amount of decentralized generators will significantly increase in the distribution networks. Among the sustainable energy sources, the research on photovoltaic generators has received much attention, especially the study of residential photovoltaic (PV) systems, which has potential of becoming a significant market. Measurements in a bungalow park in the Netherland with a high penetration of PV have shown a lot of harmonic distortions at the point of coupling. There harmonics are concerning resonances and the interaction of current harmonics generated by the inverters and the voltage harmonics coming from the grid. This paper, will study the influence of the current harmonics generated by photovoltaic systems connected to the low voltage network and the interaction with other non-linear loads and the network voltage. Basis for this simulation is a neighborhood in the Netherlands with around 96 houses. Simulations will show the effect of these harmonic currents generated by big amount of photovoltaic systems and common electronic loads and the interaction between them

Coordination of voltage regulation in active networks

This paper give an introduction about the Active Network concept that can be managed by a multi-agent system (MAS). Voltage regulation, one of Active Network's services, is then presented. The autonomous voltage control within each feeder (Cell) can be deployed by a combination of active and reactive power supports of distributed generators (DG). The coordination voltage control defines the optimal tap setting of the on-load tap changer (OLTC) while comparing amounts of control actions in each Cell. The test results show that the voltage regulation in Active Network can help to integrate more DGs and mitigate voltage violation effectively. The optimal solution can be reached within a small number of calculation iterations

Completely decentralized state estimation for active distribution network

The concept of an active network has been mentioned recently to adapt to the large-scale implementation of distributed generation. Distributed State Estimation is one of the most important functions to enable this novel concept. This paper proposes a completely decentralized state estimation (CDSE) method suitable for the active network. CDSE is based on multi-agent system technology to compute iteratively state variables, i.e., voltage magnitude and angle. The method will be compared with the classical weighted least square method in term of computation burden. As examples a 3-bus system and the IEEE 14-bus network will be investigated