Daphne Schwanz

Stochastic Assessment of Voltage Unbalance Due to Single-Phase-Connected Solar Power

A stochastic method is presented in this paper to estimate the future voltage unbalance in a low-voltage distribution network with high-penetration of single-phase photovoltaic inverters (PVIs). The location and phase allocation of the PVIs are considered as input parameters for the stochastic simulation. The method has been applied to three different low-voltage networks: two in Sweden and one in Germany. In the Swedish networks, for 6-kW single-phase PVIs, it is likely that the contribution from single-phase photovoltaic inverters to the voltage unbalance exceeds 1%. The 2% value is unlikely to be exceeded. In the German network, for 4.6-kW single-phase PVIs, the voltage unbalance is between 1.35% and 2.62%. The risk of high-voltage unbalance can be reduced by a combination of controlled distribution over the phases and a reduction of the maximum size for a single-phase PVI.

A review of solutions for harmonic mitigation

With the increasing of non-linear equipments connected in the network, mitigation solutions are needed to avoid and solve harmonic and resonance problems that may damage equipments and avoid their connection into the grid. Several are the solutions given to this problem; however, not all them are suitable for all situations. For it, in this paper a review of the most used harmonic solutions and some new technologies are presented. The advantages and disadvantages are described and the most used passive, active and hybrid solutions are described.

Active harmonic filters: Control techniques review

The use of active filters for harmonic mitigation compensation is increasing together with the improvement of their control techniques. Depending on the situation, the use of one technique instead of the other makes the difference of achieving a better harmonic mitigation or not. In this paper, a review of control techniques related to harmonic filters for harmonic mitigation is presented, together with the advantages and disadvantages. From the literature review it was observed that new techniques are being used and classical ones are being improved.

Harmonic mitigation in wind power plants: Active filter solutions

Passive solutions are the most used harmonic mitigation methods in wind power plants, but the use of active filters is also a suitable and attractive approach. However, the best location for the connection of these active filters needs to be studied and evaluated. In this paper, a study of the use of active harmonic filters placed at different locations inside a wind power plant is performed. The results for current and voltage harmonic distortion are compared and discussed to determine the most suitable location for placing active harmonic filters within a wind power plant.

Hosting capacity for photovoltaic inverters considering voltage unbalance

In this paper the hosting capacity considering voltage unbalance is estimated for single-phase photovoltaic inverters (PVIs) in low-voltage distribution networks in Sweden. A stochastic approach is used to calculate the negative-sequence voltage unbalance for each of the possible locations in the network. The method has been applied to 6 and 28-customer networks for the connection of 6-kW single-phase PVIs. The impact of three-phase motors on the unbalance was also studied. From the results, it was observed that the contribution from single-phase photovoltaic inverters to the voltage unbalance likely exceeds 1%, but unlikely that it will reach 2% of voltage unbalance.

Stochastic assessment of voltage unbalance due to single-phase-connected solar power

A stochastic method is presented in this paper to estimate the future voltage unbalance in a low-voltage distribution network with high-penetration of single-phase photovoltaic inverters (PVIs). Location and phase allocation of the PVIs are considered as input parameters for the stochastic simulation. The method has been applied to three different low-voltage networks: two in Sweden and one in Germany. In the Swedish networks, for 6-kW single-phase PVIs, it is likely that the contribution from single-phase photovoltaic inverters to the voltage unbalance exceeds 1%. The 2% value is unlikely to be exceeded. In the German network, for 4.6-kW single-phase PVIs the voltage unbalance is between 1.35% and 2.62%. The risk of high voltage unbalance can be reduced by a combination of controlled distribution over the phases and reduction of the maximum size for a single-phase PVI.

Some Thoughts about Harmonic Limits in Connection Agreements for Wind Power Plants

For the connection of wind power plants into the public grid there are power quality procedures and limits that need to be complied with. The direct aim of those is to ensure a suitable power quality in the grid, but to ultimate aim is to ensure a high probability of electromagnetic compatibility. Each country has different requirements and standards, and with this, different procedures. In this paper, an overview of these methods will be given, together with some of the advantages and disadvantages. Furthermore, a review of the modifications regarding the latest versions of IEEE 519-1992 and IEC 61000-3-6 will be presented.