The work done in this thesis considers microgrids from two different aspects. Power quality and techno-economics of microgrids. Detailed power quality measurements have been made at a single house hydrogen-solar microgrid that consists of state-of-the-art energy efficiency technology, energy production and energy storage. The microgrid can both connect to the grid and operate in islanded operation. The power quality is quantified from these measurements where several power quality parameters during islanded operation go beyond the limits set by standards such as EN 50160 and IEEE 519-2014. The effect on connected equipment from both frequency variations and voltage quality is also discussed. Four new performance indexes are presented in the thesis that are based on apparent impedances. The first with the name PHIPI quantifies how much the harmonic voltage magnitude changes with an increase in harmonic current magnitude on the same phase. The second with the name SHIPI quantifies how much the harmonic voltage magnitude changes with an increase in harmonic current magnitude on another phase. The third with the name AHSI uses the harmonic voltage and current magnitudes of all phases to create a single performance parameter expressed as an apparent impedance for the system. The fourth with the name ARMSSI quantifies the phase RMS voltage drop for a certain phase RMS current rise in terms of an apparent impedance. The thesis also shows techno-economic modeling with times series energy flow to study the investment risks related to consumption changes in a standalone microgrid. The results show that consumption changes are an important parameter when designing a standalone microgrid and that the risk can be mitigated with changes to the system design, but at a larger system cost. The projected cost reduction until the year 2050 for standalone hydrogen based microgrids and some risk aspects with hydrogen based microgrids are also discussed in the thesis. 

A techno-economic energy flow model for a standalone microgrid was developed to investigate the investment risks related to consumption changes and compare the results to a conventional grid-connection in Sweden. Two different design strategies for a standalone microgrid was used, one with the objective to minimize the life-cycle cost and the other to provide a lower investment risk. The largest contributor to an increased investment risk for both design strategies was an increase in annual energy consumption within the standalone microgrid. The design strategy with the objective to reduce the investment risk eliminated the influence on the life-cycle cost from an increase in peak consumption and reduced the overall investment risk in comparison to the design strategy with the objective to minimize the life-cycle cost. However, a larger life-cycle cost was the drawback of that design strategy. It was concluded that locations with larger annual mean capacity factors reduced the investment risk for standalone microgrids due to lower diesel fuel dependence. It was also concluded that a conventional grid-connection had a lower investment risk than a standalone microgrid, since adverse changes in consumption always increased the life-cycle cost less for a conventional grid-connection than for a standalone microgrid.

Voltage quality data has been collected in a single house nanogrid during 48 weeks of islanded operation and 54 weeks of grid-connected operation. The voltage quality data contains the voltage total harmonic distortion (THD), odd harmonics 3 to 11 and 15, even harmonics 4 to 8, voltage unbalance, short-term flicker severity (Pst) and long-term flicker severity (Plt) values, and voltage variations at timescales below 10 min. A comparison between islanded and grid-connected operation values was made, were some of the parameters were compared to relevant grid standard limits. It is shown that some parameters exceed the defined limits in the grid-standards during islanded operation. It was also found that the islanded operation has two modes of operation, one in which higher values of the short circuit impedance, individual harmonic impedance, harmonic voltage distortion and voltage unbalance were reached.

In this paper, an energy flow model for a standalone nanogrid was used to calculate the needed hydrogen storage for operation in northern Scandinavia where the electricity was produced from solar photovoltaics. A range of different input parameters such as annual energy consumption, solar production, consumption pattern and heating system was used to obtain a range of optimal system design parameters. From this, two average system configurations were created for two heating systems based on the results from simulated solar data with 2-axis solar tracking and no solar tracking. The average value from the results at 30 MWh of annual energy consumption was used since it is the average energy consumption for a household in northern Sweden. The average system configuration was applied for 15 to 40 MWh of annual energy consumption using 3 measured solar production datasets and 37 different consumption patterns to study the risk for depleting the hydrogen storage and counter measures to avoid depletion. The results show that energy saving measures must be taken during the winter in order to avoid depletion of the hydrogen energy storage, which in turn avoids a sustained interruption until the spring. It was concluded that if 2-axis solar tracking was used instead of no tracking and a stove was used for heating instead of using a heat pump, the probability for depleting the hydrogen storage reduced by 25% to 47.9% at 30 to 40 MWh of annual energy consumption in the nanogrid.

Frequency, voltage and reliability data have been collected in a nanogrid for 48 weeks during islanded operation. Frequency values from the 48 week measurements were analyzed and compared to relevant limits. During 19.5% of the 48 weeks, the nanogrid had curtailed the production due to insufficient consumption in islanded operation. The curtailment of production was also the main cause of the frequency variations above the limits. When the microgrid operated on stored battery power, the frequency variations were less than in the Swedish national grid. 39.4% of all the interruptions that occurred in the nanogrid are also indirectly caused by the curtailment of solar production. Possible solutions for mitigating the frequency variations and lowering the number of interruptions are also discussed.

The harmonic voltage distortion have been measured in a single house microgrid in Sweden. The microgrid can operate in both islanded mode and grid connected mode. A comparison of the voltage harmonic magnitudes has been made between the two operation states and also against relevant standards. Both the 10 minute average and the 3 second average values are presented in the paper. The harmonic voltage magnitudes are higher during island mode and the difference between the 10 minute value and 3 second value is also greater compared to when the microgrid is connected to the grid. At some instances the magnitudes of both total harmonic distortion and of individual harmonics exceed the limits described in the standards.

Power quality measurements have been performed during 1 year in a small-scale microgrid in Sweden. The microgrid consists of one residential house that can operate in grid-connected or grid-disconnected (islanded) modes. During the year the microgrid was disconnected from the main grid most of the time.