NEIS Conference 2016

The energy transition is a key element in the fight against climate change. Many technical papers have been written on developments that are dedicated towards new systems, improving the efficiency of existing ones, advanced control of electrical systems, etc. In Europe this type of research is found within the SET plan that describes the research line in the near and midterm future [1].Though technology is key in enabling the energy transition, a mere technology push will not make it happen. Society has to foster the developments. Especially the consumer will not join the action if he is not convinced that the quality of life is not enhanced by new service.In the seventies of the last century, both oil crisis’s have rocked the energy system, but after a few years, it turned out that things did not change too much. Some countries introduced nuclear power for electric energy generation, all other applications continued to use oil.Around and after the turn of the century, a number of megatrends have been seen in the energy system changing the system more deeply than we have ever seen before. Therefore, they are described to some detail.

Only a whole systems approach incorporating distributed generation, storage and advanced control can contribute to decarbonisation, security of supply and affordability of energy.Even among trained engineers often detailed knowledge about the competitiveness of solar energy is not fully developed. Using selected examples from the fields of solar thermal energy use and solar electric systems the multifunctional features are outlined. In combination with different storage technologies attractive technical solutions can be identified which are also very economic.

In order to perform AC load flow modelling of the European transmission system, information regarding installed reactive power compensation is required. Due to reasons of commercial sensitivity, such information is rarely made publically available by European TSO’s. Therefore, European models presented in the literature are often limited to DC load flow calculations, whereby voltage magnitudes and reactive power flows are neglected. So as to facilitate full AC modelling of the European system, the following paper presents a method through which the locations and amounts of installed reactive power compensation are estimated. For multiple demand scenarios, the compensation required to facilitate realistic voltage profiles and power flows in the synchronous European transmission system is calculated. The combination of these results provides an estimate of the installed compensation and can therefore be used to pursue AC load flow calculations for various loading and feed-in scenarios in Europe.

In many studies on the expansion and optimization of low-voltage grids for the integration of additional loads or distributed generation there is a need for extensive georeferenced grid data. In the first part of this paper a refinement and enhancement of a fully automated method for the modelling of these data from OpenStreetMap and further sources will be presented, so that a large number of synthetic low-voltage grids can be created easily. The second part introduces an optimization procedure to distribute the grid connected buildings to the substations via line sections.

Nowadays solid-state power controllers (SSPC) are widely used in aircraft secondary power supply, because of a higher count of switching cycles, small weight, flexible trip behavior, and a fieldbus connection. Typically, they protect loads and their connection lines. One drawback of these solid-state switches is the typical 28V secondary power supply for the control elements. This paper shows an effective supply arrangement to use the onboard power supply as energy source. Parallel MOSFETs represent the switching unit. This can be used for a self-test without supply interruption of connected loads. A self-test method is shown in this paper.

High-voltage DC (HVDC) transmission lines offer highly efficient transport of electric energy. If applied to comparatively weak grids, self-commutated converters are the proper choice because they allow stabilizing the grid in case of faults by injecting reactive power. At high voltages of e.g. 400 kV, modular multilevel converters (MMC) fulfill all requirements. For testing all relevant aspects of a multiterminal HVDC-transmission system, a scaled-down test bench has been realized. Four MMCs define the multiterminal DC system. With regard to practical demands, no explicit communication between the control systems is allowed for stable operation of the transmission system. This paper gives an overview of the test bench and then concentrates on the bidirectional power flow of the HVDC System in a bipolar configuration.

This article describes the energy potential of the Republic of Tajikistan and possibilities of its use for a sustainable development of neighbouring countries in the Central Asian region. Underproduction of electric power with hydroelectric power stations (HPP) due to idle water flow in summertime leads to economic losses for electric power companies in Tajikistan and the whole Central Asian region. These economic losses are quantitatively estimated, based on researches of efficient use of the hydro power potential in Tajikistan. As a result, a diversification of the country’s energy sources is necessary as well as the formation of a regional hydro power energy market. Thus, the national power companies would get increased capabilities to repay their foreign loans.

Emergency power supplies are mainly used to protect critical infrastructure in case of blackouts. For ordinary population, there are hardly any investigations on usability of different technologies for emergency power supply systems. This paper provides a detailed analysis on which requirements are relevant for laymen usage of emergency power supplies. Furthermore, a method which combines these requirements is used to evaluate a variety of technologies based on the presented criteria and to compare their individual suitability. Advantages and disadvantages of all the examined technologies are provided. With this, a quick evaluation of different technologies with respect to small scale systems is possible. As all requirements are addressed, this helps the reader to get a quite but differentiated overview. Finally, a benchmarking is presented for each criterion and each technology.

The share of wind power plants of the overall installed capacity of electrical power generation is continuously rising since the last years. Nowadays, provision of ancillary services as frequency control is mainly supported by conventional power plants. However, in connection with a decreasing number of conventional power plants, wind power plants need to contribute to frequency control to a greater extend in the future.This paper presents an analysis of the impacts of an increasing supply of control reserve by controllable wind power plants on grid performance. The grid performance is thereby measured by grid frequency response metrics after a major generation loss. The European interconnected power system is simulated with focus on the four German control areas. Providing control reserve by wind power plants can be performed by a variation of the rotor pitch angle and the tip speed ratio. A control strategy for variable speed wind turbines to supply control reserve in order to stabilize the grid frequency is presented. Comparing the frequency response metrics of the future and the present scenario, it is shown that the grid performance is equal. The maximum frequency deviation is even lower in the future scenario. A sensitivity analysis shows, that even a further decrease of rotating masses in the grid is tolerable. Apart from all these technical challenges, it needs to be reflected that the current legal framework in Germany must be changed in order to give wind power plants the possibility to participate in the primary and secondary balancing market.

This paper addresses the system implementation of voltage control architecture in wind power plants into a Real-Time Hardware-In-The-Loop framework. The increasing amount of wind power penetration into the power systems has engaged the wind power plants to take over the responsibility for adequate control of the node voltages, which has previously been accomplished by conventional generation. Voltage support at the point of common coupling is realized by an overall wind power plant controller which requires high-performance and robust control solution. In most cases the system including all controls is reproduced in continuous-time domain using Laplace transform, while in practical implementation digital control systems are employed. The scope of this paper is to elaborate on the practical implementation of the voltage control architecture into a Real-Time Hardware-In-The-Loop framework, where the focus is laid on the model development in a real-time simulator. It enables to verify the functionality of developed controls, which is one of the research priorities due to the increased complexity of large wind power plants requiring high level of communication between plant control and a large number of assets such as wind turbines and FACTS devices.

Reference test scenarios with standardized, well-defined input profiles are of high importance for the development, layout, dimensioning and comparison of energy systems. The guideline VDI 4655 provides reference load profiles for residential buildings that consider building characteristics as well as climatic and seasonal influences. These reference profiles have been extended by NEXT ENERGY with photovoltaic (PV) power profiles, such that realistic scenarios for residential energy infrastructures including PV systems can be designed. In this work, we give an overview of the VDI 4655 reference load profiles as well as the PV power profiles and demonstrate their usefulness in the context of renewable energy systems with the help of two case studies. We show how time-lapse test profiles can be constructed conveniently from the reference load profiles. They allow for the simulation of entire years in a fraction of the time using real components in a laboratory setting. The high accuracy of the reference profiles and the utilization of real components in a laboratory setting substantially facilitate the realistic evaluation of residential energy infrastructures including renewable energy components.

The transmission system operators (TSOs) started to realize reactive power requirements of sub-transmission grids at their connection points (CPs) where they are connected to transmission grids. In this paper, a proper Q-setting strategy, in other words reactive power management technique, is applied to sub-transmission grids in order to transfer minimum reactive power into transmission grids with nearly minimum losses within a voltage stable grid. The distributed wind farms (WFs) having modV and modQ operations are benefiting from this. The proposed Q-setting strategy is considered as an optimization task with an objective function. This objective function should be built in a way to satisfy the aim of reactive power management. In the end, the applicability of both selected WF operations including modV and modQ is proved within the selected objective function which is to minimize reactive power flows.

Electromobility creates new challenges for the automotive industry that exceed the original equipment manufacturers’ (OEM) existing core expertise. As the automotive and the energy industry merge, intense collaboration is crucial for developing future products and vehicles that are relevant and beneficial for the consumer. By utilizing the electric vehicles’ (EV) load shifting potential, connected charging services (CCS) might be able to harmonize customer and industry needs. Charging infrastructure and information technology of existing EVs do not meet the corresponding requirements to the full extent. In addition a common industry standardization does not exist either. However, proprietary products are already being brought to market, e.g. for optimizing the energy consumption of private households through the use of single EVs. Grid scale applications that use fleets of EVs are not commercially available, yet. The goal is to maximize the EVs’ technical and economic contribution within distributed energy systems. Therefore, the interests of all stakeholders involved need to be considered despite being heavily dependent on the application.This paper identifies future charging strategies for EVs in distributed energy systems and derives an approach how they can be successfully brought to market. After presenting critical success factors, options for future strategic collaboration models are being discussed. At the center of this study lies a stakeholder analysis that is based on qualitative, semistructured interviews with experts from academia and industry.

Low power equipment like power supplies have to fulfill tightened regulations from International Efficiency Level VI standard with 100 milliwatt standby losses since February 2016. The aim is to significantly lower the losses when the end device is not in use or is not connected to the power supply what we call “no-load” power consumption or standby losses. The United States with 300 million people had in 90´s in every household estimated five external power supplies with 15 billion Watt (15 GW) bad linear topology that could be replaced without big efforts. Measurements of the today used low power equipment have much too high losses from 0.5 W to 2 W in standby.

Grid integration of decentral power generation units and storage systems as well as new requirements from the “Network Code on Requirements for Grid Connection of Generators” (NC RfG) by the European Union lead to new grid codes in all countries of the EU. In Germany the VDE “Association for Electrical, Electronic & Information Technologies” will publish new grid requirements for power generating facilities and storage systems in the next two years. The grid codes for all voltage levels from low voltage to ultrahigh voltage are being revised at the moment. It is expected that the first public draft of the medium voltage level grid code (VDE-AR-N 4110) will be available in autumn 2016. This medium voltage grid code uses concepts of the latest public high voltage grid code VDE-AR-N 4120 which will be amended itself according to the requirements from the NC RfG. In a further step the test and certification requirements will be updated in Germany by the FGW. This paper provides an overview on the current status of the grid code requirements and the test, simulation and certification guidelines in Germany.

Stable security of energy supply requires an equilibrium of supplied and consumed power at any time. Deviations between demand and supply cause an instant increase or decrease of the grids frequency. Ancillary services ensure a constant frequency in the public transmission grid by providing inertia and balancing power in form of primary and secondary system service reserve power as well as minute reserve. In the project, funded by the DFG (Deutsche Forschungsgemeinschaft, German Research Association) scientists research the use and application of high power batteries to maintain the system frequency. Experiments and simulations were carried out with a virtual synchronous machine which responses on frequency fluctuations and provides regulating power from LFP (lithium iron phosphate) batteries.This paper deals with the electronic set-up for providing virtual inertia by use of the “virtual synchronous machine” (VISMA) and results of lifetime experiments and models for lithium-ion batteries especially for high dynamic loads are presented.

Aquifer Thermal Energy Storage (ATES) is a cost-effective and energy-saving technology associated with heating and cooling of buildings or districts. Particularly in combination with cogeneration systems, the overall system performance can be affected positively by storage and recovery of large quantities of thermal energy in the subsurface. ATES has developed from a demonstration stage to an established technology over the past decades. However, in Germany there are only three existing projects yet. Since 2010, there are plans to integrate an aquifer storage into an existing District Heating System (DHS) in Lueneburg, which is supplied by two cogeneration units. The hydrogeological conditions (e.g. water chemistry or thickness of the natural aquifer) at 450 m depth are matching with the size of the DHS. With respect to financial aspects, seasonal energy storage in an aquifer reinforces the connection between thermal and electric energy systems due to cogeneration. Purpose of this paper is to demonstrate case studies based on energetic overall system performance considerations to evaluate future energy systems with ATES. A system comparison (with ATES and without ATES) indicates an increase of cogeneration by more than 20 %. In the same way, the conventional heat production with natural gas decreases by 2.3 GWh/a while the generation of renewable electricity increases by 2.8 GWh/a.

Battery energy storage systems (BESS) are one of the key technologies for a successful energy turnaround in Germany. Several studies have shown that they are only economically efficient combining different applications [1]. In this paper, a real-time control strategy is presented, to provide peak shaving for intensive energycustomers to achieve reduced network fees in Germany as the primary application. This application is combined with the ancillary service primary frequency control to optimize the economic efficiency of the BESS. The performance of the combined applications control strategy is determined by the accuracy of short-term load forecasting, which is done by using an artificial neural network. The objective of this paper is trying to achieve an optimal design of a control strategy for peak shaving and primary frequency control, and the considered constraints include state-of-charge, rated power and power gradient. The control strategy is modelled and simulated using MATLAB Simulink R2015b.

South Africa is facing one of its greatest challenges in the electricity sector leading to frequent load shedding in order to prevent a collapse of the national grid. The South African government through its national electric utility Eskom, has put in place plans to build new power stations. There are pumped storage peaking stations at Drakensburg (1000MW) and Palmiet (400MW) which will be further supplemented by Ingula (1300MW) currently under construction and situated in KwaZulu-Natal Province. Underground pumped hydroelectric energy storage (UGPHES) is introduced as an alternative technology for bulk energy storage in South Africa and to contribute to the constrained electricity network with environmental and economic benefits. This paper evaluates and discusses the use of existing infrastructure for the implementation of this scheme, including the use of abandoned mines as it presents an existing underground cavern as well as large amounts of groundwater. Results obtained from studies and preliminary assessment are presented and discussed. The use of underground pumped hydroelectric energy storage as a technical alternative for bulk energy storage in South Africa, and a potential contribution to the constrained electricity network with environmental and economic benefits is proposed. The use of aquifers for the implementation of this proposed scheme is explored, with South Africa having large amounts of groundwater as well as transboundary aquifers which may be used for the proposed energy storage systems. An extensive literature review and document analysis of this alternative is carried out and results obtained from preliminary studies and assessments are presented and discussed.

The efficient planning and dimensioning of cold water supply systems is a complex task. Even in new buildings, chillers are often over-sized in order to accommodate for the warmest days of the year or to hold capacity available for future upgrading. The chillers are usually designed for maximum expected flow and pressure values in the cold water system and show low efficiencies in partial load times. A practical solution for enhancing system efficiencies is to integrate cold energy storage, which provides the possibility to decouple cold energy supply from demand. Thus, cold water production may be shifted to off-peak hours, when it is energetically more favorable. It is the aim of this paper to investigate the economic potentials of cold energy storage in combination with screw compression chillers by incorporating measured demand profiles from a cold water system at the IISB. The measurement data is used as input for simulations that evaluate different cold water storage and chiller dimensions with respect to energetic demands and energy saving potentials. The results show that cold water production costs can be reduced by up to 22 % depending on the considered chiller unit and the chosen storage tank volume. Via application of thermal energy storage for reduction of peak cooling loads, the size of cooling components can be reduced and the chillers can be operated more efficiently. The comparison with saving potentials of a speed-controlled chiller motor shows, that the benefits of both technologies are similar over wide working ranges. A decision for one technology or the other has to be made individually based on the system boundary conditions.

The use and integration of intermittent renewable energy sources into energy networks and the increase of primary energy efficiency are key in paving the way towards a low-carbon energy supply. This requires the available existing resources, energy flows and renewable potentials in municipal energy systems to be used as technologically efficient as possible. New innovative tools and methods are necessary to achieve this goal as well as minimizing costs and maximizing security of supply. In the paper shown here, a new method for the analysis of municipal energy systems is presented. A cellular approach is combined with energy and exergy analysis. Exergy analysis is used to determine the causes, locations and magnitudes of primary energy losses. Energy analysis is used to quantify the amounts of excess energy that can be stored using the linkage of power, gas and district heating networks in order to develop innovative hybrid grid solutions. Results of a case study for the Austrian mid-sized city of Leoben are presented as well.

Sustainable energy harvesting, above all wind energy and solar energy, uses self-commutated converters for grid connection. Modern drive systems also use self-commutated converters instead of diode bridges for grid connection to attain constant working conditions and also to improve power quality. So-called active filters base on the same technology. In this way, the total number of controlled power-electronic assets (CPE) connected to the grid increases continuously. Consequently, the relation between conventional short-circuit power and the total power of CPE decreases. The resulting interaction between the CPE at comparatively weak grids becomes more and more relevant and may lead to resonances. This paper analyzes reasons for such interaction based on a qualitative assessment of reduced short-circuit power in the presence of CPE. It then utilizes power-theory concepts to define an optimal type of load as well from a purely theoretical as from a praxis-oriented point of view. Basic rules for load characteristics at weak grids are derived.

One reason for the trend towards microgrid operation is the increased security of supply for the island itself. But if more and more generation units disconnect from the grid subsequent to a fault event, the overall grid stability might be weakened because there are less generators that provide dynamic voltage support. In this paper we propose a control strategy that combines a low-voltage ride through capability with a subsequent islanding operation. With the proposed approach, inverters are able to supply a maximum amount of grid support in the first place. If there is a collapse of the grid, the inverter disconnects and switches to islanding operation. The designed voltage and frequency control are implemented in an ordinary grid parallel inverter. Thus the method is suitable for a wide range of inverter units whether they are used in microgrids or not. The proposed control strategy was tested in simulation and experimentally validated. It was shown that the control is robust under all relevant load conditions.

Virtual Power Plants (VPPs) aggregate large numbers of Decentralized Energy Resources (DERs), such as photovoltaic (PV) generators on rooftops, to economically optimize their generation schedules and thereby maximize DER operators’ revenues. However, VPP schedules that are purely optimized according to economic aspects do not take into account the grid constraints of the affected local distribution grids in which the DERs are located. Therefore, VPPs can produce schedules that are actually infeasible in practice since they violate the grid constraints of the local Distribution System Operators (DSOs). As a consequence, DSOs are forced to switch off DERs during schedule execution in order to keep the voltage in their distribution grids within acceptable limits. This forced DSO interference may ultimately cause the VPPs and their DERs to fail at achieving their economic optimization goals. Instead of generating purely economically optimized VPP schedules, we propose to additionally take the grid constraints of the DSOs into account during VPP schedule computation. Thus, the generated coordinated schedules increase both, grid voltage limit compliance and VPP/DER revenue by avoiding critical grid states and the subsequent necessity of the DSOs to interfere with schedule execution by switching off DERs.

The pressure-dependent operation of polymer electrolyte membrane fuel cell systems is considered, following a general research methodology. Based on previous research a model refinement from a phenomenological mathematical model towards a semi-empirical mathematical model is presented. It is shown that for the fuel cell device under test and the chosen compressor a low-pressure operation in suction mode is more efficient compared to the supercharged operation. This matter of fact permits optimized operating and control strategies for (multifunctional) fuel cell systems for aircraft applications.

In this experimental work we present a novel electrolyzer system for the production of hydrogen and oxygen at high pressure levels without an additional mechanical compressor. Due to its control strategies, the operation conditions for this electrolyzer can be kept optimal for each load situation of the system. Furthermore, the novel system design allows for dynamic long-term operation as well as for easy maintainability. Therefore, the device meets the requirements for prospective power-to-gas applications, especially, in order to store excess energy from renewable sources. A laboratory scale device has been developed and high-pressure operation was validated. We also studied the long-term stability of the system by applying dynamic load cycles with load changes every 30 sec. After 80 h of operation the used membrane electrode assembly (MEA) was investigated by means of SEM, EDX and XRD analysis.

For determination of battery storage business cases key decision criteria are lifetime and State of Health (SoH), in addition to investment costs, operating costs and revenues. The lifetime and SoH strongly depend on operating conditions, such as number of equivalent full cycles (EFC), operating battery cell temperature, Depth of Discharge (DoD), C-rate and State of Charge (SoC). Those can vary depending on operating strategy and chosen application. In this analysis the lifetime of 2nd-life lithium-ion (Li-ion) battery energy storage systems (BESS) are examined and evaluated, depending on various stationary applications. Avoiding the expenses for battery cell parameterization, an improved methodology based on weighted Ah-Throughput (AhTp) and Fuzzy Logic is used to apply qualitative statements of experts into quantitative values. The investigation is carried out by using MATLAB Simulink including application-related load profiles. Based on the results statements for lifetime expectations are given.

The decrease of PV feed-in tariff and the progress on battery manufacture has significantly fostered the application for residential storage system. In order to save expense by increasing self-consumption rate, it is necessary to achieve an efficient usage of battery by developing a power control strategy in a household grid-connected PV-storage system. The strategy is also supposed to address potential curtailment power loss derived from surplus solar generation under high irradiance and strict feed-in limitation since it is a waste issue and results in avoidable energy retail cost. The challenge lies on managing surplus generation to battery and grid power flow, ideally without relying on error-prone forecasts for both load and generation in a PV-storage system. This paper proposes a fuzzy logic controller (FLC) based charging method to manage surplus power in order to avoid the waste of curtailment power loss and achieve the aim of minimum cost by battery utilization. Comparisons on curtailment losses, energy transfer via the grid and resulting savings achieved by battery installation are conducted and compared to three other reference methods, namely a direct charging / discharging strategy (“greedy”), a formerly investigated “feed-in damping” strategy and a “perfect foresight” strategy with forecast on load and generation. Using this easy implementable fuzzy logic method without forecast on generation as well as consumption power, the minimum total cost can be achieved by the proposed FLC method compared to the analyzed methods without the knowledge of power profiles in advance.

In Germany renewable energies already represent a share of about 30 % with regard to the domestic gross electricity consumption. And this contribution will most likely – according to the goals of the German government – significantly further increase in the years to come [1]. For an efficient integration of this electricity from renewable sources of energy – especially with a fluctuating characteristic – and for an ongoing secure and reliable electricity provision system, the flexibility of the overall power system has to be increased. One possibility promising a large potential at low costs is to couple the power sector with the heat sector via implementing heating cartridges in hot water storage systems, which are typically an integrated component of existing gas or oil driven heating systems used by private households as well as small-scale industry [2]. Such hybrid heating systems can consume excess electricity from the electricity provision system or stabilize the power system by means of supplying negative control power. For such applications this paper presents decentralized control approaches to coordinate the supply of control power from a multitude of such distributed hybrid heating systems. Compared with most of the existing control approaches, the decentralized control mechanisms developed within this paper also take voltage violations within the distribution grid into account. All analyses and evaluations are based on comprehensive computer simulations with NetLogo and Matpower, a Matlab based tool for power flow calculations.

In some sectors of industry like coke production, chlorine production or semiconductor manufacturing hydrogen exhaust streams accrue. The hydrogen content can range between 40 – 99 % and represents a huge energy source, which is predominantly not converted into electricity nowadays. A conversion system consisting of a diaphragm compressor, a humidifier and a fuel cell system to convert exhaust gas streams into electricity is presented in this paper. One challenge is to avoid any impact on the process facility and the process itself which is solved by an input pressure control using the compressor and a controlled bypass valve. Furthermore, the influence of nitrogen content in a hydrogen/nitrogen gas mixture on a PEM fuel cell system in flow through mode is investigated on an 8 kW PEMFC. Due to the dilution of hydrogen with up to 60 % nitrogen the maximum output power of the system is dramatically reduced by 55 % to 3.6 kW. The total conversion efficiency depends on exhaust gas conditions, mainly hydrogen concentration and pressure levels, and is expected to be between 10 – 37 %. Another major influence is the fuel cell current density whereby a reduction from 0.5 A/cm2 to 0.2 A/cm2 yields to doubled conversion system efficiency for low hydrogen contents.