Dynamic Simulation and Intelligent Management of Distributed Generation

Significantly large integration of distributed generation (DG) is expected in future power systems. Paving the way are the encouraging government policies, great concerns on environment and optimising economic benefits. This large integration is however raising a lot of concern on stability, security and reliability of power system network which will create many challenges in operating the network due to different characteristics possessed by DG. These concerns and operating challenges need to be investigated to identify the possible problems that may arise and then followed by finding a countermeasure for mitigation. Research work in this thesis addresses most important issues and challenges in operating power system with large DG penetration. The following research areas are performed: • Modeling of distributed generation: New technology embraces by DG has totally different characteristics compared to conventional generation unit based on synchronous machine, thus making it necessary to perform integration studies on various operational aspects to assess the influence of this small scale generation unit on the power system network operation and control. The studies require an accurate and easy to understand dynamic model which closely imitates the dynamics of a real DG unit. In this thesis, development of different dynamic models of micro turbine generation system, fuel cell generation system and a generalized DG dynamic model to be used in power system studies is discussed. The performance of the model developed from the simulation results is found comparable to the reported performance in the literature. • DG fault ride-through capability: Due to different characteristics possessed by DG, power system operator imposed stringent requirements on the DG connected to the grid. During critical time DG has to be able to withstand a temporary voltage dip due to fault occurrence in the grid even when the voltage reaches zero at the point of connection. At the same time, during this fault ride-through DG must also help the grid by injecting reactive power to support power system voltage recovery. Different types of DG technologies are investigated if they are able to fulfil this requirement and if not exploring the necessary modifications which has to be made on the specific DG unit. The investigation results indicate that in fulfilling new grid code requirements, modification inside DG power electronic converter hardware and controller is necessary. iii • Grid support by DG: Massive DG integration in distribution network will interfere with current practices and control scheme inside the network. With appropriate coordination and control, this negative influence on network could be changed to positive. This thesis explores the possibility of participating DGs in voltage regulation and frequency control. Clearly the studies indicate that DG coupled to the grid through power electronic converter has potential to positively contribute to power system voltage regulation and frequency stabilisation. • Influence of DG on power system stability under new grid codes: Power electronic converter utilised in DGs makes them have different characteristics in responding to grid fault and they are also demanded to provide reactive support during this period. This characteristic and new rule is feared to negatively influence the stability of a power system as to where these DG units are connected to. In this thesis the most important types of stability are analysed with different levels of DG penetration and control options. It can be concluded that if DG is properly located and controlled, DG integration will significantly improve the stability of power system network. • Predictive var management inside future distribution network: Future distribution network will contain large number of DG units and the network will be integrated with advance communication facilities. This large number of DG will create technical challenges but the communication link available will provide the opportunity to control DG centrally in real time to optimise the benefits offered by DG integration. In this thesis, a predictive technique in managing DG reactive power to reduce power loss and to control the voltage inside a distribution network is proposed and discussed. The effectiveness of the proposed approach which are developed with two staged intelligent techniques namely, adaptive particle swarm optimisation and artificial neural network, is demonstrated and the results are quite promising

Effects of energy storage systems grid code requirements on interface protection performances in low voltage networks

The ever-growing penetration of local generation in distribution networks and the large diffusion of energy storage systems (ESSs) foreseen in the near future are bound to affect the effectiveness of interface protection systems (IPSs), with negative impact on the safety of medium voltage (MV) and low voltage (LV) systems. With the scope of preserving the main network stability, international and national grid connection codes have been updated recently. Consequently, distributed generators (DGs) and storage units are increasingly called to provide stabilizing functions according to local voltage and frequency. This can be achieved by suitably controlling the electronic power converters interfacing small-scale generators and storage units to the network. The paper focuses on the regulating functions required to storage units by grid codes currently in force in the European area. Indeed, even if such regulating actions would enable local units in participating to network stability under normal steady-state operating conditions, it is shown through dynamic simulations that they may increase the risk of unintentional islanding occurrence. This means that dangerous operating conditions may arise in LV networks in case dispersed generators and storage systems are present, even if all the end-users are compliant with currently applied connection standards

Frequency support characteristics of grid-interactive power converters based on the synchronous power controller

Grid-interactive converters with primary frequency control and inertia emulation have emerged and are promising for future renewable generation plants because of the contribution in power system stabilization. This paper gives a synchronous active power control solution for gridinteractive converters , as a way to emulate synchronous generators for inerita characteristics and load sharing. As design considerations, the virtual angle stability and transient response are both analyzed, and the detailed implementation structure is also given without entailing any difficulty in practice. The analytical and experimental validation of frequency support characteristics differentiates the work from other publications on generator emulation control. The 10 kW simulation and experimental frequency sweep tests on a regenerative source test bed present good performance of the proposed control in showing inertia and droop characteristics, as well as the controllable transient response.Peer ReviewedPostprint (author's final draft

Power quality and electromagnetic compatibility: special report, session 2

The scope of Session 2 (S2) has been defined as follows by the Session Advisory Group and the Technical Committee: Power Quality (PQ), with the more general concept of electromagnetic compatibility (EMC) and with some related safety problems in electricity distribution systems. Special focus is put on voltage continuity (supply reliability, problem of outages) and voltage quality (voltage level, flicker, unbalance, harmonics). This session will also look at electromagnetic compatibility (mains frequency to 150 kHz), electromagnetic interferences and electric and magnetic fields issues. Also addressed in this session are electrical safety and immunity concerns (lightning issues, step, touch and transferred voltages). The aim of this special report is to present a synthesis of the present concerns in PQ&EMC, based on all selected papers of session 2 and related papers from other sessions, (152 papers in total). The report is divided in the following 4 blocks: Block 1: Electric and Magnetic Fields, EMC, Earthing systems Block 2: Harmonics Block 3: Voltage Variation Block 4: Power Quality Monitoring Two Round Tables will be organised: - Power quality and EMC in the Future Grid (CIGRE/CIRED WG C4.24, RT 13) - Reliability Benchmarking - why we should do it? What should be done in future? (RT 15

Supporting transient stability in future highly distributed power systems

Incorporating a substantial volume of microgeneration (consumer-led rather than centrally planed) within a system that is not designed for such a paradigm could lead to conflicts in the operating strategies of the new and existing centralised generation technologies. So it becomes vital for such substantial amounts of microgeneration among other decentralised resources to be controlled in the way that the aggregated response will support the wider system. In addition, the characteristic behaviour of such populations requires to be understood under different system conditions to ascertain measures of risk and resilience. Therefore, this paper provides two main contributions: firstly, conceptual control for a system incorporating a high penetration of microgeneration and dynamic load, termed a Highly Distributed Power System (HDPS), is proposed. Secondly, a technical solution that can support enhanced transient stability in such a system is evaluated and demonstrated

EcoBlock: Grid Impacts, Scaling, and Resilience

Widespread deployment of EcoBlocks has the potential to transform today's electricity system into one that is more resilient, flexible, efficient and sustainable. In this vision, the system will consist of self- su cient, renewable-powered, block-scale entities that can deliberately adjust their net power exchange and can optimize performance, maintain stability, support each other, or disconnect entirely from the grid as needed. This report is intended as an independent analysis of the potential relationships, both constructive and adverse, between EcoBlocks and the grid

Requirements to Testing of Power System Services Provided by DER Units

The present report forms the Project Deliverable ‘D 2.2’ of the DERlab NoE project, supported by the EC under Contract No. SES6-CT-518299 NoE DERlab. The present document discuss the power system services that may be provided from DER units and the related methods to test the services actually provided, both at component level and at system level

Technical SWOT analysis of decentralised production for low voltage grids in Flanders

The increasing energy prices, combined with high funding by the government, has resulted in a massive integration of decentralised electrical energy production units in Belgium. These systems are mainly PhotoVoltaic systems and the sudden increase of both number and power ratio of the DG systems has put additional stress on the distribution network. In this paper a technical SWOT analysis is presented. The researchers believe that the solution to decompress the stress can result in additional benefits for both, end user and distribution network operators

Decoupling and Control of Real and Reactive Power in Grid-Connected Photovoltaic Power System

The paper presents a detailed modeling and simulation of different control schemes of the real and reactive power flows in a three-phase voltage source inverter (VSI) interfacing a photovoltaic (PV) generation system to the power grid. Synchronisation of the inverter and grid AC waveforms is achieved using a phase-locked-loop (PLL) circuit. An effective decoupling strategy based on proportional-integral (PI) controllers is designed to eliminate the interaction between the two current components. Finally, the influence of the grid disturbances on the PV system and the influence of the solar energy intermittency on the power grid have been tested. The overall model is implemented in Matlab and Simulink/SimPowerSystems toolboxes. Simulations results with the PV system operating with real irradiance data will be presented to demonstrate the performance of the proposed decoupling and control strategies under different conditions of the power gridNon peer reviewe

Dynamics estimation and generalized tuning of stationary frame current controller for grid-tied power converters

The integration of AC-DC power converters to manage the connection of generation to the grid has increased exponentially over the last years. PV or wind generation plants are one of the main applications showing this trend. High power converters are increasingly installed for integrating the renewables in a larger scale. The control design for these converters becomes more challenging due to the reduced control bandwidth and increased complexity in the grid connection filter. A generalized and optimized control tuning approach for converters becomes more favored. This paper proposes an algorithm for estimating the dynamic performance of the stationary frame current controllers, and based on it a generalized and optimized tuning approach is developed. The experience-based specifications of the tuning inputs are not necessary through the tuning approach. Simulation and experimental results in different scenarios are shown to evaluate the proposal.Peer ReviewedPostprint (published version