Small-scale Embedded Generators Research Articles

Transient Stability of Synchronous Generator Connected to Micro Combined Heat and Power

Micro Combined Heat and Power (Micro CHP) refers to small-scale installations that generate heat, electricity or both connected to the low voltage distribution network at the customer side. Although the connection of the Micro CHP to the low-voltage distribution networks improves security of supply, there are many operational challenges such as stability and control. This paper study the stability of synchronous generator connected to reciprocating engine as one type of Micro CHP. Also, a several studies have been done to investigate the response of Small scale embedded generation (SSEG) to a range of network faults and thereby ascertain the range of conditions under which SSEG might be expected to trip. Many of these may be regarded as nuisance trips when the action of network protection does not isolate the SSEG from a mains supply. Any protection associated with the SSEG has not been included in order to demonstrate inherent capability and response. The critical clearing time (CCT) is used to indicate the stability of the SSEG. In this investigation the CCT of the SSEG is calculated and simulated using Power Systems Computer Aided Design PSCAD/EMTDC as well as from the mathematical calculations.

Alternatives for small, medium and micro scale enterprises participation in the renewable energy industry – small scale embedded generation review

Over the past decade South Africa has seen an increase in the uptake of solar energy as a result of the Renewable Energy Independent Power Producer Programme, which led to a sharp increase in procurement of utility-scale solar PV projects. On the other hand, the load shedding which was implemented by the national power utility in response to electricity supply and demand challenges resulted in the rise in procurement of small-scale embedded generation solar PV systems. While the REIPPPP has had minimal impact in terms of incorporating small, medium and micro scale enterprises (SMMEs) in the renewable energy value chain, there is a significant opportunity for SMMEs in the small scale embedded generation (SSEG) market segment. This study investigated the challenges and opportunities for SMMEs in SSEG.

Tensions in the transition: The politics of electricity distribution in South Africa

This paper argues that the distribution of electricity represents an important yet neglected aspect of the politics of energy transitions. In recent years, South Africa’s electricity sector has seen the introduction of new actors and technologies, including the ‘prosumer’ (producer–consumer) of electricity and small-scale embedded generation from roof-top solar photovoltaics. We analyse these recent developments in historical context and consider implications for contemporary planning, regulation and ownership of electricity. We find that the reconfiguration of electricity distribution faces significant political and economic challenges that are rooted in the country’s socio-economic and racial inequalities and its heavy dependence on coal-fired power. First small-scale embedded generation offers potential opportunities for affordable, decentralised, low-carbon energy, yet disruption to the coal-powered electric grid and the monopoly of South Africa’s electricity utility has been minimal to date. Second, small-scale embedded generation creates tensions between equitable and low-carbon energy transitions and threatens critical revenue from the country’s wealthy consumers that cross-subsidises electricity services for the poor and other municipal public services. Third, the South African experience queries common assumptions about the democratic potential of decentralised governance. Fourth, South Africa provides insights of global significance into how political institutions have responded to social and technological drivers of change, in a context where planning and regulation have followed rather than led infrastructural developments. While energy policy remains unresponsive or resistant to social and technological change, there remain significant political, economic, technical and regulatory challenges to a just and inclusive energy transition.

Technical assessment of centralized and localized voltage control strategies in low voltage networks

Abstract Both the electric power demand and the penetration of small-scale embedded generators (SSEGs) is rapidly increasing in LV distribution grids. These trends are expected to have significant effects on system performance, efficiency and reliability necessitating the adjustments to the current framework for power supply dispatch and delivery. This paper proposes hybrid voltage control schemes for LV distribution networks combining: (i) centralized control via the on-load tap-changer (OLTC) of secondary distribution transformers and (ii) localized control via both the real and reactive power management from single-phase PV inverters. Specific control algorithms are proposed for both the centralized and localized methods. All the possible operation sequences of the aforementioned methods are examined. The performance of the proposed approaches is investigated on four different test feeders considering the voltage magnitudes, the voltage unbalances, the total losses and the PV power utilization.

Analysis of the Dynamic Performance of Self-Excited Induction Generators Employed in Renewable Energy Generation

Incentives, such as the Feed-in-tariff are expected to lead to continuous increase in the deployment of Small Scale Embedded Generation (SSEG) in the distribution network. Self-Excited Induction Generators (SEIG) represent a significant segment of potential SSEG. The quality of SEIG output voltage magnitude and frequency is investigated in this paper to support the SEIG operation for different network operating conditions. The dynamic behaviour of the SEIG resulting from disconnection, reconnection from/to the grid and potential operation in islanding mode is studied in detail. The local load and reactive power supply are the key factors that determine the SEIG performance, as they have significant influence on the voltage and frequency change after disconnection from the grid. Hence, the aim of this work is to identify the optimum combination of the reactive power supply (essential for self excitation of the SEIG) and the active load (essential for balancing power generation and demand). This is required in order to support the SEIG operation after disconnection from the grid, during islanding and reconnection to the grid. The results show that the generator voltage and speed (frequency) can be controlled and maintained within the statuary limits. This will enable safe disconnection and reconnection of the SEIG from/to the grid and makes it easier to operate in islanding mode.

Optimal utilisation of small-scale embedded generators in a developing country – A case study in Malaysia

Building integrated photovoltaic (BIPV) systems are likely to become a dominant type of small-scale embedded generator (SSEG) on public low voltage (LV) distribution network in Malaysia due to the enormous amount of initiatives and efforts taken by the government to promote the use of BIPV. The growth of BIPV systems on LV distribution networks has the potential to alter the direction of power flow across the distribution networks, hence imposing several serious technical issues relating to power quality, distribution system efficiency and possible equipment overloading. Therefore, the utility companies need to study the following technical issues: (i) voltage regulation, (ii) voltage rise, (iii) voltage unbalance, (iv) network power losses, and (v) cable and transformer thermal limits. This paper describes research carried out to investigate and quantify the impacts of BIPV on LV networks with particular reference to developing countries striving to increase the utilisation of renewable energy. This paper presents and discusses the impacts of BIPV systems on two types of LV distribution network: a commercial LV distribution network and a residential LV distribution network in the state of Selangor, Malaysia. The results of these studies are compared with those from European networks to identify how the differences in the electrical network characteristics influence the allowable penetration of small-scale embedded generators.

Transforming low-voltage networks into small-scale energy zones

Integration of different types of small-scale embedded generators (SSEGs) in the UK electricity supply system has become a key issue for distribution network operators, policy makers, energy producers and the research and development community. When regarded as separate entities, SSEGs offer minimal technical, economical or environmental benefits. However, intelligent coordination of large numbers of SSEGs coupled with energy storage and demand-side management techniques have the potential to maximise these benefits. This paper introduces the small-scale energy zone (SSEZ) concept, which aims to facilitate the proliferation of SSEGs by maximising their potential commercial and environmental benefits, while also ensuring that the associated technical challenges are overcome. A distributed control approach, realised through multi-agent systems technology, is proposed in order to satisfy the specific control requirements of an SSEZ. Moreover, an application of the proposed agent-based approach to the experimental SSEZ at Durham University is presented, focusing on overcoming steady-state voltage-rise issues. Results demonstrating the deployment of direct generation agents are presented and discussed, showing that active network management schemes employed within SSEZs have the potential to increase system performance, while also increasing the annual energy yield of the connected SSEGs.

A dynamic virtual power station model comprising small-scale energy zones

Concerns over global warming and high oil prices are expected to lead to a continuous increase in electricity generated by distributed renewable energy sources and small-scale embedded generators (SSEGs). This increase in SSEG will pose numerous technical challenges for distribution network operators. The small-scale energy zone (SSEZ) concept seeks to overcome these challenges using appropriate coordinated control. An SSEZ is defined as a section of low voltage network with a high penetration of SSEGs, controllable loads and energy storage units. This paper puts forward the concept of the virtual power station (VPS), consisting of a number of aggregated SSEZs, which has the potential to offer significant improvements in the commercial value and environmental impact of the installed SSEGs by enabling provision of ancillary services. In order to evaluate the effectiveness of this concept, a dynamic power system model of a VPS has been developed.

Predicting the technical impacts of high levels of small-scale embedded generators on low-voltage networks

The anticipated high penetrations of small-scale embedded generators (SSEGs) on public low-voltage (LV) distribution networks are likely to present distribution network operators (DNOs) with a number of technical impacts relating to power quality, distribution system efficiency and potential equipment overloads. Impact studies need to be performed using suitable case study networks in order to evaluate the effects of SSEGs on LV distribution networks and quantify allowable SSEG penetration levels. The aim is to propose a methodology for predicting the technical impacts of SSEGs on LV networks without the need for developing a detailed computer-based model of the power system and simulating a range of operating scenarios. This methodology is drawn from an analysis of the key electrical characteristics that determine the response of LV networks to the addition of SSEGs, focusing on the following technical aspects: (i) voltage regulation, (ii) voltage rise, (iii) voltage unbalance, (iv) cable and transformer thermal limits and (v) network losses. The analysis is carried out on a UK generic and a European generic LV network and simulation results for both networks are presented and discussed. The proposed methodology is then applied to an existing public UK LV network operated by E.ON UK Central Networks, indicating a good agreement between predicted and simulation results.

Distributed control approach for small-scale energy zones

A small-scale energy zone (SSEZ) is a conceptual future low-voltage distribution network (LVDN) configuration, containing controllable small-scale embedded generators (SSEGs), energy storage units, and consumer demands. The SSEZ concept, coupled with an appropriate active control approach, aims to increase the commercial value and environmental impact of SSEGs. Such an approach must overcome the SSEZ's LVDN constraints and meet its operational goals. The current paper presents preliminary research to: (a) identify the SSEZ control requirements, (b) select an appropriate control approach, and (c) conduct an initial approach evaluation. A distributed control approach has been selected and realized through the use of a multi-agent system (MAS). This distributed control approach offers advantages with respect to scalability and openness, resilience and reliability, and communication efficiency. This control approach is applied to a case study SSEZ in order to evaluate its ability to overcome the distribution network constraints and to meet its operational goals. The research described in this paper brings together power systems and MAS knowledge through collaboration between the Energy and Mechanics Research Groups in the School of Engineering at Durham University.

Investigation of the reverse power flow requirements of high penetrations of small-scale embedded generation

The research carried out to investigate the ability of power transformers to facilitate the required power flows associated with the anticipated high penetrations of small scale embedded generation (SSEG), within small-scale energy zones (SSEZs) is described. A small-scale energy zone is defined as a section of low-voltage, network with a high penetration of SSEGs, controllable loads and energy storage units. SSEZs, coupled with active control techniques, have the potential to assist the growth of SSEGs by removing network constraints and enabling blocks of aggregated and controlled SSEGs to participate more effectively in energy markets and network operational tasks. The research focused on identifying the reverse power flow and thermal-rating constraints imposed by power transformers. The analysis was performed using an approved UK generic PSCAD/ EMTDC electrical network model, with varying levels of SSEGs. Simulations were carried out examining cases with a uniform distribution of SSEGs contained within a number of SSEZs. It was observed that in some cases the reverse power flow capability of the primary transformers would exceed if each customer installed an SSEG with a rating of approximately 1 kW.

AC and DC aggregation effects of small-scale wind generators

Small-scale embedded generation (SSEG) has the potential to play an important part in the future UK generation mix. If a single SSEG is considered, its environmental, commercial and network operational value is low, but if a cluster of SSEGs are considered and their outputs aggregated they have the potential to be significantly more valuable. The aggregation of small-scale wind generators is considered. Each turbine is driven by a wind that is turbulent in nature and varies from location to location. The output from an individual turbine can be very variable, but when aggregated together with the power output from a number of turbines in the same locality, can produce a power output that is much less variable. The authors examine, by simulation, how the output from a number of small turbines can aggregate together to form a more consistent power output. Aggregation of the turbine outputs both after the power inverter, at alternating current (AC), and before the inverter, at direct current (DC), are examined. In both cases power variations are shown to reduce as the number of turbines connected increases. Aggregation at DC can lead to non-optimum performance of the turbine itself, if passive rectifiers are used, but can also lead to savings in the cost of the power conversion equipment required.

Small-scale embedded generation effect on voltage profile: an analytical method

Nowadays, deep concern is focused on the introduction of small-scale embedded generation (SSEG) in LV networks, since some technologies have a natural inclination to be easily integrated into urban LV distribution networks. As a consequence, studies on the effects produced on LV distribution systems by SSEG are gaining more and more relevance. Some aspects regarding the quality of the power supplied to customers are dealt with, taking into consideration long-duration voltage variations in the presence of SSEG. In particular, the effect on the voltage profile in a LV distribution feeder is examined with reference to both distributed loads and lumped loads. Some analytical expressions are derived to determine the limit value of the power that can be injected into a single node of a distribution feeder without causing overvoltages. The expressions derived for distributed loads are compared to those for lumped loads in order to assess if the analytical evaluation of the current threshold can be performed by means of an equivalent model based on continuous quantities with a negligible error, since actually, the analysis of real cases implies dealing with lumped loads.