August 28th

Climate change: pay now or ask for credit?

An ethical as well as an economic question

If we continue business-as-usual, climate change — according to both the worst prognoses and the more optimistic ones — will confront humanity with serious consequences and a high price tag. However, the cost to society of mitigating climate change by reducing greenhouse gas emissions is also high. So inevitably, the question arises: what we should do? Pay today for mitigating climate change or pay later to deal with its consequences?

This question is most often presented as a mere economic problem. Not so, says John Broom in the Scientific American article 'The ethics of climate change'. The answer, he maintains, also entails ethical decisions.

John Broom refers to the 'Stern Review on the Economics of Climate Change' by Nicolas Stern and the UK Treasury, and to the studies of William Nordhaus at Yale University. While Stern concludes that urgent action to control Greenhouse Gas emissions is required, Nordhaus’s position is that the need to act is not acute. Broom identifies and explains the premises at the basis of this contradictory outcome.

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August 22nd

Distributed Generation and Renewable Energy Sources in Poland

Nowadays, in many countries the increase of generating capacity takes place in small units of so-called distributed generation (DG), and among them in hybrid power (generating) systems (HPS). They use primary energy conventional sources as well as renewable energy sources (RES), and in many cases produce electricity and heat (CHP). It is very often that definition of distributed generation is connected with definition of renewable energy sources.

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Control of a DFIG-based wind system in presence of large grid faults: analysis of voltage ride through capability

In this paper, the authors study a variable speed wind generation system based on Doubly Fed Induction Generator (DFIG) in case of large balanced voltage dip and analyzed a remedial solution that allows for the turbine to stay connected and helps grid recovery through reactive power injection, by supplying the grid with reactive power during faults. Simulation results show the effectiveness of the solution in different operating points of the four working regions of the power-speed turbine characteristic.

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August 21st

The contributions of American cities to global warming

A ranking according to carbon footprint per capita

As centres of energy consumption, the US metropolitan areas should play a leadership role in fighting climate change. That was the starting point for the report 'Shrinking the Carbon Footprint of Metropolitan America' by The Brookings Institution. The report investigates

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August 20th

Improving power quality with coordinated voltage control in networks with dispersed generation

Rapidly increasing share of distributed generation (DG) in distribution networks introduced the need for active distribution network operation. As current distribution networks were not designed to integrate the power generation, the DG introduced many technical challenges in sense of power quality, network planning, protection schemes, voltage stability…. This paper presents the advantages of active approach in distribution network operation.

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Power Quality Effects on the Measurement of Reactive Power in Three-Phase Power Systems in the Light of the IEEE Standard 1459-2000

Reactive power is a very important quantity in electric power systems since it affects the efficiency of these systems. Also, capacitive loads can produce over-voltages in electric transformers by Ferranti effect, which produces bad power quality, so it is necessary to measure the reactive power correctly. In this paper reactive phenomena in three-phase power systems with unbalanced voltages are expressed and measured in the light of the IEEE Std 1459-2000.

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August 19th

Optimal Measurement Devices Allocation for Harmonic State Estimation Considering Parameters Uncertainty in Distribution Networks

In many applications of power quality monitoring, distributed measurement systems are required to provide an evaluation of the harmonic status of the system. Anyway, in distribution systems, only a few network nodes can, with acceptable costs, be equipped with measurement devices. As a consequence, lack of information has to be covered by means of suitable Harmonic State Estimation (HSE) techniques.

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High Voltage Auxiliary Power Supply with the Simplified Power Circuit Topology for the DC Trains

The paper proposes a simplified power circuit topology for the auxiliary power supplies (APS) with output powers up to 50 kW to be used in 3.0 kV DC commuter trains. Focus is on the implementation of 6.5 kV IGBTs to improve power density, system integrity as well as the reliability of the APS. For instance, a topology proposal, an analysis and a comparison with other types is presented. Some problems of converter control and protection as well as hardware design considerations are discussed.

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Problems of passive filter application in systems with variable frequency

This paper is focused on problems of power quality in systems with varying frequency, equipped with passive harmonics filter. Main differences between the ship system and land network have been pointed out. Influence of varying frequency on proper work of harmonic passive filters frequency change was presented. Simulation circuit and simulations results of theoretical research have been described. Especially influence of frequency on proper work of 5th and 7th harmonic filters was commented on.

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August 15th

Decentralized control of a different rated parallel UPS systems

The paper presents the single phase uninterruptible power supply (UPS) system with galvanic separated DC-AC-DC-AC converters operating in parallel. The CAN physical layer based system of communication between converters has been developed and applied, which allow to utilize a decentralized master-slave control providing high availability factor of the whole UPS system. The control system of particular converters has been developed to ensure a high quality of the output voltage for both linear and nonlinear load.

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