A direct integration scheme for battery-supercapacitor hybrid energy storage systems with the use of grid side inverter

Battery-supercapacitor hybrid energy storage systems are becoming popular in the renewable energy sector due to their improved power and energy performances. These hybrid systems require separate dc-dc converters, or at least one dc-dc converter for the supercapacitor bank, to connect them to the dc-link of the grid interfacing inverter. These additional dc-dc converters increase power losses, complexity and cost. Therefore, possibility of their direct connection is investigated in this paper. The inverter system used in this study is formed by cascading two 3-level inverters, named as the “main inverter” and the “auxiliary inverter”, through a coupling transformer. In the test system the main inverter is connected with the rectified output of a wind generator while the auxiliary inverter is directly attached to a battery and a supercapacitor bank. The major issues with this approach are the dynamic changes in dc-link voltages and inevitable imbalances in the auxiliary inverter voltages, which results in unevenly distributed space vectors. A modified SVM technique is proposed to solve this issue. A PWM based time sharing method is proposed for power sharing between the battery and the supercapacitor. Simulation results are presented to verify the efficacy of the proposed modulation and control techniques.

Grid-side cascade inverter system as an interface for wind energy storage

Additional converters that are used to interface energy storage devices incur power losses as well as increased system cost and complexity. The need for additional converters can be eliminated if the grid side inverter can itself be effectively used as the interface for energy storage. This paper therefore proposes a technique whereby the grid side inverter can also be used as an interface to connect a supercapacitor energy storage for wind energy conversion systems. The proposed grid side inverter is formed by cascading a 3-level inverter and a 2-level inverter through a coupling transformer. The three-level inverter is the main inverter and it is powered by the rectified output of the wind turbine coupled AC generator while the 2-level auxiliary inverter is connected to the super capacitor bank that is used to compensate short term power fluctuations. Novel modulation and control techniques are proposed to address the problems associated with non-integer and dynamically-changing dc-link voltage ratio, which is caused by the random nature of wind. Simulation results are presented to verify the efficacy of the proposed system in suppressing short term wind power fluctuations.

Impacts of tillage and application methods on atrazine and alachlor losses from upland fields: Research paper

The effects of tillage practises and the methods of chemical application on atrazine and alachlor losses through run-off were evaluated for five treatments: conservation (untilled) and surface (US), disk and surface, plow and surface, disk and preplant-incorporated, and plow and preplant-incorporated treatments. A rainfall simulator was used to create 63.5 mm h^-1 of rainfall for 60 min and 127 mm h^-1 for 15 min. Rainfall simulation occurred 24-36 h after chemical application. There was no significant difference in the run-off volume among the treatments but the untilled treatment significantly reduced erosion loss. The untilled treatments had the highest herbicide concentration and the disk treatments were higher than the plow treatments. The surface treatments showed a higher concentration than the incorporated treatments. The concentration of herbicides in the water decreased with time. Among the experimental sites, the one with sandy loam soil produced the greatest losses, both in terms of the run-off volume and herbicide loss. The US treatments had the highest loss and the herbicide incorporation treatments had smaller losses through run-off as the residue cover was effective in preventing herbicide losses. Incorporation might be a favorable method of herbicide application to reduce the herbicide losses by run-off.

Application of power electronics in improving power quality and supply efficiency of AC traction networks

Major advances in power electronics during recent years have prompted considerable interest within the traction community. The capability of new technologies to reduce the AC railway networks' effect on power quality and improve their supply efficiency is expected to significantly decrease the cost of electric rail supply systems. Of particular interest are Static Frequency Converter (SFC), Rail Power Conditioner (RPC), High Voltage Direct Current (HVDC) and Energy Storage Systems (ESS) solutions. Substantial impacts on future feasibility of railway electrification are anticipated. Aurizon, Australia's largest heavy haul railway operator, has recently commissioned the world's first 50Hz/50Hz SFC installation and is currently investigating SFC, RPC, HVDC and ESS solutions. This paper presents a summary of current and emerging technologies with a particular focus on the potential techno-economic benefits.

Minimization of Torque Ripple in PWM AC Drives

A pulsewidth modulation (PWM) technique is proposed for minimizing the rms torque ripple in inverter-fed induction motor drives subject to a given average switching frequency of the inverter. The proposed PWM technique is a combination of optimal continuous modulation and discontinuous modulation. The proposed technique is evaluated both theoretically as well as experimentally and is compared with well-known PWM techniques. It is shown that the proposed method reduces the rms torque ripple by about 30% at the rated speed of the motor drive, compared to conventional space vector PWM.

FPGA based digital platform for the control of AC drives

This paper presents the new trend of FPGA (Field programmable Gate Array) based digital platform for the control of power electronic systems. There is a rising interest in using digital controllers in power electronic applications as they provide many advantages over their analog counterparts. A board comprising of Cyclone device EP1C12Q240C8 of Altera is used for developing this platform. The details of this board are presented. This developed platform can be used for the controller applications such as UPS, Induction Motor drives and front end converters. A real time simulation of a system can also be done. An open-loop induction motor drive has been implemented using this board and experimental results are presented.

Improved Algorithms for Reservoir Capacity Calculation Incorporating Storage-Dependent Losses and Reliability Norm

Two algorithms that improve upon the sequent-peak procedure for reservoir capacity calculation are presented. The first incorporates storage-dependent losses (like evaporation losses) exactly as the standard linear programming formulation does. The second extends the first so as to enable designing with less than maximum reliability even when allowable shortfall in any failure year is also specified. Together, the algorithms provide a more accurate, flexible and yet fast method of calculating the storage capacity requirement in preliminary screening and optimization models.

Simple new PWM patterns for thyristor three-phase AC/DC convertors

Thyristor forced commutated AC/DC convertors are useful for improving the power factor and waveform of AC-side line current. These are controlled through pulse-width modulation schemes for best performance. However, the 3-phase versions impose restrictions on the PWM strategies that can be implemented for excellent harmonic rejection. This paper presents new PWM control strategies for the 3-phase converters and compares them along with the conventional 4-pulse PWM strategy for harmonic elimination. Finally, two new PWM strategies are shown to be the best, for which oscillograms are presented from actual implementation.

Sediment and nutrient losses from exotic Pinus plantation management operations under simulated rainfall

Rainfall simulation experiments were carried out to measure runoff and soil water fluxes of suspended solids, total nitrogen, total phosphorus, dissolved organic carbon and total iron from sites in Pinus plantations on the coastal lowlands of south-eastern Queensland subjected to various operations (treatments). The operations investigated were cultivated and nil-cultivated site preparation, fertilised site preparation, clearfall harvesting and prescribed burning; these treatments were compared with an 8-y-old established plantation. Flow-weighted mean concentrations of total nitrogen and total phosphorus in surface runoff from the cultivated and nil-cultivated site-preparation, clearfall harvest, prescribed burning and 8-y-old established plantation treatments were very similar. However, both the soil water and the runoff from the fertilised site preparation treatment contained more nitrogen (N) and phosphorus (P) than the other treatments - with 3.10 mg N L-1 and 4.32 mg P L-1 (4 and 20 times more) in the runoff. Dissolved organic carbon concentrations in runoff from the nil-cultivated site-preparation and prescribed burn treatments were elevated. Iron concentrations were highest in runoff from the nil-cultivated site-preparation and 8-y-old established plantation treatments. Concentrations of suspended solids in runoff were higher from cultivated site preparation and prescribed burn treatments, and reflect the great disturbance of surface soil at these sites. The concentrations of all analytes were highest in initial runoff from plots, and generally decreased with time. Total nitrogen (mean 7.28, range 0.11-13.27 mg L-1) and total phosphorus (mean 11.60, range 0.06-83.99 mg L-1) concentrations in soil water were between 2 and 10 times greater than in surface runoff, which highlights the potential for nutrient fluxes in interflow (i.e. in the soil above the water table) through the general plantation area. Implications in regard to forest management are discussed, along with results of larger catchment-scale studies.

Easy to build four-terminal AC bridge

A simple four-terminal AC bridge is described which can be used with germanium resistance thermometers down to 1 K. The special features of the bridge are its ease of fabrication and extremely low cost.

A Simple Multiple Pulsewidth Modulated AC Choppe

A simple multiple pulsewidth modulated (MPWM) ac chopper using power transistors for 3-ý power control is discussed. 120ý chopping period is used for main transistors so that the circuit can accommodate resistive and lagging or leading power factor loads. Only 1-ý sensing is used for 3-ý control. An alternate economical power and control schemes for 3-ý MPWM ac choppers suitable only for resistive loads is also suggested. The experimental results for 12 choppings per cycle are given.

Cooking in the ungra area: Fuel efficiency, energy losses, and opportunities for reducing firewood consumption

Cooking efficiency and related fuel economy issues have been studied in a particular rural area of India. Following a description of the cooking practices and conditions in this locale, cooking efficiency is examined. A cooking efficiency of only 6% was found. The use of aluminium rather than clay pots results in an increased efficiency. In addition, cooking efficiency correlates very well with specific fuel consumption. The latter parameter is much simpler to analyse than cooking efficiency. The energy losses during cooking are examined in the second part of this case study. The major energy losses are heating of excess air, heat carried away by the combustion products, heat transmitted to the stove body and floor, and the chemical energy in charcoal residue. The energy loss due to the evaporation of cooking water is also significant because it represents about one-third of the heat reaching the pots.

Evaluation of Charges for Power Transmission and Losses in Bilateral Power Contracts

The paper presents a method for transmission loss charge allocation in deregulated power systems based on Relative Electrical Distance (RED) concept. Based on RED between the generator and load nodes and the predefined bilateral power contracts, charge evaluation is carried out. Generally through some power exchange mechanism a set of bilateral contracts are determined that facilitate bilateral agreements between the generation and distribution entities. In this paper the possible charges incurred in meeting loads like generation charge, transmission charge and charge due to losses are evaluated. Case studies have been carried out on a few practical equivalent systems. Due to space limitation results for a sample 5 bus system are presented considering ideal load/generation power contracts and deviated load/generation power contracts. Extensive numerical testing indicates that the proposed allocation scheme produces loss allocations that are appropriate and that behave in a physically reasonable manner.

Losses of nitrogen in surface runoff from a plantation horticulture farm in coastal Queensland, Australia.

Surface losses of nitrogen from horticulture farms in coastal Queensland, Australia, may have the potential to eutrophy sensitive coastal marine habitats nearby. A case-study of the potential extent of such losses was investigated in a coastal macadamia plantation. Nitrogen losses were quantified in 5 consecutive runoff events during the 13-month study. Irrigation did not contribute to surface flows. Runoff was generated by storms at combined intensities and durations that were 20–40 mm/h for >9 min. These intensities and durations were within expected short-term (1 year) and long-term (up to 20 years) frequencies of rainfall in the study area. Surface flow volumes were 5.3 ± 1.1% of the episodic rainfall generated by such storms. Therefore, the largest part of each rainfall event was attributed to infiltration and drainage in this farm soil (Kandosol). The estimated annual loss of total nitrogen in runoff was 0.26 kg N/ha.year, representing a minimal loading of nitrogen in surface runoff when compared to other studies. The weighted average concentrations of total sediment nitrogen (TSN) and total dissolved nitrogen (TDN) generated in the farm runoff were 2.81 ± 0.77% N and 1.11 ± 0.27 mg N/L, respectively. These concentrations were considerably greater than ambient levels in an adjoining catchment waterway. Concentrations of TSN and TDN in the waterway were 0.11 ± 0.02% N and 0.50 ± 0.09 mg N/L, respectively. The steep concentration gradient of TSN and TDN between the farm runoff and the waterway demonstrated the occurrence of nutrient loading from the farming landscapes to the waterway. The TDN levels in the stream exceeded the current specified threshold of 0.2–0.3 mg N/L for eutrophication of such a waterway. Therefore, while the estimate of annual loading of N from runoff losses was comparatively low, it was evident that the stream catchment and associated agricultural land uses were already characterised by significant nitrogen loadings that pose eutrophication risks. The reported levels of nitrogen and the proximity of such waterways (8 km) to the coastline may have also have implications for the nearshore (oligotrophic) marine environment during periods of turbulent flow.

Gaseous Nitrogen Losses Following Soil Amendment with Biosolids under Controlled Conditions.

This paper quantifies gaseous N losses due to ammonia volatilisation and denitrification under controlled conditions at 30 degrees C and 75% to 150% of Field Capacity (FC). Biosolids were mixed with two contrasting soils from subtropical Australia at a rate designed to meet crop N requirements for irrigated cotton or maize (i.e., equivalent to 180 kg N ha(-1)). In the first experiment, aerobically (AE) and anaerobically (AN) digested biosolids were mixed into a heavy Vertosol soil and then incubated for 105 days. Ammonia volatilization over 72 days accounted for less than 4% of the applied NH4-N but 24% (AN) to 29% (AE) of the total applied biosolids' N was lost through denitrification in 105 days. In the second experiment AN biosolids with and without added polyacrimide polymer were mixed with either a heavy Vertosol or a lighter Red Ferrosol and then incubated for 98 days. The N loss was higher from the Vertosol with 16-29% of total N applied versus the Red Ferrosol with 7-10% of total N applied, while addition of polymer to the biosolids increased N loss from 7 to 10% and from 16 to 29% in the Red Ferrosol and Vertosol, respectively. A major product from the denitrification process was N-2 gas, accounting for >90% of the emitted N gases from both experiments. Our findings demonstrate that denitrification could be a major pathway of gaseous N losses under warm and moist conditions.