A new medium-voltage PWM inverter topology for adjustable-speeddrives

In this paper, a new pulsewidth modulation (PWM) inverter topology suitable for medium-voltage (2300/4160 V) adjustable-speed drive systems is proposed. The modular inverter topology is derived by combining three standard three-phase inverter modules and a 0.33-pu output transformer. The output voltage is high-quality multistep PWM with low dv/dt. Further, the approach also guarantees balanced operation and 100% utilization of each three-phase inverter module over the entire speed range. These features enable the proposed topology to be suitable for powering constant-torque, as well as variable-torque type loads. Clean power utility interface of the proposed inverter system can be achieved via an 18-pulse input transformer. Analysis, simulation and experimental results are shown to validate the concepts     

Virtual-flux-based direct power control of three-phase PWMrectifiers

In this paper, direct power control (DPC) of three-phase pulsewidth-modulated rectifiers without line voltage sensors is presented. The new system is based on virtual flux (VF) estimation. Theoretical principles of this method are discussed. The steady-state and dynamic behavior of VF-DPC are presented that illustrate the operation and performance of the proposed system compared to a conventional DPC method. Both strategies are also investigated under unbalance and predistorted grid. It is shown that the VF-DPC exhibits several advantages, particularly providing sinusoidal line current when the supply voltage is not ideal. Test results show the excellent performance of the proposed system     

Optimization of switching frequencies in the limited-pool randomspace vector PWM strategy for inverter-fed drives

A space vector PWM technique for inverter fed AC drives which, in contrast with known random modulation methods, is characterized by a very small pool of randomly used switching frequencies, is presented. The limited size of the pool facilitates design of digitally implemented subsystems of the drive, whose settings depend on the length of sampling interval. A method for optimal selection of pool frequencies is described and validated by experimental evidence, including EMI measurements     

Power Scaling of End-Pumped Solid-State Rod Lasers by Longitudinal Dopant Concentration Gradients

The power scalability of solid-state rod lasers in general is limited by the thermally induced mechanical stress approaching the fracture stress of the laser material. In conventional end-pumped lasers, the spatial heat-generation density profiles follow a nearly exponential law, resulting in a reduction of the maximum possible pump power when compared with a transversally pumped rod of the same length. In this paper, an approach for power scaling of end-pumped solid-state lasers by employing crystals with longitudinally varying dopant concentration profiles is presented. The optimum continuously varying dopant concentration profiles for a pump-light single and double pass are derived. Multisegmented crystals approximate these continuous doping profiles. An algorithm for optimizing the segment lengths and dopant concentrations in these crystals is described, the resulting optimum segment data are tabulated, and the relative power capability of these crystals is given.     

Sensorless DTC-SVM for Induction Motor Driven by a Matrix Converter Using a Parameter Estimation Strategy

This paper presents a new direct torque controlled space vector modulated method to improve the sensorless performance of matrix converter drives using a parameter estimation scheme. The flux and torque error are geometrically combined in a new flux leakage vector to make a stator command voltage vector in a deadbeat manner. A new sensorless method of estimating the rotor speed, flux, stator resistance, and rotor resistance is derived and verified with experimental results. Common terms in the error dynamics are utilized to find a simpler error model involving some auxiliary variables. Using this error model, the state estimation problem is converted into a parameter estimation problem assuming the rotor speed is constant. The proposed adaptive schemes are determined so that the whole system is stable in the sense of Lyapunov. The effectiveness of the proposed algorithm is verified by experiments.     

Evaluation of growth hormone assays using ratio plots

To permit comparison between growth hormone (GH) results obtained using the Pharmacia polyclonal assay and the Delfia monoclonal assay, we used both methods to measure GH concentrations in peak GH responses to the pyridostigmine-growth-hormone-releasing-hormone (PD-GHRH) test and in unstimulated samples from 40 healthy adults and 31 patients with suspected GH deficiency. Ratio plots were used for the comparison, and acceptability criteria were based on inherent analytical imprecision and on analytical quality specifications. The mean ratio (r; Pharmacia/Delfia) for the peak GH responses in 40 healthy adults was calculated to be 1.59, and the 95% prediction interval for ratios fulfilling the imprecision criterion was applied. For GH values >1 mIU/L, the peak and unstimulated GH ratios in healthy adults and patients were within the 95% prediction interval, and fulfilled the biological criterion as well. Therefore, the conversion factor of 1.59 is applicable for the evaluation of GH-stimulation tests.     

Random pulse width modulation techniques for converter-fed drivesystems-a review

Random pulse width modulation (RPWM) techniques for voltage-controlled power electronic converters have been attracting an increasing interest due to the unique effects of these techniques on the converter-supplied drive systems. A number of RPWM strategies have been reported and a beneficial impact on the acoustic noise and vibration has been unanimously agreed upon. The paper presents a synthetic review of the state of the art in the RPWM theory and practice. Topics covered include principles of RPWM, means of randomization, review of the existing RPWM techniques, power spectra, implementation issues, and documented effects of RPWM on electric drive systems     

Analysis of milkfat by HPLC

A routine method for HPLC analysis of milkfat has been developed, which takes into account the specific phenomena of this complex and far-ranging system of triglycerides. The usual amount of injection of 1 mg has been reduced to 30 or 10 μg of fat. By this the composition of the mobile phase (acetone:acetonitrile, 35/65) and the temperature of the column (Nucleosil C18-5 μ, 15 cm + Microspher C18-3μ, 10 cm, in series, T=30–35 C) could be adjusted to a relatively high selectivity without inducing the high-melting fat components to crystallize on the column. A further advantage resulting from this consisted in permitting the eluent to be recycled over long periods of time. The extremely low amounts of samples necessitated a highly sensitive detection (Δn=5 × 10⁻⁷ RI units full scale deflection) which could be realized by an interferential refractometer in connection with a thermostat to keep up a stable temperature of the whole HPLC system (ΔT<0,005 K). By this it was possible to separate milkfat into 45 to 50 different types of triglycerides. By comparing soft and hard milkfats and fractions of milkfats, every fourth peak, starting with C 42, could be attributed to saturated triglycerides; apart from this, easily recognizable qualitative features appearing in the chromatograms permitted conclusions about the feeding regimen and energy supply of the cattle. Furthermore, due to the high stability of separating conditions achieved and due to computer software developed for this purpose it was possible to obtain and compare a large number of chromatograms under the same conditions.     

Renewable energy and the need for local energy markets

In Denmark, a technological change towards cleaner energy technologies has been developed and implemented since around 1975. This development has had two phases: The first from 1975 until around 1996, when wind power was a niche production that supplied only 3.5% of the electricity consumption and was brought close to cost competitiveness, and the present second phase, in which wind power supplies an increasing share (in 2004 18.6%) of electricity consumption along with combined heat and power plants, which supply around 50% of consumption. Denmark succeeded in overcoming the first phase, and a large green energy technology cluster was established. During the second phase, new difficulties and challenges have arisen, both with regard to local public acceptance and the need for integrating an increasing percentage of fluctuating energy sources into the energy system. In this Phase 2, a new offensive green energy policy should be introduced in order to secure both public and political acceptance. Local markets should be established in order to secure the technical integration of a large proportion of wind power and other fluctuating renewable energy sources into the energy system.