Peter Brønnum Nielsen

A new matrix converter motor (MCM) for industry applications

The trend in electrical drives is to integrate the frequency converter, the electrical motor, and even the gear or the pump into a single unit, in order to reduce the costs, to increase the overall efficiency and the equipment reliability. This paper presents the first integrated regenerative frequency converter motor for industry applications, based on a matrix converter topology. The low volume, the sinusoidal input current, the bidirectional power flow, and the lack of the bulky and limited-lifetime electrolytic capacitors recommend this topology for this application. This paper shows how the matrix converter disadvantages-the lack of bidirectional power devices, the lower voltage transfer ratio, and the overvoltages caused by the input filter during power-up-that have delayed the industrial implementation have been overcome. In order to demonstrate the validity of the solution, a 4-kW matrix converter motor prototype is built using a standard frequency converter motor enclosure for testing the requirements for an industrial drive. The tests demonstrate the good performance of the drive.

New protection issues of a matrix converter: design considerations for adjustable-speed drives

Induction motors are traditionally controlled by standard pulsewidth modulation voltage-source inverters. An alternative is the matrix converter, which consists of nine bidirectional switches. This converter has benefits compared to a standard inverter, like sinusoidal input current and bidirectional power flow. The main disadvantage is the lack of a bidirectional switch, because such a switch may be done by two transistors and two diodes. An important topic is protection of the matrix converter, and this paper proposes two new protection circuits for matrix converters with a reduced number of components. The number of protection diodes is reduced by six. Design expressions of the protection circuit are calculated and validated by simulation. The standard protection circuit and the new circuits are demonstrated by simulation to have the same performance. Experimental results on an 8 kVA matrix converter show the design expressions are correct. It is concluded that it is possible to reduce the necessary power components in a matrix converter.

Space vector modulated matrix converter with minimized number of switchings and a feedforward compensation of input voltage unbalance

This paper presents a new double-sided modulation strategy for matrix power converters based upon an indirect conversion scheme which models the matrix converter as two independent stages performing rectification and inversion. The new modulation strategy keeps the number of switchings at a minimum. This paper shows that the indirect conversion scheme contains insufficient information to achieve the minimum. The new strategy establishes a link between the two modulations. Numerical simulations as well as analytical results show a reduction of more than 10% of the switchings compared to the conventional strategy. It is shown that the indirect conversion scheme is quite useful in the analysis of the input voltage unbalance. A feedforward compensation method based upon measurements of the instantaneous values of all three input voltages is presented. It is shown that, with a further restriction on the voltage transfer ratio, it is possible to operate the power converter with balanced output voltages, even when input voltages are unbalanced.

Comparative effectiveness and safety of non-vitamin K antagonist oral anticoagulants and warfarin in patients with atrial fibrillation: propensity weighted nationwide cohort study

Objective To study the effectiveness and safety of the non-vitamin K antagonist oral anticoagulants (novel oral anticoagulants, NOACs) dabigatran, rivaroxaban, and apixaban compared with warfarin in anticoagulant naïve patients with atrial fibrillation. Design Observational nationwide cohort study. Setting Three Danish nationwide databases, August 2011 to October 2015. Participants 61 678 patients with non-valvular atrial fibrillation who were naïve to oral anticoagulants and had no previous indication for valvular atrial fibrillation or venous thromboembolism. The study population was distributed according to treatment type: warfarin (n=35 436, 57%), dabigatran 150 mg (n=12 701, 21%), rivaroxaban 20 mg (n=7192, 12%), and apixaban 5 mg (n=6349, 10%). Main outcome measures Effectiveness outcomes defined a priori were ischaemic stroke; a composite of ischaemic stroke or systemic embolism; death; and a composite of ischaemic stroke, systemic embolism, or death. Safety outcomes were any bleeding, intracranial bleeding, and major bleeding. Results When the analysis was restricted to ischaemic stroke, NOACs were not significantly different from warfarin. During one year follow-up, rivaroxaban was associated with lower annual rates of ischaemic stroke or systemic embolism (3.0% v 3.3%, respectively) compared with warfarin: hazard ratio 0.83 (95% confidence interval 0.69 to 0.99). The hazard ratios for dabigatran and apixaban (2.8% and 4.9% annually, respectively) were non-significant compared with warfarin. The annual risk of death was significantly lower with apixaban (5.2%) and dabigatran (2.7%) (0.65, 0.56 to 0.75 and 0.63, 0.48 to 0.82, respectively) compared with warfarin (8.5%), but not with rivaroxaban (7.7%). For the combined endpoint of any bleeding, annual rates for apixaban (3.3%) and dabigatran (2.4%) were significantly lower than for warfarin (5.0%) (0.62, 0.51 to 0.74). Warfarin and rivaroxaban had comparable annual bleeding rates (5.3%). Conclusion All NOACs seem to be safe and effective alternatives to warfarin in a routine care setting. No significant difference was found between NOACs and warfarin for ischaemic stroke. The risks of death, any bleeding, or major bleeding were significantly lower for apixaban and dabigatran compared with warfarin.

Restarting Anticoagulant Treatment After Intracranial Hemorrhage in Patients With Atrial Fibrillation and the Impact on Recurrent Stroke, Mortality, and Bleeding A Nationwide Cohort Study

Background— Intracranial hemorrhage is the most feared complication of oral anticoagulant treatment. The optimal treatment option for patients with atrial fibrillation who survive an intracranial hemorrhage remains unknown. We hypothesized that restarting oral anticoagulant treatment was associated with a lower risk of stroke and mortality in comparison with not restarting. Methods and Results— Linkage of 3 Danish nationwide registries in the period between 1997 and 2013 identified patients with atrial fibrillation on oral anticoagulant treatment with incident intracranial hemorrhage. Patients were stratified by treatment regimens (no treatment, oral anticoagulant treatment, or antiplatelet therapy) after the intracranial hemorrhage. Event rates were assessed 6 weeks after hospital discharge and compared with Cox proportional hazard models. In 1752 patients (1 year of follow-up), the rate of ischemic stroke/systemic embolism and all-cause mortality (per 100 person-years) for patients treated with oral anticoagulants was 13.6, in comparison with 27.3 for nontreated patients and 25.7 for patients receiving antiplatelet therapy. The rate of ischemic stroke/systemic embolism and all-cause mortality (per 100 person-years) for recurrent intracranial hemorrhage, the rate of ischemic stroke/systemic embolism, and all-cause mortality (per 100 person-years) patients treated with oral anticoagulants was 8.0, in comparison with 8.6 for nontreated patients and 5.3 for patients receiving antiplatelet therapy. The adjusted hazard ratio of ischemic stroke/systemic embolism and all-cause mortality was 0.55 (95% confidence interval, 0.39–0.78) in patients on oral anticoagulant treatment in comparison with no treatment. For ischemic stroke/systemic embolism and for all-cause mortality, hazard ratios were 0.59 (95% confidence interval, 0.33–1.03) and 0.55 (95% confidence interval, 0.37–0.82), respectively. Conclusions— Oral anticoagulant treatment was associated with a significant reduction in ischemic stroke/all-cause mortality rates, supporting oral anticoagulant treatment reintroduction after intracranial hemorrhage as feasible. Future trials are encouraged to guide clinical practice in these patients.

A new modulation method for matrix converters

This paper presents a new modulation method for matrix converters based on the indirect modulation model. During the switching period, the proposed modulation method uses a combination of only one active vector and a zero vector in the inversion stage to achieve minimum flux error, while in the rectification stage a single current vector is selected, according to the error of the input current vector angle. This reduces the number of switching sequences in the switching period, improving the accuracy of generating the output voltage vector especially in the low modulation index range. Supplementary, the direct control of the input current vector is implemented. The estimation of the angle of the input current vector is done by applying the inverse transformation, that corresponds to the applied active vector, to the output currents.

Monitoring long-term efficacy of iron chelation therapy by deferiprone and desferrioxamine in patients with beta-thalassaemia major: application of SQUID biomagnetic liver susceptometry.

Summary. In this non‐randomized prospective study, liver and spleen iron concentrations were monitored annually over a 4‐year period by non‐invasive Superconducting Quantum Interference Device biomagnetometry in 54 β‐thalassaemia major patients (age, 7–22 years) receiving treatment with deferiprone (75 mg/kg/d). Median liver iron concentrations increased significantly from 1456 to 2029 and 2449 µg/gliver at baseline, after 2·0 and 3·2 years respectively. Another group of 51 thalassaemic patients (aged 4–34 years) who received desferrioxamine s.c. for 1·9 years increased their liver iron concentration from 1076 to 1260 µg/gliver. Taking into account the increase of the daily iron input from transfusions of 3·6 mg/d, caused by weight gain in 67% of the patients treated with deferiprone, a larger total body iron elimination rate was achieved after 2 years than at baseline. A negative ferritin change was observed in 51% of the patients. In 15 non‐splenectomized patients, liver iron significantly increased from 1260 to 1937 µg/gliver (P < 0·01), but serum ferritin remained stable at 2100 µg/l, as did the spleen iron concentration at 1200 µg/gspleen. A two‐compartment model may predict an average chelation efficacy for desferrioxamine and deferiprone, with a saturation effect of the latter, for a certain chelation and transfusion regimen by a single liver iron quantification.

A new matrix converter-motor (MCM) for industry applications

The trend in electrical drives is to integrate the frequency converter, the electrical motor and even the gear or the pump into a single unit, in order to reduce the costs and to increase the overall efficiency and the equipment reliability. This paper presents the first integrated regenerative frequency converter-motor for industry applications, based on a matrix converter topology. The low volume, the sinusoidal input current, the bi-directional power flow and the lack of the bulky and limited-lifetime electrolytic capacitors recommend this topology for this application. This paper shows how the matrix converter disadvantages-the lack of bi-directional power devices, the lower voltage transfer ratio, the lack of ride-through capability and the overvoltages caused by the input filter during power-up-which have delayed the industrial implementation, have been overcome. In order to demonstrate the validity of the solution, a 4 kW matrix converter-motor (MCM) prototype is built using a standard frequency converter-motor enclosure and tested to meet the requirements for an industrial drive.

Effectiveness and safety of reduced dose non-vitamin K antagonist oral anticoagulants and warfarin in patients with atrial fibrillation: propensity weighted nationwide cohort study

Objective To examine clinical effectiveness and safety of apixaban 2.5 mg, dabigatran 110 mg, and rivaroxaban 15 mg compared with warfarin among patients with atrial fibrillation who had not previously taken an oral anticoagulant. Design Propensity weighted (inverse probability of treatment weighted) nationwide cohort study. Setting Individual linked data from three nationwide registries in Denmark. Participants Patients with non-valvular atrial fibrillation filling a first prescription for an oral anticoagulant from August 2011 to February 2016. Patients who filled a prescription for a standard dose non-vitamin K antagonist oral anticoagulant (novel oral anticoagulants, NOACs) were excluded. To control for baseline differences in the population, a propensity score for receipt of either of the four treatment alternatives was calculated to apply an inverse probability treatment weight. Intervention Initiated anticoagulant treatment (dabigatran 110 mg, rivaroxaban 15 mg, apixaban 2.5 mg, and warfarin). Main outcome measures Patients were followed in the registries from onset of treatment for the primary effectiveness outcome of ischaemic stroke/systemic embolism and for the principal safety outcome of any bleeding events. Results Among 55 644 patients with atrial fibrillation who met inclusion criteria, the cohort was distributed according to treatment: apixaban n=4400; dabigatran n=8875; rivaroxaban n=3476; warfarin n=38 893. The overall mean age was 73.9 (SD 12.7), ranging from a mean of 71.0 (warfarin) to 83.9 (apixaban). During one year of follow-up, apixaban was associated with higher (weighted) event rate of ischaemic stroke/systemic embolism (4.8%), while dabigatran, rivaroxaban, and warfarin had event rates of 3.3%, 3.5%, and 3.7%, respectively. In the comparison between a non-vitamin K antagonist oral anticoagulant and warfarin in the inverse probability of treatment weighted analyses and investigation of the effectiveness outcome, the hazard ratios were 1.19 (95% confidence interval 0.95 to 1.49) for apixaban, 0.89 (0.77 to 1.03) for dabigatran, and 0.89 (0.69 to 1.16) for rivaroxaban. For the principal safety outcome versus warfarin, the hazard ratios were 0.96 (0.73 to 1.27) for apixaban, 0.80 (0.70 to 0.92) for dabigatran, and 1.06 (0.87 to 1.29) for rivaroxaban. Conclusion In this propensity weighted nationwide study of reduced dose non-vitamin K antagonist oral anticoagulant regimens, apixaban 2.5 mg twice a day was associated with a trend towards higher rates of ischaemic stroke/systemic embolism compared with warfarin, while rivaroxaban 15 mg once a day and dabigatran 110 mg twice a day showed a trend towards lower thromboembolic rates. The results were not significantly different. Rates of bleeding (the principal safety outcome) were significantly lower for dabigatran, but not significantly different for apixaban and rivaroxaban compared with warfarin.

A new energy optimizing control strategy for switched reluctance motors

This paper describes a new and machine-independent method to minimize the energy consumption of a speed controlled switched reluctance motor (SRM). The control strategy is to vary the duty cycle of the applied DC voltage in order to obtain the desired speed quickly and when operating in steady-state vary the turn-on angle (a/sub on/) of the phase voltage to minimize the energy consumption. The power flow is measured in the DC-link and used to control the turn-on angle. Simulations carried out on a three-phase 6/4 pole SRM justify the algorithm and the physical implementation in a Siemens SAB 80C517A microcontroller is described. Measurements on two different load systems show it is possible to minimize the energy consumption on-line in a speed controlled switched reluctance motor without losing the dynamic performance. A comparison with an ordinary mode-shift controlled SRM shows more than an 8% increase in overall efficiency for some operation points. The algorithm is fully applicable to other switched reluctance motors at other power levels or with other pole configurations. >