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With the rapid increase of COVID-19 cases, identifying case severity has become a critical issue for hospital admission and intensive care treatment. Given that pre-existing comorbidities play a significant role in the severity, emerging evidence indicates coagulopathy becomes an independent condition that causes respiratory distress in COVID-19. In this metanalysis, relevant literatures reporting D-dimer, a coagulation byproduct, in COVID-19 cases were synthesized and statistically analyzed to test if the D-dimer level can predict case severity and mortality. The analysis found that D-dimer levels were higher in non-survivors/severe than in survivors/non-severe, (MD 0.64, 95% CI 0.52 to 0.75; participants = 5957, I2 = 98%). Subgroup analysis showed MD between non-survivors and survivors was MD 3.48 μg/mL (95% CI 2.69 to 4.27; participants = 1799; studies = 7; I2 = 86%) with Z-score 8.64, p

To extract maximum power from solar panel, it is essential to use different types of Maximum Power Point Tracking (MPPT) algorithms. But these algorithms need rigorous testing before it can be applied practically on Photovoltaic (PV) panel which is troublesome due to higher dependence on solar irradiance, large space requirements if power rating increases etc. These reasons lead to develop a PV emulator with acceptable performance which cost less than the commercially available PV emulators. In this paper, design of a PV emulator with resistive load is proposed to mimic the characteristics of real PV sources for different power rating and specifications. The design of the power and control stages has been validated by simulation results. Finally, the PV emulator is used for battery charging through MPPT controlled DC-DC boost converter. The results are compared with the real PV panel and it is found that they are in close agreement. This new testing bed is more flexible in terms of emulating different ratings and brands of solar panel. This portable PV emulator also provides controlled regulation in terms of irradiance and temperature which leads to more tunable optimization of MPPT controllers.

Induction heating (IH) converters operate just above resonant frequency, at near unity power factor (UPF), to supply power to the targeted work-piece. Some power electronic converter-fed IH systems use power control strategies based on dynamic tracking of the changing resonant frequency as the work-piece gets heated up (since inductance changes). Therefore, the correct in-process determination of the resonant frequency is essential. A method of dynamically detecting the resonant frequency is by calculating the phase-shift between current and voltage continuously during the process. In case of CSI- (and VSI-) fed IH, the phase-shift between voltage and current is zero at resonant frequency. Hence one way of identifying the resonant frequency is by varying the frequency until the phase-shift is zero. For controlling this phase-shift between current and voltage waveforms, most of the controllers use a phase-locked loop (PLL) IC. In this paper, a novel method for the dynamic tracking of resonant frequency is proposed and the practical implementation of the same, using a field-programmable gate array (FPGA) based digital-PLL, is presented. The scheme is first simulated with generated off-line signal samples and then implemented on a real-time model of a CSI-fed IH application. Finally, the digital-PLL logic is implemented on controller hardware and practically tested in a laboratory-made experimental set-up of 2 kW at a nominal frequency of 10 kHz. The switching frequency is auto-synchronising. This fact is practically verified both by varying (i) the geometric dimensions as also (ii) the initial temperature of the work-piece. It is practically observed in the oscillograms that the phase gets locked in few cycles (and hence ensures quick tracking of the dynamically changing resonant frequency for this set-up).

A brief study on a commutation strategy for a current source inverter (CSI)-fed parallel resonant circuit, using switches formed by IGBTs with series diodes, is presented in this paper. The dynamic behaviour of the inverter and different strategies for its reliable operation are discussed here considering parasitic inductance and overlap time between CSI switching devices. The dynamic behaviour of the switches decides the upper frequency limit for the application. IGBTs with the series diodes behave as uni-directional current switches with bi-directional voltage blocking capability. This feature should be taken into account to decide on an appropriate switching strategy for this converter configuration.

A study on the control methodology of voltage source inverter (VSI) fed series resonant circuit for induction heating has been done in this work with the goal that converter can be worked at about unity power factor. In this work, phase locked loop (PLL) has been accustomed to bring the converter’s switching frequency near to the natural frequency of series coil and capacitor branch of induction heater. Using this control method, the effectiveness of induction heater can be improved and necessity of input power is turned out to be less when compare to the fixed frequency operation. This control technique gives reliable operation of voltage source inverter fed circuit for varying load. Controlled phase locked loop gives increment or decrement in resonance frequency corresponding to the phase difference in voltage and current of resonant circuit. The coil of the induction heater is utilized as load in the resonant circuit of inverter. This power control procedure enables the inverter to operate near to the natural frequency for controlling power at all level. In this work, ZVS (zero-voltage switching) and ZCS (zero-current switching) condition has been obtained, and the switching losses are minimized. Pulse density modulated (PDM) power control method has been simulated to control the output power of a half bridge VSI fed induction heater.

Modern induction heating (IH) power converters operate marginally above resonant frequency to supply power to the targeted work-piece at near unity power factor (upf). The resonant frequency continuously increases as the work-piece gets heated up. A possible method of dynamically detecting the resonant frequency may be to calculate the phase-shift between current and voltage continuously during the process. The phase-shift between voltage and current is ideally zero at resonance. So resonant frequency may be identified by varying the frequency until the phase-shift is zero. For this some controllers use a phase-locked loop (PLL) strategy. In this paper, the dynamic tracking of resonant frequency, using a field-programmable gate array (FPGA) based digital-PLL, is presented. The scheme is first simulated off-line. Finally, the logic is implemented on controller hardware and practically tested in a laboratory made experimental set-up of 2kW at around 10kHz.

Induction heating is commonly used in the industry for the metal heating, melting, hardening etc. The power converter used is a current source inverter (CSI). High power medium frequency application like melting use thyristor based CSIs, while in medium power and high frequency induction heating application (like surface heat treatment) IGBT based CSIs are increasingly preferred. In this paper simulated and experimental performance of an SCR-based CSI and IGBT based CSI in series cascade (with common dc-link) have been presented. Two laboratory prototypes of rating 2kW, 10kHz each have been fabricated and tested, both individually and then in series cascade. Cascade mode operation of CSIs may find important application in multi-stage surface heat treatment of metals.