Search Results (9)

This paper explores a current distortion problem in totem-pole bridgeless power factor correction (PFC) converters with average current mode (ACM) control. With in-depth modeling for the current and voltage loops, it was found that the current distortion is caused by the limited current loop bandwidth and input filter capacitor. These factors lead to the presence of a susceptance component in the input admittance, which degrades the power factor (PF) and total harmonic distortion (THD) of the PFC converter. To solve this problem, this paper proposes virtual admittance feedforward compensation (VAFC) and phase correction methods to adjust the input admittance to pure conductance. The VAFC can generate virtual admittance that compensates for susceptance components in the input admittance, while phase correction can generate an equivalent current source that offsets the current in input capacitors. Furthermore, a phase lock loop (PLL) is introduced to realize the VAFC, which reduces the feedforward interference caused by input voltage sampling noise. Finally, an experimental prototype was built to verify the effectiveness of the proposed strategies. According to the test results, the proposed compensation strategy improves the PF by 1.23%, while reducing the THD by 2.52% and achieving a peak efficiency of 98.69%. Full article

The results of systematic studies of the electrospark alloying process with the introduction of dispersed materials into plasma of low-voltage pulsed discharges are presented. Technological methods have been developed for supplying the powder material straight into the treatment zone through a hollow electrode of an anode or from the side, with the electrode-anode periodically contacting the substrate of cathode. It has been established that under the same energy regimes, when powder materials were introduced into the discharge zone, the increase in the mass of the cathode per time unit increases from 10 to 15 times or more. This study presents the process of synthesis of carbide phases (TiC and WC) during electrospark alloying of steel substrates with electrodes made of Ti, W, and graphite, with additional supply powders of these materials into the processing zone. A process has been developed for the synthesis of ternary compounds, so-called MAX-phases: Ti₂AlC, Ti₂AlN and Ti₃SiC₂ by electrospark alloying with powder compositions TiAlC, TiAlN and TiSiC. These MAX phases exhibit a unique combination of properties that are characteristic of both metals and ceramics. Energy modes of the processing were optimized, which resulted in high-quality coatings with the maximum content of carbide phases and ternary compounds. It has been established that the energy of electrical pulses during electrospark alloying, when powders of materials are fed into the interelectrode gap, ranges from 0.8 to 3.0 J, depending on their thermal physical properties. High wear and corrosion resistant characteristics of C45 structural steel with such electrospark coatings are obtained. The wear of steel with coatings in comparison with uncoated steel decreased by an average of 5.5–6.0 times. It was estimated the high corrosion resistance of 40X13 steel coated with TiC and WC in 3% NaCl solution. The corrosion current for these coatings is 0.044 and 0.075 A/cm², respectively, and is significantly less than for coatings made of TiAlC, TiAlN, and TiSiC compositions. X-ray phase and optical metallographic microscopy analyses enabled the display of the amorphous-crystalline nature of the coatings. Full article

In this paper, a new control scheme for buck converters was proposed. The buck converter utilizes the dual control loop to improve transient response and has the constant switching frequency. The control scheme is mainly as follows: (a) The switch-ON time is regulated by the constant frequency mechanism. (b) The switch-OFF time is regulated by the output voltage. The spec/features of the proposed converter are listed as: (1) The buck converter has an output of 1.0–2.5 V for the input of 3.0–3.6 V. The load current ranges from 100 mA to 500 mA. (2) The actual current sensor is not required. (3) The simulation results show that the recovery time is less than 1.6 μs during load changes. (4) The variation in switching frequency is smaller than 1.05% over the output range of 1.0–2.5 V. (5) This circuit can be fabricated in future by UMC 0.18 μm 1P6M CMOS processes. This paper depicts the control scheme, theoretical analysis, and implementation. Full article

This paper presents the first design that combines pseudospark-sourced (PS) electron beams with a multiple-beam extended interaction oscillator (EIO). The PS electron beam is an excellent choice for driving EIOs because it has high current density and does not require a focusing magnetic field. The EIO with coaxial structure adopts the method of multiple electron beams, which plays a crucial role in improving the average output power. At the same frequency, the EIO operating in the high-order TM₃₁-3π mode has a larger cavity size than the EIO operating in the traditional TM₀₁-2π mode. The high-order TM₃₁-3π mode solves the problem of the EIO’s manufacture at high frequency. In order to verify the above points, a G-band PS multiple-beam EIO operating in TM₃₁-3π mode has been designed. The beam–wave interaction particle-in-cell simulation results show that the EIO’s peak output power is 39.2 kW at 217 GHz, and that its efficiency is around 6.1%. The EIO with six pencil beams operates at a voltage of 43 kV. The total current of the six electron beams is 15 A (equally distributed among the six beams), and the corresponding current density is about 5000 A/cm². Considering the ohmic loss and the effect of skin depth, the conductivity used in these simulations is 2 × 10⁷ S/m. The design is an excellent way to improve the output power of EIO operating at high frequency. Full article

A wire arc additive manufacturing system, based on cold metal transfer technology, was utilized to manufacture the Al-Mg alloy walls. ER5556 wire was used as the filler metal to deposit Al-Mg alloys layer by layer. Based on the orthogonal experiments, the process parameters of the welding current, welding speed and gas flow, as well as interlayer residence time, were adjusted to investigate the microstructure, phase composition and crystal orientation as well as material properties of Al-Mg alloyed additive. The results show that the grain size of Al-Mg alloyed additive becomes smaller with the decrease of welding current or increased welding speed. It is easier to obtain the additive parts with better grain uniformity with the increase of gas flow or interlayer residence time. The phase composition of Al-Mg alloyed additive consists of α-Al matrix and γ (Al₁₂Mg₁₇) phase. The eutectic reaction occurs during the additive manufacturing process, and the liquefying film is formed on the α-Al matrix and coated on the γ phase surface. The crystal grows preferentially along the <111> and <101> orientations. When the welding current is 90 A, the welding speed is 700 mm/min, the gas flow is 22.5 L/min and the interlayer residence time is 5 min, the Al-Mg alloy additive obtains the highest tensile strength. Under the optimal process parameters, the average grain size of Al-Mg alloyed additive is 25 μm, the transverse tensile strength reaches 382 MPa, the impact absorption energy is 26 J, and the corrosion current density is 3.485 × 10⁻⁶ A·cm⁻². Both tensile and impact fracture modes of Al-Mg alloyed additive are ductile fractures. From the current view, the Al-Mg alloys manufactured by WAAM-CMT have a better performance than those produced by the traditional casting process. Full article

This paper proposes a novel control scheme for the buck converter without an inductor current sensor. The architecture of the proposed buck converter is simple and suitable for integration and mass production. It employs an output-voltage-measurement method to determine the switch ON time; therefore, the current sensor is not required. The design specification targets the application with a standard battery power source to generate the low voltages for low-power MCU or ASIC. The load current range aims for several hundred milliamps. The proposed control scheme is analyzed and simulated by SIMPLIS. The control scheme, theoretical analysis, circuit realization, contributions, advantages, and simulation results are presented in this paper. Furthermore, the circuit can be fabricated by a 0.35 μm CMOS process. Full article

This paper presents a novel buck converter with dual-loop control technology, which does not need to detect the inductor current directly. The structure of the control loops is easy to implement, one loop controls the output voltage, and the other controls the switching frequency. With the dual loops control mechanism, the output voltage and switching frequency can be accurately controlled only by measuring the output and input voltage, without sensing the inductor current. The buck converter can generate an output voltage of 1.0–2.5 V when the input voltage and load current are 3.0–3.6 V and 100–500 mA, respectively. The design was verified by SIMPLIS. The simulation results show that the switching frequency variation is less than 1% at the output voltage of 1.0–2.5 V. The recovery time is less than 1.5 μs during the load change. The circuit can be fabricated by using the TSMC 0.35μm 2P4M CMOS processes. The control scheme, theoretical analysis and circuit implementation are presented in this paper. Full article

Lithium-ion batteries are the most used technology in portable electronic devices. High energy density and high power per mass battery unit make it preferable over other batteries. The existing constant-temperature and constant-voltage charging technique (CT–CV), with a closed loop, lacks a detailed design of control circuits, which can increase charging speed. This article addresses this research gap in a novel way by implementing a simpler feedback proportional integral and differential (PID) control to a closed-loop CT–CV charging circuit. Voltage-mode control (VMC) and average current-mode control (ACM) methods were implemented to maintain the battery voltage, current, and temperature at safe limits. As per simulation results, 23% faster charging is achieved by implementing VMC and almost 50% faster charging is attained by employing the ACM technique in the PID controller. Our proposed control strategy is validated experimentally, which yields up to 25% faster charging of a battery than the reference battery. Full article

This paper presents a buck converter with a novel constant frequency controlled technique, which employs the proposed frequency detector and adaptive on-time control (AOT) logic to lock the switching frequency. The control scheme, design concept, and circuit realization are presented. In contrast to a complex phase lock loop (PLL), the proposed scheme is easy to implement. With this novel technique, a buck converter is designed to produce an output voltage of 1.0–2.5 V at the input voltage of 3.0–3.6 V and the maximum load current of 500 mA. The proposed scheme was verified using SIMPLIS and MathCAD. The simulation results show that the switching frequency variation is less than 1% at an output voltage of 1.0–2.5 V. Furthermore, the recovery time is less than 2 μs for a step-up and step-down load transient. The circuit will be fabricated using UMC 0.18 μm 1P6M CMOS processes. The control scheme, design concept and circuit realization are presented in this paper. Full article