Shunt active filter for reactive power compensation

A simple control technique for three-phase shunt active filters without computation of the reactive current component is presented. A current controller with fast dynamics for an active filter is described. Reactive current is directly controlled without the need for sensing and computing the reactive component of the load current, thus simplifying the control system. Current compensation is done in the time domain, allowing a fast time response. The dc voltage control loop keeps the voltage across the dc capacitor constant. High power factor control by an active filter is described. All control functions are implemented in software using a singlechip microcontroller, thus simplifying the control circuit. Any current-controlled synchronous rectifier can be used as a shunt active filter through only the simple modification of the software and the addition of current sensors. It is shown through experimental results that the proposed controller gives good performance for the shunt active filter.     

The influence of enhanced closed-loop sensitivity towards breathing-type structural damage

This paper investigates the performance of a nonlinear damage detection method using sensitivity enhancing control (SEC). Damage nonlinearity due to the cyclic behavior of crack breathing could provide valuable evidence of structural damage without information of the structure’s original healthy condition. Not having such information is considered a major challenge in vibration-based damage detection. In this study, two different categories of damage detection methods are investigated: frequency and time-domain techniques focusing on the benefit of SEC for breathing-type nonlinear damage in a structure. Numerical simulations using a cantilevered beam and spring-mass-damper system demonstrated that the level of nonlinear dynamic behavior heavily depends on the closed-loop pole placement through feedback control. According to SEC theory, the characteristic of the feedback gain defines the sensitivity of modal frequency to the change of stiffness or mass of the system. The sensitivity enhancement by properly designed closedloop pole location more visually clarifies the evidence of crack nonlinearity than the open-loop case where no sensitivity is enhanced. A damage detection filter that uses time series data could directly benefit from implementing SEC. The amplitude of damage-evident error signal of the closed-loop case significantly increases more than that of the open-loop case if feedback control or SEC properly modifies the dynamics of the system.     

Switching technique for current-controlled AC-to-AC converters

The AC-to-AC converter called the matrix converter is very simple in structure and has powerful controllability. However, there are few practical applications, particularly in power electronics fields. The major reasons largely lie in the commutation problem and complexity of the control circuit. This paper proposes a novel commutation technique which is very simple to implement. This commutation scheme allows the deadtime to avoid current spikes of nonideal switches and, at the same time, establishes a current path of the inductive load to avoid voltage spikes. A switching technique of the matrix converter using a space-vector-modulation (SVM) based hysteresis current controller (HCC) is also proposed. The switching technique is implemented without any computational burden and is controlled with a simple control circuit. This technique utilizes advantages of the HCC and SVM technique. Simulation and experimental results obtained on a 5 kW single-phase AC chopper and an 11 kW three-phase to three-phase matrix converter are discussed     

ZnO nanorods, nanotubes and nanorings: controlled synthesis and structural properties

Controlled synthesis of ZnO nanorods (ZNRDs), nanotubes (ZNTs) and nanorings (ZNRs) has been carried out by a two-step sonochemical/chemical process at room temperature without any catalyst, template or seed layer. The crystallinity, structure and morphology of ZNRDs, ZNRs and ZNTs were examined by X-ray diffraction (XRD) analysis, scanning electron micrographs (SEM), high resolution transmission electron microscope (HR-TEM) and selected area electron diffraction (SAED). The as-prepared ZnO nanostructures were single crystalline with hexagonal cross-section and uniform size. The effect of precursor concentration on the growth and that of the etching duration on the hollow formation were analyzed, and the obtained results revealed that the precursor concentration and etching time play an important role in determining final morphologies of the samples. By tuning the etching time, the precise size control of ZNTs and ZNRs was achieved. Possible formation mechanisms of these nanostructures are proposed based on the experimental results.     

A novel single-stage half-bridge AC-DC converter with high powerfactor

A new single-stage AC-DC power converter based on a half-bridge converter suitable for low-power applications is proposed. The proposed converter offers high power factor and direct conversion from the line voltage to an isolated DC output voltage. High power factor is achieved by adding a resonant circuit between the rectifying diodes and half-bridge leg. For soft switching, a half-bridge series-loaded resonant converter is adopted as a DC-DC converter part. A prototype is built and tested to show the validity of the proposed converter     

A novel SVM-based hysteresis current controller

In this paper, a novel space vector modulation (SVM)-based hysteresis current controller (HCC) for squirrel cage induction motors is proposed. This technique utilizes all advantages of the HCC and SVM technique. The controller determines a set of space vectors from a region detector and applies a space vector selected according to the main HCC. A set of space vectors including the zero vector to reduce the number of switchings is determined from the sign of the output frequency and output signals of three comparators with a little larger hysteresis band than that of the main HCC. A simple hardware implementation is proposed and experimental results of the SVM-based HCC are also shown     

Improved single-phase line-interactive UPS

An improved single-phase line-interactive uninterruptible power supply (UPS) is proposed for low-power applications with low cost. The proposed UPS is comprised of two push-pull converters based on a low-voltage battery for reduced cost: one in series with the input and the other in parallel with the load. In the presence of input power, the UPS acts as an output voltage regulator and at the same time as an active filter while charging the battery. In case of loss of input power, the UPS supplies a regulated sinusoidal voltage to the load, drawing power from the battery. The series converter compensates only a small percentage of the input voltage carrying the input current and, therefore, a reduced rating is made. The parallel converter always supplies a nominal voltage and makes a seamless transition to backup mode. In the voltage determination of the parallel converter, the nominal voltage is derived using the feedback linearization concept and then a perturbed voltage is determined for the reactive power control or output voltage regulation. Experimental results obtained from a 1-kVA prototype are discussed     

Novel line conditioner with voltage up/down capability

In this paper, a novel pulsewidth-modulated line conditioner with fast output voltage control is proposed. The line conditioner is made up of an AC chopper with reversible voltage control and a transformer for series voltage compensation. In the AC chopper, a proper switching operation is achieved without the commutation problem. To absorb energy stored in line stray inductance, a regenerative DC snubber can be utilized which has only one capacitor without discharging resistors or complicated regenerative circuit for snubber energy. Therefore, the proposed AC chopper gives high efficiency and reliability. The output voltage of the line conditioner is controlled using a fast sensing technique of the output voltage. It is also shown via some experimental results that the presented line conditioner gives good dynamic and steady-state performance for high quality of the output voltage.     

Stability improvement of V/f-controlled induction motor drive systems by a dynamic current compensator

Stability improvement of V/f-controlled induction motor drive systems by a dynamic current compensator is proposed. The proposed method uses a dynamic current compensator to improve the stability of the V/f-controlled induction motor drive systems. This method is easy to implement and helps eliminate the oscillations causing the instability of V/f-controlled induction motor drive systems.