Ac Modulation Research Articles

Unraveling surface and bulk trap states in lead halide perovskite solar cells using impedance spectroscopy

Organic–inorganic hybrid perovskites (OIHPs) have been widely recognized as an excellent candidate for next-generation photovoltaic materials because of their highly efficient power conversion. Acquiring a complete understanding of trap states and dielectric properties in OIHP-based solar cells at the steady state is highly desirable in order to further explore and improve their optoelectronic functionalities and properties. We report CH3NH3PbI3−xClx-based planar solar cells with a power conversion efficiency (PCE) of 15.8%. The illumination intensity dependence of the current density–voltage (J–V) revealed the presence of trap-assisted recombination at low fluences. Non-destructive ac impedance spectroscopy (ac-IS) was applied to characterize the device at the steady state. The capacitance–voltage (C–V) spectra exhibited some distinct variations at a wide range of ac modulation frequencies with and without photo-excitations. Since the frequency-dependent chemical capacitance is concerned with the surface and bulk related density of states (DOS) in CH3NH3PbI3−xClx, we verified this by fitting the corresponding DOS by a Gaussian distribution function. We ascertained that the electronic sub-gap trap states present in the solution processed CH3NH3PbI3−xClx and their distribution differs from the surface to the bulk. In fact, we demonstrated that both surfaces that were adjacent to the electron and hole transport layers featured analogous DOS. Despite this, photo- and bias-induced giant dielectric responses (i.e. both real and imaginary parts) were detected. A remarkable reduction of at higher frequencies (i.e. more than 100 kHz) was ascribed to the effect of dielectric loss in CH3NH3PbI3−xClx.

A comprehensive study of three high‐gain DC‐DC topologies based on Cockcroft‐Walton voltage multiplier for reduced power PV applications

This work provides a comprehensive study of three different topologies founded on the well‐known Cockcroft–Walton (CW) voltage multiplier for reduced power PV Applications. A comprehensive study and investigational outcomes of each converter are offered, and a detailed comparison among the three topologies is performed. The three topologies target AC module technology application, where every PV unit consumes its identifiable DC–DC converter. In AC PV module technology, PV generated‐voltage is fit for 30 V, and the available sum of power is less than 200 W. Converters for PV use are required to have great step‐up ability and higher efficiency as a result of the reduced output voltage of PV. The three topologies have some common benefits like high step‐up abilities and moderate efficiency. The three topologies are so‐called Switched‐Inductor with Voltage Multiplier (SIVM), high gain with voltage multiplier and Z‐Source with voltage multiplier (ZSVM). © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Modulation control of Impedance inverter for Maximum Output

India has seen a notable increase in adoption of the renewable energy, Various policies and schemes had been proposed in India to focalize on renewable energy sector. For solar energy conversion, an AC module that functions as a grid-connected inverter after a PV module is needed. ZSI is being used to alleviate a myriad of issues that VSI and CSI have. An impedance source inverter provided with triggering pulses generated by maximum boost control modulation technique is presented in this paper. The triggering pulses are generated by bringing the input sinusoidal and triangular waves on the same graph. Maximum boosted output can be achieved through this method just by adjusting its modulation index and shoot-through intervals.

A Class-G Voltage-Mode Doherty Power Amplifier

This paper presents the combination of two back-off efficiency enhancement techniques, the voltage-mode Doherty and the class-G switched-capacitor power amplifier (PA), to achieve efficiency peaking at both 6 and 12 dB back off without introducing the mode-switching glitches present in previous architectures. The proposed technique enables transmission of high peak-to-average-power ratio (PAPR) signals with high efficiency while maintaining excellent linearity. The PA is fabricated in 45-nm CMOS SOI with integrated balun for power combining and matching. At 3.5 GHz a saturated output power of 25.3 dBm is measured with 30.4%/25.3%/17.4% power added efficiency (PAE) at 0/6/12 dB back off. With memoryless, non-adaptive linearization, the PA achieves 19.2% PAE with −35.8 dB error vector magnitude (EVM) while transmitting a 40 MHz 256-QAM 10.1 dB PAPR 802.11ac modulation. Significant efficiency improvement compared to class-B and EVM better than −34 dB is maintained over more than 1 GHz bandwidth.

Enhancement of near infrared light sensing using side-gate modulation

The integration of nanostructures in electronic devices utilizes their unique quantum properties for realizing discrete measuring systems. Specifically, self-assembled organic monolayers and nanocrystals (NCs), together with bottom-up production methods, can lead to new types of electronic devices. In this work, we present a wavelength-tunable near-infrared detection device in which PbS NCs are used to create an optical gate for an AlGaAs/GaAs high electron mobility device. By integrating side gates, we were able to enhance light detection sensitivity by optimizing the conductivity of the channel. Both DC and AC modulations of the side gate were tested and compared in order to enhance the detector’s signal–to-noise ratio (SNR). Higher harmonic signals of the side gate modulation supply additional information about the detection mechanism.

PV-Module-Integrated AC Inverters (AC Modules) With Subpanel MPP Tracking

For small scale roof-top systems, there is a trend towards module-integrated electronics. Module integrated ac inverters (ac modules) connect each photovoltaic (PV) module separately to the single-phase grid. They feature not only increased yield due to module-level maximum power point (MPP) tracking, but also further advantages such as reduced installation cost. This work investigates the concept of subpanel-level MPP tracking for ac modules, which allows us to increase yield thanks to reduced mismatching losses. Topology concepts to realize such a converter are systematically investigated and categorized. A topology comparison identifies two promising system concepts: first a single-stage converter with a three-port power balancer and second a two-stage topology with three paralleled dc–dc converters and a pulse width modulation full bridge. The later features the advantage of a small power-decoupling capacitor and is therefore further investigated. A model-based optimization of the investigated multi-input ac module is performed, applying high performing Gallium Nitride (GaN) devices and nanocrystalline core materials to increase efficiency. The built prototype confirms the accuracy of the model-based optimization. The performed efficiency study reveals an achievable efficiency of $\eta _{\text{EU}}$ = 94.5%. In order to compete with single-input ac modules, achieving typically an efficiency of 95.5%, the efficiency of multi-input ac modules must improve beyond the level achieved with the investigated two-stage ac-module topology. Given this result, the alternative system concept with a three-port power balancer in combination with a single-stage converter seems to be more promising, as it is conceptually similar to the high efficient single-input ac modules and may achieve the same high efficiency.

Erratum: Enhancing the spin transfer torque in magnetic tunnel junctions by ac modulation [Phys. Rev. B 95 , 115417 (2017)

Erratum: Enhancing the spin transfer torque in magnetic tunnel junctions by ac modulation [Phys. Rev. B <b>95</b> , 115417 (2017)

ANALYSIS ON SOLAR PANEL PERFORMANCE AND PV-INVERTER CONFIGURATION FOR TROPICAL REGION

In this paper, proper inverter topology for tropical region will be determined with temperature effect as a considered factor. PV characteristics on certain temperature are obtained through mathematical equations in MATLAB-Simulink and it will be represented by PV I-V and P-V characteristic curves. Based on the modeling, some PV parameters such as temperature coefficients of short circuit current (ISC), open circuit voltage (VOC), maximum output power (PMAX), and maximum power voltage (VMP) can be determined as high as 0.56%/oC, -0.31%/oC -0.4%/oC, and 0.43 %/oC respectively. As the result, for tropical region, the central inverter is the most proper inverter topology to supply 5 kWAC PV system, string inverter in the 2nd place, and AC module with utility rates of 97.34%, 96.32 %, and 88.1% based on direct measurement on PV panel’s temperature respectively. From NOCT approach, the utility rates are around 92.96 % for central inverter, 91.98% for string inverter and 91.8 % for AC module.

AN EFFICIENT ASYMMETRICAL 15-LEVEL SMART INVERTER TOPOLOGIES FOR MICRO-GRID SYSTEM USING PSO-PID TUNING ALGORITHM

A unique fruitful problem solving platform in a global optimizing area has been implemented via particle swarm optimization. So far, most of the algorithms operate by ultimate usage of effective learning pattern, which process all the swarms used in a sufficient strategy. The grid connected AC module plays a perfect stand-by solution to co-power generation scheme. It combines both PV/FC as a single arrangement for proposed power conditioning topologies via effective control objective. This single module produces the constant output voltage as 100v to 400v from 10v to 40v input source by highly recognized boost converter and interfacing to gird system by proposed asymmetrical 15-level inverter topologies. The PSO-PID controller predicts the optimal modulation index & perfect switching angles for regulating the sudden variations from grid, eradicate the harmonics, improved voltage profile, better THD resolution. In this evaluation, proposed schemes support a pure sinusoidal current which is in-phase with grid outcome voltage. The proposed inverter topologies are validated with PSO-PID controller by advanced multi-carrier modulation schemes are evaluated by Matlab/Simulink platform, pertaining results are conferred.

Voltage Mode Doherty Power Amplifier

This paper presents a new wideband Doherty amplifier technique that can achieve high efficiency while maintaining excellent linearity. By modifying a “forgotten” topology originally proposed by Doherty, a new Doherty amplifier architecture is realized with two voltage mode power amplifiers (PAs) and transformers, thus eliminating a narrowband impedance inverter. The voltage mode PA is implemented using switched capacitor PA techniques. The PA is fabricated in 65-nm low-leakage CMOS and achieves 24-dBm saturated power (at the standard supply voltage) with PAE of 45% at peak power and 34% at 5.6-dB back-off over 750 to 1050 MHz 1 dB bandwidth. With memory-less linearization, the PA can transmit 40 MHz 256-QAM 9 dB peak-to-average power ratio 802.11ac modulation centered at 900 MHz meeting the spectral mask with measured EVM of -34.8 dB and 22% PAE without backing off or equalization.

Enhancing the spin transfer torque in magnetic tunnel junctions by ac modulation

The phenomenon of spin transfer torque (STT) has attracted a great deal of interests due to its promising prospects in practical spintronic devices. In this paper, we report a theoretical investigation of STT in a noncollinear magnetic tunnel junction under ac modulation based on the nonequilibrium Green's function formalism, and derive a closed-formulation for predicting the time-averaged STT. Using this formulation, the ac STT of a carbon-nanotube-based magnetic tunnel junction is analyzed. Under ac modulation, the low-bias linear (quadratic) dependence of the in-plane (out-of-plane) torque on bias still holds, and the $\sin\theta$ dependence on the noncollinear angle is maintained. By photon-assisted tunneling, the bias-induced components of the in-plane and out-of-plane torques can be enhanced significantly, about 12 and 75 times, respectively. Our analysis reveals the condition for achieving optimized STT enhancement and suggests that ac modulation is a very effective way for electrical manipulation of STT.

Two‐switch flyback inverter employing a current sensorless MPPT and scalar control for low cost solar powered pumps

Flyback inverter is known as a low cost solution for photovoltaic (PV) ac module application. This study presents a two-switch flyback inverter followed by a low frequency unfolding bridge for fractional horse power water pumping systems. This topology mitigates the problem of high-voltage transients at switch turn off which commonly exists in single switch flyback inverters. Moreover, the proposed control strategy achieves an integration of a novel sensorless maximum power point tracking (MPPT) algorithm as well as a constant v / f control for the efficient utilisation of both the PV panel and the motor. The proposed control algorithm minimises the cost and simplifies the control strategy. The validity and capability of the proposed method are verified by both simulation and practical results of a DSP-based two-switch flyback solar micro inverter for a fractional horsepower water pumping system.

Design of Dual Light Source Photoelectric Sludge Concentration Sensor

Provided a scheme of activated sludge sensor using dual AC modulation light source. This technique can overcome interferences under nature condition and do not need to clean frequently and lower the maintenance costs. Proved the feasibility by Lambert-Beer law and also designed a series of experiments to demonstrate the requirements have been reached.

Single‐stage AC module with series power decoupling capability for connecting PV to a single‐phase power grid

In single-phase grid-connected photovoltaic inverters, the input power is constant during the grid period, whereas the output power oscillates at double-line frequency. Therefore, electrolytic capacitors are widely used to handle the input and output power differences. However, these capacitors have short lifetime which degrade the inverter reliability. This paper proposes a control strategy to turn a conventional four-switch flyback-based inverter to an inverter equipped with a series power decoupling circuit. Therefore, a long lifetime film capacitor can be used as the main energy storage. The modified inverter has an inherent snubber circuit, which can restore energy of the transformer leakage inductance and improves its overall efficiency. The control strategy can realise maximum power point tracking and inject a sinusoidal low total harmonic distortion current to the grid. A 100 W prototype inverter has been built to verify operation and feasibility of the proposed control strategy.

A single switch hybrid DC/DC converter with extended static gain for photovoltaic applications

In this paper, a hybrid DC/DC converter with a single switch and a high static gain suitable for photovoltaic applications is presented. The proposed topology combines two classical DC/DC converters, allowing an improved step-up voltage gain and the reduction of the voltage stress of all the power devices. Another feature of this topology is that it provides a common ground for the input and midpoint of the output. Thus, in a two stage AC module structure, this converter can be connected to a half bridge transformerless voltage source inverter since it offers a neutral point terminal. A theoretical analysis of the proposed converter is also presented. To verify the performance of this DC/DC power converter, a prototype was developed and tested. From the obtained experimental results it is possible to confirm the expected performance of the proposed converter.

Plug‐in repetitive control of single‐phase grid‐connected inverter for AC module applications

This study presents two-stage inverter topology for single-phase grid-connected photovoltaic (PV) applications and its control implementations. The two-stage systems are reliable and work well. Typically, the second stage inverts solar power into AC power, whereas the first stage which is used to increase low PV panel voltage can achieve maximum power point tracking. In this configuration, a boost or a flyback type DC/DC converter topology is usually employed. However, such converters have major drawbacks such as low efficiency and limited voltage gain due to power losses. In the proposed topology, a low-voltage PV panel can be connected to power grid through solar inverter by using high-gain DC/DC converter which has unique features such as galvanic isolation and continuous current for AC module applications. Conventional controller results in poor control performance due to the finite gain at desired frequencies. Hence, a plug-in repetitive controller is proposed to obtain low total harmonic distortions (THDs). The performance of the proposed system is provided for the system which injects the PV panel current in the maximum power point voltage to a grid of 220 V (rms) at a power range of 150-300 W with a unity power factor and a low input current THD.

Flyback CCM inverter for AC module applications: iterative learning control and convergence analysis

ABSTRACTThis paper presents an iterative learning controller (ILC) for an interleaved flyback inverter operating in continuous conduction mode (CCM). The flyback CCM inverter features small output ripple current, high efficiency, and low cost, and hence it is well suited for photovoltaic power applications. However, it exhibits the non-minimum phase behaviour, because its transfer function from control duty to output current has the right-half-plane (RHP) zero. Moreover, the flyback CCM inverter suffers from the time-varying grid voltage disturbance. Thus, conventional control scheme results in inaccurate output tracking. To overcome these problems, the ILC is first developed and applied to the flyback inverter operating in CCM. The ILC makes use of both predictive and current learning terms which help the system output to converge to the reference trajectory. We take into account the nonlinear averaged model and use it to construct the proposed controller. It is proven that the system output globally converges to the reference trajectory in the absence of state disturbances, output noises, or initial state errors. Numerical simulations are performed to validate the proposed control scheme, and experiments using 400-W AC module prototype are carried out to demonstrate its practical feasibility.

Measurement of the electro-optic coefficient during the photoelectric-field assisted poling using a Mach-Zehnder interferometer.

This work describes the experimental apparatus based on the Mach-Zehnder interferometer for measuring the electro-optic coefficient during and after the photo-assisted poling process using a continuous light excitation. We also show that the poling can be performed at cryogenic temperatures. The setup is based on the superposition of a Mach-Zehnder AC modulation voltage on the DC bias voltage required to promote the chromophore orientation during light excitation. The effect of the reversible polarization due to the DC bias voltage applied to the polymer film is considered to calculate the electro-optic coefficient during the photo-assisted poling process. The usefulness of our setup is demonstrated with three polymer films, with different electro-optic activities: guest-host, copolymer, and homopolymer, all based on methyl methacrylate monomers and containing disperse red-1 chromophores.

Cycloconverter-Based Double-Ended Microinverter Topologies for Solar Photovoltaic AC Module

This paper investigates a novel half-bridge cycloconverter configuration on load side with devices operating at line frequency, thus providing direct high-frequency ac to line frequency ac conversion with transformer isolation. This paper also presents a detailed comparative study and evaluation of double-ended converters, viz., full-bridge, half-bridge, and push–pull-based microinverter topologies for solar photovoltaic ac module. Double-ended converters offer merits of no transformer saturation, reduced transformer, and filter size. Simple sinusoidal pulsewidth modulation for standalone mode and current control for grid-tied mode are implemented for front-end devices. Comparative study reveals that half-bridge topology is cheaper than the other two topologies and has comparable efficiency with full bridge. A 250-W laboratory prototype of half-bridge microinverter is developed, and experimental results are demonstrated to show its performance under various conditions, i.e., standalone, grid-tied, and change of current references.

A 10-kV/400-V 500-kVA Electronic Power Transformer

This paper presents the design and development of a three-phase 10-kV/400-V 500-kVA electronic power transformer (EPT). The power circuit is designed in a modular fashion, i.e., the main circuit consists of many identical ac–dc–dc–ac modules (abbreviated as power modules). Each power module consists of a high-voltage power cell, a low-voltage power cell (LVPC), a medium-frequency isolation transformer, and a filter. The corresponding control and protection system is developed. A special three-stage startup strategy is designed to shorten the startup time and reduce the startup inrush current. The negative-sequence current compensation is introduced in the input stage to handle the unbalanced loads. To keep the dc-link voltages balanced, an individual dc voltage balancing controller based on regulating the output power of each parallel LVPC is proposed. The detailed control hardware design and software implementation are discussed. The functions of this 10-kV EPT prototype are verified through the laboratory and field tests. The results are shown in this paper. Currently, the prototype is operating in the industrial power grid.