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Islanding detection method of multi-port photovoltaic DC micro grid based on harmonic impedance measurement
摘要： DC Grid does not transmit reactive power, nor does it offer frequency and phase issues. This results in malfunction of conventional islanding detection methods (IDMs) that rely on the above quantities. At present, the DC IDMs proposed in literatures are mostly active power injection methods based on DC/DC converters. However, in a multi-photovoltaic (PV) DC system, the synchronization of the injection of converters is difficult to guarantee, which may lead to detection failure. This paper proposes an impedance measurement IDM for multi-PV DC micro grid based on the analysis of high-frequency impedance model of power electronic devices. The impedance of DC converters is constant at high frequency and the harmonic impedance of the system changes significantly after islanding, so that islanding operation can be accurately detected. The harmonic impedance change directly reflects the structural changes of the system, and its calculation requires less disturbance intensity, which avoids the requirement of synchronous injection. Therefore, the method uses a DC/DC converter for injection, without the need for additional injection equipment. The method has little influence on power quality and theoretically has no none detection zone. Simulation results show that the method can perform accurately islanding detection in multi-PV DC micro grid.
关键词： DC Grid,DC micro grid,photovoltaic,harmonic impedance measurement,islanding detection methods
更新于2025-09-16 10:30:52
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Factors contributing to degradation of organic photovoltaic cells
摘要： The performance of organic photovoltaic (OPV) cells has considerably improved over the past decade, and now exceeds an energy conversion efficiency of 10%, the benchmark for practical use. One factor contributing to this increase is the development of π-conjugated linear acceptor molecules as alternatives to fullerene derivatives. Although conversion efficiency is an important issue for practical applications, device stability is also necessary for commercialization of OPV technologies. To date, long-term stability has been examined in OPV devices based on fullerenes. However, the factors involved in performance degradation remain poorly understood. It is difficult to address this problem because of the multilayer nature of the devices and many factors involved in degradation. In recent OPV devices based on π-conjugated molecules as acceptors, there have been few reports on stability under continuous light irradiation. Ensuring the stability of the π-conjugated molecules under illumination and electrical operation is critical for achieving practical use of OPV devices. In this paper, we comprehensively analyzed OPV devices based on EH-IDTBR as an acceptor material. We identified a decrease in OPV performance of approximately 50% under 100-hour light irradiation, which we attribute to increased resistance of the organic semiconductor layer. The increase in resistance was caused by a decrease in the number of carriers, suggesting that structural changes in the EH-IDTBR molecule are an important factor affecting degradation.
关键词： Durability,impedance measurement,organic photovoltaic,stability,MALDI-TOF-MS
更新于2025-09-11 14:15:04
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Current Comparator Based Current Divider
摘要： The paper describes a current divider (or splitter), i.e., a device that allows the splitting of an alternating current (ac) in two parts in a precise and accurate current ratio. It is based on current comparator techniques so that precise current ratios can be attained with ratio errors bearing parts in 106 to 109. A binary current divider can be made virtually exact (i.e., with unitary current ratio errors of the order of some 10-9 only), if aided by electronic flux error compensation. Further, coupled transmission lines modeling can assess its current ratio errors over frequency. A current divider finds application in many areas of ac metrology as in highly accurate impedance bridges and current measurements.
关键词： Circuit and systems,current measurement,measurement uncertainty,measurement techniques,impedance measurement,current mode circuits
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Current Divider Based Impedance Comparator
摘要： The paper describes an ac impedance measurement comparator system which uses a current divider (or splitter). The divider makes use of a current comparator whose windings are connected in a way such as to allow the splitting of a single current signal in two components with very accurate ratio to be attained. Each current component flows through impedances to be compared. Preliminary investigations indicate that such an arrangement is able to provide very accurate impedance measurements with errors of parts in 106 or even smaller. Resolutions of parts in 109 were also experimentally achieved. Since the system uses a single ac current source, inherent current instabilities of the source cause negligible effects on differential voltage measurements, what alleviates requirements on the ac source. Digital sampling can easily be implemented with the system for speeded-up and automated impedance comparisons.
关键词： Circuit and systems,current measurement,Hall effect devices,measurement uncertainty,measurement techniques,impedance measurement,electronic circuits,electrical resistance
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Progress on a New Measurement of von Klitzing Constant at NIM
摘要： This paper describes the progress on a new measurement of von Klitzing constant (Rk) through an experiment linking the new calculable capacitor and the quantized Hall resistance by means of a quadrature transfer at NIM. The recent improvements of the new calculable capacitor, the optical interferometry, the impedance measurement chain are presented.
关键词： von Klitzing constant,optical interferometry,bridge circuits,Calculable capacitor,impedance measurement,measurement standards
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Progress on Simple Resistance Standard with Calculable Time Constant
摘要： This paper describes the progress on the development of the simple calculable bifilar resistors with nominal resistance below 100 W. The resistor have very simple and cheap construction that can be easily replicated. It is based on the ordinary circular cross-section resistance wire with enamel layer. Detailed characterization of the wire was made and thus the expanded uncertainty (k = 2) of the resistance is as low as 34 μW/W at 1 MHz. The expanded uncertainty of the time constant is below 0.11 ns (680 μrad/MHz).
关键词： impedance measurement,time constant,Calculable standards,resistor
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Four Terminal Pair Digital Sampling Impedance Bridge up to 1 MHz
摘要： This paper describes a new four terminal pair digital sampling impedance bridge for frequency range up to 1 MHz. The bridge was primarily designed for a calibration of a phase angle of the current shunts. However, the bridge is capable of comparing any impedance standards up to approximately 100 kW in a full complex plane. The experimental measurements of the known standards showed the bridge deviations is below 50 μW/W and below 500 μrad at 1 MHz.
关键词： Bridge circuits,sampling methods,impedance measurement,shunts (electrical),phase comparators
更新于2025-09-10 09:29:36
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Noise Behavior and Implementation of Interferometer-Based Broadband VNA
摘要： This paper analyzes and accurately models the complex noise behavior of vector network analyzers (VNAs) when measuring large-mismatch devices and subsequently shows how the VNA measurement noise performance is enhanced through implementation of a high-speed, broadband, active RF interferometer module. The presented VNA noise model provides a solid framework, benchmarked by measurement data, to analyze existing RF interferometer approaches. The performance improvement of the proposed interferometer implementation is then benchmarked in terms of magnitude and phase stability of the renormalized impedance level. A test bench employing the novel add-on RF interferometer module is presented and demonstrated to achieve high-speed cancellation of the scattered wave over a broad frequency band. The first experiment shows ultralow noise in a 1–18 GHz broadband measurement of co-planar waveguide 0.5-Ω and 5-kΩ impedance standards. Employing the proposed hardware setup improves the noise uncertainty for the 5-kΩ impedance standard by a factor of 8 and 20 at 1 and 18 GHz, respectively. In the second experiment, a factor of 2 height-resolution enhancement is achieved in a scanning microwave microscope when the RF interferometer module is added to the instrument.
关键词： vector network analyzer (VNA),impedance mismatch,noise,Extreme impedance measurement,microwave interferometry,nanoelectronics,nanostructures
更新于2025-09-09 09:28:46