A Decade-Bandwidth Low-Noise Mixer RFIC with a Distortion-Canceling Output Amplifier

This paper presents a 1-10 GHz low-noise downconvert mixer RFIC suitable for wideband receivers. A switched transconductor mixing core is adopted to reduce noise at high frequencies. By adding a series inductor to the RF transconductor, a flat 4-5 dB noise figure (NF) and a high gain of 26.5 dB can be achieved over a broad bandwidth out to 10 GHz. A CMOS output amplifier is also integrated on-chip, employing derivative superposition (DS) for high linearity and an OIP3 of 16.5 dBm. The circuit consumes less than 20 mW of dc power and occupies an active chip area of less than 0.2 mm2.

Series-L/parallel-tuned Class-E power amplifier analysis

An analysis of the operation of a new series-L/parallel-tuned Class-E amplifier and its equivalence to the classic shunt-C/series-tuned Class-E amplifier are presented. The first reported closed form design equations for the series-L/parallel-tuned topology operating under ideal switching conditions are given, including the switch current and voltage in steady state, the circuit component values, the peak values of switch current and voltage and the power-output capability. Theoretical analysis is confirmed by numerical simulation for a 500 mW (27 dBm), 10% bandwidth, 5 V series-L/parallel-tuned, then, shunt-C/series-tuned Class-E power amplifier, operating at 2.5 GHz. Excellent agreement between theory and simulation results is achieved.

Voltage and current spectra for matrix power converters

Matrix power converters are used for transforming one alternating-current power supply to another, with different peak voltage and frequency. There are three input lines, with sinusoidally varying voltages which are 120◦ out of phase one from another, and the output is to be delivered as a similar three-phase supply. The matrix converter switches rapidly, to connect each output line in sequence to each of the input lines in an attempt to synthesize the prescribed output voltages. The switching is carried out at high frequency and it is of practical importance to know the frequency spectra of the output voltages and of the input and output currents. We determine in this paper these spectra using a new method, which has significant advantages over the prior default method (a multiple Fourier series technique), leading to a considerably more direct calculation. In particular, the determination of the input current spectrum is feasible here, whereas it would be a significantly more daunting procedure using the prior method instead.

Implications of low breakdown voltage of component subcells on external quantum efficiency measurements of multijunction solar cells

The electrical and optical coupling between subcells in a multijunction solar cell affects its external quantum efficiency (EQE) measurement. In this study, we show how a low breakdown voltage of a component subcell impacts the EQE determination of a multijunction solar cell and demands the use of a finely adjusted external voltage bias. The optimum voltage bias for the EQE measurement of a Ge subcell in two different GaInP/GaInAs/Ge triple-junction solar cells is determined both by sweeping the external voltage bias and by tracing the I–V curve under the same light bias conditions applied during the EQE measurement. It is shown that the I–V curve gives rapid and valuable information about the adequate light and voltage bias needed, and also helps to detect problems associated with non-ideal I–V curves that might affect the EQE measurement. The results also show that, if a non-optimum voltage bias is applied, a measurement artifact can result. Only when the problems associated with a non-ideal I–V curve and/or a low breakdown voltage have been discarded, the measurement artifacts, if any, can be attributed to other effects such as luminescent coupling between subcells.

A low frequency MEMS energy harvester scavenging energy from magnetic field surrounding an AC current-carrying wire

This paper reports on a low frequency piezoelectric energy harvester that scavenges energy from a wire carrying an AC current. The harvester is described, fabricated and characterized. The device consists of a silicon cantilever with integrated piezoelectric capacitor and proof-mass that incorporates a permanent magnet. When brought close to an AC current carrying wire, the magnet couples to the AC magnetic field from a wire, causing the cantilever to vibrate and generate power. The measured average power dissipated across an optimal resistive load was 1.5 μW. This was obtained by exciting the device into mechanical resonance using the electro-magnetic field from the 2 A source current. The measurements also reveal that the device has a nonlinear response that is due to a spring hardening mechanism.

Supporting mature-aged students from a low socioeconomic background

The aim of the current study was to examine mature-aged student perceptions of university support services and barriers to study. Using a mixed methods approach, interviews and focus groups were conducted with mature-aged students to identify barriers to study, knowledge and use of current student support services, and suggestions to improve upon these services. From these data and an audit of university support services, an online survey was created to examine study barriers and patterns of support service use, as well as, perceptions of proposed support services not currently offered by the university within a larger sample of mature-aged students. Analysis of survey data indicated distinct patterns of barriers and support service use according to socioeconomic status as well as other demographic factors such as, age and enrolment status. Study findings are discussed in terms of generating support services for the retention of mature-aged students of low socioeconomic status and for the retention of mature-aged students in general.

EMI issues in high power and high level diode-clamped converters

Planar busbar is a good candidate to reduce interconnection inductance in high power inverters compared with cables. However, power switching components with fast switching combined with hard switched-converters produce high di/dt during turn off time and busbar stray inductance then becomes an important issue which creates overvoltage. It is necessary to keep the busbar stray inductance as low as possible to decrease overvoltage and Electromagnetic Interference (EMI) noise. In this paper, the effect of different transient current loops on busbar physical structure of the high-voltage high-level diode-clamped converters will be highlighted. Design considerations of proper planar busbar will also be presented to optimise the overall design of diode-clamped converters.

Self-commutated current source converter with multi-level current reinjection

The multi-level current reinjection concept described in literature is well-known to produce high quality AC current waveforms in high power and high voltage self-commutating current source converters. This paper proposes a novel reinjection circuitry which is capable of producing a 7-level reinjection current. It is shown that this reinjection current effectively increases the pulse number of the converter to 72. The use of PSCAD/EMTDC simulation validates the functionality of the proposed concept illustrating its effectiveness on both AC and DC sides of the converter.

Optimal allocation and sizing of capacitors to minimize the transmission line loss and to improve the voltage profile

To allocate and size capacitors in a distribution system, an optimization algorithm, called Discrete Particle Swarm Optimization (DPSO), is employed in this paper. The objective is to minimize the transmission line loss cost plus capacitors cost. During the optimization procedure, the bus voltage, the feeder current and the reactive power flowing back to the source side should be maintained within standard levels. To validate the proposed method, the semi-urban distribution system that is connected to bus 2 of the Roy Billinton Test System (RBTS) is used. This 37-bus distribution system has 22 loads being located in the secondary side of a distribution substation (33/11 kV). Reducing the transmission line loss in a standard system, in which the transmission line loss consists of only about 6.6 percent of total power, the capabilities of the proposed technique are seen to be validated.

Corona discharges on the surfaces of high voltage composite insulators

The degradation of high voltage electrical insulation is a prime factor that can significantly influence the reliability performance and the costs of maintaining high voltage electricity networks. Little information is known about the system of localized degradation from corona discharges on the relatively new silicone rubber sheathed composite insulators that are now being widely used in high voltage applications. This current work focuses on the fundamental principles of electrical corona discharge phenomena to provide further insights to where damaging surface discharges may localize and examines how these discharges may degrade the silicone rubber material. Although water drop corona has been identified by many authors as a major cause of deterioration of silicone rubber high voltage insulation until now no thorough studies have been made of this phenomenon. Results from systematic measurements taken using modern digital instrumentation to simultaneously record the discharge current pulses and visible images associated with corona discharges from between metal electrodes, metal electrodes and water drops, and between waters drops on the surface of silicone rubber insulation, using a range of 50 Hz voltages are inter compared. Visual images of wet electrodes show how water drops can play a part in encouraging flashover, and the first reproducible visual images of water drop corona at the triple junction of water air and silicone rubber insulation are presented. A study of the atomic emission spectra of the corona produced by the discharge from its onset up to and including spark-over, using a high resolution digital spectrometer with a fiber optic probe, provides further understanding of the roles of the active species of atoms and molecules produced by the discharge that may be responsible for not only for chemical changes of insulator surfaces, but may also contribute to the degradation of the metal fittings that support the high voltage insulators. Examples of real insulators and further work specific to the electrical power industry are discussed. A new design concept to prevent/reduce the damaging effects of water drop corona is also presented.

Investigation of shaft voltage in wind turbine systems with induction generators

This paper presents the analysis of shaft voltage in different configurations of a doubly fed induction generator (DFIG) and an induction generator (IG) with a back-to-back inverter in wind turbine applications. Detailed high frequency model of the proposed systems have been developed based on existing capacitive couplings in IG & DFIG structures and common mode voltage sources. In this research work, several arrangements of DFIG based wind energy conversion systems (WES) are investigated in case of shaft voltage calculation and its mitigation techniques. Placements of an LC line filter in different locations and its effects on shaft voltage elimination are studied via Mathematical analysis and simulations. A pulse width modulation (PWM) technique and a back-to-back inverter with a bidirectional buck converter have been presented to eliminate the shaft voltage in a DFIG wind turbine.