Virtual Short Circuit Research Articles

Utilization of Virtual Short-Circuit in Wireless Power Transfer System: Mutual Inductance Identification via Second Harmonic

Utilization of Virtual Short-Circuit in Wireless Power Transfer System: Mutual Inductance Identification via Second Harmonic

PERMITTIVITY MEASUREMENT WITH A NON-STANDARD WAVEGUIDE BY USING TRL CALIBRATION AND FRACTIONAL LINEAR DATA

Modifications in the measurement of the complex permittivity are described, based on the transmission and reflection coefficients of a dielectric slab. The measurement uses TRL two- port calibration to bring the reference planes accurately to the sample surface. The complex permittivity as a function of frequency is computed by minimizing the difference between the measured and the ideal scattering parameters. An alternative procedure for determining the complex permittivity uses the fractional linear data fitting to a Q- circle of the virtual short-circuit and/or virtual open circuit data. In that case, the sample must be a multiple of one-quarter wavelength long within the measured range of frequencies. Comparison with results obtained by other traditional procedures is provided.

A Sensorless Field Oriented Control of Induction Motor Using Ripple Currents in Space Phasor Based PWM Control

A scheme for sensorless flux estimation for the induction motor drives is presented in this paper, where the flux information is derived from the current ripple. The scheme measures the stator current phasor deviation to determine the back emf vector position during the zero vectors of the inverter. The position of the rotor flux is detected indirectly by computing the position of the motor back emf, which is orthogonal to the rotor flux position. The space vector PWM generates a current ripple pattern in the machine current, which depends upon the ripple voltage and equivalent stator leakage inductance. For high speed operation when the time duration for the zero vector switching states are small, an indirect method for estimation of flux position is proposed, where the effect of active voltage vectors on the stator ripple current is eliminated by creating a virtual short circuit at the motor terminals. This is achieved by linear transformation of the fundamental components of two immediate current space phasor deviations within a switching period. The whole scheme is implemented in a space phasor based PWM drive with constant inverter switching frequency. The position of the back emf is estimated for both high speed and low speed by implementing the proposed method in a TMS320LF2407 DSP based board.

Transport of sodium and chloride across earthworm skin in vitro

We present a new invertebrate model for the study of epithelial sodium transport in tight epithelia, the earthworm integument. Dissected segments of earthworm integument were mounted in modified Ussing chambers and perfused with either pond water (PW) or earthworm ringer solution (ERS) on the apical side. In order to investigate ion transport under near-in vivo physiological conditions, measurements were performed under current-clamp conditions by monitoring the transepithelial potential (V (T)), as well as the transepithelial resistance (R (T)). These were recorded continuously and the virtual short circuit current (I (SC)) was calculated. The integument has a high transepithelial resistance (R (T) = 9,037 +/- 502 Omega cm(2) for PW, n = 24, and 11,055 +/- 1,320 Omega cm(2) for ERS, n = 32). V (T) was -3.7 +/- 2.2 mV for PW (n = 24) and -1.5 +/- 1.0 mV for ERS (n = 32), and I (SC) was -0.57 +/- 0.30 microA/cm(2) for PW (n = 24) and -0.44 +/- 0.24 microA/cm(2) for ERS (n = 32). Only under PW, but not under ERS conditions, was there a pronounced inhibition of I (SC) by low doses of amiloride or its analogues phenamil and benzamil. The resistance of the paracellular pathway was found to be very high. The terrestrial oligochaete Lumbricus seems especially adapted to the environmental conditions because it has an ultra-tight integument and a very fast up- and down-regulation of apical Na(+) channels.

Fatty acid flip-flop and proton transport determined by short-circuit current in planar bilayers

The effect of palmitic acid (PA) and oleic acid (OA) on electrical parameters of planar membranes was studied. We found a substantial difference between the effects of PA and OA on proton transfer. PA induced a small increase in conductance, requiring a new technique for estimating proton-mediated currents across low-conductance planar bilayers in which an electrometer is used to measure the transmembrane current under virtual short circuit (SCC). Open-circuit voltage and SCC were used to determine proton and leak conductances. OA caused a marked increase in membrane conductance, allowing the use of a voltage-clamp technique. From SCC data, we were able to estimate the flip-flop rate constants for palmitate (1 x 10(-6) s(-1)) and oleate (49 x 10(-6) s(-1)) anions. Cholesterol, included in the membrane-forming solution, decreased importantly the leak conductance both in membranes unmodified by FA and in membranes modified by PA added to the bath.

Subharmonic injection‐locking balanced oscillator

AbstractA subharmonic injection‐locked balanced oscillator is presented in this paper. Subharmonic injection locking is preferred to fundamental injection locking, because the central injection point is a virtual short‐circuit at the fundamental frequency for a balanced oscillator. An analytical model is described to predict the locking range whereby power series are used to model the device's nonlinearity. An injection‐locked balanced oscillator is designed at 5.8 GHz and very good agreement is achieved between the predicted and measured locking ranges. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 306–309, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20124

A Sensorless Vector Control Scheme for Induction Motors using a Space Phasor Based Current Hysteresis Controller

The increasing use of a.c. machines compared to d.c. motors in electrical drive applications has several reasons. A very important advantage of a.c. machines is their simple construction. However, a.c. drives often need mechanical sensors (tachometers, position encoders) for field orientation. In many applications these sensors reduce robustness and increase costs of a drive considerably. The objective of this paper is to present the practical implementation of a Sensorless Vector Control Scheme for Induction Motors using a Space Phasor based Current Hysteresis Controller. This scheme measures the stator current hysteresis error direction to determine the rotor flux position, during inverter zero vector states. This measurement of the rotor flux position is done indirectly by sensing the motor back emf which is orthogonal to the rotor flux position. The basic idea is to measure the current hysteresis error direction of the stator current on the application of an inverter zero vector i.e. “short circuit at machine terminals”. A generalization is possible by a combination of two (different) active states of the inverter. By a linear transformation of the electrical equations for both inverter slates, a mathematical zero state is constructed. The use of this virtual short circuit is necessary at higher speeds when the inverter output voltage is fully utilized. However at low speeds the drop across the stator resistance is comparable to the motor back emf, to overcome this a simple parameter adaptation scheme is also presented here. The proposed scheme enables a smooth transition to six-step mode of operation.The whole scheme is implemented using a Space Phasor based Current Hysteresis controller, in which the inverter voltage vectors close to the machine back emf vector is selected, without measuring the back emf vector. The back emf vector is sensed indirectly from the direction of the current error space phasor. A single chip solution is arrived at by using the TMS320F240 DSP.

EMF-based rotor flux detection in induction motors using virtual short circuits

This paper presents the practical implementation of EMF-based flux-detecting algorithms for induction machines using current measurement only. The basic idea is to measure the reaction of the stator current on the change of the rotor flux during the "short circuit at machine terminals" inverter state. A generalization is possible by a combination of two different active states of the inverter. By a linear transformation of the electrical equations for both inverter states, a mathematical zero state is constructed. The use of this virtual short circuit is necessary at higher speed when the inverter output voltage is fully utilized. Both variants were implemented in real time on an induction motor drive with an insulated gate bipolar transistor (IGBT) inverter and floating-point digital signal processor (DSP). In order not to disturb the current controller, the algorithms use naturally occurring inverter switching states only. Measurement results during load steps demonstrate the excellent flux information of the method.

Conceptual study of a shunt power quality compensator

This paper describes how the different methods of eliminating the power disturbances: (1) outages by shunt UPS action, (2) low frequency harmonic disturbances by the "virtual short circuit" principle, (3) swells/sags by the inductive/capacitive reactance principle, and (4) high frequency disturbance by passive filtering, can all be integrated into a single strategy based on reference voltage tracking control. The control law has been derived from first principles. Digital simulation results are presented to prove that the strategy fulfils the multi-functional requirements. The PWM converter which implements the control law is modelled as an ideal linear amplifier.

Current-mode techniques for high-speed VLSI circuits with application to current sense amplifier for CMOS SRAM's

The speed of VLSI chips is increasingly limited by signal delay in long interconnect lines. A simple analysis shows that major speed improvements are possible when using current-mode rather than conventional voltage-mode signal transporting techniques. The key to this approach is the use of low-resistance current-signal circuits to drastically reduce the impedance level and the voltage swings on long interconnect lines. As an example, a simple four-transistor current-sense amplifier for fast CMOS SRAMs is proposed. The circuit presents a virtual short circuit to the bit lines, thus reducing the sensing delay, which is rendered practically insensitive to the bit-line capacitance. In addition, the virtual short circuit ensures equal bit-line voltages, thus eliminating the need for bit-line equalization during a read access. >