Electrical impedance

About: Electrical impedance is a research topic. Over the lifetime, 36015 publications have been published within this topic receiving 371891 citations. The topic is also known as: electrical impedance & complex impedance.

Impedance feedback electrosurgical system

Abstract: An impedance feedback electro-surgical system (100) is useful with electro-surgical tools (102) to maintain a preselected control range of tissue impedance within the tissue in contact with the tool (102). The system comprises an active electrode (108) associated with an electro-surgical tool (102), a return electrode (112), in the form of a remote ground pad which is in contact with the patient, an impedance monitoring device (116) and a power control unit (120). Energy sufficient to affect tissue is delivered through the active electrode (108) to tissue and to the return electrode. The impedance measuring device (116) determines the impedance of the tissue based on the voltage differential between the active electrode (108) and ground pad (112). A signal representative of the measured impedance is communicated to the power control unit (120) which adjusts the energy applied to the tissue to maintain a preselected impedance range.

High frequency power measurement

Abstract: A monitoring circuit (10) for an electrosurgical generator (11) has active and return output conductors. Voltage, current (24) and the inverse of current (24) picked up inductively are provided to adder circuits for summing the picked up voltage (20) and current (24) and computing the difference of the picked up voltage (20) and the current (24). Root mean square to direct current converters (26 and 28) signal RMS average values of the sum and difference. A microprocessor squares the values and applies them to a formula wherein the sum signals (22) have subtracted therefrom the difference signals (25); the results are divided by four to provide the root mean square of the power applied to the load (12). During desiccation the output is regulated in response to impedance to shut off output. A diagnostic circuit relates impedance load and output response during operation to a look up table or a microprocessor algorithm to calibrate. Feedback modifies the output when the adders determine the power applied to the load (12) in real time. A method has generator output to active and return conductors (14 and 15) and to inductive pick ups (16 and 17) for voltage and current (24), computes sum and differential values (25), changes root mean square to direct currents (24), squares the values and subtracts the differential from the summation, then divides the result finding the root mean square value of the power.

Analysis of D-Q Small-Signal Impedance of Grid-Tied Inverters

Abstract: This paper analyzes the small-signal impedance of three-phase grid-tied inverters with feedback control and phase-locked loop (PLL) in the synchronous reference ( d-q ) frame. The result unveils an interesting and important feature of three-phase grid-tied inverters – namely, that its q–q channel impedance behaves as a negative incremental resistor. Moreover, this paper shows that this behavior is a consequence of grid synchronization, where the bandwidth of the PLL determines the frequency range of the resistor behavior, and the power rating of the inverter determines the magnitude of the resistor. Advanced PLL, current, and power control strategies do not change this feature. An example shows that under weak grid conditions, a change of the PLL bandwidth could lead the inverter system to unstable conditions as a result of this behavior. Harmonic resonance and instability issues can be analyzed using the proposed impedance model. Simulation and experimental measurements verify the analysis.

Laser surgical unit

Abstract: Apparatus monitors RF return current to maximize the AC signal of impedance at two return electrodes. A transformer with driving and driven windings isolates ESU and patient. At ends of the driving winding are signal and ground terminals joined to the return electrodes with capacitors returning current. An AC coupling capacitor at the signal terminal has a timing circuit in sync to the voltage wave and relative to impedance of the return electrodes. Microprocessing the voltage at the signal terminal of the driving winding watches impedance and determines if the RF return current path is adequate. Voltage detection within the timing circuit has a voltage shaping circuit. A voltage comparator after the voltage detection forms a square wave. A current detection circuit and a coupling capacitor allow AC flow to the driving winding. Current shaping circuit in the current detection circuit has a voltage comparator at the output to form a square wave. Phase detection at the voltage and current detection circuits outputs filters the phase difference that is sampled and held as DC input to a switch, with an output and a few inputs to DC voltages. Phase locking an oscillating voltage source directly and/or through the sample and hold or DC switch tunes oscillation frequency and maximizes the voltage detection circuit output. Monitoring the return current with a signal from the voltage detection circuit connected to an oscillating voltage that is phase locked to the current phase therein shows that no phase difference and maximum signal voltage occur simultaneously.

Design and Analysis of the Droop Control Method for Parallel Inverters Considering the Impact of the Complex Impedance on the Power Sharing

Abstract: This paper investigates the characteristics of the active and reactive power sharing in a parallel inverters system under different system impedance conditions. The analyses conclude that the conventional droop method cannot achieve efficient power sharing for the case of a system with complex impedance condition. To achieve the proper power balance and minimize the circulating current in the different impedance situations, a novel droop controller that considers the impact of complex impedance is proposed in this paper. This controller can simplify the coupled active and reactive power relationships, which are caused by the complex impedance in the parallel system. In addition, a virtual complex impedance loop is included in the proposed controller to minimize the fundamental and harmonic circulating current that flows in the parallel system. Compared to the other methods, the proposed controller can achieve accurate power sharing, offers efficient dynamic performance, and is more adaptive to different line impedance situations. Simulation and experimental results are presented to prove the validity and the improvements achieved by the proposed controller.