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The anti-islanding algorithm proposed by the Sandia National Laboratories is analyzed in this study because this scheme, also known as the Sandia scheme, is considered to be effective in detecting islanding of distributed generation systems. Previously, other than heuristic approaches, there has not been any quantitative analysis for tuning the control gains of the algorithm based on the power rating and bandwidth of the distributed generation (DG) power converter. The paper interprets the components of the algorithm that affect the voltage magnitude and frequency into block diagrams that can be linearized and studied using continuous time approximations. This paper uses frequency domain approach to analyze the range for the gains required by anti-islanding algorithm to effectively determine the disconnection of the mains grid within an acceptable time duration. The analysis provides guidelines for using the Sandia's schemes under different application conditions. The results are validated using detailed time domain DG and power system simulations. Index Terms--Anti-islanding, distributed generation (DG), inverters, power conditioning, power system protection, power system simulation, power system state estimation, Sandia frequency scheme, Sandia voltage scheme.

This paper presents a novel method for measuring the magnetizing inductance of an induction machine. The approach uses a static dc excitation technique which can be employed whenever the neutral of the machine is accessible. The proposed method measures only the magnetizing inductance and not the self inductance which normally includes the effect of the stator leakage inductance. Because this test uses a dc excitation, the iron losses in the motor are considerably reduced as well and minimally influence the measurement when compared to the traditional 60-Hz no-load test. By using the proposed method for measuring only the magnetizing inductance, the stator leakage inductance can be later individually determined by performing a separate no-load test. Test results using the method are compared with theoretical values and confirm its feasibility. Index Terms--DC test, inductance measurement, induction machines, leakage inductance, locked-rotor test, magnetizing inductance, no-load test.

This paper deals with an active gate drive (AGD) technology for high-power insulated gate bipolar transistors (IGBT's). It is based on an optimal combination of several requirements necessary for good switching performance under hard-switching conditions. The scheme specifically combines together the slow drive requirements for low noise and switching stress and the fast drive requirement for high-speed switching and low switching energy loss. The gate drive can also effectively dampen oscillations during low-current turn-on transient in the IGBT. This paper looks at the conflicting requirements of the conventional gate drive circuit design and demonstrates using experimental results that the proposed three-stage AGD technique can be an effective solution. Index Terms: Active gate drive, gate drive circuit, gate resistor, insulated gate bipolar transistor switching transient

The use of a coaxial current transformer (CCT) is an interesting choice for pulsed measurement of current through power devices during switching transients. The CCT is used to reflect current for convenient external measurement with minimal insertion impedance in the critical power circuit. This paper analyzes the characteristics of the CCT and explains how it can be integrated into test setups for both press-pack and module packages. Finite-element techniques are applied to the study of the CCT to obtain detailed electrical and magnetic characteristics. Current distribution in the primary and secondary circuits, flux densities, and insertion inductance and resistance are among the design information that can be obtained through finite-element analysis. Analytical and numerical results are obtained for the proposed CCT that is integrated in test setups for MOS turn-off thyristors (press-pack) and high-voltage insulated gate bipolar transistors (module) characterization. Index Terms--Coaxial current transformer, current measurement, semiconductor device characterization.

Identification of fault current during the operation of a power semiconductor switch and activation of suitable remedial actions are important for reliable operation of power converters. A short circuit is a basic and severe fault situation in a circuit structure, such as voltage-source converters. This paper presents a new active protection circuit for fast and precise clamping and safe shutdown of fault currents of the insulated gate bipolar transistors (IGBT's). This circuit allows operation of the IGBT's with a higher on-state gate voltage, which can thereby reduce the conduction loss in the device without compromising the short-circuit protection characteristics. The operation of the circuit is studied under various conditions, considering variation of temperature, rising rate of fault current, gate voltage value, and protection circuit parameters. An evaluation of the operation of the circuit is made using IGBT's from different manufacturers to confirm the effectiveness of the protection circuit. Index Terms - Fault current, fault under load, hard-switched fault, insulated gate bipolar transistors, protection, short circuit.