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This paper introduces a new controller for three-phase four-wire inverters, with the control goal of generating high-quality three-phase output voltages for all sorts of linear/nonlinear and balanced/unbalanced loads. The proposed controller employs a circuit-level decoupling method, and it is implemented by logic circuitry in combination with a control core and a feedback signal processor. Almost all dc--dc control methods can be adapted as the control core, while the feedback signal processor can be implemented by either voltage compensator and/or current compensator. The implementation of the controller is simple and flexible with only logic and analog circuitry needed. Yet, it demonstrated experimentally excellent load handling and source voltage noise l rejection ability. The prototype is tested under balanced and unbalanced resistive and nonlinear loads, as well as under extreme load transients. It is also tested with power from a noisy dc input source. In all cases, the prototype demonstrated high-quality output voltages. Index Terms--Analog control, inverter, three-phase, uninterruptible power supply.

This paper discusses the situation in a 3-phase motor or any other 3-phase system operating under unbalanced operating conditions caused by an open fault in an inverter switch. A dc voltage source is assumed as the input to the inverter, and under faulty conditions of the inverter switch, the actual voltage applied between the line to neutral (open neutral) of the 3-phase circuit is derived, based on the inverter switching table. This issue is very important, since during motor analysis and simulation it very often becomes necessary to use a line-to-neutral voltage as input to the simulation process or analysis, for which current is the output. The paper studies the necessary and sufficient conditions required for the line-to-neutral voltages indicated in the switching truth table to be true. Index Terms--3-phase system, electric drives, inverter, motor, open circuit fault, power electronics, short circuit fault, unbalanced 3-phase system.

This paper investigates the impact of positive-feedback anti-islanding methods on the small-signal stability of grid-connected inverter-based distributed generation. The maximum power transfer capability of a distributed generator (DG) is analyzed. Sensitivity studies are conducted for DGs equipped with the Sandia frequency shift anti-islanding scheme. Factors such as positive-feedback gain, initial chopping fraction, local load level, and network line impedance are investigated. The maximum power transfer limit versus positive-feedback gain curve is proposed as an index for the stability analysis. The results show that the positive-feedback anti-islanding scheme does have the potential to destabilize the grid-connected DG system when the grid is weak or the DG size is large. A curve that relates the maximum stable DG power transfer level versus the islanding detection time is proposed to quantify the destabilizing effect of the positive-feedback-based anti-islanding schemes. Index Terms--Distributed generation, inverter-based generator, islanding detection, positive-feedback anti-islanding protection, small-signal stability.

This paper proposes predictive direct power control (P-DPC), a new control approach where the well-known direct power control is combined with predictive selection of a voltage-vectors' sequence, obtaining both high transient dynamics and a constant-switching frequency. The developed P-DPC version is based on an optimal application of three voltage vectors in a symmetrical way, which is the so-called symmetrical 3 + 3 vectors' sequence. The simulation and experimental results of the P-DPC are compared to standard voltage-oriented control (VOC) strategies in a grid-connected three-phase voltage-source inverter under 400-V 15-kVA operation conditions. The P-DPC improves the transient response and keeps the steady-state harmonic spectrum at the same level as the VOC strategies. Due to its high transient capability and its constant-switching behavior, the P-DPC could become an interesting alternative to standard VOC techniques for grid-connected converters. Index Terms--DC/AC power conversion, inverters, predictive control.

In this paper, a simple power-control scheme for a constant-frequency class-D inverter with variable duty cycle at constant frequency is proposed. It is more suitable and acceptable for high-frequency induction-heating (IH) jar applications. The proposed control scheme has the advantages of not only wide power-regulation range but also ease of output-power control. In addition, it can achieve stable and efficient zero-voltage switching in the whole load range. The control principles of the proposed method are described in detail, and the validity is verified through the simulated and experimental results on the 42.8-kHz insulated gate bipolar transistor for an IH rated on 1.6 kW with constant-frequency variable power. Index Terms--Class-D inverter, constant-frequency variable power (CFVP), induction heating (IH), zero-voltage switching (ZVS).

This letter describes a high-resolution technique called thermally stimulated depolarization current (TSDC) that can be used for the measurement of space charge accumulation in the medium voltage magnet wires operating on pulsewidth modulated (PWM) inverters. Index Terms--Fast rise time pulses, induction motors, inverterfed drive motors, magnet wires, space charge injection.

The occurrence of high-frequency discharge bearing currents (also called 'electric discharge machining (EDM) currents') that can occur in machines of inverter-based drive systems depends strongly on the value of the capacitive voltage divider 'bearing voltage ratio' (BVR) of the machine. This paper presents a straightforward approach to calculate the involved motor capacitances in order to predict the voltage across the bearing and, thereby, the likeliness of such EDM currents that are caused by this voltage to occur. The approach is based on the design parameters of the machine and does not involve additional measurements. It combines ease of application and satisfying accurateness, and allows prediction of the risk of endangerment of an inverter-based drive system due to discharge bearing currents. Index Terms--Bearings (mechanical), failure analysis, variable-speed drives.

This paper presents the results of an investigation regarding the thermal behavior of a three-phase induction motor when supplied by a reconfigured three-phase voltage source inverter with fault-tolerant capabilities. For this purpose, a fault-tolerant operating strategy based on the connection of the faulty inverter leg to the dc link middle point was considered. The experimentally obtained results show that, as far as the motor thermal characteristics are concerned, it is not necessary to reinforce the motor insulation properties since it is already prepared for such an operation. Index Terms--Alternating current (AC) motor drives, fault tolerance, thermal performance.

This paper presents a half-bridge single-phase two-wire (1[phi]2W) photovoltaic (PV) inverter system that can perform both active power filtering and real power injection. In the proposed system, it needs only two active switches, reducing cost significantly. In addition, output current of the inverter can be controlled to prevent switches from exceeding their current ratings. Thus, power rating of the inverter can be effectively used and power quality can be improved. For controlling inverter output current, an amplitude-clamping algorithm and an amplitude-scaling algorithm are proposed, which can determine inverter current command without needs of complicated calculation. Simulations and experimental results have verified the feasibility of the proposed PV inverter system and the two current control algorithms. Index Terms--Active power filtering (APF), amplitude-clamping algorithm (ACA), amplitude-scaling algorithm (ASA), half-bridge inverter, photovoltaic (PV) power injection.

In this paper, an algorithm is presented, suitable for simulating the dynamic behavior of LV Microgrids both under grid connected and autonomous operation. The algorithm follows the stability approach, focusing on low-frequency dynamics, and adjusts the standard methodology so that the dynamic analysis of the system can be carried out, even in the absence of a synchronous machine when all the sources are interfaced to the network with inverters. Proper network representation allows for the modeling of all the characteristic unbalances of the LV network. The capability of the algorithm to simulate the operating modes of a Microgrid is demonstrated by representative study cases. Index Terms--Distributed generation (DG), inverter control, low-voltage (LV) networks, microgrids.

Abstract: Harmonic distortion is a form of electrical noise. It is a superposition of signals, which are of multiples of fundamental frequency. Proliferation of large power electronic systems results in [...]

Most sensorless algorithms for a motor drive are based on a mathematical model including electrical variables such as motor current and voltage. Therefore, the accuracy of such variables largely influences the performance of the sensorless motor drive. However, the output voltage of the space vector pulsewidth modulation of the voltage-source inverter supplying a motor is error-prone in the motor's low-speed range because it has a poor resolution in a low-output voltage command. This letter proposes a variation of the dc-link voltage as a high-performance strategy for overcoming the above problem in a sensorless induction motor drive. The proposed strategy is verified through simulation and experimentation. Index Terms--Sensorless induction motor drive, space vector pulsewidth modulation (SVPWM), variable link voltage, voltage source inverter (VSI).

This paper presents an implementation of integrated inductor for typical dimmable electronic ballasts having two power processing stages. The inductor used in the front-stage power factor corrector is integrated with the resonant inductor in the output-stage of the ballast inverter, so that the usage of the magnetic core material, and thus the cost, can be reduced. Existing circuit schematic can be retained without requiring any modification. Most importantly, the ballast performance is similar to the original design with two separate inductors. Based on using a z-parameter gyrator-capacitor model, modeling, design, and analysis of the ballast operation will be presented. A comparative study of using two separate inductors and integrated-inductor designs on the core volume, conduction and hysteresis losses, inductor current waveforms, input current harmonics, output lamp crest factor, overall efficiency, and costing will be carried out. Simplified design procedures will be given. The structure has been successfully applied to a 36-W prototype. Index Terms--Electronic ballast, integrated magnetics (IM), series resonant inverters.

This paper describes the control and parallel operation of two active power filters (APFs). Possible parallel operation situations of two APFs are investigated, and then the proposed topology is analyzed. The filters are coupled in a combined topology in which one filter is connected in a feedback loop and the other is in a feedforward loop for harmonic compensation. Thus, both active power filters bring their own characteristic advantages, i.e., the feedback filter improves the steady-state performance of the harmonic mitigation and the feedforward filter improves the dynamic response. Another characteristic of the proposed topology is the possibility of joint operation of both filters either as frequency-sharing or load-sharing, with or without redundancy. The frequency-sharing operation is possible due to the control algorithm, which is based on selective harmonic compensation using equivalent harmonic integrators. Implementation details and a discussion on the efficiency improvement for various switching frequencies are provided. The evaluation of the proposed topology concludes that this approach is very practical for achieving both low and high order harmonic compensation and stable grid operation. This is supported by extensive measurement results on a 15-kVA laboratory setup, indicating a reduction in total harmonic current distortion from the existing 30% to less than 2% for a typical adjustable speed drive application. Index Terms--Active filters, harmonic analysis, interconnected power systems, power system harmonic, pulse width modulated inverters.

In this paper, a novel four-level inverter will be presented and analyzed. The proposed inverter topology, which is composed of a conventional two-level and a three-level neutral-point clamped (NPC) inverter, is suitable for high-voltage and high-power applications. The proposed inverter, when it is compared with the conventional four-level NPC pulsewidth modulation inverter, exhibits the following advantages: a) ability of changing the power losses distribution profile among the devices by selecting a suitable switching strategy; b) reduction of total inverter power semiconductor device losses; c) ability of bidirectional operation for all power semiconductor switches; and d) easy implementation using existing power semiconductor modules. The effect of conduction and switching losses profiles of the proposed inverter for different switching strategies is examined under different loads, power factors, and modulation indices. The dc-link capacitors voltages are effectively balanced via a proposed self-voltage balancing topology, without the need of isolated dc voltage sources or additional voltage stabilizing circuits. Finally, the theoretical results are confirmed by simulation and experimental results. Index Terms--DC-Link capacitor voltage balance, multilevel voltage source inverter (VSI), semiconductor device power losses, sinusoidal pulsewidth modulation (SPWM).

A limitation of many high-frequency resonant inverter topologies is their high sensitivity to loading conditions. This paper introduces a new class of matching networks that greatly reduces the load sensitivity of resonant inverters and radio frequency (RF) power amplifiers. These networks, which we term resistance compression networks, serve to substantially decrease the variation in effective resistance seen by a tuned RF inverter as loading conditions change. We explore the operation, performance characteristics, and design of these networks, and present experimental results demonstrating their performance. Their combination with rectifiers to form RF-to-dc converters having narrow-range resistive input characteristics is also treated. The application of resistance compression in resonant power conversion is demonstrated in a dc-dc power converter operating at 100 MHz. Index Terms--Class E inverter, high frequency, integrated converter, matching network, radio frequency (RF) dc--dc resonant converter, RF power amplifier (RF PA), rectenna, resonant rectifier, self-oscillating inverter, very high frequency (VHF).

There are advantages of installing distributed generation (DG) in distribution systems: for example, improving reliability, mitigating voltage sags, unloading subtransmission and transmission system, and sometimes utilizing renewables. All of these factors have resulted in an increase in the use of DGs. However, the increase of fault currents in power systems is a consequence of the appearance of new generation sources. Some operating and planning limitations may be imposed by the resulting fault currents. This paper discusses a model of inverter based DGs which can be used to analyze the dynamic performance of power systems in the presence of DGs. In a style similar to protective relaying analysis, three-dimensional plots are used to depict the behavior of system reactance (X) and resistance (R) versus time. These plots depict operating parameters in relation to zones of protection, and this information is useful for the coordination of protection systems in the presence of DG. Index Terms--Distributed/dispersed generation, fault calculation, inverters, power distribution, power system protection.

Optimum PV/inverter sizing ratios for grid-connected PV systems in selected European locations were determined in terms of total system output, system output per specific cost of a system, system output per annualised specific cost of a system, PV surface orientation, inclination, tracking system, inverter characteristics, insolation and PV/inverter cost ratio. Maximum total system output was determined for horizontal, vertical and 45[degrees] inclined surfaces for a low efficiency inverter for sizing ratios of 1.5, 1.8 and 1.3, respectively; and for a medium efficiency inverter with sizing ratios of 1.4, 1.5 and 1.2. PV surface orientation and inclination have little impact on the performance of a high efficiency inverter. For different PV tracking systems and for different inverter characteristics, the optimum sizing ratio varied from 1.1 to 1.3. The PV/inverter cost ratio and the PV and inverter lifetimes have significant impact on the optimum PV/inverter sizing ratio. A correlation relating optimum sizing ratio and PV/inverter cost ratio has been developed; the correlation coefficients were found to be functions of insolation and inverter type. The impact of PV/inverter sizing ratio on PV array performance was less when PV array has a much higher cost than the inverter. The optimum sizing ratio for PV/inverter cost ratio of 6 and low efficiency inverter system varied from 1.4 to 1.2 for low to high insolation sites. For a high efficiency inverter system, the corresponding variation was from 1.3 to 1.1. Keywords: Grid-connected photovoltaics; TRNSYS; PV/inverter sizing ratio; Orientation and inclination; Performance ratio

The concept of hybrid clamped is proposed in multilevel-inverter topologies, and a hybrid-clamped multilevel-inverter topology comprising active and passive clamping devices is presented in this paper. In this topology, the dc-link capacitor voltages can be balanced without additional circuitry or separated dc voltage sources, regardless of load characteristics. It can be used in real and reactive power conversion applications. The topology structure, operating principle, and self-voltage balancing ability are analyzed. In addition, the validity is confirmed by simulations and experiments based on a five-level inverter. Finally, the functions of different clamping devices are compared. Index Terms--Hybrid clamped, multilevel inverter, neutral-point voltage balancing, topology.

In this paper, the application of an additional excitation in induction motor (IM) drives for static, dynamic, and mixed eccentricity diagnosis is proposed. The additional excitation consists in a predefined inverter-switching pattern that is applied on the motor for a short time, while the fundamental excitation is canceled. This excitation was used previously to implement a position estimation strategy. The strategy obtains information about the rotor position from the motor saliencies effects over the zero-sequence voltage. The air-gap eccentricity is a kind of saliency that affects the zero-sequence voltage and allows the use of the additional excitation for eccentricity diagnosis. For the evaluation of the feasibility of this proposal, a multiple-coupled circuit model of the IM is used. The effects of series and series-parallel stator winding connections on the diagnosis signals are shown. Experimental results to validate the proposal are also given. These results show that it is possible to use the diagnosis strategy in a self-commissioning scheme. Index Terms--Air-gap eccentricity, fault diagnosis, induction motor drives, position estimation.

This letter presents a powerful tool for the study of the performance of control strategies and consists of a versatile modulator capable of synthesizing triggering signals for various fixed-frequency and pulse width modulation controls based on a digital implementation. Among many other advantages, the approach provides a straightforward, flexible, and rapid means for prototyping because of its reprogramming capability and user-friendly interface. Field programmable gate array was chosen as the hardware platform because of the additional benefits it provides, such as high operating frequency and parallel processing capabilities. Several practical examples of its application demonstrate the utility of this approach. Index Terms--Asymmetrical voltage-cancellation control, control strategies, field programmable gate array (FPGA) digital control, pulsewidth modulation (PWM) control, voltage-fed inverters.

This paper presents a practical approach to eliminating both bearing current and ground leakage current from an inverter-driven motor rated at 400 V and 3.7 kW. When the shaft voltage with respect to the motor frame exceeds the dielectric breakdown voltage of thin lubricating grease films in two metal bearings at the drive and non-drive ends, an electrical discharge machining (EDM) current flows through the bearings. A passive electromagnetic interference (EMI) filter can keep the shaft voltage in check, as a result of having eliminated high-frequency common-mode voltage from the motor terminals. Hence, no dielectric breakdown occurs in the grease films, so that no EDM current flows in the bearings. Experimental results verify the viability and effectiveness of the passive EMI filter designed in this paper. Index Terms--Bearing current, common-mode voltage, electromagnetic interference (EMI), ground leakage current, inverters, motor drives, shaft voltage.

A new low-cost and efficient cold cathode fluorescent lamp (CCFL) inverter for liquid crystal display (LCD) application is suggested in this paper. The topology of the inverter is derived from modified class E-type resonant electronic ballasts and has a dc-like input current. In addition, a new sensing circuit for lamp current and transformer voltage is proposed. A simple RC-network measures the voltage of a ballasting capacitor in series with the lamp instead of the lamp current itself while the lamp is floated. Utilizing the printed circuit board capacitors for the sensing capacitors and integrating small-valued sensing resistors into a control integrated circuit make the inverter very simple, efficient, and cost-effective. The new sensing circuit can solve many problems that arise when a terminal of the lamp is grounded to sense the lamp current. The control circuits for the prototype experiments are also described in detail. The frequency control scheme with a fixed off-time and a varying on-time was chosen to maintain the operation of zero-voltage switching in the entire dimming range and to reduce the complexity of the control circuits. The control circuits have an analog dimming function using a current control loop, a low frequency pulsewidth modulation dimming, open-lamp protection and voltage regulation, and soft-on/off functions. Index Terms--Class E, cold-cathode fluorescent lamp (CCFL), current sensing, electronic ballasts, printed circuit board (PCB) capacitance, protection, resonant inverter, voltage sensing.