Showing papers on "Inverter published in 2002"

Multilevel inverters: a survey of topologies, controls, and applications

Abstract: Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate DC sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.

Inverters for single-phase grid connected photovoltaic systems-an overview

Abstract: An overview on developments and a summary of the state-of-the-art of inverter technology in Europe for single-phase grid-connected photovoltaic (PV) systems for power levels up to 5 kW is provided in this paper. The information includes details not only on the topologies commercially available but also on the switching devices employed and the associated switching frequencies, efficiency, price trends and market share. Finally, the paper outlines issues associated with the development of relevant international industry standards affecting PV inverter technology.

Evaluation of Islanding Detection Methods for Utility-Interactive Inverters in Photovoltaic Systems

Abstract: This report describes the various methods and circuits that have been developed to detect an islanding condition for photovoltaic applications and presents three methods that have been developed to test those methods and circuits. Passive methods for detecting an islanding condition basically monitor parameters such as voltage and frequency and/or their characteristics and cause the inverter to cease converting power when there is sufficient transition from normal specified conditions. Active methods for detecting the island introduce deliberate changes or disturbances to the connected circuit and then monitor the response to determine if the utility grid with its stable frequency, voltage and impedance is still connected. If the small perturbation is able to affect the parameters of the load connection within prescribed requirements, the active circuit causes the inverter to cease power conversion and delivery of power to the loads. The methods not resident in the inverter are generally controlled by the utility or have communications between the inverter and the utility to affect an inverter shut down when necessary. This report also describes several test methods that may be used for determining whether the anti-islanding method is effective. The test circuits and methodologies used in the U.S. have been chosenmore » to limit the number of tests by measuring the reaction of a single or small number of inverters under a set of consensus-based worst-case conditions.« less

A new cascaded multilevel H-bridge drive

Abstract: In this paper, a general structure for cascaded power converters is presented in which any number of H-bridge cells having any number of voltage levels are series connected to form an inverter phase leg. Equations are introduced for determining an optimal voltage ratio of DC voltages for the H-bridge cells which will maximize the number of voltage levels obtainable resulting in high power quality. Special cases of the generalized inverter are presented including novel 11-level and 15-level inverters. Laboratory measurements demonstrate the proposed inverter performance.

Automatic phase-shift method for islanding detection of grid-connected photovoltaic inverters

Abstract: The traditional frequency-shift methods for islanding detection of grid connected PV inverters (the active frequency-drift method and the slip mode frequency-shift method) become ineffective under certain paralleled RLC loads. The automatic phase-shift method is proposed in this paper to alleviate this problem. The method is based on the phase shift of the sinusoidal inverter output current. When the utility malfunctions, the phase-shift algorithm keeps the frequency of the inverter terminal voltage deviating until the protection circuit is triggered. Simulation and experiments are performed for verification.

Digital field oriented control for dual three-phase induction motor drives

Abstract: A direct rotor-field-oriented control of a dual-three phase induction motor drive is described in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The stator windings are fed by a current-controlled pulsewidth-modulation (PWM) six-phase voltage-source inverter. Three key issues are discussed: (1) the machine dynamic model is based on the vector space decomposition theory; (2) the PWM strategy uses the double zero-sequence injection modulation technique which gives good results with low computational and hardware requirements; and (3) to eliminate the inherent asymmetries of the drive power section, a new current control scheme is proposed. Experimental results are presented for a 10-kW dual three-phase induction motor drive prototype.

Switching frequency imposition and ripple reduction in DTC drives by using a multilevel converter

Abstract: A new strategy for direct torque control with imposed switching frequency (DiCoIF) is proposed. This strategy was specially designed to operate with a multicell (flying capacitors) inverter with any number of levels, which means it can also be used for standard two-level inverters. This approach combines the well known advantages of the multicell. inverter with those of a direct torque controlled (DTC) based strategy. It is shown that the multicell topology presents enough degrees of freedom to control both torque and flux with very low ripple and high dynamics on one hand, and to impose the switching frequency and the capacitors voltage balance on the other hand. Experimental and simulation results, obtained with a standard two-level inverter and with a four-level multicell inverter, are presented and discussed. Finally, a comparative analysis either with the classical DTC and field oriented techniques is carried out.

Torque ripple reduction in DTC of induction motor driven by three-level inverter with low switching frequency

Abstract: A torque ripple reduction technique of direct torque control (DTC) for high power induction motors driven by three-level inverters with the inverter switching frequency limited around 0.5-1 kHz level is presented. It is noted that conventional two-level DTC algorithms to reduce torque ripple are devised for applications with relatively high switching frequency above 2-3 kHz and cannot accomplish satisfactory torque ripple reduction for three-level inverter systems with such lower switching frequencies. A new DTC algorithm, especially for low switching frequency inverter system, illustrates quite reduced torque ripple characteristics all over the operating speed region. Simulation and experimental results show effectiveness of the proposed control algorithm.

Topology for hybrid multilevel inverter

Abstract: A new topology for a hybrid multilevel inverter is presented, which significantly increases the level number of the output waveform and thereby dramatically reduces the low-order harmonics and total harmonic distortion. To the best of the authors' knowledge, the presented topology has the greatest level number for a given number of stages. Moreover, the stage with higher DC link voltage has lower switching frequency; and thereby reduces the switching losses. Comparison of the results of various multilevel inverters is investigated to reflect the merits of the presented topology. The details of the PWM control using the harmonic elimination technique for the hybrid inverter are presented and confirmed by both simulation and experimental results.

Natural balancing of three-level neutral-point-clamped PWM inverters

Abstract: This paper explores the natural balancing mechanisms of the three-level neutral-point-clamped (NPC) multilevel inverter. An equivalent circuit of the three-level NPC inverter is derived that facilitates an understanding of the balancing mechanisms. This is followed by a detailed analysis of the balancing mechanisms. The theory is applied to a three-level NPC inverter under vector control. It is shown that this inverter possesses natural balancing mechanisms in which the load impedance and spectra of the switching functions play an important role. Finally, it is illustrated how the natural balancing can be enhanced by using a passive balancing circuit which provides a low impedance at the sampling frequency.

Multilevel inverter by cascading industrial VSI

Abstract: In this paper, the modularity concept applied to medium-voltage adjustable speed drives is addressed First, the single-phase cascaded voltage-source inverter that uses series connection of insulated gate bipolar transistor (IGBT) H-bridge modules with isolated DC buses is presented Next, a novel three-phase cascaded voltage-source inverter that uses three IGBT triphase inverter modules along with an output transformer to obtain a 3-pu multilevel output voltage is introduced The system yields in high-quality multistep voltage with up to four levels and low dv/dt, balanced operation of the inverter modules, each supplying a third of the motor rated kVA The concept of using cascaded inverters is further extended to a new modular motor-modular inverter system where the motor winding connections are reconnected into several three-phase groups, either six-lead or 12-lead connection according to the voltage level, each powered by a standard triphase IGBT inverter module Thus, a high fault tolerance is being achieved and the output transformer requirement is eliminated A staggered space-vector modulation technique applicable to three-phase cascaded voltage-source inverter topologies is also demonstrated Both computer simulations and experimental tests demonstrate the feasibility of the systems

A flyback-type single phase utility interactive inverter with low-frequency ripple current reduction on the DC input for an AC photovoltaic module system

Abstract: In recent years, interest in natural energy has grown because of increased environmental concerns. Many kinds of inverter circuits and their control schemes for photovoltaic (PV) power generation systems have been studied. In a conventional system, the PV array in which many PV modules are connected in series is used to obtain sufficient DC-bus voltage for generating an AC utility line voltage from an inverter circuit. However, the total power generation of the PV array is sometimes decreased remarkably when a few modules are partially covered by shadows, thereby decreasing its inherent current generation, and preventing the generation current attaining its maximum value on the array. To overcome this drawback, an AC module strategy has been proposed. In this system, a small power DC-AC utility interactive inverter is mounted on each PV module individually. This inverter operates so as to generate the maximum power from its corresponding PV module. This paper proposes a novel flyback-type utility interactive inverter circuit suitable for AC module systems. The features of the proposed system are that it: (1) is small in volume and lightweight; (2) allows stable AC current injection into the utility line; (3) enables the stable parallel operation without AC current sharing control; and (4) enables the capacitance of the DC capacitor to be small. The effectiveness of the proposed system is clarified through simulation and experiments.

A DC link capacitor minimization method through direct capacitor current control

Abstract: If we make the converter side DC link current the same as the inverter side DC link current in a PWM converter-inverter system, no current will flow through the DC link capacitor and as a result, no DC link voltage variation occurs. This leads to the possibility of significantly reducing the size of DC link capacitors which are expensive, bulky and have a lifetime limit, if we can manage to match inverter and converter currents at the DC link. However, a converter inherently involves a delay in supplying the required current. Therefore, matching the converter current to the inverter current necessitates the use of a differentiator to meet the requirements of a fast dynamic response. But in practice, differentiating the measured value is almost impossible. In this paper, the authors propose a new differentiation method that utilizes a one-step predictor developed from converter and inverter dynamics. In the model, the DC link voltage is regarded a variable. Since the inverter current compensation term is applied in terms of voltage, the response is fast. Simulation and experiments are performed with only 40 /spl mu/F DC link capacitance for a 9 kW motor, and the results support the validity of the proposed scheme.

Dynamic NBTI of p-MOS transistors and its impact on MOSFET scaling

Abstract: For the first time, a dynamic negative bias temperature instability (DNBTI) effect in p-MOSFETs with ultrathin gate oxide (1.3 nm) has been studied. The interface traps generated under NBTI stressing corresponding to p-MOSFET operating condition of the "high" output state in a CMOS inverter, are subsequently passivated when the gate to drain voltage switches to positive corresponding to the p-MOSFET operating condition of the "low" output state in the CMOS inverter. Consequently, this DNBTI effect significantly prolongs the lifetime of p-MOSFETs operating in a digital circuit, and the conventional static NBTI (SNBTI) measurement underestimates the p-MOSFET lifetime. A physical model is presented to explain the DNBTI. This finding has significant impact on future scaling of CMOS devices.

Seamless transfer of grid-connected PWM inverters between utility-interactive and stand-alone modes

Abstract: This paper proposes a control algorithm for utility interactive PWM inverters to maintain a continuous, uninterrupted voltage across critical and sensitive loads in the event of a fault on the grid. The algorithm switches the inverter between voltage-controlled and current-controlled modes and can easily be implemented using a DSP.

UPS inverter design using discrete-time sliding-mode control scheme

Abstract: This paper presents a novel discrete-time sliding-mode control algorithm for an uninterruptible power supply (UPS) inverter design. The approach offers a dual-loop design, in which a current predictor utilizes the tracking error of output voltage to estimate the desired inductor current, while a current controller is adopted to regulate the inductor current and, thus, produces a control command to the pulsewidth modulation inverter. An explicit condition for stable controller design is derived. The efficacy of this scheme is validated via a successful implementation on a digital-signal-processor-based UPS inverter. The proposed scheme has shown its robustness on low output voltage distortion, excellent voltage regulation, and it is insensitive to load variation, even under nonlinear loads. Experimental studies were performed to further validate the effectiveness of this scheme.

Nanocell logic gates for molecular computing

Abstract: Molecular electronics seeks to build electrical devices to implement computation - logic and memory - using individual or small collections of molecules. These devices have the potential to reduce device size and fabrication costs, by several orders of magnitude, relative to conventional CMOS. However, the construction of a practical molecular computer will require the molecular switches and their related interconnect technologies to behave as large-scale diverse logic, with input/output wires scaled to molecular dimensions. It is unclear whether it is necessary or even. possible to control the precise regular placement and interconnection of these diminutive molecular systems. This paper describes genetic algorithm-based simulations of molecular device structures in a nanocell where placement and connectivity of the internal molecular switches are not specifically directed and the internal topology is generally disordered. With some simplifying assumptions, these results show that it is possible to use easily fabricated nanocells as logic devices by setting the internal molecular switch states after the topological molecular assembly is complete. Simulated logic devices include an inverter, a NAND gate, an XOR gate and a 1-bit adder. Issues of defect and fault tolerance are addressed.

Space Vector PWM Control of Dual Inverter Fed Open-End Winding Induction Motor Drive

Abstract: The technique of space vector PWM control of dual voltage source inverter fed three phase open-end winding induction motor is presented in this paper. A space vector PWM technique is developed based on the combination of space vectors from dual inverters feeding the induction motor from both ends (open-end winding without neutral point). A total of 64 voltage space vector combinations are available for PWM voltage control of the inverter fed machine with open-end winding A space phasor based PWM scheme is proposed with minimum number of switching in a cycle per inverter coupled with equal number of switching for each inverter. All the voltage space vector combinations are utilized for generating the reference voltage vector to cover the entire speed range. The open-end winding structure can have significant third harmonic currents unless suitable third harmonic filters are used to suppress it. The third harmonic currents are suppressed by using isolated transformers for both inverters.

Multiphase space vector pulse width modulation

Abstract: Pole-phase modulation adjusts the pole-phase ratio of an induction machine and requires a multileg, multiphase inverter. This paper analyzes an n-leg, n-phase inverter, and presents techniques for n-phase space vector pulse width modulation (SVPWM). In particular, nine-phase SVPWM is developed and implemented on a nine winding induction machine. The nine-phase SVPWM is compared to nine phase sine-triangle PWM in terms of DC bus utilization.

Performance of Interior Permanent Magnet Motor Drive over Wide Speed Range

Abstract: This paper investigates the performance of an interior permanent magnet synchronous motor (IPMSM) drive over wide speed range for high precision industrial applications. The scheme incorporates the maximum torque per ampere (MTPA) operation in constant torque region and the flux-weakening operation in constant power region in order to expand the operating limits for an IPMSM. Improved mathematical expressions are derived to analyze the performances of the IPMSM. The power ratings of the motor and the inverter are considered. The effects of motor parameters particularly, the saliency ratio (X/sub q//X/sub d/) on the voltage limit constraint and the power capability of the inverter are also investigated. The efficacy of the above mentioned drive system and the improved steady-state analysis are evaluated by both experimental and computer simulation results. The complete drive is implemented in real-time using digital signal processor (DSP) controller board DS 1102 on a laboratory 1 hp interior permanent magnet synchronous motor.

Operation of a DSTATCOM in voltage control mode

Abstract: This paper presents the operating principles of a distribution static compensator (DSTATCOM) that is used to maintain the voltage of a distribution bus. A three-phase, four-wire distribution system is assumed in this study. A three-phase bridge inverter circuit that is supplied by two neutral-clamped dc storage capacitors realizes the DSTATCOM. Three filter capacitors, one for each phase, are connected in parallel with the DSTATCOM to eliminate high-frequency switching components. The voltage across the filter capacitor is controlled by a dead-beat controller to maintain the ac bus voltage. The magnitude of the bus voltage is chosen as a nominal value, i.e., 1.0 per unit, while its phase angle is obtained through a feedback loop that maintains the voltage across the dc storage capacitors. Through detailed simulation and experimental results it has been shown that the DSTATCOM can maintain the voltage against any unbalance and distortion in either the load or supply side.

Failures-tolerance and remedial strategies of a PWM multicell inverter

Abstract: The aim of this paper is to explain the intrinsic short-circuit tolerance of an IGBT multicell inverter when a commutation failure occurs. Such a failure may either be a wrong gate voltage (malfunctioning of the driver board, auxiliary power supply failure, dv/dt disturbance) or an intrinsic IGBT failure (over-voltage/avalanche stress, temperature overshoot). IGBT stresses are studied and show that no opening of the bonding can appear and consequently no risk of explosion. That is why, owing to the imbricated cells structure, an IGBT short-circuit failure may be withstood for a few switching periods, with nevertheless nonoptimized output waveforms. The design, the lab-test of a sensor able to perform monitoring as well as the failure diagnosis are also presented. This real-time diagnosis allows either a safe stop or a remedial control strategy based on the reconfiguration of the PWM modulator. The reconfiguration strategy enables decrease of internal stresses and optimization of the output shape. A fail-safe operating may be gained for high power applications.

Novel vector control system using deadbeat controlled PWM inverter with output LC filter

Abstract: This paper proposes a novel high-performance vector control system of an ac motor using a low-switching-frequency (2 kHz) pulsewidth-modulation voltage-source inverter with an output LC filter. Excellent high-speed response characteristics of the LC filter output voltage have been realized using a novel deadbeat control algorithm. As for the experimental results, the torque current response that is similar to the response of the conventional system without an LC filter has been obtained. In addition, it has been confirmed by simulation that errors of the LC filter constants within /spl plusmn/10% can be permitted.

Innovative remedial strategies for inverter faults in IPM synchronous motor drives

Abstract: Interior permanent magnet (IPM) synchronous motors are used extensively in many industrial drives, and the development of fault-tolerant control techniques may extend their use to applications where high reliability, also in the flux-weakening region, is a key-feature. This paper proposes some innovative fault-remedial control strategies for failures occurring in the drive voltage inverter.

A comparative study of resonant inverter topologies used in induction cookers

Abstract: In this paper, a comparison is performed between four inverter topologies commonly used in induction cookers. The considered topologies are the full-bridge inverter, the half-bridge inverter, and two single-switch inverters. All of them are designed for the same specifications and they are compared in aspects such as power device stresses, efficiency, frequency control and electromagnetic emissions.

High-efficiency and low acoustic noise drive system using open-winding AC motor and two space-vector-modulated inverters

Abstract: The combining of the outputs of two inverters using interphase reactors is a widely used method for supplying large AC drives rated at more than several thousands kilowatts. Certain drawbacks are associated with this method, such as high acoustic noise and high losses due to the interphase reactors. To overcome these problems, the authors propose a new high-efficiency drive system using an open-winding motor and two space-vector-modulated inverters. This configuration consists of a three-level inverter with switching at once every cycle and a two-level inverter of about 1-kHz switching frequency, connected, respectively, to the opposite terminals of the open-winding AC motor. With the proposed configuration, good current waveforms, high efficiency, and low acoustic noise can be obtained.

A 31-level cascade inverter for power applications

Abstract: Power inverter modules fed with separate DC voltage sources of voltage ratio 1:2:4:8 are connected to form a cascade multilevel inverter. This new proposal combines the advantages of the static phase-shifter and chain-cell converter concept. Using the same number of power devices as a standard nine-level inverter, the proposed converter operates as a high-power digital-to-analog converter with 31-level resolution. Electrolytic capacitors used in the proposed inverter for providing the DC voltage sources will never be connected in opposite polarity in all cases, thus ensuring high reliability. The proposal has the potential for uninterruptible power supply and flexible AC transmission applications.

IPM synchronous machine drive response to a single-phase open circuit fault

Abstract: This paper investigates the steady-state and dynamic response of an interior permanent magnet (IPM) synchronous machine drive to a single-phase open-circuit fault. This fault results in rotational electromagnetic asymmetry on both the stator and rotor, making it difficult to analyze using classical dq-transformation techniques. This paper presents a new dq synchronous-frame machine model that is capable of handling this highly asymmetrical fault condition, including the effects of q axis magnetic saturation. Fault responses with two alternative post-fault control strategies are investigated: (1) opening all of the inverter switches so that the machine behaves as an uncontrolled generator (UCG), with the two unfaulted phases connected to the inverter DC link via the antiparallel diodes; and (2) shorting the two remaining unfaulted phases together using the inverter switches. Results of this investigation show that the fault response is generally more benign using the UCG control strategy, with significantly lower phase currents and pulsating torque than corresponding values delivered using the phase-shorting strategy.

On-line stator winding fault diagnosis in inverter-fed AC machines using high frequency signal injection

Abstract: The diagnosis of stator winding faults in inverter fed AC machines using an injected high frequency carrier signal is presented and analyzed in this paper. Measurement of the resulting high frequency negative sequence current (or alternatively of the negative sequence impedance) is used to detect turn faults at an incipient stage. Though sharing the same physical principles of similar techniques applied to line-connected machines, the use of a high frequency signal will be shown to present important advantages, such as providing the same performance almost independent of the fundamental excitation frequency, and drastically reducing the sensitivity to the working condition of the machine, i.e. torque and flux levels.

Maximum power point tracking using adaptive fuzzy logic control for grid-connected photovoltaic system

Abstract: In this paper proposed method of maximum power point tracking using adaptive fuzzy logic control for grid connected photovoltaic system. The system composed of boost converter single-phase inverter connected to utility grid. The maximum power point tracking control is based on adaptive fuzzy logic to control MOSFET switch of boost converter and single phase inverter uses predicted current control to control four IGBTs switch for grid-connected control. Adaptive fuzzy logic controllers provide attractive features such as fast response, good performance and it can also change fuzzy parameter for improving control system. The fuzzy logic predicted current control provide current with sinusoidal waveshape and inphase with voltage. This system can provide energy with low harmonics and high power factor.