Showing papers on "Inverter published in 2005"

A review of single-phase grid-connected inverters for photovoltaic modules

Abstract: This review focuses on inverter technologies for connecting photovoltaic (PV) modules to a single-phase grid. The inverters are categorized into four classifications: 1) the number of power processing stages in cascade; 2) the type of power decoupling between the PV module(s) and the single-phase grid; 3) whether they utilizes a transformer (either line or high frequency) or not; and 4) the type of grid-connected power stage. Various inverter topologies are presented, compared, and evaluated against demands, lifetime, component ratings, and cost. Finally, some of the topologies are pointed out as the best candidates for either single PV module or multiple PV module applications.

Maximum boost control of the Z-source inverter

Abstract: This paper explores control methods for the Z-source inverter and their relationships of voltage boost versus modulation index. A maximum boost control is presented to produce the maximum voltage boost (or voltage gain) under a given modulation index. The control method, relationships of voltage gain versus modulation index, and voltage stress versus voltage gain are analyzed in detail and verified by simulation and experiment.

Pulse-width modulation of Z-source inverters

Abstract: Z-Source inverters have recently been proposed as an alternative power conversion concept as they have both voltage buck and boost capabilities. These inverters use a unique impedance network, coupled between the power source and converter circuit, to provide both voltage buck and boost properties, which cannot be achieved with conventional voltage-source and current-source inverters. To facilitate understanding of Z-source inverter modulation, this paper presents a detailed analysis, showing how various conventional pulse-width modulation strategies can be modified to switch a voltage-type Z-source inverter either continuously or discontinuously, while retaining all the unique harmonic performance features of these conventional modulation strategies. This paper starts by analyzing the modulation requirements of a single-phase H-bridge Z-source inverter, and subsequently extends the analysis to cover the more complex three-phase-leg and four-phase-leg Z-source inverters, with carrier-based implementation reference equations derived for all the inverters. The theoretical and modulation concepts presented have been verified both in simulation and experimentally.

Spin-wave logical gates

Abstract: A universal approach to spin-wave logic gates is presented. The feasibility of a spin-wave based NOT gate has been demonstrated experimentally. We propose to use a Mach–Zender-type current-controlled interferometer based on spin-wave propagation in a ferromagnetic film to construct logical gates. We investigate the performance of the main element of such interferometric logical gates—the controlled phase shifter implemented as a spin-wave device.

Harmonic optimization of multilevel converters using genetic algorithms

Abstract: In this letter, a genetic algorithm (GA) optimization technique is applied to determine the switching angles for a cascaded multilevel inverter which eliminates specified higher order harmonics while maintaining the required fundamental voltage. This technique can be applied to multilevel inverters with any number of levels. As an example, in this paper a seven-level inverter is considered, and the optimum switching angles are calculated offline to eliminate the fifth and seventh harmonics. These angles are then used in an experimental setup to validate the results.

Z-source inverter for motor drives

Abstract: This paper presents a Z-source inverter system and control for general-purpose motor drives. The Z-source inverter system employs a unique LC network in the dc link and a small capacitor on the ac side of the diode front end. By controlling the shoot-through duty cycle, the Z-source can produce any desired output ac voltage, even greater than the line voltage. As a result, the new Z-source inverter system provides ride-through capability during voltage sags, reduces line harmonics, improves power factor and reliability, and extends output voltage range. Analysis, simulation, and experimental results will be presented to demonstrate these new features.

An improved deadbeat control for UPS using disturbance observers

Abstract: A digital control technique for the inverter stage of uninterruptible power supplies is proposed, which is based on a predictive regulator on both output voltage and inductor current. Its aim is to achieve a deadbeat dynamic response for the controlled variables (output voltage and inverter current). Besides the linear state feedback which allocates system poles at the origin so as to achieve deadbeat response for all state variables, the use of a disturbance observer for the estimation of the load current and of any other source of errors (such as dead-times, parameter, and model mismatches) is investigated. The proposed solution is able to guarantee a fast dynamic response and also a precise compensation of any source of unpredictable disturbance. Moreover, with a proper design of observer parameters, it is possible to reduce control sensitivity to model uncertainties, parameter mismatches, and noise on sensed variables, which usually characterizes existing deadbeat control techniques. Finally, the control algorithm is quite simple and requires only the measurements of the output voltage and inductor current. Experimental results on a single-phase 2 kVA prototype show the effectiveness of the proposed approach.

Pulse-Width Modulation of Z-Source Inverters

Abstract: Z-Source inverters have recently been proposed as an alternative power conversion concept as they have both voltage buck and boost capabilities. These inverters use a unique impedance network, coupled between the power source and converter circuit, to provide both voltage buck and boost properties, which cannot be achieved with conventional voltage-source and current-source inverters. To facilitate understanding of Z-source inverter modulation, this paper presents a detailed analysis, showing how various conventional pulse-width modulation strategies can be modified to switch a voltage-type Z-source inverter either continuously or discontinuously, while retaining all the unique harmonic performance features of these conventional modulation strategies. This paper starts by analyzing the modulation requirements of a single-phase H-bridge Z-source inverter, and subsequently extends the analysis to cover the more complex three-phase-leg and four-phase-leg Z-source inverters, with carrier-based implementation reference equations derived for all the inverters. The theoretical and modulation concepts presented have been verified both in simulation and experimentally.

Control of single-stage single-phase PV inverter

Abstract: In this paper the issue of control strategies for single-stage photovoltaic (PV) inverter is addressed. Two different current controllers have been implemented and an experimental comparison between them has been made. A complete control structure for the single-phase PV system is also presented. The main elements of the PV control structure are: - a maximum power point tracker (MPPT) algorithm using the incremental conductance method; - a synchronization method using the phase-locked-loop (PLL), based on delay; the input power control using the dc voltage controller and power feed-forward; - and the grid current controller implemented in two different ways, using the classical proportional integral (PI) and the novel proportional resonant (PR) controllers. The control strategy was tested experimentally on 1.5 kW PV inverter

Boost DC-AC inverter: a new control strategy

Abstract: Boost dc-ac inverter naturally generates in a single stage an ac voltage whose peak value can be lower or greater than the dc input voltage. The main drawback of this structure deals with its control. Boost inverter consists of Boost dc-dc converters that have to be controlled in a variable-operation point condition. The sliding mode control has been proposed as an option. However, it does not directly control the inductance averaged-current. This paper proposes a control strategy for the Boost inverter in which each Boost is controlled by means of a double-loop regulation scheme that consists of a new inductor current control inner loop and an also new output voltage control outer loop. These loops include compensations in order to cope with the Boost variable operation point condition and to achieve a high robustness to both input voltage and output current disturbances. As shown by simulation and prototype experimental results, the proposed control strategy achieves a very high reliable performance, even in difficult transient situations such as nonlinear loads, abrupt load changes, short circuits, etc., which sliding mode control cannot cope with.

Evaluation of the low-frequency neutral-point voltage oscillations in the three-level inverter

Abstract: The nearest vectors to the reference vector are commonly used in space-vector modulation (SVM) strategies. The main advantages of these modulation strategies are the low switching frequencies of the devices, the good output voltage spectra, and the low electromagnetic interference. However, when these techniques are applied to the three-level neutral-point (NP)-clamped inverter, low-frequency oscillations appear in the NP voltage for some operating conditions. As a result, the value of the dc-link capacitors must be increased in order to attenuate such oscillations. In this paper, these amplitudes are quantified for two modulation strategies that use nearest vectors to the reference vector. Owing to the nondimensional variables used in the analysis, the information provided will help for the calculation of the dc-link capacitors in a given specific application. Simulated and experimental examples are presented.

Operation of a medium-voltage drive under faulty conditions

Abstract: This paper presents a method for operating cascaded multilevel inverters when one or more power cells are damaged. The method is based on the use of additional switches in the power circuit to bypass the faulty cell. To control the cells, the angle of phase shifting in the carrier signals is modified according to the number of operating cells, to minimize the load voltage distortion, when the inverter operates in failure mode. The reference signals of the pulsewidth-modulation modulators are also modified to increase the output voltage. Simulation and experimental results show the effectiveness of this method, which significantly increases the reliability of the drive.

Low Frequency Current Ripple Reduction Technique with Active Control in a Fuel Cell Power System with Inverter Load

Abstract: A fuel cell power system that contains a single-phase dc-ac inverter tends to draw an ac ripple current at twice the output frequency. Such a ripple current may shorten fuel cell life span and worsen the fuel efficiency due to the hysteresis effect. The most obvious impact is it tends to reduce the fuel cell output capacity because the fuel cell controller trips under instantaneous over-current condition. In this paper, the ripple current propagation path is analyzed, and its linearized ac model is derived. The equivalent circuit model and ripple current reduction with passive energy storage component are simulated and verified with experiments. An advanced active control technique is then proposed to incorporate a current control loop in the dc-dc converter for ripple reduction. The proposed active ripple reduction method has been verified with computer simulation and hardware experiment with a proton exchange membrane type fuel cell using a multiphase dc/dc converter along with a full-bridge dc-ac inverter. Test results with open loop, single voltage loop, and the proposed active current-loop control are provided for comparison

Fault detection and diagnosis in an induction Machine drive: a pattern recognition approach based on concordia stator mean current vector

Abstract: The aim of this paper is to study the feasibility of fault detection and diagnosis in a three-phase inverter feeding an induction motor. The proposed approach is a sensor-based technique using the mains current measurement. A localization domain made with seven patterns is built with the stator Concordia mean current vector. One is dedicated to the healthy domain and the last six are to each inverter switch. A probabilistic approach for the definition of the boundaries increases the robustness of the method against the uncertainties due to measurements and to the PWM. In high-power equipment where it is crucial to detect and diagnose the inverter faulty switch, a simple algorithm compares the patterns and generates a Boolean indicating the faulty device. In low-power applications (less than 1 kW) where only fault detection is required, a radial basis function (RBF) evolving architecture neural network is used to build the healthy operation area. Simulated experimental results on 0.3- and 1.5-kW induction motor drives show the feasibility of the proposed approach.

Optimal pulse-width modulation for three-level inverters

Abstract: The three-level neutral-point-clamped voltage source inverter is widely used in high power, medium voltage applications. This paper studies continuous and discontinuous pulse-width modulation for this inverter. Detailed analysis of discontinuous modulation shows that the average switching frequency is not directly proportional to the carrier or sampling frequency, since additional switching transitions occur between different regions of discontinuity. At typical switching frequencies for high power applications (up to 2 kHz) these additional transitions contribute significantly to the inverter's total losses, so that a proper comparison of the harmonic performance can only be carried out under constant loss conditions with varying carrier frequency. This comparison is performed for a typical industrial medium voltage inverter. The paper then considers the major issues of neutral-point voltage balancing and loss distribution within the inverter, for the identified optimal modulation schemes.

Variable speed distributed drive train wind turbine system

Abstract: A variable speed wind turbine employing a rotor (103) connected to a multiplicity of synchronous generators (106 - 112) with wound field or permanent magnet rotors. A passive rectifier (114 - 120) and an inverter (136 - 142) are used for power transfer back to the grid. A Turbine Control Unit (TCU) (132) commands a required generator torque based on rotor speed and power output of the turbine inverters. Torque is controlled by regulating the DC current by control of the inverter. A main-shaft-damping filter is provided by measurement of the DC bus voltage. In high winds the turbine remains at a constant average output power through a constant torque command and a varying pitch command to a rotor pitch servo system (102). A set point is fixed at the inverter output such that output VAR load is minimized running the turbine at very nearly unity power factor. Dynamic VAR and power factor control is provided by a separate VAR apparatus.

Operation modes and characteristics of the Z-source inverter with small inductance

Abstract: The Z-source inverter utilizing a unique LC network and forbidden shoot-through states provides unique features, such as the ability to buck and boost voltage with a single stage simple structure. The analysis and control methods provided in the literature are based on an assumption that the inductor is relatively large and the inductor current is continuous and has small ripple. This assumption becomes invalid when the inductance is small in order to minimize the inductor's size and weight for some applications where volume and weight are crucial. Under this small inductance condition, the inductor current becomes high ripple or even discontinuous. As results, the Z-source inverter exhibits new operation modes that have not been discussed before. This paper analyzes these new operation modes and voltage boost relationship of the Z-source inverter under the low inductance and large current ripple condition.

Voltage and frequency control of inverter based weak LV network microgrid

Abstract: In this paper voltage and frequency control of islanded microgrid after intentional and unintentional switching events are investigated. The weak low voltage (LV) network based microgrid consists of two inverter based distributed generation (DG) units. One unit is a storage (battery) unit and the other is a photovoltaic (PV) cell. In this case the battery inverter with rapid response is considered to act as a master and it has the main responsibility to control the voltage and frequency in microgrid when islanded from the main distribution network. The studies are performed on a PSCAD simulation software package. Simulation studies show the voltage - active power and frequency - reactive power dependency in weak LV network. The studies also show that in order to maintain frequency balance in islanded microgrid, there is need for a reference sine wave generator inside master unit which imitates the main network phase voltages and gives the input for master units' (battery storage) PLL (phase locked loop) during islanding

Mechanical sensorless drives of IPMSM with online parameter identification

Abstract: A mechanical sensorless drive system for an interior permanent-magnet synchronous motor, for which parameters including the inverter are identified, is proposed in this paper. The rotor position is estimated by a signal-injection sensorless scheme at standstill. The resistance, including the on-resistance of the insulated-gate bipolar transistor, the voltage error caused by the dead time of the inverter, and the d-axis and q-axis inductances are identified at standstill using the estimated position. After the motor starts by the signal-injection sensorless control, the sensorless scheme changes to a scheme based on the extended electromotive force estimation, which uses the identified parameters. The magnet flux linkage is also identified under the sensorless operation. The effectiveness of the proposed method is verified by several experimental results

Space vector PWM signal generation for multilevel inverters using only the sampled amplitudes of reference phase voltages

Abstract: A pulse width modulation (PWM) scheme for multilevel inverters is proposed. The proposed PWM scheme generates the inverter leg switching times, from the sampled reference phase voltage amplitudes and centres the switching times for the middle vectors, in a sampling interval, as in the case of conventional space vector PWM (SVPWM). The SVPWM scheme, presented for multilevel inverters, can also work in the overmodulation range, using only the sampled amplitudes of reference phase voltages. The present PWM technique does not involve any sector identification and considerably reduces the computation time when compared to the conventional space vector PWM technique. The present PWM signal generation scheme can be used for any multilevel inverter configuration. A five-level inverter configuration, using an open-ended winding induction motor drive, is used to verify the SVPWM generation scheme experimentally.

A multilevel inverter system for an induction motor with open-end windings

Abstract: In this paper, a multilevel inverter system for an open-end winding induction motor drive is described. Multilevel inversion is achieved by feeding an open-end winding induction motor with two two-level inverters in cascade (equivalent to a three-level inverter) from one end and a single two-level inverter from the other end of the motor. The combined inverter system with open-end winding induction motor produces voltage space-vector locations identical to a six-level inverter. A total of 512 space-vector combinations are available in the proposed scheme, distributed over 91 space-vector locations. The proposed inverter drive scheme is capable of producing a multilevel pulsewidth-modulation (PWM) waveform for the phase voltage ranging from a two-level waveform to a six-level waveform depending on the modulation range. A space-vector PWM scheme for the proposed drive is implemented using a 1.5-kW induction motor with open-end winding structure.

Multilevel PWM inverters suitable for the use of stand-alone photovoltaic power systems

Abstract: This paper presents a new multilevel pulse width-modulation (PWM) inverter scheme for the use of stand-alone photovoltaic systems. It consists of a PWM inverter, an assembly of LEVEL inverters, generating staircase output voltages, and cascaded transformers. To produce high-quality output voltage waves, it synthesizes a large number of output voltage levels using cascaded transformers, which have a series-connected secondary. By a suitable selection of the secondary turn-ratio of the transformer, the amplitude of an output voltage appears at the rate of an integer to an input dc source. Operational principles and analysis are illustrated in depth. The validity of the proposed system is verified through computer-aided simulations and experimental results using prototypes generating output voltages of an 11 level and a 29 level, respectively, and their results are compared with conventional counterparts.

Implementation and control of distributed PWM cascaded multilevel inverters with minimal harmonic distortion and common-mode voltage

Abstract: Cascaded multilevel inverters can be implemented through the series connection of single-phase modular power bridges. This work presents details on how these bridges should be implemented and operated to synchronize their pulse-width-modulation (PWM) carriers, fundamental references and sampling instances to implement a network-controlled cascaded inverter with distributed PWM computation and overall optimal system performance. The paper begins by detailing the development and control of an integrated power bridge, designed with its own digital signal processor and associated control circuitry. Details describing the networked control algorithm and signal protocol needed for synchronizing the multiple power bridges through a dynamically fast data communication network, are then presented to achieve optimum harmonic cancellation and reduced common-mode voltage. The practicality and performance of the presented modular implementation concepts have been confirmed through the close match between simulation and experimental results obtained using a modular cascaded five-level inverter prototype.

An integrated inverter with maximum power tracking for grid-connected PV systems

Abstract: An inverter for grid-connected photovoltaic systems is presented in this paper. It can globally locate the maximum power point of the panel over wide insolation and feed the solar energy to the grid. Its structure mainly integrates a previously developed maximum point tracking method and output current shaping function into a buck-boost-derived converter and then inverts the shaped current through a grid frequency bridge to the grid. Instead of having a storage capacitor connecting in parallel with the converter output, series connection is used, so that the required capacitor voltage rating is lower than that in classical inverters. Most importantly, the inverter output current harmonics are less sensitive to the capacitor value. A 30-W laboratory prototype has been built. The tracking capability, inversion efficiency, and large-signal responses at different insolations have been investigated. Detailed analysis on the inverter performance has been performed. The theoretical predictions are verified with the experimental results.

Voltage control with inverter-based distributed generation

Abstract: This letter proposes a method to use the voltage-source inverters with distributed generation to control the voltage in a distribution network A droop line is used to prevent hunting between controllers Analytical expressions are derived for the voltage along a feeder with uniformly distributed load/generation The proposed algorithm will alleviate the voltage-control problem reported when installing distributed generation

An adaptive dead-time compensation strategy for voltage source inverter fed motor drives

Abstract: This paper presents an adaptive dead-time compensation strategy to obtain fundamental phase voltage for inverter fed vector controlled permanent magnet synchronous motor drives. The amplitude of phase dead-time compensation voltage (DTCV) to compensate disturbance voltage due to undesirable characteristics of inverter, such as dead-time, turn-on/off time of switching devices, and on-voltages of switching devices and diodes is adaptively determined according to a dead-time compensation time (DTCT). DTCT is identified on-line with using a /spl delta/-axis disturbance voltage in the current reference frame that is synchronized with current vector. The /spl delta/-axis disturbance voltage is estimated by a disturbance observer. The accuracy of identified DTCT is experimentally confirmed by calculating the mean absolute percentage error (MAPE) between a calculated active power and a measured one. MAPE for adaptive DTCT is almost within 5% at any operating point.

Space vector modulation schemes for a five-phase voltage source inverter

Abstract: Application of power electronics in electric drives enables utilisation of AC machines with a phase number higher than three. Such multiphase motor drives are nowadays considered for various applications. Multiphase drives are invariably supplied from multiphase voltage source inverters (VSIs) and adequate methods for VSI pulse width modulation (PWM) are therefore required. This paper analyses different space vector PWM (SVPWM) schemes for a five-phase VSI, which can be used for five-phase motor drives. A detailed model of a five-phase VSI is presented first in terms of space vectors. Next, the existing technique of utilising only large space vectors is elaborated. It is shown that this SVPWM method leads to generation of high amounts of low-order output voltage harmonics. Finally, a novel SVPWM method is introduced, which enables operation with pure sinusoidal output voltages up to a certain reference voltage value, which is smaller than the maximum achievable with the given DC link voltage. To enable full utilisation of the DC bus voltage, this SVPWM scheme is complemented with another one, which unavoidably does lead to generation of some low order harmonics. These harmonics are however of significantly lower values than when only large vectors are used. A detailed performance evaluation of the existing and newly developed schemes is done and it is presented in terms of quality of the output voltage waveforms. Simulation results are included throughout the paper to illustrate and verify the theoretical considerations

Suppression of line voltage related distortion in current controlled grid connected inverters

Abstract: The influence of selected control strategies on the level of low-order current harmonic distortion generated by an inverter connected to a distorted grid is investigated through a combination of theoretical and experimental studies. A detailed theoretical analysis, based on the concept of harmonic impedance, establishes the suitability of inductor current feedback versus output current feedback with respect to inverter power quality. Experimental results, obtained from a purpose-built 500-W, three-level, half-bridge inverter with an L-C-L output filter, verify the efficacy of inductor current as the feedback variable, yielding an output current total harmonic distortion (THD) some 29% lower than that achieved using output current feedback. A feed-forward grid voltage disturbance rejection scheme is proposed as a means to further reduce the level of low-order current harmonic distortion. Results obtained from an inverter with inductor current feedback and optimized feed-forward disturbance rejection show a THD of just 3% at full-load, representing an improvement of some 53% on the same inverter with output current feedback and no feed-forward compensation. Significant improvements in THD were also achieved across the entire load range. It is concluded that the use of inductor current feedback and feed-forward voltage disturbance rejection represent cost-effect mechanisms for achieving improved output current quality.

A single-phase inverter system for PV power injection and active power filtering with nonlinear inductor consideration

Abstract: This paper proposes a single-phase two-wire inverter system for photovoltaic (PV) power injection and active power filtering (APF) with nonlinear inductor consideration. The proposed system can fully or partially perform APF, process PV power, eliminate harmonic currents, improve power factor, and take into account the nonlinear effect of its output filter inductor. In the system, even though only the utility current is sensed, both APF and maximum power point tracking features can be still achieved, reducing the number of current sensors and cost significantly. To prevent output current from exceeding switch ratings, inverter current is properly controlled through a current estimator and a defined limit circle. A self-learning algorithm is also proposed to determine nonlinear inductance, which can increase the accuracy of the estimated current. Simulations and experimental results have verified the feasibility of the proposed PV inverter system and the algorithm.

Multuple-light discharge lamp lighting device

Abstract: A multiple-light discharge lamp lighting device in which each of the tube currents of a plurality of discharge lamps can be stabilized and equalized at a low cost without providing a ballast element on the secondary side of an inverter transformer. The discharge lamp lighting device (10) comprises an inverter means (12) and a plurality of inverter transformers TR1-TRn having secondary windings Ns1-Nsn connected with discharge lamps La1-Lan, respectively. Furthermore, variable impedance elements Z1-Zn, preferably variable inductance elements, are connected in series with the primary windings Np1-Npn of the plurality of inverter transformers TR1-TRn and thereby each tube current can be stabilized and equalized without using a high withstand voltage element.