Showing papers on "Inverter published in 2010"
TL;DR: A survey of different topologies, control strategies and modulation techniques used by cascaded multilevel inverters in the medium-voltage inverter market is presented.
Abstract: Cascaded multilevel inverters synthesize a medium-voltage output based on a series connection of power cells which use standard low-voltage component configurations. This characteristic allows one to achieve high-quality output voltages and input currents and also outstanding availability due to their intrinsic component redundancy. Due to these features, the cascaded multilevel inverter has been recognized as an important alternative in the medium-voltage inverter market. This paper presents a survey of different topologies, control strategies and modulation techniques used by these inverters. Regenerative and advanced topologies are also discussed. Applications where the mentioned features play a key role are shown. Finally, future developments are addressed.
2,111 citations
TL;DR: An inverter configuration based on three-level building blocks to generate five-level voltage waveforms is suggested and it is shown that such an inverter may be operated at a very low switching frequency to achieve minimum on-state and dynamic device losses for highly efficient MV drive applications while maintaining low harmonic distortion.
Abstract: This paper gives an overview of medium-voltage (MV) multilevel converters with a focus on achieving minimum harmonic distortion and high efficiency at low switching frequency operation. Increasing the power rating by minimizing switching frequency while still maintaining reasonable power quality is an important requirement and a persistent challenge for the industry. Existing solutions are discussed and analyzed based on their topologies, limitations, and control techniques. As a preferred option for future research and application, an inverter configuration based on three-level building blocks to generate five-level voltage waveforms is suggested. This paper shows that such an inverter may be operated at a very low switching frequency to achieve minimum on-state and dynamic device losses for highly efficient MV drive applications while maintaining low harmonic distortion.
1,150 citations
TL;DR: In this article, the authors describe the control and operating performance of a modular multilevel PWM inverter for a transformerless medium-voltage motor drive, where the inverter is prominent in the modular arm structure consisting of a cascaded stack of multiple bidirectional choppercells.
Abstract: This paper describes the control and operating performance of a modular multilevel PWM inverter for a transformerless medium-voltage motor drive. The inverter is prominent in the modular arm structure consisting of a cascaded stack of multiple bidirectional chopper-cells. The dominant ac-voltage fluctuation with the same frequency as the motor (inverter) frequency occurs across the dc capacitor of each chopper-cell. The magnitude of the voltage fluctuation is inversely proportional to the motor frequency. This paper achieves theoretical analysis on the voltage fluctuation, leading to system design. A downscaled model rated at 400 V and 15 kW is designed and built up to confirm the validity and effectiveness of the nine-level (17-level in line-to-line) PWM inverter for a medium-voltage motor drive.
653 citations
TL;DR: In this paper, a switched inductor (SL) Z-source inverter is proposed to enlarge voltage adjustability, which employs a unique SL impedance network to couple the main circuit and the power source.
Abstract: On the basis of the classical Z-source inverter, this paper presents a developed impedance-type power inverter that is termed the switched inductor (SL) Z-source inverter. To enlarge voltage adjustability, the proposed inverter employs a unique SL impedance network to couple the main circuit and the power source. Compared with the classical Z-source inverter, the proposed inverter increases the voltage boost inversion ability significantly. Only a very short shoot-through zero state is required to obtain high voltage conversion ratios, which is beneficial for improving the output power quality of the main circuit. In addition, the voltage buck inversion ability is also provided in the proposed inverter for those applications that need low ac voltages. Similar to the classical Z-source inverter, the proposed concepts of SL Z-source inverter can be applied to various applications of dc-ac, ac-ac, dc-dc, and ac-dc power conversion. A detailed topology analysis and a generalized discussion are given. Both simulation and experimental results verify the analytical results.
546 citations
TL;DR: A model predictive current control algorithm that is suitable for multilevel converters and its application to a three-phase cascaded H-bridge inverter and experimental results validate the proposed control algorithm.
Abstract: This paper presents a model predictive current control algorithm that is suitable for multilevel converters and its application to a three-phase cascaded H-bridge inverter. This control method uses a discrete-time model of the system to predict the future value of the current for all voltage vectors, and selects the vector which minimizes a cost function. Due to the large number of voltage vectors available in a multilevel inverter, a large number of calculations are needed, making difficult the implementation of this control in a standard control platform. A modified control strategy that considerably reduces the amount of calculations without affecting the system's performance is proposed. Experimental results for five- and nine-level inverters validate the proposed control algorithm.
478 citations
TL;DR: A new current feedback method for PR current control is proposed, where the weighted average value of the currents flowing through the two inductors of the LCL filter is used as the feedback to the current PR regulator.
Abstract: For a grid-connected converter with an LCL filter, the harmonic compensators of a proportional-resonant (PR) controller are usually limited to several low-order current harmonics due to system instability when the compensated frequency is out of the bandwidth of the system control loop. In this paper, a new current feedback method for PR current control is proposed. The weighted average value of the currents flowing through the two inductors of the LCL filter is used as the feedback to the current PR regulator. Consequently, the control system with the LCL filter is degraded from a third-order function to a first-order one. A large proportional control-loop gain can be chosen to obtain a wide control-loop bandwidth, and the system can be optimized easily for minimum current harmonic distortions, as well as system stability. The inverter system with the proposed controller is investigated and compared with those using traditional control methods. Experimental results on a 5-kW fuel-cell inverter are provided, and the new current control strategy has been verified.
465 citations
TL;DR: In this paper, the ground current in a 1.5kW PV installation is measured under different conditions and used to build a simulation model, which allows the study of the influence of the harmonics injected by the inverter on the ground currents.
Abstract: For low-power grid-connected applications, a single-phase converter can be used. In photovoltaic (PV) applications, it is possible to remove the transformer in the inverter to reduce losses, costs, and size. Galvanic connection of the grid and the dc sources in transformerless systems can introduce additional ground currents due to the ground parasitic capacitance. These currents increase conducted and radiated electromagnetic emissions, harmonics injected in the utility grid, and losses. Amplitude and spectrum of the ground current depend on the converter topology, the switching strategy, and the resonant circuit formed by the ground capacitance, the converter, the ac filter, and the grid. In this paper, the ground current in a 1.5-kW PV installation is measured under different conditions and used to build a simulation model. The installation includes a string of 16 PV panel, a full-bridge inverter, and an LCL filter. This model allows the study of the influence of the harmonics injected by the inverter on the ground current.
418 citations
TL;DR: The proposed single-phase H-bridge multilevel converter for PV systems governed by a new integrated fuzzy logic controller (FLC)/modulator offers improved performance over two-level inverters, particularly at low-medium power.
Abstract: Converters for photovoltaic (PV) systems usually consist of two stages: a dc/dc booster and a pulsewidth modulated (PWM) inverter. This cascade of converters presents efficiency issues, interactions between its stages, and problems with the maximum power point tracking. Therefore, only part of the produced electrical energy is utilized. In this paper, the authors propose a single-phase H-bridge multilevel converter for PV systems governed by a new integrated fuzzy logic controller (FLC)/modulator. The novelties of the proposed system are the use of a fully FLC (not requiring any optimal PWM switching-angle generator and proportional-integral controller) and the use of an H-bridge power-sharing algorithm. Most of the required signal processing is performed by a mixed-mode field-programmable gate array, resulting in a fully integrated System-on-Chip controller. The general architecture of the system and its main performance in a large spectrum of practical situations are presented and discussed. The proposed system offers improved performance over two-level inverters, particularly at low-medium power.
406 citations
TL;DR: The number of gate driving circuits is reduced, which leads to the reduction of the size and power consumption in the driving circuits, and the total harmonic of the output waveform is also reduced.
Abstract: A novel multilevel inverter with a small number of switching devices is proposed. It consists of an H-bridge and an inverter which outputs multilevel voltage by switching the dc voltage sources in series and in parallel. The proposed inverter can output more numbers of voltage levels in the same number of switching devices by using this conversion. The number of gate driving circuits is reduced, which leads to the reduction of the size and power consumption in the driving circuits. The total harmonic of the output waveform is also reduced. The proposed inverter is driven by the hybrid modulation method. In this paper, the circuit configuration, theoretical operation, Fourier analysis, simulation results with MATLAB/SIMULINK, and experimental results are shown. The experimental results accorded with the simulation results.
397 citations
TL;DR: In this article, the leakage current suppressing method, in which all common-mode paths are considered, has been proposed, and the existing full-bridge and half-bridge type converters have been analyzed by using the developed model and rules, and then, a new fullbridge-type converter structure and a compensation strategy for half-branched inverter have been presented finally.
Abstract: Due to the characteristics of low cost and high efficiency, the transformerless photovoltaic (PV) grid-connected inverters have been popularized in the application of solar electric generation system in residential market. Unfortunately, the leakage current through the stray capacitors between the PV array and the ground is harmful. This paper focuses on the leakage current suppressing method, in which all common-mode paths are considered. First, the common-mode analytical model at switching frequency is developed, and the rules of eliminating switching frequency common-mode source are summarized based on this model. The existing full-bridge- and half-bridge-type converters have been analyzed by using the developed model and rules, and then, a new full-bridge-type converter structure and a compensation strategy for half-bridge-type inverter have been presented finally.
365 citations
21 Jun 2010
TL;DR: These new networks exhibit some unique advantages, such as the increased voltage gain and reduced voltage stress in the voltage-fed trans-ZSIs and the expanded motoring operation range in the current- fed trans- ZSIs, when the turns ratio of the transformer windings is over 1.
Abstract: This paper extends the impedance-source (Z-source) inverters concept to the transformer based Z-source (trans-Z-source) inverters. The original Z-source inverter (ZSI) employs an impedance network of two inductors and two capacitors connected in a special arrangement to interface the dc source and the inverter bridge. It has overcome the conceptual limitations of the traditional voltage-source inverter and the current-source inverter. In the proposed trans-Z-source inverters, the impedance network consists of a transformer and one capacitor. While maintaining the main features of the previously presented Z-source network, the new networks exhibit some unique advantages, such as the increased voltage gain in the voltage-fed trans-ZSIs and the expanded motoring operation range in the current-fed trans-ZSIs when the turns-ratio of the transformer windings is over 1. Simulation and experimental results of one of the voltage-fed trans-Z-source inverters are provided to verify the analysis.
TL;DR: In this paper, a new family of extended-boost quasi Z-source inverter (ZSI) is proposed to fill the research gap left in the development of original ZSI, which can be operated with same modulation methods that were developed for original Zsi.
Abstract: The Z-source inverter has gained popularity as a single-stage buck-boost inverter topology among many researchers. However, its boosting capability could be limited, and therefore, it may not be suitable for some applications requiring very high boost demand of cascading other dc-dc boost converters. This could lose the efficiency and demand more sensing for controlling the added new stages. This paper is proposing a new family of extended-boost quasi Z -source inverter (ZSI) to fill the research gap left in the development of ZSI. These new topologies can be operated with same modulation methods that were developed for original ZSI. Also, they have the same number of active switches as original ZSI preserving the single-stage nature of ZSI. Proposed topologies are analyzed in the steady state and their performances are validated using simulated results obtained in MATLAB/Simulink. Furthermore, they are experimentally validated with results obtained from a prototype developed in the laboratory.
TL;DR: In this article, an extremum seeking (ES) controller that utilizes the natural inverter ripple is designed and tested on a simulated solar array with a grid-tied inverter.
Abstract: This study develops a maximum power point tracking algorithm that optimizes solar array performance and adapts to rapidly varying irradiance conditions. In particular, a novel extremum seeking (ES) controller that utilizes the natural inverter ripple is designed and tested on a simulated solar array with a grid-tied inverter. The new algorithm is benchmarked against the perturb and observe (PO) method using high-variance irradiance data gathered on a rooftop array experiment in Princeton, NJ. The ES controller achieves efficiencies exceeding 99% with transient rise-time to the maximum power point of less than 0.1 s. It is shown that voltage control is more stable than current control and allows for accurate tracking of faster irradiance transients. The limitations of current control are demonstrated in an example. Finally, the effect of capacitor size on the performance of ripple-based ES control is investigated.
TL;DR: In this article, the authors present controller design and optimization methods to stably coordinate multiple inverter-interfaced DGs and to robustly control individual interface inverters against voltage and frequency disturbances.
Abstract: Microgrids are a new concept for future energy distribution systems that enable renewable energy integration and improved energy management capability. Microgrids consist of multiple distributed generators (DGs) that are usually integrated via power electronic inverters. In order to enhance power quality and power distribution reliability, microgrids need to operate in both grid-connected and island modes. Consequently, microgrids can suffer performance degradation as the operating conditions vary due to abrupt mode changes and variations in bus voltages and system frequency. This paper presents controller design and optimization methods to stably coordinate multiple inverter-interfaced DGs and to robustly control individual interface inverters against voltage and frequency disturbances. Droop-control concepts are used as system-level multiple DG coordination controllers, and control theory is applied to device-level inverter controllers. Optimal control parameters are obtained by particle-swarm-optimization algorithms, and the control performance is verified via simulation studies.
TL;DR: In this article, the authors proposed a feedforward function of the grid voltage for the grid-connected inverter with an LCL filter, which can effectively suppress the current distortion arising from the Grid voltage harmonics, and the steadystate error of the injected current can be substantially reduced even if a conventional proportional and integral regulator is applied.
Abstract: The grid-connected inverter with an LCL filter has the ability of attenuating the high-frequency current harmonics. However, the current distortion caused by harmonics in the grid voltage is difficult to be eliminated. Increasing the loop gain can reduce the current distortion, but this approach is compromised by the system stability requirement. Without increasing the loop gain, applying feedforward of the grid voltage can suppress the effect of grid voltage harmonics. This paper proposes the feedforward function of the grid voltage for the grid-connected inverter with an LCL filter. Specifically, the proposed feedforward function involves proportional, derivative, and second derivative of the grid voltage, and can be simplified according to the dominant harmonics in the grid voltage. The proposed feedforward scheme can effectively suppress the current distortion arising from the grid voltage harmonics, and the steady-state error of the injected current can be substantially reduced even if a conventional proportional and integral regulator is applied. A 6-kW experimental prototype has been tested to verify the effectiveness of the proposed feedforward scheme.
TL;DR: Comparisons among the modulation techniques are discussed, and it is proven that the proposed modulation for two- and three-level inverters presents the best results.
Abstract: In some photovoltaic (PV) applications, it is possible to remove the transformer of a system in order to reduce losses, cost, and size. In transformerless systems, the PV module parasitic capacitance can introduce leakage currents in which the amplitude depends on the converter topology, on the pulsewidth modulation, and on the resonant circuit comprised by the system components. Based on the common-mode voltage model, modulation techniques are proposed to eliminate the leakage current in transformerless PV systems without requiring any modification on the converter and any additional hardware. The main drawback is that the proposed modulation technique for two-level inverters can only be used with 650-V dc link in the case of a 110-V (rms) grid phase voltage. Comparisons among the modulation techniques are discussed, and it is proven that the proposed modulation for two- and three-level inverters presents the best results. To validate the models used in the simulations, an experimental three-phase inverter is used.
TL;DR: A single-phase multistring five-level photovoltaic (PV) inverter topology for grid-connected PV systems with a novel pulsewidth-modulated (PWM) control scheme that offers much less total harmonic distortion and can operate at near-unity power factor.
Abstract: This paper presents a single-phase multistring five-level photovoltaic (PV) inverter topology for grid-connected PV systems with a novel pulsewidth-modulated (PWM) control scheme. Three PV strings are cascaded together in parallel configuration and connected to a five-level inverter to produce output voltage in five levels: zero, +1/2V dc, V dc, -1/2V dc, and -V dc. Two reference signals that were identical to each other with an offset that was equivalent to the amplitude of the triangular carrier signal were used to generate PWM signals for the switches. DSP TMS320F2812 is used to implement this PWM switching scheme together with a digital proportional-integral current control algorithm. The inverter offers much less total harmonic distortion and can operate at near-unity power factor. The validity of the proposed inverter is verified through simulation and implemented in a prototype. The experimental results are compared with a conventional single-phase multistring three-level grid-connected PWM inverter.
TL;DR: In this article, an optimal sizing methodology based on an energy approach is described and applied to grid-connected photovoltaic systems taking into account the PV module technology and inclination, the inverter type and the location.
21 Jun 2010
TL;DR: This paper focuses on the research advances in developing the cascade multilevel inverter topologies and their system configurations for power system applications from reviewing the traditional power conversion technology and the needs to eliminate zigzag transformers required in the traditional technology, to how to configure the cascade multi-level inverters to deal with unbalance and real-power (or active-power) flow.
Abstract: Multilevel converters and inverters have become the enabling power conversion technology for high voltage high power applications in today's power systems and large motor drives. Although the neutral-point clamped (NPC, a 3-level) inverter was invented in 1979, the multilevel concept was not formally established until the early 1990s when the diode-clamped multilevel inverter, the capacitor-clamped (or flying capacitor) multilevel inverter, and the cascade multilevel inverter were proposed and fully studied. In this paper, we will first focus on the research advances in developing the cascade multilevel inverter topologies and their system configurations for power system applications from reviewing the traditional power conversion technology and the needs to eliminate zigzag transformers required in the traditional technology, to how to configure the cascade multilevel inverters to deal with unbalance and real-power (or active-power) flow. These research breakthroughs have made the cascade multilevel inverters a perfect topology for power system applications such as FACTS devices. For example, the cascade multilevel inverter based 75 Mvar and 50 Mvar STATCOMs have been reported. Since the mid of 1990s, many contributors have made great effort in developing more multilevel inverter topologies because all the three multilevel topologies have certain limitations and are not operable in some applications. Then, we will review the generalized multilevel inverter topology, its topological advances to other multilevel inverters/ converters, and their potential applications. This paper also provides insights to how multilevel inverter topologies are related to each other and their pros and cons in practical applications.
TL;DR: In this article, the authors proposed a new dead time compensation method for a PWM inverter, which can be easily implemented by feedforwardly adding compensation voltages to the output reference voltage of the synchronous d-axis proportional-integral current regulator.
Abstract: A new dead time compensation method for a pulsewidth modulation (PWM) inverter is proposed. In the PWM inverter, voltage distortion due to the dead time effects produces fifth and seventh harmonics in the phase currents of the stationary reference frame, and a sixth harmonic in the d- and q-axis currents of the synchronous reference frame, respectively. In this paper, the sixth harmonic of the integrator output of the synchronous d-axis proportional-integral (PI) current regulator is used to compensate the output voltage distortion due to the dead time effects, since the integrator output has ripple corresponding to six times the stator fundamental frequency. The proposed method can be easily implemented by feedforwardly adding compensation voltages to the output reference voltage of the synchronous PI current regulator. The proposed method, therefore, has some significant advantages such as simple implementation without additional hardware, easy mathematical computation, no offline experimental measurements, and application in both the steady state and the transient state. The validity of the proposed compensation algorithm is shown through several experiments.
TL;DR: In this paper, the stability analysis of multi-inverter systems has been performed in a computationally intensive manner by considering the entire microgrid, where each inverter is controlled by decentralized active power/voltage frequency and reactive power/volage magnitude droop control laws.
Abstract: Microgrid-containing parallel-connected inverters, where each inverter is controlled by decentralized active power/voltage frequency and reactive power/voltage magnitude droop control laws results in flexible and expandable systems. These systems have been known to have stability problems for large values of active power/voltage frequency droop control gain. However, so far the stability analysis of multi-inverter systems has always been performed in a computationally intensive manner by considering the entire microgrid. In a practical microgrid, where the number of inverters may be large or the capacity of the units may differ, it becomes essential to develop a method by which stability can be examined without much computational burden. The system of differential algebraic equations has been simplified using justifiable assumptions to result in a final expression that allows the stability of the microgrid to be examined separately with respect to the droop control laws of each inverter transformed into an equivalent network. Moreover, the procedure allows taking into consideration the R/X ratio of the interconnecting cables. Analysis of final expressions validate the stability results reported in literature. Experimental results on hardware show the stable operation of the microgrid.
TL;DR: In this paper, a second-order general-integrator (SOGI) scheme is proposed to implement the virtual impedance, which is less sensitive to the output current noise, avoids to perform the time derivative function, achieves better output-voltage total harmonic distortion, and enhances the sharing of nonlinear loads.
Abstract: This paper explores the impact of the output impedance on the active and reactive power flows between parallelized inverters operating with the droop method. In these systems, a virtual output impedance is usually added to the control loop of each inverter to improve the reactive power sharing, regardless of line-impedance unbalances and the sharing of nonlinear loads. The virtual impedance is usually implemented as the time derivative of the inverter output current, which makes the system highly sensitive to the output current noise and to nonlinear loads with high slew rate. To solve this, a second-order general-integrator (SOGI) scheme is proposed to implement the virtual impedance, which is less sensitive to the output current noise, avoids to perform the time derivative function, achieves better output-voltage total harmonic distortion, and enhances the sharing of nonlinear loads. Experimental results with two 2-kVA inverter systems under linear and nonlinear loads are provided to validate this approach.
01 Jan 2010
TL;DR: In this article, the authors discuss issues and solutions for dealing with fault current contributions from inverter-based distributed energy resources, and propose a fault-tolerant distributed energy system.
Abstract: This report discusses issues and provides solutions for dealing with fault current contributions from inverter-based distributed energy resources.
TL;DR: A high performance and also efficient torque and flux controllers are obtained, enabling a DTC solution for multilevel-inverter-powered motor drives.
Abstract: This paper presents a hybrid cascaded H-bridge multilevel motor drive direct torque control (DTC) scheme for electric vehicles (EVs) or hybrid EVs. The control method is based on DTC operating principles. The stator voltage vector reference is computed from the stator flux and torque errors imposed by the flux and torque controllers. This voltage reference is then generated using a hybrid cascaded H-bridge multilevel inverter, where each phase of the inverter can be implemented using a dc source, which would be available from fuel cells, batteries, or ultracapacitors. This inverter provides nearly sinusoidal voltages with very low distortion, even without filtering, using fewer switching devices. In addition, the multilevel inverter can generate a high and fixed switching frequency output voltage with fewer switching losses, since only the small power cells of the inverter operate at a high switching rate. Therefore, a high performance and also efficient torque and flux controllers are obtained, enabling a DTC solution for multilevel-inverter-powered motor drives.
TL;DR: In this paper, all possible steady states of a Z-source inverter are identified and analyzed with the objective of deriving design guidelines for the symmetrical impedance network. And the proposed design method can also be used to predict the critical values of capacitance and inductance below which static states appear during the operating cycle.
Abstract: All possible steady states of a Z-source inverter are identified and analyzed with the objective of deriving design guidelines for the symmetrical impedance network. This paper shows that, in addition to the desired three dynamic states, an operating cycle can contain another three static states that do not contribute to the power conversion process. These three static states can be avoided by selecting suitably large capacitors and inductors. By using the equations derived in the steady-state analysis, this paper presents guidelines to design the impedance network accurately for the case where the inverter is operated only in active and shoot-through states. The proposed design method can also be used to predict the critical values of capacitance and inductance below which static states appear during the operating cycle. Computer simulations and laboratory experiments are used to verify the design method and to demonstrate the appearance of static states when the capacitors and inductors are sized lower than their critical values.
TL;DR: Simulation and experimental results show that the proposed method can obtain the desired voltage much faster and minimize commutation torque ripple more efficiently at both high and low speeds.
Abstract: Brushless dc motor still suffers from commutation torque ripple, which mainly depends on speed and transient line current in the commutation interval. This paper presents a novel circuit topology and a dc link voltage control strategy to keep incoming and outgoing phase currents changing at the same rate during commutation. A dc-dc single-ended primary inductor converter (SEPIC) and a switch selection circuit are employed in front of the inverter. The desired commutation voltage is accomplished by the SEPIC converter. The dc link voltage control strategy is carried out by the switch selection circuit to separate two procedures, adjusting the SEPIC converter and regulating speed. The cause of commutation ripple is analyzed, and the way to obtain the desired dc link voltage is introduced in detail. Finally, simulation and experimental results show that, compared with the dc-dc converter, the proposed method can obtain the desired voltage much faster and minimize commutation torque ripple more efficiently at both high and low speeds.
14 Mar 2010
TL;DR: In this article, a new medium voltage drive has been developed based on the active neutral-point clamped 5-level (ANPC-5L) topology, which can be used to increase the efficiency of standard, low cost direct online (DOL) machines.
Abstract: A new medium voltage drive has been developed based on the active neutral-point clamped 5-level (ANPC-5L) topology. In the last decade three-level neutral-point clamped (NPC) converters have become the industry standard in MV Drives. This configuration has proved very successful for applications where high power and high performance requirements necessitated the use of inverter grade motors and the associated costs. On the other hand, there is an increasing demand by industry for drives which can be used to increase the efficiency of standard, low cost direct online (DOL) machines. The problems of high harmonic content, high dv/dt and common mode voltage have been significantly improved in this new drive solution. The structure of the converter will be described with explanation of the multiple levels of redundancy available. The necessary conditions for regulating the neutral-point and phase (or floating) capacitor voltages will be illustrated. The highly dynamic direct torque control (DTC) method has been chosen the inverter control. The synchronous frame current regulator used for rectifier control allows for full four-quadrant operation on the network side. The mechanical design philosophy will be displayed along with the salient technical features: rectifier and inverter operating waveforms, protection concept, and ride through behavior. Finally experience in pilot installations will be reviewed.
TL;DR: A feedback linearization technique is proposed to control the output voltage control of three-phase uninterruptible power supply systems and gives high dynamic responses in response to load variation as well as a zero steady-state error.
Abstract: In this paper, a feedback linearization technique is proposed to control the output voltage control of three-phase uninterruptible power supply systems. First, a nonlinear model including the output LC filters is derived from the power balance condition between the inverter output terminal and the load side. Then, input-output feedback linearization is applied to the nonlinear model to make it linear. The controller of the linearized model is designed by linear control theory. The tracking control law is obtained with a pole placement technique. It is shown experimentally that the proposed control scheme gives high dynamic responses in response to load variation as well as a zero steady-state error.
TL;DR: In this article, a new family of embedded EZ-source inverters that can produce the same gain as the Z-source, but with smoother and smaller current/voltage maintained across the dc input source and within the impedance network.
Abstract: Z-source inverters are recent topological options proposed for buck-boost energy conversion with a number of possible voltage- and current-type circuitries already reported in the literature. Comparing them, a common feature noted is their inclusion of an LC impedance network, placed between the dc input source and inverter bridge. This impedance network allows the output end of a voltage-type Z-source inverter to be shorted for voltage boosting without causing a large current flow and the terminal current of a current-type inverter to be interrupted for current boosting without introducing overvoltage oscillations to the system. Therefore, Z-source inverters are, in effect, safer and less complex and can be implemented using only passive elements with no additional active semiconductor needed. Believing in the prospects of Z-source inverters, this paper contributes by introducing a new family of embedded EZ-source inverters that can produce the same gain as the Z-source inverters but with smoother and smaller current/voltage maintained across the dc input source and within the impedance network. These latter features are attained without using any additional passive filter, which surely is a favorable advantage, since an added filter will raise the system cost and, at times, can complicate the dynamic tuning and resonant consideration of the inverters. The same embedded concept can also be used for designing a full range of voltage- and current-type inverters with each of them tested experimentally using a number of scaled-down laboratory prototypes.
04 Jul 2010
TL;DR: In this article, the basic features of the PLL technique are presented and the most employed solutions for the internal filtering: Low Pass Filter, Resonant Filter, Moving Average Filter, Repetitive Controller.
Abstract: The knowledge of the phase, amplitude and frequency of the utility voltage is a fundamental aspect for the design of the grid-connected inverter systems. In this paper are presented the basic features of the PLL technique. A particular attention is dedicated to the Synchronous Reference Frame-PLL scheme. About the generation of the orthogonal voltages system an evaluation of the most employed techniques is shown: Transport Delay, Inverse Park Transformation, Hilbert Transformation, Second Order Generalized Integrators (SOGI). Moreover some problems in filtering are treated. The internal filtering - due to the PD structure - and the external filtering - due to the harmonics presence in the grid voltage. In both the cases the most employed solutions are shown. For the internal filtering: Low Pass Filter, Resonant Filter, Moving Average Filter, Repetitive Controller. For the external filtering two alternative schemes are presented: the Dual SOGI-PLL and the Enanched-PLL (EPLL).