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Z-source inverter has recently been introduced to overcome the limitations of conventional voltage source inverter. This paper deals with a novel topology of single-phase Z-source inverter (ZSI). This topology reduced the number of passive elements and active switches in order to make the inverter cheaper and smaller in size compared to traditional ZSI. Detailed analysis of the proposed topology is presented in this paper which includes calculations of boost factor, total harmonic disorder, magnitude of output voltage etc. Modulation technique used to control the switching of the proposed inverter is explained in detail. This paper also compares the proposed topology with conventional topologies of Z-source inverter. Simulation results of MATLAB and real-time simulators are shown to explain the working of the proposed topology. [ABSTRACT FROM AUTHOR]

In this paper, the design of a new robust model reference adaptive PI (MRAC-PI) current controller is proposed for a two-stage grid connected photovoltaic (PV) inverter. Perturb & observe (P&O) algorithm is implemented in the boost part in order to extract the maximum power from the PV array. Firstly, the current dynamics with considering the system uncertainties are written in dq frame and are simplified by employing a decoupling system. Then, the MRAC-PI controller is designed based on a sliding mode control (SMC) to improve the robustness of the controller under system uncertainties. The parameters of PI controller are tuned based on SMC laws to track the desired reference model and provides fast and desirable dynamic response. The stability of the robust MRAC-PI is proven by using Lyapunov's theory and Barbalet's lemma. Finally, the performance of the proposed current controller and the conventional PI based voltage oriented control (VOC) during variations in filter inductance and solar irradiance are compared through simulation results. These results show the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

This paper presents the application of a newly developed 21-level hybrid multilevel inverter. A high frequency modulation technique known as sinusoidal pulse width modulation (SPWM) is applied to the hybrid inverter. This modulation methodology operates the switching sequences of the multilevel inverter to produce the desired 21-level output voltage. To validate the proper application of this inverter, it is further utilized to maintain the speed of a single phase induction motor. The velocity control of the motor is established on the principle of V/f control technique. The speed control strategy along with the compatibility of the SPWM modulation technique were verified by means of simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a hysteresis band (HB) current control technique to reduce the power losses in a shunt active filter. During a switching period in the zero-crossing region, the inverter output current flows through a transistor. By changing the direction, it flows through the free-wheeling diode of the same switch in an inverter leg, or vice versa. The shunt active filter current typically has 6 zero-crossing regions during a fundamental frequency cycle. This paper presents a HB current control technique where there is not any switching in these 6 zero-crossing regions per period, which results in reducing the power losses. The experimental results clearly show that the power losses of the shunt active filter are reduced by using the proposed technique. [ABSTRACT FROM AUTHOR]

The 3-level T-type neutral point clamped (T-NPC) inverter has become the most popular multilevel inverter used in low-voltage applications. However, the realization of a bidirectional switch located at the midpoint leg of the T-NPC inverter is achieved using two insulated gate bipolar transistors (IGBTs) with two antiparallel diodes. Power dissipation in these switches is high since there are two semiconductors (an IGBT and a diode) in the current path at the midpoint leg. Switch losses can be reduced and thus the highest conversion efficiency can be achieved if the bidirectional switches in the T-NPC inverter are replaced by highly efficient reverse-blocking IGBTs (RB-IGBTs). The objective of this paper is to assess the performance of a 3-phase 3-level grid-connected advanced T-NPC (AT-NPC) inverter with RB-IGBT for low-voltage applications. This paper describes the operating principle of the grid-connected AT-NPC inverter, analyzes the power losses, and discusses the control strategy. A 1.7-kW laboratory prototype is designed and built to verify the feasibility and the effectiveness of the proposed 3-phase 3-level grid-connected AT-NPC inverter. Real-time control of the inverter is experimentally achieved using a dSPACE DS1103 controller. The experimental results show that the efficiency of the proposed grid-connected inverter is about 96.3%. [ABSTRACT FROM AUTHOR]

In this paper, the control of a multifunction grid-connected photovoltaic (PV) system with a three-phase threelevel (3L) neutral point clamped (NPC) inverter is proposed, which can perform shunt active filtering. Normally, the shunt active filtering is achieved by detecting the harmonic and reactive currents of the nonlinear load and then injecting the compensating current into the grid. Therefore, the proposed system can inject PV power to a grid with power factor correction and current harmonic filtering features simultaneously. In addition, a single-stage compact and efficient transformerless power conversion topology is used in this paper for the grid-connected solar PV system with maximum power point tracking capability. In order to control the multilevel inverter-based combined system, a synchronous reference frame control technique and hysteresis current control pulse width modulation method have been applied. The system configuration and control strategy are verified and validated by simulations based on MATLAB/Simulink and implemented in real-time using the dSPACE DS1103 controller board. The simulation with experimental results indicates that the injected currents are sinusoidal and current total harmonic distortion is about 3.9%, lower than the IEEE 519 harmonic limit. [ABSTRACT FROM AUTHOR]

In this paper, a new hybrid pulse width modulation technique is proposed to enhance the performance of output voltage from a ternary progression based multilevel inverter. For high power applications, the multilevel inverter can appropriately replace the traditional converter without a transformer and the separate DC sources will be indispensable for various renewable energy sources. The classy split switching technique for the multicarrier pulse width modulation technique is adopted and the concept about new topology is presented in this paper. An arm controller has been chosen to implement the modulation due to its superior features, easy software, and hardware design. Simulation and experimental results are also presented. [ABSTRACT FROM AUTHOR]

This paper introduces a new method to track the saliency of a permanent magnet synchronous motor (PMSM) motor fed by a 4-leg inverter in the case of a single-phase open circuit fault through measuring the dynamic current response of the motor line currents due to the insulated-gate bipolar transistor (IGBT) switching actions. In the case of a single-phase open circuit fault, a fault-tolerant control strategy that includes taking appropriate actions to control the 2 remaining healthy currents results in minor system performance degradation. The new strategy introduced in this paper includes software modifications only to the saliency tracking algorithm used in healthy mode in order to make it applicable to the reconfigured converter in the presence of a fault. The new method uses only the fundamental pulse width modulation (PWM) waveform (i.e. there is no modification to the operation of the 4-leg inverter), similar to the fundamental PWM method proposed for a 3-leg inverter. Simulation results are provided to verify the effectiveness of the proposed strategy of saliency tracking of a PMSM motor driven by fault-tolerant 4-phase inverter over a wide range of speeds under the case of a single-phase open circuit fault. [ABSTRACT FROM AUTHOR]

This paper proposes a discrete-time model-reference sliding mode control of three-phase four-leg voltage source inverters for stand-alone distributed generation systems. Three-phase four-leg voltage source inverters (VSIs) are used in a broad area. A discrete-time model-reference sliding mode controller, having superior advantages such as insensitivity to external disturbances, system parameter variations, and modeling errors, is applied to control the output voltage of three-phase four-leg VSIs. As a new study, the discrete-time model-reference sliding mode control with a supplemented output feedback integral controller is proposed so that the controlled output voltages of the VSI tracks the input reference signal. The controller is designed using the augmented discrete-time error dynamics presented in this paper and is applied to control the output voltage control of a three-phase four-leg based uninterruptable power supply. It is shown that the output voltage of the VSI controlled by the proposed method is accurately regulated for various load conditions such as linear balanced/unbalanced, nonlinear balanced/unbalanced, and instantaneous load changes. The robustness of the proposed method against variations by 20%-50% in R, L, and C filter parameters and 5 different cases are showed. [ABSTRACT FROM AUTHOR]

This paper presents a deadbeat-based proportional-integral (PI) controller for a stand-alone single-phase voltage source inverter using a battery cell as the primary energy source. The inverter system is simulated in MATLAB/ Simulink. It consists of a lead acid battery, third-order Butterworth low-pass DC filter and AC filter, H-bridge inverter, step-up transformer, and a variety of loads, as well as its sinusoidal pulse-width modulation (SPWM) deadbeat-based PI controller. In this paper, 2 simulation case studies are carried out, which are the abrupt load changes from a 400 W resistive load to a 500 W resistive load, and from a 400 W resistive load to an inductive load of 500 W 0.85 power factor lagging. From the simulation results for both cases, the state-of-charge of the battery decreases due to supplying power to the loads, yet the battery voltage remains constant at about 36 V and the battery current exhibits a smooth ripple despite the current spikes produced by the H-bridge inverter, which will prolong the lifespan of the battery. This shows that the DC filter performs satisfactorily to isolate the current spikes generated by the SPWM controller and H-bridge inverter. Moreover, even though the load varies for both cases, the sinusoidal inverter output voltage can be tracked and maintained at 230 Vrms with a 50 Hz frequency within a few cycles from the instant that the load is changed, as well as a low total harmonic distortion voltage (THDv) content of 1.53% and 2.78%, respectively. This indicates that the controller proves its robustness and stiffness characteristics in maintaining the output load voltage at the desired value to supply the power for a variety of loads with a minimum THDv. [ABSTRACT FROM AUTHOR]

Optimal minimization of total harmonic distortion (OMTHD) and selective harmonic elimination (SHE) switching techniques are usually employed to reduce generated harmonics of multilevel inverters. In the former technique, the THD of waveform is reduced without elimination of any harmonic order and the latter, in contrast, eliminates selected harmonic orders. In this paper, the harmonic elimination ability of the SHE technique is added to OMTHD and an improved OMTHD technique is proposed for an n-level cascaded multilevel inverter with adjustable DC sources. The main novelty of this switching technique is elimination of some harmonic orders, beside THD minimization. Moreover, optimal DC voltages and switching angles can be estimated simpler than conventional OMTHD technique. To show the advantages of the proposed technique, which is formulated for an n-level inverter, a 7-level one is simulated in MATLAB/Simulink with both improved and conventional OMTHD techniques. The obtained results show the elimination of two elective harmonics as well as THD minimization. Moreover, experiments on a 7-level inverter verify the superiority of the proposed technique. [ABSTRACT FROM AUTHOR]

This article presents the application of the harmony search (HS) optimization algorithm for selective harmonic elimination PWM (SHEPWM) in a new topology of multilevel inverters with reduced number of electronic switching elements. The main objective of the harmonic elimination strategy is eliminating undesired low-rank harmonics in order to improve the quality of the output waveform. The harmonic elimination strategy is achieved by solving a system of nonlinear equations. In this paper harmony search optimization is applied using artificial neural networks (ANNs) on a new 21-level inverter topology. The algorithm is based on a music improvisation process. MATLAB programming software is used to develop a harmony search optimization program for harmonic elimination. A small-scale laboratory of the proposed 21-level inverter is built to validate the simulation results and to prove the efficiency of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper proposes the use of a static synchronous series compensator (SSSC) to increase the power capacity of a 230 KV transmission line. The power capacity is increased by 30%. The proposed SSSC is a 21-level inverter based on the cascade connection of improved double ying capacitor multicell (CI-DFCM) converter. The main advantages of the CI-DFCM multilevel inverter are the low number of power-electronic devices, as well as reduction in the number and voltage diversity of ying capacitors in comparison with other ying capacitor-based inverters. The CI-DFCM multilevel inverter uses only two ying capacitors in each phase. The theory of instantaneous p-q power is applied to control the proposed SSSC. By applying the presented control method, the dc-link capacitors are charged to the desired voltage value. The modulation method of the CI-DFCM multilevel inverter is a modified phase shifted pulse width modulation (PS-PWM) technique. In order to validate the accurate performance of the proposed compensator, a three-phase transmission line with the transmitted active power of 160 MW is simulated. The simulation results are provided by MATLAB/Simulink. [ABSTRACT FROM AUTHOR]

Custom power devices are widely employed to mitigate power quality issues affecting critical loads. The dynamic voltage restorer is one of the custom power devices designed to inject a voltage in series with line to present a pure sinusoidal voltage of the desired RMS value to the sensitive loads, if the supply side is affected by voltage disturbances. The design and implementation of a DVR with a quasi-impedance source inverter and variable structure control is discussed in this paper. The voltage boosting ability of a quasi-impedance (Z) source inverter is used here to improve the performance of the DVR with reduced energy storage. The control system designed based on variable structure control effectively supports the DVR with good dynamic response, even under parameter variations. Performance of the proposed system in a single phase network is evaluated against the conventional DVR system using MATLAB simulation studies. An experimental model of the proposed system was developed to validate the simulation results. Implementation of the proposed DVR in a 3 phase distribution system is investigated with the help of simulation studies. [ABSTRACT FROM AUTHOR]

The multilevel inverter's impact in the area of power electronics is augmented because of its nimble nature. This paper presents an efficient switching pattern for multilevel inverters using the nearest leveled vector (NLV) strategy through a space vector control (SVC) technique. The objective is to reduce the total harmonic distortions by generating an optimal switching sequence with the newly introduced NLV-SVC for multilevel inverters. The proposed NLV modulation is applied for an asymmetrical multilevel inverter, which has a high number of levels with reduced switch count, sources, and lower switching losses. The effectiveness of the proposed method is verified on a 27-level 3-cell asymmetrical multilevel inverter. The efficacy of the proposed method in terms of total harmonic distortions is compared with the existing nearest vector control (NVC) modulation strategy. Implementation and experimental verification of the proposed NLV-SVC modulation strategy for an asymmetrical cascaded H-bridge multilevel inverter is presented for real-time validation with the comparison of the NVC modulation strategy. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for power generation from rotating machines in textile mills using externally coupled repulsive magnets and a new stepped DC coupled Quasi Z-inverter. Power is obtained as a byproduct of the effective harnessing of rotational energy with the use of repulsive magnets. This derived power is stored in a battery arrangement and is retrieved, buck/boosted, and converted to multilevel AC voltage with the new stepped DC coupled quasi Z-inverter. The proposed inverter is powered by isolated voltage sources, uses fewer switches, and produces less distortion in the resulting multilevel voltage compared to its counterpart, and thus reduces the fiter requirements. The derived AC power from the system can be used for light-load applications in textile mills, thus compensating for the energy demands. Simulation of the entire proposed setup is performed in MATLAB/Simulink and the results are presented. The repulsive force produced by the magnets is assessed with K & J Magnet software. To validate the simulation, experimentation is done using rotating machines available in the laboratory. The prototype model of the stepped DC coupled quasi Z-inverter is used to study the performance of the system and the results are evaluated. The optimum modulation index is identified for different numbers of sources at the input. [ABSTRACT FROM AUTHOR]

This paper presents a new constant frequency hysteresis current controller for the grid interface of a PVfed three-phase voltage source inverter (VSI) for a dual mode operation, feeding real power during the daytime and reactive power alone during nights, thereby acting as a STATCOM. The constant frequency is inherently achieved by means of digital implementation in a simplified manner without any complex manipulations to choose a variable band width; rather the hysteresis band varies as a natural consequence of selecting appropriate constant sampling frequency. Analytical proof is presented for the switching frequency to remain constant, without compromising on the performance indices. The design of the proposed controller for a grid-connected inverter operating in dual mode is presented, along with simulation results. The proposed controller is successfully implemented using a 1.1 kW PV array-fed inverter. The hardware results presented show the grid current harmonics complies with IEEE 1547 and has been achieved in a simpler means when compared to other existing techniques. The proposed controller is expected to be an attractive solution for grid-connected inverter applications including distributed generation, power quality, and drive applications. [ABSTRACT FROM AUTHOR]

In this paper, a new DC-link balancing method for a 7-level inverter fed by a photovoltaic system is proposed. The proposed redundant state technique is associated with selective harmonics elimination (SHE)-PWM instead of space vector (SV)-PWM. The switching angles related to the SHE are computed via the resultant theory method. Moreover, the study of this inverter is carried out on its equivalent matrix model. On the basis of this model, the link between the capacitor voltage, switching states, and load current is established. This allows understanding the switching redundancies' effect on the DC capacitor voltage balance. An algorithm is then developed to select the appropriate switching state, since there are 300 switching states and 720 unbalanced cases of the voltage capacitor. The proposed balancing method is tested in the case where the input DC inverter is provided by a photovoltaic generator (PVG) system and feeding an induction motor. The obtained results show that the 6 DC PVG capacitor voltages are kept balanced while cancelling the most undesirable harmonics row (5th, 7th, and 11th) in the inverter output voltage. Thus, using this cascade, photovoltaic supplying DC power can be amplified into high quality AC power. [ABSTRACT FROM AUTHOR]

This paper proposes a new space vector pulse width modulation (SVPWM) algorithm for multilevel inverters that achieves a minimum number of switch state changes in one sampling cycle in order to reduce switching losses. The algorithm can be implemented with minimum computational burden and it does not require any look-up tables. The essence of the technique is to exploit the redundancy of switching functions in the implementation of the voltage vectors and dividing the entire vector space into three sectors in which switching functions have some common features. Careful observations showed that these common features lend themselves to be expressed as closed form analytical equations that can be readily implemented in an embedded digital platform. The concepts are developed using a three-level inverter. However, generalized equations are given so that the proposed technique can be applied to inverters with an arbitrary number of levels. [ABSTRACT FROM AUTHOR]

This paper presents the performance characteristics of two induction motors of the same parameters and ratings connected in parallel and fed by a single inverter. A nature observer is employed to estimate the rotor speeds and rotor fluxes of both induction motors. It also estimates the load torques of both the motors by load torque adaptation. Under unbalanced load conditions, the speed difference between the two induction motors is reduced by considering the average and differential motor parameters and currents. Mean rotor flux is maintained constant by a rotor flux control scheme and the estimation of rotor angle is carried out by direct vector control technique. The prototype experimental setup is made for validating the proposed method and the experimental results are demonstrated for various running conditions. The natural observer algorithm for speed and torque estimation is executed by TMS320F2812 DSP controller. [ABSTRACT FROM AUTHOR]

This paper presents a comparative performance evaluation of voltage source inverter (VSI) as well as current source inverter (CSI) based DSTATCOM systems in terms of power quality improvement in a three-phase four-wire distribution network. Due to increasing use of high-performance semiconductor based power electronic switches, the CSI based DSTATCOM is developed as a suitable option in high power applications. However, the VSI based DSTATCOM system is the best suited for medium power applications. The VSI based DSTATCOM offers advantages over the CSI based DSTATCOM in terms of current harmonic compensation, power factor correction, lower losses (both conduction and power losses), and simplicity in both power and control circuits. The control strategies of both the DSTATCOM systems are based on conventional PI and synchronous reference frame (SRF) theory. The performance of the VSI and CSI based DSTATCOM systems is tested under unbalanced and nonlinear load conditions. Analytical expectations of complete DSTATCOM systems are verified using simulations in the MATLAB/Simulink environment. [ABSTRACT FROM AUTHOR]

Virtual impedance is usually introduced to the control system of parallel inverters in order to change the inverter equivalent output impedance and to enhance control accuracy and power sharing. In this paper, a current feedback control strategy using a third-order general-integrator crossover-cancellation method that can be implemented in a virtual impedance loop is proposed. This method consists of 2 parts: a crossover-cancellation feedback network, which achieves the band-pass effect, and a multilevel TOGI-OSG link, which acts as a filter. Compared with the conventional virtual impedance method, the proposed method can avoid derivation of output current, reduce system calculating burden, and enhance dynamic response. Additionally, this method can reduce the THD of output voltage in the case of nonlinear load and can also drastically restrain the impact of DC component on output voltage. A prototype consisting of 2 sets of 2-kW photovoltaic inverters operating in parallel was built in the laboratory. Simulated and experimental results are examined to verify the effectiveness and feasibility of this method. [ABSTRACT FROM AUTHOR]

In high frequency induction heating systems, the effective load parameters change during the different operating conditions. It is necessary to maintain constant input voltage to the induction heating load to improve the quality of the heating. The resonant based high frequency converter is generally used for these applications for the reduction of switching losses. The resonant condition is also affected during the variation in load parameters. The controller should provide a good voltage regulation with less response time and less overshoot during the loading conditions. In this paper, a load adaptive fuzzy logic control scheme is proposed to perform the voltage control of the high frequency inverter under variable load conditions. A frequency tracking control system is also employed for the inverter system using the phase lock loop. The phase lock loop ensures the resonant frequency operation of the inverter during the change in load parameters. The state space model of the system is discussed to study the inverter during different operating conditions. The fuzzy logic controller based closed loop control scheme is developed using the MATLAB simulation tool. The responses of the conventional and fuzzy logic controllers are studied for load voltage regulation and the effectiveness of the control schemes is verified. The dynamic behavior of the system is studied under no load and loaded conditions with the two controllers. The fuzzy based closed loop control scheme improves the dynamic response of the system compared to the conventional controller. The response of the induction heating system is validated with a hardware prototype. The results are presented in order to confirm the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper presents a three-dimensional (3-D) space vector pulse width modulation (SVPWM) technique via a 4 x 4 orthonormal transformation matrix that has been used as a new approach in controlling a three-phase four-leg voltage source inverter (VSI). A fully optimal digital control scheme for the closed-loop regulation of the three-phase four-leg VSI has been used to synthesize a sinusoidal waveform with the help of the proposed method. Discrete-time modelling of each phase has been obtained independently in abc reference frame, and its optimal controller has been designed using a predefined performance index. A DSP-based controlled three-phase four-leg prototype VSI has been designed to verify the proposed discrete time modelling and the control scheme. The simulations and the real-time experiments show that satisfactory results have been obtained for the modelling of the three-phase four-leg VSI in abc reference frame and the 3-D SVPWM technique via 4 x 4 orthonormal transformation matrix at 20 kHz switching frequency. [ABSTRACT FROM AUTHOR]

This paper presents a single-phase, cascaded half-full-bridge PWM multilevel inverter topology. It is made up of a main inverting H-bridge legs and level-clamping half-bridge circuits, each having its own dc source. The singlecarrier, multilevel PWM scheme is employed to generate gating signals for the power switches. The modulation scheme is hybridized to enable the output voltage of the proposed inverter configuration to inherit the features of switchingloss reduction from fundamental PWM and good harmonic performance from multiple sinusoidal PWM. Moreover, a simple base PWM circulation scheme is also introduced in this work to obtain a resultant sequential switching hybrid PWM (SSHPWM) circulation that balances power dissipation among the four power switches of the main H-bridge module. Operational principles with switching functions are given. For a modulation index of 0.9, the proposed inverter configuration was subjected to an R-L load and the respective numbers of output voltage level were synthesized. FFT analyses of the output voltage waveforms were carried out and the corresponding THD value of 13.16% was obtained. To verify the performance of the proposed inverter architecture, simulations and experiments were carried out on a 2.95 kW rated prototype of the proposed inverter for an R-L load and adequate results were obtained. [ABSTRACT FROM AUTHOR]

A special cascaded configuration of asymmetric multilevel inverter is presented in this paper. This configuration cancels the redundancy of output voltage steps and maximizes the number of levels in the output voltage. This structure is built by using series connected stages, which minimize the number of semiconductor switches, gate drive arrangements, occupying area, and cost. It is a modular type inverter model and the number of voltage levels can be increased by adding new stages without changing the previous connection. Space vector modulation has been applied as the control strategy. A prototype of the proposed inverter topology has been built in the laboratory. The attached hardware results indicate the accuracy of the proposed model, which include the topology as well as the control technique. [ABSTRACT FROM AUTHOR]

This paper proposes a new 3-phase multilevel inverter that is able to generate 7 levels in line-to-line voltage with only 11 switches. The inverter is formed from the 6-switch conventional full-bridge topology with the addition of 5 bidirectional switches in which 2 of them are shared among the three phases. By doing so, the number of power switches can be minimized, thus reducing the complexity in generating and controlling PWM signals. A novel voltage control scheme based on space vector modulation is developed by introducing a virtual vector in every sector of the vector hexagon. This is to overcome the difficulty in decomposing the reference vector in some parts of each sector. To evaluate the performance of the inverter and the effectiveness of the modulation technique in real time, a hardware prototype is constructed and the algorithm is implemented on a TMS320F2812 DSP. From the experimental results the optimum operating range of the inverter is determined to achieve the best output voltage possible with respect to quality and amplitude. [ABSTRACT FROM AUTHOR]

This paper introduces a new three-phase three-level voltage source inverter. The proposed topology consti- tutes the conventional three-phase two-level inverter with three bidirectional switches. For purpose of generating the appropriate switching gate signals, two different commutation strategies are suggested and analyzed. A comparison between both strategies in terms of power losses and efficiency are presented. To ensure the feasibility of the proposed configuration with its suggested commutation strategies, the prototype of the proposed inverter was manufactured and the experimental results are given. [ABSTRACT FROM AUTHOR]

This paper investigates the design and performance of a 150 W single-phase current-source grid-connected inverter topology that is based on a PV array and DC link inductor acting as a constant-current source. The inverter is implemented using a single boost switch, an H-bridge inverter, and a CL output filter. The inverter output current is simply controlled using the boost switch and open-loop or feedforward control. The dark I-V configuration is used to simulate two series PV modules. Comprehensive test results are obtained to validate the computer simulation results. Furthermore, the proposed inverter's ability to deliver a sinusoidal current to the grid while meeting the appropriate standards, i.e. total harmonic distortion and power factor requirements, is also examined for various modulation index values and irradiances. [ABSTRACT FROM AUTHOR]

The photovoltaic power generation and active filter (PV-AF) system can realize photovoltaic grid-connected power regulation, and meanwhile it can also improve the power quality of power grid effectively. The four-leg grid-connected inverter has successfully been used in the three-phase four-wire system. In this paper, a three-dimensional space vector pulse width modulation (3D-SVPWM) method based on the ghγ coordinate system for a four-leg inverter has been proposed. As the switching vectors of the four-leg inverter are in the three-dimensional space, it is difficult to realize the complex modulation process. In order to simplify the modulation process, the reference vector is placed into ghγ coordinates in the proposed modulation strategy, and then the vectors are selected and the duration times are acquired directly by a group of intermediate variables, which could be obtained by linear transformation of the coordinates. As the intermediate variables are used, the modulation can be easily implemented by the proposed modulation strategy without excessive mathematical calculations. The simulation and experimental results all confirmed the validity and effectiveness of this strategy. [ABSTRACT FROM AUTHOR]

This paper proposes sharing active and reactive power in autonomous voltage source inverter (VSI)-based microgrids with no physical communication links. In decentralized VSI-based microgrids, when the demand or generation changes, the output voltage of distributed generation units and the frequency of the system will also change. This study presents a novel adaptive nonlinear droop (ANLD) scheme for preserving network stability, improving the system's dynamics, and controlling power sharing in multibus microgrids in a decentralized manner. Subcontrollers are modeled in a state space and combined together so that a complete dynamic model of the network can be developed. Note that controller coefficients are optimized to improve small-signal stability and to obtain a good operating point. To this end, an optimization problem is formulated and solved using the particle swarm optimization method. For the purposes of comparison, the proposed ANLD method and three other schemes are applied to two case studies: a 5-bus microgrid and a modified 37-bus IEEE microgrid. The stability margin analysis and time response simulations prove that the proposed algorithm performs much better and can be applied to large-scale microgrids. [ABSTRACT FROM AUTHOR]

In this paper, the transient and steady-state performances of an isolated self-excited induction generator driven by a wind turbine and feeding power to a dynamic load such as a three-phase induction motor are analyzed. Mathematical modeling and simulation study of the whole system, including the wind turbine, induction generator, capacitor, pulse width modulated voltage source inverter, and dynamic load, are carried out with closed-loop voltage and frequency controller. The complete system is modeled in the stationary d-q frame and validated by comparing simulation and experimental results at no-load. The same mathematical model is then used to study the transient performance of the self-excited induction generator supplying to a dynamic load. When the induction motor is connected to the induction generator without any voltage and frequency controller, it causes severe transients in electrical and mechanical variables of the generator. Due to the large starting-current requirement of the induction motor, there is a collapse of the terminal voltage of the generator. A bidirectional pulse width modulated source inverter with DC link battery is connected with the generator and operated in closed-loop control mode to maintain voltage and frequency and to operate the induction motor successfully with variable wind speed and mechanical load. [ABSTRACT FROM AUTHOR]

This paper proposes a multilevel hybrid cascade-stack (HCS) converter. Recently, different new topologies for cascade-type converters have been suggested with the goal of reducing switch number, loss, switch PIV, etc. Meanwhile, output voltage steps increase, and the number of switches is predominately reduced in the suggested inverter in comparison to conventional cascade converters. Additionally, a reduction in the number of on-state switches in the introduced topology causes power loss and voltage drop to decrease. Firstly, the fundamental parts of inverter configuration are described. Afterwards, symmetric and asymmetric converter types are discussed. Simulation and experimental results for 11- and 23-level symmetric types and a 31-level asymmetric form of converter are described. [ABSTRACT FROM AUTHOR]

In this study, a novel single-phase grid-connected microinverter system and its control applications are introduced for solar energy systems. The proposed system consists of two stages to transfer solar power to the grid. In the first stage, an isolated high-gain DC/DC converter is used to increase low solar panel output voltage. In the second stage, an inverter is used to supply a sinusoidal current to the grid. Moreover, a proportional resonant controller is adopted to reduce grid current total harmonic distortions (THDs) and an LCL filter is used to provide better harmonic attenuation. However, the ratio between the sampling frequency fs and the resonance frequency fres should be greater than 6 in the LCL filter with the inverter current feedback for a stable system. In order to obtain higher phase margins, the sampling frequency should be increased, which increases the inverter switching frequency. The present study shows that fs/fres can be lower than 6 by placing a phase delay on the inverter current feedback path to guarantee adequate stability margins. The effectiveness and feasibility of the proposed method are confirmed by the experimental test results based on a 300-W laboratory prototype. [ABSTRACT FROM AUTHOR]