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This study presents an approach for robust current and power control for a three‐phase grid‐connected inverter set up with an L‐filter that operates under an unbalanced AC grid‐voltage source. This control method consists of two paralleled current control for the positive and negative sequences to accomplish one of three selective control targets: a) supplying balanced three‐phase current; b) supplying non‐oscillated real power; and c) supplying non‐oscillated imaginary power to the AC grid for a given reference value utilizing the identical control gains. The real and imaginary power references, together with the measured grid voltages, are used in the computation of the reference current for each control target. In addition, the proposed dual‐current control system has a control law that comprises state feedback to offer stability and an integral effect to get rid of the offset error in the dq‐frame. To reduce settling time under uncertain system conditions, an optimization problem based on linear matrix inequalities is solved to determine a set of robust stabilizing gains. Simulation and experimental results using a TMS320F28377D digital signal processor validate the proposed control performance under three control targets. [ABSTRACT FROM AUTHOR]

Background and Objectives: Model predictive control (MPC) is a practical and attractive control methodology for the control of power electronic converters and electrical motor drives. MPC has a simple structure and enables the simultaneous consideration of different objectives and constraints. However, when applying MPC for multilevel inverters (MLIs), especially at higher voltage levels, the number of switching states dramatically increases. This issue becomes more severe when MLIs are used to supply electrical motor drives. Methods: This paper proposes three different MPC strategies that reduce the number of iterations and computation burden in a 3-phase 4-level flying capacitor inverter (FCI). Traditional MPC with a reduced number of switching conditions, split MPC, and hybrid MPC-PWM control are investigated in this work. Results: In all methods, the capacitor voltages of the FCI are balanced during different operational conditions. The number of iterations is reduced from 512 in traditional MPC to at least 192 in the split MPC. Moreover, the split MPC strategy eliminates the usage and optimization of weighting factors for capacitors voltage balance. However, in the hybrid MPC-PWM control method in comparison to other methods, the voltage balancing time is much lower, the phase current tracks the reference more accurately, the transient time is lower, and the efficiency is higher. In addition, the capacitors voltage ripple is negligible in the hybrid MPCPWM control method. Conclusion: Simulation results manifest the effectiveness of the suggested hybrid MPC-PWM methodology. Results manifest that the hybrid MPC-PWM control offers perfect dynamic characteristics and succeeds in maintaining the voltage balance during different operational conditions. [ABSTRACT FROM AUTHOR]

The operation of parallel inverters in microgrids is an important way to expand system capacity, but there are problems of circulating current fluctuations and power sharing errors in parallel inverters' operation. In this paper, a parallel operation strategy for inverters based on improved adaptive droop control and Equivalent Input Disturbance (EID) is proposed. Firstly, the model and control topology of parallel inverters are presented. Secondly, in order to solve the power sharing error caused by impedance difference and the voltage drop caused by virtual impedance, a reference voltage generator based on improved adaptive droop control is proposed. Then, considering the circulating current fluctuation as a disturbance, a voltage controller based on an equivalent input disturbance approach is proposed to reduce the disturbance. Finally, simulation in MATLAB/Simulink is carried out to verify the effectiveness of the parallel operation strategy. [ABSTRACT FROM AUTHOR]

This article proposes several solutions for the use of novel AC voltage regulators as electrical energy quality conditioners and for the use of a half-bridge voltage inverter circuit as an active filter. This study was carried out with a real object, and more attention was paid to it. Structural models of electrical energy quality assurance systems, the calculation of control system elements and experimental results are presented. In particular, the use of a half-bridge voltage inverter circuit was considered as a replacement for the passive filter of the battery charger and rectifier device. AC voltage regulators are also used as compensators for higher-current harmonics, namely active filters and reactive power, voltage drop, voltage unbalance and flicker effect compensators. Block diagrams of power quality conditioners are presented, control algorithms are developed and the results of the current high-frequency harmonics compensation, reactive power and signal balancing are presented. The results of an active filter experiment based on the NRT 160.220 charge-rectifier device circuit showed a reduction in ripple of up to 1% with smaller dimensions compared to a passive filter. The control characteristics and external characteristics of the regulators are removed. The dependences of the current THD factor and the power factor are presented depending on the modulation depth for AC voltage regulator circuits used as power quality conditioners. [ABSTRACT FROM AUTHOR]

Multi‐level inverters are widely used in high‐voltage and high‐power applications due to the increasing demand for renewable energy. This study proposes a novel single‐phase reduced switch multi‐level inverter topology that generates 11 levels of output voltage steps, operates in asymmetric mode, and uses fewer power electronic switches with efficient switching control. To optimize the inverter's performance, Moth Flame Optimization (MFO), Particle Swarm Optimization (PSO), and Whale Optimization Technique (WOA) are utilized to apply the selective harmonic elimination technique. The proposed circuit is implemented in PSIM software using optimized switching angles, and the fitness functions and switching angles for the three optimizers are evaluated and reported. The inverter's performance at optimal modulation points for the three optimizers is computed and analyzed, with the Total Harmonic Distortion (THD) measured at 0.82 modulation point before and after filtering. Results show that MFO outperforms PSO and WOA with the lowest THD values of 0.85% and 0.78%, respectively; therefore, complying with the IEEE 519 standard. The experimental validation of MFO's superiority is performed using the Typhoon HIL‐402 hardware device. This study provides a promising solution for the design and optimization of multi‐level inverters, paving the way for more efficient and reliable renewable energy systems. [ABSTRACT FROM AUTHOR]

Significant interest has been shown in switched capacitor (SC)-based multi-level inverters (MLIs), which decrease the need for a DC supply and enhance power quality. The common issues with SC-MLIs include an uneven distribution of conducting paths, increased voltage drop across capacitors, the sum of all inverter DC link voltages across the highest voltage rated switches, and a higher total standing voltage (TSV). The purpose of this paper is to create a SC-MLI with less components in order to maintain a constant voltage across the capacitors, to obtain higher voltage gain with fewer parts, fewer conducting routes, lower TSV, and to create a more affordable and effective inverter. The structure of the MLI is created by a cascade interconnection between the number of SC cells. A single input multiple output (SIMO) converter boosts the DC-link voltage over the stable DC voltage of the solar panels using a modified perturb and observe (P&O) method. Additionally, fewer switches in the conduction path and 50 % of the switches operating at normal frequency guarantee a decrease in an overall loss of power in the proposed network. The benefits of the recommended MLI are made clear by comparing them with 17-level MLIs in terms of the number of elements, stress, gain, and cost factor. Detailed experimental results are shown under various transient conditions to show that the 17-level prototype is operationally viable. The total harmonic distortion (THD) is found to be identical and is less than 5 %, which meets IEEE standards. [ABSTRACT FROM AUTHOR]

Due to their numerous advantages, multilevel inverters are commonly utilized in high and medium voltage applications. Design and simulation of Six-Switch Five-Level Active Neutral Point Clamped Inverter (6S-5L-ANPC) associated with LC filter is presented, the inverter can produce pure sinusoidal voltage, the proposed modulation can satisfy the regulation of the flying capacitor voltage, the behavior of 6S-5L-ANPC inverter is validated through simulation, limitation in the present design of the inverter is discussed. However, the converter is not able to maintain the FC voltage balancing under modulation index variation. To overcome this limitation, a PID Controller based in output voltage control is proposed. The aim of control is: i) create a sinusoidal voltage at the converter output with amplitude and frequency set by the reference signal, ii) guarantee the self-balancing of the FC capacitor under variable load and reference voltage variation. The controller is tested under various operating situations in simulation. The validity of this strategy is demonstrated using simulation results. [ABSTRACT FROM AUTHOR]

A grid-connected inverter's stability is easily influenced by the system's internal and external characteristics, especially when the grid-connected inverter is connected to the grid by an LCL filter, which complicates the system design and operating conditions. To handle the problem of disturbance in the high-order grid-connected system of the inverter, a linear active disturbance rejection control (LADRC) strategy based on LCCL (which divides the capacitor of the LCL filter into two halves in a specified proportion) is proposed in this paper. First, the system is reduced from third order to first order by using the split capacitor control method, which solves the difficulties of complicated LCL grid-connected inverter controller design and easy resonance. Meanwhile, the internal and external disturbances of the inverter system are treated as generalized disturbances. Then, the LADRC control is used to adjust the closed-loop system's parameters, which enhances the quality of the grid current and the system's stability. Finally, the impacts of PI and LADRC control on the power mutation and voltage drop of an LCCL grid-connected inverter are compared by the experiments. The experimental results show the effectiveness of the proposed LADRC control strategy. [ABSTRACT FROM AUTHOR]

A three-phase dual-port T-type asymmetrical multilevel inverter (ASMLI) using two sources, solar forming the high voltage level and the battery forming the low voltage level, is considered for grid interconnection. A vertical shifted SPWM is used for the ASMLI circuit. A transformerless system for grid interconnection is achieved for a 100-kW power range. A well-designed boost converter and a Buck/Boost converter is used on the front side of the inverter. Design of battery charge controller and its controlling logic are done and its SOC is found to be efficient during charging and discharging conditions. A closed-loop control using PQ theory is implemented for obtaining power balance at 0.7 modulation index. The THD of the current harmonics in the system is observed to be 0.01% and voltage harmonics is 0.029% which are well within the permissible limits of IEEE-519 standard. The power balance is found to be good between the inverter, load, and the grid during load disconnection for a period of 0.15s. A comparison of THD's, voltage, current stresses on the switches, and conduction losses is also presented for a single-phase system with respect to a two-level inverter which shows improved efficiency and low THD. Hence this system can be proposed for use in grid interconnection with renewable energy sources. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents an adaptive power sharing control method of parallel‐connected hybrid inverters in microgrid. Normally the AC microgrid is composed of hybrid inverters, other power generation equipment and some loads in parallel. Droop control or virtual synchronous generator is usually adopted to control parallel inverters, so the output power ratio between each inverter is fixed by droop parameters. The input of hybrid inverter is PV panel and battery, so the power output ability of each hybrid inverter is different because of the different PV panel capacity, illumination condition, battery capacity and battery state of charge. Hence, the output power of some hybrid inverters is short or redundant sometimes, which makes microgrid unstable or causes power generation restraints. It is necessary to recognize the actual power capacity of each inverter and control the output power reasonably. This paper analyzes the characteristics of parallel‐connected hybrid inverters with droop control in microgrid. An adaptive power sharing method is developed to identify the unbalanced between the each inverter on DC bus. By adjusting the droop parameters, the output power of each inverter is regulated where the controlled parameters are defined in system transfer function with an optimal target. Experimental tests are executed following the numerical simulation. The results show that the output power of each inverter can be adjusted adaptively according to the practical needs. The excessive power from one inverter can be absorbed by the others. Therefore, the stability and the power capability in the system are both ensured by adopting the proposed methods. The outcomes of the study provide a reference to the development of the adaptive inverter in microgrid. [ABSTRACT FROM AUTHOR]

This article presents a single-sourced hybrid binary-cascaded multilevel inverter (BCMLI) with front-end high-frequency-link (HFL) converters. The purpose of HFL converters is to boost a dc-source voltage to three bus voltages in a binary ratio. In this article, one of the HFL converters is removed from the system and the voltage of the floating capacitor caused by the removal is controlled by a newly proposed floating-capacitor-voltage (FCV) control. Compared with the conventional BCMLI, the system size and cost can be significantly reduced while maintaining promising features, including 15-level output, high voltage gain, galvanic isolation, and reactive-power capability remain unchanged. The proposed FCV control utilizes one of the switching angles at the voltage-level transitions as the control variable in a single-loop design, which facilitates control simplicity in the proposed system. The hybrid BCMLI with the proposed FCV control shows relative advantages of voltage gain, isolation capability, reactive supply, and simple control system over the state-of-the-art hybrid inverter topologies with FCV control methods. The details of the hybrid BCMLI, modulation schemes, proposed FCV control design, and comparative assessment are included in this article. In order to validate the proposed system and FCV control, a set of experiments with a 1-kW BCMLI prototype has been conducted for wide-range load levels and power factors. [ABSTRACT FROM AUTHOR]

Parallel connected inverters in islanded mode, are getting momentous attention due to their ability to increase the power distribution and reliability of a power system. When there are different ratings of Distributed Generation (DG) units, they will operate in parallel connection due to different output voltages, impedance mismatch, or different phase that can cause current to flow between DG units. The magnitude of this circulating current sometimes can be very large and damage the DG inverters and also cause power losses that affect powersharing accuracy, power quality, and the efficiency of the Microgrid (MG) system. Droop control, improved droop control, and virtual impedance control techniques and modifications in the virtual impedance control technique are widely used to suppress the circulating current. However, the addition of the virtual impedance to each inverter to compensate the output impedance is resistive or inductive in nature. The resistive nature of the output impedance always causes a certain voltage drop, whereas the inductive nature of the output impedance causes phase delay for the output voltage. Both problems are addressed by the proposed control mechanism in this paper. Negative resistance, along with virtual impedance, is utilized in the proposed control strategy. The output impedance is to be maintained as inductive in nature to achieve good load sharing in droop control MGs. The simulation results validate the proposed control scheme. [ABSTRACT FROM AUTHOR]

This article presents an input-series output-equivalent-parallel (ISOEP) multi-inverter system for high-power wireless power transfer (WPT), where preisolation dc/dc converter is concealed to achieve higher efficiency, and the number of inverter modules is allowed to be flexibly adjusted to satisfy different voltage and power requirements. The main contribution of this article is to analyze the possible factors that may lead to voltage unbalance in the series inverters of the proposed ISOEP multi-inverter topology. At the same time, the dividing capacitor suppression and duty cycle adjustment are adopted to achieve input voltage sharing. To confirm and validate the effectiveness and merit of the proposed WPT system, a prototype consisting of three inverters connected in series was designed, built, and tested. Experiments show that the proposed topology achieved both high-power output and effective input voltage sharing. The maximum output power is 38.37 kW with an efficiency of 89.31%. [ABSTRACT FROM AUTHOR]

All-metal induction heating (IH) systems have been introduced to heat both ferromagnetic and non-ferromagnetic pots using dual resonant frequencies. They are designed for heating ferromagnetic pots using a first harmonic operation mode (FHOM) and for heating the non-ferromagnetic pots using a third harmonic operation mode (THOM). All-metal IH systems employing dual resonant frequencies consist of an IH inverter and a power factor correction (PFC) circuit to transfer desired power to pots by increasing the input voltage of the IH inverter. In this paper, the input voltage is designed to obtain an efficiency-optimized operating point. To obtain an appropriate input voltage, power loss analyses are conducted using first harmonic approximation (FHA). Based on analysis results, the input voltage of the IH inverter can be selected to improve its power conversion efficiency. A 2-kW half-bridge series resonant inverter prototype is implemented to verify the effectiveness of the proposed design by heating ferromagnetic pots using the FHOM with a 2-kW transfer power and by heating non-ferromagnetic pots using the THOM with a 1-kW transfer power. [ABSTRACT FROM AUTHOR]

Copyright of Technical Electrodynamics / Tekhnichna Elektrodynamika is the property of National Academy of Sciences of Ukraine, Institute of Electrodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Switched-boost inverter (SBI) is a single-stage power converter suitable for interfacing between photovoltaic (PV) arrays and loads. Although, it has many advantages such as it's not requiring an expensive complex dead-time circuitry, yet its duty ratio is limited between 0 and 0.5. This means that it has some difficulties in increasing both the DC-link output voltage and its AC-output voltage. So, most researchers proposed it for low-voltage power applications or using with step-up transformers. Accordingly, this study contributes towards improving the performance of the SBI for being used in the modified nanogrid within an open energy system. It introduces a novel approach closed-loop control technique to overcome most of the inverter drawbacks. Also, it enhances both the DC-link and the transformer-less rated AC output voltages to a sufficient value suitable for feeding domestic loads. And in the same time, the proposed robust controller utilizes a hysteresis band for balancing between voltage stability and PV-maximum power achievement. This research also includes a more sophisticated fast-charging slow-discharging control strategy for the battery energy management system that depends on a bidirectional buck-boost converter. Test results ensure the robustness of the proposed controller against sensitivity, nonlinearity, and time-variant parameters of the overall system. [ABSTRACT FROM AUTHOR]

In this paper, a transformerless distribution static synchronous compensator (DSTATCOM) based on the cross-switched (CS) multilevel inverter (CSMLI) is introduced. In comparison with the well-known cascaded h-bridge (CHB) topology, CS inverter produces higher number of voltage levels using fewer number of power components. Since CS inverter produces ac side voltage with high quality and has the ability to work at high voltage and power levels, the proposed CS-DSTATCOM is directly connected to the distribution grid without the need for a transformer. In the proposed CS-DSTATCOM, all the dc sources are replaced with dc capacitors. In this paper, an effective voltage balancing control scheme is proposed to keep the capacitors voltages balanced in the CS structure. The control scheme balances the capacitors voltages in two levels, i.e., inter-cell and within-cell level. On the other hand, the over-voltage and under-voltage phenomena are of the most common power quality (PQ) issues in distribution grids. The proposed DSTATCOM is able to cope with these issues by exchanging reactive power with the grid. Applying the CSMLI in the DSTATCOM structure as well as the capacitors voltage balancing methods are the main novelties of the paper. Also, the capacitors values are considered to be different (which is unavoidable in practice) while their voltages are balanced using the proposed voltage balancing methods. In this paper, a CS-DSTATCOM has been designed for 11 kV distribution grid and several simulation results are provided in the MATLAB/Simulink environment which validate the feasibility and performance of the proposed CS-DSTATCOM. [ABSTRACT FROM AUTHOR]

In this article, the generalized symmetrical step-up multilevel inverter (MLI) using a single dc source and crisscross capacitor units (CCUs) is proposed. Compared with the conventional MLIs, the capacitor in each CCU can get self-voltage balance without auxiliary methods. The output level and boost factor of the proposed topology can be increased with fewer devices. And, importantly, its maximum voltage stress for the switching devices is limited below a low degree even though the peak output voltage increases. However, the maximum voltage stress of most other boost MLIs will rise badly with output voltage increasing. The abovementioned merits of the proposed topology in all show its suitability in renewable energy generation systems, distributed generation, and other applications of high power quality. The operation principles of the proposed MLI are fully described in the this article. The self-balance of capacitors is deduced based on the adopted modulation method. The capacitance calculation is also presented in detail. Afterward, the power loss of the proposed topology has been analyzed. And the comparative study illustrates its advantages on reduced active devices, lower voltage stress, boost ability, and self-balance against other MLIs. Finally, the simulation and the 1.2-kVA experimental prototype with two CCUs and 13-level output are implemented. The results verify the feasibility and performance of the proposed topology. [ABSTRACT FROM AUTHOR]

In this paper, SHE based on Newton–Raphson algorithm is used for open-loop control of flying capacitor multilevel inverter. Without measuring current and capacitor voltages, as well as not using any controller and voltage feedback, proposed control strategy generates accurate switching angles, capable of balancing flying capacitor voltage and eliminates lower order harmonics while considering load power factor variation. Efficiency and robustness of proposed algorithm are verified by simulation and experiments. Results show that proposed method does effectively eliminate specific low-order harmonics, and inverter output voltage is resulted in low total harmonic distortion with desired number of levels and balanced capacitor voltages. [ABSTRACT FROM AUTHOR]

In this article, a single-phase transformerless inverter for photovoltaic (PV) applications is introduced. The proposed inverter provides common ground between input and output terminals, which results in the elimination of the leakage current in the PV systems. Moreover, the voltage gain of the proposed inverter is higher than that of the single-phase quasi-Z-source and semi-Z-source inverters. Utilizing the film capacitors makes the proposed inverter more reliable and also increases its lifetime. The operation of the proposed inverter is analyzed in detail. Finally, the performance of the proposed inverter is verified through the experimental results both in off-grid and grid-tied operation modes. [ABSTRACT FROM AUTHOR]

A universal controller is proposed in this article to operate parallel inverters in both grid-connected (GC) state and standalone (SA) state and ensure seamless transfer between them without reconfiguring the control structure. The universal controller is mainly composed of frequency-locked-loop and three cascaded control loops: a grid current loop, capacitor voltage loop, and inductor current loop. A proportional-integral regulator is adopted in the grid current loop, and a limiter is inserted after the integrator. In the GC state, the proposed controller accurately regulates the grid current of an individual inverter. When islanding occurs, the proposed controller can automatically convert from grid current control to vC– ig-based droop control; critical islanding detection is not needed. This universal controller has several advantages. First, it can realize seamless transfer of parallel inverters; microgrid reliability can be guaranteed in the SA state, and power sharing can be achieved among parallel inverters without communication lines. Second, compared with droop control, it can regulate the grid current accurately and output constant power when the grid voltage fluctuates in the GC state. Third, the grid current harmonics in the GC state and capacitor voltage harmonics in the SA state can be mitigated. Simulation and experimental results verify the effectiveness of the controller. [ABSTRACT FROM AUTHOR]

In this article, a concept of separation of an inverter-fed induction motor drive from its mains supply by two transistor switches inserted in the dc-link circuit is re-examined based on the proposed parallel quasi-resonant dc-link inverter (PQRDCLI). The objective of the article is to show an advantage of the proposed topology in limiting high-frequency common-mode voltage and bearing currents. In the laboratory setup, an induction machine was equipped with hybrid ceramic bearings and an insulated clutch to measure the shaft-to-frame bearing voltage and the shaft-grounding current. Experimental tests of the PQRDCLI confirm significant reduction of common-mode voltage and shaft-to-frame bearing voltage at dc-link zero voltage notches. By controlling the output voltage slopes, the shaft-grounding brush current and the ground leakage current are also reduced. The efficiency measurement and evaluation of the proposed topology, as compared with a two-level hard switched inverter, reveal comparable efficiency of around 95% and indicate loss distributions in both inverters. [ABSTRACT FROM AUTHOR]

In view of the low voltage and high current working condition in the voltage source inverter of low-voltage electric vehicle， by considering the nonlinear factors such as the dead-time and the turn-on / off delay of power device， especially， the voltage drop across the power device was taken into consideration． After that， the inverter output characteristic equation was established． Based on the output characteristic equation and the reference voltage， the error could be derived， thus it will accurately be compensated under the low voltage and high current working condition． At the same time， accurate current polarity is essential during the nonlinear characteristic compensation． However， the current ripple and the zero current clamp effect exist near the zero of phase current， which will result in inaccurate current polarity detection． So a method of reverse compensation was proposed to make the current pass zero in advance， which avoids the complicated determination and calculation of current polarity near the zero of current，in the meantime，the nonlinear characteristic of VSI was compensated effectively，too． Finally，the accuracy and feasibility of the proposed inverter output characteristic equation and compensation method are proved by simulation and experimental results． [ABSTRACT FROM AUTHOR]

Summary: This paper presents cascaded topology of three‐phase neutral‐point‐clamped converters (NPCC)s. Two or more NPCCs are cascaded in their AC sides through transformers. This multilevel inverter (MLI) is a transformer‐based single‐source inverter with trinary asymmetry. Compared with conventional and advanced diode‐clamped multilevel inverters, the proposed MLI achieves more levels on output voltage. From cost, number of components, volume, complexity and efficiency aspects, the proposed inverter is an optimized and advanced inverter. An individual space vector modulation (SVM) method has been developed for voltage control of the inverter. The neutral‐point voltage of the inverter is balanced conveniently by the SVM method. The proposed inverter is suitable for constant‐frequency applications. Simulation and experimental results of a 17‐kVA prototype verify the efficiency of the proposed arrangement. [ABSTRACT FROM AUTHOR]

This paper focuses on the control design of a differential boost inverter when used in single-stage grid-tied PV systems. The inverter performs both Maximum Power Point Tracking (MPPT) at the DC side and Power Factor Correction at the AC side. At first, the state-space time-domain averaged model of the inverter is derived and the small signal frequency domain model is obtained using a quasi-static approximation in which the inverter is treated as a DC–DC converter with a slowly varying output voltage. Then, the controllers are designed using a three-loop strategy in which the inverter inductor currents loop is used for suitable compensation, the DC Photovoltaic (PV) voltage loop is used for MPPT and the output grid current loop is used for Power Factor Correction (PFC) and active power control. The selection of the control parameters is based on a compromise among suitable system performances such as settling time of the input PV voltage, the sampling period of the MPPT, total harmonic distortion of the output grid current, power factor as well as suppression of subharmonic oscillation for all the range of the operating duty cycle. The resulting design ensures that the oscillations of the voltage, current and power at the DC side and the grid current at the AC side are effectively controlled. The validity of the proposed control design is verified by numerical simulations performed on the switched model of the system demonstrating its robustness and fast response under irradiance variations and MPPT perturbations despite the nonlinearity and complexity of the system. [ABSTRACT FROM AUTHOR]

In this paper, a new cascade multilevel inverter based on series connection of several basic units is proposed. The basic topology consists of 5 dc voltage sources and 12 switches. The required mathematical analysis consisting of voltage on switches, power losses and the values of dc voltage sources is provided. To verify the advantages of proposed topology, the suggested structure is compared with other multilevel inverter topologies in terms of used dc voltage sources, switches, voltage on switches and the number of on-state switches. The proposed structure uses the least numbers of dc voltage sources and switches compared to other multilevel inverters for the same number of levels. Also, voltage rating on the switches in the proposed topology is less than other topologies. These characteristics cause the weight, size and cost of proposed topology to be reduced. The proposed inverter is implemented using experimental setup. The experimental results verify the performance of proposed structure. [ABSTRACT FROM AUTHOR]

An impedance-source inverter can offer the voltage buck-boost function in a single-stage circuit. Its advantages include a simple structure, safety, and reliability. This article proposes a Cockcroft–Walton multiplier voltage (CWMV) impedance-source inverter consisting of a modified CWMV circuit and an impedance-source inverter. There are two types of circuits: the CWMV Z-source inverter (ZSI) and the CWMV quasi-Z-source inverter (qZSI). In a CWMV qZSI, the input current is continuous, the voltage overshoot across the bridge is small, and the boost capability is great, with the disadvantage is that its passive component count is increased. This article studies the static and dynamic characteristics of the two inverters. The operating modes of the CWMV qZSI is studied, the voltage and current stress of each device are analyzed, the small signal model of the circuit is established, and a proportional-integral-differential controller with good control performance is designed. Compared with existing impedance-source inverters, a CWMV qZSI has obvious advantages in terms of the voltage and current stresses on components, and also in terms of its inductor size, magnetic core volume, and overall efficiency. The theoretical analysis was verified by a 1 kW laboratory prototype. The experimental results were consistent with the theoretical analysis. [ABSTRACT FROM AUTHOR]

To improve grid-connected inverter operation performance, a power oscillation and current harmonic suppression coordinate control strategy that considers the problem of overcurrent is proposed in this work. First, the internal relationship between power fluctuation suppression and current balance is analyzed, and then, combining dynamic regulation of the active and reactive power settings, the peak value of the grid-connected current is limited within a safe range. Second, a simplified Fourier transform algorithm is proposed for the detection of fundamental positive and negative sequence vector components and band-pass filtering the three-phase input signals. By simplifying the transform and introducing a recursion algorithm, the online computational complexity is reduced and the controller based on this algorithm is used as an inner current loop regulator. Finally, the controller was investigated using simulations, and experimental results indicated that the output power quality of the grid-connected inverter under unbalanced grid voltages can be substantially improved. [ABSTRACT FROM AUTHOR]

Summary: A favorable option to supply unbalanced loads and provide the neutral wire is the four‐leg inverter. Controllers with high robustness and dynamic response should be used to adjust the inverter load voltages for unknown, unbalanced, and nonlinear loads. Sliding mode controls (SMCs) have a simple structure, good robustness against model parameter uncertainties, and desirable transient response. However, chattering phenomena, variable switching frequency, and error convergence to the operating point on infinite time are the main weaknesses of the conventional SMC method. In this paper, to restrict the conversion time to a finite and controllable value, terminal sliding mode control (TSMC) and fast terminal sliding mode control (FTSMC) procedures are proposed to regulate the load voltages of the four‐leg inverter. In these methods, a continuous control output is suggested to fix the switching frequency and reduce chattering phenomena significantly. Furthermore, the proposed methods are highly robust against model parameter uncertainties. Different simulation and experimental results on a 3‐kW test bench under different loading conditions are done to validate the significant performance of the proposed methods. [ABSTRACT FROM AUTHOR]

Summary: This study presents an innovative and optimized reactive power support (ORPS) strategy for photovoltaic (PV) inverters to improve the dynamic voltage stability (DVS) of islanded microgrid (MG) with induction motor (IM) load. On the occurrence of the fault, voltage instability (VI) happens due to the low‐inertia IM load and poor ride through capability of PV inverters of MG. Supplement of optimal RPS promptly, without exceeding the rated current value of the inverter, is aimed at the proposed control, to maintain DVS during severe voltage downfall as a result of a fault. Once the profiled voltage value is restored and the necessity of RPS is fulfilled, the PV inverter returns to its prefault power production combination. The detailed model of an inverter‐based islanded MG with IM load is built to examine the DVS, and the theoretical analysis and technical discussion are conducted. A comparison between the conventional and proposed strategies is carried out. From the demonstrated results, employing the proposed ORPS control can provide RPS effectively and helps to improve the DVS. This proposed strategy can also provide an equivalent service as an expensive 610‐kVA dynamic volt‐ampere reactive support device (ie, D‐STATCOM) in the studied MG. [ABSTRACT FROM AUTHOR]

Voltage imbalances are one of the most severe challenges in electrical networks, which negatively affect their loads and other connected equipment. This paper proposes a voltage support control strategy to mitigate the voltage imbalance in inverter-based low voltage distribution networks. The control scheme is derived taking in mind the following control objectives: a) to increase the positive sequence voltage as much as possible, b) to decrease the negative sequence voltage as much as possible, c) to inject the power generated by the primary source, and d) to minimize the output current of the inverter. The innovative contribution of the proposed solution is based on the design of a control algorithm that meets the aforementioned objectives without resorting to communications with other grid components. The theoretical results are experimentally validated by selected tests on a laboratory setup with X/R ratio close to one. [ABSTRACT FROM AUTHOR]

The presented article deals with the steadystate analysis of five-phase Induction Motor (IM), which is supplied by rectangular voltage from a fiveleg Voltage Source Inverter (VSI). The new proposed approach is derived from complex Fourierseries using to express inverter terminal voltages. Based on mathematically described inverter output voltages, a formula for VSI output space phasor was derived. Assuming sinusoidal motor winding distribution and on the basis of motor parameters, stator and rotor current space phasors for defined motor load were determined. Finally, the electromagnetic torque ripple waveforms for different IM operation states were investigated. [ABSTRACT FROM AUTHOR]

Hierarchical schemes are widely used for the designing of the inverter-based AC microgrids control strategies. To ensure reliable operation, hierarchical control must consider together all the functionalities that allow the regulation of key variables and guarantee a safe transition between operation modes. Conventionally, in the literature are proposed three-layer schemes which present relevant drawbacks: they include limited functionalities and they use droop method for the primary layer which, despite its decentralised nature, suffers from issues that have motivated the development of alternative strategies. Considering this, the contribution of this study is two-fold. First, a droop-free hierarchical control strategy that satisfies a proper operation of AC microgrids is proposed. Control objectives such as power-sharing, frequency regulation, optimal power dispatch and voltage regulation are considered. Second, a closed-loop small-signal model, which facilitates the control parameters design and fills a gap in the literature is presented. Differences between the proposal and previous controls are discussed. Selected tests are carried out in a laboratory microgrid under different conditions, including normal operation and the response to failures in the central controller and to communication impairments. The experimental results show a good performance of the proposal even in adverse conditions. [ABSTRACT FROM AUTHOR]

Symmetrical and asymmetrical multilevel inverters (MLIs) have demonstrated its usefulness in a wide range of applications. This is accomplished due to the ongoing improvement by reducing the converter size and enhancement in the voltage quality. In this article, a generalized cascaded MLI structure is developed, which can operate in both symmetric and asymmetric modes. Comparative assessment in terms of the number of components and voltage stress warrants the design superiority. A new selective harmonic elimination (SHE) control using flower pollination algorithm (FPA) is investigated for the developed asymmetrical MLI. The salient features of the FPA such as less burdensome compilation and ability tos single-stage local and global search ascertain the elimination of the targeted harmonics through optimum angles computation. Moreover, the competence of the FPA is verified by comparing it with well-known SHE algorithms. Simulation analysis is carried out in MATLAB/Simulink environment, which validates the workability of the developed system. Experimental tests using fundamental and high switching frequency control techniques are further conducted under a dynamic environment to demonstrate the efficacy of the proposed methodology. [ABSTRACT FROM AUTHOR]

Boost rectifiers are commonly used as the input for power inverters. The output voltage of the boost rectifiers should have high quality and precise value to enable the power inverters to achieve maximum performance. However, the grid occasionally supplied unbalanced voltage and current to the boost rectifiers so that the performance of the rectifiers is impaired. When unbalanced AC voltages occurred, the frequency of DC voltage ripples may become two times higher than the AC voltage frequency. The unbalance voltage and current may occur when the grid is supplied by several single-phase Distribution Generators (DGs) with varied capacities. This condition becomes more complicated if the DG is renewable energy in which the output power is intermittent. This study proposes a novel three-phase pulse-width modulated (PWM) boost rectifier control using Voltage Oriented Control (VOC) with a Combined error adaptive fuzzy-PI (CEAF). CEAF is a combination of the Delta error adaptive fuzzy (DEAF) and the Absolute error adaptive fuzzy (AEAF). DEAF is a self-tuning fuzzy-PI method that is generally used as an adaptive fuzzy controller with inputs of errors e(t) and delta error de(t). As for AEAF, it is a modified DEAF of which the inputs are the absolute values of e(t) and de(t). This adaptive Fuzzy-PI is used to determine Kp and Ki values that suit the needs, especially when the sources are fluctuating or unbalanced. The performance of the proposed controller is then compared with a conventional DEAF and with a well-adjusted PI controller. Based on the simulation in Matlab/Simulink, the proposed method would result in a significant reduction in DC voltage ripples and DC steadystate error when fluctuating, unbalanced voltages occur. The resulted ripple voltage decreases from 0.16% to become 0.12%. The steady-state error decreases from 0.27% to become 0.19%. [ABSTRACT FROM AUTHOR]

Summary: Voltage unbalance and harmonics are the major power quality issues in inverter‐based low voltage microgrids (MGs). In the presence of nonlinear load, the interconnecting inverters in the MG may not be able to compute the amount of reactive power and harmonics to be compensated independently without violating their respective ratings. This may result in disproportionate sharing of power by the individual inverters, and consequently resulting in the overloading of some of the inverters. Therefore, in the proposed work, a repetitive controller (RC) in addition to an existing controller has been developed and added in the outer most. This RC can control the individual inverters to compensate voltage unbalance and nonlinear loading through proportionate effort sharing by individual inverters in the MG. This technique has been successfully implemented on three‐phase voltage source inverter which is controlled to maintain perfect three‐phase balanced set of voltages under unbalance nonlinear loading conditions. The proposed strategy has shown an effective compensation even under highest degree of unbalance and nonlinear loading in MG. The proposed controller is designed and simulated with MATLAB/Simpower system. Field programmable gate array‐based hardware prototype has been developed to validate the control approach experimentally. [ABSTRACT FROM AUTHOR]

A novel single-phase transformerless dual-mode interleaved multilevel inverter (DMIMI) is proposed in this paper, which can inject a highly sinusoidal ac current to the grid even with the input dc voltage less than the peak grid voltage. Furthermore, dead-beat controllers are developed to directly calculate the optimal duty cycles in a digital control platform. As compared to the traditional dual-mode multilevel approaches, the DMIMI offers high efficiency, less number of components conducting simultaneously in each operation mode, and the capability of reactive power exchange. This paper presents the theoretical analysis and the experimental results obtained from a 1-kW prototype. The experimental results reveal that the proposed DMIMI can achieve high conversion efficiency and low leakage current as well as high quality grid current. [ABSTRACT FROM AUTHOR]

An improved division–summation (D–Σ) digital control strategy without high-speed communication is proposed in this paper. Unlike the traditional zero-sequence circulating current control method, the interphase circulating current suppression method is discussed and implemented on the basis of the single-phase equivalent circuit in this strategy. The generation mechanism of the interphase circulating current is emphatically analyzed. Output voltage compensation and virtual impedance compensation are studied and integrated with the D–Σ digital control method to suppress the circulating current. Experimental platform with three paralleled three-level T-type grid-connected inverters has been set up. The experiments are carried out under the conditions of the impedance match or mismatch among the inverters, the unbalanced grid voltages, and the dynamic process such as start-up and step current change. The experimental results verify that the improved D–Σ digital control strategy may effectively restrain the circulating current under various conditions. [ABSTRACT FROM AUTHOR]

Linear AC power supplies can be replaced by their nonlinear switching counterparts due to the lower voltage drops and higher efficiency and power density of switching-mode inverters. Multilevel cascaded H-bridge (CHB) converters are the preferred inverter structure because of modular configuration, control, and protection. The output voltage quality in CHB converters depends on the number of output levels. Asymmetric CHBs (ACHBs) produce an output voltage with higher number of levels with respect to CHBs for the same number of cascaded modules. This results in the reduction of power supply size, voltage drops, and losses. Considering the relative high switch counts, analysis of the effect of conduction and dead-time voltage drops on the inverter output characteristics is an important challenge in designing multilevel converters. In this paper, a generic algorithm is presented to calculate the conduction and dead-time voltage drops of ACHBs utilizing level-shifted modulation. These voltage drops give the necessary information for the design of heatsinks, switch selection, output impedance estimation, and the compensation schemes. It is shown through theoretical and simulation studies that the aforementioned voltage drops of ACHBs are to be calculated in a different manner with respect to the CHBs which mostly use the phase-shifted modulation. [ABSTRACT FROM AUTHOR]

In this paper, a transformer-less grid-tied single-phase inverter is proposed which is directly connected to the topology. The voltage across the leakage capacitor has the base frequency, which decreases the leakage current under the defined value in the standards. This inverter's active switches are high- and low-frequency types. High-frequency switches control the inductor's current. In addition, the low-frequency switches are synchronous with the grid and operate in the base frequency. Since no power electrolytic decoupled capacitor is utilized between the high- and low-frequency switches, the system's total efficiency and lifespan are improved. The proposed inverter has the capability of stepping up/down the output voltage, making it suitable for operating in a wide range of voltages and also providing large range of powers to the grid. This topology is directly connected to the grid, without any output filter, leading to elimination of the losses caused by the filter and increased efficiency. In the proposed inverter, a digital current controller is employed to control the injected current to the grid. Furthermore, P&O algorithm is adapted to extract the maximum power from the input source. For proving the proposed converter's performance, a 770-W prototype has been implemented and comprehensive experimental results are presented. [ABSTRACT FROM AUTHOR]

This paper presents a review of the impact of rooftop photovoltaic (PV) panels on the distribution grid. This includes how rooftop PVs affect voltage quality, power losses, and the operation of other voltage-regulating devices in the system. A historical background and a classification of the most relevant publications are presented along with the review of the important lessons learned. It has been widely believed that high penetration levels of PVs in the distribution grid can potentially cause problems for node voltages or overhead line flows. However, it is shown in the literature that proper control of the PV resource using smart inverters can alleviate many of those issues, hence paving the way for higher PV penetration levels in the grid. [ABSTRACT FROM AUTHOR]

Active damping is a popular approach to suppress the resonance in LCL-filtered grid-connected inverter owing to lossless damping and efficient system design. In capacitor voltage (CV) damping methods, a differential compensator is essentially needed in feedback path, where the damping effectiveness depends on emulated derivative characteristics of the compensator. Such CV feedback compensation methods face design limitation at the critical resonance frequency and may require additional delay reduction to ensure stability. In this article, an alternative parallel feedforward compensation method is proposed to synthesize an almost strictly positive real plant and achieved damping with modified stability characteristics. A second-order bandpass section is employed as a compensator in damping loop based on the proposed control scheme. The main features of the proposed method are effective damping without critical resonance frequency damping limit, extended stable damping region, improved control performance, and good robustness under filter parameters and grid inductance variation conditions. The simulation and experimental results are presented to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Precise power sharing considered is necessary for the effective operation of an Autonomous microgrid with droop controller especially when the total loads change periodically. In this paper, reactive power sharing control strategy that employs central controller is proposed to enhance the accuracy of fundamental reactive power sharing in an islanded microgrid. Microgrid central controller is used as external loop requiring communications to facilitate the tuning of the output voltage of the inverter to achieve equal reactive power sharing dependent on reactive power load to control when the mismatch in voltage drops through the feeders. Even if central controller is disrupted the control strategy will still operate with conventional droop control method. additionally, based on the proposed strategy the reactive power sharing accuracy is immune to the time delay in the central controller. The developed of the proposed strategy are validated using simulation with detailed switching models in PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

This study presents a new and robust single-phase inverter based on the buck-boost converter. The proposed inverter topology has minimised numbers of active and passive elements that provide less complexity and cost. Unlike similar studies in the literature, an efficient hybrid control technique is used for the control of the inverter operation. The hybrid control technique is comprised of the traditional feedback proportional-integral-derivative (PID) controller and the new proposed openloop control technique called 'control law'. This hybrid control technique provides stable and high response performance operation for the proposed inverter while the system parameters change. The proposed inverter can operate with a wide range of output frequency and output voltage value on different load conditions while satisfying <5% voltage total harmonic distortion (THD) value of the output voltage. An experimental laboratory setup with the values of 0.5 kW, 0-100 Vp and 0-50 Hz is built for the proposed inverter. The experimental results demonstrate that the proposed inverter can produce high-quality output voltage with <5% THD on different input and output system parameters. [ABSTRACT FROM AUTHOR]

In this paper, a neutral point (NP) voltage balancing scheme suitable for three phase 5-level active NP clamped and T-type NP clamped (TNPC) inverters is discussed. Carrier-based pulsewidth modulation is used for the balancing of dc-link capacitors and floating capacitors (FC) in the inverter. The FC voltages are regulated with the help of redundant switching states of pole voltage levels and the dc-link capacitor voltages are controlled using zero-sequence voltage injection. Though the balancing approaches are different for dc-link capacitors and FCs, they are not decoupled from each other. This is due to the effect of certain redundant switching states used for FC balancing causing NP voltage variation. To address this issue, the redundant state time ratio is estimated online every sample and based on this dynamic time ratio, an optimal relationship between neutral current and zero-sequence voltage is established. It is found that the use of dynamic time ratio helps in achieving better transient performance than that of generally adopted fixed time ratio. Simulation and experimental results prove that the proposed balancing scheme works well under all operating conditions and exhibits fast and stable transient performance. [ABSTRACT FROM AUTHOR]

This work aims at suggesting a frequency tracking system for a dual half-bridge series resonant inverter applied to induction heating (IH) system. The modulation technique incorporated is asymmetric voltage cancellation method. In this new tuning method, the control range is enhanced to the whole range of inverter operation. Also, the inverter discussed here is capable of driving two (dual) loads simultaneously compared to the conventional inverter feeding single load. Small-signal modeling of the dual-load IH system is discussed in this article to facilitate stability and controllability of the IH load. Also, the power control margin is determined with the necessary pole-zero plots. The simulation study of the proposed system is incorporated in the MATLAB/Simulink and also experimentally validated for the dual-coil induction cooking system. [ABSTRACT FROM AUTHOR]

The proposed work mainly deals with transformer-based three-phase Multi-Level Inverter (MLI) where the switches in MLI are controlled by Multi-Carrier PWM (MC-PWM) techniques. In this article, 48V DC input voltage is fed to 48/400V High-Voltage DC-DC boost converter which is controlled by Proportional-Integral (PI) and Neural-Network (NN) tuned PI controllers. 400V DC output from boost converter is connected to three-phase MLI where the MLI switches are controlled by three different types of MC-PWM techniques like Phase Disposition (PD), Phase Opposition and Disposition (POD) and Alternate Phase Opposition and Disposition (APOD). The overall system performance in terms of Total Harmonic Distortion (%THD) is analyzed and it is depicted that the proposed system under different modulation indices gives improved THD results with an NN tuned PI controller-based boost converter. The whole analysis is performed on the MATLAB\Simulink platform. [ABSTRACT FROM AUTHOR]

This paper implements a 125 level asymmetric cascaded multilevel inverter using fuzzy logic which is used in the dynamic voltage restorer. The inverter is designed with a reduced number of switches. The higher switching frequency is defined for the better performance of the multilevel inverter. The 125 level output is obtained in this proposed approach with only twelve switches and six voltage sources. By changing the switching frequency, the proposed output voltage level is obtained in the inverter. The paper is organized into two phases. In the first step the design of 125 level inverter is proposed, and in the second phase, the power quality improvement using the designed inverter is discussed. The proposed design of an inverter is implemented for dynamic voltage restorer solves the power quality problems such as are voltage sag, voltage swell, and harmonics. The power quality issue mitigation performance is increased with the proposed 125 level inverter. The enrichment of the proposed design is investigated using the comparison of existing works. The proposed work is implemented in the Matlab/Simulink environment. [ABSTRACT FROM AUTHOR]

This article presents the possibility of decreasing the inverter output voltage distortions that are caused by the typical distortions in the output voltage pulses of an impedance network using the qZ-source as an example. DC sources, such as photovoltaic cells with the qZ-source, increase the dc voltage; an impedance network operates in the continuous current mode and the discontinuous current mode (DCM). Both of these, but particularly DCM, implement the characteristic distortions to the impedance network output pulses, which results in the distortions in the inverter output voltage. It is possible to decrease these distortions in a passive way (increasing the capacitors of the network) or by using an efficient instantaneous controller of the inverter output voltage. Two controllers—a single-input single-output PID controller and a multi-input single-output improved passivity-based controller—were compared using the experimental model voltage source inverter with the input qZ-source. [ABSTRACT FROM AUTHOR]