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This paper underpins the principles for generating reactive power in single-phase transformerless photovoltaic (PV) inverters. Two mainstream and widely adopted PV inverters are explored, i.e., H5 and HERIC. With conventional modulation techniques, reactive power cannot be realized in H5 and HERIC due to the absence of freewheeling path in negative power region. Based on the study, modulation techniques are proposed to provide bidirectional current path during freewheeling period. With proposed modulation technique, reactive power control is achieved in H5 and HERIC inverters, without any modification on the converter structures. The performances of the proposed modulation techniques are studied via MATLAB simulation and further validated with experimental results. [ABSTRACT FROM PUBLISHER]

Switch-sharing-based multilevel inverter can be useful to develop an improved-performance DC–AC converter for low-power photovoltaic applications. However, this cannot be fully achieved without having a reliable control solution. Hence, this study presents a smart control strategy equipped with an adaptive proportional–integral controller. The adaptive characteristic is established through a tuning module that continuously fine tunes only one parameter. With the tuning mechanism, the load current quality is able to be continuously retained at the acceptable level even during the presence of disturbances. To validate the control performance, experimental work has been conducted on a laboratory prototype under load disturbance conditions. [ABSTRACT FROM AUTHOR]

Current source inverters (CSIs) have increasingly become popular because of their inherent advantages over voltage source inverter. In a single phase system, the operation of multilevel current source inverter (MCSI) requires large and bulky DC link inductor and the employment of switching state redundancy to balance the inductor currents limit the advantages of MCSI. This study proposed a new configuration for parallel MCSI. The proposed energyrecovery scheme provides a major path to release its stored energy in order to balance the sharing inductor currents and introduces a novel single state switching technique for the generation of MCSI output current. In addition, a chopper circuit with smaller inductor size is employed to replace the large and bulky input DC link inductor. An integration of five-level MCSI and a chopper based DC-current source with energy recovery scheme circuits produce a five-level MCSI with a simple converter structure. The performance of the proposed MCSI is analysed through MATLAB and is verified by constructing a prototype. The results demonstrate that the proposed circuit with the balancing inductor current scheme significantly reduces the input DC link inductor size, eliminate the control complexity in balancing the inductor currents and has excellent sharing inductor current characteristics. [ABSTRACT FROM AUTHOR]

This paper presents a simple approach for the selective harmonic elimination (SHE) of multilevel inverter based on the transistor-clamped H-bridge (TCHB) family. The SHE modulation is derived from the sinusoidal voltage-angle equal criteria corresponding to the optimized switching angles. The switching angles are computed offline by solving transcendental non-linear equations characterizing the harmonic contents using the Newton-Raphson method to produce an optimum stepped output. Simulation and experimental tests are conducted for verification of the analytical solutions. An Altera DE2 field-programmable gate array (FPGA) board is used as the digital controller device in order to verify the proposed SHE modulation in real-time applications. An analysis of the voltage total harmonic distortion (THD) has been obtained for multiple output voltage cases. In terms of the THD, the results showed that the higher the number of output levels, the lower the THD due to an increase number of harmonic orders being eliminated. [ABSTRACT FROM AUTHOR]

In this article, the performance of the split-capacitor H-bridge topology as a single-phase transformerless photovoltaic inverter is studied. By connecting the midpoint of its two series DC-link capacitors to the ground, the split-capacitor H-bridge is able to clamp the common-mode voltage of the system, effectively suppressing leakage ground current. To overcome the issue of capacitor voltage balancing, a simple balancing circuit and its control are introduced. The operation modes, common-mode voltage, and leakage ground current characteristics of the split-capacitor H-bridge topology are discussed, subsequently validated using both simulation and experimental tests. Comparison with a conventional transformerless H-bridge topology proves the superiority of the split-capacitor H-bridge topology in terms of leakage ground current and efficiency. [ABSTRACT FROM AUTHOR]

Independently controlled multimotor drives are typically realized by using a common dc link and independent sets of three-phase inverters and motors. In the case of an open-circuit fault in an inverter leg, one motor becomes single phase. To enable continued controllable operation by eliminating single phasing, the supply for the motor phase with the faulted inverter leg can be paralleled to a healthy leg of another inverter using hardware reconfiguration. Hence, the two motors are now supplied from a five-leg inverter, which has inherent voltage and current limitations. Theoretically, violating the voltage limit leads to inverter overmodulation and large torque oscillations. It is shown here that the finite-control-set model predictive control, designed to control the machines' stator flux and torque, can consider the inherent voltage limit dynamically in the control loop. Apart from preserving the independent control of the two machines, the additional constraint consideration significantly widens the operating speed ranges of the machines. In particular, it is shown that, whenever the voltage limit is entered, the controller reduces the stator flux level automatically, without requiring external flux reference change. The obtained performance is illustrated using experimental results and is also compared to the conventional two-motor field-oriented control scheme. The control concept is thus fully experimentally verified. [ABSTRACT FROM PUBLISHER]

This paper proposes an active front-end solution to balance the dc-link capacitor voltage of the five-level diode-clamped inverter. Capacitor voltage balancing is performed by a three-level boost converter connected to the two inner capacitors of a five-level diode-clamped inverter and additional balancing circuits at the other two outer capacitors. The proposed configuration is tested through simulation and experiment for various load power factor conditions at a high modulation index. The result demonstrates the reliability of the proposed configuration to balance the dc-link capacitor voltage at the desired level. [ABSTRACT FROM PUBLISHER]

A two-motor drive, supplied by a five-leg inverter, is considered in this paper. The independent control of machines with full dc-bus voltage utilization is typically achieved using an existing pulsewidth modulation (PWM) technique in conjunction with field-oriented control, based on PI current control. However, model predictive control (MPC), based on a finite number of control inputs [finite-control-set MPC (FCS-MPC)], does not utilize a pulsewidth modulator. This paper introduces three FCS-MPC schemes for synchronous current control in this drive system. The first scheme uses all of the available switching states. The second and third schemes are aimed at reducing the computational burden and utilize a reduced set of voltage vectors and a duty ratio partitioning principle, respectively. Steady-state and transient performances are analyzed and compared both against each other and with respect to the field-oriented control based on PI controllers and PWM. All analyses are experimental and use the same experimental rig and test conditions. Comparison of the predictive schemes leads to the conclusion that the first two schemes have the fastest transient response. The third scheme has a much smaller current ripple while achieving perfect control decoupling between the machines and is of low computational complexity. Nevertheless, at approximately the same switching loss, the PI-PWM control yields the lowest current ripple but with slower electrical transient response. [ABSTRACT FROM PUBLISHER]

This paper presents an investigation of the finite-control-set model predictive control (FCS-MPC) of a five-phase induction motor drive. Specifically, performance with regard to different selections of inverter switching states is investigated. The motor is operated under rotor flux orientation, and both flux/torque producing (d-q) and nonflux/torque producing (x-y) currents are included into the quadratic cost function. The performance is evaluated on the basis of the primary plane, secondary plane, and phase (average) current ripples, across the full inverter's linear operating region under constant flux–torque operation. A secondary plane current ripple weighting factor is added in the cost function, and its impact on all the studied schemes is evaluated. Guidelines for the best switching state set and weighting factor selections are thus established. All the considerations are accompanied with both simulation and experimental results, which are further compared with the steady-state and transient performance of a proportional-integral pulsewidth modulation (PI-PWM)-based current control scheme. While a better transient performance is obtained with FCS-MPC, steady-state performance is always superior with PI-PWM control. It is argued that this is inevitable in multiphase drives in general, due to the existence of nonflux/torque producing current components. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Low cost passive islanding is developed for single phase grid connected inverter. [•] Drastically improved disconnection time in the proposed method for single phase inverter. [•] Low cost, effective and minimal of external components are the forte for this method. [•] Effectively detect islanding for different loads, inverter output powers and quality factors. [Copyright &y& Elsevier]

Despite the advantages offered by multilevel inverters, one of the main drawbacks that prevents their widespread use is their circuit complexity as the number of power switches employed is usually high. This paper presents a new multilevel inverter topology with a considerable reduction in the number of power switches used through the switch-sharing approach. The fact that the proposed inverter applies two bidirectional power switches for sharing among the three phases does not prevent it from producing seven levels in the line-to-line output voltage waveforms. A modified scheme of space vector modulation via the application of virtual voltage vectors is developed to generate the PWM signals of the power switches. The performance of the proposed inverter is investigated through MATLAB/SIMULINK simulations and is practically tested using a laboratory prototype with a DSP-based modulator. The results demonstrate the satisfactory performance of the inverter and verify the effectiveness of the modulation method. [ABSTRACT FROM AUTHOR]

This paper presents a three-phase cascaded multilevel inverter that uses five-level transistor-clamped H-bridge power cells. Multicarrier phase-shifted pulse-width modulation method is used to achieve balanced power distribution among the power cells. A new method to balance the midpoint capacitor voltage in each cell is developed and tested. The analysis of the output voltage harmonics and the total power losses covering the conduction and the switching power losses are carried out and compared with the cascaded neutral-point-clamped and the conventional cascaded H-bridge inverters. For verifications, the proposed inverter is experimentally tested on an induction motor. From the results, the proposed inverter provides higher output quality with relatively lower power loss as compared to the other conventional inverters with the same output quality. [ABSTRACT FROM PUBLISHER]

Model predictive control (MPC) for a two-motor drive, supplied from a five-leg inverter, is presented in this paper. As an alternative to existing methods, use of MPC in multimachine drives has the advantages of independent fast current control of the machines, elimination of the closed-loop system's cascaded structure, and a reduced number of microcontrollers. A vector control algorithm is required, necessitating state-space modeling, with each machine's direct- and quadrature-axis currents chosen as state variables. Prediction of future states is via a discrete-time model of the five-leg inverter and a piecewise-affine model of two permanent-magnet synchronous motors (PMSMs). A method which eliminates unfeasible switching states inherent in reduced-switch-count inverters while reducing computation and sampling times is proposed. The algorithm is implemented in a TMS320F28335 DSP microcontroller, which controls the five-leg inverter and the two PMSMs. Simulation and experimental results validate the presented control concept. [ABSTRACT FROM PUBLISHER]

Abstract: This paper describes a strategy to optimize the switching angle of a modified H-bridge single-phase seven-level inverter for stand-alone photovoltaic (PV) system. The inverter comprises a conventional H- bridge inverter and two bidirectional switches. It can generate seven-level output voltage level, namely +Vdc, +2/3Vdc, +1/3Vdc, 0, -1/3Vdc, -2/3Vdc and -Vdc. Optimized Harmonic Elimination Stepped Waveform (OHESW) technique was employed to improve the output waveform quality. Newton- Raphson method is engaged to solve the transcendental equations from OHESW technique which produces all possible solutions with any random initial guess. Among which sets, the one producing the least output-voltage THD was chosen. Computation resulting from the optimized switching angle was simulated. A small-scale laboratory prototype was built and tested. Its results indicated the proposed method''s effectiveness and the application feasibility of the fundamental frequency switching. [Copyright &y& Elsevier]

This paper aims to compare the performance of three phase induction motor drives using Five Leg Inverter (FLI) and Three Leg Inverter (TLI) configurations. An Indirect Field Oriented Control (IFOC) method using a TLI is well established and incorporated for high performance speed drives in various industries. The FLI dual motor drive system on the other hand shows good workability in the independent control of two induction motor drives simultaneously. In this experiment, the IFOC method is utilized for both drive systems, and Space Vector Pulse Width Modulation (SVPWM) is used to generate pulses for both inverters. For the FLI, the Double Zero Sequence (DZS) Injection technique is used to generate the modulation signal. The complete experiment setup is done by using a DSpace 1103 controller board. The individual motor performances are analyzed using similar schemes, equipment setups and controller parameter values. The results show similar speed performance response capability between the single motor operation using a TLI system and the two motor operation using a FLI system based on the variable speed range either in forward or reverse operation. They also show similar load rejection abilities. However, the single motor with a TLI has a better power quality aspect such as ripple current and total harmonics distortion (THD). [ABSTRACT FROM AUTHOR]