Search

The extra-LC auxiliary-resonant-snubber-based converter (ELCARSC), as a soft-switching converter, has the advantages of low switching loss, low electromagnetic interference noise, and low-output distortion caused by the dead-time effect. However, the dead-time effect is still the main problem in a high-precision application. Besides, the traditional control and compensation methods rely on the accuracy of the circuit parameters, especially the junction capacitance, thus resulting in compensation error. Therefore, this paper proposed a novel high-precision control method through modulating the initial resonant current to eliminate the dead-time effect of ELCARSC. The method does not need complicated online calculation and reduces the dependence on the accuracy of the circuit parameters, especially the influence of the junction capacitances of the switches. In this paper, the dead-time effect of the ELCARSC is analyzed. The output voltage error with the conventional variable-timing control method is analyzed. Subsequently, the proposed modulated initial resonant current control is introduced. Finally, a prototype was developed that verified the effectiveness of the control method. The quality of the output current and voltage is improved by utilizing the proposed control method. However, the peak current of the auxiliary switch is increased. [ABSTRACT FROM AUTHOR]

This paper proposes a variable off-time control method for a single-phase microinverter operating in the discontinuous conduction mode (DCM) for efficiency improvement. First, the fixed off-time control method is analyzed. The concept is to fix the off-time of the active switch throughout a line cycle for all output powers and scale the on-time of the active switch to shape a sinusoidal output current. Then, based on the fixed off-time control method, a variable off-time control method is proposed to modulate the preset fixed off-time in order to decrease the switching frequency during ac line zero-crossings and light load conditions. Compared with existed fixed-frequency DCM control or boundary conduction mode control, the variable off-time control is more flexible to optimize the efficiency under different load conditions as the switching frequency range can be automatically adjusted according to the output power. The switching frequency is high at heavy loads to limit the maximum peak current and is low at light loads to increase the light load efficiency. In addition, a predictive on-time method is adopted to simplify inverter control and reduce hardware costs. The parameter design principle is detailed in this paper. A 300 W prototype is built to verify the performance of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, two structures are proposed for the switched-inductor quasi-Z-source inverter. In the proposed structures to extend the voltage gain of inverter, two new switched-inductor structures are used. In the proposed structures, voltage across the capacitors in the Z-source network and in the switched-inductor is symmetric and small. The other advantage of proposed inverters is known as achieving higher voltage gain per smaller duty cycle ratio (of shoot-through). Compared with a conventional continuous input current switched-inductor quasi-Z-source inverter at the same gain voltage, there is less of a ripple of input current in the proposed inverters. In this paper, at first the both the conventional and the proposed switched-inductor Z-source inventers are thoroughly investigated to find out their governing relations. Then, the proposed Z-source inverters are compared with the conventional ones by simulating them to assess their performance efficiency. Next, applying the simple boost pulse width modulation the simulation is carried out with PSCAD/EMTDC software. After that, to evaluate the obtained results, the prototypes of the proposed inverters with 48 Vdc input voltage are used. [ABSTRACT FROM PUBLISHER]

In this paper, new half-bridge and full-bridge topologies for a switched-boost inverter are proposed. These topologies have a high boost factor in comparison with conventional types. In addition, the proposed topologies have continuous input current and can generate zero-voltage level in output. In this paper, the operation of the proposed inverters in different operating modes is analyzed. Then, the values of inductors and capacitors are designed. Moreover, the used switching pattern and its logical diagram are introduced. A comprehensive comparison between the proposed and conventional topologies in terms of the boost factor, the number of elements, and the efficiency shows the good features of the proposed inverters. Finally, to verify correct operation of the proposed topologies and derived equations, simulation and experimental results are presented. [ABSTRACT FROM AUTHOR]

A novel hybrid pulse width modulation (PWM) technique is proposed in this paper for two parallel interleaved, two-level, three-phase voltage source inverters (VSIs). The two parallel interleaved VSIs are analyzed as a three-level (3L) inverter. A 3L inverter provides minimum line current ripple when nearest three voltage vectors are applied. In this paper, a novel carrier-based PWM technique is developed that ensures the application of nearest voltage vectors, keeping average circulating current to zero over a switching period. For carrier-based implementation of the proposed PWM, generalized common-mode (CM) offsets are derived in terms of maximum and minimum values of reference signals. Each 3L space-vector sector is divided into seven subsectors. For each subsector, a CM offset is calculated, addition of which to reference signals ensures the minimum line current ripple and zero average circulating current. Simulation and experimental results are provided to validate the proposed technique. [ABSTRACT FROM PUBLISHER]

This paper proposes a switching strategy for the Z-source inverter (ZSI), which has unequal short-through intervals to reduce the current ripple in the inductor of its impedance source. A size reduction of the inductor of the ZSI is one of the important issues in improving the power density of the ZSI, and the inductor current ripple reduction is required to achieve it. The proposed method can reduce the inductor current ripple by 27.8% compared with the conventional method that has equal short-through intervals without increasing the number of inverter switching. The proposed operation and ripple reduction were confirmed in experiments with a 3-kW-class laboratory prototype. Its result agreed to the calculated results, and it was confirmed that there is no increase in circuit losses caused by the application of the proposed method. [ABSTRACT FROM AUTHOR]

Paralleled inverters are not only a suitable approach to increase the power capacity, but also have the capability of common mode voltage (CMV) reduction, or even elimination. The original zero CMV modulation scheme for paralleled inverters suffers from the current jump problem in phase-leg currents. This current jump phenomenon amplifies the peak values of differential-mode circulating current (DMCC) and zero-sequence circulating current (ZSCC), which is adverse for the design of coupled inductor and common-mode inductor. This paper introduces the modified modulation scheme, which can keep volt-seconds balance in whole fundamental period and mitigate the current jump in phase-leg currents. In addition, the reduction effect of the DMCC and ZSCC can be achieved. To verify the analysis, both the simulation and experimental results are presented, which validates the proposed methods and show that they are beneficial for DMCC and ZSCC reduction. [ABSTRACT FROM AUTHOR]

This paper presents a direct model predictive current control (MPC) strategy for quasi-Z-source inverters (qZSIs). A discrete-time model is derived that accurately captures all operating modes of the converter. Both sides of the qZSI are controlled simultaneously based on the inductor current and capacitor voltage on the dc side as well as the output current on the ac side. To improve the closed-loop performance of the converter, a long prediction horizon is implemented. However, the underlying optimization problem may become computationally intractable because of the substantial increase in the computational power demands, which in turn would prevent the implementation of the control strategy in real time. To overcome this and to solve the problem in a computationally efficient manner, a branch-and-bound strategy is used along with a move blocking scheme. Simulation and experimental results are provided to verify the effectiveness of the presented control strategy. [ABSTRACT FROM AUTHOR]

This paper presents a new single-phase switched-coupled-inductor dc–ac inverter featuring higher voltage gain than the existing single-phase qZ-source and semi-Z-source inverters. Similar to the single-phase qZ-source and semi-Z-source inverters, the proposed inverter also has common grounds between the dc input and ac output voltages, which is beneficial especially for photovoltaic inverter systems. The inverter volume and maximum current flowing can be reduced significantly through the coupling of all inductors. A theoretical analysis of the proposed inverter is described and a 280-W experimental prototype is built to verify the performance of the inverter. [ABSTRACT FROM AUTHOR]

This paper proposes a single-phase, single-stage buck–boost inverter for photovoltaic (PV) systems. The presented topology has one common terminal in input and output ports which eliminates common mode leakage current problem in the grid-connected PV applications. Although it uses four switches, its operation is bimodal and only two switches receive high-frequency pulse width modulation signals in each mode. Its principle of operation is described in detail with the help of equivalent circuits. Its dynamic model is presented, based on which a bimodal controller is designed. Experimental results, in stand-alone and grid-connected mode, obtained with a 300-W laboratory prototype are presented to validate its performance. [ABSTRACT FROM AUTHOR]

This paper identifies the characteristics of a current source inverter operating in discontinuous conduction mode, and proposes a new multiobjective pulse-width modulation (PWM) method to mitigate voltage boosting and harmonic distortion effects. The method takes into account load impedance effects. Controls are also developed to enable transition between the multiobjective PWM method and conventional PWM as the current source inverter operates in discontinuous and continuous modes of operation. The concept is verified experimentally on a 3 kW test bed. [ABSTRACT FROM AUTHOR]

Multiterminal converters eliminate using several single-input-single-output converters and simplify their topologies and reduce their cost. In this paper, a new family of multi-input converters based on three switches leg is introduced. Inputs of the proposed converters are similar and they are topologically interchangeable and have boost or buck operation modes. The proposed converter has one output that operates as an inverter. Here, all operating modes of the proposed converters and their effects on each other are investigated, in details. Also, an appropriate switching technique for the converters is given. A detailed comparison between conventional and proposed two-input converters is also presented. A two-input, one-output prototype converter has been implemented to validate the given analyses and to verify the proposed converter's performance. The experimental results are in good agreement with the theoretical and simulated analyses. [ABSTRACT FROM AUTHOR]

A new single-phase \uppi-\texttype 5-level inverter using 3-terminal switch-network (3TSN) is proposed in this paper. The topology is considered as a variant of T-type 3-level structure or dual-buck inverter with coupled inductors. This new inverter is suitable for multilevel power inversion with low dc-bus voltage. The merit of the proposed topology is to apply only four active power switches to achieve 5-level operation. Other benefits include double frequency operation of output inductor and equal division of the current that flows through power switches and filter inductor. Hence, it leads to high efficiency and low harmonics. These characteristics allow improvement of losses distribution and volume reduction of output filter inductor. The operation scenario with sinusoidal pulsewidth modulation (SPWM) is described in details. Meanwhile, the magnetic analysis and design are studied and discussed. Finally, a prototype is built to verify the theoretical analysis and demonstrate the benefits of the proposed topology. [ABSTRACT FROM AUTHOR]

This paper discusses a control method that achieves high weighted efficiency in solar microinverters. A challenge in microinverters is to achieve high efficiency over a range of output powers. To address this challenge, the proposed controller presents two primary benefits that enable such an efficiency profile, a switching frequency that scales with power, and a low peak current that enables efficient magnetic design of the inductor. At high powers, the switching frequency increases to minimize the root-mean-square (rms) current, and at low powers, the switching frequency decreases to minimize the switching loss. Since the peak inductor current is low, the inductor may be designed with fewer turns of wire, or with lower flux density, and is thus highly efficient. The proposed constant peak current switching scheme is implemented by a cycle-by-cycle predictive controller that uses a fast integrator to control the switching period, achieving high bandwidth and stability. This controller senses only the peak inductor current and, therefore, does not require expensive average current sensors. We demonstrate a low-cost inverter prototype with a 300-W solar panel. The prototype uses standard silicon devices and a small inductor of 360 μH to achieve a weighted efficiency of 99.15%. [ABSTRACT FROM PUBLISHER]

The distributed generation (DG) should supply continuous power to the local critical load, even in the condition of utility outage. And many efforts have been made for the three-phase inverter in the DG to transfer between the islanding mode and the grid-tied mode seamlessly. This paper proposes a transfer strategy based on indirect current control for the three-phase inverter in the DG, which is composed mainly of two cascaded feedback loops, i.e., capacitor voltage loop and external grid current loop, in synchronous reference frame. In the grid-tied mode, the grid current is controlled by regulating the capacitor voltage. When islanding happens, the reference of the voltage loop is fixed by the limiter. As the local load is located in parallel with the filter capacitor in the proposed strategy, the load voltage is always controlled by the capacitor voltage loop directly, and the quality of the load voltage can be guaranteed. Besides, the performance of the capacitor voltage loop is further improved by introducing an inner capacitor current loop. Moreover, the steady state and transient state of the system, including the output of the limiter, are comprehensively analyzed, and then the compensators and limiters are designed. Finally, the proposed control strategy is verified by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a multilevel current-source inverter (MCSI) topology is analyzed. The issue of constructing a novel modular single-rating inductor MCSI is explored, taking advantage of the features of field-programmable gate arrays (FPGA) for control and gate signal generation. The proposed topology is built with identical modules where all inductors carry the same amount of current, simplifying the construction and operation of industrial applications with higher efficiency. A new state-machine approach, which is easy to implement in an FPGA, and a proper implementation of the phase-shifted carrier sinusoidal pulse width modulation (PSC-SPWM) allow both current balance in all modules and effective switching-frequency minimization. The performance of the MSCI proposed is simulated with Matlab and is verified by constructing a prototype. [ABSTRACT FROM PUBLISHER]

Renewable energy sources, such as solar energy and fuel cells, are desirable due to their pollution-free properties. In order to utilize the present infrastructure of the utility grid for power transmission and distribution, grid-connected inverters are required for distributed generation systems, which should have high reliability. However, a shoot-through problem, which is a major deterrent to the reliability of the inverters, exists in the conventional bridge-type voltage-source inverters. In order to solve the aforementioned problem, this paper proposes a two-switch dual-buck grid-connected inverter. The freewheeling current flows through the independent diodes instead of the body diodes of the switches, so reverse-recovery loss of the diodes can be reduced. Half of the power devices operate in high frequency; the others switch at grid period with zero-current switching. Moreover, unipolar modulation is used. The operating principle, design guidelines and example, and stability analysis are provided. The proposed inverter can be simplified to a current amplifier with hysteresis current control, so it is globally stable. Simulation and experimental results verify the theoretical analysis and satisfy IEEE Std. 929-2000. A comparison of a full-bridge inverter and the proposed inverter shows that the proposed inverter is more attractive in high-reliability applications. [ABSTRACT FROM AUTHOR]

This paper proposes an indirect current control algorithm for seamless transfer of three-phase utility-interactive voltage source inverters. With the proposed method the inverter is able to provide critical loads with a stable and seamless voltage during the whole transition period including both clearing time and control mode change. The LCL filter design which is suitable for the indirect current control is also proposed to meet the harmonic limits. The proposed control method is validated through simulation and experiment. [ABSTRACT FROM AUTHOR]