http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

Photovoltaic (PV) energy has grown at an average annual rate of 60% in the last five years, surpassing one third of the cumulative wind energy installed capacity, and is quickly becoming an important part of the energy mix in some regions and power systems. This has been driven by a reduction in the cost of PV modules. This growth has also triggered the evolution of classic PV power converters from conventional singlephase grid-tied inverters to more complex topologies to increase efficiency, power extraction from the modules, and reliability without impacting the cost. This article presents an overview of the existing PV energy conversion systems, addressing the system configuration of different PV plants and the PV converter topologies that have found practical applications for grid-connected systems. In addition, the recent research and emerging PV converter technology are discussed, highlighting their possible advantages compared with the present technology. Solar PV energy conversion systems have had a huge growth from an accumulative total power equal to approximately 1.2 GW in 1992 to 136 GW in 2013 (36 GW during 2013) [1]. This phenomenon has been possible because of several factors all working together to push the PV energy to cope with one important position today (and potentially a fundamental position in the near future). Among these factors are the cost reduction and increase in efficiency of the PV modules, the search for alternative clean energy sources (not based on fossil fuels), increased environmental awareness, and favorable political regulations from local governments (establishing feed-in tariffs designed to accelerate investment in renewable energy technologies). It has become usual to see PV systems installed on the roofs of houses or PV farms next to the roads in the countryside. Grid-connected PV systems account for more than 99% of the PV installed capacity compared to

An Overview of Recent Research and Emerging PV Converter Technology

Photovoltaic (PV) energy has grown at an average annual rate of 60% in the last five years, surpassing one third of the cumulative wind energy installed capacity, and is quickly becoming an important part of the energy mix in some regions and power systems. This has been driven by a reduction in the cost of PV modules. This growth has also triggered the evolution of classic PV power converters from conventional single-phase grid-tied inverters to more complex topologies to increase efficiency, power extraction from the modules, and reliability without impacting the cost. This article presents an overview of the existing PV energy conversion systems, addressing the system configuration of different PV plants and the PV converter topologies that have found practical applications for grid-connected systems. In addition, the recent research and emerging PV converter technology are discussed, highlighting their possible advantages compared with the present technology.

Grid-Connected Photovoltaic Systems: An Overview of Recent Research and Emerging PV Converter Technology

Impedance networks cover the entire of electric power conversion from dc (converter, rectifier), ac (inverter), to phase and frequency conversion (ac-ac) in a wide range of applications. Various converter topologies have been reported in the literature to overcome the limitations and problems of the traditional voltage source, current source as well as various classical buck-boost, unidirectional, and bidirectional converter topologies. Proper implementation of the impedance-source network with appropriate switching configurations and topologies reduces the number of power conversion stages in the system power chain, which may improve the reliability and performance of the power system. The first part of this paper provides a comprehensive review of the various impedance-source-networks-based power converters and discusses the main topologies from an application point of view. This review paper is the first of its kind with the aim of providing a “one-stop” information source and a selection guide on impedance-source networks for power conversion for researchers, designers, and application engineers. A comprehensive review of various modeling, control, and modulation techniques for the impedance-source converters/inverters will be presented in Part II.

Impedance-Source Networks for Electric Power Conversion Part I: A Topological Review

The voltage-fed Z-source inverter/quasi-Z-source inverter (qZSI) has been presented suitable for photovoltaic (PV) applications mainly because of its single-stage buck and boost capability and improved reliability. This paper further addresses detailed modeling and control issues of the qZSI used for distributed generation (DG), such as PV or fuel cell power conditioning. The dynamical characteristics of the qZSI network are first investigated by small-signal analysis. Based on the dynamic model, stand-alone operation and grid-connected operation with closed-loop control methods are carried out, which are the two necessary operation modes of DG in distributed power grids. Due to the mutual limitation between the modulation index and shoot-through duty ratio of qZSI, constant capacitor voltage control method is proposed in a two-stage control manner. Minimum switching stress on devices can be achieved by choosing a proper capacitor voltage reference. Experimental results are presented for validation of the theoretical analysis and controller design.

Modeling and Control of Quasi-Z-Source Inverter for Distributed Generation Applications

This paper presents a quasi-Z-source inverter (qZSI) that is a new topology derived from the traditional Z-source inverter (ZSI). The qZSI inherits all the advantages of the ZSI, which can realize buck/boost, inversion and power conditioning in a single stage with improved reliability. In addition, the proposed qZSI has the unique advantages of lower component ratings and constant dc current from the source. All of the boost control methods that have been developed for the ZSI can be used by the qZSI. The qZSI features a wide range of voltage gain which is suitable for applications in photovoltaic (PV) systems, due to the fact that the PV cell's output varies widely with temperature and solar irradiation. Theoretical analysis of voltage boost, control methods and a system design guide for the qZSI in PV systems are investigated in this paper. A prototype has been built in the laboratory. Both simulations and experiments are presented to verify the proposed concept and theoretical analysis.

Quasi-Z-Source Inverter for Photovoltaic Power Generation Systems

This paper presents a novel grid-connected boost-half-bridge photovoltaic (PV) microinverter system and its control implementations. In order to achieve low cost, easy control, high efficiency, and high reliability, a boost-half-bridge dc-dc converter using minimal devices is introduced to interface the low-voltage PV module. A full-bridge pulsewidth-modulated inverter is cascaded and injects synchronized sinusoidal current to the grid. Moreover, a plug-in repetitive current controller based on a fourth-order linear-phase IIR filter is proposed to regulate the grid current. High power factor and very low total harmonic distortions are guaranteed under both heavy load and light load conditions. Dynamic stiffness is achieved when load or solar irradiance is changing rapidly. In addition, the dynamic behavior of the boost-half-bridge dc-dc converter is analyzed; a customized maximum power point tracking (MPPT) method, which generates a ramp-changed PV voltage reference is developed accordingly. Variable step size is adopted such that fast tracking speed and high MPPT efficiency are both obtained. A 210 W prototype was fabricated and tested. Simulation and experimental results are provided to verify the validity and performance of the circuit operations, current control, and MPPT algorithm.

Grid-Connected Boost-Half-Bridge Photovoltaic Microinverter System Using Repetitive Current Control and Maximum Power Point Tracking

This paper presents a novel synchronous-frame repetitive controller for three-phase UPS inverters. Distinguished from conventional repetitive control techniques, the proposed synchronous-frame approach minimizes the repetitive control time delay to one-sixth of the fundamental period such that the dynamic response is significantly improved. In order to overcome the harmonic distortions under severe load conditions (e.g., unbalanced and nonlinear), in this paper, three synchronous rotating frames are deliberately selected, in each of which the repetitive controller is incorporated. Resultantly, the (6n ±1)th harmonics as well as the triplen harmonics are compensated. Moreover, a high-performance fourth-order linear phase infinite-impulse-response filter is applied to further enhance the accuracy of steady-state tracking. The proposed controller is programmed on the 16-bit fixed-point digital signal processor (TI TMS320LF2407) and eliminates high-resolution current sensors for cost effectiveness. Simulations and experimental tests have been carried out based on an 18-kW three-phase UPS system. Low total harmonic distortion (<;0025;) has been achieved under heavily distorted nonlinear load and unbalanced load. Fast dynamic response has been demonstrated during step load transients.

Low-THD, Fast-Transient, and Cost-Effective Synchronous-Frame Repetitive Controller for Three-Phase UPS Inverters

In this paper the Quasi-Z-Source Inverter (QZSI) with Energy Storage for Photovoltaic Power Generation Systems is presented. The energy storage device was integrated to QZSI topology with no need for an extra charging circuit. This upgraded topology acquires the operating characteristics from the traditional QZSI, plus the capability of operating under very low PV power conditions. Its main operating points are classified into two modes, the low PV power mode, where the battery is discharged and the high power mode, where the battery is charge up. An extended input power operating range is achieved since the lack of Photovoltaic power can be compensated by the battery. Quasi-Z-Source inverters are very suitable for Photovoltaic power generation systems and this upgrade makes them even more suitable for this type of applications. To obtain the experimental data, a prototype was built and used to demonstrate that the Quasi-Z-Source inverter is capable of managing the State of Charge of a battery and the AC output voltage in each operating mode.

Yuan Li

Papers

Modeling and Control of Quasi-Z-Source Inverter for Distributed Generation Applications

Quasi-Z-Source Inverter for Photovoltaic Power Generation Systems

Grid-Connected Boost-Half-Bridge Photovoltaic Microinverter System Using Repetitive Current Control and Maximum Power Point Tracking

Low-THD, Fast-Transient, and Cost-Effective Synchronous-Frame Repetitive Controller for Three-Phase UPS Inverters

Quasi-Z-Source inverter with energy storage for Photovoltaic power generation systems