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This two-part paper presents a comprehensive comparative study on parallel power processing (PPP) and standard schemes in dc/dc converters for photovoltaic (PV) energy systems. It is demonstrated how PPP can improve direct energy transfer (DET), which results in PV systems operating at higher voltage and efficiency. Discussions of the concepts, hypotheses and computer simulations are presented in Part I. Part II provides the experimental results, which confirm the validity of the analysis and simulations.

This two-part paper presents a comprehensive comparative study on parallel power processing (PPP) and standard schemes in dc/dc converters for photovoltaic (PV) energy systems. It is demonstrated how PPP can improve direct energy transfer (DET), which results in PV systems operating at higher voltage and efficiency. Discussions of the concepts, hypotheses, and computer simulations are presented in Part I. Part II provides the experimental results, which confirm the validity of the analysis and simulations.

The performance, including efficiency, harmonics and dead-time effect of the three major digital sinusoidal pulse width modulations (DSPWMs) presented in Part 1 are investigated in this study using a 2 kVA single-phase full-bridge inverter. Each DSPWM is implemented using a low-cost 8-bit micro-controller and the effect of different switching frequencies on the inverter performance is analysed and the inverter switching, conduction and transformer losses investigated. The experimental results confirm the validity of the mathematical and simulation analysis presented in Part 1. The work shows that the type of DSPWM used for a single-phase full-bridge inverter and the switching frequency selected can have a significant effect on the inverter performance and that switch and transformer losses make up the majority of the inverter losses.

Nowadays, Digital Sinusoidal Pulse Width Modulation (DSPWM) is playing a major role in the generation of pure sinusoidal waveforms using micro-controller based inverters (Kawabata, Miyashita and Yamamoto 1991; Herrmann, Langer and Broeck 1993; Ying-Yu 1995; PICREF-1 1997; Shih-Liang, Meng-Yueh, Jin-Yi, Li-Chia and Ying-Y 1999; The Electrical Engineering Handbook 2000; Koutroulis, Chatzakis, Kalaitzakis and Voulgaris 2001; Skvarenina 2002; Pop, Chindris and Dulf 2004; Zhongyi, Mingzhu and Yan 2005). The types of DSPWM that can be generated depend on the micro-controller hardware resources and are therefore limited, but provide performance benefits not possible with an analogue controller. For instance, digital controllers offer a programmable solution and therefore more flexibility, as advanced algorithms and additional features can be added to the system in software instead of hardware (Monti, Santi, Dougal, and Riva 2003; Brush 2005). Digital controllers are also less sensitive to environmental condition...

Voltage source inverters (VSI) have been widely used in uninterruptible power supplies, unified power flow controllers or unified power quality conditioners, and distributed generation systems (DGS). VSIs are inherently efficient, compact, and economical devices used to control power flow and provide quality supply. VSIs can be classified as voltage-controlled VSIs (VCVSIs) and current-controlled VSIs (CCVSIs), depending on their control mechanism. In this paper, a detailed comparison of VCVSIs and CCVSIs for DGS applications is presented. This paper examines the advantages and limitations of each control technique in a single-phase DGS, without incorporating additional hardware and/or extra complex control techniques. Discussions on the concepts, hypotheses, and computer simulations of different VSIs in the presence of different loads and conditions are presented. The experimental results confirm the validity of the analysis and simulations outlined. The paper provides design recommendations for the use of VCVSIs and CCVSIs in various applications

In this paper a novel space vector modulation method for single-phase inverters is presented. Mathematical analysis, simulation and comparison of conventional sinusoidal pulse width modulation (SPWM) techniques with the proposed space vector modulation for single-phase inverter are included. These modulation techniques are compared, evaluated and classified for different single-phase applications, including deadband effects. The proposed modulation method combines the flexibility of the well-known unipolar PWM scheme for single-phase inverters result in maximum harmonic mitigation. The new technique is suitable for simple digital implementation. Experimental results, obtained by a digital signal processor (DSP) board, are included.

This paper presents an improved parallel processing uninterruptible power supply (UPS) for a strong grid using a bi-directional voltage-controlled voltage source inverter (VCVSI). To maintain the load voltage at the desired value and to control the active power flow between the VCVSI and grid, the amplitude and phase angle of the inverter output voltage (power angle) must be controlled. Selecting the power angle operating range is an important factor which has a direct effect on various parameters, such as the size of a decoupling inductor, grid power factor and the power ratings of VCVSI components. It is shown how the optimum power angles can be chosen and by restricting the operation of this, the power factor can be maintained above 0.9 at different loads and operating conditions. The paper examines the steady state modeling and analysis of a single phase parallel processing UPS while maintaining a high system power factor under different conditions. Experimental and simulation results of a prototyped 1 KVA VCVSI confirms the validity of the proposed method.

This paper presents a comparative analysis of the parallel operation of different switches in a switch mode power converter. In high power applications, multi-switch PWM power conditioners may be preferred despite a higher component count, due to the absence of low frequency filters, reduced switching losses and fault tolerance. The paper demonstrates how current sharing (CSH) and time sharing (TSH) lead to the reduction of switching stress in the parallel operation of switches in any converter. The solutions proposed in this study can be applied on different scales to other power conditioners for renewable energy applications. Discussions of the concepts, hypotheses and computer simulations are verified by 1 kW experimental results

This paper presents a grid-connected photovoltaic (PV) system with direct coupled power quality controller (PQC), which uses an inner current control loop (polarized ramp time (PRT)) and outer feedback control loops to improve grid power quality and maximum power point tracking (MPPT) of PV arrays. To reduce the complexity, cost and number of power conversions, which results in higher efficiency, a single stage CCVSI is used. The system operation has been divided into two modes (sunny and night). In night mode, the current controlled inverter (CCVSI) operates to compensate the reactive power demanded by nonlinear or variation in loads. In sunny mode, the proposed system performs PQC to reduce harmonic current and improve power factor as well as MPPT to supply active power from the PV arrays simultaneously. It is shown that the proposed system improves the system utilization factor (SUF) to 100%, which is generally low for PV systems (20%). Mathematical modelling, computer simulations and experimental results for a 1 kVA CCVSI are presented

This paper presents a study on the effect of different parameters on the DC bus of a single-phase voltage controlled voltage source inverter with conventional rms voltage feedback control and a wave-shaping controller. As rms voltage feedback control does not compensate for variations in the DC bus voltage due to its inherently slow response, the addition of DC bus feedback compensation can provide performance improvement. The paper demonstrates how a DC bus compensation controller improves the performance of a wave-shaping controller, which maintains a sinusoidal load voltage for all loading conditions. Mathematical modelling, computer simulations and experimental results based on a 2 kVA inverter are presented

This paper analyses a wave-shaping controller (WSC) in detail and examines the effect of different parameters, their advantages and limitations on the stability of a single-phase voltage controlled voltage source inverter (VCVSI) without incorporating additional hardware and/or extra complex control techniques. It is shown that the proposed improved WSC can maintain power quality in the presence of non-linear loads and abnormalities. Discussions of the concepts, mathematical modelling, computer simulations and experimental results for a 2 kVA inverter are presented

In this paper, a control and design consideration of PV/ diesel hybrid distributed generation system using dual inverter for weak grid is presented. The dual inverter employs a combination of a voltage controlled voltage source inverter (VCVSI) and a current controlled voltage source inverter (CCVSI), connected in series on the DC side and in parallel on the AC side. This system is able provide an uninterruptible power supply (UPS), load voltage stabilization, unity power factor correction, maximum power point tracking (MPPT), and demand side management (DSM). To verify the proposed system, a comprehensive evaluation with theoretical analysis and experimental results is presented.

This paper describes a novel space vector modulation method for single-phase inverters suitable for an uninterruptible power supply (UPS) and other applications. This modulation method combines the flexibility of the wellknown unipolar PWM for single-phase inverters with the maximum harmonic mitigation. Six switching methods are presented, evaluated and classified for different single-phase applications, including deadband effects. Simulations using Matlab/Simulink confirm the validity of the proposed PWM. Mathematical analysis and comparison of SPWM with the proposed space vector modulation for single-phase inverter are presented.

In this paper a novel multifunctional power processing unit capable of extracting maximum power from solar photovoltaic panels is described. It employs a combination of a voltage controlled voltage source inverter (VCVSI) and a current controlled voltage source inverter (CCVSI), connected in series on the DC side and in parallel on the AC side Chem Nayar et al. (2003), H. Dehbonei et al. (2002), H. Dehbonei (2003). This power processing unit is able to provide an uninterruptible power supply feature, load voltage stabilisation, unity power factor operation, maximum power point tracking, higher efficiency for charging the battery from renewable energy sources and more reactive power support. The experimental results from the prototyped system confirm the validity of the proposed topology.

Digital control techniques are used to control a voltage source inverter in a photovoltaic system. A digital signal processor is implemented in the voltage source inverter which provides rapid maximum power point tracking through the control of the inverter output current. In addition to this, the digital signal processor provides other necessary system functions including calculation of the inverter switching instants used for current regulation and maximum power point tracking and synchronization with the grid. The system is presented as a fully operational unit and the inclusion of simulation results, analysis of the control implementation technique and experimental verification exhibit the system's functionality.

This paper describes an application of the space vector modulation (SPM) technique to a photovoltaic assisted single-phase line-interactive inverter operating as an uninterruptible power supply (UPS). The performance of this inverter is comparable to a unipolar sinusoidal pulse width modulation (SPWM) operating at higher switching frequencies. Preliminary experimental results using a DSP-based system and simulation using Matlab/Simulink confirm the validity of the proposal. This UPS has built in features such as active filtering, demand side management and integration of renewable energy sources such as photovoltaic (PV). In this paper, comparison of SVM and SPWM in single-phase together with simulation and experimental results are also included.