Hooman Dehbonei

Application of voltage- and current-controlled voltage source inverters for distributed generation systems

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

Direct Energy Transfer for High Efficiency Photovoltaic Energy Systems Part I: Concepts and Hypothesis

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.

A new modular hybrid power system

This paper presents a new modular hybrid power system incorporating photovoltaic and small scale wind generators connected to an AC bus. The system is based on voltage source inverters using both current control and voltage control. Preliminary experimental and simulation results are included.

Power electronics for renewable energy sources

Publisher Summary This chapter focuses on solar photovoltaic and wind power. Stand-alone PV energy system requires storage to meet the energy demand during periods of low solar irradiation and nighttime. Blocking diodes in series with PV modules are used to prevent the batteries from being discharged through the PV cells at night when there is no sun available to generate energy. Two of the main factors that have been identified as limiting criteria for the cycle life of batteries in PV power systems are incomplete charging and prolonged operation at a low state-of-charge (SOC). The power output of the PV array is sampled at an every definite sampling period and compared with the previous value. Voltage source inverters are usually used in stand-alone applications. They can be single phase or three phase. There are three switching techniques commonly used: square wave, quasi-square wave, and pulse width modulation. Centrifugal pumps are used for low-head applications especially if they are directly interfaced with the solar panels. Centrifugal pumps are designed for fixed-head applications and the pressure difference generated increases in relation to the speed of pump.

Direct Energy Transfer for High Efficiency Photovoltaic Energy Systems Part II: Experimental Evaluations

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.

Investigation of a Low-Cost Grid-Connected Inverter for Small-Scale Wind Turbines Based on a Constant-Current Source PM Generator

This paper describes a novel low-cost grid-connected inverter for small-scale wind turbines based on a high-inductance PM generator operating in a constant-current output mode. The PM generator is connected to a switched-mode rectifier (SMR) which consists of an uncontrolled rectifier and a switch. The combination of the high-inductance generator and uncontrolled rectifier produces a constant DC current. The switch is used to modulate this current and produces an output current whose fundamental component is a full-wave rectified sinewave and is in-phase with the grid voltage. A line-frequency commutated H-bridge inverter and LC output filter is used to produce a sinusoidal output grid current. The concept is verified using simulations and experimental results

A Grid-Connected Photovoltaic System with Direct Coupled Power Quality Control

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

A review and a proposal for optimal harmonic mitigation in single-phase pulse width modulation

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.

A Control Approach and Design Consideration of PV/Diesel Hybrid Distributed Generation System Using Dual Voltage Source Inverter for Weak Grid

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

A multifunctional power processing unit for an off-grid PV diesel hybrid power system

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.