Stephen J. Finney

Fuzzy-Logic-Control Approach of a Modified Hill-Climbing Method for Maximum Power Point in Microgrid Standalone Photovoltaic System

A new fuzzy-logic controller for maximum power point tracking of photovoltaic (PV) systems is proposed. PV modeling is discussed. Conventional hill-climbing maximum power-point tracker structures and features are investigated. The new controller improves the hill-climbing search method by fuzzifying the rules of such techniques and eliminates their drawbacks. Fuzzy-logic-based hill climbing offers fast and accurate converging to the maximum operating point during steady-state and varying weather conditions compared to conventional hill climbing. Simulation and experimentation results are provided to demonstrate the validity of the proposed fuzzy-logic-based controller.

A Maximum Power Point Tracking Technique for Partially Shaded Photovoltaic Systems in Microgrids

A modified fuzzy-logic controller for maximum power point (MPP) tracking is proposed to increase photovoltaic (PV) system performance during partially shaded conditions. Instead of perturbing and observing the PV system MPP, the controller scans and stores the maximum power during the perturbing and observing procedures. The controller offers accurate convergence to the global maximum operating point under different partial shadowing conditions. A mathematical model of the PV system under partial shadowing conditions is derived. To validate the proposed modified fuzzy-logic-based controller, simulation and experimentation results are provided.

A review of IGBT models

In this paper, insulated gate bipolar transistor (IGBT) models published in the literature are reviewed, analyzed, compared and classified into different categories according to mathematical type, objectives, complexity, accuracy and speed. Features of the different models are listed. Different modeling criteria are discussed according to various circuit conditions, structures, thermal considerations and accuracies. Some problems and trends in IGBT modeling are discussed.

New Breed of Network Fault-Tolerant Voltage-Source-Converter HVDC Transmission System

This paper proposes a new breed of high-voltage dc (HVDC) transmission systems based on a hybrid multilevel voltage source converter (VSC) with ac-side cascaded H-bridge cells. The proposed HVDC system offers the operational flexibility of VSC-based systems in terms of active and reactive power control, black-start capability, in addition to improved ac fault ride-through capability and the unique feature of current-limiting capability during dc side faults. Additionally, it offers features such as smaller footprint and a larger active and reactive power capability curve than existing VSC-based HVDC systems, including those using modular multilevel converters. To illustrate the feasibility of the proposed HVDC system, this paper assesses its dynamic performance during steady-state and network alterations, including its response to ac and dc side faults.

Passive Filter Design for Three-Phase Inverter Interfacing in Distributed Generation

With the growing use of inverters in distributed generation, the problem of injected harmonics becomes critical. These harmonics require the connection of low pass filters between the inverter and the network. This paper presents a design method for the output LC filter in grid coupled applications in distributed generation systems. The design is according to the harmonics standards that determine the level of current harmonics injected into the grid network. Analytical expressions for the maximum inductor ripple current are derived. The filter capacitor design depends on the allowable level of switching components injected into the grid. Different passive filter damping techniques to suppress resonance affects are investigated and evaluated. Simulated results are included to verify the derived expressions.

Capacitor Balance Issues of the Diode-Clamped Multilevel Inverter Operated in a Quasi Two-State Mode

A new operational mode for diode-clamped multilevel inverters termed quasi two-level operation is proposed. Such operation aims to avoid the imbalance problem of the dc-link capacitors for multilevel inverters with more than three levels and reduces the dc-link capacitance without introducing any significant voltage ripple at the dc-link nodes. The proposed operation can be generalized for any number of levels. The validity of the proposed multilevel inverter operational mode is confirmed by simulations and experiments on a prototype five-level diode-clamped inverter.

Distributed Control of a Fault-Tolerant Modular Multilevel Inverter for Direct-Drive Wind Turbine Grid Interfacing

Modular generator and converter topologies are being pursued for large offshore wind turbines to achieve fault tolerance and high reliability. A centralized controller presents a single critical point of failure which has prevented a truly modular and fault-tolerant system from being obtained. This study analyzes the inverter circuit control requirements during normal operation and grid fault ride-through and proposes a distributed controller design to allow inverter modules to operate independently of each other. All the modules independently estimate the grid voltage magnitude and position, and the modules are synchronized together over a controller area network (CAN) bus. The CAN bus is also used to interleave the pulsewidth modulation switching of the modules and synchronize the analog to digital converter (ADC) sampling. The controller structure and algorithms are tested by laboratory experiments with respect to normal operation, initial synchronization to the grid, module fault tolerance, and grid fault ride-through.

Improved Instantaneous Average Current-Sharing Control Scheme for Parallel-Connected Inverter Considering Line Impedance Impact in Microgrid Networks

A new control scheme for parallel-connected inverters taking into account the effect of line impedance is presented. The system presented here consists of two single-phase inverters connected in parallel. The control technique is based on instantaneous average current-sharing control that requires interconnections among inverters for information sharing. A generalized model of a single-phase parallel-connected inverter system is derived. The model incorporates the detail of the control loops that use a proportional-resonant controller, but not the switching action. The voltage- and current-controller design and parameters selection process are discussed. Adaptive gain scheduling is introduced to the controller to improve the current and power sharing for a condition, where the line impedance is different among the inverters. The simulation results show that the adaptive gain-scheduling approaches introduced improve the performance of conventional controller in terms of current and power sharing between inverters under difference line impedance condition. The experiments validate the proposed system performance.

A Modified Stationary Reference Frame-Based Predictive Current Control With Zero Steady-State Error for LCL Coupled Inverter-Based Distributed Generation Systems

This paper proposes a modified stationary reference frame-based predictive current controller with zero steady-state error for LCL coupled inverter-based distribution generation systems. Analytical expressions for the predictive current control error sources are investigated. The stability margin for the predictive current gain is derived. Online adaptive control for the grid voltage is embedded in the control system to eliminate steady-state real and reactive power errors. The grid voltage estimation expressions for sensorless operation are employed to enhance system robustness and performance. Finally, simulated and practical results verify the derived expressions and the proposed control system performance.

Three-Phase, Three-Wire, Five-Level Cascaded Shunt Active Filter for Power Conditioning, Using Two Different Space Vector Modulation Techniques

The three-phase, three-wire, five-level cascaded Inverter is used as a medium-voltage shunt active power filter. The capacitor voltage-control technique used as a harmonic current extraction method for the two-level inverter is extended to the five-level shunt active power filter, with a technique proposed for balancing capacitor voltages. Predictive current control based on the supply current (not the active filter current) is employed. Two different space vector modulation (SVM) techniques viz., phase-shifted SVM and hybrid SVM, are used for multilevel inverter pulsewidth-modulation generation. The proposed five-level shunt active power filter is validated by simulation and practically for both modulation techniques. The proposed technique results in the same software and hardware requirements for any m-level inverter.