Shibashis Bhowmik

Novel control strategies for variable-speed doubly fed wind power generation systems

This paper presents a novel control strategy for a brushless doubly fed machine (BDFM) applied to variable-speed wind power generation systems. A 7 kW proof-of-concept laboratory prototype is used to investigate the proposed control algorithm. The paper discusses the use of an adaptive maximum power point tracking (MPPT) strategy to implement an efficiency maximization loop in parallel with the regular maximum tip speed ratio tracker, without the measurement of mechanical quantities. The overall power output of the generation system is increased with a minimal increase in controller cost. A 100 kW case study is included to describe the prospects of the proposed control strategy for a typical wind power generation site on the Oregon coast.

Voltage sag ride-through for adjustable speed drives with active rectifiers

Adjustable speed drives (ASDs) trip due to voltage sags, interfering with production and incurring financial losses. In this paper, a methodology for incorporating voltage sag ride-through in the design of ASDs with active rectifiers is presented. The magnitude of the voltage sag for which ride-through can be provided is determined by the current rating of the active rectifier and load condition of the ASD but a sag of any duration can be compensated for.

Sensorless current control for active rectifiers

A novel model-based sensorless input current controller for three phase active rectifiers is presented. The proposed algorithm is based upon a load conductance rectifier controller, which was previously implemented using current sensors. The paper presents analytical studies, simulation results and discusses a simple implementation using a low-cost integrated microcontroller. Experimental verification utilizes a 50 kVA active input/output IGBT converter. Simulation and experimental results for the proposed controller are compared to that of the sensor based version to validate the efficacy of this novel algorithm.

New simplified control algorithm for synchronous rectifiers

A new simplified control strategy for three-phase AC-DC rectifiers is presented. The proposed control algorithm is simple, robust and inexpensive and can be used for unity and variable power factor operation. The paper describes the proposed control strategy and its implementation with the help of a low-cost Intel 80C196KC microprocessor using fixed switching frequency PWM. The control algorithm is experimentally verified on a 50 kVA active input/output IGBT AC/AC converter. Experimental results and waveform of the input current and voltages are provided to prove the efficacy of the proposed controller.

Design and implementation of distributed control architecture of an AC-stacked PV inverter

A control scheme for a distributed Inverter Molecule™ architecture is analyzed and implemented in this paper. An Inverter Molecule is a building block for a novel distributed inverter architecture suitable for PV/Battery applications which exceeds the performance metrics obtained by Central/String- inverters with or without DC/DC optimizers or by Micro-Inverters. The proposed transformerless architecture utilizes low-voltage semiconductor devices with much higher yields than their high-voltage counterparts. A group of Inverter Molecules operate autonomously and cooperatively to maintain the grid interconnection requirements while providing maximum power control on each molecules PV panel. This paper overviews the state-of the-art control methods implemented mostly on cascaded H-bridge derived topologies and further establishes a distributed control scheme for Inverter Molecule architecture that does not need any high bandwidth communications except a heartbeat signal at line frequency. Experimental results are presented for a lab-scaled prototype.

Adaptive control strategies for variable-speed doubly-fed wind power generation systems

The paper presents an adaptive control strategy for the brushless doubly-fed machine (BDFM) applied to variable speed wind power generation systems. A 7 kW proof-of-concept laboratory prototype is used to investigate the proposed control algorithm. The paper discusses the use of an adaptive maximum power point tracking (MPPT) strategy to implement an efficiency maximization loop in parallel with the regular maximum tip-speed-ratio tracker, without the measurement of mechanical quantities. The overall power output of the generation system is increased with a minimal increase in controller cost. A 100 kW case study is included to describe the prospects of the proposed control strategy for a typical wind power/generation site on the Oregon coast.<<ETX>>

Locking frequency band detection method for grid-tied PV inverter islanding protection

Islanding is an undesired event in which a portion of utility system containing both load and distributed resources remains energized while it is isolated from the remainder of the utility system. In case of islanding, successful detection is required to protect the equipment, and provide safety of the maintenance service workers. This paper shows an implementation of a novel algorithm named Locking Frequency Band Detection (LFBD) method on a distributed PV inverter architecture. Fast detection, easy implementation, no impact on the power quality and zero Non Detection Zone (NDZ) are among many benefits of the proposed algorithm.

On reactive power injection control of distributed grid-tied AC-stacked PV inverter architecture

In this paper, two different Reactive Power Injection (RPI) methods for a fully distributed PV inverter architecture are investigated. RPI methods are parts of ancillary service requirements for modern PV systems to play a more active role in grid regulation and control in future high penetrated PV generation networks. The main objective of this paper is to demonstrate and test RPI methods on a panel-level AC-stacked PV-inverter string which is controlled with distributed control scheme with minimum communication requirements and propose a combined RPI method. Effectiveness and feasibility of distributed control architecture and RPI methods are verified by experimental results during normal operation and voltage disturbance conditions using a lab-scale PV inverter string setup.

A novel comparative robustness index for evaluating the performance of grid-tied PV inverters

Increasing the integration of PV systems requires more reliable and more robust PV inverter architectures. This paper presents a novel index called Smart Inverter Robustness Index (SIRI) to evaluate the robustness of grid-tied PV inverters. Proposed index considering four major operational characteristics such as efficiency, Total Harmonic Distortion (THD), Maximum Power Point Tracking (MPPT) effectiveness and Power Factor (PF) compliance provides a comparative evaluation of PV inverters. Robustness of a single-phase grid-tied PV inverter under varying manufacturing inaccuracies is analyzed by using SIRI index and a boundary for robust operation is determined. Statistical analysis and Random Latin Hypercube Sampling (RLHS) algorithm are used to model the impact of physical variations of passive components on PV inverter operation with minimum sampling points. Effectiveness and feasibility of proposed index is verified by simulation and experimental results of a single-phase grid-tied PV inverter.

Hybrid Current-/Voltage-Mode Control Scheme for Distributed AC-Stacked PV Inverter With Low-Bandwidth Communication Requirements

This paper shows the feasibility of a novel decentralized control scheme for the grid-tied ac-stacked photovoltaic (PV) inverter architecture. The proposed decentralized control scheme with low-bandwidth communications requirements enables a fully distributed PV inverter architecture. Detailed modeling and theoretical analyses will be provided to support the existence of such decentralized control scheme. Simulation and experimental results on a representative laboratory-scale prototype will be presented under symmetrical and asymmetrical conditions as well as 10% grid voltage sag to show the effectiveness of the proposed control scheme in different operating conditions.