Khalifa Al Hosani

Space-Vector-Based Synchronized Three-Level Discontinuous PWM for Medium-Voltage High-Power VSI

The high-power voltage source inverters are switched at low frequency to reduce the losses in the inverter. The discontinuous pulsewidth-modulation (PWM) sequences reduce the switching frequency to two-thirds compared to the conventional continuous PWM sequences. At low switching frequency, the output will be rich in harmonics, and synchronization is a must to avoid subharmonics. This paper presents four basic types of synchronized discontinuous PWM (DPWM) sequences that ensure synchronization, three-phase symmetry, and half-wave symmetry. The proposed synchronized DPWM sequences are verified through simulation and experiment on a constant- v/f open-loop induction motor drive. The performance of the proposed DPWM algorithms is studied in the entire modulation region, including the overmodulation region, and is compared with that of the conventional synchronized space vector PWM. A different type of DPWM with low common-mode voltage is suggested for low-modulation region and verified experimentally.

A Multitasking Control Algorithm for Grid-Connected Inverters in Distributed Generation Applications Using Adaptive Noise Cancellation Filters

This paper proposes a multitasking control algorithm for grid-connected inverters (GCIs) in distributed generation (DG) applications. A single-phase H-bridge voltage source inverter is used as a power electronic interface between the DG system and the grid. The proposed control algorithm operates the GCI in current control mode to achieve desired active power injection to the grid. In addition to active power injection, the proposed control algorithm has current harmonics mitigation and reactive power compensation capabilities for power quality enhancement. The control algorithm utilizes only the remaining capacity of the GCI for power quality improvement. The proposed control algorithm employs a current decomposition structure based on multiple adaptive noise cancellation (ANC) filters for extraction of harmonic and reactive currents of the local loads. The extracted harmonics are used in estimating compensating currents to be injected by the GCI. A single-phase phase-locked loop (PLL) using ANC filters has been developed to synchronize the GCI at fundamental frequency, which makes the proposed control algorithm adaptive to grid frequency fluctuations and immune to grid voltage distortions. The effectiveness of the proposed control is illustrated through computer simulation and experimental results. The influence of PLL dynamics on GCI performance has also been studied using results.

Interpolating sliding mode observer for a ball and beam system

ABSTRACT A principle of interpolating sliding mode observer is introduced in this paper. The observer incorporates multiple linear observers through interpolation of multiple estimates, which is treated as a type of adaptation. The principle is then applied to the ball and beam system for observation of the slope of the beam from the measurement of the ball position. The linearised model of the ball and beam system using multiple linearisation points is developed. The observer dynamics implemented in Matlab/Simulink Real Time Workshop environment. Experiments conducted on the ball and beam experimental setup demonstrate excellent performance of the designed novel interpolating (adaptive) observer.

Design of a gain matrix for a sliding mode observer for an artificial gas lift system

An Artificial gas lift system is an existing technology in the oil sector; which utilizes the fact that a pressure differential exists in the reservoirs tubing leading to enhanced oil recovery from the reservoir. Studies were conducted to control this process as it improves the stability and performance of gas lift. The current industrial practice depends on flow measurement as a process variable, yet, it does not depend on the measurements which would be obtained several kilometers below the ground that are technically difficult to approach due to several limitations such as huge pressures. Proper knowledge of the states would leads to a better controller design for this system. In this paper, a methodology towards the design of a sliding mode observer is investigated. The purpose of the observer is to acquire the states of a nonlinear system representing the physical system of a gas lift process in oil wells. The proposed design of an observer is based only on measurements taken above the surface.

Adaptive notch filter based multipurpose control scheme for grid-interfaced three-phase four-wire DG inverter

The power electronic converter and its control system form an integral part of distributed generation (DG) systems interfacing renewable energy sources to the utility network. This paper proposes an adaptive notch filter-based multipurpose control scheme for grid interfacing DG inverter under corrupted grid conditions. The proposed control scheme uses a frequency adaptive sequence components extractor which is capable of extracting instantaneous symmetrical components and harmonic components of three-phase signals. The DG inverter in this study consists of three single-phase voltage source inverters with common dc bus and coupled to utility grid via three single-phase transformers. The DG sources are represented as constant dc voltage source on its dc side. The proposed control scheme enables the DG inverter to perform multiple tasks such as: reference power injection to grid, load reactive power support and compensation of harmonic, unbalanced and neutral currents. The effectiveness of the proposed control scheme is evaluated through MATLAB/Simulink simulations and experimentally verified using a hardware-in-the-loop (HIL)-based system.

Mitigation of harmonics in drilling rigs using shunt active power filters

Harmonics and low power factor are major concerns in modern industry. Even though several solutions are available, mitigating these problems in already established heavy industries is still a challenge. On-shore oil rigs are one such case where the problem becomes unique because of the extreme operating conditions and limited space. This paper presents a case study of mitigating the harmonic problem in on-shore oil rigs operating in deserts. It is proposed to use multiple shunt active power filters. One or more shunt active filters may go out of operation but the drives continue to run without filters resulting in distortion of voltage. The active filters which are in operations should work under distorted voltage conditions. Operation of shunt active power filter under distorted voltages is demonstrated both through simulation and experiments.

Seamless transition scheme between grid-tied and stand-alone modes of distributed generation inverters

In this paper, an enhanced control strategy of the smooth transition between the grid-tied and stand-alone operation modes of the distributed generation (DG) inverter is proposed. In the grid-connected mode, the DG inverter controls active and reactive powers flowing into the grid by regulating grid currents using typical proportional integral plus resonant (PI+R) controllers, while direct voltage controllers utilizing a feedback linearization (FBLN) technique are applied to control the load voltages in the stand-alone mode. Applying the FBLN control gives a better performance than those of using the linear control methods for the DG inverter, which possesses a nonlinear relation between the inverter terminal and load voltages. Furthermore, initiating the value of integral terms in the PI+R regulators and FBLN as null at the instances of the operation mode changes results in a smooth transition between the current and voltage controllers for the grid-tied and stand-alone modes, respectively. The PSIM simulation results are shown to verify the feasibility of the proposed control strategy.

Switching Frequency Optimization of DC/AC Inverters Using Sliding Mode

It is common that a DC/AC converter for three-phase load is designed for controlling two variables (for example, speed and flux of AC motor). An additional degree of freedom can be utilized to minimize the switching frequency, which depends on the voltage of the load neutral point. In this chapter, a methodology of switching frequency minimization is proposed in the framework of the modified hysteresis control. The load neutral point voltage is selected as the third variable to be controlled. First, the tracking system algorithm is developed and then optimization with the switching frequency as a criterion is performed by a proper choice of the reference input for the neutral point voltage. The system accuracy is determined by the width of hysteresis loop and is the same for any switching frequency.

A novel DC voltage control for a cascade H-bridge multilevel STATCOM

Cascade H-bridge multilevel inverter is a best candidate for static VAr compensation in medium and high voltage applications. The topology consists of several capacitors to provide dc link voltage support for H-bridge inverters. Regulation of the dc link voltages at the required levels is a major research challenge in VAr compensated inverters. This paper presents a novel and simple control strategy for a five level cascade H-bridge multilevel STATCOM. The scheme realizes the required objectives with fewer PI controllers and produces accurate results. Rigorous simulation study is carried out in MATLAB SIMULINK to validate the control scheme and results are presented.

Real-time simulation based performance analysis of active filters for oil drilling rigs

In this paper performance analysis of active power filter (APF) is studied for oil drilling rigs through real-time simulation. A typical oil drilling rig consisting of adjustable speed drives powered by diesel engine generators is modelled and simulated. Conventional filters are not suitable for autonomous power systems as the system is not stiff bus system. APF are better suited for this application. Performance of filters can be tuned and assessed accurately if they are tested under actual operating conditions of the rig, particularly weak bus and dynamic loading characteristics. A real-time test procedure to experimentally test the performance of APF connected to a diesel generator and drive system is developed. Then the drives are loaded as per the data collected from rig over a drilling cycle and harmonic filtering performance of APF is studied. In this method, dynamic models of diesel engine, synchronous generator, AC/DC converter and DC drive are solved on a digital signal processor in real time and the solution is fed to current controller controlling a voltage source inverter to emulate the oil rig system. A physical shunt APF is then connected to the setup and its dynamic performance is evaluated while load is changing. Dynamic models of for all the components are presented and simplifications are suggested so as to reduce the computational need of processor. These models are validated through computer simulations by comparing with detailed models.