Showing papers in "International Journal of Power Electronics in 2012"

A Review of Power Electronics Based Microgrids

Abstract: The increased penetration of Distributed Energy Resources (DER) is challenging the entire architecture of conventional electrical power system. Microgrid paradigm, featuring higher flexibility and reliability, becomes an attractive candidate for the future power grid. In this paper, an overview of microgrid configurations is given. Then, possible structure options and control methods of DER units are presented, which is followed by the descriptions of system controls and power management strategies for AC microgrids. Finally, future trends of microgrids are discussed pointing out how this concept can be a key to achieve a more intelligent and flexible power system.

A new life estimation method for lithium-ion batteries in plug-in hybrid electric vehicles applications

Abstract: This paper presents a new approach to life estimation for lithium-ion batteries used in plug-in hybrid electric vehicles (PHEVs) applications. A new framework for battery life estimation is developed which investigates the effects of two primary factors of battery life reduction in PHEVs applications, namely, depth of discharge (DOD) and temperature (Tbatt), under typical driving conditions, driving habits, and average commute time of typical user over a year. This framework, whose development is built upon a weighted ampere-hour throughput model of the battery, is based on the novel concept of severity factor map which captures and quantifies the battery damage caused by different operating conditions. The proposed methodology can be a suitable tool to estimate battery life in terms of miles/year on-board of the vehicle.

Development of a generic fuel cell model: application to a fuel cell vehicle simulation

Abstract: In this paper, a novel approach to fuel cell modelling is proposed. The model is obtained from manufacturer datasheets and is able to represent the behaviour of any hydrogen fuel cells. The simulation results are as expected with an error in the range of ±1%, provided a controlled stack internal humidity. The procedure to extract data from fuel cells datasheet is described along with the method to estimate cell’s parameters. The model is integrated in SimPowerSystems (SPS) and used in the simulation of a fuel cell vehicle. The vehicle is modelled with the same characteristics as the Honda FCX-Clarity. The performance obtained from the vehicle model is close to reality in terms of fuel consumption, maximum speed and acceleration.

Comparison and evaluation of different DC/DC topologies for plug-in hybrid electric vehicle chargers

Abstract: The battery charging system is a critical part of a plug-in hybrid electric vehicle (PHEV). The efficiency, charging speed, and cost of such chargers are crucial to the commercialisation of PHEVs. In this paper, the advantages and drawbacks of four potential PHEV charger topologies were compared based on their operations through simulation and experiments. Their electrical stress, efficiency, cost, and the feasibility were discussed in detail. It was concluded that a full-bridge based PHEV charger is the most favourable choice among the four available topologies due to its power capability, soft switching capability, low electric stress, high efficiency, but slightly elevated cost.

The hybrid RFNN control for a PMSM drive system using rotor flux estimator

Abstract: The hybrid recurrent fuzzy neural network (HRFNN) control permanent magnet synchronous motor (PMSM) drive system using rotor flux estimator is developed to control electric motorcycle in this paper. First, the dynamic models of a PMSM drive system and electric motorcycle are built through experimental tests and parameter measurements. Then, a HRFNN control system using rotor flux estimator is developed to control PMSM drive system in order to drive electric motorcycle. The rotor flux estimator consists of the estimation algorithm of rotor flux position and speed based on the back electromagnetic force (EMF). Moreover, the HRFNN controller consists of the supervisor control, RFNN and variable structure control (VSC) is applied to PMSM drive system using rotor flux estimator. The parameters of RFNN are trained to control command current in order to achieve different output torque of various speeds. The electric motorcycle is operated to provide constant disturbance torque. Finally, the effectiveness of the ...

Power quality disturbances classification using support vector machines with optimised time-frequency kernels

Abstract: Detection and classification of power system disturbances is necessary to ensure good power supply. The paper presents a method for accurate classification of power quality signals using support vector machines (SVM) with optimised time-frequency kernels. The Cohen’s class of time-frequency-transformation has been chosen as the kernel for the SVM. A stochastic genetic algorithm (StGA) has been used to optimise the parameters of the kernels. Comparative simulation results demonstrate a significant improvement in the classification accuracy with such optimised kernels.

Practical insight on scope of sliding mode control in arc welding process

Abstract: Unlike most control systems, a single arc welding controller performs different welding functions using dynamics of different arc characteristics meeting complex output characteristics – that includes apart from joint characteristics are arc light intensity, fumes and particulate matters, etc. Moreover, unavailability of feedback in major loop for control of heat input to joint divides the parameters of the complete process into external and intrinsic ones. Intrinsic parameters define arc characteristics. Dynamic non-linear intrinsic parameters cannot be made insensitive even through sliding mode control. Representative dynamical systems for starting, stopping and normal welding are also different. This article explores the scope of practical implementation of SMC to complete range of arc welding process. In constant current (CC) manual arc welding process, arc is extinguished by increasing the arc length much beyond the controller can sustain. In that process, it produces large unusable heat causing discomfort to the welder and co-workers. The present article, as well, discusses implementation mechanism of SMC to optimise arc light intensity and reduce heat generation in arc column in order to convert mechanism of manual arc extinction of SMAW welder friendly. Chattering issue is not important.

A novel invariable carrier frequency multi-level inverter PWM for balancing switching transitions and better distribution of harmonic power

Abstract: The number of switching per modulation cycle at each level in a multi-level inverter depends on the carrier frequency and the duration that the reference waveform dwells within the level. The variable carrier frequency band (VFCB) approach creates as many clusters as the number of carrier frequencies and consequent deterioration of the harmonic spectrum. Therefore, a new pulse width modulation (PWM) strategy, with the view to ensure that the power devices at all the levels are switched equal number of times, is proposed in this paper. It is designed such that the frequency of the carrier waves is allowed to remain constant for the chosen application while maintaining the number of switching for all devices is same. The MATLAB-based simulation response and its experimental validation are included to highlight the fact that there is a significant enhancement in harmonic power distribution besides contributing to reduce the switching losses and improve the efficiency.

SiC Mosfets with Schottky power diodes help optimise the design of multi-functional arc welding equipment in popular power range

Abstract: Logistics, welder’s comfort, productivity and quality need of weld joint and jobs in hand at site etc., together decide the required arc (constant current (CC) or constant voltage (CV) or their combination) characteristics. Multi-functional arc welding equipment meets such needs. High across the load efficiency, fast settling time of output variables and light and compactness are major pre-requisites of arc welding equipment. Some of them are achieved if switching frequency of inverter is kept high. Constraint of efficiency at high switching frequency is, generally, overcome by adopting proper soft switching topology. This paper suggests that better design is possible for narrow power range arc welding equipment (3–20 kW) using traditional hard-switched inverter with just optimisation in input materials. Reduced component count and reduced interconnections between sub-assemblies in hard-switched full-bridge inverter generate superior design for manufacturability issues.

Buck-boost converter controller design using queen-bee assisted GA

Abstract: We propose a new method of controller design for a buck-boost type dc-dc converter in this paper. An optimisation model for the controller design is developed and solution is sought through a novel optimisation algorithm named as queen-bee assisted genetic algorithm (GA) which combines standard GA with evolution of queen bee in a hive. Computed and measured results suggest that the new algorithm converges to best designs on a limited number of iterations.

A power-flow control method for hybrid active front-end converters

Abstract: The hybrid active front-end converter, which is composed of a capacitor and a voltage source converter in series connection, has been presented recently. Compared with grid-connected converter, the hybrid converter could be operated with reduced dc voltage as well as small-sized passive filters due to series-connected capacitor. This paper presents a power flow control method for a hybrid active front-end converter. Real power of the converter is controlled by the output voltage vector perpendicular to the grid voltage, whereas reactive power of the converter is determined by the output voltage vector parallel to the grid voltage. By dynamically adjusting voltage vector, power conversion between low-voltage dc side, such as PVs or batteries, and high-voltage grid side could be accomplished with no low-frequency transformer required. In addition, a harmonic resistance is emulated in the proposed method to avoid inrush current flowing into the converter due to unintentional voltage spike coming from the power system. Operation principles are explained in detail, followed by both computer simulations and experimental results validating effectiveness.

Rotor flux-based MRAS for three level inverter fed induction motor drive using fuzzy logic controller

Abstract: This paper proposes a sensorless vector control scheme for induction motor to operate at low speed. Low speed operation of rotor flux model reference adaptive system (MRAS) have the problems of dc drift and dead time due to pure integrator present in the reference model. A control scheme is proposed with non-linear integrator in the reference model of the rotor flux-based MRAS speed observer to obtain the compensating voltage. Adaptive model tuning is done with fuzzy logic controller (FLC) in place of PI controller. Multilevel inverter with space vector pulse width modulation (SVPWM) technique is used to improve the performance of drive. A SIMULINK model is developed to compare performance of conventional rotor flux MRAS and proposed control scheme with PI controller and FLC.

Modelling, design and control of a SEPIC power factor corrector for single-phase rectifiers: experimental validation

Abstract: In this paper, a new general case switching-function-based model is proposed for a DC-to-DC single ended primary inductance converter (SEPIC). Compared to conventional buck or boost converters, this topology allows a low current ripple at the input for a relatively low level of the DC-bus voltage. The converter is used as a power factor correction (PFC) circuit for a single-phase rectifier and, based on the obtained model, steady-state analysis is performed and new design criteria were established for a proper selection of the inductors and capacitors. In order to verify the performance of the converter in PFC applications, a simple hysteretic-based feedback control is implemented and verified through simulations. For validation purpose, experiments are carried out on a 1kW laboratory prototype of the converter. The system performance is evaluated in terms of source current total harmonic distortion (THD), voltage regulation, robustness and dynamic behaviour.

FPGA-based solution for real-time tracking of time-varying harmonics and power disturbances

Abstract: A field programmable gate array (FPGA)-based implementation scheme of the universal amplitude demodulation is proposed for real-time tracking of time-varying harmonics and power disturbances in power systems. The scheme implements the required lowpass filtering with canonical signed digit (CSD) coded infinite impulse response (IIR) filters and uses the coordinate rotation digital computer (CORDIC) algorithm for the amplitude reconstruction. The proposed scheme has low complexity and is suitable for practical implementations. An FPGA-based circuit had been built to validate the proposed scheme. The circuit can track harmonics and power disturbances in about one cycle. Experimental results show the real-time performance of the scheme.

Design and control of an LCL series parallel resonant converters using bacterial foraging optimisation

Abstract: The paper introduces a design technique for robust PID controllers for inductance capacitance inductance-T network (LCL-T) series parallel resonant converts. AC analysis and stability analysis for LCL-T series parallel converter are premeditated. The converter controllers' designs are based on bacterial foraging optimisation (BFO). A BFO algorithm is utilised in order to obtain the controller parameters and guarantee superior step response performance criterion. Simulation results of the designed controllers are compared with that of conventional controllers whose parameters are tuned by using will known Ziegler-Nichols technique. Results imply the perfection of the proposed technique over the conventional method. Experimental measurements of system performance validate the proposed technique and emphasise its feasibility.

Control and small-signal analysis of battery and supercapacitor hybrid energy storage systems

Abstract: This paper is devoted to control strategies for an active battery and supercapacitor hybrid energy storage system using the master-slave control scheme, where the charging and discharging currents of the supercapacitor are dependent on that of battery and the current sharing ratio depends upon the load conditions. A small-signal model is proposed, which considers the variations in the currents of individual energy storage devices and the DC bus voltage as state variables, the variations in the power converter duty cycles as control variables, the variations in the voltages of battery and supercapacitor and the load current as external disturbances. This paper also studies the effects of the variations in the controller and filter parameters on system performance using frequency-domain analysis. Simulation results verify the proposed control strategies and the effects on the final states of the energy storage devices and also validate frequency-domain analysis.

Improving load regulation in current mode control through inductor current filtering

Abstract: Current mode control (CMC) though offers improved line regulation, phase margin and high bandwidth suffers from high output impedance. Although load regulation can be improved by incorporating an integral gain, it reduces the phase margin and increases the overshoot. The objective of this paper is to achieve improved output impedance without using an integral controller. Incorporating a high pass filter in series with the current sensor in CMC, the closed loop DC gain of a CCM buck converter is shown to be almost independent of the load resistance, thus improving load regulation using a proportional controller only. Improved features of CMC are also retained. Following VMC modeling approach, we develop a method to obtain the small signal model of the proposed scheme, and extended to CMC with an accurate low frequency characterisation. The proposed scheme is implemented on a buck converter, and the theoretical results are validated by experiments.

Low distortion three-phase sine PWM using a general purpose micro-controller

Abstract: Three-phase balanced sine-PWM pulses are required for the purpose of generation of sinusoidal output voltage and/or currents from inverters, used for UPS/motor-control applications. Such pulse-generation is possible using micro-controllers/DSPs with PWM output pins. This paper discusses a simple algorithm to generate low distortion balanced three-phase sine-PWM pulses from a general purpose micro-controller, without using PWM pins. It is shown via simulation and experimentation that such an algorithm is capable of achieving current-distortions well below 5%. An inverter, controlled by such an algorithm, is also tested for three-phase AC induction motor control application in V/f mode, using a feed-forward control-methodology. A performance-comparison is made between a general-purpose micro-controller (using the above strategy) and a micro-controller (used for motor-control applications) for the above application-area.

Minimisation of VA loading of UPQC in three-phase four-wire distribution system

Abstract: Unified power quality conditioner (UPQC) is a combination of series and shunt active power filters with a common DC link. This device is used to enhance power quality by injecting required amount of Volt-Ampere (VA) into the system. In view of the cost effectiveness, it is desirable to have VA loading of UPQC without compromising the compensation capability. This paper presents a methodology to minimise VA loading of UPQC, considering the effects of unbalance in load and distortions in both load current and source voltage during the compensation of voltage sag with phase jumps in a distribution system. The minimum VA loading of the UPQC is achieved by injecting a series voltage at an optimum angle using series active power filter with respect to the voltage sag. In this paper, a particle swarm optimisation (PSO)-based technique is used to minimise the VA loading of UPQC. The proposed method has been validated through detailed simulation studies and the results are presented.

Two-level 24-pulse double-way voltage source converter-based STATCOM

Abstract: This paper presents a two-level 24-pulse double-way voltage source converters (VSCs) configuration for the static synchronous compensator (STATCOM) It uses four identical six-pulse double-way VSC sets to form a 24-pulse VSC configuration of STATCOM Each six-pulse double-way VSC set consists of two sets of two-level three-phase six-pulse gate turn off thyristor (GTO) VSCs The phase angle difference between the fundamental ac voltages of two three-phase six-pulse GTO VSCs is varied for the reactive power control The STATCOM is operated at a constant dc link voltage which results in better utilisation of the converter compared to the operation of the STATCOM with variable dc link voltage The STATCOM is designed for ±100 MVAR and connected to a 33 kV/60 Hz ac system to evaluate its performance by varying the reference reactive power The model of proposed STATCOM is developed using MATLAB along with Simulink, sim-power system (SPS) toolboxes and simulation results demonstrate its satisfactory steady state and dynamic performances

Artificial neural network-based harmonics extraction algorithm for shunt active power filter control

Abstract: This paper presents a harmonics extraction algorithm using artificial neural network methods. The neural network algorithm was used due to the simpler calculation process compared with conventional method such as fast Fourier transform (FFT). Two types of neural network, i.e., multi-layer perceptron (MLP) and radial basis function (RBF) were employed to extract harmonics current component from its distorted wave current. Further, the extracted harmonics current was used as reference current for shunt active power filter (APF) control. This paper compared the performance of MLP and RBF for harmonics extraction. The advantages of RBF are simpler shape of the network and faster learning speed. Unfortunately, the RBF need to be trained recursively for various harmonics component. MLP can be used to extract various harmonics component in specific data range but need large number of data training hence slower training process.

Selective harmonic frequency-based non-linear load compensation using hybrid active power filter

Abstract: This paper presents a hybrid active power filter for harmonics and reactive current compensation while reducing the rating of active power filter. The proposed topology of hybrid active power filter uses the combination of active power filter and a new self-tuned passive filter. The control technique of the proposed system separates the compensation frequency band for active and passive filters. The self-tuned passive filters are tuned to suppress two lower most harmonic components, i.e., fifth and seventh and the active power filter compensates the remaining higher order harmonics. The active power filter control is based on reference current estimation in a-b-c frame. An analytical study of thyristor controlled reactor (TCR)-based self-tuned passive filters is presented to keep the passive filters in the resonant state during deviation of their parameters under the influence of external factors like temperature rise, aging, etc. The firing angle of the TCR is derived as a function of the deviation of passive filter parameters. The proposed hybrid active power filter is also capable to damp out the harmonics propagation due to passive filter resonance. The proposed algorithm is simulated in MATLAB/Simulink environment under various operation conditions to show the effectiveness of the controller.

Robust vector control strategy for variable speed wind turbines

Abstract: The efficiency of the wind power conversions systems can be greatly improved using an appropriate control algorithm. In this work, a robust control for variable speed wind power generation that incorporates a doubly feed induction generator is described. The electrical systems incorporate a wound rotor induction machine with back-to-back three phase power converter bridges between its rotor and the grid. In the presented design, it is applied the so called vector control theory. The proposed control scheme uses stator flux-oriented vector control for the rotor-side converter bridge control and grid voltage vector control for the grid-side converter bridge control. The proposed robust control law is based on a sliding mode control theory that, as it is well-known, presents a good performance under system uncertainties. The stability analysis of the proposed controller under disturbances and parameter uncertainties is provided using the Lyapunov stability theory. Finally, simulated results show, on the one hand, that the proposed controller provides high-performance dynamic characteristics, and on the other hand, that this scheme is robust with respect to the uncertainties that usually appear in the real systems.

Modified stator flux estimation-based direct torque controlled induction motor drive with constant switching frequency operation

Abstract: A space vector pulse width modulated (SV-PWM) direct torque controlled (DTC) induction motor drive, having reduced torque ripple even at low operating speeds and maintaining constant switching frequency has been studied and implemented with a modified stator flux estimation scheme. It utilises a compensator for the phase and magnitude error introduced by low pass filter, which is being used to avoid DC drift, problem of saturation and to enhance the transient response of the machine. Detailed simulation studies are carried out to verify the efficacy of the system. The viability of the scheme is confirmed by performing detailed experimental studies.

Control of chaos in positive output Luo converter using slope compensation method

Abstract: This paper illustrates the control of chaotic behaviour in positive output Luo converter by slope compensation method. Bifurcation analysis is carried out in the discrete domain for a current controlled Luo converter operating in the continuous conduction mode. As the reference current is varied, periodic 1 orbit undergoes a flip bifurcation, periodic doubling and finally enters into chaotic regime. Variable ramp compensation technique is proposed to dynamically adjust the slope of the inductor current such that the upper bound of Iref is increased thereby widening the operating range. An iterative function that describes the dynamics of the inductor current with and without variable ramp compensation and the equivalent criteria for bifurcation-free operation is derived. A computer simulation using MATLAB/Simulink confirms the predicted bifurcations. The simulated results are validated through hardware implementation.

Sensorless observers with speed estimate for direct field orientation of induction motor and PMSM drives

Abstract: The paper discusses the problem of sensorless rotor position/rotor flux angle estimation for the permanent magnet synchronous motor (PMSM) and for the induction motor (IM) and presents a family of sensorless observer designs that use a speed estimate. In sensorless field-oriented AC drive control, it is typical to measure the motor’s voltages and currents and to estimate the other quantities of interest: speed, fluxes (or EMFs) and the field orientation angle. The simultaneous estimation of these quantities is possible, however, the methods available are rather complicated and the accuracy is often questionable, especially under parameter variations. The paper proposes a sequential estimation approach which is much simpler: first, estimate the drive’s speed; then, use this speed estimate along with the measurements to estimate the states of the motor model and to obtain the field orientation angle. A family of observers for the IM and the PMSM is presented – these are constructed using the respective moto...