New Publications are available for Current control
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New Publications are available now online for this publication.
Please follow the links to view the publication.Improving power quality in distribution feeders with high PV penetration through inverter controls
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0749
Voltage fluctuations caused cloud transients in distribution systems with a high level of distributed photovolaic systems is of concern to electric utility companies since this can lead to power quality issues. This article proposes a scheme that can minimize this problem by allowing grid-tie inverters to generate controllable amounts of reactive current in a way to neutralize the change in active current. Inverter oversizing is not required by the implementation of this method. The performance of this technique is verified through computer simulations using PSCAD software. (4 pages)Self-sensing control of PM synchronous machines for the entire speed range with reduced computational effort based on a novel MRAS approach
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0268
This paper focuses on some of the remaining challenges of self-sensing control for permanent magnet synchronous machines (PMSM), which are in detail: combination of EMF-based and magnetic saliency-based methods; influence of the fundamental current control on saliency-based methods; position transducerless system identification of “key parameters/effects” (saturation effects,...); and reduction of computational effort. These demands are taken into account by a novel Model Reference Adaptive System (MRAS) which is based on an armature flux observer. (6 pages)Reduction of passive filtering in aerospace starter/generator systems using a multilevel converter with predictive current control
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0250
The application of predictive current control to a multilevel converter is investigated in an aerospace starter-generator system. The use of a multilevel inverter with predictive current control enables the system to reduce the harmonic distortion in the current waveform when compared to a conventional Field Orientated Controller. It is important that the power converter is optimized to control the current harmonics as aerospace starter-generators are typically low inductance machines. Experimental results taken from a prototype inverter show a substantial reduction in THD is achieved using the proposed controller. (5 pages)Discrete hardware controllers design of a single phase PFC boost converter with FPGA
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0188
A discrete control design of a single phase PFC boost converter with FPGA is presented. The average current mode control (with current reference) and Self Control (without current reference) are analyzed when implemented with discrete hardware controller. Simulation and experimental results are shown to verify the performance of both controllers. (5 pages)Simple control method for parallel connected three-phase PWM converters
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0221
This paper presents a current-controlled parallel connected three phase converters scheme. Two voltage source inverters with a front end diode rectifier are directly paralleled without intermodule reactors. The proposed method divides the switching cycle evenly between the equally rated converters, and each converter employs just one PI regulator to get good current characteristics, both in steady states and transient states. Unlike in most previous studies, the converters utilize local feedback information to obtain equal current sharing without using any circulating current control scheme. Using MATLAB/Simulink, simulation results are given to verify the control proposed. (5 pages)Capacitor voltage balancing in modular multilevel converters
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0158
A universal capacitor voltage control method for converters built from series connected modules is presented. It fully exploits both the circulating currents and the common-mode voltage without affecting the phase current control. The controllability of the capacitor voltages in various such converters is investigated. It is found that the nonzero branch currents and terminal voltages are necessary for capacitor voltage balancing. (5 pages)Comparison of 3- and 9-phase brushless PM drive systems for aerospace actuation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0249
Nearly all electric vehicles (EVs), hybrid electric vehicles (HEVs), more electric aircraft, electric ship propulsion and others power conversion industrial applications uses power electronic inverters to convert AC to DC or vis versa, as in the starter/generator machine system and generation/regeneration process of the traction motor. Also, it has become possible to integrate HEVs power electronics component in one package with one set of liquid cooling. Recently, compactness and reliability of the power conversion and generation system design in automotive, in particular, and in aerospace industries are growing with global necessity of shifting from conventional airborne emission vehicles and aircrafts to the green all electric ones. Therefore, an advanced technology in the area of energy storage, conversion and dc-link capacitors, which account for a major fraction of the volume, weight and also cost of the inverter, is demanded by the developer of HEVs and other industrial areas. In three-phase system a dc-link voltage source inverters (VSI) are fed via controlled or uncontrolled rectifier bridges from a main source. Here, a dc-link capacitor is usually used to maintain a stiff dc-link voltage across the VSI, and to perform other tasks, as in [1]. Such that, in this application, the dc-link capacitor deals with the main voltage fluctuation and provides a dc-link current ripple to suppress the generated electromagnetic interface (EMI) caused by pulsating current (ripple current) associated with the inverter switching. It is recognized in the literature [1-7] that for voltage stiff inverter the dc-link capacitor adequate selection, sizing and minimizing presents a major issue for improving electrical system compactness and utilization. Lai et al discusses the use of low-inductance high current film capacitor in a high-power dc-bus inverter for battery-powered traction motor drives [2]. Another discussion that shows merits of an advanced film capacitor technology over conventional electrolytic capacitor for dc-link applications was presented by Grinberg et al [3]. A dc-link capacitor minimization method via direct capacitor current control has been described by Gu and Nam [4]. Such that, the dc-link capacitor can be minimized by making the converter side dc-link current similar to the inverter side dc-link current waveform in a pulse width modulation (PWM) converter-inverter system. However, the dc-link capacitor reduction technique of Gu et al is not for stiff voltage-source inverter. A simple analytical expression for current stress on the dc-link capacitor caused by the load-side inverter of the voltage dc-link converter system is derived by Kolar and Round [1]. Conclusions have been obtained by some of the previous papers, which declare that the dc-link capacitor of practical systems usually determined by the effective capacitor current stress and not, for example, by a given maximum admissible value of the amplitude of the dc-link voltage ripple [1]. In Dahono paper [5], analysis and minimization of output current ripple of multiphase PWM inverters was presented. The minimization of this current ripple is achieved for three-phase PWM inverter by injecting a twenty-five percent third harmonic in the reference sinusoidal signal. Whilst, minimization of the output current ripple of a multiphase PWM inverters can not be attained and it will become unsymmetrical if harmonics are injected into the sinusoidal reference signal [5]. Also the paper discussed by Dahono mentioned that multiphase PWM inverters with number of phases equal to multiple of three will give better results than the one that is not a multiple of three, for example, if the number of phases is a multiple of three, the multiphase PWM inverter can be operated as several three-phase PWM inverters. As for the authors knowledge, no verification nor investigation of this claim have been found in depth in the literature. In the paper, 3-phase and 9-phase PWM inverter modules with different threeand nine-phase brushless permanent magnet (BLPM) machine configurations will be analysed in detail to show the adequate use of this configuration to either eliminate the need or significantly reduce the size of the dc-link capacitor that suppress the generated EMI caused by pulsating current associated with the inverter switching for stiff voltage-source inverter. In addition, different operating points on the general torque speed curve for different BLPM machine drive configurations will be investigated to give decision of the adequate and best machine drive configuration, in terms of improving power and torque capabilities with the minimization of output torque ripple, which can be practically implemented and used in many promising industrial areas. (2 pages)Bidirectional current controller for combination of different energy systems in HEV/EV
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0204
High energy traction batteries for plug-in-hybrid-electric-vehicles can deliver an extended driving range, but are limited in power. In contrast, high power systems are limited in energy content. The combination of high energy and high power systems can solve this problem but will be usually realized through a cost intensive DC-DC converter. This paper presents a low cost yet powerful solution to drive hybrid vehicles with increased pure electric range. This is realized through a variable frequency current controller combining high-energy and high- power-sources. The presented controller shows efficiencies higher 98%. (5 pages)Control scheme evaluation for class-D amplifiers in a power-ultrasonic system
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0237
Power-converters or amplifiers are required to drive high-power piezoelectric transducers and attached processing equipment, at the optimum resonance mode for best processing efficacy, while under varying loading conditions. The driving power converter must synthesize relatively low-distortion sinusoidal output current to prevent harmonic- current excitation of neighbouring, less-productive or desirable resonant modes. Continuously-variable output-voltage capability is required to maintain output power at a level which optimises processing. Three output synthesis methods have been reviewed in this paper for the Class-D amplifier constituting the transducer driver. Typical output-waveform quality is assessed, and PSPICE simulation and laboratory results are presented to illustrate performance. (6 pages)DC-link voltage control of a single-phase photovoltaic inverter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0352
This paper investigates DC-link voltage control in a single- phase photovoltaic (PV) inverter. Recent research has shown that a right-half-plane (RHP) zero exists in the output current control dynamics of a voltage source inverter (VSI) and that the sign of current control loop changes when the VSI is fed from a current source, such as PV generator. Accordingly, VSI with a high-bandwidth current control becomes unstable in such a case without input-voltage control. The use of conventional cascaded control scheme transforms the RHP zero into a RHP pole in the input-voltage control dynamics. Based on this observation, design rules can be determined regarding the dc-link voltage control and input capacitor selection. (6 pages)Hybrid excitation synchronous machine control in electric vehicle application with copper losses minimization
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0252
This paper presents an optimal current control for the hybrid excitation synchronous motor in electric vehicle application. The control aims to meet the torque and speed requirements while insuring minimal copper losses. Extended Lagrange multipliers optimization method (Kuhn-Tucker conditions) is used to elaborate analytical expressions for the optimal reference armature currents as well as for the field current if with respect to armature current and voltage constraints. Simulation over the new European driving cycle proves that the proposed optimal control leads to the lowest copper losses compared to the results obtained by any other commonly used synchronous motor control strategy. (6 pages)Star connection of grid connected single phase VSIs to supply unbalanced or nonlinear loads under normal and fault condition considering the transmission line impedances
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0178
This paper presents a proposed circuit topology and control system to supply both linear and nonlinear loads under unbalanced conditions of the grid voltage and fault conditions by using three, single phase, star connected VSIs and a proposed load current controller. The main contribution is the capability of the proposed controller to supply unbalanced and nonlinear loads and reduce the grid voltages and currents ripple using simple PI controller. Moreover, the proposed topology of connection of three singlephase inverters gains the advantage of parallel connection of VSIs. (6 pages)Examination of new current control methods for modern PMW controlled AC electric locomotives
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0314
A railway electrification system supplies electrical energy to railway locomotives and multiple units. There are several different electrification systems in use throughout the world. The single-phase AC network systems are widespread (25 kV 50 Hz or 15 kV 16 2/3 Hz). The Hungarian system is 25 kV 50 Hz AC. This article is just dealing with the AC network supplied locomotives. Nowadays in our country the series wound DC traction motor driven locomotives are still widely used. These vehicles are equipped with diode or thyristor rectifier circuits that inject harmonics into the AC line and distort the line voltage. In our work we examined and compared current control methods that can be achieved by "network-friendly" locomotives connected to distorted line. We worked out a new current control strategy that possesses several advantages. The modern locomotives endeavour to consume sinusoidal current from the AC network, in phase with the network voltage fundamental. In generator mode these endeavour to supply back to the grid sinusoidal current in antiphase to the voltage fundamental. We compared current control methods with this "common" strategy. One of them can reduce the consumed root mean square (RMS) or fundamental current of a distorted line connected modern locomotive in motor mode. Other one can increase the generated RMS and fundamental current in generator mode. With these strategies the harmonic currents can be used for active power. Moreover it turned out that the harmonic content of the network can be reduced by the "new" strategies. For the study, we built a test system. We can model the line side converter of a modern locomotive DC-link frequency converter with the system. A common solution in locomotives is when several line-side converters feed two DC-links. In the test system we modelled these with one converter, while the motor-side voltage source inverters and the electric traction motors were taken into account as a controllable current source DC-link. (5 pages)A versatile control modulator for optimal bidirectional battery charging
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0200
This paper presents a versatile control modulator (VCM) for optimal bi-directional battery charging. The VCM is capable of adapting to all the existing optimum battery charging techniques, i.e., Constant Current (CC)-Constant Voltage (CV) charging (two- mode charging), Pulse charging, and Reflex charging. The VCM is capable of testing the chargeability of a deeply discharged battery as well. The proposed VCM enables the converter to work as a current source with a controlled output current, when the battery state-of-charge (SOC) is below a predefined reference level and automatically reverts to a voltage source with the controlled output voltage, when the battery SOC exceeds a predefined reference level. Current feed-back clamping, used in the VCM ensures that the error amplifier never gets saturated and the transition between CC to CV mode is smooth and fast. Experimental and simulation results verify the operation of the proposed VCM on a 250 W bi-directional buck/boost converter with coupled inductor. (5 pages)An improved dead-beat current control for cascaded H-bridge active rectifier with low switching frequency
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0219
The use of high power multi-level converters as an interface for renewable energy sources allows modern power grids to achieve a higher flexibility and reliability. Cascaded H-Bridge Converters (CHB) are particularly suitable in these applications but more advanced control techniques are required. In particular Dead-Beat current control methods are a promising solution for high-power CHB. However in high-power applications, a reduced switching frequency is required to ensure high efficiency operation and the performance of the control, in term of quality of the AC side current, may be reduced. As a result a more accurate approximation of the derivative, used in the discretised control law, may be required to ensure accurate operation. In this paper three different methods for the discretisation of the converter model are analysed and compared. The most suitable one is then chosen to implement an improved Dead-Beat current control for AC current regulation of a 7-level, CHB active rectifier. (6 pages)Voltage control on unbalanced LV networks using tap changing transformers
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0006
This paper investigates how an on-load tap changer (OLTC) can be used to regulate the unbalanced three-phase voltages when single phase unbalanced loads are connected to a radial LV distribution feeder. An overview of current voltage regulation technologies for distribution network is presented. Two voltage regulation strategies are developed to eliminate the effect of the unbalanced single phase loads and provide a balanced three-phase supply for the downstream loads. In PSCAD, these two strategies are modelled and examined in several scenarios, based on which, a comparison between their performances is given. (6 pages)Adaptive-hysteresis current controller based active power filter for power quality enhancement
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0325
This paper presents a shunt active power filter for power quality enhancement in terms of harmonics and reactive-power compensation due to the non-linear loads in the distribution network. The compensation approach uses calculation of real-power (p) losses only, which is simpler and different from the conventional p-q theory. The voltage source inverter based active filter switching pulses are generated from adaptive-Hysteresis Current Controller (HCC). This adaptive-HCC changes the hysteresis-bandwidth according to the instantaneous compensation current variation that is used to optimize the required switching frequency. This would improve the active power filter performances. The three-phase shunt active power filter system is investigated under both steady state and transient conditions with non-linear loads.Grid-interfacing fuel cell system with active and reactive power flow control
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0422
This paper deals with the design, analysis, modeling and control of Power Conditioning Unit interfacing the Fuel Cell to the Utility Grid with proper power flow control. The output of the Fuel Cell Stack is connected to the DC side of the Voltage Source Inverter for interfacing to the Grid. The active power transfer is based on the phase angle between DC-AC converter output voltage and Grid voltage and reactive power management is based on magnitude of these voltages. The designed control scheme of the inverter consists of a cascade of two independent controllers, where the external PI power controllers generates the reference currents that is tracked by the inner hysteresis current controllers which generates the pulses for the inverter switches. The entire system is modeled in MATLAB/Simulink environment and simulations carried out to verify the operation and the control principle. Various simulation results are presented for the proposed Fuel Cell Grid interfaced system.Novel delta-sigma modulator for DC-AC converter applications-an experimental evaluation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0369
This paper presents a comparative study between two current control techniques, namely, a basic delta modulator and novel delta-sigma modulator. The delta modulator is used widely in induction motor drives as a known method for converting analog signal in to digital form; to optimize (harmonic minimization) pulse width modulated (PWM) inverter waveforms on-line without conventional optimization processes, like selective harmonic elimination or harmonic weighting techniques. The quantization noise arises from the A/D conversion is distributed uniformly to the frequency axis. But in the delta-sigma modulator the noise varies. It provides several advantageous over Delta modulation. It can be successfully applied to over-sampling digital-to-analog and analog-to-digital data converters switch mode power supplies and switch mode inverters. The spread spectrum nature of delta-sigma modulator, noise level within unnecessary band is much reduced. It is relatively easy to implement, smooth inverter operation and provides low harmonics at the inverter output. The comparative study between delta and delta-sigma current controllers has been verified by the simulation undertaken by the MATLAB/SIMULINK environment in terms of the high switching frequency power spectra density, average switching frequency, rms current error and total harmonic distortion of load current waveforms. The obtained theoretical results are validated with experimental platform based on TMS320F2812 digital signal processor for effectiveness of the study.Simple VSI-based single-phase inverter: dynamical effect of photovoltaic generator and multiplier-based grid synchronization
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0118
Photovoltaic generator is internally a current source with nonlinear characteristics resembling both current and voltage source depending on the operating point in respect to the maximum power point. In order to transfer maximum power, input voltage of the inverter has to be controlled in addition to grid current control, resulting in cascaded input-output-control scheme. For proper modelling, the input-source characteristics and the input voltage control cannot be omitted. It is observed that the cascaded-control scheme produces negative-resistor-like behaviour at the inverter output, which is amplified by the multiplier-based grid synchronization. The negative impedance makes the inverter prone to instability and the utility grid for harmonic resonances. (6 pages)Current matching control system for multi-terminal DC transmission to integrate offshore wind farms
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0200
The inherent features of Voltage Source Converters (VSCs) are attractive for practical implementation of Multi-Terminal HVDC transmission systems (MTDC). MTDC can be used for large-scale integration of offshore wind power with onshore grids. However, many of the control strategies for MTDC that have been proposed previously for offshore wind farm integration depend on local control of the wind turbine generators. This paper proposes a new control strategy, termed Current Matching Control (CMC), which can be used with any number of converter terminals, and is independent of the types of wind turbines used within each wind farm. The proposed CMC matches the current reference of the grid side converter to that of the wind farm side converters. In order to achieve such current matching, a telecommunication system will be required to facilitate calculations of the grid side current references to be carried out in real time. To validate the performance of the proposed control strategy, a generic four-terminal MTDC network, which integrates two offshore wind farms with two mainland grids, is simulated and results relating to several steady state and transient scenarios are presented. (6 pages)Processing energy from fuel cell modules using cascade converters
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0175
A fuel cell system produces a low DC voltage with wide variations; therefore, a DC-DC converter is required to step up and regulate the output voltage. This voltage can be used as an input for an inverter to obtain an AC voltage. In this work, an interface is proposed to connect a fuel cell system to an inverter. This interface consists of a DC-DC switching regulator using a three-stage cascade boost converter and an average current-mode controller. The proposed converter provides a high step-up conversion voltage ratio. The switching regulator is tested using a power module, which uses polymer electrolyte membrane fuel cells. This module delivers an output voltage between 26 V to 42 V. Experimental results verify the well-known benefits of current-mode control. The proposed control scheme can be easily implemented using a minimum number of IC elements; therefore, it is cost effective for a practical application. (6 pages)Digitally-controlled power factor corrector with interleave transition current mode control
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0056
A novel digital-controlled transition current mode control technique for interleaved power factor corrector (PFC) is proposed in this paper. For the presented technique, the switching period to retain zero current switching is predicted rather than sampling the current in real time. Moreover, the related turn-on period is determined by the voltage controller. Therefore, neither zero-current detection nor high frequency A/D converter for current sampling is required. Moreover, for interleaved topology with master-slave control, a new on-time compensation technique is proposed to significantly improve the slave inductor current distortion and thereby achieving current sharing control between phases. Experimental results derived from a DSP-based controller are presented for confirmation. The power factor corrector is with 100 V/AC 50Hz input and 400 V/DC output. The power rating is 460 W. Experimental results show that the power factor is higher than 0.98, efficiency is greater than 96%, and the current sharing can be achieved by the proposed on-time compensation technique. These results confirm the above-mentioned claims very well. (6 pages)Ripple current reduction by optimizing load dependend switching losses using adaptive current control
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0174
In modern inverter fed drive applications the power semiconductors used are typically designed to operate at their maximum thermal operation conditions. Semiconductors worst case thermal considerations in general define the uppermost inverter switching frequency dependent on maximum load current. Fixing this frequency to a constant value, the drive will not be operated with best possible performance at partial load. With the help of the proposed modified predictive current controller it is possible to control both machine current as well as inverter switching frequency at once. Using a thermal model of the power semiconductors hence enables operation at their thermal limit as well as a reduction of current ripple. In a first step the modified predictive current controller as well as the thermal model of the power semiconductors is described. Finally measurement results on a 220kW high precision industrial load dynamometer are presented to compare the performance of a classical predictive current controller and the proposed modification with switching frequency adaptation. (6 pages)Ancillary services of VSC interfaced energy sources - voltage harmonics compensation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0057
With the envisaged high integration of distributed generation (DG), the use of their own technology to provide other services to the grid seems a practical option. The use of a PWM voltage source converter (VSC) to attenuate grid voltage harmonics, in the absence of measurement data at the grid side and lack of knowledge about the grid loads in close proximity, is investigated in this paper. The outer harmonic regulator is adaptive, in order to cope with the dynamic nature of the grid and modulation non-linearity. The grid voltage harmonics are extracted using least mean square (LMS) method, and the inner controller is a synchronous reference frame current controller. It has been shown through simulation that the controller is capable of attenuating the voltage harmonics to an acceptable limit. However, a direct current controller is recommended for better performance. (6 pages)Analysis of various control strategy performances of BDCM for industrial applications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0087
In this paper, performances of a Brushless DC motor (BDCM) are assessed primarily in open loop control, using several control strategies: square wave, Hysteresis current control and Pulse Width Modulation with several techniques (hard and soft, 120° and 180° mode). The system is examined based on a simulation model developed under Matlab-Simulink. For accuracy, the real back EMF is taken into account. The simulation results show satisfactory static and dynamic performances over a large speed range, but when compared, they highlight some differences in term torque ripple and speed response according to each control technique. Therefore, the application of these techniques would depend on the requirements of the load operating conditions. A test bench is set up using an industrial motor to demonstrate the effectiveness of the approach used and to validate obtained results. (6 pages)Adaptive control scheme for a practical bidirectional DC-DC converter with a 80 kHz switching and a 10 kHz sampling frequency
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0175
This paper discusses an adaptive control scheme for a bidirectional boost converter used in a hybrid gasolineelectric vehicle. The converter transforms the voltage of the low-voltage battery, approximately 96 V, to 400 V on the DC-link of the motor inverter. The switching frequency of the inverter is 80 kHz, which enables the usage of rather compact 64 μH inductors. However, the sampling frequency of the control scheme is 10 kHz, so the duty cycle of the switches will only be updated after 8 consecutive switching periods. Due to the large dead-time of the switches in comparison with the switching frequency, the response of the current to changes in the duty cycle is highly non-linear. The low sampling frequency of the control scheme combined with the highly non-linear current response makes it impossible for a simple Pi-controller to regulate the current in a satisfactory way. At first the cause of the non-linear response is investigated. Based on that knowledge, a control scheme is developed that adjusts the duty cycle when necessary and switches between two Pi-controllers, one for small currents and one for large currents. This current controller is implemented on two interleaved bidirectional boost converters. The current controller's set point is regulated by the DC-link voltage controller. (6 pages)Comparative analysis of three starting methods for parallel resonant current source inverter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0035
In this paper three starting methods for an inductive heating equipment are proposed and analyzed. Starting concerns energization and control sequence. The equipment is based on a parallel resonant inverter connected to a resonant tank (coil and susceptor in parallel with a capacitor) for inductive heating applications. The inverter consists of a current source single-phase H bridge, which operates at the resonant frequency of the tank. The inverter is fed by a current controlled buck DC-DC converter, connected to the output of a six pulses bridge diode rectifier. The paper details the proposed starting methods and experimental results obtained in a 15kW, 540V DC laboratory prototype are presented. The operating frequency of the DC-DC buck converter is 2kHz and a the load resonant frequency is around 4,3kHz. (6 pages)Real-time DSP implementation of DTC neural network-based for induction motor drive
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0189
This paper discusses the application of neural networks to control induction machines using direct torque control (DTC). The authors proposes to replace the conventional selector switches statements of the voltage inverter by a selector based on artificial neural networks (ANN), which is able to manage in the same way the switches states. In order to improve the low speed performance a closed loop voltage-current model estimator is employed to evaluate the stator flux. Experimental results for a 3kW induction motor are presented and analyzed using a dSPACE system with DS1104 controller board based on digital processor Texas Instruments TMS320F240 DSP. (5 pages)Comparative study of current vector control performance of alternate fault tolerant inverter topologies for three-phase pm brushless ac machine with one phase open circuit fault
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0052
Reliability and fault tolerance of drive systems has received renewed research interest over last decade with several fault tolerant drive topologies and control schemes having been proposed and investigated. In this paper, the performance of hysteresis current vector control methodologies when applied to three common fault tolerant drive topologies has been investigated and compared theoretically and experimentally. Their advantages and limitations in terms of current value, current and torque ripples, and operating speed range etc. are considered and verified by both simulated and measured results. It is proven that by simply modifying the hysteresis current control methodology, the maximum torque per ampere (MTPA) can still be achieved in post-fault operation, albeit with potentially increased current value, low frequency current and torque ripples, and compromised speed operating range. (6 pages)Analysis of a closed loop control for current unbalance compensation based on AC/AC converters
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0674
In this paper a stability analysis method for unbalance compensation system based on AC-chopper is proposed. Employing AC-choppers and Steinmetz theory it's possible to obtain a dynamic compensation system. This system's performance and stability are not depending only on the cause of unbalance but also on grid parameters such as line impedances and other connected loads. If a quasi-static sinusoidal steady-state approximation is hypothesized, through the multivariable control theory it's possible to study the compensation system stability propriety in relation with grid parameters. (4 pages)An improved method for grid impedance estimation by digital controlled PV inverters suitable for ENS detection
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080549
In this paper an improvement to an existing method for impedance estimation based on inter-harmonic current injection is presented, suitable for ENS detection. This feature is integrated directly in the power converter and shares with this power electronics, sensors and DSP for data processing and control. Realistic simulations using Matlab/Simulink tool are made to verify the effectiveness of the proposed solution within a complete photovoltaic (PV) converter model, including panels, input DC-DC converter and controller running the maximum power point tracking algorithm, DC-AC inverter running dc-link voltage and output current control, LC output filter and accurate grid model. Measurement uncertainty, system non-idealities and specific features (e.g. pulse width modulation and power converter model) have been considered and accurately modelled.Variable frequency adaptive selective compensation for active power filters
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080475
This paper investigates an adaptive current controller for active power filters for aeronautic applications, which compensate selected load current harmonics. The attention is focused on the load current harmonic compensation when the fundamental frequency varies over a wide range (typically between 400 Hz and 800 Hz) and the harmonics produced by distorting loads (such as the 5<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">th</sup> and the 7<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">th</sup>) are above the achievable current loop bandwidth. Compared to previously reported resonant controllers, this paper proposes an adaptive leading angle compensation in the resonant filter, which - by compensating the variable process delay -is potentially able to guarantee the theoretical current control stability when the selected frequency is up to the Nyquist frequency. However, the presence of intermodulation, i.e. distortion introduced due to the compensation of frequencies approaching the Nyquist limit, introduces an additional distortion, which limits the maximum compensation frequency. Experimental results are also presented.Modified current control of three-phase inverter interfacing in distributed generation
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080552
This paper presents a modified current controller technique for three-phase inverter based grid interfaced distribution generation systems. The measurements and digital processor calculation delay is compensated by using a modified Kalman filter. For system robustness two current loops are implemented. Also, the states of the control variables can be observed and the number of the measurements sensors can be decreased. Stability and dynamic performance are analyzed. Simulation and experimental results confirm the validity of the proposed approach.Stability analysis and bifurcation control of hysteresis current controlled CUK converter using Filippov's method
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080548
An autonomous Cuk converter controlled by a hysteresis current controller is studied in this paper. Filippov's method is employed for the first time to investigate the stability of an autonomous power converter. The Neimark bifurcation, via which the converter loses its stabile period one operation, was stabilized by applying two alternative control strategies based on the analysis of the behaviour of the complex eigenvalues of the monodromy matrix of the system.Control of a doubly-fed induction generator via a direct two- stage power converter
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080527
In this work, the control of a doubly-fed induction generator using a direct two-stage power converter, connected between the stator and the rotor, is presented. The control of the generator rotor currents is carried out using standard vector control approach with a reference frame aligned with the stator flux. The modulation of the input stage of the power converter is carried out in order to have close-to-unity power factor operation. Experimental results, using a 2.5 kW experimental setup, are presented showing the performance of the rotor current controllers, the bidirectional power flow through the rotor converter for operation below and above synchronous speed, and operation in a variable speed generating system, with the generator driven by a DC drive.Overview of stray current control in DC railway systems
http://dl-live.theiet.org/content/conferences/10.1049/ic_20080043
In DC rail transit systems, the running rails are usually used as the return conductor for traction current. This arrangement mainly focuses on economic considerations, since it does not require the installation of an additional return conductor. Low resistance between the traction return rails and the ground allows a significant part of the return current to leak into the ground. This is normally referred to as leakage current or stray current. The amount of leaking current depends on the conductance of the return tracks compared to the soil; and on the quality of the insulation between the tracks and soil. The stray currents represent serious problems for any electrified rail transit system. The corrosion problem has been a major concern to the railway and other parties involved since the early days of DC railways. The stray currents create or accelerate the electrolytic corrosion of metallic structures located in the proximity of the transit system. This causes metal pipes, cables and earthing grids laid in the ground near the tracks have a much shorter life which is high importance in regard to safety and economy. Hence, great efforts and research have been carried out to control stray current in DC electrified rail transit system. Stray current control is essential in these railway transit systems where the rail insulation is not of sufficient quality to prevent severe corrosion to the rails and third-party infrastructure. Good control of stray current is also of direct benefit to the operational and safety aspects of the DC electrified railway systems; it could reduce the rail touch voltage. This paper provides an overview of control schemes currently applied to the DC traction electrified rail transit system.Application of active power filter for compensating unbalanced load currents using symmetrical component theory
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070663
The excessive unbalanced current in the network cause voltage distortion, excessive flow of neutral current, heating of electrical machines, transformers and poor power factor in the most primitive form of load compensation. The load compensation based on application of active power filter for symmetrical component theory is much simpler than p-q theory. It does not require complex transformations of currents and can effectively control the unbalanced load currents. The application of active power filter based on symmetrical component theory used for six different cases and the load compensation results obtained through MATLAB programming.Improvement of STATCOM performance with multi variable control methods
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070595
Static Synchronous Compensator (STATCOM) is a device capable of solving the power quality problems at the power system. These problems happen in milliseconds and because of the time limitation, it requires the STATCOM that has continuous reactive power control with fast response. In this way, optimal exploitation of STATCOM by classical controllers has been a controversial issue in reputable journals. One of the most common controlling devices in the market is the PID controller. In this article, the STATCOM is controlled by PI and PID controllers. Also, pole-placement control is another method to control the STATCOM. The best constant values for PID or Pole-placement controller's parameters are laboriously obtained through trial and error, although time consuming. Genetic algorithm is employed to find the best values for PID and pole placement controller's parameters in a very short time. The simulation results show the improvement in current control response. These methods are tested in MATLAB, and their results are obtained.An improved high performance three phase AC-DC boost converter with input power factor correction
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070615
A three-phase 3-level unidirectional AC/DC converter is proposed to achieve almost unity power factor and reduction of harmonics distortion. A power factor corrector using the hysteresis current control technique is presented to improve the power quality at the rectifier side. A high-power-factor rectifier based on a neutral point switch clamped scheme is presented. A control scheme for the proposed rectifier is propounded to draw a sinusoidal line current with nearly unity power factor, achieve balanced neutral point voltage and regulate the DC bus voltage. A hysteresis current control scheme is used to track the line current in phase with the mains voltage. The line current command is derived from a voltage controller and a phase- locked loop circuit. A capacitor voltage compensator is employed in the proposed control algorithm to achieve the balanced neutral point voltage. The effectiveness and validity of the proposed control strategy is verified through computer simulation results. The simulation result reveals that the proposed control technique offers considerable improvement in Power factor and reduction in total harmonic distortion.Fault tolerant control using a hybrid predictive strategy applied to a current controlled four-legged three-phase converter
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070031
This paper deals with the fault tolerant control of a four-legged inverter/rectifier included in a full-stand alone generator dedicated to aircraft power supply. The controller proposed here is based on a predictive strategy allowing to keep an invariable architecture supervised by a fault detection subsystem. Finally, it is validated by simulations. (6 pages)A fuzzy logic controlled three-phase neutral-point clamped bidirectional PFC rectifier
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070617
In this paper, a fuzzy logic controlled three-phase neutral-point clamped power factor correction (PFC) bidirectional rectifier is proposed. The fuzzy logic control is based on the linguistic description and does not require a mathematical model of the system. The outer loop PI voltage controller and the inner loop PI current controllers are replaced respectively by the fuzzy PI voltage controller and fuzzy PI current controllers. The performance of the fuzzy logic controller based converter is compared with the conventional PI controller based converter. The fuzzy controller based converter is relatively more robust than the conventional PI controller and gives better dynamic response of the converter. The MATLAB Fuzzy Logic Toolbox is used for implementing the fuzzy logic control scheme. Various simulation results are presented under steady-state and transient conditions to validate the utility of fuzzy logic controllers.Comparison of topologies of hybrid active power filter
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070664
Hybrid active power filters are used for reducing harmonics in the power system. This paper deals with different topologies of hybrid active power filter discussed along with their control. In a hybrid active power filter the active power filter is used to filter out higher order harmonics, while the lower order harmonics are filtered by the passive filters tuned for particular frequency. This combination reduces the cost and size of active power filter considerably; at the same time the problems associated with passive filter installed alone are also eliminated. With this study a comparison of different topologies of hybrid active power filter is presented on different indices such as THD, complexity and cost and topology- I has been proven to be superior. Here active power filter of HAPF is of voltage source inverter type with current control, the passive filters are tuned to fifth and seventh harmonic frequencies, the source taken is 3-phase, 3- wire type and a 3-phase diode rectifier with resistive load is considered as load. The simulation is done on MATLAB / Simulink-PSB.A circuit with good linearity based on standard optocouplers
http://dl-live.theiet.org/content/conferences/10.1049/cp_20070320
This article presents a circuit with good linearity based on standard optocouplers. The circuit takes advantage of inverse feedback to improve the linearity. It chooses two ordinary optocouplers of same characteristic. One phototransistor is typically used in a feedback mechanism to control the LED (light-emitting diode) drive current which has the effect of compensating for the LED's non-linear time and temperature characteristics. The other output phototransistor is used to provide the galvanic isolation between the input and output circuit. Simulate the circuit in Multisim, the results show that the circuit has good linearity and it can be used not only in DC circuits, but also in AC circuits of low frequency.An interface for renewable energy sources using a multilevel rectifier with enhanced DC link control
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060136
This paper the control of the neutral point current in a neutral point clamped rectifier. This control ensures that the voltages across the DC link capacitors remain equal, even in the presence of unbalanced loads or sources in the DC side. The method employs an offset which is added to each of the inverter modulation waves. This offset causes a zero sequence voltage in the rectifier which can drive the desired neutral point current to counteract the unbalanced capacitor currents. Simulation and experimental results confirm the method.Design and analysis of high performance current control for shunt active filters
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060078
This paper proposes an accurate and simple current control for shunt active filters (SAF) based on a P+Resonant compensator. The proposed current control system is designed to operate with a single dq reference frame, synchronous with the 50 Hz supply voltage, for the compensation of 5th and 7th harmonics. Another major advantage of this strategy is the ability to eliminate the external disturbance from the 5th and 7th harmonic components caused by the power supply. The principle of the proposed control method and the design procedure is here presented. Simulation and experimental results confirm the effectiveness of the suggested approach.A wavelet controller for shunt active power filter
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060075
A wavelet-based controller for shunt active power filter (APF) has been proposed in this paper. The constructed controller based on multi resolution analysis has the advantage of better frequency bandwidth selection. The tuning parameters of the controllers are the gains to be applied to the time-frequency signals at different resolutions. This has the advantage of aiding the process of a proper choice of coefficients of tuning parameters. The developed simulation model of the APF with wavelet-based control shows satisfactory steady state and dynamic performance. A comparison with standard PI controller shows that the dynamic response of the proposed wavelet controller is much faster. This is of advantage in specific applications where the fast dynamic response of the controller is of importance to achieve a desired reference within a short duration of time. The novel technique of the generation of control signal ensures that even when the steady state error is zero, the controller can generate a steady control signal. The wavelet data window width is chosen optimally such that frequencies above 600 Hz are eliminated. This avoids the generation of high frequency spikes in the reference control current signal and ensures stability.Predictive current controlled shunt active power filter using three-level cascaded type inverter
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060137
In this paper, the three-level cascaded inverter is used as a shunt active power filter, making use of the multilevel inverter advantages of better total harmonic distortion, reduced semiconductor switches ratings, and reduced switching losses. A capacitor voltage control technique previously used as a harmonic current extraction technique is extended to the three-level shunt active power filter. Predictive current control based on the supply current (not the active filter current) is proposed. Three-level space vector modulation is used as a pulse width modulation technique. The proposed three-level shunt active power filter is validated by simulation using MATLAB/SIMULINK and practically with a laboratory prototype.Transient model for VSC-HVDC and its control design
http://dl-live.theiet.org/content/conferences/10.1049/cp_20062025
In this paper, the mathematical model and control strategy of the VSC-HVDC system are studied. The transient mathematical model for the VSC-HVDC system in d-q synchronous reference frame is developed, in which direct current control strategy and dual closed loop structure are proposed. Decoupled control structure consisting of current feedback and voltage feed-forward is adopted in the inner current control loop that can track the reference current quickly. The outer loop is power regulators, which combines the inverse steady state model with PI regulator, and can control the active and reactive power separately. Simulation results realized by PSCAD/EMTDC show that the designed control system contains satisfying performance. (6 pages)An improved servo control system for high speed flat industrial sewing machine
http://dl-live.theiet.org/content/conferences/10.1049/cp_20061077
This paper presents a permanent magnet synchronous motor (PMSM) servo drive system for high speed flat industrial sewing machine. In order to satisfy the special function of sewing machine, several approaches are applied in this servo system: using voltage feed-forward decoupling control in current loop to improve speed and position control performance; variable gain control is adopted in system to compensate incomplete decoupling caused by disturbance and inaccuracy of parameter; PMSM used in system is specially designed with concentrated winding and lean charge magnetism barrel-drain rotor, which can effectually improve motor operating and reduce torque harmonics. The experimental curves of sewing procedure show that: the speed feedback can accurately track speed reference under different sewing conditions, which proof the servo control system meet purpose of industrial sewing machines well.