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This paper introduces an improved predictive control for the control of the current in a three-phase active shunt power filter (ASF). The proposed control system compensates for unavoidable digital controller delays, and provides an accurate prediction of the ASF behaviour in the next sampling period. A "two ahead" current reference prediction is proposed which estimates the filter current two samples in advance. The predictor is based on a second order extrapolation method, and can also account for sudden changes in the reference waveform. A genetic algorithm is used for parameter optimisation in the reference prediction/extrapolation formula. In addition to good tracking performance, the proposed controller is insensitive to measurement noise. The effectiveness of the proposed method is verified through experiment.

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.

The Hybrid ac/ac Direct Power Converter (HDPC) has the advantage of improved voltage transfer ratio and higher robustness against supply voltage unbalances over the Conventional Matrix Converters (CMC). The HDPC also has the inherent advantages of the CMC such as: adjustable input power factor, sinusoidal supply currents and no bulky energy storage elements which reduce the life time of the converter. This paper proposed a predictive current controller scheme for a HDPC based on 2-stage matrix converter providing unity voltage transfer ratios; even in the case the supply voltage is highly unbalanced. The proposed predictive current controller is simple in digital implementation, provides higher bandwidth control, requires no additional circuitry and maintains a constant switching frequency which allows synchronizing the switching of the HDPC for sinusoidal supply currents.

A discrete-time predictive current controller, for the application of active power filtering, is designed and analyzed in this paper. A modified algorithm of reference current prediction in the conditions of step change in amplitude and/or frequency is proposed. The theoretical analysis and the validity of the proposed method are verified by simulations. Comparison for the 5th and the 7th harmonic current control is made with the results achieved using synchronous PI plus lead compensator.

In this paper an improved predictive control is proposed for the control of the current in a three-phase voltage source converter. The application for this work is an active shunt power filter (ASF). The proposed control system takes into account unavoidable digital controller delays, which make it difficult to predict the ASF behaviour in the next sampling period. A “ Two Ahead” current reference prediction is proposed which predicts the filter current two samples in advance. The predictor is based on a polynomial-type extrapolation method, and can also account for step changes in the reference waveform. In addition to good tracking performance, the controller has good stability with respect to the system parameters and model mismatch, and good resistance to the measurement noise. The design and implementation of the digital controller are developed in detail in this paper and the effectiveness of the proposed method is verified through experiment.

In recent years the problem of controlling power quality is becoming more relevant because of the widespread use of nonlinear and time-varying loads. Nonlinear loads should not be considered the only cause of the detrimental effects related to power systems, but the responsibility for the power quality deterioration should be shared between supplier and customer. Traditional indices cannot give this kind of information since they are able to give only a measure of the current and voltage waveform nonconformities. The aim of this paper is to define a new weighted index that is able to separate the responsibility for harmonic distortion between the suppliers and the customers. Experimental results show the proposed index gives reliable information about the actual contribution of a nonlinear load in the process of deterioration of the voltage waveform at the point of common coupling.

This paper presents the definition of a new weighted power quality index to be used to coherently evaluate the level of harmonic distortion in electrical systems and quantify the share of responsibility between loads and mains. Simulation and experimental tests carried out under different load conditions, show the proposed performance index gives correct information about the actual contribution of a non-linear load to the voltage quality at the point of common coupling (PCC)

The paper discusses the uncertainty associated to power measurements performed via swept-tuned spectrum analyzers. The analysis deals with channel power technique and provides practical guidelines for the evaluation of measurement uncertainty according to the "Guide to the Expression of Uncertainties in Measurement". Meaningful experimental results are reported and commented. Practical hints for the optimization of the spectrum analyzer setup and the reduction of uncertainty are also discussed

This Special Section is aimed to research academics and practicing engineers of the industrial electronics and industrial informatics communities to present their most recent findings related to digital control systems in power electronics. It is our pleasure to present this third part of the Special Section on Digital Control Systems in Power Electronics and Drives. The first part was already published in the IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS in August 2012. The second part was published in the IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS in February 2013. Now, we present the third and final part of this Special Section where more than 60 papers will be published. This Special Section presents to the power electronics community the most recent advances with topics such as the following: Modern digital control strategies and algorithms; Modulation methods; Advances in hardware implementation: FPGA, DSP, microcontrollers, etc.; Application to all type of topologies in power electronics; Application to all type of AC drives; and Other applications like renewable energies and smart grids, transportation, mining, pulp and paper, etc.

In this paper a new low frequency predictive current control is proposed for a single phase cascaded H-bridge multilevel rectifier. The control method has been fully investigated with theoretical analysis, simulation and experiments on a laboratory prototype with five series-connected H-bridges. However the analysis and technique is valid for any general N-level structure. The simulations and experimental results presented demonstrate the excellent performance of the predictive control in terms of ac current waveform quality, power factor and reduced switching frequency of each bridge in comparison to traditional PI based control schemes.

This paper describes the automated design of the current controller in an active shunt filter. The design method employs a genetic algorithm (GA) based routine. A suitable user definable fitness function assesses the performance of several control parameters, and select which values will evolve to the next generation. Evolution over many generations evaluates a wide range of controller structures and values, and ultimately determines which one best achieves the control goals. Simulation and experimental results show that the method produces a good current controller design, but equally importantly, the design is carried out with very little user interaction. As such the design method is attractive to commercial manufacturers of active shunt filters, as it can significantly reduce commissioning times.

This paper describes the use of on-line impedance estimation for power quality improvement. The impedance measurement technique can be embedded into the normal operation of an active shunt filter, to provide regular updates to the estimate of the supply impedance to source. In this work, the supply impedance estimates are then use in conjunction with the measurement of supply voltage, to generate the reference currents for the active shunt filter. Experimental results show both the accuracy of the impedance measurement, and the effective operation of the active filter in reducing the voltage distortion at the point of connection.

Power-quality monitoring is a very complex task and recently it is assuming a growing importance because of the large diffusion of nonlinear and time-varying single-phase and three-phase loads and their interactions with the power supply system. A set of two indexes capable of evaluating the power quality at the point of common coupling (PCC) in terms of harmonic distortion and unbalance is proposed in this paper. By means of these new performance parameters, which are based on voltage and current waveform measurements at the PCC, it is possible not only to evaluate separately unbalance and distortion, but also to localize polluting loads and separate the responsibilities of distributors and customers. Numerical simulations and experimental tests prove the effectiveness of the presented indexes and their low sensitivity to the network voltage conditions compared with the traditional ones.

This paper describes the design philosophy, simulation and testing of AC power supplies using matrix converters. Instead of the classical design using a diode bridge rectifier, a DC link and a PWM inverter, a 3-phase to 3-phase direct AC-AC (matrix) converter has been used as the power conditioning core of the system. An optimizing control design method, using a genetic algorithm approach, has been used which yields designs to minimize a cost function taking into account both the transient and steady state performance targets. A 40 kVA ground power supply unit (GPU) for aircraft servicing and a 10 kVA advanced mobile generator set have been used as design examples to test the matrix converter approach in this application. Extensive simulations and experimental tests prove also the efficiency of the designed systems in meeting the international standards requirements.

The 17 papers in this special section are aimed to research academics and practicing engineers of the industrial electronics and industrial informatics communities to present their most recent findings related to digital control systems in power electronics.

A digital implementation of a new generation strategy for multilevel voltage-source inverters employing a fast microprocessor and logic circuits is presented in this paper. Using a generic multilevel inverter structure, this technique permits an output voltage of any number of levels to be generated with a simple on-line algorithm and some logic circuitry. Simulation tests carried out by means of "Simulink" have been performed for many generation cases, while experimental results are reported for a five level prototype.

A novel method for power system impedance estimation is presented. The method employs a power converter to inject a voltage transient onto the supply system. The impedance is estimated through correlation of the measured voltage and current transients. Simulations and experimental results demonstrate the effectiveness of this measurement technique.

A method for power system impedance estimation is presented. The method employs a power converter to inject a voltage transient onto the supply system. As the technique employs controlled power electronic devices it may be used as a stand alone piece of a portable measurement equipment, or it may be embedded into the functions of an active shunt filter for improved harmonic control. The impedance is estimated through correlation of the measured voltage and current transients. Simulations and experimental results demonstrate the measurement technique is highly accurate and effective.

The paper presents a space-vector current control scheme for a PWM inverter based on a fuzzy logic estimation of the power devices duty cycles, implemented on a low cost fuzzy logic dedicated microcontroller. The simulation analysis carried out in the Simulink environment and experimental results show the good performance of the proposed fuzzy logic current control.

This paper describes a novel technique for measuring power system impedance back to source. The technique employs a power electronic converter which injects a voltage transient onto the network via an inductor. The resulting current is correlated with the disturbance voltage to determine the impedance. Simulation results indicate that this technique works effectively for various simple network topologies. As the technique employs controlled power electronic devices it may either be used as a stand alone piece of measurement equipment, or it may be embedded into the functions of an active shunt filter for improved harmonic control.

The paper presents a new current control scheme of a PWM shunt active filter with fuzzy logic estimation of the power devices duty cycles. The innovative control drives the inverter so the feedback current follows the real one without delay as a deep simulation campaign highlights. The effectiveness of such control has been tested when the distorting load is represented by both a variable speed induction motor drive and a fully controlled AC/DC power converter. The fuzzy control proposed shows a very high reduction of the line current harmonic distortion using a medium filter switching frequency.

This paper deals with a comparison among some current controlled PWM techniques for induction motor drives working under different load conditions and sampling frequencies. Nonoptimal, optimal, pre-optimized and, more in detail, three fuzzy logic-based controllers are considered. The analysis is carried out by means of simulations done by using Simulink/sup (R)/. A novel useful switching frequency tool is also presented and discussed.

In this paper we carry out an extended analysis of 6-pulse AC/DC converters, when the DC motor supplied by the converter itself is modelled with its internal R-L parameters and e.m.f. E in series equivalent, considering also the real commutation of power devices. The motor current is calculated without usual simplifying hypotheses, then the r.m.s. values of each harmonic component are determined by means of the expansion in Fourier series of the line currents. Finally we calculate some important performance factors such as the fundamental factor, the displacement factor and the power factor, the total and individual harmonic distortion of the line currents, for different load conditions.

This study presents the design, modelling, control and implementation of a `long-pulse` three-phase resonant converter. A d - q equivalent circuit model of the resonant tank system is established first. Based on that, a model of the whole power supply and a state-space multivariable feedback control has been developed. The soft switching, zero current switching, is achieved by combining frequency and phase control together. An experimental prototype was designed and developed on a small scale. Experimental results confirm the expectations from the simulation study and validate the feasibility of the converter.

An improved predictive current controller for active shunt power filters is proposed in this work. The algorithm is based on the conventional deadbeat control and introduces a modified approach to compensate for delays incurred through digital implementation of the control, by predicting a system behaviour one and two sample instants in advance with respect to the measurement instant. Compared with the conventional deadbeat control the proposed solution is more suitable for practical implementations where measurement noise is very likely to appear. An analytical study of the sampled-quantities' noise propagation through the controller is provided. A polynomial-type extrapolation predictor is considered to predict the active shunt filter reference currents and some issues related to its use are addressed. As an alternative, a more robust predictor based on the fact that in practice most distorted loads exhibit a periodic behaviour is also proposed. The system stability under model uncertainties is analysed. The theoretical expectations are verified through experimental tests.

One of the most recent trends in the aerospace industry is the increased use of electrical power in place of hydraulic, pneumatic and mechanical power. This study presents an analytical and experimental feasibility study regarding the application of an electro-mechanical actuator for the aileron of an aircraft using a real flight profile as a reference. The analysis is focused on the input power flow of the actuator converter, showing that the total amount of energy that would be regenerated into the aircraft power network is small and that the use of a bi-directional power flow converter has the advantage of reducing the size of the braking circuit. The investigation is carried out assuming a two-stage matrix converter as the candidate power conversion topology. However, many of the conclusions are equally applicable to other conversion topologies that are capable of bi-directional power flow.

Matrix converters are sine wave in/out forced commutated single-stage AC/AC direct frequency changers using a single bi-directional switch to connect any input to any output. Indirect two-stage matrix converters provide similar input and output performance with no passive component in the dc-link. The difference is that some of these topologies require less switching devices or are able to achieve multilevel output voltage capability. This paper proposes a new indirect matrix converter topology with a three-level phase to neutral output voltage capability and reduced number of devices. A new modulation scheme, simpler that a standard 3-level scheme, is proposed. The performance of the converter in terms of input and output waveform quality and power losses is evaluated through simulations and on an experimental prototype.

The matrix converter is an AC/AC converter constituted by an array of controlled semiconductor switches that connects directly the three-phase source to the three-phase load. The major development of matrix converters begins when Alesina and Venturini proposed the basic principles of operation in the ‘80s. In their modulation methods, through the common-mode-voltage addition technique a voltage ratio of 86.6% can be obtained. In this paper, a novel method which preserves the same voltage ratio of traditional modulations is proposed. The key concept of this approach is to use only the two closest input voltages instead of all three-phase voltages. The duties cycle are computed on the knowledge of output power demand. With this arrangement, lower switching losses in addition to better harmonic content on output current can be achieved. Hence, this paper presents a detailed mathematical treatment of new modulation approach developed for matrix converter. To validate the proposed strategy, significantly simulation results achieved in co-simulation MATLAB/SIMULINK/PLECS environment will be shown and compared with Venturini's modulation.

In this paper a new voltage control for shunt active power filters is presented. The proposed system is able to compensate one harmonic current flowing into the electric network without the need for measuring the non linear load current, or supply line current. Only the line voltage is measured. The developed control sets, by means of a genetic algorithm, the suitable values of amplitude and phase of the harmonic compensating current used as reference signal for a carrier modulated PWM voltage source inverter. Simulation tests carried out using Simulink and the Power System Blockset, show the reliability and the effectiveness of the compensation action.

This paper describes an automated control system design strategy for power electronics and drives. The design method employs a genetic algorithm (GA) based optimization routine that can be implemented off-line and on-line. A suitable user definable fitness function assesses the performance of several control parameters, and selects which values will evolve to the next generation. Evolution over many generations evaluates a wide range of controller structures and values, and ultimately determines which one best achieves the control goals. Simulation and experimental results carried out using as applications an active filter and an induction motor drive show that the method produces an excellent controller design, but equally importantly, the design is carried out with very little user interaction. As such the design method is attractive to commercial manufacturers, as it can significantly reduce commissioning times.

A matrix converter and variable-speed diesel generator are integrated to create a three-phase utility power supply. The matrix converter is designed to meet tight harmonic and transient response requirements while allowing variable voltage and frequency input from the generator's permanent magnet alternator; This enables the generator to provide stable power over a range of engine speeds and load conditions. Test results for the 10 kW offline power supply are provided to demonstrate system performance.

The matrix converter is seen as potentially the ultimate topology for compact, high power density, high waveform quality, efficient four-quadrant AC-AC conversion. A matrix converter has been developed to meet a specific military application, with stringent requirements for output waveform quality, transient response and supply current harmonics. In order to meet the input and output waveform requirements resonant filters are used. These have driven the design, resulting in a relatively large equipment. The achievement of waveform quality and transient performance together poses a special problem for the control design. To optimise the power density, it is very important to start with a specification that does not needlessly over constrain the design. Output filter considerations illustrate the very large impact that specifications can have on static converter equipment design. It is very important to avoid over specification when considering static conversion replacements for MG type equipment. Bi-directional switches based on IGBT technology, capable of blocking voltage and conducting current in both directions, are now available in industry standard packages. The area of protection has been seen as the last remaining obstacle to the commercial exploitation of the matrix converter topology. The paper describes how control and protection of the matrix converter may be achieved using modern DSP/FPGA devices. The matrix converter is compared with a state-of-the-art PWM inverter using a DC link capacitor, designed to meet a less onerous specification. The matrix converter is best suited to applications where power density carries a premium. Its advantages will become clearer with the advent of high temperature silicon carbide devices. (18 pages)

High speed multi-phase machine has drawn widely attention towards the development of electrification due to its high power density and fault tolerant capability. A 50 kW high speed nine-phase permanent magnet synchronous machine has been designed for more electric aircraft, of which the fundamental frequency is up to 2 kHz. Analysis in terms of stability, parameter sensitivity, system stiffness, transient and steady-state responses are carried out to compare the conventional proportional-integral (PI) and the complex vector current controllers. Simulation results show that the combination of complex vector current controller with virtual resistance and the improved anti-windup scheme is the best choice in all test aspects. What is more, by using the double sampling technique, the current THD is maintained less than 10% at the desired operation points when the switching frequency to fundamental frequency ratio ( $R$ ) is above 10, and the system stability is maintained when the $R$ is only 5.

One of the main issues when designing a control strategy for a power electronic system is the development of a reliable model of the real system. It ensures that a simulation presents the same behavior as the real system, providing a useful instrument for control design. Consequently, the designer would avoid wasting time manually adjusting parameters of controllers which have achieved good performance in simulation but poor performance in the real system. However, the evaluation of the actual plant parameters is always a hard job for the designer due to the mismatch between rated and actual values and the presence of unmodelled dynamics. This paper presents a technique for the optimization of the parameters of the simulation model of a shunt active power filter system using genetic algorithms (GAs). The optimization process is based on experimental data measured during the normal operation of the real system. After this, the identified model has been used to optimize in simulation the controllers of the shunt active power filter. Experimental results prove that the optimized controllers greatly improve the system performance

This paper considers the design of a "long-pulse" modulator supply rated at 25 kV, 10 A (250 kW peak power, duty ratio 10%, 25 kW average power, pulse length ap 1-2 ms). The supply is based on direct modulation of a multi-phase resonant power supply, fed by an active rectifier. The objectives of the development are to produce a compact power supply, with low stored energy and with high power quality at the utility supply. The paper provides a brief overview of the technology, followed by a discussion of the design choices

This paper presents a novel finite control set Model Predictive Control (MPC) approach, for grid connected converters. The advantage of using MPC for this application lies in the fact that it does not require cascaded control loops, PWM modulators or PLLs. However, the supply impedance is generally unknown causing remarkable errors in the MPC control action, in the case its value is not negligible compared to the converter inductance. This paper presents a novel idea for estimating the supply inductance, based on the difference between the grid voltage magnitudes at two consecutive sampling instants. The grid voltage magnitudes are calculated on the basis of the supply current and converter voltage directly within the MPC algorithm, in order to achieve a fast estimation and integration between the controller and estimator. The proposed method is verified via simulation tests on a three-phase two level active front-end.