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This article deals with the design of a digital current control applied to a variable-speed low inductance brushless dc (BLdc) motor drive. A robust static full-state feedback control law is determined by means of a convex optimization problem, subject to linear-matrix-inequality constraints. The optimization is used to achieve a fast time response with reduced overshoot under the parametric variation. Results from a 5 kW/48 V BLdc motor prototype is used to validate the proposed approach with a superior performance when compared to two other control strategies.

This work deals with the control law design and experimental verification of a grid-forming dispatchable distributed generation based on a back-to-back converter. The proposed system brings several improvements to the prime mover as well as to the microgrid voltage quality. The control strategy is based on an inner current and an outer voltage loop for both sides of the converter. The external loop of the back-to-back input side, which is connected to the generator, is responsible for regulating the DC voltage. On the other hand, in the output side, the voltage loop ensures a high-quality AC waveform to feed the loads. A comprehensive discussion regarding the current controller with harmonic mitigation is performed to justify the controller's choice. It is shown that a suitable current controller significantly improves the disturbance rejection. A feed-forward compensation based on the load current prediction without any additional sensor is proposed to improve the output voltage quality. Experimental results are used to validate the proposed control law and to show the improvements and benefits of the system.

This article proposes a systematic state-space procedure to design an optimal discrete-time linear quadratic regulator applied to grid-forming converters. A comprehensive mathematical modeling of a voltage-sourced converter with an LC output filter is performed and a systematic way of including digital resonant compensators is addressed. The choice of weights is based on the minimization of selected transfer functions infinity norm, as well as on the stability margin and bandwidth. The effects of weighting on closed-loop transfer functions shape are analyzed and important points are discussed in order to establish a methodical way of choosing the weighting matrices. Experimental results are presented to validate the design and to demonstrate the system effectiveness with high loading and highly nonlinear balanced and unbalanced loads.

This paper presents an improvement in an energizing strategy for a three-phase four-wire modular multilevel converter connected to an electric network as a static synchronous compensator. The new procedure comprises three stages. During the first stage, two thyristors control the current drained from the grid in order to charge the capacitors of the submodules of the positive and negative arms of two phases of the converter. After that, the energy stored in these capacitors is shared with the others submodule capacitors by firing the semiconductor switches of the converter in a strategic way. In addition of limiting the current drained from the grid during all the energizing procedure, the proposed strategy does not produce overvoltage at the converter dc terminals. The results of digital simulations are presented to validate the mathematical analysis and to demonstrate the performance of the proposed energizing strategy.

This paper proposes a strategy to improve the efficiency of a low-frequency Wireless Power Transfer (WPT) system used to charge the battery of an Autonomous Underwater Vehicle (AUV) through an Inductive Power Transfer (IPT). The IPT system uses a Split-Core Transformer (SCT) to transfer power from the docking base to the AUV, without electric contact. Under gap variation, the efficiency is changed because the variation of SCT parameters. Therefore, the input frequency is changed in order to improve the efficiency of the system trough the Maximum Efficiency Point Tracking algorithm (MEPT) without communication between primary and secondary sides. Experimental results are presented to validate the theoretical analysis and to demonstrate the behaviour of the transformer under different values of gap and excitation frequency.

This paper presents a new control algorithm for a distribution static synchronous compensator (DSTATCOM) based on consumer's voltage unbalance assessment. The proposed controller quantifies, in real time, the parcels of voltage unbalances due to the supplier (utility) and consumer by using local measurements of voltages and currents. The compensator mathematical model is used to derive small signal models in such a way to design controllers to compensate for the negative sequence voltage caused by a consumer. Two inner control loops, designed in synchronous reference frame, assure the DSTATCOM tracks the reference signals generated by the voltage controllers. Digital simulation results obtained with an unbalanced distribution network are used to validate the proposed methodology. The comparison of the results shows that the capacity of the compensator can be significantly reduced when only the unbalanced voltage portion caused by the load is compensated.

This work presents a hybrid simulation tool that combines fast analysis of transient stability programs with accurate results of electromagnetic transients ones to evaluate the dynamic behavior of transmission power systems with high penetration of power electronic-based devices. The interaction between the two programs is performed by controllable current and voltage sources, which are used to interface external and detailed systems. The double second order generalized integrator is used to extract the positive-sequence phasor to transfer information between the environments. A local network server controls the data communication between the two simulation environments by means of the TCP/IP protocol. In the present paper, the proposed tool is used to simulate the integration of a aggregate wind power plant, based on a doubly-fed induction generator, into a 29-bus electrical network. Results and computational timings are then compared with the ones obtained with an electromagnetic transients program, demonstrating the accuracy and speed of the proposed strategy.

This paper presents a zero-sequence voltage compensation strategy for a three-phase four-wire modular multilevel static synchronous compensator used to regulate the network voltages. The control strategy is based on a synchronous reference frame mathematical modelling used to control the positive and zero-sequence voltages and currents of a MMC static synchronous compensator. The static compensator is controlled to synthesize AC currents in such a way to restore the positive-sequence voltage to its rated value and to mitigate the zero-sequence voltage at the point of common coupling. Digital simulations are presented to validate the static synchronous compensator mathematical analysis and to demonstrate the performance of the proposed control strategy.

This paper proposes a novel energizing strategy for a three-phase modular multilevel converter connected to the electric network as static synchronous compensator. The energizing system is comprised of two thyristors and its controller. A comprehensive mathematical model is developed for each energizing stage. Based on the models, a control law is designed in order to compute the thyristors firing angle. This is performed in such a way that the maximum value of the energizing current drained from the grid is limited. First, during the positive half-cycle of the mains voltage, the current flows through two arms of the modular converter charging its DC capacitors. In the following half-cycles, the pre-charged capacitors transfer part of their stored energy to the other arms capacitors. The process is repeated until the total DC voltage of the modular converter reaches the grid voltage peak value. Digital simulation results are presented to validate the proposed methodology.

This paper deals with the output voltage control problem of a three-phase three-wire voltage source Inverter (VSI) with LC output filter. A novel discrete-time active damping technique is proposed in order to damp the filter resonance without the need of current feedback. The method is based on an inner voltage feedback with digital lead compensator on the feedback path. A modified digital resonant controller is also proposed to reject the current harmonic disturbance drawn by nonlinear loads. The resonant controllers are connected in series and the design is based on its zeros damping. Results from a small scale experimental setup are used to validate the proposed control strategy.

The static synchronous compensator (STATCOM) is a power electronic converter designed to be shunt-connected with the grid to compensate for reactive power. Although they were originally proposed to increase the stability margin and transmission capability of electrical power systems, there are many papers where these compensators are connected to distribution networks for voltage control and power factor compensation. In these applications, they are commonly called distribution static synchronous compensator (DSTATCOM). In contrast to transmission systems, electric distribution networks generally operate with voltage imbalances caused by the connection of unbalanced loads, short circuits between the coils of transformers and motors, asymmetries of feeders’ impedances, among other problems. Although balancing single- and two-phase electric loads between the distribution feeders can contribute to minimize this undesired effect, the penetration of grid-connected single-phase distributed generation systems, especially those based on alternative energy sources, such as rooftop photovoltaic systems, and the increasing number of battery chargers for electric vehicles, may compromise the voltage unbalance indexes of modern electric networks. Multilevel converters have the advantage of not requiring complex transformers, high-order harmonic filters, or sophisticated magnetic interface structures to be connected to the mains. Among them, the modular multilevel converter (MMC) is one of the promising topologies in multilevel converter family, especially for medium- and high-voltage applications. Thus, the MMC-DSTATCOM can be connected to medium-voltage distribution networks to regulate the positive-sequence voltage and to compensate the negative- and zero-sequence voltage imbalances at the point of common coupling. In addition to providing details regarding the operation and control of modular multilevel converters, this chapter presents the steps to derive mathematical models for designing the positive-, negative- and zero-sequence voltage and current control loops for DSTATCOM based on an MMC capable to synthesize output voltages with 29 levels.

Neste trabalho é apresentado um estudo com o uso de um controlador preditivo para controle de corrente de um conversor elevador pré-regulador de fator de potência para aplicação no lado receptor (ou secundáario) de sistemas de transferência indutiva potência. Para isso, são apresentadas as equações do controlador, simulações digitais e resultados experimentais que descrevem o funcionamento do sistema em enfoque.

O presente trabalho apresenta a aplica ca do controle preditivo baseado em modelo com conjunto de controle finito (FCS-MPC) a um conversor com fi ltro LCL conectado a rede. Este controle preve o comportamento futuro das vari aveis de controle e, com essa informa cao, escolhe o melhor estado de comutacao do conversor de acordo com a minimizacao de uma fun cao custo. No entanto, e necess ario elaborar o modelo matem atico do sistema, onde foi desenvolvido utilizando o m etodo de espa co de estados e posteriormente discretizado. Para amortecer a ressonância intr inseca do filtro LCL, e detalhado o projeto de uma estrat egia de amortecimento ativo baseada no resistor virtual (VR), bem como a inclusao dessa restricao na funcao custo. Resultados de simula cao sao utilizados para validar o m etodo proposto e mostrar sua e fic acia.

Este artigo apresenta a modelagem e o controle de duas topologias de conversores de capacidade plena aplicados a um sistema de geração eólica conectado a rede elpetrica. Os modelos matemáticos são desenvolvidos no sistema de coordenadas síncrono (dq0). O controle dos conversores é realizado em espaço de estados sendo os ganhos calculados usando a metodologia baseada no regulador linear quadrático. Resultados de simulação são usados para verificar amodelagem e os controladores projetados para duas as topologias de conversores investigadas.

The increasing use of renewable energies, especially photovoltaic energy generation, has motivated research in the area of power electronics in order to optimize the integration of these sources into the conventional electric system. In general, photovoltaic systems are connected to the AC grid and, for this purpose, use voltage Inverters. Several topologies can be used for this, among them, the Micro-Inverters and the Multi-Modular Converters, both having their advantages and disadvantages. Therefore, the objective of this paper is to integrate the concepts of both technologies in a Modular Multilevel Converter in which each module is given by a Micro-Inverter. The proposed system is modeled in PSIM and simulation results show that the proposed system presents satisfactory results even under conditions of total or partial shading of PV modules.

This work presents an analysis on the integration of energy harvesting technologiesused for low power applications. The main goal e is to develop a simulation platform representing a nanogrid using the consolidated models of three of the most mature energy harvest sources: photovoltaic, thermoelectric and piezoelectric. The resulting model is used to evaluate the advantages of adding energy harvesters to a battery supplied applicaiton. It will be presented a short literature review, as well as a discussion about equivalent circuit models for each one of the sources used on the proposed 100 mW nanogrid. Aspects regarding modelling and simulation of the system on PSIM is presented and some case studies are performed to validate the proposed methodology.

Este artigo apresenta um estudo de um sistema de transmissão CC de alta tensão (HVDC) baseado na conexão em série de conversores de fonte de corrente autocomutados e comutados pela linha com objetivo de reduzir a potência reativa demandada pelas estações conversoras. Um modelo matemático baseado no conceito de função de chaveamento é usado para representar o comportamento não linear das estações conversoras comutadas pela linha e autocomutadas, de modo a derivar relações para calcular os ângulos ideais para a operação de ambas as estações HVDC. O desempenho do sistema HVDC híbrido proposto foi verificada com base em um estudo de caso de sistema de alta potência, envolvendo análises estáticas e dinâmicas nos programas PSCAD/EMTDC e Matlab/Simulink. Os resultados da simulação digital são apresentados para demonstrar a eficácia da configuração proposta em comparação com um sistema de transmissão convencional LCC-HVDC.

This paper presents a methodology to identify in "real-time" the parcels of responsibility of the utility and the consumer for the zero-sequence unbalance at the point of common coupling. The output signal of the proposed algorithm is used to generate the reference signals for the voltage control-loop of a four-wire three-phase distribution static synchronous compensator. Digital simulation results are used to validate the presented methodology. In addition to the proposed algorithm to identify the responsibility of the consumer unbalance, the capacity of the static compensator can be designed to only compensate for the zero-sequence voltage in the PCC caused by the consumer.

This paper presents steps of an unified modeling and controller design for a back-to-back converter applied to a grid forming system. The proposed procedure captures in a single state-space model a grid-interface converter with an output L filter, a grid-forming converter with an output LC filter and DC capacitor. This approach deals with a modern multivariable linear quadratic regulator control strategy for taking full advantage of the unified model. A full state-feedback controller has been designed for control the grid-interface converter input currents, grid-forming converter output voltages and DC-bus voltage behavior. Resonant controllers are also proposed to reject the current harmonic disturbance drawn by nonlinear loads. The controllers are designed and tested in PSIM, then simulation results are show to verify the proposed control strategy.

This paper presents an adaptation of a Model Predictive Controller for current control in two-phase three-wire grid connected converters. The discrete model of the system and the controller algorithm are described in detail. Fixed switching frequency is achieved by integrating the proposed predictive controller with Space Vector Modulation. This integration eases the implementation in digital signal controllers. Simulation studies were performed to test the suitability of this controller in tracking sinusoidal and nonsinusoidal current references. Simulation results are presented to confirm the effectiveness of the proposed controller.

This paper presents a simplified analysis of a multi-grounded distribution network compensated by a four-wire three-phase power conditioner. The effect of the neutral conductors and grounding resistances on the voltage unbalance factor are demonstrated, in steady-state, performing digital simulations using the OpenDSS package. Then, a power conditioner is connected to the distribution network to compensate for the currents drained by an unbalanced load. The control loops used to control the AC currents and the DC voltage of the power conditioner are also presented. Results of time-domain simulations show that, although the unbalance can not be fully mitigated, the power conditioner can reduce the voltage unbalance and neutral voltages of the distribution network.

This paper proposes a method to design an adaptive proportional-resonant (PR) controller for equalize and suppress the third harmonic in the capacitors voltages of NPC converters applied to a wind energy conversion system. This problem with NPC converters capacitors voltages occurs in all applications, but when the frequency of the AC system varies, as occurs in wind systems, a fixed frequency resonant controller could not be sufficient. Then, using a PR controller with adaptive resonant frequency is possible to improve the controller performance. A mathematical model for the capacitors voltages dynamic behavior is developed, as well as the control system used to equalize these voltages and suppress the third harmonic. A quasi-PR controller is used, which allows to increase the bandwidth, make it less sensitive to frequency variations. At least, is a method to design the controllers parameters. In order to verify the system operation and the controllers performance, results from simulations in PSCAD/EMTDC are used.

The hybrid active power filter is one of the topics most discussed by researchers concerning power quality issues. However, most of the works presented in literature do not deal with the design of the hybrid active power filter’s components. Thus, this paper proposes a design method of a shunt hybrid active power filter used to compensate for a non-linear load connected to a three-wire three-phase network. The methodology is based on the superposition theorem and the instantaneous power theory. This method is performed in such a way to ensure a low voltage at the DC bus, compared to the DC voltage value commonly adopted in voltage-sourced inverters. Therefore, the ratings of the active power filter are reduced. Results of digital simulations are presented in order to validate the design method proposed in this paper.

This paper presents a voltage control strategy for a static synchronous compensator (STATCOM). The control algorithm proposed in this paper allows the STATCOM to regulate the voltage at a remote bus of a power system. The mathematical modelings and control-loops developed for the static compensator are validated through results of digital simulations. The results presented show that the STATCOM can regulate the voltage at a remote bus in real-time. Moreover, it is shown also that, if the STATCOM regulates the voltage of the remote bus at the nominal value of the system, the voltages of the upstream buses of the power system may exceed its limits.

This paper presents a three-phase static synchronous compensator with five legs to be connected to a multi-grounded neutral distribution network. Several strategies are proposed in the literature to compensate for the imbalances in multi-grounded networks. Typically, three-phase static synchronous compensators with four legs can compensate for positive-, negative- and zero-sequence network voltages. However, they cannot simultaneously compensate also for the neutral voltage of multi-grounded network. Thus, the fifth-leg of the proposed compensator is controlled as a single-phase converter in order to compensate the neutral-voltage at the point of common coupling. Linearised mathematical models, in the synchronous reference frame, are developed and used to design the controllers used to compensate the network’s neutral voltage and to regulate the current synthesized by the fifth-leg of the compensator. A multi-grounded network, derived from the IEEE NEV test feeder, is modelled in the PSCAD/EMTDC to investigate the performance of the proposed compensator. The results of the digital simulations demonstrate the effectiveness of the neutral voltage compensation strategy and validate the control loops designed for the three-phase five-wire static synchronous compensator.

This work proposes an air-core DC-DC solid state transformer to connect the wind turbines of an offshore wind farm in series with a DC transmission link. This emerging layout does not use a power transformer to increase the voltage from the offshore collector network to the transmission level, nor does it require a rectifier station to convert the electrical energy to DC. The diode-clamped rectifiers, connected to each permanent-magnet generator, are controlled to drain sinusoidal currents from the generators in order to extract the maximum power from the wind turbines. The air-core transformer, designed by means of a finite element software, ensures the galvanic isolation between the wind generator and the HVDC link. From the generator side, a single-phase full-bridge three-level inverter feeds the primary coil of the transformer, whereas the secondary coil is wound using by means of an XLPE-insulated cable. This paper also presents a strategy for designing the controllers that regulate the output voltage of each wind conversion unit. Results from digital simulations, obtained with PSCAD/EMTDC, are presented to validate the technical feasibility of the proposed DC-DC solid-state transformer scheme, as well as to demonstrate its performance under different operational conditions.

This paper presents a negative-sequence voltage compensation strategy of a distribution network by using a static synchronous compensator based on modular multilevel converter. Mathematical relations of the static compensator are used to derive small-signal linearised models, in the synchronous reference frame, and to design voltage and current controllers to compensate for unbalanced voltages at the point of common coupling. Moreover, a comprehensive model of the DC bus voltage with a control loop implementation are presented. Furthermore, a notch filter is connected in the feedback path of the DC voltage control loop to eliminate the oscillation in the DC voltage. Digital simulations results, obtained with a 10 MVA / 24 kV MMC-DSTATCOM with 14 submodules per arm, will be used to validate the small-signal linearised mathematical models, and the performance of the designed controllers, during steady-state and faulty grid conditions. In addition experimental results obtained with a small-scale MMC prototype, with 03 submodules per arm, will be presented to demonstrate the feasibility of the compensation strategy proposed here.

This paper presents the modelling and control design steps of a two-stage static conversion structure used as interface to integrate a diesel generator set into a secondary distribution network. In order to guarantee that the inverter works within the PWM linear range, a boost converter is used to increase the DC voltage level. The proposed structure allows two operation modes, connected to the AC mains or isolated. In the isolated mode the interface converter may be controlled as grid-forming or grid-conditioning (active power filter). The inverter current controllers are designed in the synchronous reference frame together with multiple integrators in order to effectively track non-sinusoidal currents. The stability analysis is performed through the Nyquist plot. Experimental results obtained with a 5.5 kW diesel generator set are presented to validate the proposed system operation and control strategies.

This study presents the design and implementation steps of a digital predictive controller to regulate a low-inductance, three-phase, three-wire permanent magnet brushless DC motor currents. These types of motors are usually driven by multi-stage converters, switched at high frequencies, or use additional inductances to limit the current ripple. The motor's trapezoidal back electromotive force and rectangular currents waveforms make the design and the tuning process of linear controllers difficult. This task complexity increases when a wide speed range is considered. Digital predictive controllers are easily implemented in digital signal processors (DSPs), being successfully used to regulate currents of different types of power electronic converters. A unipolar pulse width modulation predictive controller is proposed here to regulate the rectangular currents of a brushless DC motor, without the need for any additional filter or converter. Experimental and simulation results using a 5 kW/48 V three-phase brushless DC (BLDC) motor are presented to demonstrate the feasibility of this proposal. It will be presented a methodology to compensate the conditioning and sampling circuits delays as well as the inverter's semiconductors voltage drop. The control algorithm was implemented in a TMS320F28335 DSP.

This paper presents design steps of a distributed generation system with load power compensation. A single-phase full-bridge converter is used to connect the alternative source to the mains. Besides injecting active power, the distributed generation also provides load power compensation capability. In this context, a current reference strategy based on single-phase circuit theory is proposed for grid-connected multi-task converters. The main idea is to synthesize the signal reference for control loop generating orthogonal signals from grid voltage and current load. A Third Order Sinusoidal Integrator is used to extract fundamental component and generate the orthogonal waveforms of grid voltage and load current. Current controller loop for interface converter is developed based on Linear Quadratic Regulator theory. Simulation results are presented to verify the system behavior.

This paper proposes a novel DC-side discrete-time voltage controller for grid-connected voltage-sourced converters during asymmetrical faults. The main objective is to eliminate the second-order voltage oscillation on the VSC’s DC-side, as well as the positive sequence third-order harmonic current injection into the grid during asymmetrical faults. The compensator is designed based on the comprehensive discrete-time model of the DC-side dynamics. It is shown that DC-side average voltage can be controlled by the positive sequence direct axis current, while the oscillating component can be fully controlled by negative sequence dq-axes currents. The negative sequence current references are obtained using a discrete resonant controller plus a lead filter in order to achieve zero steady state error and asymptotically stability, without injecting harmonics currents into the grid. Simulation results showed the effectiveness of the proposed strategy under severe fault conditions.

This paper presents a control algorithm, based on consumer-generated voltage imbalance assessment, for a distribution static synchronous compensator (DSTATCOM). The proposed algorithm quantifies, in the time-domain, the parcels of voltage unbalance due to the supplier (utility) and consumer using measurements of the instantaneous voltages and currents at the point of common coupling. Small-signals models are derived and used to design the controllers for the DSTATCOM in order to compensate for the negative and zero sequence voltages caused by the consumer. These controllers are designed in the synchronous reference frame, with two inner current loops and two outer voltage loops for each compensated sequence, to ensure the DSTATCOM tracks the reference voltages generated by the unbalance assessment algorithm. Digital simulation results obtained with an unbalanced distribution network are used to validate the proposed methodology. Through the comparison of the results obtained with and without the proposed unbalance assessment algorithm it is possible to conclude that the capacity of the compensator can be significantly reduced when only the unbalanced voltage parcel caused by the load is compensated.