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This chapter discusses the modeling of wind generators from the model predictive control (MPC) perspective using common notation for both synchronous and induction machines. The active and reactive power reach rated values because of the rated load connected to the generator terminals. The chapter also presents modeling of various control variables, such as stator currents, stator fiux linkages, rotor speed, electromagnetic torque, and stator active and reactive powers, for both Synchronous generators (SG) and induction generator (IG). The predicted currents are compared with the reference currents to identify the power converter switching state that provides the overall minimal error among the three???phase currents. The rotor winding is connected to a converter through slip rings and brushes or brushless connection. Radial flux (RF)???permanent magnet synchronous generator (PMSGs) can be constructed with either inner or outer rotors, and the later designs can easily accommodate the multi???pole structure. The RF???PMSG offers simple and robust construction and is used by many wind turbine (WT) manufacturers.

This chapter discusses the predictive control of full‐scale low‐voltage (LV) and medium voltage (MV) voltage source converters (VSCs) employed in permanent magnet synchronous generator (PMSG) wind energy conversion systems (WECS). The variable voltage and frequency output of PMSG is first rectified to DC by using the generator‐side 2L‐VSR. An imbalance between DC‐link capacitors voltage is undesirable because it can cause high stress and damage to semiconductor devices. Digital control systems play an important role in the power conversion of WECS. They enable the safe, reliable, and efficient operation of power converters to ensure maximum energy capture and compatibility to the grid integration requirements. After initializing the digital controller and calculating the reference generator and grid currents, the PCC algorithm enters an iterative loop where the generator and grid currents are predicted and cost function minimization is performed. The control objectives of PMSG WECS can be achieved by regulating the stator currents, torque and flux, active and reactive powers, and rotor speed.

This chapter discusses wind energy preliminaries briefly in terms of installed wind power capacity, wind energy installations by various countries, wind kinetic energy to electric energy conversion, and evolution of major wind turbine (WT) technologies since the 1980s. WTs produce negligible power when wind speed is below the cut‐in value; thus, because of which such turbines are usually kept in parking mode. The turbine is shut down and kept in parking mode when wind speed is above the cut‐out value or during emergency condition to ensure safety. The passive stall or simply stall control is the first‐generation power regulation method employed for WTs and is the simplest method among the three classes. This approach does not use any sensors, electronic controller, or actuator, thus making it less expensive and robust. Low‐ and medium‐power WTs can also be used in grid‐connected DG to reduce electricity consumption from the utility grid. When the electricity produced by the WT exceeds the household or community requirements, the electricity is sold to the utility without employing any energy storage.

This chapter deals with the predictive control of full‐scale low‐voltage (LV) and medium voltage (MV) voltage source converters (VSCs) employed in SCIG wind energy conversion systems (WECS). The generated power is instantaneously injected to a utility grid via the full‐scale converter connected between the generator stator and grid terminals. The generator‐side 2L voltage source rectifier (2L‐VSR) enables full variable‐speed operation by controlling the output voltage amplitude and frequency. The overall SCIG model includes both electrical and mechanical variables. The electrical model includes stator voltages, currents and fiux linkages, and rotor fiux linkages, whereas the mechanical model includes the dynamics of rotor speed, moment of inertia, and electromagnetic torque. The electromagnetic torque is computed by the cross product of estimated stator flux vector and measured stator current vector. The perturbations in stator voltage measurement and stator winding resistance lead to inaccurate flux estimation, especially at low‐speed operation.

This chapter discusses the basics for wind energy and examines enough background to select wind generator‐power converter configuration for modeling and predictive control. Power converters in first generation of wind turbines (WTs) (Type 1) are used only for smooth grid connections, which are disconnected from the circuit once the generator is tied to the grid. Power converters that are identical on the generator‐side and grid‐side and are linked through a DC link are classified as back‐to‐back (BTB) connected converters. Parallel power converters increase power handling capacity but with the drawbacks of circulating currents and the subsequent power converter derating. The semiconductor device switching frequency is limited to few hundred hertz to minimize the switching losses and allow proper heat dissipation. The minimization of AC circulating currents and balancing of capacitors voltage between submodules is required to ensure the proper operation of the modular multilevel converter (MMC).

This chapter deals with the modeling of power converters employed in Type 3 and 4 variable???speed wind energy conversion systems (WECS), particularly for 2L??? voltage source converters (VSCs) and NPC converters. Model Predictive Control (MPC) uses a completely different approach and does not require comprehensive knowledge on the space vector diagram, SV diagram sectors, reference voltage vector, and adjacent vectors. All the voltage vectors are utilized to predict the future behavior of the variable to be controlled, and an optimal voltage vector that fulfills the control objective is selected from them. The proper selection of switching signal leads to the accurate control of reference variables, such as generator or grid currents and balancing of DC???link capacitors voltage. The generalized approach for the modeling reveals that the models can be extended to multilevel and multiphase applications in an intuitive manner. The operational modes and space vector diagrams of various power converters are presented to aid the discussion and to show proof of concept.

This chapter discusses how the process of transforming or mapping continuous functions, models, and equations into discrete counterparts is related to discrete mathematics and is often referred to as discretization. The finite control‐set model predictive control (FCS‐MPC) strategy is an intuitive and powerful tool for controlling power converters compared with the classical linear control with proportional‐integral (PI) regulator and space vector modulation (SVM). The closed‐loop stability is a classical subject matter in control engineering. In the closed control of power converters, state variables such as voltages, currents, and power have a tendency to diverge from the set‐point value. The definition of the cost function is an important design stage in FCS‐MPC for fulfilling the operational requirements in various power conversion applications. In general, the cost function design is simple and flexible and can handle multivariable systems with different physical natures, magnitudes, frequencies, and phase angles for control variable. Numerous power conversion applications employ current control in the inner control loop, irrespective of the power converter topology.

This chapter discusses the classical and advanced digital control techniques, including predictive control and examines the operating principle of these control techniques with an intuitive example of generator or grid current control. When closed, a switch allows the passage of any amount of current without any on‐state voltage drop. The power diode belongs to the family of uncontrolled semiconductor devices because its switching on and off instances depend on natural commutation and power circuits. This device has been widely used in industrial applications from the 1950s and is still widely used. More powerful digital control platforms are expected to be developed in the near future, thus resulting in lower costs and higher computational capacity than existing control platforms. Hysteresis current control does not require the system parameters, converter model, or prior knowledge of the user, thus making it one of the simplest and robust current control techniques. The relative magnitudes of these error signals are then used by a lookup table to generate the switching signals to the converter. To implement these methods on digital platforms, a high‐sampling frequency is needed to force the variables within the hysteresis band limits.

This chapter deals with the model predictive control (MPC) of grid‐side converters (GSCs) in different reference frames, with the predictive current control (PCC) and predictive power control (PPC) being discussed for both LV and MV power converters. The generator‐side variable voltage and variable frequency is converted to grid compatible fixed voltage and fixed frequency by a single‐stage AC/AC power converter, also known as a matrix converter. The grid currents or active and reactive power can be controlled in a decoupled manner by employing grid voltage orientation or grid fiux orientation. The most favorable situation to use the voltage‐oriented control (VOC) method with pulse width modulation (PWM) or space vector modulation (SVM) is in fixed switching frequency operations. The MPC is a nonlinear control method and provides an approach that is suitable for controlling power converters while mitigating the aforementioned disadvantages associated with the VOC method. The control delay in experimental tests should be compensated to achieve high‐performance operation similar to the simulation tests.

This work suggests a three-phase interleaved multi LLC resonant converter with variable frequency control. The suggested converter yields high gain of the voltage with Zero Voltage Switching (ZVS) for all primary active switches. The converter accomplishes significant load variation using variable frequency control, whereby the converter gain is studied with regards to the tank impedance that is based on the relation of the switching frequency to the resonant frequency. Furthermore, the use of magnetizing inductance guarantees zero voltage switching for all switches. Matlab/Simulink was used to simulate the suggested converter. The proposed converter is proven to offer a wide load variation up to 36% of the full load, with 400V input and 2.5 kV/2.77 A output based on the simulation results.

In this paper, a single stage Quazi Z-Source (qZS) with active switched inductor based high gain DC-DC converter is proposed for grid-connected photovoltaic system. The active switched inductor structure contributes the additional gain factor in the existed qZS DC-DC converter. Whereas, the proposed converter possessing continuous input current and achieve the high voltage gain at lower duty ratio in a single stage. The operating principle of proposed single stage converter in shoot through and non-shoot through state with respect to characteristics waveform depicted in this article. The detail mathematical analysis with consideration of non-idealities and designing equations of active (L and C) components are derived based on the theoretical hypotheses. The proposed converter simulated in Matlab simulation software and results are validating the functionality of theoretical predictions.

Photovoltaic energy systems are one of the most widely adopted distributed generation facilities. This book chapter presents predictive based current and voltage control strategies for four-leg converters employed in grid-connected and standalone photovoltaic energy systems, respectively. The proposed approach employs the novel stationary frame sampled-data models of the four-leg converters with inductive (L) and inductive-capacitive (LC) filters on the output side to predict the control variables such as output currents and load voltages. These predictions are performed using all the possible switching states of four-leg converters. The objective of minimizing the error between reference and predicted variables (load currents or voltages) is fulfilled through a cost function in the predictive control schemes. In addition, the voltage balancing of DC-bus capacitors is considered with the four-leg neutral-point clamped converters. The optimal switching states corresponding to the minimal cost function value are chosen and directly applied to the converter. The predictive control strategies fulfil the control requirements such as load current/voltage control, DC-bus voltage balancing, and neutral-leg switching frequency minimization. The simulation and experimental studies conducted using unbalanced and nonlinear loads to validate the proposed predictive control strategies.

Wind energy conversion systems have become mature and competitive with conventional and other renewable energy sources. Electric generators, power converters, and control systems ensure safe, efficient, reliable, and high-performance operation for wind energy systems, while meeting the strict grid codes. This book chapter presents power conversion systems and predictive control strategies for permanent magnet synchronous generator, squirrel cage induction generator, and doubly-fed induction generator-based wind energy conversion systems. Various forms of predictive control techniques including predictive current control, predictive torque control, and predictive power control are discussed with case studies. The discrete-time models of overall system are presented in terms of power converter switching states. The predictive control strategies fulfill the control requirements such as maximum power point tracking, regulation of DC-link voltage, grid synchronization, generation of reactive power to a three-phase grid, and fault-ride through operation. The intuitiveness of material presented in this book chapter allows readers extending the predictive control strategies for other power conversion applications.

With the increasing popularity of electric vehicles, there is an urgent demand to shorten the charging time, so the development of high-power charging stations with fast chargers is necessary to alleviate range anxiety for drivers. The charging station based on the neutral-point-clamped (NPC) converter can bring many merits, but it has unbalanced power problems in the bipolar dc bus. To solve this issue, comprehensive dc power balance management (PBM) in conjunction with high-power three-level dc–dc converter based fast charger is proposed in this paper. The active dc power balance management (APBM) is proposed to assist the central NPC converter in balancing power so that the additional balancing circuit is eliminated; while the passive dc power balance management (PPBM) is proposed to eliminate the fluctuating neutral-point currents and to ensure the balanced operation of fast chargers. The principles of APBM and PPBM are researched, the efficient integration between them is studied, and the overall control scheme for the fast charger is proposed. The power balance limits of APBM are explored, while the circulating currents of PPBM are analyzed. Simulation and experimental results are presented to verify the effectiveness of the proposed fast charger with PBM functions.

This paper proposes a model predictive control (MPC) strategy for a nested neutral point-clamped (NNPC) converter to control output currents and voltages of flying capacitors. The NNPC converter is a four-level converter topology for medium-voltage applications with interesting properties such as operating over a wide range of voltages (2.4–7.2 KV) without the need for connecting power semiconductor in series, high quality output voltage, less number of components compared to other classical four-level topologies. A discrete-time model of the converter is presented and all the control objectives are formulated in terms of the switching states. During each sampling interval, the predicted variables are assessed by the cost function and the best switching state which gives minimum value for the cost function is selected and applied to the converter gating terminals. The performances of the NNPC converter and predictive control scheme are verified through MATLAB/Simulink simulations and their feasibility is evaluated experimentally.

Multilevel power converter control is more efficient and flexible nowadays thanks to microprocessors. They allow to have a dynamic system with the Model Predictive Control algorithm. Many medium-voltage voltage source inverters use three-level Neutral-Point Clamped technology. There are two types of Model Predictive Control: Continuous Control Sets and Finite Control Sets. This paper uses the finite control model prediction control algorithm to control stacked Neutral-Point Clamped forming a thirteen-level Cascaded H-Bridge multicellular converter symmetric. The highly dynamic performance of multicell converters controlled by the Model Predictive Control are used to predict the current that feeds a three-phase line by inverter who are using of low-voltage components such as 1400-V IGBTs that are mass produced with a cost advantage over high-voltage (>1700 V) IGBTs. The 3rd harmonic injection method is introduced to boost the output voltage of each H-Bridge.

The authors Dekka et al. proposed a model predictive control with common-mode voltage injection for modular multilevel converters in the paper published in IEEE Trans. Power Electron. , vol. 32, no. 3, pp. 1767–1778, Mar. 2017. As a part of implementation and analysis, a detailed mathematical model of various current components including input current ( $i_s$ ), output current ( $i_x$ ), and circulating current ( $i_{xz}$ ) are developed. During the review, we found some minor mistakes in the discrete-time model of the circulating current. In this correspondence, the authors present a detailed derivation of the revised circulating current model.

This paper provides guidelines for the MATLAB-based simulation and dSPACE-based real-time implementation of predictive current control scheme for grid-connected two-level voltage source converters. A step-by-step procedure for the calculation and extrapolation of reference grid currents, and design of predictive model and cost function is provided. The predictive model uses grid voltages, grid currents, DC voltage, system parameters, and discrete-time mathematical model of the system to calculate the future values of grid currents. The cost function evaluates the error between reference and predicted grid currents and selects an optimal switching state based on the minimum error value. The proposed design and implementation approaches are validated by the simulation and experimental results. This paper serves as a valuable reference for novice readers in the model predictive control area.

In this paper is proposed a finite control-set model predictive control (FCS-MPC) strategy which uses a two-sample-ahead prediction horizon to achieve high-performance operation for a three-phase four-leg neutral-point-clamped (NPC) inverter with an output LC filter. The control strategy is proposed in order to minimize the error between the output voltages and their references, maintain equal voltage among the dc-link capacitors, and reduce the overall switching frequency of the inverter. One-sample-ahead and two-sample-ahead prediction horizon are evaluated and compared in terms of reference tracking error and THD, under steady-state and transient operating conditions with linear and non-linear loads. The experimental results demonstrate that the proposed two-sample-ahead prediction horizon is more suitable for high power applications where lower switching frequency operation is mandatory.

This paper presents a comprehensive study on the state-of-the-art and emerging wind energy technologies from the electrical engineering perspective. In an attempt to decrease cost of energy, increase the wind energy conversion efficiency, reliability, power density, and comply with the stringent grid codes, the electric generators and power electronic converters have emerged in a rigorous manner. From the market based survey, the most successful generator-converter configurations are addressed along with few promising topologies available in the literature. The back-to-back connected converters, passive generator-side converters, converters for multiphase generators, and converters without intermediate dc-link are investigated for high-power wind energy conversion systems (WECS), and presented in low and medium voltage category. The onshore and offshore wind farm configurations are analyzed with respect to the series/parallel connection of wind turbine ac/dc output terminals, and high voltage ac/dc transmission. The fault-ride through compliance methods used in the induction and synchronous generator based WECS are also discussed. The past, present and future trends in megawatt WECS are reviewed in terms of mechanical and electrical technologies, integration to power systems, and control theory. The important survey results, and technical merits and demerits of various WECS electrical systems are summarized by tables. The list of current and future wind turbines are also provided along with technical details.

This paper proposes two novel dc/dc choppers with dc circuit breaker functionality for HVDC transmission lines. These converters feature step-up and/or step-down functions with instant interruption of short-circuit faults. Compared to other state-of-the-art converter topologies described in the literature, the proposed topologies have better control functions, lower manufacturing costs and reduced energy losses. A double closed-loop controller is designed to regulate the inductor current and output voltage of the converters. An auxiliary controller is also proposed to ensure proper shut-down of the circuit breaker in the event of dc short-circuit faults. The simulation and experimental results are presented to validate the effectiveness of the proposed converter configurations and control scheme.

This paper presents a finite control set model predictive strategy and its application to the load voltage control of two-level four-leg inverters. The proposed approach uses the novel discrete-time model of the inverter and output LC filter in order to predict the variables to be controlled. These predictions are carried out for the 16 switching states of the inverter and are evaluated using a cost function. The switching state that forces the load voltages to be closest to their respective references is chosen and applied to the inverter. The behavior of the predictive controller has been investigated, and the changes to both inductive and capacitive filter parameters have been considered. In order to improve the reliability of the fourth leg as well as the overall inverter efficiency, a solution is proposed, which combines hardware and software reconfigurations. The feasibility of the proposed method is verified through simulation and experimental results considering single-/three-phase, balanced/unbalanced, and linear/nonlinear loads.

In this paper, a new medium voltage power converter topology using a diode rectifier, three-level boost (TLB) converter, and neutral-point-clamped (NPC) inverter is proposed for a high-power permanent magnet synchronous generator-based wind energy conversion system. The generator-side TLB converter performs the maximum power point tracking and balancing of dc-link capacitor voltages, while the grid-side NPC inverter regulates the net dc-bus voltage and reactive power to the grid. A significant improvement in the grid power quality is accomplished as the NPC inverter no longer controls the dc-link neutral point voltage. A model predictive strategy is proposed to control the complete system where the discrete-time models of the proposed power electronic converters are used to predict the future behavior of control variables. These predictions are evaluated using two independent cost functions, and the switching states which minimize these cost functions are selected and applied to the generator- and grid-side converters directly. In order to comply with the high-power application, the switching frequencies of the TLB converter and NPC inverter are minimized and maintained below 1.5 and 1 kHz, respectively. The proposed topology and control strategy are verified through MATLAB simulations on a 3-MW/3000-V/577-A system and dSPACE DS1103-based experiments on 3.6-kW/208-V/10-A prototype.

The neutral-point piloted (NPP) converter with bidirectional switches produces less switching losses than the neutral-point clamped converter while preserving best qualities of multilevel operation. This paper proposes NPP converter for multiphase power conversion applications. The discrete-time modeling of NPP converter load currents and DC capacitors voltage is presented in terms of switching states. A generalized procedure for the predictive current control (PCC) of two-leg, three-leg, four-leg and five-leg NPP converters is presented. The simulation results validate that the PCC scheme forces the load currents to track their reference currents with less steady-state error and fast transient response while maintaining the DC capacitors voltage balanced during all operating conditions.

The following work introduces the use of a modified four-level medium voltage converter in a back-to-back configuration for its application on wind energy conversion systems (WECS). The proposed converter topology is based on a three-level neutral-point clamped converter (3L-NPC) without clamping diods or power switches, so that dc-link capacitors are in a floating condition respect to the neutral point. The implementation of the back-to-back configuration enables the topology for its application in variable speed SM - Permanent Magnet Synchronous Generator WECS.

The double-star converter (DSC) is a recently introduced medium-voltage 4-level multilevel inverter topology, with a reduced number of active switches. This topology has several advantages over existing commercial topologies (single dc-source, no clamping elements, no bidirectional switches or flying capacitors), which can satisfy the needs of several medium voltage applictions such as pumps, fans and compressors. The main challenge with this topology is the voltage balance of the three dc-link capacitors across the modulation index range. Classic controllers require sophisticated PWM techniques with closed loop compensation to maintain the capacitor voltages balanced. In this paper, a control algorithm based on model predictive control (MPC) is applied to the DSC, allowing a direct regulation of the converter output currents while simultaneously ensuring the dc-link capacitors voltage balance. Simulation results show the effectiveness of MPC when applied to this converter.

Wind energy is one of the fastest growing renewable energy sources. Since 1980s, power electronics technology is being used in commercial grid-connected wind energy conversion systems (WECS) to increase energy capture from wind. This article discusses the state-of-the-art and emerging power electronics for fixed-speed, semivariable speed, and full-variable speed WECS. The single-, two-, and three-stage power electronics are presented in low-voltage and medium-voltage categories for variable-speed WECS. The grid integration of wind farms is discussed with respect to high-voltage alternating current and direct current transmission systems. The future trends in high-power WECS are also reviewed.

In this paper, a model-predictive control of medium voltage, grid-tied four-level diode-clamped inverter for use in high-power wind energy conversion systems is presented. The control objectives such as regulation of net dc-link voltage, reactive power generation to meet the grid operator request, dc-link capacitor voltages balancing, and switching frequency minimization are included in the cost function. The latter objective is an important requirement for high-power converters, and this has been achieved without any modifications to the software or hardware configuration. The future behavior of the grid currents and dc-link voltages is predicted for all the possible switching states using the discrete-time model of the inverter, dc-link, inductive filter, and grid. The switching state that minimizes the cost function has been chosen and applied to the inverter directly. During different operating conditions, the switching frequency is regulated between 750 and 850 Hz with the help of a lookup-table-based weighting factor, and thus, the proposed methodology appears as a promising tool to control the high-power grid-tied inverters. The results obtained through the MATLAB simulations on 4 MVA/4000 V system and dSPACE DS1103-based experiments on 5 kW/208 V prototype are in a close relationship and thus validate the proposed control strategy.

A new power conversion system is explored in this paper aiming wind turbines rated at the megawatt level. The proposed configuration consists of a medium-voltage, permanent magnet synchronous generator connected to a low-cost three-phase diode bridge rectifier, a dc-dc four-level boost converter as the intermediate stage, and a four-level diode-clamped inverter on the grid-side. The dc-link capacitor voltages are balanced by the boost converter, and thus the control complexity for the grid-tied inverter is greatly simplified. To control the boost converter and grid-tied inverter, a simple method based on a two-step model predictive strategy is presented. In the first part of this paper, the continuous- and discrete-time modeling of the proposed power conversion system is analyzed. The control objectives such as maximum power point tracking, dc-link capacitor voltages balancing, regulation of net dc-bus voltage, reactive power generation, lower switching frequency operation, and common-mode voltage minimization are considered in the design of controller.

In this paper, a simple model predictive current control strategy is proposed for four-leg inverters to deliver power to the (un)balanced/(non)linear loads. Unlike classical control schemes, the proposed method does not require current PI controllers or a complex modulation stage. The discrete-time model of the inverter, filter, and load are used to predict the future behavior of the load currents for each of the 16 possible switching states. The control method chooses a switching state that minimizes the error between the output currents and their references. The performance of the proposed method has been investigated for perturbations in the filter and load parameters. The neutral-leg switching frequency reduction algorithm is also proposed to improve the efficiency of the converter. The feasibility of the proposed method is verified in this first part, through simulation results.

This paper describes the experimental implementation of the model predictive current control algorithm for a two-level four-leg inverter operating under balanced, unbalanced, and nonlinear loading conditions. The proposed scheme is designed to predict the future behavior of the load currents for each of the 16 possible switching states of the converter. The control method chooses a switching state that minimizes the error between the output currents and their references. The algorithm is embedded using a MATLAB/Simulink software environment, and experimental results based on the dSPACE DS1103 controller are provided. These results verify the advantages of the proposed control strategy in terms of robustness under filter and load parameter variations, average neutral-leg switching frequency reduction, reference tracking error, and percentage total harmonic distortion.

This paper describes a matrix converter with a three-phase input and single-phase output that can be used as a building block for high-power cascaded converters. In this paper a sinusoidal pulse width modulation technique with a linear controller is proposed for the single-phase output matrix con¬verter. The proposed modulation and control will be used in the cascade configurations for high-power applications. Simulation and experimental results are presented to validate the proposed modulation and control approach.

In this paper, finite control-set model predictive control of two-level and three-level four-leg voltage source converters (VSCs) is presented. The predictive current control (PCC) and predictive voltage control (PVC) schemes are presented considering grid-connected and standalone distributed generation applications respectively. The discrete-time model of load currents, load voltages, DC-link capacitors voltage and VSC terminal voltages is formulated in terms of four-leg converter switching states. A cost function is defined with the PCC scheme to minimize the error between reference and predicted load currents. Similarly, in PVC scheme, the cost function deals with the minimization of error between reference and predicted load voltages. The balancing of split DC-link capacitors voltage is considered with the three-level four-leg VSCs. The optimal switching states which minimize the cost function are chosen and applied to the four-leg VSC directly without involving linear regulators and modulation stage. The proposed PCC and PVC strategies are verified through simulation results considering single-/three-phase, balanced/unbalanced and linear/nonlinear loads.

This paper proposes a variable sampling frequency model predictive control (VSF-MPC) to achieve fixed-switching frequency operation for a neutral-point clamped (NPC) inverter. The proposed control technique simultaneously considers load current control, balancing of DC-link capacitor voltages, mitigation of common-mode voltage, and elimination of even-order and inter-harmonics in the load current harmonic spectrum, while maintaining fixed-switching frequency operation. The challenges associated with weighting factor design are also addressed. Through the simulation and experimental tests on an NPC inverter, it has been demonstrated that the proposed method preserves high dynamic response nature of MPC, and predefined harmonic spectrum characteristic of classical space vector modulation.

This paper proposes an effective voltage balance control (VBC) together with a new modulation technique for a high-power bidirectional three-level dc-dc converter based fast charger. The proposed VBC method can assist charging stations in balancing the dc-bus voltages so that additional balancing circuits are eliminated, leading to improved system efficiency. Meanwhile the proposed modulation method is not only intuitive to be implemented, but also have merits of reduced switching frequency, resulting in lower switching losses. The modulation principle is formulated, and its effective combination with the voltage balance control are analysed in detail. Based on which, the overall control scheme for the charging system is proposed. Simulation results are presented to validate the effectiveness of the proposed methods.

In this paper a Predictive Current Control strategy is proposed for constant switching frequency operation and verified with a neutral-point-clamped (NPC) converter for load current regulation and DC-link capacitor voltages balancing. The aim of this control technique is to obtain a modulated waveform at the output of the converter, whilst maintaining all the desired characteristics of FCS-MPC. The feasibility of this strategy is evaluated using simulation and compared to the classical FCS-MPC strategy.

Advances in power electronic converters technology along with the wide range of applications require sophisticated digital control schemes. In the recent years Finite Control Set Model Predictive Control (FCS-MPC) has been successfully proposed as an alternative to the traditional control techniques, due to its fast dynamic response, easy inclusion of nonlinearities and constraints in the control algorithm and the ability of incorporate several control requirements in one cost function. However, FCS-MPC is characterized by a variable switching frequency which can cause a degradation in system performance, or demand higher output filtering. In this paper a Modulated Model Predictive Control (M2PC) strategy is proposed for constant switching frequency operation and verified with a neutral-point-clamped (NPC) converter for load current regulation and DC-link capacitor voltages balancing. The aim of this control technique is to obtain a modulated waveform at the output of the converter, whilst maintaining all the desired characteristics of FCS-MPC. The feasibility of this strategy is evaluated using simulation and compared to the classical FCS-MPC strategy.

This study proposes a generalised approach based on model predictive strategy for the current control, dc-link capacitor voltages balancing, switching frequency reduction and common-mode voltage mitigation in multilevel diode-clamped converters. A generalised discrete-time model of the converters is presented, where all the control objectives are formulated in terms of the switching states. The control goals are expressed as a cost function, and with the help of suitable weighting factors these goals are met simultaneously. The cost function minimisation is used as criteria for choosing the best switching state which would be applied to the converter during next sampling interval. The real-time digital control issues such as computational burden and delay compensation are also discussed. The feasibility of the proposed method is verified by simulations in three- to six-level converters, and by experiments in three- and four-level converters.

This paper proposes a novel architecture for plug-in electric vehicles (PEVs) dc charging station at the megawatt level, through the use of a grid-tied neutral point clamped (NPC) converter. The proposed bipolar dc structure reduces the step-down effort on the dc–dc fast chargers. In addition, this paper proposes a balancing mechanism that allows handling any difference on the dc loads while keeping the midpoint voltage accurately regulated. By formally defining the unbalance operation limit, the proposed control scheme is able to provide complementary balancing capabilities by the use of an additional NPC leg acting as a bidirectional dc–dc stage, simulating the minimal load condition and allowing the modulator to keep the control on the dc voltages under any load scenario. The proposed solution enables fast charging for PEVs concentrating several charging units into a central grid-tied converter. In this paper, simulation and experimental results are presented to validate the proposed charging station architecture.

This paper presents a new, simple and generalized approach to calculate flying capacitor currents for an n-level flying capacitor converter without the use of look-up tables. The performance of the proposed method has been studied for a three-, fourand five-level flying capacitor converter in MATLAB/Simulink environment. Introduction Multilevel voltage source converters are the most attractive converters for medium-voltage (MV), high power applications. The multilevel structure has some features including; high voltage capability, low dv/dt’s, smaller output filters, and reduced common mode voltages [1]-[6]. The most commercialized multilevel converter topologies are the diode-clamped, flying capacitor, and cascaded H-bridge converters [7]. Compared with the other two configurations, flying capacitor (FC) converter does not require clamping diodes and isolated dc sources. DC capacitor voltages balancing of an n-level diode-clamped converter has practical limitations. To ensure DC-link capacitor voltages balancing during all operating conditions, an additional power circuitry is required [8]. Compared with an n–level diode-clamped converter, the n-level FC converter constitutes simple structure and control [7]. For FC multilevel inverter topologies, several modulation strategies have been developed [8]-[14]. Generally, the multilevel converters are intended to be used in high-power and medium -voltage applications; therefore two major challenges in the selection of modulation strategies should be considered; power quality and switching frequency. The switching frequency should be minimized as much as possible to reduce the switching losses in the converter which is almost about 600Hz for medium-voltage applications. One of the modulation strategies that are the most preferred for high power multilevel converters is space vector modulation (SVM). The SVM method benefits from redundancy for a given switching states. This redundancy makes the flexibility to select the best switching states to satisfy different criteria including, output harmonic content, common mode voltage, and regulating voltages of capacitors in multilevel converters [10]-[14]. Various types of SVM algorithms have been proposed in the technical literatures [10]-[11]. In order to implement SVM-based modulation scheme, the following steps should be followed; transform the reference voltage from three-phase system to two-phase system, identify the sector and the triangle where the reference vector is located, determine the three adjacent switching vectors, calculation of duty-cycle corresponding to the switching states, investigate the redundant switching state, select the best switching states based on minimization of the defined cost function and finally generate and apply the gating signals to the converter. The flying capacitor voltages should be maintained at their desired nominal values to ensure proper operation of an FC converter. The capacitor voltages can diverge/drift in different conditions [15][16]. There have been proposed some techniques to balance and regulate the capacitor voltages [15]– [21]. The methods proposed in [15]-[19] use open-loop control technique based on the phase-shiftedPWM technique, which benefits from natural self-balancing property. However, in practice, the switching frequency should be high or an external control algorithm is required to balance the capacitor voltages due to non-idealities, system imbalance, and disturbances [20]. Another method is using extra power circuitry to regulate the capacitor voltages [21]. The approach proposed in [21] shows a closed-loop space vector modulation (SVM)-based capacitor voltage balancing method. This method uses the SVM switching state redundancy to regulate the capacitor voltages at their desired values. The proposed strategy in [23] does not have any deteriorating impact on the ac-side waveforms and is general and applicable to an n-level FC converter with any number of levels. The work in [22] demonstrate the balancing of the FC voltages for a fourlevel diode clamped converter by selecting suitable cost function and using SVM. In order to minimize the cost function to balance flying capacitors, the current of flying capacitors should be measured. However, to reduce the cost and complexity associated with the current sensors, the relationship between the flying capacitor currents and output currents can be obtained based on a table defined for different switching states [22]. When the number of levels increases the dimension of the table will increase and consequently the complexity of the calculation of the flying capacitor currents will increase significantly. In this paper, a new, simple and generalized method is proposed to calculate flying capacitor currents for an n-level FC converter. The proposed approach eliminates the use of look-up tables, and thus greatly reduces the complexity of the control algorithm. The performance of the proposed method has been studied for a three-level, four-level and five-level FC converter in MATLAB/Simulink environment. In the following sections, the SVM strategy for an n-level multilevel converter is summarized and the proposed approach to calculate flying capacitor currents based on output currents will be explained and finally simulation results validate the performance of the proposed technique. Review of SVM for an n-Level Flying Capacitor Multilevel Converter The procedure for the implementation the SVM strategy for an n-level FC multilevel converter, shown in Fig. 1, is summarized based on [22]-[25]. This procedure has the following steps;  Identify the sector and triangle where reference vector is located in α-β coordinate system;  Determine the adjacent switching vectors;  Duty-cycle calculation;  Determine of redundant switching state combinations;  Calculate the average capacitor currents;  Select the best switching states based on minimization of the defined cost function.  Generate the gating signals for the n-level converter. This procedure is explained in [25] in details. In this paper, a new, simple and generalized approach to calculate the average flying capacitor currents for an n-level flying capacitor converter is proposed. This approach facilitates and helps to implement SVM for the multilevel flying capacitor converter in order to regulate voltage of flying capacitors at nominal values. Capacitor voltage balancing strategy Based on the SVM strategy, there are redundant switching states for a given switching state. This redundancy can help to regulate voltage of flying capacitors in a multilevel FC converter. In order to regulate voltage of FCs, the best switching states should be selected among the available redundant switching state to minimize the voltage deviation of the flying capacitors from their nominal values. In order to regulate voltage of flying capacitors, the cost function J can be defined as

In this paper, two fast acting dc circuit breakers are investigated to interrupt the short-circuit faults in HVDC transmission lines. These circuit breakers are realized using dc/dc choppers which can also perform step-up and/or step-down functions. Compared to the existing topologies, the number of active switches in the proposed configurations are minimized to achieve lower initial cost and higher conversion efficiency. A double closed-loop controller based on PI regulators is designed to regulate the inductor current and output voltage of the converters. An auxiliary controller is also proposed to ensure proper shut-down of the chopper in the event of short-circuit faults. The simulation and experimental results are presented to validate the proposed converter topologies and control scheme.

Interharmonics exist in the ac supply currents in ac/dc/ac drives mainly due to the poor decoupled behavior of the dc-link stage. This issue is particularly evident when different input/output operating frequencies are used, causing harmful effects on power transformers and reducing the system efficiency and power quality. Consequently, large interharmonics can be found in converters with single-phase stages, as they require large electrolytic capacitors to filter out the dc-link second harmonic of voltage and current, which is usually not fully accomplished. This is the case of the cascade multilevel converter based on single-phase power cells, where each module has a single-phase rectifier and a single-phase inverter stage that cannot be effectively decoupled with standard size capacitors. This paper shows that it is possible to improve the quality of the power cell input currents when the input/output frequencies are different in the cascade multilevel converter. This is achieved by means of magnetic couplings among the dc-links of the power cells that feed different output phases, while keeping the high power quality on the load side.

This paper presents a novel model predictive current control method for current source inverters (CSI) following the duality with voltage source inverters (VSI). The method is based on the discrete prediction model of the system, including the converter and output filter. The model is used to predict how the system variables will behave for each switching state of the converter. The predictions are evaluated using a cost function that weights the level of accomplishment of the control goals. The switching state with the best performance is then generated. The proposed algorithm predicts the output currents (including the output filter capacitors), ensuring sinusoidal current generation without the need for cascaded control loops, coordinate transformations, and modulation schemes found in traditional solutions. In addition, low switching frequency is imposed by including a new term in the cost function. Simulation results validate the proposed control scheme, with performance comparable to the traditional solutions, especially in terms of the current and voltage harmonic distortion.