The HVDC based electrical energy transmission is being used by decades where the LCC and the MCC are the natural options. The versatility of the MCC option is clearly an advantage over the LCC when it comes to reactive power compensation. But the higher reliability of the LCC option over the MMC is widely recognized where the thyristor-based topology is the main reason. Recent blackouts in interconnected main grids have raised some discussions on what the main criteria should be considered to prefer either solution. This work studies the operating region in terms of reactive power range of both approaches under similar conditions. A detailed modelling of the topologies is used to establish and present the operating boundaries.

This study investigates power injection management in photovoltaic systems integrated into microgrids with voltage unbalances. An advanced technique of modulated predictive control is implemented to address variations in voltage frequency and amplitude, incorporating new algorithms based on the study of the operational region, allowing for an expanded operational range of the system. The findings show notable improvements in the system’s availability under these adverse conditions. It’s concluded that such strategies are essential for ensuring effective integration and sustainability of renewable energies in contemporary microgrids, which are subject to network fluctuations.

The UPQC has been widely used to improve power quality. Therefore, in this new topology, it is relevant to study the limitations in order to obtain maximum benefit. This paper presents the stationary analysis of a three-phase unified power quality conditioner with the injection of active power in the DC link from a solar panel farm. The transformation from abc axes to dq axes is used to convert sinusoidally varying quantities into constant quantities. This allows finding an explicit solution of the system's state variables and inputs for a specific operating condition, which is useful for obtaining the system's operating region. Hence, establishing the voltage variations at the Point of Common Coupling (PCC) and the power factor of the load that the UPQC can compensate, in order to maintain the voltage at the load at nominal values and a specified power factor at the PCC. Another condition imposed in this work is that the topology should not absorb active power from the grid, aiming to reduce the losses of the topology. The preliminary results show that injecting active power from solar panels into the DC link enhances the ability to compensate sags and swells at the PCC.

Nowadays, static power converters have a transcendental role at an industrial level. The two-level converter is still the most used, such as in the case of use in AC electrical machine drives or the inclusion of renewable energies in electrical systems. However, due to its admirable advantages, the multilevel converter is a valid alternative for higher quality and efficiency benefits. In particular, one of the most studied topologies is the cascaded H-Bridge, which can be classified according to its DC voltage ratios as symmetrical and asymmetrical. The latter makes it possible to obtain a high-quality output voltage waveform using fewer inverters per phase. However, this has drawbacks such as: (i) regeneration due to the modulation technique, (ii) asymmetric power distribution among the inverters, and (iii) loss of modularity. In this work, it is proposed to design a modulation technique for the generation of a stepped phase voltage based on the sum of modified square waves generated by H-bridge inverters in cascade with asymmetric DC voltage ratio in order to obtain a distribution of symmetrical active power between the cells and a minimum THD of the output phase voltage. For the above, the minimization of the THD of the output phase voltage is performed. As a result, the DC voltages and firing angles are obtained for each modified square waveform. Thus, for six cells per phase with m = 1.0, 6.976% of THD is obtained, and an efficiency of 95.32%.

The performance of model predictive control of power electronics converters depends upon an accurate discrete-time model to properly evaluate the effect of the control action over the controlled variables. One of the most used methods to obtain a discrete-time model from the continuous-time equations is to use an Euler approximation of the derivative. However, when sampling times are increased, an Euler discretized model may incur in error in the variables. This work presents an alternative discretization method based on the input-state linearization concept of nonlinear control. An auxiliary linear model is obtained which is then discretized by an exact linear approach. The method is illustrated using the dc-dc boost type converter as a case study showing improved results a compared with the Euler approximation.

The need to decarbonate the planet, due to the massive use of fossil energy, has led to turn to employ renewables energies in many applications. Among the most common energy sources are the wind, solar, and sea, being one of the most relevant the solar energy, particularly in some countries as Chile. To transport the energy, solar system must be connected to a middle voltage level lines and therefore different topologies have been proposed where some of them are based on H-Bride. This work presents the use of H-Bridge power converters connected in parallel in the dc side and connected to a transformer in the ac side to pump up to middle voltage level. Additionally, as all phases of the H-Bridge are connected in parallel in the dc side, the third harmonic, typical of this topology, is compensated and therefore the ac waveform results free of low frequency harmonics. To get the maximum power from the solar array, it is employed a maximum power point tracker which uses measuring cells, avoiding oscillations around the maximum power point. The results show the feasibility of the proposal.

Power conversion has gain relevance because of the capacity to transform the electric energy as needed in many applications such as electrical drives, electromobility, reactive power compensation, renewable energies, among others. In this context, the proper control of the power converter may lead to improve the efficiency and protect the entire power converter system. This paper presents a deadbeat control with the capability to enhance the fast dynamic response, typical of this technique, and therefore to be used for current and voltage control applications that require slower dynamic. The proposed technique is implemented in a three-phase power converter with satisfactory results; moreover, this technique is simple and light in computational cost. Finally, to corroborate the proposal, simulations are included with satisfactory results showing an improved dynamic and making the deadbeat control softer as some applications may require.

An interleaved DC/DC power cells-based topology is proposed in combination with a control method for photovoltaic plants. For this, two partial power and two interleaving methods are evaluated in terms of efficiency and performance. The selected topology consists of input-parallel-output-parallel interleaved DC/DC converters, which together with the control strategy, allows a high efficiency photovoltaic system, unlike conventional topologies. However, this type of topology is prone to present an unbalanced power distribution between the DC/DC power cells, mainly due to the natural differences between their components. This paper shows the application of a power balancing control strategy for interleaved partial power converters, which guarantees an equitable power distribution, therefore, it enables a correct sizing of the components. The simulation results show the correct operation of the power cells, in terms of overall high efficiency and power distribution among the power cells.

Hybrid transformers are an attractive solution for improving power quality problems in distribution grids, due to the capability of power converters to provide precise current and voltage regulation. A hybrid transformer using a low-frequency transformer, which processes the biggest amount of power, and two converters connected in series and shunt, with an additional cascaded H-bridge converter connected in parallel, is presented. The use of a series converter on the primary side and a shunt converter on the secondary side allows to provide voltage regulation and load current compensation, respectively. Both converters improve the transformer power quality, extending its lifetime. Meanwhile, the cascaded H-bridge converter establishes a common DC-Link to support both converters operation. In this work, the model, control, and simulation results of the proposed configuration are presented, showing the improvement on the distribution transformer.

This paper proposes a hybrid control scheme based upon both a linear and a predictive control approach for a grid-tie inverter for photovoltaic applications. The proposed strategy uses the complex representation of the switching states and splits them choosing the best one without using an iterative loop. The resulting algorithm, in terms of the dynamic and static response, performs like the traditional Finite Set Model Predictive Control (FS-MPC). However, the proposed scheme is easy to implement, it does not need to tune parameters nor need a cost function and nor require iterating all the possible states to choose the best. Over the abovementioned advantages, it has the capability to operate the photovoltaic module at the maximum power point (MPP) and the ability to impose a sinusoidal current at the grid side with a unitary displacement power factor. Preliminary results are presented to validate the proposed control method.

Power quality has become a concern nowadays, due to the increasing and highly variable renewable energy systems connected to the distribution network and also due to the nonlinear loads that pollute the grid. A solution to this problem is the use of compensators to attenuate these disturbances. The use of a hybrid transformer composed by a conventional low-frequency transformer in conjunction with a power converter has become an interesting solution due to the high controllability and overall efficiency. In this paper, the model, control, and simulation of a hybrid transformer, where the converter is connected in series with the primary side and in parallel to the secondary side, is presented. Results show the correct operation of the converter in steady and transient state, successfully compensating grid voltage variations and load non-linear currents.

This paper proposes a mixed linear control and model predictive control (MPC) scheme with extended horizon for a neutral point inverter topology (NPC) for photovoltaic applications connected to the AC network. The strategy is able to minimize the unbalance of the voltages of the capacitors in the DC link and to draw a sinusoidal current on the network with a unity displacement power factor. Unlike other MPCs, the resulting algorithm is easy to implement, the weighing factors of the cost function are not needed, and the computational cost is reduced. These advantages are added to the ability to operate the photovoltaic module at the point of maximum power (MPP).

Finite Control Set Model Predictive Control is an emerging alternative for the control of power converters. Its main advantages are its conceptual simplicity, fast control response, flexibility and direct consideration of non linearities as well as constraints. Due to computational constraints, short prediction horizons are usually desired in power converters. However, control issues may appear when applied in topologies that exhibit non-minimum phase behavior such as active front end rectifiers and boost dc-dc converters. This work proposes the use of the concept of statically equivalent outputs in order to control these systems with the shortest prediction horizon. The proposed predictive controller partially inverts the plant dynamics, determining an auxiliary output by means of nonlinear control tools. Theoretical and simulated results show the feasibility of the proposal.

This paper presents the use of a real-time simulation platform for the study of a high-power cycloconverter drive. Advantages of this strategy are reported, especially when compared to off-line simulation tools when evaluating electrical systems in presence of complex high-power static converters. Characteristics of a cycloconverter drive are presented, together with a real-time simulation model running in a multi-core platform from OPALRT. Time-domain simulation results with a time-step of 50μ s are shown. Capabilities of the model are exemplified with the analysis of two harmonic-current compensation strategies and the integration of the model with an external power converter for a power-hardware-in-the-loop application.

This work shows the use of the operating region of a D-STATCOM based on multilevel current-source inverters to define its operating point and its LC filter. A multilevel current-source D-STATCOM model is defined to compute its operating region and obtain a relation between reactive power compensation and the device power losses. Using this relationship the losses costs of the reactive power compensation is computed and used to define a methodology to get an operating point and design the LC as a function of the desired cost for nominal power compensation. The methodology is tested in the design of a 125kVA/380V distribution grid, where simulation results corroborate the analysis, including changes from one operating point to another, in open loop, to show the compensation capabilities, the power topology effort and the grid mains variables with compensation.

This paper proposes an algorithm that effectively allows a PV plant to inject a given amount of reactive power into the grid regardless of the irradiance and temperature levels. In the presence of irradiance (daylight hours), the system injects active and reactive power into the grid, and the losses of the topology are supplied from the PV. Under absence of irradiance (clouds and at night) the system keeps the reactive power level into the grid, and the losses of the converter are supplied by the grid. Moreover, the proposed algorithm is capable of injecting a constant and given amount of reactive power during the transitions among the operating modes regardless of the active power level being injected into the grid. Thus, providing an overall robust ancillary service to support the grid.

This paper proposes an algorithm capable of estimate the global maximum power point of a large photovoltaic (PV) array system operating under partially shaded conditions. The power-voltage characteristic of a photovoltaic array is a nonlinear function that becomes more complex under partial shading conditions, in fact, the power-voltage curve may exhibit multiple local maximum power points. The proposed algorithm uses two PV reference cells, every 900 m2, one operating in open-circuit and the other one in short-circuit, to estimate the solar radiation and the ambient temperature conditions of the PV arrays. The results show an estimation error of the ambient conditions lower than 1% of the actual values. As a result, the arrays provide the maximum power possible for any distribution of irradiance and temperature conditions.

This work explores reactive power compensation on a small photovoltaic generation at residential installation to enhance reliability on a Smart Grid. In order to accomplish this goal, the modulator values of the inverter are determined to obtain the allowable range of reactive power compensation in a photovoltaic system connected to the grid trough out a single-phase voltage source inverter. Mathematical validation in addition to simulations and experimental results are included to validate the proposed approach. Although the method is used in small generation systems, it can be extended to large power systems.

To generate medium and high voltage with low Total Harmonic Distortion (THD) are used multilevel converters, through use of low voltage semiconductors devices, for applications as AC drives, PV farms and active power filters. This converter uses between the AC supply and the power cells a multipulse transformer, which is in charge of the harmonic cancellation of the input current harmonics generated by the three - phase rectifier. This transformer is expensive, heavy, bulky and must be designed according to the power, and the number of power cells. This work uses a THD minimization strategy based on a Finite Control Set - Model Predictive Control (FCS - MPC), which propose change the multipulse transformer by a simpler transformer, achieving a low THD in the input current of multi-cell AFE rectifier. The work is centered in the solution in one disadvantage of the FCS - MPC, high switching frequency. To solve this drawback, an additional objective function is used, which reduces the states changes of the power switches. Unfortunately, because of this the FCS - MPC loses an advantage, fast dynamic response to changes. In order to improve this issue, is necessary a modified control scheme, which detects the steady state and transient state to change the objectives of the FCS-MPC. Simulation results shows the feasibility of the proposed control.

Multi-cell topologies based on three-phase input / single-phase output power converters have the drawback of dealing with an important oscillatory second harmonic current in the DC link. This requires the use of a large DC link capacitor in order to minimize the DC link voltage ripple. Different control schemes have been presented to reduce the second harmonic generated for the H bridge inverter aiming the design of the DC link capacitor without oversizing it. However, this is achieved at expense of much distorted AC supply currents and increased modulating signals amplitudes. In this paper, these problems are accurately characterized with the objective of mathematically identify the limitations of those schemes.

Proportional Resonant Control (PRC) is a well-known control technique applied on ac systems in order to ensure zero steady state error for sinusoidal references. However, this control technique is not suitable to operate in a variable frequency environment, which is typically found on weak micro grids and aircraft systems. Once the controller is designed, the resonant frequency is fixed, and therefore no zero steady state error can be ensured under operating frequency fluctuations. This paper extends the resonant control approach to operate in a larger frequency range in order to be applied in power inverters and achieving zero steady state error. A back-to-back topology case is studied, connected to a distorted supply (with variable frequency) feeding a critical load. The load-connected to the back-to-back topology- requires a given frequency and amplitude voltage which is easily achieved if the grid side converter successfully regulates the dc link voltage. In addition, a desired power factor at the point of common coupling can also be imposed. The approach is based in a discrete implementation of the PRC, where its resonant frequency tracks the grid frequency, independently of grid frequency variations. This issue is mathematically demonstrated and tested with accurate results.

This paper presents a deadbeat control technique applied in a voltage source rectifier to regulate both the dc voltage (active power) and reactive power injected to the grid. As the deadbeat control is based on the system model, it leads to a faster response, without overshoot and no need to tune the controller parameters. Hence, it is used to fully control the voltage source rectifier, achieving a fast dynamic response for both the dc voltage and the power factor at the point of connection. However, there are some issues related to the high amount of power required to reach the references -especially in the dc voltage- in a few control steps. The proposed technique also protects the equipment by limiting the maximum power drained to/from the source. The mathematical development is made as a function of the converter power in order to limit it, but at the same time tracking the references with high dynamics, characteristic typical of deadbeat control.

This paper proposes a control strategy for a single-stage, three-phase photovoltaic (PV) system connected to a distribution network. The control entails obtaining the maximum power point of the PV system by means of a control strategy that is based on an inner current-control loop and an outer DC-link voltage regulator. The current-control mechanism decouples the PV system dynamic from those of the network and searches for unitary power factor at the grid side. The DC-link voltage-control scheme achieves maximum active power output. The maximization of the output power is performed by operating the PV array at its maximum power point that is estimated by a proposed technique that uses two PV measuring cells, one operating in open-circuit and the other one in short-circuit.

The control strategies that use modulation techniques have great acceptance in the current control of static power converters. Indeed, they offer a wide variety of alternatives to address the steady-state characteristics required by the system. Nevertheless, its computation and modulation delay negatively affects its dynamic performance. In order to improve the time response of the system, the modulator is avoided and the strategies of direct choice of the switching state have been presented. They can provide a very fast dynamic response; however, the absence of switching state sequences makes more complex the task of establishing specific switching features for improved steady-state performance. In this work, a control scheme that selects a specific control strategy according to the operating condition of the system is proposed. This allows using modulators to satisfy the switching characteristics required in steady-state and avoids its use when a rapid dynamic response is required. In addition, a soft transition method between the control strategies is presented to prevent unwanted behaviors when these are alternated. The proposed control scheme allows simplifying the design and keeps the main advantages of each selected strategy. To validate the scheme, experimental results are obtained for a control structure that alternates between a finite set model predictive control (direct type for rapid dynamic response) and a proportional integral (PI) control with sinusoidal pulse width modulation (SPWM) (modulated type for high steady-state performance).

Multilevel converters are widely used in medium voltage applications. One of the most popular topologies in this field is the 18 pulses diode rectifier, which uses a muItipuIse transformer that realizes a current harmonics cancelation that are generated by the three phase diode rectifiers. In this work an efficiency comparison of the aforementioned topology and a Multi-Cell Active-Front-End (AFE) Rectifier operating with Finite Control Set - Model Predictive Control is performed. This efficiency comparison is focused on the rectifier losses divided into two types. The first one is the semiconductors switching and conduction losses. The second one evaluates the transformer losses, which are studied under two criteria: copper losses (Standard IEEE C57.10-1998) and the K - Factor (Standard IEEE / ANSI C57.110). The results show that the diode based rectifier topology has lower semiconductors losses, while the topology based on AFE rectifiers has lower transformers losses and a less complex design. Indeed, a reduction of a 7.2% in copper losses is achieved in the transformer secondary with respect to a multi-pulse transformer secondary.

Current source converters (CSC) are used in AC-Drives and Electrochemical applications requiring large and controlled currents. Usually, a controller/modulating block using pulse width modulation is employed to provide current control. Although, several works describing predictive controllers have been presented for both two-level and multilevel voltage source converters. Only a few report predictive control in CSC This paper proposes a predictive control strategy for CSC. The performance of proposed controller is compared with linear PI controllers in terms of speed, harmonic distortion and switching frequency. It is shown that the proposed strategy is suitable for Modular CSC. Theoretical analysis and simulation results that validate the proposed controlled are shown.

This work compares multi-cell topologies based on Current Source Inverters (CSIs) which are connected in a Cascade H-Bridge (CHB), where the large DC inductor size needed to compensate the oscillating power drained by the inverter is the main drawback. In order to reduce the DC inductor size, two compensation methods which compensated the oscillating power are evaluated and compared with the basic topology that use a large DC inductor. The first method consists in reducing the oscillating power through active compensation, which needs to supply the oscillating power from the rectifier, and the second method consists in reducing the oscillating power through magnetic coupling. The comparison considers the operating region, the DC inductor size, the magnetic power requirements, and the cell supply voltage requirements. Because the operating region is based on the converter and load parameters but independent of the DC inductor value, the passive parameters are designed as a function of the imposed rectifier input current quality and the load voltage THD. The comparison is done for a 9.33 MVA topology, simulating in PSEVI® in order to corroborate the components design and both the input current and load voltage quality. The operating region comparison is computed with one and two cells per phase and the achieved DC inductor reduction.

Single-phase inverters have gained important acceptance last time. This is because single phase inverters have been used in renewable energy, ac drives and many other applications and controlled by name ways as linear, nonlinear predictive between others. This paper studied the control of a Single-Phase Current Source Inverter (SP-CSI) for multi-cell and three-phase applications. Cascaded H-Bridge (CHB-CSI) topology is formed by the stack of SP-CSI, with all advantages that CHB implies, as modularity and commutation noise reduction. However the control for single-phase systems cannot be achieved by Park Transformation if the current load or the current source are unbalanced. Therefore, this work proposed the Proportional Resonant Control (PRC) for the CHB based on CSIs, where the control study is formulated in continuous as well as discrete time. To complete this study a stability analysis is accomplished showing the feasibility of this control for CSI. Finally, simulation results are shown in order to corroborate the mathematical and theoretical analysis.

This work presents a case study of a modular photovoltaic (PV) plant where PV panel arrays are connected to the grid through cascaded single-phase current-source inverters. It is shown that, under non-uniform insolation conditions of the PV arrays, the output voltages of the cascaded inverters become unbalanced. Therefore, a dc voltage elimination control loop is proposed to balance the output voltage of the H bridges. Additionally a control technique called virtual synchronous generator (VSG) is applied to the PV plant in order to support the control of the grid frequency emulating an inertial response and providing damping and droop power. For the simulated cases the PV plant was always capable of performing the VSG functions, in spite of the unbalance condition of the output voltages of the H bridges. However, when the proposed dc voltage elimination control loop was in operation the maximum peak output voltage and the amplitude of its fundamental component were reduced in 13.3 % and 27 % respectively.

In the last decades, finite control set-model predictive control (FCS-MPC) has been extensively investigated. This control strategy uses the system model to determine the optimal input that minimizes a predefined cost function. This procedure is performed by evaluating the admissible inputs of the converter model. In order to achieve a proper performance of the control strategy, a small sampling time must be used. In practice, the computational effort and processing time are critical factors that depend directly on the number of admissible states of the topology. With the objective of reducing the execution time needed by the algorithm, it is possible to take advantage of the high degree of parallelism that can be obtained from a field-programmable gate array (FPGA). This paper deals with the implementation of FCS-MPC in an FPGA XC3S3500E to control a power cell of a cascaded half bridge (CHB) converter. The design is divided into subparts, called modules, which can be projected to control multiple cells using only one chip. In addition, with the aim to restrict the use of hardware to the available resources, the document presents a series of considerations related to the algorithm and its implementation. This paper presents a detailed guide with emphasis on the design and outlining of each module in order to reduce the developing times for researchers in the area of power converters.

Nowadays the control of medium voltage motors has two main alternatives for its development: voltage source inverters (VSI); or current source inverters (CSI). The cascaded multilevel inverters derive from high voltage, high power quality and high reliability requirements in both development alternatives. Up to now, the cascaded multilevel converters have been implemented using voltage source power cells. However, they can also be implemented using current source units. One factor against CSIs is the large size of the inductive filters needed in the DC links, especially when single-phase inverters are considered. This paper presents a current-source cascaded multilevel converter (CS-CMC), based on single-phase power cells and their implementation alternatives, which enable a reduction in the sizes of the DC-link inductors. It is demonstrated that these sizes can be reduced using magnetic couplings between the DC links of the power cells. These magnetic couplings can eliminate second harmonic currents, as well as other even harmonics of current in the DC link of the power cells. This work asserts that the implementation of a current-source cascaded multilevel converter, based on single-phase power cells, must consider magnetic couplings between its DC links. Design results and the simulation of a development alternative of the system, aim to demonstrate the feasibility of implementing the cascaded multilevel converter.

Multi-cell converters allow the use of AC motor drives for medium and high voltage level applications using low voltage semiconductors. This type of converter has a multi-pulse transformer which performs the cancellation of the low frequency harmonics generated by the three-phase diode rectifiers. Despite this advantage, the multi-pulse transformer is bulky, heavy, expensive, and must be designed according to the number of power cells, making the transformer topology dependent. This work proposes to reduce the complexity of the transformer in multi-cell converters using Active Front End rectifiers in combination with a Finite Control Set - Model Predictive Control strategy. This is achieved by the strategy as it emulates the multi-pulse transformer harmonic cancellation thanks to the predictive algorithm and the generation of input current references with a phase shift angle for each Active Front End rectifier.

Multilevel inverters are the alternative for medium voltage applications. Within the inverters types there are symmetric and asymmetric topologies. The asymmetric inverters have different DC voltage values. The most common topology is when the different cells are implemented in cascade arrangement, where the DC voltage are in multiples of 3, obtaining an AC voltage with 3n= 27 levels (n = 3 cascaded inverters). This topology provides a load voltage with low harmonic content, THD <; 3%. However, this high quality voltage has a non-negligible drawback, which is the presence of regeneration in some of the inverters, independent of load type. This phenomenon is due to the modulation technique (Nearest Level Modulation) used by this inverter. In this work, the asymmetric 15 level inverter is presented. This inverter is designed to avoid the regeneration problem - power flow from the load to the inverter - in some of the power cells. This is achieved by obtaining the firing angles associated with the power cells considering a minimum load voltage THD. Finally, a power flow analysis is accomplished and simulated results show the feasibility of this approach.

Nowadays Finite-Control-Set Model Predictive Control (FCS-MPC) is being successfully used in static power converters. The algorithm requires defining a functional in order to optimize it and thus find the best switch combination. So far the functional optimizes either the steady state or the transient operation. In fact, for steady state operation, the minimization of the switching frequency as well as high quality waveforms are the basic objectives. Contrary, during transient conditions the settling time minimization is usually used as a basic objective. This work presents an algorithm that is able to detect if the system is either under steady state or transient operating mode and applies the appropriate control algorithm. Hence, both operating modes are controlled under optimum conditions. Simulated results show the performance of the proposed control scheme.

This work deals with a multi-cell topology based on current-source converters based power cells. The main disadvantage of this configuration is the bulky DC inductor required in each cell which must be designed in order to compensate the oscillating power drained by the single-phase inverter. In order to avoid the use of a large DC inductor, the use of magnetic couplings among DC links of different power cells is considered. Additionally, active front end rectifiers are used in order to control the DC current and ensure a unitary displacement power factor in each power cell. A control scheme based on non-linear controllers is proposed in order to control each cell in a decoupled way. The topology feasibility is tested experimentally, while the control scheme performance is tested by simulation, showing that it is possible to obtain an excellent overall input current quality and a load voltage with lesser dv/dt than the classic multi-cell topology, reducing the requiered DC inductor from 400 mH to 30 mH for the studied case.

This work deals with the use of single-phase converters based on current-source inverters connected in a cascaded array (CSI-CHB) in order to get the dual topology of the classic Cascaded H-Bridged based on voltage-source inverters (CHB). The proposed configuration has similar advantages as the classic voltage source CHB as the use of semiconductors with lower voltage rating with respect to the load voltage. Moreover the CSI-CHB load voltage has a smaller distortion than the classic CHB due to the first order capacitive filter used at the inverters AC side. Also, the use of modulation techniques as phased-shifted carrier sinusoidal pulse modulation (PSC-SPWM) allows both, reduce the capacitive filter size and reduce the commutation frequency of the inverter switches. A theoretical analysis of the proposed topology and design guidelines for the capacitive filter are presented, considering a desired Total Harmonic Distortion (THD) on the load voltage and the SPWM modulation technique. Simulation results confirm the topology features.

A switching losses analysis is performed for an asymmetric multilevel Shunt Active Power Filter aimed to simultaneously compensate linear and nonlinear currents. The asymmetric approach consists in the inclusion of two types of modules; one meant for reactive power compensation and the other to cancel out the harmonic currents. Using the non-ideal behavior of the switching process in the power valves, the commutation losses of the presented approach are determined. Moreover, a comparison is performed with the symmetric counterpart and a power losses evaluation is made for both approaches. The analyses are carried out for a single operating point and for the entire operating region, considering the distorted power coming from the load. The presented results are supported with theoretical considerations and simulated waveforms.

In this paper is presented an alternative to generate sinusoidal output voltage waveforms using predictive control in an indirect matrix converter while achieving sinusoidal source currents on the input side. These objectives are accomplished by using a predictive control scheme which calculates the future values of the variables to be controlled in order to choose the converter state that produces the minimal error between them and their references. The proposed predictive method is tested by simulation results, obtaining sinusoidal output voltage and achieving a desired input displacement factor, with a low THD on both source currents and load voltages.

This work presents a new control scheme based on a finite states model predictive control aimed to fix the switching frequency and to reduce the spectrum dispersion on the output variables of static converters while regulating the sate variables as required by the references. These topics are particularly important in the operation of power converters including filters with resonant modes and in the overall efficiency due to the switching losses. The proposed scheme allows obtaining continuous outputs from the optimization process of MPC, thus exploiting the advantages of modulated schemes like known spectrum and fixed switching frequency. Simulated results show the proper performance of the proposed scheme, without significant reduction on the dynamic response in comparison to previous schemes using direct, non-modulated outputs.

Distributed and nonconventional power generation sources could lead to a wide varying grid frequency, particularly in weak systems or islanding mode operation of micro-grids. This work studies a predictive control scheme for power converters that are directly connected to the AC network featuring large frequency variations. The proposed scheme considers a fixed number of samples per period independent of the network frequency, leading to a variable sampling time under varying frequency conditions. This feature is advantageous when frequency has an important operating range because it ensures a constant resolution of the measured system variables. As discrete predictive control requires the sampling time to make accurate predictions, a synchronization system is proposed that ensures a fixed number of samples per cycle through continuous adjustment of the sampling time. Simulations show good performance of the proposed algorithms.

A new predictive control strategy for current source rectifiers which allows an effective control of source and load currents is presented in this paper. This method uses the commutation states of the converter in the subsequent sampling time according to an optimization algorithm given by a cost function and the discrete system model. The two control goals are: (a) regulation of dc-link current according to an arbitrary reference, and (b) a good tracking of the source current to its sinusoidal reference. The feasibility of the proposed method is verified by MATLAB/Simulink software.

Digital signal processors (DSPs) and field-programmable gate arrays (FPGAs) are predominant in the implementation of digital controllers and/or modulators for power converter applications. This paper presents a systematic comparison between these two technologies, depicting the main advantages and drawbacks of each one. Key programming and implementation aspects are addressed in order to give an overall idea of their most important features and allow the comparison between DSP and FPGA devices. A classical linear control strategy for a well-known voltage-source-converter (VSC)-based topology used as Static Compensator (STATCOM) is considered as a driving example to evaluate the performance of both approaches. A proof-of-concept laboratory prototype is separately controlled with the TMS320F2812 DSP and the Spartan-3 XCS1000 FPGA to illustrate the characteristics of both technologies. In the case of the DSP, a virtual floating-point library is used to accelerate the control routines compared to double precision arithmetic. On the other hand, two approaches are developed for the FPGA implementation, the first one reduces the hardware utilization and the second one reduces the computation time. Even though both boards can successfully control the STATCOM, results show that the FPGA achieves the best computation time thanks to the high degree of parallelism available on the device.

Modular current source converters (MCSCs) have been proposed as an alternative method for increasing the power range of medium voltage PWM AC drives. MCSCs are built by stacking parallel current source converters. Two advantages that make MCSCs attractive are: (a) extended current/voltage ratings beyond the device ratings and (b) simplicity in balancing the DC link current in each module. This can be accomplished using two optimized modulating patterns that have been proposed for such topologies: (a) multilevel selective harmonic elimination (MSHE) and (b) displaced selective harmonic elimination (DSHE). Both techniques are based on SHE patterns but there are slight differences in their digital implementation due to the way they generate the harmonic cancellation. Furthermore, when these techniques are used in the rectifier stage, it is reported that MSHE and DSHE do not eliminate all the unwanted harmonics due to practical issues such as changes in the modulating indexes to control the DC link currents. This work compares the operation of DSHE and MSHE when used in rectifiers of an MCSC in terms of execution time, robustness to poor sampling frequency, and quality of harmonic profiles on AC input currents under different operating conditions. Experimental results are presented to validate the theoretical considerations.

This paper addresses to some of the latest contributions on the application of Finite Control Set Model Predictive Control (FCS-MPC) in Power Electronics. In FCS-MPC , the switching states are directly applied to the power converter, without the need of an additional modulation stage. The paper shows how the use of FCS-MPC provides a simple and efficient computational realization for different control objectives in Power Electronics. Some applications of this technology in drives, active filters, power conditioning, distributed generation and renewable energy are covered. Finally, attention is paid to the discussion of new trends in this technology and to the identification of open questions and future research topics.

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.

The existence of single-phase inverters in cascaded multilevel AC/DC/AC converters implies the use of large capacitors in the DC links, because the H-bridge inverters demand considerable second harmonic currents that must be filtered out by the DC stage. If the filtering out is not strictly performed, the AC input current of each module is affected with the appearance of non-characteristic harmonics, sub-harmonics or inter-harmonics; thus, the RMS currents in the multi-pulse transformer secondaries increases. This problem may become even more evident if the converter output frequency is lower than the AC mains frequency, because the capacitor presents higher impedance at low frequency, causing that part of the harmonic currents demanded by the inverter is supplied directly by the rectifier. This paper presents an alternative to eliminate the unexpected harmonics and thus reduce the RMS values of the power cells input current in cascaded multilevel converters. The proposed solution uses magnetic couplings between the power modules of the converter; such approach is presented as a low cost solution compared to the conventional oversized DC-link capacitors.

The asymmetric multi-cell inverters are an alternative to provide an AC voltage with low THD. Considering a voltage DC ratio 1: 3: 9 for three inverters connected in series an AC voltage featuring 27 levels is obtained. The most common modulation used in asymmetric inverters is the Nearest Level Modulation (NLM) which has the drawback of bringing some cells into regeneration for some values of the modulation index, regardless of the load conditions. This paper presents a new modulation strategy for this asymmetric inverter that forces all the cell to have identical power flow direction. This strategy is based on the fact that the fundamental voltage amplitude of each inverter is required to be always greater than or equal to zero. To confirm the proposed technique, an active power flow analysis is performed as well as simulated and selected experimental results are included.

Rectifiers delivering large DC currents (>1000 Ampere) at low voltages ( < 24 V) have significant conductive losses. Using controlled rectifiers to provide an output current following a reference increase those losses. An approach proposed in several works uses multi stage converters connected in cascade, where an AC/AC frequency changer is connected to an AC/DC diode based converter across a high frequency magnetic link. The AC/AC converter connected to the ac mains voltage boosts the frequency and provides control on the current delivered to the load. The DC converter delivers the output current at the load voltage. The main goal of these approaches is the reduction of conductive losses by performing the control on the AC/AC converter. Additionally, approaches using modular topologies offer additional advantages, especially in terms of reliability. This work presents a modular topology based on voltage source DC links. The topology is explained and simulations are presented in order to validate theoretical considerations.

The main drawback of a Multi-Cell topology based on Current Source Converters is the oscillating power drained by the single-phase inverters from the DC link which requires a large DC reactor in order to avoid a significant variation of the DC current. In this work, a control scheme is proposed in order to compensate the oscillating power, avoiding to oversize the DC reactor at the expense of increasing the distortion of the input currents in each power cell and the instantaneous peak of the modulation index. However, the overall input currents present very low distortion and the instantaneous peak of the modulation index can be reduced by properly designing the multi-pulse transformer in terms of voltage ratio and phase shift. Both, the input currents distortion and the effect in the modulation index are mathematically characterized. Simulation result illustrates the effectiveness of the proposed control approach.

A comprehensive solution to simultaneously compensate both reactive power and currents harmonics is presented for a multilevel STATic COMpensator (STATCOM). The proposed approach includes asymmetric power cells that independently compensate reactive power at fundamental frequency and cancel out the current harmonics coming from a nonlinear load. The presented analysis demonstrates that, under certain conditions, the modules aimed for harmonic cancellation require lower power than the modules that compensate the fundamental power factor. Thus, each module can be implemented with specialized power valves in order to improve the overall system performance. Simulated preliminary results confirm the correctness of the proposed approach.

Multi-cell topologies based on three-phase input/singlephase output power modules have the drawback of dealing with an important oscillatory power in the DC link. This requires the use of a large DC link capacitor in order to minimize the DC link voltage ripple. Instead, this paper proposes a control scheme based on predictive control aimed to compensate the oscillatory power that allows the design of the DC link capacitor without oversizing it. However, this is achieved at expense of much distorted AC supply currents and amplified modulating signals. Such effects of the proposed compensating technique based on predictive control are mathematically characterized. The results show that the multi-pulse transformer guarantees distortion free overall AC currents. Simulated results show the feasibility of the proposed scheme.

This paper presents a novel model predictive control method for current source converters (CSC) following the duality with voltage source converters (VSC). In VSC the predictive control is applied to the output current, while in this work the CSC is controlled through the output voltage. The method is based on the discrete prediction model of the system, including the converter and output filter. The model is used to predict future behavior of the system variables for each switching state of the converter. The predictions are evaluated in a cost function that weights the level of accomplishment of the control goals. The switching state with best performance is then generated. The proposed algorithm predicts the output terminal voltages (includes the output filter capacitors), ensuring sinusoidal voltage generation without the need of cascaded control loops, coordinate transformations and modulation schemes found in classic solutions. In addition, low switching frequency is imposed by including the switching frequency in the cost function. Simulation results show a preliminary validation of the proposed control scheme, with comparable performance to the classical solutions, especially in terms of the current and voltage harmonic distortion.

Presented in this paper is a new strategy for indirect matrix converters that effectively mitigates common-mode voltages and allows an optimal control of source and load currents. This method uses the commutation state of the converter in the subsequent sampling time according to an optimization algorithm given by a simple cost function and the discrete system model. The control goals are regulation of output current according to an arbitrary reference and also a good tracking of the source current to its reference, which is imposed in order to obtain a sinusoidal waveform with low distortion. The technique is enhanced by a reduction of the common-mode voltage with an extra term in the cost function so as to avoid early motor winding failure and bearing deterioration. Simulation results support the theoretical development.

Due to the increasing use of distributed and non-conventional power generation sources, grid synchronization and control of static power converters under variable grid frequency is of particular interest. This work develops a discrete-time phase locked loop (PLL) based on a rotating reference frame to be used in variable frequency systems. The PLL is used in combination with a time-varying transformation based on a rotating frame for control purposes. Finally, for a back-to-back static converter topology, linear and nonlinear control strategies are proposed and evaluated under frequency variations and different operating points. The results - including stability analysis - show their particular performance under frequency variations.

This paper presents a current control scheme with instantaneous reactive power minimization for an indirect matrix converter. The strategy uses the commutation state of the converter in the subsequent sampling time according to an optimization algorithm given by a simple cost function and the discrete system model. Using this strategy, harmonics in the input current generated by the resonance of the input filter are strongly reduced. Simulation and experimental results with a laboratory prototype are provided in order to validate the control scheme, and the effects of a distorted source voltage and filter resonance are analyzed.

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.