System reliability represents a fundamental aspect in power converter operation. Within the spectrum of critical components, semiconductor devices and capacitors stand out as the most significant elements. This research examines the implementation of diverse pulse-width modulation (PWM) strategies within two-level voltage source inverters (VSI), with emphasis on both continuous and discontinuous modulation approaches. These methodologies are assessed regarding their influence on system efficiency and harmonic-related losses within the DC-link capacitor. The investigation encompasses essential operational variables including switching frequency, apparent power, and power factor. This work seeks to determine which modulation strategy provides optimal performance for capacitor loss reduction and to establish the most suitable technique based on specific application demands.

This paper presents the design, implementation, and comparative analysis of three current control strategies for a 0.2 MW three-phase Neutral Point Piloted (NPP) T-type inverter connected to the grid. The study compares Proportional–Integral (PI) controller, a first-order Sliding Mode Controller (SMC), and a Pseudo–Second–Order Super–Twisting Sliding Mode Controller (STSMC), all applied to the inner current control loop. The inverter is modeled with an RL output filter for current shaping and grid interfacing. While PI controllers offer simplicity, they suffer from limited disturbance rejection and tracking performance. Classical SMC improves robustness but introduces chattering. The proposed STSMC reduces chattering while preserving the benefits of SMC. Simulation results in MATLAB/Simulink assess each controller’s performance in terms of power injection and harmonic compliance with IEEE 519. The study highlights the superior transient and steady-state behavior of higher-order SMC methods.

DC microgrids (DCMG) enable efficient integration of renewable energy systems (RES) and energy storage systems (ESS). However, stability under constant power loads and disturbances remains challenging. Existing studies often overlook how control strategies concretely improve stability. This paper focuses on the dc/dc boost converter within the ESS and investigates how the introduction of a disturbance observer can improve overall system performance. A comprehensive model of the DCMG, including the RES, ESS, and electric vehicle (EV) loads, is established. Control strategies and observer design are presented, followed by a stability analysis using the minor loop gain methods. Simulation results validate the theoretical analysis and demonstrate improved dynamic response and robustness of the overall system.

In this paper, a generalized proportional integral observer (GPIO)-based finite-time sliding mode control scheme is proposed to enhance the convergence rate and disturbance rejection capacity of the grid-connected three-level neutral-point-clamped (NPC) converter. Firstly, a generalized super-twisting algorithm (GSTA) is designed in the voltage regulation loop and the instantaneous power loop of the NPC converter. Compared with the conventional super-twisting algorithm (STA), this method provides a faster convergence speed while the system trajectories are far from the origin, which is applied to the NPC converter to improve its dynamic performance and robustness. Additionally, by introducing a generalized proportional integral observer (GPIO) combined with the GSTA in the voltage regulation loop, the unknown time-varying disturbances can be rejected effectively. The stability of the proposed control scheme is proved. Finally, a set of comparative experiments between the proposed controller and the classic STA-based method have been carried out based on a three-level NPC converter prototype, and the results confirmed the efficacy of the proposed control strategy.

This article explores a novel variable-gain super-twisting observer (VGSTO)-based fixed-time sliding mode control (FTSMC) method for the dc-link voltage control of three-level neutral-point-clamped (NPC) active front-end (AFE) converters. Among the literature review, the super-twisting observer is an attractive solution for disturbance estimation. However, its convergence velocity is limited when the trajectories are far away from the origin. To overcome this drawback, a novel VGSTO is proposed in this work, whose innovation lies in adopting dynamically adapted exponent coefficients in the conventional super-twisting observer; thus, it turns into a linear observer outside a ball around the origin, which increases the convergence rate of conventional super-twisting observer, and the disturbance rejection ability is enhanced significantly. In addition, an FTSMC is designed for the NPC converter and its settling time is independent of the initial states, which breaks through the limitation of the traditional finite-time sliding mode controllers and assures the dynamic performance of the NPC converter. The proposed control scheme is assessed and compared with other representative observer-based sliding mode control methods based on a three-level NPC AFE converter test bench, and the experimental results verify its feasibility and effectiveness.

The paper proposes a low switch count multilevel inverter topology having a four-level space vector structure. The proposed MLI demonstrates a reduced number of active switches in relation to the number of output voltage levels. This inverter has an increased DC bus utilization, reaching up to 0.637 times the DC link voltage compared to the conventional multilevel inverters limited to 0.577 times the DC link voltage.The proposed multilevel inverter configuration integrates a two-level inverter with a cascaded H-bridge (CHB) converter in each phase. The each CHB capacitor voltage are regulated to one third of dc link voltage. The enhanced utilization of the DC bus voltage is due to the space vector redundancies provided by the CHB units. Both simulation and experimental validation of the proposed scheme are conducted on an induction motor drive across for various operating conditions. Field-oriented control (FOC) is employed to control the speed of the induction machine, while examining capacitor balancing under various transient conditions.

In this article, on the basis of an existing dual layer nested (DLN) adaptive sliding-mode control (ASMC) strategy, an observer-based sliding-mode control strategy with an improved DLN adaptive tuning mechanism (IDLN-ASMC) is proposed for a three-level neutral-point-clamped converter. The proposed controller not only ensures good system performance but also mitigates two problems of the existing DLN-ASMC strategy. Meanwhile, three objectives are achieved. First, an adaptive supertwisting algorithm is utilized in the power tracking loop to converge power tracking errors to bounded regions in finite time. Next, a disturbance observer-based IDLN-ASMC strategy is proposed in the dc-link voltage regulation loop to regulate the dc-link voltage to its reference value. Finally, a simple proportional-integral controller is used in the dc-link voltage-balancing loop to reduce the voltage difference between the two dc-link capacitors. The results of simulation and experiment demonstrate the effectiveness and superiority of the proposed strategy.

Phase-shifted pulse width modulation (PS-PWM) is one of the preferred modulation strategies for cascaded H-bridge (CHB) converters due to its excellent harmonic performance. Nevertheless, this modulation strategy needs a fast sampling frequency, which can increase with the number of H-bridge sub-modules (SMs). Moreover, the advantages related to the harmonic content of the output voltages are usually lost for applications that require unbalanced operation conditions regarding SM power or voltage references, such as solar PV or battery energy storage systems. This work proposes a feed-forward compensation technique that reduces the sampling frequency to two times the carrier frequency while maintaining the good harmonic performance of the CHB output voltages. Simulation results are carried out to compare and demonstrate the superior performance of the proposed technique.

This paper is concerned with the controller design for grid-connected inverter facing parameter variation and stochastic perturbation. Considering these two factors, a stochastically perturbed linear parameter varying (LPV) system for the inverter is formulated, upon which the stability analysis and controller synthesis have been conducted. Parameter dependent sufficient conditions have been obtained to guarantee the asymptotical and exponential mean square stability, with which the asymptotical and exponential controllers are designed respectively. A two-level three-phase inverter is used to verify the effectiveness of proposed theories. Simulation results show that both the controllers are effective under parameter variation and stochastic perturbation, and the exponential controller performs better than the asymptotical controller.

In this paper, a disturbance observer based control strategy is proposed to regulate the dc-link voltage of three-phase two-level pulse-width-modulation active-front-end rectifiers. In the voltage regulation loop, a linear disturbance observer is designed to improve the system performance. The load connected to the dc-link capacitor is considered as an external disturbance and the observer is used to estimate its value. The estimated disturbance is compensated to the PI controller. Simulations are carried out to verify the effectiveness and advantage of the proposed control strategy. Three different loads have been provided to test the robustness of the control strategy. Simulation results show that the proposed control strategy improves the transient response of the dc-link voltage, meanwhile maintains the steady-state performance in term of the output current total harmonic distortion, and has strong robustness against the external load variation.

A multi-level inverter circuit for generation of a dense multilevel 24-sided polygonal voltage space vector structure (VSVS) with real active vectors is proposed in this paper for open-end winding configuration induction motor (OEIM) drive. Generation of real active vectors compared to the switched average vectors, reduces switching frequency and improves phase voltage quality. Dense structure allows to generate 24-stepped output voltage waveform in full speed range with approximately 2Hz resolution. Due to 24-stepped waveform, output voltage is free from lower order harmonics upto 19th order in full speed range. The proposed inverter consists of inverter-1 and inverter-2, feeding from both the ends of the motor. The DC sources for the inverter scheme are generated by using simple delta-star-delta transformer connections while providing isolation from the grid. Capacitors in the power circuit are balanced using pole voltage redundancies without employing any extra circuit. The effectiveness of the proposed scheme is verified using MATLAB simulation and results are in agreement with the proposed theory. © 2022 IEEE.

The control of three-phase inverters with output LC filter is of great importance in many applications such as renewable energy, energy storage systems and uninterruptible power supplies, where the generation of sinusoidal output voltages with required amplitude, frequency and lowest harmonic distortion is desired. However, the inevitable parameter uncertainties and disturbances caused by manufacturing tolerance, aging of electrical components and load changes will degrade controller performance, which have always been challenges to traditional model predictive control methods. To deal with these challenges, a data-driven predictive control scheme is proposed in this paper. All unknown parameters and load current can be estimated online with a moving window adaptive observer. The estimation results are used to build a predictive model. Then, predictive control is applied to minimize the error between the output voltage and the reference value. Simulation results verify that the proposed scheme has a better ability to deal with parameter uncertainties and load changes than the traditional model predictive control scheme.

This article proposes a sliding-mode-observer (SMO)-based control strategy to regulate the dc-link voltage for a three-phase two-level active front end (AFE). The SMO is designed for the voltage control loop to estimate the external load which is abruptly connected to the AFE dc-link and consequently causes the dc-link voltage fluctuation. The estimated load value is used to compensate the voltage loop controller, therefore, the voltage loop gains more robustness against the load perturbation and its disturbing effect is greatly reduced. The effectiveness and advantage of the proposed control strategy has been verified through theoretical analysis, simulations, and the real-application experiments conducted on a 5 KVA laboratory AFE. The results show that the proposed control strategy provides obvious improvement of the dc-link voltage control performance comparing with the conventional PI controller and demonstrates stronger robustness against the operating point variations caused by the changes in external load and dc-link capacitance.

A 21-concentric 42-sided polygonal space vector structure (SVS) for suppression of lower order harmonics for Open-End Induction Motor drive applications is proposed in this work. The Open-End Induction Motor is fed with primary and secondary inverters from either side. The primary inverter providing active power for motor operation is fed with an active DC link. The primary inverter is switched at low switching frequency to minimize stress on high voltage switching devices. As a result, the primary inverter consists of lower order harmonics in the pole voltage. The secondary inverter is employed only to suppress the harmonics generated by primary inverter and does not contribute any active power for motoring operation. Hence, the secondary inverter can be fed with a capacitive supply balanced at a nominal voltage. The secondary inverter, operating at lower voltages is switched with high frequency to suppress the lower order harmonics upto 39thorder in the motor phase voltage. The advantages of polygonal space vector structures are retained throughout the modulation index, by generating 21-concentric layers of 42-sided polygons. This results in lower switching losses in low frequency switching main inverter and low voltage secondary inverter. A single DC link is employed in the power circuit topology to facilitate four-quadrant operation of the inverter. The proposed scheme is tested in MATLAB simulations and laboratory prototype. The simulation and experimental results are presented.

In order to obtain a simple and efficient control strategy for three-phase two-level grid-connected power converters with improved system performance including reduced computation and communication burdens, an event-triggered continuous control set-model predictive control (CCS-MPC) is proposed in this paper. In the DC-link voltage regulation loop, a simple but efficient controller is designed to track the DC-link voltage to its reference value. In the power tracking loop, a simple event-triggered CCS-MPC is utilized to ensure that the active power and reactive power also track their reference values. The control signals to the converter are updated and transmitted only when the triggering condition is satisfied. Compared with periodic sampling control strategies, which require the calculation and transmission of control signals in each sampling period, the proposed controller reduces the utilization of limited computation and communication resources while maintaining good tracking performance. By comparing with the periodic sampling proportional-integral strategy, the effectiveness and superiority of the proposed strategy are shown through simulation results.

This paper presents voltage regulation and current tracking control strategies for three phase two-level grid-connected power converters. By using power-invariant Park's transformation, an averaged mathematical model of power converters is obtained in dq synchronous reference frame. Then a novel control strategy using adaptive control and H∞technique is proposed to regulate the dc-link output voltage as well as track a desired current reference for three-phase power rectifiers. More specifically, an efficient adaptive controller is established in the external loop for regulating dc-link output voltage in the presence of external disturbances. A set of H∞controllers are designed in the internal loop to force the input currents track their desired values. Finally, simulation results obtained from the proposed control method are presented, analyzed, and compared with that of sliding mode control, and the superiority of the proposed control laws is verified.

This paper proposes the generation of a multilevel 30-sided space vector structure (SVS) from a single DC-link for an open-end induction motor (OEIM) drive. This scheme exhibits the inherent advantages of multilevel inverters like usage of low voltage blocking switches, less dv/dt in phase voltage etc. As the SVS generated is a 30-sided, lower order harmonics till 25thorder is eliminated from the motor phase voltage. Linear modulation range is also extended till 99.63% of the base speed as the SVS is closer to a circle. The topology consists of a DC-link fed hybrid 5-level inverter feeding one end of the OEIM and a capacitor fed hybrid 5-level inverter feeding from the other end of the OEIM. Active DC-link fed inverter acts as the only source of active power while the inverter feeding from the other end acts as a switched harmonic filter. Simulation studies and experimental verification of the proposed scheme are performed and presented in this paper.

In this article, a linear extended state observer (LESO) based second-order sliding mode (SOSM) control strategy with the direct power control is proposed for a three-phase neutral-point-clamped (NPC) power converter connected to a dc microgrid. Comparing with the PI control method, the proposed approach implements the advanced SOSM controller into the voltage regulation loop and instantaneous power tracking loop to enhance the dynamic and steady state performance. Furthermore, saturation function is applied in the SOSM method to weaken the chattering phenomenon. On the other hand, since the dc load is regarded as an external disturbance, an efficient LESO is designed in the voltage regulation loop to reject this disturbance. The design process of the proposed control strategy is shown based on the continuous averaged model of the NPC converter. Finally, comparison experiments among PI, LESO-based PI, and proposed LESO-based SOSM control strategies are implemented, which validate the superiority of the proposed approach.

In this paper, the method to extend linear modulation range till full base speed irrespective of the load power factor (p.f.) is presented using a 5-Level inverter scheme. Using this method, inverter can be operated linearly till peak phase fundamental voltage of 0.637Vdc(i.e. till full base speed) without exceeding machine phase voltage rating. The 5-level inverter is realized by a dual-fed inverter scheme for Open-End Induction Motor (OEIM) drive. A 2-Level inverter cascaded with a H-Bridge inverter acts as primary inverter and feeds the drive from one end whereas capacitor fed 2-Level inverter acts as secondary inverter and feeds the drive from another end. A single DC source is connected with primary 2-Level inverter. The ratio of the DC-link voltage to the primary H- Bridge inverter capacitor voltage is 4:1 and the DC-link to the secondary inverter capacitor voltage is maintained at 2:1 ratio for proper 5-Level inverter operation. Simulation and experimental results for inverter operation till full base speed are presented in this paper for OEIM and resistive load under steady state and dynamic conditions.

This paper presents an adaptive sliding mode observer (ASMO) to estimate three-phase grid voltage parameters, including both positive and negative sequences of voltage and grid frequency under unbalanced grid faults. First, the dynamic of three-phase voltage is reformulated as the second-order uncertain system, which can transform the traditional phase locked loop problem to the observer design problem. Based on the obtained dynamic system, an ASMO is constructed to estimate three-phase grid voltage parameters, using the adaptive and sliding mode techniques. The stability of the overall system including the observer estimation errors, sliding variable and adaptive estimation errors is rigorously proved by Lyapunov stability theory. The performance of proposed observer is assessed for estimation of three-phase grid voltage parameters by simulation in which two types of faults, i.e., the amplitude of voltage and grid frequency variations. are considered.

Reduction of switching losses in power converters is especially important for very high power applications looking for improving the reliability and efficiency. In contrast to carrier-based modulations, selective harmonic elimination and mitigation techniques use optimal waveform computation to generate a fundamental component while managing voltage harmonic content. However, these techniques, and specially selective harmonic mitigation, impose a high non-linear set of expressions to be solved. Therefore, complexity and computational burden rise up. Meta-heuristic algorithms are commonly used to solve the mathematical optimization problem involved. Preliminary application of Exchange Market Algorithm for harmonic mitigation problem has already been presented. However, in this paper a redefinition of the optimization is proposed to consider harmonic content for a wider range of frequencies. Results from computation for a wide range of modulation index are presented.

Nowadays, the design of power converters has been focused on the optimization in terms of reliability, fault-tolerant capability and power density. The use of modular converters leads to natural fault-tolerant capability because the power system can be still operating even when some module has failed. In this paper, the reliability of modular converters, which is high-dependent of several factors like as thermal stress, is studied. In the paper, the power devices aging of dc/dc interleaved power converters is managed. The proposed method is based on sharing conveniently the total managed power between the power modules. This can be done without losing performance in the power system. The proposed power routing technique has been tested in a three-module interleaved boost converter which is used in multiple applications.

Cascaded H-bridge (CHB) and modular multilevel converter (MMC) are effective solutions for medium and high voltage motor drive applications. However, the choice between the two converters is not particularly clear. This paper presents a loss evaluation of cascaded H-bridge and modular multilevel converter as a reference for loss calculation. A brief description of CHB and MMC are provided and the explicit expression of conduction loss and switching loss for MMC and CHB is derived respectively to show the relationship between the loss and the main variables of MMC and CHB directly based on carrier phase-shifting PWM (CPS-PWM). In the derivation of switching loss, a novel switching loss calculation method based on PWM is proposed to simplify the theoretical calculation process. Finally, the total loss comparison of the two converters based on different conditions are shown for a better selection in motor drive application.

This paper proposes an effective method to control the modular multilevel converters (MMC). The whole control scheme can be divided into three stages. Firstly, the prediction technique is employed to derive a quadratic programming problem from a cost function, leading to the voltage reference for each arm of the MMC. Secondly, the simple nearest level control is adopted to get the number of on-state SMs for each arm. At last, within each arm the submodules (SMs) are selected based on the sorting results of their capacitor voltages. Simulation based on a three-phase grid connected MMC system is conducted to evaluate the effectiveness of the proposed method. The results show that the proposed technique is capable of tracking the output current reference with very low distortion, while the SM capacitor voltages are well balanced and the circulating currents are almost suppressed. The transient response is fast and accurate as well.

This paper presents a novel control scheme for DC-DC boost converter, maintaining the desirable voltage regulation performance under high load variation and large change of voltage reference. The model of converter is reformulated, in which the unknown equivalent load, input voltage, model uncertainties and unmodeled dynamics are lumped as external disturbance. The control strategy is designed with backstepping control technology, similar to the cascade control method in which the intermediate variable is introduced to fast respond the control demand, effectively dealing with the nonlinearity of the boost converter dynamics. The disturbance observers are established to estimate the lumped disturbances, rejecting disturbances and removing steady-state errors to improve the closed-loop performance. The simulation results demonstrate that the proposed control strategy, backstepping control combined with disturbance observer, provides lots of advantages superior to the conventional PI control such as faster dynamic response and less output voltage drop.

A new approach to the control of three-phase two-level grid-connected power converters is proposed in this paper. The proposed control is an extended state observer (ESO)based second order sliding mode (SOSM), which comprises two control loops: the outer loop is a voltage regulation loop, as well as inner loop is an instantaneous power tracking loop. The outer loop is accomplished by an H∞controller plus an ESO, which is designed to regulate dc-link capacitor voltage of the converter and asymptotically reject external disturbances and parameter perturbations. The SOSM strategy is employed in the inner loop to drive the active and reactive power convergence to their desired values. Control objectives of nearly unity power factor and dc-link capacitor voltage regulation are simultaneously satisfied. Availability of the ESO-based SOSM is compared with the classic proportional-integral control in simulations, and the comparison implies that the proposed strategy not merely achieves an almost perfect tracking performance, but also provides a complete robustness against resistance load variation.

This paper presents a comprehensive overview of power converters and their control techniques for AC microgrids. The aim is to give an insight and direction for researchers and applications on promising topologies, control, and application within future smart grid. The paper first focuses on presenting various power converter topologies used in AC microgrids. Then, suitable control techniques for grid-connected and islanded operation modes are critically reviewed and analyzed. Finally, challenges of these converter topologies and control techniques are identified along with their potential solutions.

An efficient modulation stage is required for power conversion to achieve a good performance fulfilling the requirements of output filtering. On a high competitive market, the ability to adjust output harmonic content beforehand is required to adapt to a wide range of operating conditions. For this purpose, selective harmonic mitigation (SHM) is a very attractive solution for high-power applications because of its versatility and ease to accomplish with different goals. However it presents a drawback based on a high computation load due to non-linearity of problem definition. In this paper, it is presented a SHM implementation based on the Exchange Market Algorithm. This implementation aims to reduce execution time, heading to future online implementations, avoiding the use of offline calculations and look-up-tables, gaining the ability of adapt on real time the point of operation. Simulation results show the feasibility of the algorithm for solving the problem on a reasonable time for the online implementation in modern microprocessor demonstrators.

This paper employs second-order sliding mode control (SOSMC) to carry out the current tracking and voltage regulation tasks of a grid-connected three-phase two-level power converter. For dc-link voltage regulation, a disturbance observer is adopted to improve the whole control performance. In this paper, four different types of disturbance observers are proposed for comparison, which are conventional linear observer (LINO), second-order sliding mode observer (SOSMO), linear extended state observer (LESO) and nonlinear extended state observer (NESO). To ensure fair comparison, the parameters of the observers are tuned to make the power converter achieve almost same current total harmonic distortion (THD) and steady error of dc-link voltage. The performances are compared in the term of transient response of the dc-link voltage. The simulation results show: first, the disturbance observers improve the control performance of SOSMC; second, SOSMO outperforms the other three observers.

The search of efficient, robust and fault-tolerant electronic power converters is a challenge for the industry and academia. Nowadays, the integration and exploitation of the renewable energy sources and energy storage systems is required. In these terms, the multilevel power converters and specifically the cascaded H-bridge (CHB) power converter is a very good candidate. However, if a CHB power converter operates under an unbalanced operation a low-frequency high-distortion content appears in the output voltage spectrum. In order to reduce this problem, an extra cell, equipped with a low voltage battery or supercapacitor, is added to the original CHB converter. The idea is to operate the extra cell with the convenient duty cycle value in order to eliminate the low-order harmonic distortion generated by the unbalanced operation. This makes the proposed method very interesting because it leads to a reduction of the grid connection filter.

Multilevel power converters are very attractive for medium- and high-voltage applications because they present some advantages compared with the traditional two-level converters. In this way, the multilevel technology is backed by the industry and academia support. Among multilevel converters, the modular multilevel converter (MMC) is very popular because it is well-suited for the high-voltage dc (HVDC) power transmission systems as well as it permits the connection of different nature ac grids. To operate the MMC power converter is required a proper modulation strategy. It can be based on carrier-less or pulse-width modulation (PWM) strategies. In order to determine the optimum modulation technique, several simulations have been performed in order to extract some conclusions related with the power losses and the power converter behavior.

This paper proposes an induction motor drive scheme generating multilevel twenty-four sided voltage space vector structure using single DC source. The topology consists of basic units with DC-source fed main three-level flying-capacitor (FC) inverter cascaded with two low-voltage floating-capacitor fed H-Bridge cells (CHB). The generated space vector structure has six concentric 24-sided polygons. The CHBs are modular and independent in operation performing low voltage switched filtering action canceling dominant low-order harmonics generated by the main inverter. Linear modulation index as close to base speed is achieved with 24-sided structure. Single DC source based topology allows four quadrant operation of drive system simpler. Modulation scheme with minimum switching operation for FC inverter is verified. Simulation results under steady state and transient operations for V/f scheme are presented in the paper and validated through experiment.

The modular multilevel converter (MMC) is considered among the top choices for very high-power applications due to its superior features. To operate with good performance, effective control and modulation techniques are required to suppress the detrimental effects, including the circulating current and the capacitor voltage ripples. This paper proposes an efficient variable nearest level control-model predictive control (VNLC-MPC) technique. With few control actions to evaluate at each controller sampling period, the proposed method can achieve high controllability of the converter output current and power with reduced computational burden. Simulations are carried out on a three-phase MMC-based power system. The simulation results validate the VNLC-MPC strategy achieving higher quality of output current waveforms, reduced circulating currents and smaller capacitor voltage ripples.

In this paper, a novel scheme of disturbance observer based second order sliding mode (SOSM) control for DC-DC buck converters is proposed. A cascade-control structure is established to regulate the output voltage and force the inductor current to track its reference, which comprises two control loops. The voltage regulation loop which is based on an SOSM controller combined with extended state observer (ESO) is the external loop. The current tracking loop also accomplished by SOSM controller is the internal loop. The fast motion is dominated by the dynamics of the current tracking loop whereas the slow motion stems from the dynamics of the output voltage. In addition, the load resistance that influences significantly the dynamics of whole system is regarded as the external disturbance in this papper. A disturbance observer, ESO, aims at asymptotically rejecting disturbances to converter. The proposed control strategy is verified using simulation test.

In the last decades, multilevel converters have been developed usually for medium-voltage high-power applications. They have become a mature solution for the increasing power demand of multiple applications such as renewable energy systems, power quality improvement, and motor drives. In this paper, the operation of multilevel converters is addressed focusing on control and modulation techniques for different well-known applications. The new developments are presented as an extension of conventional methods for two-level voltage-source converters which are still the mainstream solution for most cases.

The use of interleaved power converters is a mature solution for multiple applications where the power is shared between several power converters. The interleaving method is used in order to improve the quality of the total output current. However, the performance of the complete power system is poor if an unbalanced operation is present in each power converter. In this paper, a variable-angle interleaving method is presented where the angle to be applied to carry out the interleaving is not fixed, but it is variable and calculated in real time depending on the operational conditions of the overall system. Simulation results are presented in order to demonstrate the good performance of the proposal.

This paper proposes a new forty nine level stacked inverter topology using low voltage devices for drives applications. The forty nine level inverter is developed by stacking three seventeen level inverters. The seventeen level inverter is developed by cascading a flying capacitor inverter and three H-Bridges. The inverter can operate with lower number of voltage levels if any of the H-Bridges fail. The capacitor voltage balancing in the inverter can be done irrespective of modulation index and load power factor. The topology is further modified to reduce the capacitor and switch count. Also, the inverter does not use any pulse width modulation between the different voltage levels. Therefore switching losses are reduced. In addition, since the switches need to block only lower voltages, MOSFETs can be used which will further improve the efficiency. An induction motor driven by this inverter using V/f control is simulated in MATLAB simulink and both steady state and transient results are presented.

Among multilevel converters, the cascaded H-bridge topology is one of the most industrially accepted solution for multiple applications, mostly for motor drives and flexible AC transmissions systems. Besides, other applications are being considered taking advantage of its modularity. The conventional phase-shifted PWM is the common method to generate the power devices switching of the converter. However, the performance is poor when an unbalanced operation is present. In this paper, an adaptive modulation method is presented where the angle to be applied to the phase-shifted PWM modulator is not fixed, but it is variable and calculated in real time depending on the operational conditions. Some simulation results are presented in order to demonstrate the good performance of the system.

In this paper, Selective Harmonic Mitigation (SHM) and Selective Harmonic Elimination (SHE) modulation techniques are combined to generate the appropriated firing pulses for a 4-leg 3-Level Neutral Point Clamped (NPC) inverter. SHM modulation technique is applied to the phase legs in order to get a desired modulation index (ma) and to mitigate the lower order odd non-triplen harmonics (5th, 7th, ...) while the fourth leg firing pulses are generated using SHE modulation technique to eliminate the major low order odd triplen harmonics (3rd, 9th, ...) completely. It is demonstrated that this hybrid modulation technique can reduce significantly a vast range of harmonic orders in the NPC inverter output voltage when compared with the results achieved when using only SHE modulation technique in the four legs of the inverter. To avoid the generation of odd non-triplen harmonics in the SHM phase legs that can not be eliminated with the fourth SHE leg, the Simulated Annealing (SA) heuristic algorithm used to find the SHM switching angles is tuned in order to provided suitable oddnon-triplen harmonics distortions which can be eliminated with SHE technique. Moreover, since in dynamical applications the modulation index has to be changing continuously, the SA algorithm has also been designed in order to provide a smooth switching angles set to avoid undesired transients harmonic contents.

In this paper, a model based robust control for three-phase three-level Neutral Point Clamped (NPC) power converters is studied. Based on the continuous averaged model of the system, a Second Order Sliding Mode (SOSM) technique is employed to the control design. The control objectives are to achieve desired dc-link capacitor voltage regulation, voltage balance in the two dc-link capacitors and the instantaneous active and reactive power tracking. In order to achieve fast dynamic response of the proposed controller in the presence of external disturbances, an Extended State Observer (ESO) is employed to asymptotically reject the disturbances which are integrated in the controller design. The proposed control strategy has a cascaded structure which consists of power tracking (inner loop) ESO-based dc-link voltage regulation and capacitors voltage balance (outer loop). Multi-rate simulation illustrates the effectiveness and robustness of the proposed controller under parametric uncertainties and load variations.

The integration of renewable energy systems and specifically of solar photovoltaic (PV) systems into the grid has become an important issue in the last decade because of the huge expansion of new power plants. PV systems have experienced an important evolution in the overall efficiency and in the variety of locations from low power installations (PV roof systems in domestic and residential applications) to high-power power plants currently reaching up to 550 MW. This fact has led to the appearance of new PV converter topologies and, among them, multilevel converters are very attractive due to its good features such as high nominal power and high quality of output waveforms. In this paper, a multilevel cascaded H-bridge converter is used to directly integrate the PV arrays into the grid. The proposed controller implements independent MPPT algorithms for each H-bridge extracting all the possible power from the available irradiation. Simulation results are presented to demonstrate the good performance of the PV system. The proposed system is modular and can be easily scaled to reach higher power so it could be used in large PV plants just adding extra H-bridges to the converter.

In the present paper, a novel topology for generating a 17-level inverter using three-level flying capacitor inverter and cascaded H-bridge modules with floating capacitors. The proposed circuit is analyzed and various aspects of it are presented in the paper. This circuit is experimentally verified and the results are shown. The stability of the capacitor balancing algorithm has been verified during sudden acceleration. This circuit has many pole voltage redundancies. This circuit has an advantage of balancing all the capacitor voltages instantaneously by switching through the redundancies. Another advantage of this topology is its ability to generate all the 17 pole voltages from a single DC link which enables back to back converter operation. Also, the proposed inverter can be operated at all load power factors and modulation indices. Another advantage is, if one of the H-bridges fail, the inverter can still be operated at full load with reduced number of levels.

This work presents the design and experimental validation of a Model Predictive Control (MPC) strategy for a Voltage Source Inverter (VSI) used in a three-phase uninterruptible power supply (UPS) for critical loads. The solution is obtained in two steps: first an unconstrained MPC problem is solved, which computes the continuous values of the voltage that must be provided by the converter. Then, a PWM modulation scheme is used to define the switching sequence of the switches that generate the desired input voltage to the LC filter. The first stage implies a dynamic optimization while the second one is just a static relationship. The solution of the unconstrained MPC problem gives rise to an explicit control law that can be computed beforehand, allowing the prediction horizon to be easily extended. This can improve the performance of other MPC formulation that use very short prediction horizons. The effect of the length of the prediction horizon and the control-weighting factor over the system performance is also evaluated experimentally in the paper. This study addresses how these parameters should be tuned to minimize the error between the actual and the desired output voltage. The proposed control strategy has been tested on a UPS supplying a three-phase RL load. The experimental results show that the proposed MPC controller achieves high performance of the overall system, even in the case of a model mismatch.

In this work, a Model Based Adaptive Direct Power Control (MB-ADPC) with constant switching frequency for Three-Phase Three-Level Neutral Point Clamped (3L-NPC) converters is proposed. The rectifier and inverter operation mode are used to illustrate the flexibility of the proposed MB-ADPC controller. The control design process is based on the continuous averaged model of the system. Depending on the operation mode different control objectives have to be guaranteed. The proposed controller ensures the voltage regulation of the dc-link capacitors for the rectifier operation mode and to achieve voltage balance in the dc-link capacitors and the active and reactive power tracking for the rectifier and inverter operation modes. In addition, adaptive techniques are used to avoid system parameters uncertainties as smoothing inductors and grid frequency values. This work shows that the application of advanced control strategies based on the system model allows enhancing the performance of the overall system. The details of the controllers design process and the experimental results using a 50 kVA Three-Phase Three-Level NPC prototype are presented in this paper validating the proposed controllers.

Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.

This paper presents a new approach to indirect vector control of induction motors. Two nonlinear controllers, one of sliding mode type and the other PI-fuzzy logic-based, define a new control structure. Both controllers are combined by means of an expert system based on Takagi-Sugeno fuzzy reasoning. The sliding-mode controller acts mainly in a transient state while the PI-like fuzzy controller acts in the steady state. The new structure embodies the advantages that both nonlinear controllers offer: sliding-mode controllers increasing system stability limits, and PI-like fuzzy logic based controllers reducing the chattering in permanent state. The scheme has been implemented and experimentally validated.

A multirate architecture for implementation of SD modulator is proposed in this paper. The performance of the called MM (multirate-multibit) SD modulator is the same that a conventional multibit SD modulator working at the clock rate of the first integrator, but the ADC in the forward path is replaced by an increase at the clock rate of the second integrator. Theoretical and simulation results are presented.

Among the different pulse codification techniques, stochastic pulse codification has its own arithmetic based on the similarity between Boolean algebra and statistical algebra. Summation and multiplication are the two basic arithmetic operations treated in depth in the literature. In this paper we present two digital stochastic circuits that extend traditional stochastic algebra: a division circuit and a square-root circuit, and the interfaces between the analog and stochastic domain. As a result, we are able to process analog input signals with a simple and complete processing system. These circuits can be implemented in low-cost and low-power digital programmable devices.

A CAD tool for analog circuit synthesis is presented. This tool, called FASY, uses fuzzy-logic based reasoning to select one topology among a fixed set of alternatives. For the selected topology, a two-phase optimizer sizes all elements to satisfy the performance constraints minimizing a cost function. In FASY, the decision rules used in the topology selection process are introduced by an expert designer or automatically generated by means of a learning process that uses the optimizer mentioned above. The capability of learning topology selection rules by experience, is unique in FASY. Practical examples demonstrate the tool ability of this tool to learn topology selection rules and to synthesize analog cells with different circuit topologies.

This paper presents a fuzzy-logic based approach to circuit performance modeling. Starting from a set of input-output vectors obtained by simulation (the training set), an automatic process adapts model parameters by means of neurofuzzy techniques. The resulting model can accurately reproduce the training set, even for a moderate number of rules. The results obtained in several analog and digital examples, show that accurate models can be obtained with a simple, completely automatic process. To demonstrate the usefulness of the proposed model, it is used to evaluate the circuit performances in the optimization process of an analog cell, achieving considerable speed-up.

This paper presents a chip intended for learning in fuzzy logic-based controllers. It uses the weight perturbation method to tune the parameters of the controller. This circuit can be used as a co-processor of any fuzzy logic-based controller whose internal parameters (e.g, output singletons and input membership function parameters) are externally accessible. The chip has been designed using a commercial 1.0 /spl mu/m CMOS technology.

This paper presents two digital circuits that allow the implementation of a fully parallel stochastic Hopfield neural network (SHNN). In a parallel SHNN with n neurons, the n*n stochastic signals s (ij) pulse with probability which are proportional to the synapse inputs, are simultaneously available. The proposed circuits calculate the summation of the stochastic input pulses to neuron i(F(i)=Sigma(j) s(ij)). The resulting network achieves considerable speed up with respect to the previous network.

Although many design tools have been developed for digital design, analog design tools are just being introduced. This paper deals with device sizing of analog cells. A new method using the Tabu Search heuristic is proposed. It minimizes a given cost function, which depends on a set of designer specifications. The results obtained show that this method can approach very close the global minimum of the cost function with only a few number of iterations. Hence, an analog simulation program, such as SPICE, can be used for the evaluation of the cost function at each iteration.>

This paper presents a tool for the automatic selection of circuit topology in analog synthesis. This tool uses fuzzy rules in the selection process. The decision rules can be entered by a human expert or can be automatically generated by means of a learning process. The capability of learning from previous experience in analog design is unique in this tool. Practical examples demonstrate its ability to select a topology in the design of CMOS operational amplifiers, and to learn the decision rules from experience.>

A digital implementation of a fuzzy-logic controller is presented. The controller uses stochastic logic to implement the operations involved in the defuzzification process. A proper selection of the different parts of the controller and the use of stochastic logic leads to a very simple architecture. A prototype is being designed using a 1.5 ¿m CMOS technology. In spite of its simple architecture, the proposed controller achieves more than 100000 FLIPs.