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.

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.

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.

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 Electric Vehicle (EV) application, the in-wheel motors are driven by the same dc-link voltage. To reduce the space, the Voltage Source Inverters (VSIs) can share one dc-link capacitor. Long-term experiences and experimental data demonstrate that the capacitors are one of the major failures in the motor drive system. The current profile of the dc-link capacitors is the main factor for this degradation, therefore, by reducing the current harmonic components of the dc-link capacitors can increase the lifetime. In this paper, a dc-link capacitor current harmonic reduction method for dual Permanent Magnet Synchronous Motor (PMSM) drive system in EV application is proposed. The Phase Shift Pulse Width Modulation (PSPWM) is employed in the dual inverters to reduce the harmonic components of dc-link capacitor. To verify the proposed method, a experimental platform is established and the experimental results are presented.

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 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.

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.

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 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.

Solar systems have become very competitive solutions for residential, commercial, and industrial applications for both standalone and grid connected operations. This paper presents an overview of the current status and future perspectives of solar energy (mainly photovoltaic) technology and the required conversion systems. The focus in the paper is put on the current technology, installations challenges, and future expectations. Various aspects related to the global solar market, the photovoltaic (PV) modules cost and technology, and the power electronics converter systems are addressed. Research trends and recommendations for each of the PV system sectors are also discussed.

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.

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.

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.

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.