This paper proposes a convex optimization-based strategy for the design of vector current controllers in a grid-interactive single-phase nine-level Packed E-Cell (PEC9) inverter under uncertain grid conditions, from stiff to weaker conditions, and non-ideal grid voltage conditions. The non-ideal grid-interactive PEC inverter with the grid impedance uncertainty is modeled by a multivariable polytopic model subject to a disturance in a state space framework. By virtue of this novel modeling approach, a robust two-degree-of-freedom H-infinity multivariable Proportional-Integral (PI) vector current control strategy is then proposed. The proposed control mechanism guarantees robust stability, employing a quadratic Lyapunov function, and robust performance against the uncertainty in grid impedance and non-ideal grid voltage conditions, also it provides inverter currents with Total Harmonic Distortion and harmonic components complying with IEEE Standard 1547 requirements. The effectiveness of the proposed grid-interactive smart PEC9 inverter equipped with the proposed robust vector control strategy is evaluated by simulation and hardware-in-the-loop experimental case studies.

The control of interleaved converters is commonly implemented through pulsewith modulation (PWM) techniques. A common element in these implementations is the use of phase shift between carriers to improve the system performance. When working with a balanced system, this phase shift is equally distributed between modules, but for an unbalanced system, this is no longer the best alternative. Changing the phase shift in these controllers requires the implementation of new capabilities in the control platforms, and for the controller to manage more variables of different nature. On the other hand, finite control set model predictive control (FCS-MPC) has shown to be a promising control strategy, especially when managing multiple control objectives of different natures or dynamics. In general, FCS-MPC does not present a fixed switching pattern, but this issue has been recently addressed with the so called period control approach (PCA). This article expands on the PCA-FCS-MPC to achieve the switching phase regulation for interleaved dc/dc power converters. A switching pattern similar to that of PWM techniques is achieved, while keeping the advantages of FCS-MPC and achieving the phase shift required for interleaved operation. Simulation and experimental results confirm the effectiveness of the proposed method.

This article incorporates a novel ultralocal model (ULM) control based on single input interval type-2 (SIT2) fuzzy logic control (FLC) to ensure the stable operation of a nine-level packed E-cell (PEC9) inverter in a grid-connected mode. By adopting seven switching components and a single dc source, the number of circuit components has been reduced in the PEC9 topology. This inverter has the possibility to switch various multilevel voltages (nine-, seven-, or five-level) under faulty switching devices without the need for any modification in the inverter configuration. This article proposes a ULM for the regulation of PEC9; it utilizes the input/output data of the system without adopting any parameters of the inverter where it is devoid of issues brought on by model mismatch. In the proposed structure, an extended observer error (ESO) is utilized to estimate the unmodeled dynamics of the inverter and to eliminate their effects in the feedback. Since the observer can remove the uncertainties from an unknown system, the ULM controller does not need to accurate setting of the control coefficients, which makes it a good option to be easy implementation for practical applications. In addition, an SIT2-FLC can be adopted as the supplementary controller to improve the inverter's stability by eliminating the estimation error of ESO. The time-domain experimental examinations have been carried out by conducting practical scenarios on a laboratory prototype of PEC9 to appraise the superior feasibility of the proposed scheme.

Common-mode voltage (CMV) in electric drives causes leakage current causing consequently EMI problems, loss and reduction of their components' lifetime. Several solutions have been proposed which usually lead to higher cost because additional components are used. This paper is focused on the mitigation of the resulting CMV produced by the operation of the VSD by means of a specifically designed PWM method. The proposal is based on the analysis of the CMV harmonic spectrum using the Fourier analysis. The CMV mitigation is achieved by modifying the time-shift displacement of the carriers each sampling time considering a multi-carrier PWM technique. The resulting method has been evaluated in a down scaled experimental setup and it is easily implementable on mostly off-the-shelf mid-range micro-controller control platforms.

This article proposes hybrid selective harmonic mitigation (SHM)-pulsewidth modulation (PWM) that is characterized by both features harmonic mitigation and elimination aimed to reduce the common-mode voltage (CMV) and to mitigate the selected nontriplen harmonics in a three-phase neutral-point-clamped (NPC) inverter. As CMV harmonic modeling only shows triplens, the specified triplens are eliminated using the selective harmonic elimination (SHE) operation to control CMV pulsewidths and consequently to mitigate CMV magnitude that appears as its root-mean-square (rms) reduction. The determined nontriplen harmonics are also mitigated using the SHM approach by the same cost function. The proposed hybrid SHM-PWM empowered by both harmonic elimination and mitigation is implemented on a three-phase NPC inverter to confirm its performance on reducing CMV through experimental and theoretical analyses. It is shown that hybrid SHM is superior over pure SHE or SHM in dealing with multiobjective system, including CMV reduction and no ntriplen harmonics mitigation.

Hand-in-hand with the smart-grid paradigm development, power converters used in high-power applications are facing important challenges related to efficiency and power quality. To overcome these issues, the pre-programmed Pulse-Width Modulation (PWM) methods have been extensively applied to reduce the harmonic distortion with very low power switching losses for high-power converters. Among the pre-programmed PWM techniques, Selective Harmonic Elimination (SHE) has been the prevailing solution, but recently, Selective Harmonic Mitigation (SHM) stands as a superior alternative to provide further control of the harmonic spectrum with similar losses. However, the large computational burden required by the SHM method to find a solution confines it as an off-line application, where the switching set valid solutions are pre-computed and stored in a memory. In this paper, for the first time, a real-time implementation of SHM using an off-the-shelf mid-range microcontroller is presented and tested. The Exchange Market Algorithm (EMA), initially focused on optimizing financial transactions, is considered and executed to achieve the SHM targets. The performance of the EMA-based SHM is presented showing experimental results considering a reduced number of switching angles applied to a specific three-level converter, but the method can be extrapolated to any other three-level converter topology.

Modular converters such as the multilevel cascaded H-bridge (CHB) are an attractive option for multiple applications mainly because of inherent modularity and fault-tolerant operation. This article is focused on the CHB converter operating with unbalanced conditions (different dc voltages and/or modulation indexes). Under these circumstances, applying the conventional control and modulation strategies, the output voltage harmonic spectrum is degraded. In this article, a generalized variable-angle phase-shifted pulsewidth modulation (PS-PWM) technique for CHB converters with a large number of power modules (>3) is presented. The method considers all possible cells' combinations to form groups and assigns the role of each cell in the group. This cell role defines the identifier of the cell in the variable-angle PS-PWM technique. In the steady state, in each group of cells, the harmonic distortion of the CHB output voltage located at twice the carrier frequency f(c) is eliminated, while the distortion at 4f(c) is also diminished. Experimental results show how the proposed technique achieves superior harmonic performance without introducing any significant disadvantage.

In this paper, a modified selective harmonic mitigation pulse amplitude modulation (SHM-PAM) is presented to be capable of canceling all triplen harmonic orders and suitable for single-phase application of five-level type of voltage source inverters. To this end, a new constraint is established for the two switching angles (alpha(1), alpha(2)) to derive the new formula for the harmonics' amplitude, which results in self-elimination of all triplen harmonics (e.g., 3rd, 9th, 15th, ... ). The fifth and seventh harmonic orders are mitigated through normal operation of the proposed SHM-PAM technique. It is also shown that the proposed technique is extendable to other multilevel voltage waveforms and a flowchart of self-elimination of all triplen harmonics has been presented. Mathematical analysis supported by experimental investigations show the desired performance of the proposed SHM-PAM algorithm on a two-cell single-phase cascaded H-bridge inverter as a typical five-level configuration in dealing with linear and nonlinear loads. Then, it is demonstrated that the maximum number of harmonic orders would be controlled with the minimum number of available angles in a low switching frequency voltage waveform.

Multilevel cascaded H-bridge converters have become a mature technology for applications where high-power medium ac voltages are required. Normal operation of multilevel cascaded H-bridge converters assumes that all power cells have the same dc voltage, and each power cell generates the same voltage averaged over a sampling period using a conventional phase-shifted pulse width modulation (PWM) technique. However, this modulation method does not achieve good results under unbalanced operation per H-bridge in the power converter, which may happen in grid-connected applications such as photovoltaic or battery energy storage systems. In the paper, a simplified mathematical analysis of the phase-shifted PWM technique is presented. In addition, a modification of this conventional modulation method using variable shift angles between the power cells is introduced. This modification leads to the elimination of harmonic distortion of low-order harmonics due to the switching (triangular carrier frequency and its multiples) even under unbalanced operational conditions. The analysis is particularized for a three-cell cascaded H-bridge converter, and experimental results are presented to demonstrate the good performance of the proposed modulation method.

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 increase in electric power demands and the project to develop a high voltage DC power distributions system in future aircrafts has created the need for a new generation of DC/DC power converters. The design of these systems has to take into account the stringent electromagnetic compatibility requirements typical of aeronautic applications, which combined with strict weight and volume restrictions make it often very difficult to comply with the emissions limits established in the applicable electromagnetic compatibility norms. In this context it is highly advisable to incorporate electromagnetic compatibility considerations from the beginning of the design process. In this work we perform a through comparison of two candidate topologies for 270VDC/28VDC and 540VDC/28VDC 3kW power converters in terms of emission of conducted noise. We compare two topologies with four switches in the high voltage side: a full bridge and a three level NPC converter. We show that a careful modeling of the parasitic effects that cause noise emissions allows for obtaining valuable preliminary conclusions in the simulation stage of the design process. Also, we take advantage of the circuit models developed to compare these converters in terms of output voltage spectrum distortion and efficiency. We have found some differences between the performance of the converters in function of the input voltage and the topology. In particular, we have found that the three level converter is slightly less efficient and does not provide significant improvement in terms of reduction of common mode noise. We explain this apparent paradox by close analysis of the effect of the parasitic elements that model capacitive couplings in the converter.

This paper presents a hybrid selective harmonic mitigation (SHM)-selective harmonic elimination (SHE) switching technique based on pulse-amplitude modulation (PAM) concept. It has been applied on a four-leg neutral-point-clamped (NPC) inverter to eliminate and mitigate more harmonic orders than recently proposed hybrid SHM-SHE-pulse width modulation (PWM) method while generating switching pulses at the same frequency. In conventional SHE and SHM techniques, equations are solved to attain the switching angles. Regarding the PAM, value of inverter dc voltage can be considered as an additional degree of freedom by which the flexibility of such techniques would be increased maintaining the switching frequency. In the proposed SHM-SHE-PAM, the conventional equations are reformulated to obtain constant switching angles for a vast range of modulation index (m a ) applied on a four-leg NPC inverter. Switching pulses of the three-phase legs and the fourth leg are calculated to mitigate the nontriplen harmonics and eliminate the triplen ones, respectively. Due to the unique switching angles valid in the whole range for ma, the calculation time and volume (storage capacity) are significantly reduced leading to a simpler controller implementable on a low-risk and cheap AVR chip. Experimental tests' results of a four-leg NPC inverter as UPS application prove the good dynamic performance and accuracy of the proposed implemented switching technique in producing associated pulses for the inverter switches at very low frequency to mitigate/eliminate undesired harmonic orders from the output phase/line voltage waveforms without using bulky filters.

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 odd-non-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.

This paper addresses the problems associated with the dc-link capacitor voltages of the three-level neutral-point-clamped power converter: the imbalance of the capacitor voltages as well as the presence of an ac-voltage low-frequency oscillation in the dc link of the converter. In order to cope with them, a mathematical analysis of the capacitor voltage difference dynamics, based on a direct average continuous model, is carried out, considering a singular perturbation approach. The analysis leads to a final expression where a sinusoidal disturbance appears explicitly. Consequently, the two problems can be handled together using the ordinary formulation of a problem of regulating the output of a system subject to sinusoidal disturbances, applying classical control theory to design the controller. In this way, the controller is designed including the disturbance estimate provided by a Luenberger observer to asymptotically cancel the disturbance, while also keeping the capacitor voltages balanced. Experiments for a synchronous three-level neutral-point-clamped converter prototype are carried out to evaluate the performance and usefulness of the converter working as a grid-connected inverter under the proposed control law.

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 cascaded H-bridge converters have found industrial application in the medium-voltage high-power range. In this paper, a generalized modulation technique for this type of converter based on a multidimensional control region is presented. Using the multidimensional control region, it is shown that all previous modulation techniques are particularized versions of the proposed method. Several possible solutions to develop a specific implementation of the modulation method are addressed in order to show the potential possibilities and the flexibility of the proposed technique. In addition, a feedforward version of this technique is also introduced to determine the switching sequence and the switching times, avoiding low harmonic distortion with unbalanced dc voltages. Experimental results are shown in order to validate the proposed concepts.