Showing papers on "Total harmonic distortion published in 2021"

Design and Implementation of Seventeen Level Inverter With Reduced Components

Abstract: The multilevel inverters (MLI) are resourceful in producing a voltage waveform with superior-quality staircase counterfeit sinusoidal and depressed harmonic distortion (THD). Several conventional topologies are proposed to realize the MLI however, the limitations of these topologies may involve more DC sources and power-switching devices, and less THD, which in turn, increases the cost and size of the inverter. These drawbacks can be eliminated with the proposed hybrid Cascaded H-Bridge Multilevel Inverter with reduced components topology. As compared with the established MLI topologies the recommended topology having a reduced number of DC sources, power-switching devices, component count level factor, lesser TSV, more efficient, lesser THD, and cost-effective. The proposed MLI is a blend of a single-phase T-Type inverter and an H-Bridge module made of sub switches. This article incorporates the design and simulation of the multilevel inverter with staircase PWM technique. Further, the 9-level and 17-level MLI is examined with different combinational loads. The proposed inverter is stable during nonlinear loads, and it is well suited for FACTS and renewable energy grid-connected applications. An operational guideline has been explained with correct figures and tables. The Output voltage wave is realized in numerical simulation. Finally, the experimental demonstrations were performed by implementing a hardware prototype setup for both linear and nonlinear loads using the dSPACE controller laboratory.

A Comprehensive Review on Space Vector Modulation Techniques for Neutral Point Clamped Multi-Level Inverters

Abstract: The Neutral Point Clamped (NPC) Multi-Level Inverters (MLI) have been ruling the power electronics industries for the past two decades. The Multi-Carrier Pulse Width Modulation (MCPWM) is common PWM techniques which are widely used in NPC-MLI applications. However, MCPWM is not having a good impact on the balancing of DC-link voltages, Common Mode Voltage (CMV) and limiting the Total Harmonics Distortion (THD). The Selective Harmonic Elimination (SHE) technique is introduced for reducing the THD, however all the switching angles should be maintained less than $\pi $ /2 to keep the eliminated harmonics at constant level which narrows down the modulation index range. Hence, in recent days Space Vector Modulation (SVM) technique is widely used in NPC-MLI, which gives better DC-link voltage balancing, self-neutral point balancing, near-zero CMV reduction, better-quality harmonics profile and switching loss minimization. Hence, it is a preferred solution for the majority of electrical conversion applications such as electric traction, high power industrial drives, renewable power generation, and grid-connected inverters, etc. The paper gives a comprehensive review of the SVM for NPC-MLI. First, this paper deliberates the state of art for two-level SVM and extends it to three-level (3L) SVM. Also compares the 3L SVM performance with other MCPWM techniques. Followed by the various modified MLI SVM techniques in terms of their implementations, DC-link capacitor balancing, and reduction of CMV. Further, the review of MLI SVM is widened to open-end winding Inverters and multiphase MLIs. The final part of this paper discussed the future trends and research directions on MLI SVM techniques and its applications.

Optimal Harmonic Mitigation in Distribution Systems with Inverter Based Distributed Generation

Abstract: In recent years, with the widespread use of non-linear loads power electronic devices associated with the penetration of various renewable energy sources, the distribution system is highly affected by harmonic distortion caused by these sources. Moreover, the inverter-based distributed generation units (DGs) (e.g., photovoltaic (PV) and wind turbine) that are integrated into the distribution systems, are considered as significant harmonic sources of severe harmful effects on the system power quality. To solve these issues, this paper proposes a harmonic mitigation method for improving the power quality problems in distribution systems. Specifically, the proposed optimal planning of the single tuned harmonic filters (STFs) in the presence of inverter-based DGs is developed by the recent Water Cycle Algorithm (WCA). The objectives of this planning problem aim to minimize the total harmonic distortion (THD), power loss, filter investment cost, and improvement of voltage profile considering different constraints to meet the IEEE 519 standard. Further, the impact of the inverter-based DGs on the system harmonics is studied. Two cases are considered to find the effect of the DGs harmonic spectrum on the system distortion and filter planning. The proposed method is tested on the IEEE 69-bus distribution system. The effectiveness of the proposed planning model is demonstrated where significant reductions in the harmonic distortion are accomplished.

Multilevel Switching-Mode Operation of Finite-Set Model Predictive Control for Grid-Connected Packed E-Cell Inverter

Abstract: In this article, we propose a modified finite-set model predictive control (M-FS-MPC) for multilevel switching-mode operation of grid-connected nine-level packed E-cell (PEC9) inverter With a single-dc source, six power switches, back-to-back-connected switches as bidirectional and two capacitors horizontally extended, PEC9 inverter topology has remarkably reduced the components count Packed E-cell (PEC) prominent feature has the capability of switching among different multilevel voltages: nine-, seven-, or five-level under faulty switch cases without any structural modification and only if the controller is appropriately designed M-FS-MPC is proposed to operate the grid-connected PEC with the multilevel switching mode under bidirectional switch fault operation Switching among five-, seven-, or nine-level voltages is attained by proper dc capacitors’ voltages regulation, whereas the desired current injection with low total harmonic distortion (THD) and requested power factor for addressing grid connectivity applications is guaranteed The system discrete model is developed and the experimental results verify the performance and robustness of M-FS-MPC in targeting the capability of PEC multilevel switching-mode operation and grid connectivity requirements in both steady and transient states

Grid Impedance Estimation Through Grid-Forming Power Converters

Abstract: In more-electronics power systems, grid-forming power converters, which operate as ac voltage sources, regulate the grid frequency and voltages in replacement of synchronous generators. Notably, grid impedances greatly influence the small signal and voltage stability of grid-forming converters. As such, prior knowledge of grid impedances can be very helpful for controller design. However, grid impedance estimation schemes are normally designed for current-controlled grid-following converters. Moreover, they are either very complicated or only yield grid inductances in a generally intrusive way. To fill this research gap, an impedance estimation method well suited to grid-forming converters is proposed. The method consists of four operating modes, which work well in voltage and power control cases. In the voltage control case, the voltage amplitude perturbation or phase angle information is exploited. Subsequently, the grid inductance and resistance are derived from power measurement. Alternatively, the active or reactive power information serves to estimate the grid impedance in the power control case. The proposed method features an easy implementation without any harmonic distortion, safety concern, or dependence on control parameters. Moreover, the method operates nonintrusively in most scenarios. Furthermore, a novel Kalman filtering scheme is proposed to provide added incentives. Finally, simulation and experimental results validate the effectiveness and simplicity of the proposed method.

Robust ANN-Based Control of Modified PUC-5 Inverter for Solar PV Applications

Abstract: Conventional PI controllers are vulnerable to changes in parameters and are difficult to tune. In this work, an artificial neural network (ANN) based controller is developed for the robust operation of a single-phase modified packed U-cell five-level inverter (MPUC-5) for solar PV application under variable insolation conditions. An MPUC-5 is a converter with a main and an auxiliary dc link of equal magnitude; although five-level operation is also still feasible with different voltages also. The maximum power point (MPP) of a PV array changes with the variation in the solar insolation. This results in a variable voltage at the output of the boost converter while maintaining the load line at the MPP. Consequently, the fundamental value of the output of the MPUC-5 also tends to change. Thus, it is required to produce angles that commit to an ac output voltage with a constant fundamental value and constrained to a minimum total harmonic distortion along with a third-order harmonic mitigation as per the grid codes, irrespective of the change in the dc-link voltages. A genetic algorithm is employed for this purpose. A large dataset is prepared for two-angle and four-angle operation of MPUC-5 under various dc-link voltages and constraints with which an ANN-based controller is trained. A neural network with a hidden layer is trained with the backpropagation technique; and once a correlation is developed, the network can be operated for a wide range of operating conditions. The robustness of the controller is verified through simulation in MATLAB/Simulink environment and validated by experimental emulation in an hardware in loop environment.

Harmonic Reduction Methods at DC Side of Parallel-Connected Multipulse Rectifiers: A Review

Abstract: This article gives a detailed literature review of harmonic reduction methods at the dc side of parallel-connected multipulse rectifiers (MPRs). First, passive and active harmonic reduction mechanisms are derived. Then, some commonly used and novel dc-side passive, active, and hybrid harmonic reduction circuits are discussed in terms of their structures, operation principles, and harmonic elimination performances mainly reflected on input current total harmonic distortion (THD) values. Comparisons of their design complexity, reliability, adaptability, and other aspects are also considered. Finally, simulation results are presented to verify the effectiveness of the reviewed dc-side harmonic reduction methods. This article can provide a guideline for selecting or designing rectifiers with reduced dc-side harmonics for specific applications. Anticipated trends in MPRs with lower harmonic content are also summarized.

Three-Vector-Based Model Predictive Torque Control for a Permanent Magnet Synchronous Motor of EVs

Abstract: This article presents an optimal control strategy for a permanent magnet synchronous motor (PMSM) drive using three voltage vectors. First, in order to simultaneously control torque and flux excellently, three voltage vectors including two active vectors and one zero voltage vector are selected. Second, the duration of the three voltage vectors in one period is calculated by the principle of simultaneous deadbeat control of torque and flux. Moreover, the cost function which eliminates the weight coefficient is proposed to reduce the amount of calculation. Finally, the proposed method is compared with the one- and two-vector-based model predictive torque control (MPTC) methods both in simulation and experiment. It is found that the proposed three-vector-based MPTC can obtain better performance such as smaller torque ripple and current total harmonic distortion (THD) both in steady and dynamic states.

Impact of Harmonic Currents of Nonlinear Loads on Power Quality of a Low Voltage Network–Review and Case Study

Abstract: The paper presents a power-quality analysis in the utility low-voltage network focusing on harmonic currents’ pollution. Usually, to forecast the modern electrical and electronic devices’ contribution to increasing the current total harmonic distortion factor (THDI) and exceeding the regulation limit, analyses based on tests and models of individual devices are conducted. In this article, a composite approach was applied. The performance of harmonic currents produced by sets of devices commonly used in commercial and residential facilities’ nonlinear loads was investigated. The measurements were conducted with the class A PQ analyzer (FLUKE 435) and dedicated to the specialized PC software. The experimental tests show that the harmonic currents produced by multiple types of nonlinear loads tend to reduce the current total harmonic distortion factor (THDI). The changes of harmonic content caused by summation and/or cancellation effects in total current drawn from the grid by nonlinear loads should be a key factor in harmonic currents’ pollution study. Proper forecasting of the level of harmonic currents injected into the utility grid helps to maintain the quality of electricity at an appropriate level and reduce active power losses, which have a direct impact on the price of electricity generation.

A Novel Modulated Model Predictive Control Applied to Six-Phase Induction Motor Drives

Abstract: Model-based predictive control techniques, with finite set control, are considered an interesting option to control multiphase drives due to their control flexibility and fast dynamic response. However, those techniques have some drawbacks such as a high computational cost, poor ( $x-y$ ) currents reduction, and steady-state error, especially at high speeds. To improve some of these drawbacks, modulation stages have been presented as an alternative. However, some of those drawbacks have not been improved. This article proposes a novel approach to the classic predictive current control (PCC) applied to an asymmetrical six-phase induction machine, where a space vector modulation with specific vectors is used in order to improve the ( $x-y$ ) currents, the steady-state error and total harmonic distortion (THD) at high operation speeds. Experimental results are presented to demonstrate the characteristics of the proposed control technique in terms of current tracking, ( $x-y$ ) currents reduction and THD of stator currents compared to the classic PCC.

Model Predictive Two-Target Current Control for OW-PMSM

Abstract: Open-winding permanent magnet synchronous machine (OW-PMSM) could obtain the higher bus voltage utilization and more robustness against the component damage and faults. However, the additional torque ripples and total harmonic distortion (THD) caused by zero-sequence current would limit the further applications of OW-PMSM. In this article, a novel model predictive two-target current control (MPTCC) scheme is presented to deal with such problem through model predictive control concept. First, a basic model predictive current control is proposed to deal with the torque production in fundamental components. Then, another modified cost function is proposed to provide more precise voltage vectors in torque production. After that, the deadbeat predictive control concept is proposed to calculate the required voltage vectors in zero-sequence loop. This zero-sequence voltage is injected in the voltage vectors, which are responsible for torque production. It needs to be mentioned that the limitation of inverter is analyzed. And the real-time judgment is proposed to assess the performance of MPTCC in some work conditions. Finally, both simulation and experiments have been both applied to assess the performances of the proposed control scheme. Comparing with those existing q -axis current injection methods and modified space vector pulse width modulation (SVPWM) technologies, the proposed control scheme could eliminate the torque ripple and THD at the same time and thus possess the better performances.

Power Quality Improvement in HRES Grid Connected System with FOPID Based Atom Search Optimization Technique

Abstract: An intelligent control strategy is proposed in this paper which suggests the Optimum Power Quality Enhancement (OPQE) of grid-connected hybrid power systems with solar photovoltaic, wind turbines, and battery storage. Unified Power Quality Conditioner with Active and Reactive power (UPQC-PQ) is designed with Atom Search Optimization (ASO) based Fractional-order Proportional Integral Derivative (FOPID) controller in the proposed Hybrid Renewable Energy Sources (HRES) system. The main aim is to regulate voltage while reducing power loss and reducing Total Harmonic Distortion (THD). UPQC-PQ is used to mitigate the Power Quality (PQ) problems such as sag, swell, interruptions, real power, reactive power and THD reductions related to voltage/current by using ASO based FOPID controller. The developed technique is demonstrated in various modes: simultaneous to improve PQ reinforcement and RES power injection, PRES > 0, PRES = 0. The results are then compared to those obtained using previous literature methods such as PI controller, GSA, BBO, GWO, ESA, RFA, and GA and found the proposed approach is efficient. The MATLAB/Simulink work framework is used to create the model.

Harmonic Analysis of Grid-Connected Solar PV Systems with Nonlinear Household Loads in Low-Voltage Distribution Networks

Abstract: Grid-connected rooftop and ground-mounted solar photovoltaics (PV) systems have gained attraction globally in recent years due to (a) reduced PV module prices, (b) maturing inverter technology, and (c) incentives through feed-in tariff (FiT) or net metering. The large penetration of grid-connected PVs coupled with nonlinear loads and bidirectional power flows impacts grid voltage levels and total harmonic distortion (THD) at the low-voltage (LV) distribution feeder. In this study, LV power quality issues with significant nonlinear loads were evaluated at the point of common coupling (PCC). Various cases of PV penetration (0 to 100%) were evaluated for practical feeder data in a weak grid environment and tested at the radial modified IEEE-34 bus system to evaluate total harmonic distortion in the current (THDi) and voltage (THDv) at PCC along with the seasonal variations. Results showed lower active, reactive, and apparent power losses of 1.9, 2.6, and 3.3%, respectively, with 50% solar PV penetration in the LV network as the voltage profile of the LV network was significantly improved compared to the base case of no solar. Further, with 50% PV penetration, THDi and THDv at PCC were noted as 10.2 and 5.2%, respectively, which is within the IEEE benchmarks at LV.

A Family of Dual-Boost Bridgeless Five-Level Rectifiers With Common-Core Inductors

Abstract: In this article, a family of dual-boost bridgeless five-level rectifiers with common-core inductors is proposed, which is composed of two coupled inductors, one bidirectional switch unit, and the dual-boost bridgeless power factor correction (PFC) rectifier. A bidirectional switch unit is embedded in the midpoint between the two capacitors and the bridge arm of the dual-boost bridgeless PFC (DBBL-PFC) to directly generate the five-level waveforms in each line cycle. The proposed topologies have the characteristics of lower voltage/current stresses and low total harmonic distortion. Additionally, the proposed five-level rectifiers employ a pair of common-core coupled inductors at the input side to replace the inherent independent inductors to improve the core utilization and the power density. First, the characteristics of the proposed topologies are analyzed and compared, and one of the topologies is taken as an example to illustrate its operating principle. Second, the modulation strategy with strong topology applicability and control system is designed for the proposed topologies. The advantage of the proposed pulsewidth modulation method is that it only needs to change the pulse distribution of the five-level topology to realize the five-level rectification, and the program debugging is simple. Then, the coupled inductors are designed, compared, and analyzed by the equivalent model in detail. Finally, a rated output of 1 kW/400 V experimental prototype is built, and the experimental results are presented to demonstrate the performance and effectiveness of the proposed topologies.

Correction to “Optimal Design of Passive Power Filter Using Multi-Objective Pareto-Based Firefly Algorithm and Analysis Under Background and Load-Side’s Nonlinearity”

Abstract: In this paper, the optimal designing of passive power filter (PPF) is formulated as a multi-objective optimization (MOO) problem under several constraints of system’s performance indices (PIs) such as individual as well as total harmonic distortion (THD) in the line current and the point of common coupling’s (PCC) voltage, distribution line’s ampacity under harmonic currents overloading, steady-state voltage profile, load power factor (PF) and a few associated with the filter itself. The optimal design parameters of a third-order damped filter are simultaneously determined for achieving maximum PF at the PCC while keeping system’s other indices such as total demand distortion (TDD) in the line current, total voltage harmonic distortion (TVHD) at the PCC and total filter cost (FC) incurred at a minimum by obtaining a best-compromised solution using the newly proposed multi-objective Pareto-based firefly algorithm (pb-MOFA). A novel MOO approach inspired by the modified firefly algorithm and Pareto front is established in order to deal with PPF design problems. The extension of MOFA is considered for producing the Pareto optimal front and various conclusions are drawn by analysing the trade-offs among the objectives. The efficiency and accuracy of the proposed pb-MOFA, in solving the concerned MOO problem, is validated by comparing an obtained solution and three computed PIs viz. convergence metric (CM), generational distance (GD) and diversity metric (DM) with those obtained from popular multi-objective Pareto-based PSO (pb-MOPSO), non-dominated sorting genetic algorithm (NSGA-II) and recently introduced multi-objective slime mould algorithm (MOSMA). The need for true Pareto front (TPF) is served by the one obtained by Monte Carlo method. At last, the impacts of different background voltage distortion (BVD) levels and load-side’s nonlinearity levels (NLLs) on filter performance are analysed.

A Novel Asymmetrical 21-Level Inverter for Solar PV Energy System With Reduced Switch Count

Abstract: This article presents a novel asymmetrical 21-level multilevel inverter topology for solar PV application. The proposed topology achieves 21-level output voltage without H-bridge using asymmetric DC sources. This reduces the devices, cost and size. The PV standalone system needs a constant DC voltage magnitude from the solar panels, maximum power point tracking (MPPT) technique used for getting a stable output by using perturb and observe (P&O) algorithm. The PV voltage is boosted over the DC link voltage using a three-level DC-DC boost converter interfaced in between the solar panels and the inverter. The inverter is tested experimentally with various combinational loads and under dynamic load variations with sudden load disturbances. Total standing voltage with a cost function for the proposed MLI is calculated and compared with multiple topologies published recently and found to be cost-effective. A detailed comparison is made in terms of switches count, and sources count, gate driver boards, the number of diodes and capacitor count and component count level factor with the same and other levels of multilevel inverter and found to be the proposed topology is helpful in terms of its less TSV value, devices count, efficient and cost-effective. In both simulation and experimental results, total harmonic distortion (THD) is observed to be the same and is lower than 5% which is under IEEE standards. A hardware prototype is implemented in the laboratory and verified experimentally under dynamic load variations, whereas the simulations are done in MATLAB/Simulink.

Carrier wave optimization for multi-level photovoltaic system to improvement of power quality in industrial environments based on Salp swarm algorithm

Abstract: The use of multi-level inverters is increasing in different structures, high power and medium power applications due to advantages such as low switching losses, harmonic distortion and electromagnetic interference at the output which could be used in microgrid systems. A microgrid can be defined as groups of renewable energy sources such as photovoltaic and wind turbine i.e. The switching technique for inverter control plays a significant role in reducing or eliminating the harmonics of inverter output voltage and reducing the switching losses. To minimize the distortion of the output voltage of the cascaded H bridge multi-level inverter due to low-order harmonics, an optimization method used for frequency selection, i.e. the carrier wave amplitude in the SPWM strategy within this study. The proposed method is called OSPWM, which employs a new optimization method based on the Salp swarm algorithm. The proposed method applied to a cascade H bridge five-level inverter. The simulation results show the reduction of the low-frequency harmonics amplitude and THD output voltage by optimizing the OSPWM carrier wave parameters with the optimization algorithm. The proposed method also compared with the classical SPWM method.

Design and Implementation of 31-Level Asymmetrical Inverter With Reduced Components

Abstract: This paper presents a novel topology for the single-phase 31-level asymmetrical multilevel inverter accomplished with reduced components count. The proposed topology generates maximum 31-level output voltage with asymmetric DC sources with an H-bridge. The fundamental 13-level multilevel inverter (MLI) topology is realized, and further, the topology is developed for 31-level can be used for renewable energy applications. This reduces the overall components count, cost and size of the system. Rather than the many advantages of MLIs, reliability issues play a significant role due to higher components count to reduce THD. This is a vital challenge for the researchers to increase the reliability with less THD. Several parameters are analyzed for both fundamental 13-level and developed 31-level MLIs such as total standing voltage (TSV), cost function (CF) and power loss. The inverter is tested experimentally with various combinational loads and under dynamic load variations with sudden load disturbances. Total standing voltage with the cost function for the proposed MLI is compared with various topologies published recently and is cost-effective. A detailed comparison of several parameters with graphical representation is made. Less TSV and components requirement is observed for the proposed MLI. The obtained total harmonic distortion (THD) is under IEEE standards. The topology is simulated in MATLAB/Simulink and verified experimentally with a hardware prototype under various conditions.

Improved Direct Torque Control Method for Dual-Three-Phase Permanent-Magnet Synchronous Machines With Back EMF Harmonics

Abstract: In this article, we propose a novel switching-table-based direct torque control (ST-DTC) method to eliminate the current harmonics in dual-three-phase permanent-magnet synchronous machines due to the back electromotive force (back EMF) harmonics and voltage vector selection. By employing a novel space voltage vector selection strategy and the optimal action time for different groups of vectors, a novel ST-DTC method is developed. Furthermore, in order to implement standard pulsewidth modulation (PWM) switching sequence, a centralization PWM method for 36 voltage vectors is introduced. The proposed method can effectively reduce the phase current harmonics caused by both back EMF distortion and voltage vector selection, and still reserve the advantages of the conventional ST-DTC, such as fast torque response and simple structure. Its effectiveness is verified by simulations and experiments.

Dynamic-Space-Vector Discontinuous PWM for Three-Phase Vienna Rectifiers With Unbalanced Neutral-Point Voltage

Abstract: Neutral-point (NP) voltage imbalance is an inherent issue of three-level converters The alternating input current distortion is generated by using the conventional discontinuous pulsewidth modulation (DPWM) scheme without NP voltage balance control In this article, the deviation vector between the synthesis vector and the reference vector, which is the fundamental cause of alternating input current distortion under NP voltage unbalance conditions, is revealed Then, by optimizing the subsector division and the switching state sequence, a dynamic-space-vector DPWM (DSV-DPWM) is proposed to eliminate the deviation vector Further, the comparisons of the proposed DSV-DPWM, the conventional DPWM, and an existing triangle carrier-based DPWM (TCB-DPWM), are addressed Finally, a 10-kW prototype was built to verify the effectiveness of the proposed DSV-DPWM scheme Experimental results show that, compared with the conventional DPWM scheme and the TCB-DPWM scheme, both the current THD performance and efficiencies can be significantly improved by the proposed DSV-DPWM scheme under unbalanced NP voltage conditions

High-efficiency high-voltage class F amplifier for high-frequency wireless ultrasound systems.

Abstract: This paper presents a novel amplifier that satisfies both low distortion and high efficiency for high-frequency wireless ultrasound systems with limited battery life and size. While increasing the amplifier efficiency helps to address the problems for wireless ultrasound systems, it can cause signal distortion owing to harmonic components. Therefore, a new type of class F amplifier is designed to achieve high efficiency and low distortion. In the amplifier, the resonant circuit at each stage controls the harmonic components to reduce distortion and improve efficiency. Transformers with a large shunt resistor are also helpful to reduce the remaining noise in the input signal. The proposed class F amplifier is tested using simulations, and the voltage and current waveforms are analyzed to achieve correct operation with adequate efficiency and distortion. The measured performance of the class F amplifier has a gain of 23.2 dB and a power added efficiency (PAE) of 88.9% at 25 MHz. The measured DC current is 121 mA with a variance of less than 1% when the PA is operating. We measured the received echo signal through the pulse-echo response using a 25-MHz transducer owing to the compatibility of the designed class F amplifier with high- frequency transducers. The measured total harmonic distortion (THD) of the echo signal was obtained as 4.5% with a slightly low ring-down. The results show that the low THD and high PAE of the new high-efficiency and high-voltage amplifier may increase battery life and reduce the cooling fan size, thus providing a suitable environment for high-frequency wireless ultrasound systems.

Variable-Angle PS-PWM Technique for Multilevel Cascaded H-Bridge Converters With Large Number of Power Cells

Abstract: 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.

Direct Torque Control for Induction Motors Based on Minimum Voltage Vector Error

Abstract: The traditional direct toque control (TDTC) for induction motors (IM) is afflicted by large torque ripple, high current total harmonic distortion (THD), and variable switching frequency. Recently, some improved direct torque control (DTC) methods have been proposed to address the above problems, but they often suffer from obscure concept, intensive computation, and poor robustness. To further improve the performance, this article proposes a DTC method based on minimum voltage vector (VV) error. The proposed strategy effectively optimizes the duty ratio of fundamental VV to minimize the error between reference VV and final VV imposed on motor terminals. The optimization algorithm dose not increase the system's complexity much and can be intuitively understood by a graphical interpretation. Experiment comparisons between the proposed strategy and some existing DTC methods are conducted on a 0.55-kW IM platform. The proposed DTC method has proven to achieve better steady-state performance, while retaining fast dynamic response of TDTC. Furthermore, the proposed method can obtain almost constant average switching frequency in the entire speed range, especially with rated load, due to the utilization of proportional-integral type torque regulator.

A 112-dB SFDR 89-dB SNDR VCO-Based Sensor Front-End Enabled by Background-Calibrated Differential Pulse Code Modulation

Abstract: This article presents a high-dynamic-range (DR) voltage-controlled oscillator (VCO)-based front end for sensor readout applications. Unlike conventional VCO-based quantizers, which suffer from large voltage-to-frequency non-linearities, the proposed design leverages differential pulse-code modulation (DPCM) from compression theory to substantially reduce the amplitude of the signal incident to the VCO quantizer, thereby achieving an ultra-low total harmonic distortion (THD) of −112 dB. In addition, background digital gain calibration is employed to overcome gain deviation of the VCO, thus ensuring a robust design. Together with dynamic element matching (DEM), the techniques enable a high DR using only the first-order noise shaping inherent in VCO-based quantizers and a moderate $32\times $ oversampling ratio. Fabricated in 65 nm, the sensor front end consumes 3.2- $\mu \text{W}$ power and achieves an SNDR of 89 dB and a DR of 94 dB in 500 Hz of bandwidth. Together with a 1.18- $\mu \text{V}~_{\text {rms}}$ integrated input-referred noise, it achieves a noise efficiency factor (NEF) of 4 and a Schreier FoM of 171 dB.

Quantitative Analysis of Asymmetric Multilevel Inverters With Reduced Device Count From Reliability and Cost Function Perspective—A Review

Abstract: To more efficiently harness the renewable energy sources, advanced power converters have become an indispensable part in real time implementation. Multilevel inverters (MLI) appear to be a promising alternative to the classical inverters in medium power applications. This article attempts to present a quantitative review of recent reduced switch multilevel inverter topologies. The topology selection plays a vital role in utility applications. The figure of merits that have been considered for the quantitative analysis are switching losses, cost function, and reliability. The analysis has been carried out for eight asymmetric topologies, which involve reduced device count. To have a common platform for comparison, all the eight topologies are selected with 15-level output. The exhaustive analysis has been compiled in a pictorial fashion and solid conclusions have been derived for future utility. A new 15-level asymmetric MLI has been proposed in this article. The proposed inverter is validated through MATLAB/Simulink, and the results are presented. The proposed topology has been compared with existing inverter. The proposed topology has been exhaustively analyzed to figure out the impact of switching frequency and duration on time from reliability perspective. Also, the implementation level cost has been provided in detail including the various factors. The results reveal that the proposed topology provides superior performance in terms of total harmonic distortion (THD), losses, cost, and reliability.

A novel design and performance improvement of symmetric multilevel inverter with reduced switches using genetic algorithm

Abstract: Multilevel inverter (MLI) synthesizes the preferred level of alternating voltage from multiple input sources of lower-level direct voltage. By adopting a suitable harmonic elimination technique, the MLI produces stepped sinusoidal waveforms with reduced total harmonic distortion (THD) without using any filter-based applications. MLI will be an apt choice for industries operating under medium- and high-power alternating current (AC) drives, and this finds application in interfacing non-conventional energy sources with power grid lines. This paper emphasizes a novel design of performance-enhanced cascaded MLI (PEC-MLI) with less quantity of switching devices for renewable energy system. The desired switching of MLI cost function is calculated using Genetic Algorithm (GA), and the appraised firing angle is calculated and the same is given as input to the Pulse Width Modulation (PWM) technique coded with chosen Nearest Voltage Level (NVL) control scheme. The gating signals generated for switching devices with the control strategies of NVL—PWM and hybrid PWM techniques using Genetic Algorithm. The MATLAB/Simulink model successfully evaluates the performance of proposed MLI. The simulated results analyze the system efficiency by comparing it with other similar MLI configuration cited in recent research articles. An effective realization of proposed MLI is experimented successfully and whose results are found be satisfactory with the simulated results.

Artificial Neural Network and Newton Raphson (ANN-NR) Algorithm Based Selective Harmonic Elimination in Cascaded Multilevel Inverter for PV Applications

Abstract: In this article, a hybrid Artificial Neural Network - Newton Raphson (ANN-NR) is introduced to mitigate the undesired lower-order harmonic content in the cascaded H-Bridge multilevel inverter for solar photovoltaic (PV). Harmonics are extracted by the excellent choice of opting switching angles by exploiting the Selective Harmonic Elimination (SHE) PWM technique accompanying a unified algorithm in order to optimize and reduce the Total Harmonic Distortion (THD). ANN is trained with optimum switching angles, and the estimates generated by the ANN are the initial guess for NR. In this study, the CHB-MLI is combined with a traditional boost converter, it boosts the PV voltage to a superior dc-link voltage Perturb and Observe (P&O) based Maximum Power Point Tracking (MPPT) algorithm is used for getting a stable output and efficient operation of solar PV. The proposed system is proved over an eleven-level H-bridge inverter, the work is carried out in MATLAB/Simulink environment, and the respective results are confirmed that the proposed technique is efficient, and offers an actual firing angles with a few iterations results in a better capability of confronting local optima values. The suggested algorithm is justified by the experimental development of eleven-level cascaded H-bridge inverter.