Showing papers on "Total harmonic distortion published in 2013"

An Improved Repetitive Control Scheme for Grid-Connected Inverter With Frequency-Adaptive Capability

Abstract: The power quality of grid-connected inverters has drawn a lot of attention with the increased application of distributed power generation systems. The repetitive control technique is widely adopted in these systems, due to its excellent tracking performance and low output total harmonic distortion (THD). However, in an actual system, the ratio of the sampling frequency to the grid frequency cannot always maintain an integer, and then, the resonant frequencies of the repetitive control technique will deviate from the real grid fundamental and harmonic frequencies. This will degrade the performance of the system, particularly when the grid frequency varies. Even if the ratio is a fixed integer, the auxiliary function for stabilization in the conventional repetitive control technique will also increase the steady-state tracking error and THD of the system. In this paper, an improved repetitive control scheme with a special designed finite impulse response (FIR) filter is proposed. The FIR filter cascaded with a traditional delay function can approximate the ideal repetitive control function of any ratio. The proposed scheme varies the FIR filter according to varied grid frequency and maintains its resonant frequencies matching the grid fundamental and harmonic ones. Finally, the simulation and experimental results show that the improved repetitive control scheme can effectively reduce the tracking error and compensate harmonics of the inverter systems.

Reduction of Current Harmonic Distortion in Three-Phase Grid-Connected Photovoltaic Inverters via Resonant Current Control

Abstract: The resonant current control has been extensively employed to reduce the current harmonic distortion in a wide range of grid-connected distributed generation applications, including photovoltaic (PV) inverters, wind and water turbines, and fuel-cell inverters. However, the performance of these systems is deteriorated when the utility grid voltage experiences abnormal conditions such as voltage harmonics and imbalances. Several advanced control solutions have been recently introduced to cope with this problem but at the cost of a significant increase in the control computational load. This paper first analyzes the limitations of the standard resonant current control operating under abnormal grid conditions and then introduces a control scheme that improves the current harmonic distortion in such adverse conditions without increasing the computational load of the standard current control. This theoretical contribution is validated by means of selected experimental results from a three-phase PV inverter.

A Sliding-Mode Controller With Multiresonant Sliding Surface for Single-Phase Grid-Connected VSI With an LCL Filter

Abstract: This paper presents a sliding-mode control (SMC) scheme via multiresonant sliding surface for single-phase grid-connected voltage source inverter with an LCL filter to eliminate the grid current tracking error as well as suppress its total harmonic distortion (THD). In general, the design of SMC leads to a sliding surface that is a linear combination of the system state variables and the generated references. The sliding surface would drift while the system parameters change or external disturbance exists, which affects the tracking error and THD of system output seriously. Moreover, for ac tracking system, integral SMC can reduce, but not fully alleviate the sinusoidal tracking error and has limited ability to suppress the grid current harmonics, especially for high-order harmonics. In order to fully eliminate the grid current tracking error and suppress its THD effectively, multiple resonant terms of the grid current error are added to the sliding function. It is used for the first time in the SMC. This method can be used for an arbitrary ac tracking system. Simulation and experimental results on a 5-kVA single-phase grid-connected inverter prototype show the effectiveness of the proposed control strategy. The tracking precision of the grid current is about 0.91% and the THD of the grid current is 0.76%.

Cascaded Current–Voltage Control to Improve the Power Quality for a Grid-Connected Inverter With a Local Load

Abstract: In this paper, a cascaded current-voltage control strategy is proposed for inverters to simultaneously improve the power quality of the inverter local load voltage and the current exchanged with the grid. It also enables seamless transfer of the operation mode from stand-alone to grid-connected or vice versa. The control scheme includes an inner voltage loop and an outer current loop, with both controllers designed using the H∞ repetitive control strategy. This leads to a very low total harmonic distortion in both the inverter local load voltage and the current exchanged with the grid at the same time. The proposed control strategy can be used to single-phase inverters and three-phase four-wire inverters. It enables grid-connected inverters to inject balanced clean currents to the grid even when the local loads (if any) are unbalanced and/or nonlinear. Experiments under different scenarios, with comparisons made to the current repetitive controller replaced with a current proportional-resonant controller, are presented to demonstrate the excellent performance of the proposed strategy.

Selective Harmonic Mitigation Technique for Cascaded H-Bridge Converters With Nonequal DC Link Voltages

Abstract: Multilevel converters have received increased interest recently as a result of their ability to generate high quality output waveforms with a low switching frequency. This makes them very attractive for high-power applications. A cascaded H-bridge converter (CHB) is a multilevel topology which is formed from the series connection of H-bridge cells. Optimized pulse width modulation techniques such as selective harmonic elimination or selective harmonic mitigation (SHM-PWM) are capable of preprogramming the harmonic profile of the output waveform over a range of modulation indices. Such modulation methods may, however, not perform optimally if the dc links of the CHB are not balanced. This paper presents a new SHM-PWM control strategy which is capable of meeting grid codes even under nonequal dc link voltages. The method is based on the interpolation of different sets of angles obtained for specific situations of imbalance. Both simulation and experimental results are presented to validate the proposed control method.

Adaptive Dead-Time Compensation for Grid-Connected PWM Inverters of Single-Stage PV Systems

Abstract: This study presents a new software-based plug-in dead-time compensator for grid-connected pulsewidth modulated voltage-source inverters of single-stage photovoltaic (PV) systems using predictive current controllers (PCCs) to regulate phase currents. First, a nonlinear dead-time disturbance model is reviewed, which is then used for the generation of a feed-forward compensation signal that eliminates the current distortion associated with current clamping effects around zero-current crossing points. A novel closed-loop adaptive adjustment scheme is proposed for fine tuning in real time the compensation model parameters, thereby ensuring accurate results even under the highly varying operating conditions typically found in PV systems due to insolation, temperature, and shadowing effects, among others. The algorithm implementation is straightforward and computationally efficient, and can be easily attached to an existent PCC to enhance its dead-time rejection capability without modifying its internal structure. Experimental results with a 5-kW PV system prototype are presented.

Digital Predictive Current Control of a Three-Phase Four-Leg Inverter

Abstract: While the classical control techniques for three-phase two-level four-leg inverters are based on pulsewidth modulation or 3-D space vector modulation, this paper presents a simple digital current control strategy without the modulation stage. The proposed controller uses the discrete nature of the four-leg inverter and filter to generate the switching states. Using a predictive cost function, the optimal switching state to be applied in the next sampling interval is selected. The proposed controller offers excellent reference tracking with less current harmonic distortion for balanced and unbalanced loading conditions. The feasibility of the proposed strategy is verified by digital implementation on a dSPACE DS1104-based rapid prototype platform.

Residential Distribution System Harmonic Compensation Using PV Interfacing Inverter

Abstract: The increased non-linear loads in today's typical home are a growing concern for utility companies. This situation might be worsened by the harmonic resonance introduced by the installation of capacitor banks in the distribution network. To mitigate the harmonic distortions, passive or active filters are typically used. However, with the increasing implementation of distributed generation (DG) in residential areas, using DG systems to improve the power quality is becoming a promising idea, particularly because many DG systems, such as photovoltaic (PV), wind and fuel cells, have DG-grid interfacing converters. In this paper, the potential for using photovoltaic (PV) interfacing inverters to compensate the residential system harmonics is explored. A system model including the residential load and DG is first developed. An in-depth analysis and comparison of different compensation schemes based on the virtual harmonic damping impedance concept are then carried out. The effects of the capacitor banks in the system are also studied. The effectiveness of the harmonic compensation strategies under different conditions is verified through analysis and simulations.

Harmonic Droop Controller to Reduce the Voltage Harmonics of Inverters

Abstract: In this paper, the load and/or grid connected to an inverter is modeled as the combination of voltage sources and current sources at harmonic frequencies. As a result, the system can be analyzed at each individual frequency, which avoids the difficulty in defining the reactive power for a system with different frequencies because it is now defined at each individual frequency. Moreover, a droop control strategy is developed for systems delivering power to a constant current source, instead of a constant voltage source. This is then applied to develop a harmonic droop controller so that the right amount of harmonic voltage is added to the inverter reference voltage to compensate the harmonic voltage dropped on the output impedance due to the harmonic current. This forces the output voltage at the individual harmonic frequency to be close to zero and improves the total harmonic distortion (THD) of the output voltage considerably. Both simulation and experimental results are provided to demonstrate that the proposed strategy can significantly improve the voltage THD.

A Comparison of Carrier-Based and Space Vector PWM Techniques for Three-Level Five-Phase Voltage Source Inverters

Abstract: Multilevel inverter supplied multiphase variable-speed drive systems have in recent times started attracting more attention, due to various advantages that they offer when compared to the standard three-phase two-level drives. For proper functioning of such systems good pulsewidth modulation (PWM) strategy is of crucial importance. Control complexity of multiphase multilevel inverters increases rapidly with an increase in the number of phases and the number of levels. This paper deals with a three-level neutral point clamped (NPC) inverter supplied five-phase induction motor drive and analyses five PWM strategies: three are carrier-based (CBPWM) and two are space vector based (SVPWM). The aim is to provide a detailed comparison and thus conclude on pros and cons of each solution, providing a guideline for the selection of the most appropriate PWM technique. Experimental results are provided for all analysed PWM methods. The comparison of the PWM techniques is given in terms of the voltage and current waveforms and spectra, as well as the total harmonic distortion (THD) in a whole linear modulation index range, which is used as the global figure of merit. Properties of the common mode voltage (CMV) are also investigated. Complexity of the algorithms, in terms of the computational time requirements and memory consumption, is addressed as well. It is shown that the performance of the PWM techniques is very similar and that one CBPWM and one SVPWM technique are characterised with identical performance. However, using the algorithm complexity as the main criterion, space vector techniques are more involved.

Design of High-Performance Stand-Alone and Grid-Connected Inverter for Distributed Generation Applications

Abstract: In this study, a high-performance inverter, including the functions of stand-alone and grid-connected power supplies, is developed so that distributed generation units can operate individually or in a microgrid mode. In the stand-alone power-supply mode, the output ac voltage can supply to ac loads. In the grid-connected power-supply mode, the goal of power management can be achieved by controlling the amplitude and direction of the output current in the inverter. An adaptive total sliding-mode control (ATSMC) scheme is designed for the proposed high-performance inverter with a full-bridge framework. As a result, the proposed high-performance inverter with the ATSMC scheme has the output voltage with a low total harmonic distortion in the stand-alone power-supply mode and the output current with a high power factor in the grid-connected power-supply mode to provide an ac output with high-performance power quality. The effectiveness of the proposed high-performance inverter with the ATSMC is verified by experimental results of a 5-kW prototype, and the merit of the proposed ATSMC scheme is indicated in comparison with conventional proportional-integral and proportional-resonant control strategies.

Generalized Optimal Pulsewidth Modulation of Multilevel Inverters for Low-Switching-Frequency Control of Medium-Voltage High-Power Industrial AC Drives

Abstract: A generalized optimal pulsewidth modulation (PWM) technique applicable to multilevel inverters for low-switching-frequency control of medium-voltage high-power industrial ac drives is presented. Proposed synchronous optimal PWM method allows setting the maximum switching frequency to a low value without compromising the harmonic distortion of machine currents. Low switching frequency reduces the switching losses of the power semiconductor devices, resulting in higher inverter power output and efficiency. The proposed optimization results in low harmonic distortion at low switching frequency. Experimental results of a five-level inverter drive using optimal PWM are presented.

Digital Plug-In Repetitive Controller for Single-Phase Bridgeless PFC Converters

Abstract: This paper investigates a plug-in repetitive control scheme for bridgeless power factor correction (PFC) converters to mitigate input current distortions under continuous conduction mode and discontinuous conduction mode operating conditions. From the PFC converter model and the fact that a type-II compensator is used, a design methodology to maximize the bandwidth of the feedback controller is suggested. After that, the error transfer function including the feedback controller is derived, and the stability of the repetitive control scheme is evaluated using the error transfer function. The implementation of the digital repetitive controller is also discussed. The simulation and experimental results show that the input current THD is significantly improved by using the proposed control scheme for a 1-kW single-phase bridgeless PFC converter prototype.

Application of Four-Switch-Based Three-Phase Grid-Connected Inverter to Connect Renewable Energy Source to a Generalized Unbalanced Microgrid System

Abstract: In this paper, a four-power-semiconductor-switch-based three-phase inverter is proposed for renewable energy source integration to a generalized microgrid system. The proposed topology b-4 of three-phase inverter is investigated to make the commercial microgrid system to be cost effective and hardware optimized. A simple sine-pulse-width-modulation-based (SPWM) control strategy is proposed for the b-4 inverter topology instead of the traditional complex four-switch-based space vector techniques. The overall control structure is implemented using the Lyapunov function-based nonlinear controller to track the inverter current directly in the a-b-c frame so that a specific amount of active and reactive grid power flow to the grid can be controlled in a decoupled manner along with low total harmonic distortion of grid currents in the presence of nonlinear load at the point of common coupling (PCC). A novel technique of using the spatial repetitive controller (SRC) is also proposed to eliminate the effect of midpoint voltage fluctuation of the dc link even in the case of asymmetrically split dc-link capacitors without any extra voltage or current sensors unlike conventional methods. Detailed experimental results are provided to show the efficacy of the proposed hardware system for grid-connected applications in the microgrid.

Model Predictive Current Control of Two-Level Four-Leg Inverters—Part II: Experimental Implementation and Validation

Abstract: This paper describes the experimental implementation of the model predictive current control algorithm for a two-level four-leg inverter operating under balanced, unbalanced, and nonlinear loading conditions. The proposed scheme is designed to predict the future behavior of the load currents for each of the 16 possible switching states of the converter. The control method chooses a switching state that minimizes the error between the output currents and their references. The algorithm is embedded using a MATLAB/Simulink software environment, and experimental results based on the dSPACE DS1103 controller are provided. These results verify the advantages of the proposed control strategy in terms of robustness under filter and load parameter variations, average neutral-leg switching frequency reduction, reference tracking error, and percentage total harmonic distortion.

Investigation of Carrier-Based PWM Techniques for a Five-Phase Open-End Winding Drive Topology

Abstract: This paper discusses the implementation of level-shifted and phase-shifted carrier-based modulation methods, in conjunction with a multiphase open-end winding drive topology. The considered drive is supplied using two five-phase two-level voltage source inverters (VSIs), with input provided from two isolated supplies of equal dc voltages. The topology is known to yield the same space-vector pattern as a corresponding three-level inverter in single-sided supply mode. It is shown in this paper that, with the application of a simple logic, the same phase voltage waveforms result as those obtainable with the appropriate carrier-based modulation scheme applied to the three-level VSI in single-sided supply mode. While the outcomes of the modulation techniques are the same, the open-end winding topology offers certain advantages, such as modularity and absence of capacitor voltage balancing requirements. The analysis is conducted for selected modulation methods using voltage and current waveforms, spectra Fast Fourier Transform (FFT), and total harmonic distortion as figures of merit. Theoretical considerations are verified by means of simulation and experimental results.

Optimal Control of Medium-Voltage Drives—An Overview

Abstract: Carrier modulation is the most common method for inverter control of ac drive systems Operation at switching frequencies of several kilohertz is customary to restrain the harmonic distortion of the motor currents Lower switching frequency is preferred for medium-voltage drives, owing to the higher switching losses of the semiconductor devices This calls for optimizing the performance of the pulsewidth modulator Improvements are achieved by abolishing carrier modulation with its equidistant time spacing of the voltage pulses Optimal pulse patterns can be precalculated for every steady-state operating point of the drive The patterns are stored in a memory of the drive system, from which they are retrieved and used for inverter control Control at transient operation is achieved by adapting the optimal steady-state pulse patterns to the respective situation Specific trajectories of the motor current space vector are then created by online optimization An alternative method of online optimization relies on predicting the space vector trajectories for the next possible inverter switching states The switching state that leads to minimum switching frequency is then selected Optimal pulsewidth modulation reduces harmonic distortion It permits operation at very low switching frequency and reduces the switching losses This increases the current-carrying capability of the semiconductor devices to the extent that the power rating of an inverter approximately doubles

A DSP-Based Implementation of the p-q Theory in Active Power Filtering Under Nonideal Voltage Conditions

Abstract: This paper presents a three-phase three-wire shunt active power filtering system based on two level voltage source inverter which is intended to compensate both current harmonic distortion and reactive power under nonideal voltage conditions. The concepts of the p-q theory are used to calculate the reference compensating current according to the compensation strategy. An improvement in an existing phase-locked loop circuit is proposed to handle the shape of the small amount of additional current needed to cover the power system losses. In the dc-voltage loop, an optimal set point value which minimizes the harmonic distortion of the supply current and depends on power to be compensated is also proposed. Digital signal processor based implementation of the whole control system is described with details on the developed experimental platform dSPACE DS1103 for rapid prototyping. Experimental results obtained from a 15 kVA laboratory setup verify the effectiveness of the active filtering system.

An Active Damping Technique for Small DC-Link Capacitor Based Drive System

Abstract: A small dc-link capacitor based drive system shows instability when it is operated with large input line inductance at operating points with high power. This paper presents a simple, new active damping technique that can stabilize effectively the drive system at unstable operating points, offering greatly reduced input line current total harmonic distortion. The proposed method requires only a first-order, high-pass filter with a gain. Active damping voltage terms, linked directly to the dc-link voltage ripple through gain units, are injected to the drive machine for stabilizing the operating points. The stabilizing effect of the active damping terms is demonstrated for an induction machine based drive system. The effects of the added damping terms on the machine current and dc-link voltage are analyzed in detail. A design recommendation for the proposed active damping terms is given. Experimental results verifying the effectiveness of the new active damping method are presented.

A Neutral-Point Balancing Controller for a Three-Level Inverter With Full Power-Factor Range and Low Distortion

Abstract: Neutral-point (NP) balancing issues in the neutral-point-clamped three-level converters have been widely discussed in the last decades. Numbers of prior NP control algorithms have been proven working well in terms of NP potential balancing. However, it seems that the impact of these algorithms on the ac side did not draw much attention in the past, e.g., some algorithms inject additional common mode voltages with considerable amplitude that may saturate the duty cycles or inject low-order harmonic currents into the ac load. As a consequence, compared with the original system without NP controls, the total harmonic distortion (THD) performance at the ac side becomes worse, i.e., the THD standards are violated and a redesign of the system (e.g., ac filter) may be essential. Therefore, particularly for industrial applications, low distortion and high margins for duty cycles are typically important criteria for designing an NP controller. In this paper, a novel NP controller with full power-factor (PF) range and low distortion is proposed, which has the minimum common voltage injection at no unbalance or slight unbalance conditions. On the other hand, at heavy unbalance conditions, the controller has the maximum balancing ability at any PFs. Its superior performance is summarized via a comparison between different NP controls in this paper.

Decoupling Capacitor Selection in DCM Flyback PV Microinverters Considering Harmonic Distortion

Abstract: Electrolytic capacitors as a decoupling reservoir restrict the lifetime of photovoltaic (PV) microinverters This has led to the development of several improved decoupling circuits that can reduce the capacitor value to allow the use of nonelectrolytic types In this paper, the minimum decoupling capacitor value for the proper operation of discontinuous conduction mode flyback PV microinverters is analyzed by taking into account the total harmonic distortion (THD) and PV power utilization ratio The results presented show that the decoupling capacitor value influences the THD more than PV power utilization A decoupling capacitor selection method for single-stage and two-stage flyback inverters is proposed Experimental results obtained on an 80-W test bench are presented

A Model-Based Controller for the Cascade H-Bridge Multilevel Converter Used as a Shunt Active Filter

Abstract: This paper presents the modeling and control processes of the single-phase cascade H-bridge multilevel converter used as a shunt active filter. Based on the obtained model, a controller is proposed to compensate for harmonic distortion and reactive power caused by a nonlinear load. These issues are solved by guaranteeing tracking of the line current toward an appropriately defined current reference. In the proposed approach, the current reference has been selected to be a signal proportional to either the line voltage or to its fundamental component; however, the proposed method can also be extended to other reference definitions. The proposed controller also includes voltage loops to guarantee regulation and balance of the involved capacitor voltages toward constant references. Experimental results on a 2-kVA prototype are presented to assess the performance of the proposed controller.

Highly linear silicon traveling wave Mach-Zehnder carrier depletion modulator based on differential drive.

Abstract: We present measurements of the nonlinear distortions of a traveling-wave silicon Mach-Zehnder modulator based on the carrier depletion effect. Spurious free dynamic range for second harmonic distortion of 82 dB·Hz1/2 is seen, and 97 dB·Hz2/3 is measured for intermodulation distortion. This measurement represents an improvement of 20 dB over the previous best result in silicon. We also show that the linearity of a silicon traveling wave Mach-Zehnder modulator can be improved by differentially driving it. These results suggest silicon may be a suitable platform for analog optical applications.

Design-Oriented Analysis and Performance Evaluation of a Low-Cost High-Brightness LED Driver Based on Flyback Power Factor Corrector

Abstract: This paper presents a new control strategy for power factor correctors (PFCs) used to drive high-brightness light-emitting diodes (HB-LEDs). This control strategy is extremely simple and is based on the use of standard peak-current-mode integrated controllers (PCMICs), reducing its cost and complexity in comparison to traditional PFC controllers. In fact, this method is an alternative implementation of the one-cycle control to PFCs belonging to the flyback family of converters, without introducing high complexity for reducing the total harmonic distortion. In this case, the use of a simple exponential compensation ramp instead of a linear one is the proposed solution for drawing a sinusoidal input current. Moreover, the line current is cycle-by-cycle controlled, and therefore, the input-current feedback loop is extremely fast, which allows the use of this type of control with high-frequency lines. The proposed idea is to apply this simple control to a one-stage PFC in order to design a low-cost ac-dc HB-LED driver. However, the application of this control strategy to PFC belonging to the flyback family of converters is not obvious. Design-oriented considerations about its implementation in PCMIC will be provided. Finally, an experimental prototype of this driver was developed.

A Low-Cost Power-Quality Meter With Series Arc-Fault Detection Capability for Smart Grid

Abstract: This paper presents a low-cost digital single-phase power-quality measurement device for consumer use with a wide range of features, including series arc-fault detection, load trip on failure, and phase/neutral line wiring mix up indication. A wavelet multiresolution analysis technique was utilized for the voltage transient event detection and the current drop pattern recognition, specifically to arc fault. The last feature also involved the use of adaptive thresholding, peak detection, and repetition frequency calculation. A computationally efficient and accurate Goertzel filter was used for total harmonic distortion calculation. In addition, this meter can measure phase fundamental frequency (using the zero-crossing technique), rms values, and power. MATLAB and MathCAD packages were used to build and simulate arc-fault model and phase voltage distortion, to design and test part of the developed algorithms, which were further implemented in Embedded C and Assembler programming languages. A prototype circuit board with the required sensors and relay, analog isolation, indication, user controls, communication link, and a low-cost microchip microcontroller (MCU) dsPIC33 was designed and built to validate implemented algorithms and conduct experiments.

A Noniterative Optimized Algorithm for Shunt Active Power Filter Under Distorted and Unbalanced Supply Voltages

Abstract: In this paper, a single-step noniterative optimized algorithm for a three-phase four-wire shunt active power filter under distorted and unbalanced supply conditions is proposed. The main objective of the proposed algorithm is to optimally determine the conductance factors to maximize the supply-side power factor subject to predefined source current total harmonic distortion (THD) limits and average power balance constraint. Unlike previous methods, the proposed algorithm is simple and fast as it does not incorporate complex iterative optimization techniques (such as Newton-Raphson and sequential quadratic programming), hence making it more effective under dynamic load conditions. Moreover, separate limits on odd and even THDs have been considered. A mathematical expression for determining the optimal conductance factors is derived using the Lagrangian formulation. The effectiveness of the proposed single-step noniterative optimized algorithm is evaluated through comparison with an iterative optimization-based control algorithm and then validated using a real-time hardware-in-the-loop experimental system. The real-time experimental results demonstrate that the proposed method is capable of providing load compensation under steady-state and dynamic load conditions, thus making it more effective for practical applications.

Sliding-mode control of a wind turbine-driven double-fed induction generator under non-ideal grid voltages

Abstract: Control algorithms for the rotor- and grid-side power converters of a double-fed induction generator (DFIG)-based wind turbine under non-ideal grid voltage conditions are proposed, and guidelines for tuning the controller parameters are presented. The control schemes are based on sliding-mode control (SMC) theory. Apart from directly controlling the DFIG's average active and reactive powers, the proposed methods also fulfil two additional control targets during voltage unbalance and harmonic distortion, that is, the rotor-side converter (RSC) eliminating electromagnetic torque fluctuations and the gridside converter (GSC) compensating for the stator current harmonics to ensure a sinusoidal total current from the overall generating unit. The described control strategies are proved to be robust against parameter deviations and of fast dynamic response. In spite of the discontinuous nature of the standard SMC, constant converter switching frequency is achieved. Besides, the RSC control algorithm does not require a phase-locked loop and, furthermore, there is no need for decomposing the grid voltage and different currents into symmetrical sequences or harmonic components in any of the converters' control systems. Finally, the excellent performance of the system, as well as its robustness, is verified by means of simulation results under different grid voltage conditions.

Model Predictive Pulse Pattern Control for the Five-Level Active Neutral-Point-Clamped Inverter

Abstract: In this paper, the recently introduced model predictive pulse pattern control (MP3C) strategy is adapted to the ACS 2000 medium-voltage (MV) drive of ABB. The drive system consists of a five-level active neutral-point-clamped (ANPC-5L) rectifier, an inverter, and an induction machine (IM). The inverter is fed with offline-computed optimized pulse patterns (OPPs) that produce minimum harmonic distortion in the stator windings of the ac machine. An optimal stator flux trajectory is calculated from these OPPs, and a trajectory controller tracks it in real time. In the proposed approach, trajectory tracking is based on model predictive control: a constrained optimal control problem is formulated and solved in real time in a computationally efficient manner. An event-based prediction horizon is employed in order to ensure fast tracking of the stator flux trajectory. The advantages of the proposed method are optimal steady-state behavior in terms of harmonic distortion and fast torque response. The method was tested on an MV ANPC-5L inverter coupled to a general-purpose 1.21-MW IM. Experimental results were obtained from this industrial setup, and they are presented in this paper to demonstrate the high performance of MP3C.

Interleaved Boundary Conduction Mode (BCM) Buck Power Factor Correction (PFC) Converter

Abstract: An interleaved boundary conduction mode power-factor-correction buck converter that maintains high efficiency across entire load and line range is proposed. The adaptive master-slave interleaving method maintains stable 180° out-of-phase operation during any transient. By interleaving two parallel-connected buck converters, the input current ripple is halved while the ripple frequency is doubled, which leads to a smaller differential mode line filter. The line current harmonic distortion is analyzed to examine the allowable output voltage range while meeting harmonic regulations. The operation and performance of the proposed circuit is verified on a 300 W, universal line experimental prototype with 80 V output. The measured efficiencies remain above 96% down to 20% of full load across the entire universal line range. Even at 10% of full-load condition, the efficiency remains above 94%. The input current harmonics also meet the IEC61000-3-2 (class D) standard.

Offline LED Driver for Street Lighting With an Optimized Cascade Structure

Abstract: This paper presents a converter structure applied to supply high-power light-emitting diodes (LEDs) from the ac line in a street lighting system, based on the reduced redundant power processing principle. To guarantee high power factor and low harmonic distortion for the input ac current, a buck-boost operating in discontinuous conduction mode is employed as a power factor corrector. The second converter of the structure controls the current on the LED string, but it does not process all the power. This is done by summing the voltages of the first with the second converters. Avoiding the double processing of the power, the efficiency is improved. In addition to that, the capacitance value of the first converter is dramatically reduced by increasing the ripple limits, making possible the use of film capacitors to increase the life span of the system. The power and control designs are shown in detail. A laboratory prototype, with a rated power of 75 W for a rated input voltage of 220 Vrms, was built to show the feasibility of the idea.