Showing papers on "Total harmonic distortion published in 2014"
TL;DR: In this paper, an impedance shaping method is proposed with virtual impedances, and the current control loop can be designed independently under the practical considerations, which can work stably over a wide range of the typical inductive resistive grid impedance and exhibit strong rejection ability of grid-voltage harmonics.
Abstract: The current-controlled grid-connected inverter with LCL filter is widely used in the distributed generation system (DGS), due to its fast dynamic response and better power quality features. However, with the increase of power injected into the grid, control performances of the inverter will be significantly influenced by the nonideal grid conditions. Specifically, the possible wide variation of the grid impedance challenges the system stability. Meanwhile, background harmonics of the grid can greatly distort the injected current. Therefore, the control of the inverter should be designed with strong stability-robustness and high harmonic-rejection-ability, both of which correlate closely with the inverter output impedance. However, it is difficult to shape the output impedance into the one with a desirable characteristic simply by adjusting the current loop gain. In this paper, an impedance shaping method is proposed with virtual impedances, and the current control loop can be designed independently. The implementation and parameter design of the virtual impedances are studied under the practical considerations. With this proposed method, the grid-connected inverter can work stably over a wide range of the typical inductive-resistive grid impedance and exhibit strong rejection ability of grid-voltage harmonics. Experimental results from a 6-kW single-phase grid-connected inverter confirm the effectiveness of the proposed method.
378 citations
TL;DR: A new dual neural-network-based methodology to detect and classify single and combined PQ disturbances is proposed, consisting of an adaptive linear network for harmonic and interharmonic estimation that allows computing the root-mean-square voltage and total harmonic distortion indices.
Abstract: The detection and classification of power quality (PQ) disturbances have become a pressing concern due to the increasing number of disturbing loads connected to the power line and the susceptibility of certain loads to the presence of these disturbances; moreover, they can appear simultaneously since, in any real power system, there are multiple sources of different disturbances. In this paper, a new dual neural-network-based methodology to detect and classify single and combined PQ disturbances is proposed, consisting, on the one hand, of an adaptive linear network for harmonic and interharmonic estimation that allows computing the root-mean-square voltage and total harmonic distortion indices. With these indices, it is possible to detect and classify sags, swells, outages, and harmonics-interharmonics. On the other hand, a feedforward neural network for pattern recognition using the horizontal and vertical histograms of a specific voltage waveform can classify spikes, notching, flicker, and oscillatory transients. The combination of the aforementioned neural networks allows the detection and classification of all the aforementioned disturbances even when they appear simultaneously. An experiment under real operating conditions is carried out in order to test the proposed methodology.
266 citations
TL;DR: A combined system of a thyristor-controlled reactor (TCR) and a shunt hybrid power filter (SHPF) for harmonic and reactive power compensation is proposed and the simulation and experimental results are found to be quite satisfactory to mitigate harmonic distortions and reactivePower compensation.
Abstract: This paper proposes a combined system of a thyristor-controlled reactor (TCR) and a shunt hybrid power filter (SHPF) for harmonic and reactive power compensation. The SHPF is the combination of a small-rating active power filter (APF) and a fifth-harmonic-tuned LC passive filter. The tuned passive filter and the TCR form a shunt passive filter (SPF) to compensate reactive power. The small-rating APF is used to improve the filtering characteristics of SPF and to suppress the possibility of resonance between the SPF and line inductances. A proportional-integral controller was used, and a triggering alpha was extracted using a lookup table to control the TCR. A nonlinear control of APF was developed for current tracking and voltage regulation. The latter is based on a decoupled control strategy, which considers that the controlled system may be divided into an inner fast loop and an outer slow one. Thus, an exact linearization control was applied to the inner loop, and a nonlinear feedback control law was used for the outer voltage loop. Integral compensators were added in both current and voltage loops in order to eliminate the steady-state errors due to system parameter uncertainty. The simulation and experimental results are found to be quite satisfactory to mitigate harmonic distortions and reactive power compensation.
263 citations
TL;DR: Algorithms with the aim of addressing limitations in islanded operation were proposed and results were presented to show the suitability of the proposed algorithms in achieving reactive power sharing and in improving the voltage harmonic distortion at the point of common coupling (PCC).
Abstract: When paralleling multiple inverters that are capable of operating as an island, the inverters typically employ the droop control scheme. Traditional droop control enables the decentralized regulation of the local voltage and frequency of the microgrid by the inverters. The droop method also enables the inverters to share the real and reactive power required by the loads. This paper focuses on some of the limitations of parallel islanded single phase inverters using droop control. Algorithms with the aim to address the following limitations in islanded operation were proposed: reactive power sharing and reduction of the voltage harmonic distortion at the point of common coupling (PCC). Experimental results were then presented to show the suitability of the proposed algorithms in achieving reactive power sharing and in improving the voltage harmonic distortion at the PCC.
236 citations
TL;DR: An overview of power inverter topologies and control structures for grid-connected photovoltaic systems is given in this article, where some solutions to control the power injected into the grid and functional structures of each configuration are proposed.
Abstract: In grid-connected photovoltaic systems, a key consideration in the design and operation of inverters is how to achieve high efficiency with power output for different power configurations. The requirements for inverter connection include: maximum power point, high efficiency, control power injected into the grid, and low total harmonic distortion of the currents injected into the grid. Consequently, the performance of the inverters connected to the grid depends largely on the control strategy applied. This paper gives an overview of power inverter topologies and control structures for grid connected photovoltaic systems. In the first section, various configurations for grid connected photovoltaic systems and power inverter topologies are described. The following sections report, investigate and present control structures for single phase and three phase inverters. Some solutions to control the power injected into the grid and functional structures of each configuration are proposed.
227 citations
TL;DR: In this paper, a two-stage onboard battery charger is analyzed for plug-in electric vehicles (PEVs), and an interleaved boost topology is employed in the first stage for power factor correction (PFC) and to reduce total harmonic distortion (THD).
Abstract: In this paper, a two-stage onboard battery charger is analyzed for plug-in electric vehicles (PEVs). An interleaved boost topology is employed in the first stage for power factor correction (PFC) and to reduce total harmonic distortion (THD). In the second stage, a full-bridge LLC-based multiresonant converter is adopted for galvanic isolation and dc/dc conversion. Design considerations are discussed, focusing on reducing the charger volume and optimizing the conversion efficiency over the wide battery-pack voltage range. A detailed design procedure is provided for a 1-kW prototype, charging the battery with an output voltage range of 320–420 V from 110-V 60-Hz single-phase grid. Experimental results show that the first-stage PFC converter achieves THD of less than 4% and a power factor higher than 0.99, and the second-stage LLC converter operates with 95.4% peak efficiency and good overall efficiency over wide output voltage ranges.
224 citations
TL;DR: A design procedure with remarkable results under severe grid inductance variation is proposed, which considers active damping using lead-lag network and capacitor current feedback and selects the proper ratios between the switching and resonance frequency, the grid and converter inductance, and the filter capacitance and total inductance.
Abstract: Grid-connected converters employ LCL-filters, instead of simple inductors, because they allow lower inductances while reducing cost and size. Active damping, without dissipative elements, is preferred to passive damping for solving the associated stability problems. However, large variations in the grid inductance may compromise system stability, and this problem is more severe for parallel converters. This situation, typical of rural areas with solar and wind resources, calls for robust LCL-filter design. This paper proposes a design procedure with remarkable results under severe grid inductance variation. The procedure considers active damping using lead-lag network and capacitor current feedback. Passive damping is also discussed. The design flow, with little iteration and no complex algorithms, selects the proper ratios between the switching and resonance frequency, the grid and converter inductance, and the filter capacitance and total inductance. An estimation for the grid current total harmonic distortion (THD) is also proposed. Simulation and experiments validate the proposals.
203 citations
TL;DR: In this paper, a quadrature phase-locked loop (PLL) with an adaptive notch filter (ANF) is proposed for the model-based sliding-mode observer (SMO) to improve the performance of sensorless interior permanent magnet synchronous motor (IPMSM) drives.
Abstract: To improve the performance of sensorless interior permanent magnet synchronous motor (IPMSM) drives, a quadrature phase-locked loop (PLL) with an adaptive notch filter (ANF) is proposed for the model-based sliding-mode observer (SMO). The position estimation error with the sixth harmonic distortion caused by the inverter nonlinearity and the flux spatial harmonics is analyzed. The ANF based on adaptive noise canceling principle combined with the quadrature PLL is proposed to diminish the estimation harmonic error. This method can adaptively compensate the harmonics in the estimated electromotive force to eliminate the corresponding position estimation error. The estimated harmonic coefficients from the ANF can be continuously self-tuned using the least-mean-squares algorithm according to the estimated position information. The effectiveness of the proposed method is verified with the experimental results at a 2.2-kW IPMSM sensorless drive.
186 citations
TL;DR: The results show the increased performance of the modulated model predictive control with respect to the classic finite control set model predictive Control in terms of current waveform total harmonic distortion (THD).
Abstract: Multilevel converters are known to have many advantages for electricity network applications. In particular, cascaded H-bridge converters are attractive because of their inherent modularity and scalability. Predictive control for power converters is advantageous as a result of its applicability to discrete system and fast response. In this paper, a novel control technique, named modulated model predictive control, is introduced with the aim to increase the performance of model predictive control. The proposed controller addresses a modulation scheme as part of the minimization process. The proposed control technique is described in detail, validated through simulation and experimental testing, and compared with dead-beat and traditional model predictive control. The results show the increased performance of the modulated model predictive control with respect to the classic finite control set model predictive control in terms of current waveform total harmonic distortion (THD). Moreover, the proposed controller allows a multi-objective control, with respect to dead-beat control that does not present this capability.
184 citations
TL;DR: This paper presents a single-phase transformerless grid-connected photovoltaic converter based on two cascaded full bridges with different dc-link voltages, which can synthesize up to nine voltage levels with a single dc bus.
Abstract: This paper presents a single-phase transformerless grid-connected photovoltaic converter based on two cascaded full bridges with different dc-link voltages. The converter can synthesize up to nine voltage levels with a single dc bus, since one of the full bridges is supplied by a flying capacitor. The multilevel output reduces harmonic distortion and electromagnetic interference. A suitable switching strategy is employed to regulate the flying-capacitor voltage, improve the efficiency (most devices switch at the grid frequency), and minimize the common-mode leakage current with the help of a novel dedicated circuit (transient circuit). Simulations and experiments confirm the feasibility and good performance of the proposed converter.
180 citations
TL;DR: In this article, a modulation strategy that balances the neutral-point voltage for three-level neutral-clamped inverter systems is proposed, which replaces the P-type or N-type small switching states with other switching states that do not affect the neutral point voltage.
Abstract: This paper proposes a new modulation strategy that balances the neutral-point voltage for three-level neutral-clamped inverter systems. The proposed modulation replaces the P-type or N-type small switching states with other switching states that do not affect the neutral-point voltage. The zero and medium switching states are employed to help the neutral-point voltage balancing. This method little bit increases the switching events and output total harmonic distortion. However, this method has a strong balancing ability at all regions. Further, it is very simple to implement in both space vector modulation and carrier-based PWM methods. Simulation and experimental results verify the validity and feasibility of the proposed new modulation strategy.
TL;DR: In this article, a combined vector and direct power control (CVDPC) is proposed for the rotor side converter (RSC) of doubly fed induction generators (DFIGs).
Abstract: In this paper, a combined vector and direct power control (CVDPC) is proposed for the rotor side converter (RSC) of doubly fed induction generators (DFIGs). The control system is based on a direct current control by selecting appropriate voltage vectors from a switching table. In fact, the proposed CVDPC enjoys the benefits of vector control (VC) and direct power control (DPC) in a compacted control system. Its benefits in comparison with VC include fast dynamic response, robustness against the machine parameters variation, lower computation, and simple implementation. On the other hand, it has benefits in comparison with DPC, including less harmonic distortion and lower power ripple. An extensive simulation study, using MATLAB/Simulink, is conducted on a 9-MW wind farm composed of six 1.5-MW DFIG-based wind turbines. The performance of the proposed CVDPC method is compared with both VC and DPC under steady-state and transient conditions. Simulation results confirm the superiority of the CVDPC over either VC or DPC.
TL;DR: In this paper, the authors presented an extensive comparative study between a two-and three-level inverter for electric vehicle traction applications, where an advanced control strategy for balancing the two dc-link capacitors is also proposed.
Abstract: This paper presents an extensive comparative study between a two- and three-level inverter for electric vehicle traction applications. An advanced control strategy for balancing the two dc-link capacitors is also proposed. In this paper, the main focus is on the total voltage harmonic distortion (%THDv), the analytical derivation of the three-level capacitor currents, and the voltage balancing of two capacitor voltages. For generating the gate signals, space vector pulse width modulation (SV-PWM) is used. The developed voltage-balancing scheme helps to reduce the number of converter switching sequences, compared with the conventional SV-PWM strategy, and keeps the voltage difference between the two dc-link capacitors at the desired voltage level. The developed test-bench is used for a permanent magnet synchronous machine drive for electric vehicle (EV) applications. Detailed simulation studies are performed using MATLAB/Simulink block set and experimental verification is achieved using dSpace based real-time simulator. Both the simulation and experimental results show a significant improvement in reduction of total harmonic distortion (%THDv) for the three-level inverter.
TL;DR: Simulation and experimental results are shown to demonstrate that the new SVM method can generate good performance of the input/output waveforms and provide CMV reduction.
Abstract: A new space vector modulation (SVM) process for use in an indirect matrix converter (IMC) has been proposed in this paper to reduce the common-mode voltage (CMV) in a high voltage transfer ratio. The principles of selecting suitable active vectors and then properly arranging the switching sequence in the inverter stage of the IMC are described. The IMC with the new SVM method significantly reduces the peak-to-peak voltage of the CMV without any extra hardware. The new SVM method has some other advantages such as a lower total harmonic distortion of line-to-line output voltage and a reduced switching loss at the inverter stage through a minimum number of switching commutations as compared to the conventional reduced CMV-SVM method. The proposed modulation can be easily implemented in software without any additional hardware modifications. Both simulation and experimental results are shown to demonstrate that the new SVM method can generate good performance of the input/output waveforms and provide CMV reduction.
TL;DR: This paper suggests a new approach for the optimal sizing of hybrid active power filter parameters, which is presented for three-phase industrial power systems, and uses Fortran Feasible Sequential Quadratic Programming to determine the filter optimal sizing.
Abstract: The development of new passive, active, and hybrid filtering techniques is important; and the issues of higher quality, reduced complexity, higher efficiency, and lower cost are important conditions that need to be addressed with regard to the expected stringent trends in power quality obligations. This paper suggests a new approach for the optimal sizing of hybrid active power filter (HAPF) parameters, which is presented for three-phase industrial power systems. Hybrid filter topology can be used to compensate harmonic currents, as well as for power factor corrections, without concern for importing and exporting harmonics, or simply the series and parallel resonance that may occur. The new trend in harmonic power filter design is not to obtain the best solution from a single objective optimization but to obtain a good compromise solution accomplished under other conflicting objectives. Fortran Feasible Sequential Quadratic Programming is used to determine the proposed filter optimal sizing to minimize the total voltage harmonic distortion as the main objective function, where maintaining the load power factor at an acceptable limit is desired. If the total harmonic voltage distortion achieves the specified goal, then the objective is redirected into minimizing the resultant voltage and current total harmonic distortions. The optimal design of the HAPF is analyzed by means of three case studies.
TL;DR: In this article, a mathematical model between the output current iout and the reference current iref in BCM through theoretical derivation is proposed, and a novel control strategy is proposed to generate a reference current that can decrease the THD of output current.
Abstract: Flyback inverter has the advantages such as compact conformation, simple control loop, electric isolation, high step-up ratio, high efficiency, etc., therefore is an attractive solution for photovoltaic ac module applications. In this topology, BCM is more preferred compared to DCM and CCM, because of its higher power level, higher efficiency and wider switching frequency bandwidth. However, the control of BCM is more complicated due to its variable switching frequency. This also leads to the difficulty to get the accurate mathematical model between the output current iout and the reference current iref, which has a great influence on the THD of iout. This paper analyzes and proposes a mathematical model between iout and iref in BCM through theoretical derivation, and proposes a novel control strategy to generate the reference current that can decrease THD of output current. Meanwhile the realization of MPPT based on the mathematical model is also investigated. Finally, simulation and experiment results based on an improved flyback-inverter prototype are presented, which validates the proposed mathematical model and the control strategy.
TL;DR: Experimental results show that, with a well-designed multirate RC, the total harmonic distortion can be very low and the switching control frequency of the converter can be increased to compensate the control performance loss.
Abstract: In this paper, a multirate repetitive control (RC) scheme is developed and applied to constant-voltage constant-frequency pulsewidth modulation converter systems. In this scheme, the converter has a fast sampling rate, while the repetitive controller has a reduced sampling rate. The learning is based on the downsampled input and error signals in previous periods. The multirate RC synthesis method, as well as its convergence and stability conditions, is discussed in detail. Systematic experiments are also carried out to illustrate the effectiveness of multirate RC. Experimental results show that, with a well-designed multirate RC, the total harmonic distortion can be very low. This approach can reduce the computation delay caused by the plug-in RC in each switching control period and will enhance the system stability. Consequently, the switching control frequency of the converter can be increased to compensate the control performance loss. This approach is suitable for design of cost-effective and flexible converter control systems.
08 Dec 2014
TL;DR: The goal of this paper is to provide a review of various LDSF modulation techniques proposed in the literature and also discuss in detail about one of the emerging LDSF control techniques known as synchronous optimal pulsewidth modulation.
Abstract: Multilevel converters (MLCs) have emerged as standard power electronic converters for medium-voltage high-power industrial applications. Owing to dominating device switching losses in high-power applications, it is preferable to use low device switching frequency (LDSF) modulation techniques. Then, it is possible to achieve higher device utilization, higher converter efficiency, and reduced cooling requirements. However, there exists a tradeoff between device switching frequency and harmonic distortion of converter output currents. Therefore, the main challenge for LDSF modulation techniques is to minimize the harmonic distortion of the output currents. The goal of this paper is to provide a review of various LDSF modulation techniques proposed in the literature and also discuss in detail about one of the emerging LDSF control techniques known as synchronous optimal pulsewidth modulation. Finally, challenges to LDSF modulation techniques for emerging multilevel topologies and future trends in applications of MLCs are discussed to motivate further research, to enhance the proposed LDSF techniques, and to explore for new alternatives.
TL;DR: In this paper, a novel cascaded multilevel inverter topology is proposed in which symmetric and asymmetric form of converter is discussed and a comparison study is done between the proposed topology and cascaded H-Bridge (CHB) converter.
Abstract: Recently, multilevel converters have received the largest amount of attention because of some advantages such as high quality output waveform, lower harmonic distortion and reduced electromagnetic interference. A novel cascaded multilevel inverter topology is proposed in this study. First basic part of inverter configuration is described and then symmetric and asymmetric form of converter is discussed. Comparison study is done between the proposed topology and cascaded H-Bridge (CHB) converter. Number of components such as switch number and gate driver has been reduced in the suggested topology compared to multilevel CHB converter. Furthermore, Peak inverse voltage of suggested topology is lower than that of conventional CHB converter. Reduction in number of on-state switches in introduced topology leads to the reduction of power loss and voltage drop. Moreover, modularity is other characteristic of this configuration. Finally, simulation and experimental results are presented. The presented results show the validity and the effectiveness of the proposed multilevel structure.
TL;DR: The proposed combination of UP-P WM and BP-PWM can improve the current distortion and reduce THD, while still can sustain high efficiency even with the power factors other than unity.
Abstract: To eliminate leakage ground current while achieve high efficiency, many transformerless photovoltaic inverters with unipolar pulse width modulation (UP-PWM) have been proposed and verified with real power injection only. However, in 2011, German standard VDE-AR-N 4105 updated the requirement that the inverters should satisfy the power factor from 0.9 leading to 0.9 lagging at power level higher than 4.6 kVA. When compensating the reactive power under a leading power factor, the inverter with UP-PWM might not have sufficient voltage to magnetize the inductor, which results in current distortion at zero crossing. It is hard to comply with the requirement of 1% displacement-factor accuracy. The reactive power can be well compensated with a bipolar PWM (BP-PWM) scheme; however, this will result in high current ripple and high switching loss. In this study, for reducing the current distortion under leading power factors and increasing the inductor current in the negative power region, UP-PWM is changed to BP-PWM. While in the positive power region, the inverter operation is still kept with UP-PWM to yield higher efficiency and lower current ripple. The proposed combination of UP-PWM and BP-PWM can improve the current distortion and reduce THD, while still can sustain high efficiency even with the power factors other than unity. Experimental results measured from a 5 kVA PV inverter have verified the analysis and discussion of the proposed approach.
16 Mar 2014
TL;DR: In this article, a detailed comparative evaluation of several direct torque control (DTC) strategies for permanent magnet synchronous machines (PMSMs) is presented, namely basic DTC, model predictive DTC (MPDTC), and DTC with duty ratio modulation (dTC-duty).
Abstract: This paper presents a detailed comparative evaluation of several direct torque control (DTC) strategies for permanent magnet synchronous machines (PMSMs), namely basic DTC, model predictive DTC (MPDTC) and DTC with duty ratio modulation (DTC-duty). Moreover, field orient control (FOC) is also included in this study. The aforementioned control strategies are reviewed and their performances are analyzed and compared. The comparison is carried out through simulation of a 60 kW PMSM fed by a two-level voltage source inverter (VSI). With the intent to fully reveal advantages and disadvantages of each control strategy, critical evaluation has been conducted on the basis of several criteria: torque and stator flux ripple, inverter switching frequency, machine parameter sensitivity, computational complexity and stator current total harmonic distortion (THD). The choice of control scheme can be determined based on specific requirements of particular application under consideration.
TL;DR: Constrained optimization is used to find the optimal sizing of parameters of the hybrid passive filter in order to reduce both harmonic voltages and harmonic currents in the power system to an acceptable level, as well as to improve the load power factor.
Abstract: In view of many problems associated with harmonics pollution within industrial firms, the development of new passive and/or hybrid filtering techniques of higher quality, higher efficiency, and lower cost is a necessity for the forthcoming power quality age. This article suggests a hybrid passive filter, which consists of a certain combination of a shunt passive filter (SPF) with a series passive portion as a substitute to overcome the shortcomings of conventional shunt passive filtering techniques. Constrained optimization is used to find the optimal sizing of parameters of the hybrid passive filter in order to reduce both harmonic voltages and harmonic currents in the power system to an acceptable level, as well as to improve the load power factor. The optimal design of the hybrid passive filter and its feasibility are compared with those of the C-type passive filter and the conventional SPF by means of four study cases taken from existing publications. Several simulation results are shown in order to highlight the viability of the proposed filter.
TL;DR: Compensation of the dc-side voltage harmonics of a medium-voltage 12-pulse ac/dc converter is achieved using a series active power filter (APF) to reduce inverter losses.
Abstract: In this paper, compensation of the dc-side voltage harmonics of a medium-voltage (MV) 12-pulse ac/dc converter is achieved using a series active power filter (APF). The output voltage harmonics are dependent on the converter firing delay angles and, consequently, on the specific power locus followed by the ac/dc converter. This power locus ensures minimum fifth and seventh harmonics (total rms) in the input current which provides minimum input current total harmonic distortion when the reactive power is less than 0.5 p.u. The series APF is connected between the load and the converter output via a magnetic amplifier to eliminate the dc current from the APF inverter, thus reducing inverter losses. Voltage harmonic compensation using a series APF, with and without a magnetic amplifier, is examined with both resistive and inductive loads. The simulation results for compensating a 3.3-kV MV 12-pulse converter system are experimentally verified using a scaled prototype 12-pulse converter with a series APF.
TL;DR: This paper presents the design and implementation of a simple neutral point potential (NPP) regulator for a three-level diode-clamped inverter employing a sine-triangle regulator in conjunction with a closed-loop controller with reduced switching losses.
Abstract: This paper presents the design and implementation of a simple neutral point potential (NPP) regulator for a three-level diode-clamped inverter employing a sine-triangle regulator in conjunction with a closed-loop controller with reduced switching losses. The regulator principle is based on adding a continuous variable offset voltage which regulates the midpoint potential of the dc bus. The novelty of the proposed NPP regulator is in the determination of the magnitude of variable offset voltage based upon the average value, peak-to-peak amplitude, total harmonic distortions, and third harmonic content in NPP. Aside from maintaining dc-bus voltage balance, the proposed regulator leads to a significant reduction in the voltage distortion at the NP, resulting in the reduction of the required dc-bus capacitance. It also reduces the switching losses of the inverter by inserting the “no-switching” zone within each half cycle of the fundamental voltage wave. Analytical, computer simulation, and experimental results verifying the approach are presented in this paper for various load power factor angles.
TL;DR: In this article, a mixed conduction mode (MCM) digital controller with a digital signal processor (DSP)-based DCM detection technique is presented to realize total harmonic distortion (THD) and power factor improvements in boost power factor correction (PFC) converters operating in both continuous conduction modes (CCM) and DCM during a single ac line half-cycle.
Abstract: This paper presents a novel mixed conduction mode (MCM) digital controller with a digital signal processor (DSP)-based discontinuous conduction mode (DCM) detection technique to realize total harmonic distortion (THD) and power factor improvements in boost power factor correction (PFC) converters operating in both continuous conduction mode (CCM) and DCM during a single ac line half-cycle. By using the integrated comparators found on many DSPs, simplification and cost-reductions over existing DCM and zero-current detection methods are made possible. Additionally, performance improvements over a conventional CCM digital control technique are possible with simple software modification, and can be extended to existing boost PFC converter designs provided a compatible DSP is present. At an output power of 98 W, an experimental 650 W boost PFC converter operating in the MCM controlled by a TMS320F28035 provides a THD reduction of 40.2% and power factor improvement of 1.5% over a conventional digital controller.
TL;DR: Each proposed hybrid PWM is shown to outperform its constituent PWM methods in terms of harmonic distortion, and reduces the total harmonic distortion considerably at low- and high-speed ranges of a constant volts-per-hertz induction motor drive, compared to centered space vector PWM.
Abstract: Novel switching sequences have been proposed recently for a neutral-point-clamped three-level inverter, controlled effectively as an equivalent two-level inverter. It is shown that the four novel sequences can be grouped into two pairs of sequences. Using each pair of sequences, a hybrid pulsewidth modulation (PWM) technique is proposed, which deploys the two sequences in appropriate spatial regions to reduce the current ripple. Further, a third hybrid PWM technique is proposed which uses all the five sequences (including the conventional sequence) in appropriate spatial regions. Each proposed hybrid PWM is shown, both analytically and experimentally, to outperform its constituent PWM methods in terms of harmonic distortion. In particular, the third proposed hybrid PWM reduces the total harmonic distortion considerably at low- and high-speed ranges of a constant volts-per-hertz induction motor drive, compared to centered space vector PWM.
TL;DR: A multiobjective optimization method using an imperialist competitive algorithm as the solver is established to maximize efficiency, power factor, and power-to-weight ratio, as well as to reduce rotor spatial harmonic distortion and voltage regulation simultaneously.
Abstract: In view of its special features, the brushless doubly fed induction generator (BDFIG) shows high potentials to be employed as a variable-speed drive or wind generator. However, the machine suffers from low efficiency and power factor and also high level of noise and vibration due to spatial harmonics. These harmonics arise mainly from rotor winding configuration, slotting effects, and saturation. In this paper, analytical equations are derived for spatial harmonics and their effects on leakage flux, additional loss, noise, and vibration. Using the derived equations and an electromagnetic-thermal model, a simple design procedure is presented, while the design variables are selected based on sensitivity analyses. A multiobjective optimization method using an imperialist competitive algorithm as the solver is established to maximize efficiency, power factor, and power-to-weight ratio, as well as to reduce rotor spatial harmonic distortion and voltage regulation simultaneously. Several constraints on dimensions, magnetic flux densities, temperatures, vibration level, and converter voltage and rating are imposed to ensure feasibility of the designed machine. The results show a significant improvement in the objective function. Finally, the analytical results of the optimized structure are validated using finite-element method and are compared to the experimental results of the D180 frame size prototype BDFIG.
TL;DR: With the proposed SRPC strategy, a cost-effective microcontroller can be adopted to achieve an effectively reactive power control and the current-mode asynchronous sigma-delta modulation (CASDM) is adopted to enhance the current control's dynamic response and reduce both the current harmonic distortion and electromagnetic interference.
Abstract: The objective of this paper is to propose a simplified reactive power control (SRPC) strategy for single-phase grid-tied photovoltaic (PV) inverters. With the proposed SRPC strategy, a cost-effective microcontroller can be adopted to achieve an effectively reactive power control. Moreover, the current-mode asynchronous sigma-delta modulation (CASDM) is adopted to enhance the current control's dynamic response and reduce both the current harmonic distortion and electromagnetic interference. In this paper, the operational principle of the proposed SRPC is introduced. Then, the small signal analysis for the PV inverter with the CASDM is presented. Finally, a 1-kVA single-phase PV inverter was built to verify the performance of the proposed control strategy.
TL;DR: In this paper, a simplified space vector modulation (SVM) technique is proposed for the seven-level cascaded H-bridge (CHB) inverter, which is based on decomposing the sevenlevel space vector hexagon into a number of two-level SVM hexagons.
Abstract: A simplified space vector modulation (SVM) technique is proposed for the seven-level cascaded H-bridge (CHB) inverter. It is based on decomposing the seven-level space vector hexagon into a number of two-level space vector hexagons. The presented technique significantly reduces the calculation time and efforts involved in the SVM of a seven-level inverter; without any loss in the output voltage magnitude or increase in the total harmonic distortion content. A further simplified technique is also presented in this study, which significantly reduces the complexity and effort involved in the seven-level SVM. Simulation results for the seven-level CHB inverter using the proposed techniques are presented. The results are compared with results using sinusoidal pulse-width modulation (PWM) and third harmonic injection PWM to prove the validity of the proposed techniques. The proposed technique is perfectly general and can be applied to all types of multilevel inverters and extended to higher level inverters.
TL;DR: In this article, the authors proposed a modified space vector PWM method (SVPWM) control method for the current-fed quasi-Z-source inverter (QZSI), which can buck and boost voltage and provide bidirectional power flow.
Abstract: The recently proposed current-fed quasi- Z-source inverter (QZSI) can buck and boost voltage and provide bidirectional power flow . A crucial criterion for the size of three-phase PWM converters is the cooling of the power semiconductors and thus determination of power dissipation at certain operating points. In the modified space vector PWM method (SVPWM) control method for this circuit, different PWM sequences can lead to different switching loss, current ripple, total harmonic distortion, and also the voltage spike on the switching devices. In order to select the best PWM sequence to obtain the best performance and efficiency, a complete analysis and calculation for the four mentioned criterions are presented for different sequences. For each criterion, the best sequences are selected to obtain better performance. Finally, the optimized PWM sequence in the modified SVPWM control for this circuit is selected with the optimized hardware design together to achieve the best efficiency at the full operation range. The optimized hardware design has been built in the lab, including the optimal design of the coupled inductor, optimal design and selection of Z-source capacitors and output capacitors, the selection of Z-source diode, and the final layout of the hardware. In order to bring the prototype into real application in a hybrid electrical vehicle , the inverter efficiency is measured according to the motor P-V curve. The estimated efficiency curve and experiment results are plot and compared. The best efficiency at 15 kW reaches 97.6% at unity voltage gain.