Low Current Total Harmonic Distortion Research Articles

Development of Sliding Mode Control-Adaptive Neuro-Fuzzy Inference Strategy Algorithm for Three-Phase 15-Level MLI

A comparative analysis was conducted in current research on the control strategies utilized in three-phase 15-level Cascaded H-Bridge Multilevel inverter (CHBMLI)-fed different RL loads with a three-phase induction motor, generally applied in industries. The analysis of 15-level CHBMLI, with Sliding Mode Control (SMC), the sliding mode control with an artificial neural network (SMC-ANN), and sliding mode control with an Adaptive Neuro-Fuzzy Inference Strategy (SMC-ANFIS) controller are explained. The study compared the performance achieved by controllers at four different speeds of a 3ϕ inductor motor and parallel-connected RL load dynamic change under closed-loop operations. The comparative study results demonstrate that there should be a reduction in the methodology suggested in terms of both the quantity of power devices and Total Harmonic Distortion (THD). The researcher conducted the experimentation procedures to authenticate the proposed 15-level MLI topology's performance. The SMC-ANFIS control technique produces less voltage and lower current total harmonic distortion of 5.53% and 2.74% compared to the SMC-ANN control technique in both simulation and real-time implementations.

Performance analysis of a bridgeless power factor correction (PFC) buck–boost LED driver with ripple diversion scheme for extended lifespan

SummaryIn the state of the art of AC‐fed light‐emitting diode (LED) drivers, power factor correction (PFC), second harmonic LED current ripple elimination, low current total harmonic distortion (iTHD), removal of electrolytic capacitors (EC) and flicker‐free operation are the major challenging issues. This paper proposes a bridgeless universal voltagerange AC‐fed LED driver that overcome the major issues of LED driver. The bridgeless buck–boost PFC configuration minimizes the losses relative to the front‐end bridge rectifier‐based configurations. Operating in discontinuous conduction mode (DCM), the source current tracks the input voltage shape for a wide operating range, achieves inherent PFC and maintains low input current THD. Also, this provides significant reduction in the output current ripple with the ripple diversion circuit (RDC) connected in shunt across the LED load, which relatively reduces and utilizes low value of output capacitance. Hence, a flicker‐free operation is achieved without the use of electrolytic capacitors. In addition, the elimination of ECs improves the operating lifespan of the proposed LED driver. A detailed theoretical analysis and results of the proposed LED driver are validated on DSP and analog controller platforms with a 62 W/62 V experimental laboratory prototype. The experimental results confirm that the proposed LED driver achieves a power factor of 0.94–0.997, input current THD of maximum 6.8%, output current ripple of 5%, and a peak efficiency of 91.25% for the wide range of input voltage variation. These indices also satisfy IEC‐61000‐3‐2 and IEEE 1789‐2015 standard limits.

An Input-Current Shaping and Soft-Switching Drive Circuit Applied to a Piezoelectric Ceramic Actuator.

Piezoelectric ceramic actuators utilize an inverse piezoelectric effect to generate high-frequency vibration energy and are widely used in ultrasonic energy conversion circuits. This paper presents a novel drive circuit with input-current shaping (ICS) and soft-switching features which consists of a front AC-DC full-wave bridge rectifier and a rear DC-AC circuit combining a stacked boost converter and a half-bridge resonant inverter for driving a piezoelectric ceramic actuator. To enable ICS functionality in the proposed drive circuit, the inductor of the stacked boost converter sub-circuit is designed to operate in boundary-conduction mode (BCM). In order to allow the two power switches in the proposed drive circuit to achieve zero-voltage switching (ZVS) characteristics, the resonant circuit of the half-bridge resonant inverter sub-circuit is designed as an inductive load. In this paper, a prototype drive circuit for providing piezoelectric ceramic actuators was successfully implemented. Experimental results tested at 110 V input utility voltage show that high power factor (PF > 0.97), low input current total harmonic distortion (THD < 16%), and ZVS characteristics of the power switch were achieved in the prototype drive circuit.

Analog Controlled Critical Conduction Mode Three-Phase Vienna Rectifier

This paper proposed a novel analog-based critical conduction mode (CRM) control method for the three-phase three-level Vienna rectifier. By the proposed method, the simple analog CRM control can be achieved in each phase of the Vienna rectifier. All the control schemes are implemented with three low-cost analog CRM PFC IC controllers. The operation analysis of the CRM Vienna rectifier considering the parasitic capacitances is performed. Experimental results demonstrate that the valley-switching (VS) for IGBTs and the zero-current-switching (ZCS) for diodes are indeed achieved. A relatively high efficiency, a low input current total harmonic distortion, and a high power factor are tested at a 5.8 kW three-phase Vienna rectifier.

Assessment of a single-phase single-stage grid-connected photovoltaic system

A grid-connected photovoltaic (GCPV) system plays an important role in the development of green technology. However, generated photovoltaic (PV) power that is injected into the grid causes instability in the grid system. Previous studies have shown that power quality for a three-phase system is thoroughly being discussed, but not for a single-phase system. Single-phase system also contribute to instability in low-voltage grid networks during high power penetration as majority of the single-phase GCPV nowadays are installed on rooftops. Thus, in this study, the power quality of a single-phase single-stage GCPV system is investigated based on the total harmonic distortion (THD), power factor (PF), and the generated active (P) and reactive (Q) power during different solar irradiance and varying loads conditions. A model of the GCPV system was developed in MATLAB/Simulink, so that certain variables can be varied to observe their effect towards the power quality. The results show that the current and voltage of generated PV power are synchronized and having low current THD which is less than 1% for all cases. PF values are also in the acceptable range in compliance to IEC 61727 standard which is 0.9971, and the generated PQ is in accordance to the connected load.

Soft-Switched Integrated AC–DC Bidirectional Converter With Natural Grid Harmonic Elimination

Two-stage ac–dc converters have hard-switched ac–dc stage followed by soft-switched dc–dc stage. Since devices in the ac–dc stage are switched at low frequency (typically 10–20 kHz), bandwidth of current control loop of this stage is limited (typically less than 2 kHz). This low bandwidth current loop fails to reject current harmonic disturbances arising due to distorted grid voltages, thus necessitating multiple harmonic compensation loops or complex control algorithms for meeting IEEE Std 519-2014. Lack of soft-switching prohibits devices of the ac–dc stage from being switched at a frequency above 100 kHz and thereby attain a bandwidth of around 10 kHz for natural rejection of grid current harmonics. This article proposes an integrated three-phase bidirectional isolated ac–dc converter, where soft-switching operation is extended to devices in ac–dc stage as well. Thus, high bandwidth current loop can be achieved without reduction in efficiency. The proposed modulation scheme decouples ac–dc and dc–dc operations using <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xor</small> logic. An iterative procedure for design of resonant tank is provided. The integration also leads to 25% fewer devices. Experiments carried out on a 5-kW prototype demonstrate that a low current total harmonic distortion, complying with IEEE standard, can be achieved with good efficiency, even under distorted grid voltages.

A New H8 Inverter Topology With Low Common Mode Voltage and Phase Current THD for 3- Induction Motor Drive Applications

Common mode voltage (CMV) reduction in a traditional H6 (six switch) 3-φ inverter usually demands additional power semiconductors to avoid poor harmonic performance. However, apart from tending to the CMV related issues, these extra switches do not add any other capability to the inverter. To address this limitation, in this article, a novel H8 inverter configuration is proposed which not only reduces the CMV by 66.6%, the phase current total harmonic distortion (THD) is also improved. The proposed H8 inverter employs two additional power semiconductor devices along with the conventional H6 inverter in a manner that it can generate 15 space vectors (SV). By considering the CMV attribute of each SV, a unique sector configuration is proposed where the SV diagram is divided into 18 asymmetrical sectors and three distinct SV sequences are identified. A special pulsewidth modulation scheme is devised to operate the proposed topology to achieve reduced CMV and improved harmonic performance. A comparison study reveals that the proposed topology offers better phase current THD, low CMV, low losses, and low semiconductor requirement. Simulation and experimental results are included to justify the various claims.

Generalized Clarke Transformation and Enhanced Dual-Loop Control Scheme for Three-Phase PWM Converters Under the Unbalanced Utility Grid

Three-phase grids imbalance causes serious alternating input current distortion in three-phase pulsewidth modulation (PWM) rectifiers where the conventional control scheme is employed. In this article, a generalized Clarke transformation is proposed to convert three-phase unbalanced sinusoidal quantities to two orthogonal sinusoidal quantities with equal amplitudes. Then, these two orthogonal sinusoidal quantities could be converted to two direct quantities by the Park transformation. Furthermore, based on the generalized Clarke transformation, an enhanced dual-loop control (EDLC) scheme is proposed to control the three-phase PWM rectifier in the synchronous rotating frame. Finally, a 5-kW Vienna-type rectifier prototype was built to verify the proposed generalized Clarke transformation and the proposed EDLC control scheme. Experimental results show that, by using the proposed EDLC scheme, the low current total harmonic distortion is achieved even both the amplitude and phase of the utility grid voltages are unbalanced.

Reactive power compensation for grid by Packed-U-Cell inverter using model predictive control strategy with intelligent multi-objective scheme

This paper proposes a model predictive control strategy for 15 level Packed-U-Cell inverter that satisfies multiple-objectives of low current total harmonic distortion (THD), capacitor voltage balances, supply of desired active and reactive power, as well as lower switching and lower voltage stresses on the switching devices. The proposed device performs well under dynamic conditions and can successfully track the current command during step changes in the power demand. A detailed modeling is presented and discussed. MATLAB/Simulink is used for obtaining the simulation results, and the results are validated in the real time by using a hardware-in-the-loop (HIL) Typhoon 402 real-time emulator.

A high efficiency static VAr compensation scheme using modified magnetic energy recovery switch (MERS) with parameters selection of passive elements for low harmonic injection

In this paper, a minimum switch count modified magnetic energy recovery switch (MERS) topology has been proposed as a shunt static VAr compensator (SVC-MERS). Whereas, the existing scheme uses four active switches for the same purpose. Thus, conduction loss of the switch is reduced in the proposed scheme due to the minimum switch count and thus promises a high-efficiency compensator. Moreover, a coupling inductor (L) and a capacitor (C) are used in the proposed scheme for reactive energy storing and exchanging. Improper selection of L and C may instigate harmonic resonance. To examine its impact on modified MERS performance, an equivalent harmonic model using mathematical equations has been developed by introducing switching functions. The characteristics analysis of the proposed modified MERS has been done by using this harmonic model. Based on the above analysis a suitable ratio (S) of resonant angular frequency to line angular frequency and corresponding optimum L, C parameters have been selected for low harmonic injection. The key features of this proposed scheme are low current total harmonic distortion (THD), lesser switching losses, reduced cost, and low voltage rating of the switch as compared to the existing MERS scheme. To verify the proposed concept simulation has been carried out using a 6 kVA rating inductive load in MATLAB Simulink environment. The both analytical and simulation results confirm that the proposed reduced switch count compensator model with optimum L=30mH and C=150μF can be used efficiently for power quality improvement in a low voltage grid. \\

A new switching look-up table for direct power control of grid connected 3L-NPC PWM rectifier

This paper presents a comprehensive and systematic approach in developing a new switching look-up table for direct power control (DPC) strategy applied to the three-phase grid connected three-level neutral-point clamped (3L-NPC) pulse width modulated (PWM) rectifier. The term of PWM rectifier used in this paper is also known as AC-DC converter. The approach provides detailed information regarding the effects of each multilevel converter space vector to the distribution of input active and reactive power in the converter system. Thus, the most optimal converter space vectors are able to be selected by the switching look-up table, allowing smooth control of the active and reactive powers for each sector. In addition, the proposed DPC utilizes an NPC capacitor balanced strategy to enhance the performance of front-end AC-DC converter during load and supply voltage disturbances. The steady state as well as the dynamic performances of the proposed DPC are presented and analyzed by using MATLAB/Simulink software. The results show that the AC-DC converter utilizing the new look-up table is able to produce almost sinusoidal line currents with lower current total harmonic distortion, unity power factor operation, adjustable DC-link output voltage and good dynamic response during load disturbance.

A lyapunov‐based adaptive voltage controller for a grid connected PV system

A new Lyapunov-based adaptive controller (LBAC) for a single stage three-phase grid-connected PV system (GCPVS) is proposed here. The uncertainties in solar irradiation affects the performance of the GCPVS. Further, ageing in the DC-link capacitor affects the PV voltage tracking. To achieve an improved performance of the GCPVS under both high and low irradiation, and under an aged DC-link capacitor, a new LBAC scheme has been proposed to control the PV voltage. In this LBAC, the gains of the controller are adapted online by a Lyapunov-based adaptation mechanism to provide the nominal tracking response of PV voltage. Further, a maximum power point tracking algorithm and grid current controllers are designed to transfer the maximum PV power to the grid, ensuring good power quality. As a result, improved performances of the GCPVS are achieved in terms of low PV voltage ripple, enhancement of delivered grid energy, and low grid current total harmonics distortion (THDs). Computer simulation studies are carried out in MATLAB/Simulink environment to verify the effectiveness of the proposed LBAC. Further, experiments are performed in a 2.5 kW GCPVS prototype for real time implementation of the proposed controller. The total harmonics distortion (THD) of grid currents is found to be within IEEE-1547 standards.

A Centralized Control Strategy for Grid-Connected High-Speed Switched Reluctance Motor Drive System With Power Factor Correction

Conventionally, the converter of switched reluctance motor (SRM) is fed by the uncontrollable diode bridge rectifier (DBR), which leads to a low grid-side power factor (PF) and high current total harmonic distortion (THD). In this paper, an alternative solution for the grid-connected high-speed SRM drive system with improved PF is proposed. In the proposed drive system, the three-level active front end (AFE) is connected in cascade with the midpoint converter for SRM operation. A centralized strategy, which controls the AFE and SRM together, is proposed to govern the motor speed and grid-side PF by regulating the real power and reactive power of the system, respectively. Specifically, the real power, reactive power, and the voltage balancing of split capacitors are controlled by the model predictive directed power control (MP-DPC) algorithm, which significantly reduces the control complexity and guarantees the fast dynamic response. Consequently, satisfying speed regulation, high PF, low current THD, and bi-directional power-transfer capability are achieved. An idea-proofed testbench is constructed in laboratory, and the applicability of the proposed drive system is verified by a series of experimental results.

Optimal IP Current Controller Design Based on Small Signal Stability for THD Reduction of a High-Power-Density PFC Boost Converter

This paper presents an optimal design for the inner current-control loop of the continuous current conduction mode (CCM) power factor correction (PFC) stage, which can be used as the front stage of the two-stage AC/DC telecom power supply. The conventional single-phase CCM-PFC boost converter is implemented with proportional–integral (PI) controllers in both the voltage and current-control loops to regulate the output DC voltage to the specified value and to ensure the input current follows the input voltage, which offers a converter with a high-power factor (PF) and low current total harmonic distortion (THD). However, due to the slow dynamic response of the PI controller at the zero-crossing point of the input supply current, the input current cannot fully follow the input voltage, which leads to high THD. In this paper, we investigate a digitally controlled PFC converter with an optimally designed inner current-control loop using a doubly-fed control loops integral-proportional (IP) controller to reduce the THD and to offer an input current with a unity PF. For the economic design of a digitally controlled PFC converter, two isolated AC and DC voltage sensors are designed for interfacing with the microcontroller unit (MCU). PSIM software as well as experimental prototype was used to test the converter performance using the proposed designed current controllers and isolated voltage sensors. We achieved a high-power-density, digitally controlled, telecom PFC stage with a power factor more than 99% and THD of about 5.50%.

Recent Achievements in Model Predictive Control Techniques for Industrial Motor: A Comprehensive State-of-the-Art

Model predictive control (MPC), manly based on a direct use of an explicit and identifiable model, has been widely used in controller design in different applications both by academia and industry. The reason for such popularity is due to its strong ability for providing high performance electric drive systems, as highly recognized as the most reliable control approach compared with field-oriented control (FOC) and direct torque control (DTC). In general, the MPC has numerous features and advantages, such as direct switching states to the converter without any modulation, online optimization with multivariable control, low current total harmonic distortion, low switching loss, etc . The aim of this paper is to provide a comprehensive review for major development and achievements of the recent progress on the MPC for electrical machines and drives. This review begins with the innovative topologies and operating principles of fundamental MPC, and ends to summary on different advanced MPC algorithms. Typical MPC techniques have been fully adopted to enhance the drive performance of the electrical drives, mainly including finite-set model predictive control (FS-MPC) based on tuning weighting factors, without weighting factors, maximum torque per ampere, low number of switching vectors, and multi voltage vectors in one sample period. Finally, great attention has been paid to the discussion of the new trends and future research topics.

A high‐gain IΓ‐source hybrid single‐phase multilevel inverter for photovoltaic application

Impedance-based step-up converters are widely developed for photovoltaic applications due to providing single-stage conversion, high-efficiency, low voltage and current stresses, and high boost-factor. An improved Γ-source (IΓ-source) single-phase hybrid multilevel inverter is proposed. This structure has a better voltage gain characteristic, high-efficiency, multilevel output voltage, low output current total harmonic distortion (THD), and continuous input current. It is extensible for attaining higher voltage levels. Furthermore, higher non-shoot-through modulation indexes are obtainable by this topology in comparison with previous works due to performing higher gains in lower shoot-through duty cycles. Also, the output harmonics are reduced because of applying lower shoot-through duty cycles. This article demonstrates the operating principle of this hybrid multilevel inverter in detail. Simulation and experimental results are exhibited to evaluate the performance of this converter. Results confirm the proposed IΓ-source hybrid multilevel inverter, its operating principle, and the modulation strategy.

Non‐local harmonic current and reactive power compensation for a multi‐microgrid system using a series–shunt network device

In this study, a new non-local active compensation method is developed for a multi-microgrid (MMG) system. The current industry practice is to utilise local harmonic current and reactive power compensation methods, however, local compensation methods are not practical for large MMG system with widely dispersed non-linear loads, because each non-linear load would require its own compensator. To overcome this problem, a novel compensating technology called a series–shunt network device (SSND) is installed between a pair of microgrids in the proposed MMG system. The SSND reduces the number of local compensators required while also performing additional functions in comparison with conventional devices. For effective control of the SSND, an improved model predictive control (MPC) algorithm, which gives better tracking accuracy and faster set-point change than that of a conventional proportional–integral controller, is also presented. Analysis and simulations verify the capability of SSND in performing both local and non-local active compensation of harmonic current and reactive power in the proposed MMG system under various test scenarios. Simulation results show that the MPC-controlled SSND can achieve effective compensation, thereby resulting in a very low current total harmonic distortion value of 2.4% and a unity power factor at the distribution grid side.

Device-Level Loss Balancing Control for Modular Multilevel Converters

Modular multilevel converter (MMC) is a promising topology in medium/high-voltage applications for its merits, e.g., scalability, low output current total harmonic distortion, and high efficiency. But the reliability of MMCs is questionable due to more semiconductor devices used than other topologies. Another reliability problem of MMC is the significant uneven loss distribution between the top and bottom semiconductor devices within one submodule (SM) owing to the dc component in the arm currents. The stress difference caused by the uneven loss distribution between the top and bottom semiconductor modules will lead to the lifetime difference of the semiconductor devices, which shortens the lifetime of the whole MMC system. To extend the lifetime of MMCs without the modification of system hardware, this article proposes a device-level loss balancing control method. In this method, the accurate device loss models are established to feedback real-time device losses into the loss balancing controller. The controller (by regulating the SM capacitor voltages) adjusts the semiconductor conducting duty cycles to even the loss distribution without affecting the performance of the ac output and capacitor-voltage balancing. The effectiveness of the proposed control method is validated through experimental results.

An Improved SEPIC- Based Single Switch Buck-Boost PFC Converter Fed Brushless DC Motor Drive

In this paper an improved SEPIC-based single switch Buck-Boost PFC converter fed brushless DC motor drive is proposed. This converter works by one switch and voltage stress across the switch is also low. In this converter, a non-inverting output voltage is obtained. It operates at wide output voltage range by changing the duty cycle of the power switch. As only one power switch is used, the presented converter can be easily controlled. It has very low source current total harmonic distortion and achieves unity power factor which results in high efficiency operation of BLDC motor. The voltage source inverter feeding the BLDC motor operates at line frequency so that the switching loess are very low.

Three‐phase thyristor controlled reactor using two sets of delta connected switches with low current harmonics

This work presents a three-phase thyristor-controlled reactor (TCR), which makes use of two constituent banks of controlled reactors, with coordinated control of the triggering angle of both the banks. The first reactor bank has a set of `delta' connected back-to-back thyristor switches with a balanced set of reactors in series with each switch, while the second reactor bank also has back-to-back thyristor switches in `delta' connection but with a balanced set of reactors in series with each line. It is demonstrated that this arrangement prevents some major current harmonics in the supply line by proper choice of the maximum kVAr ratio between the two reactor banks. The use of delta connected switches in both banks reduces the current rating of the switches. Hence, without using any phase-shifting isolation transformer or filters, the proposed technique permits control of reactive power over a reasonable range, with a low current total harmonic distortion meeting existing harmonics standards. Simple construction and operation of the proposed TCR make it an attractive and cheaper solution. The modelling, analysis and performance assessment of the new TCR are presented.