Terms Of Total Harmonic Distortion Research Articles

Multifaceted Functionalities of Bridge-Type DC Reactor Fault Current Limiters: An Experimentally Validated Investigation

With the ongoing expansion and interconnection of electrical power systems, alongside the rapid proliferation of renewable distributed generations (DGs), the short-circuit extent in the power grid is experiencing a significant rise. Fault current limiters (FCLs) have been introduced in an effort to address this issue, ensuring the robustness and sustainability of expensive power system components when confronted with short-circuit faults. Among the various types of FCLs, bridge-type DC reactor fault current limiters (BDCR-FCLs) have emerged as one of the most promising options. While BDCR-FCLs have shown excellent properties in limiting harmful short-circuit currents, they are also advantageous in other respects. This paper investigates the supplementary functionalities of BDCR-FCLs as a multifaceted device towards the enhancement of the quality of supplied energy in terms of total harmonic distortion (THD) reduction, power factor (PF) correction, peak current reduction for nonlinear loads, and soft load variation effects, as well as their capability to limit fault current. To this aim, the capabilities of BDCR-FCLs have been studied through various simulated case studies in PSCAD/EMTDC software V5.0.1, in addition to experimental tests considering an AC microgrid connected to a DC system. The experimental and simulation investigations verify the superior multifaceted functionalities BDCR-FCLs introduce in addition to their excellent fault current-limiting capabilities. The results show that PF improved by 6.7% and 7%, respectively, in simulation and experimental tests. Furthermore, the current THD decreased by 20% and 18% in the simulation and experiment, respectively.

A Comparison of Digital Constant On-Time and Variable On-Time Control in Buck/Buck-Boost PFC Converter

This study compares two frequently used control strategies in the context of completely digitally controlled critical conduction mode (CRM) buck/buck-boost converters, namely constant on-time (COT) and variable on-time (VOT). The aim of this research is to compare and assess the performance of different control systems in terms of power factor (PF) and total harmonic distortion (THD). The COT control technique employs a fixed on-time period for each switching cycle, resulting in a predictable and straightforward control scheme. On the other hand, VOT control dynamically adapts the on-time period based on the input and output voltage conditions, offering potential advantages in terms of load regulation and stability. The analysis results provide valuable insights into the strengths and limitations of each control technique. Additionally, the dynamic behavior of the converters under various operating conditions is investigated, shedding light on the stability and robustness aspects of each control scheme. The study is conducted using a fully digital setup and evaluated in Matlab/Simulink environment. The findings show that VOT control outperforms COT in terms of THD and PF under steady-state conditions. These findings offer valuable guidance for selecting the appropriate control technique for PFC converters, depending on specific requirements of their applications.

Improved the two DC capacitors’ voltage balancing of three-level NPC inverters applied in electric vehicles

Excessive unbalance of the DC capacitor voltages of the inverter can cause overvoltages on power components and capacitors, causing unintended low-order harmonics on the load side such as second harmonics, 3rd, 4th, 5th, ..., causing direct harm to the motor load, reducing the controllability of the reverse voltage and filter compensating current for the active filter circuit, affect to the performance of electric vehicles (EVs). Therefore, maintaining the DC capacitors' voltage balance will control the multi-level inverter's input quality and ensure the output quality in terms of Total Harmonic Distortion (THD). The paper proposes a method to control the two DC capacitors’ voltage balance of the 3-level inverter, using the principle of offset function separation. The analysis results suggest that the NPC three-level modulation technique should be implemented to satisfactorily achieve the neutral line current (iNP). Compared with recent international publications, the proposed new algorithm can save and reduce switching loss; the transient dynamic response can be adjusted easily. Maintaining the capacitor voltage balance allows the design with the smallest capacity to reduce voltage stress on components. The proposed results are partially verified through simulation and experiment.

Power quality improvement in distributed generation system using intelligent control methods

Hybrid <span>electric power generation and its integration with the grid to supply consumer demand is main focus of this paper. The use of nonlinear load and advanced power electronic equipment-based devices at the consumer end introduces power quality issues in the power system network in terms of voltage and current. This paper explains the design of a control algorithm for a unified power quality conditioner used for mitigating both voltage and current-based power quality issues. The dynamic voltage restorer of unified power quality controller (UPQC) is designed with a unit vector control algorithm and the distribution static synchronous compensator (DSTATCOM) is designed with fuzzy logic and adaptive network-based fuzzy inference system based instantaneous reactive power theory control algorithm. The simulation model built using the MATLAB platform includes a three-phase voltage source along with hybrid electric power generation connected to linear and non-linear loads operating under different conditions. The result is analyzed in terms of voltage and current total harmonic distortion compared with IEEE 512 power quality standards and power factor improvement. The paper shows the adaptive neuro-fuzzy inference systems (ANFIS)-based control algorithm gives better results in terms of total harmonic distortion (THD) compared to the fuzzy-based control algorithm. The power factor is improved using ANFIS-based controller proving the efficiency of the controller</span>.

Application of machine learning controller in matrix converter based on model predictive control algorithm

Finite control set model predictive control (FCS-MPC) algorithms are famous in power converter for its easy implementation of constraints with cost function than classical control algortihms. However computation complexity increases when swicthing state is high for converters such as matrix converter, multilevel converters and this impose a serious drawback to compute multi-step prediction horizon MPC algorithm which further increases the computation. To overcome the above said difficulty, machine learning based artificial neural network (ANN) controller for matrix converter is proposed. The training data for ANN controller is derived from MPC algorithm and trained offline with an accuracy of 70.3%. The proposed ANN controller shows a similar and better performance than MPC controller in terms of total harmonic distortion (THD), peak overshoot during dynamic change in reference current and dynamic change in load parameter and less computation with less execution time. Further, ANN controller for matrix converter is tested in OPAL-RT using hardware in-loop (HIL) simulation and showed that it outperforms MPC controller.

A new nonlinear control of an active rectifier for variable speed generating units

This paper deals with a newly conceived (state-feedback) nonlinear control strategy for an active rectifier that is supplied by a Permanent Magnet Synchronous Generator (PMSG). The aim of the proposed control strategy is properly regulate the DC-link voltage within a wide range of system operating conditions by: (i) taking into account a sufficiently rich model, in which the classical simplification – imposing to the DC voltage dynamics a relative degree equal to two – is avoided (so that the input power is not assumed to supply instantaneously the sum of load power and charging rate of the capacitor energy, with the resistance loss and the switching device loss being neglected); (ii) resorting to neither input–output linearizing strategies (involving the DC-link voltage regulation error) that lead to unstable regulation dynamics nor to simplifying design assumptions that overlook derivatives of intermediate reference signals; (iii) avoiding the computational-effort-requirements of Model Predictive Control (MPC) techniques. Simulation and Hardware in the loop (HIL) results illustrate the effectiveness of the proposed control – exhibiting a rather simple structure while guaranteeing local exponential stability for the resulting error system – in terms of Total Harmonic Distortion (THD) and controller response to load and DC voltage reference steps: high band-width and good steady-state waveforms are achieved. Robustness issues and control adaptiveness with respect to uncertain model parameters are also finally addressed.

A novel combined FFOC-DPC control for wind turbine based on the permanent magnet synchronous generator

The quality of the electrical energy produced from renewable energies is a preponderant need sought by electricity producers. It is in this vision that this present article tries to design a control that combines two control algorithms in order to improve the operation of a variable speed wind energy conversion system (VSWECS). Interestingly, combined control brings together fuzzy field oriented control (FFOC) with direct power control (DPC). The complete conversion chain includes the 1.5 MW permanent magnet synchronous generator (PMSG) and two full-scale mounted back-to-back power converters. Compared to FOC method based on the classical PI regulator, the proposed FFOC scheme is employed to guarantee a better performance between the effect of artificial intelligence (AI) and the simplicity of the standard regulator. This is because the FFOC smart control algorithm is used to control the machine-side-converter (MSC). The DPC control algorithm which uses a relatively low sampling frequency of around 5 kHz is proposed to estimate the active and reactive powers injected into the grid through the grid-side converter (GSC). In addition to the simplicity of implementation and the reduced simulation time, the combination of the FFOC-DPC control algorithm is very reassuring in terms of stability, robustness and tracking of set-points. The overall control scheme is simple to implement and the simulation results clearly show that the proposed control system offers very good performance in terms of total harmonic distortion (THD), which does not exceed 1.49%, a wave of well-balanced injected electric current, and a power factor almost equal to unity. Therefore, the proposed solution is finally compared with other alternatives to validate the results developed by the MATLAB/Simulink platform and consequently guarantee the improvement of the variable speed direct drive WECS.

An Implicit Controlling of Adaptive Neuro Fuzzy Inference System Controller for The Grid Connected Wind Driven PMSG System

The article presents the design and control of the adaptive neuro fuzzy Inference system (ANFIS) for the wind-driven permanent magnet synchronous generator (PMSG) in the grid connected system. The rectifier and inverter are connected with the PMSG output and the grid for maintaining the voltage at the grid under variable wind operations. Such interconnections have many challenges, like high harmonics at the output and an improper voltage profile. The harmonics are measured in terms of total harmonic distortion (THD). Performance parameters like peak overshoot and settling time of DC link voltage and rotor speed have been measured. The control of the rectifier and inverter has been assessed with the ANFIS and PID controllers. A closed strategic mechanism has been developed for the ANFIS and PID controllers for improving the performance parameters and harmonics.. Finally, it is observed that the peak overshoot (%) and settling time (sec) of the DC link voltage with ANFIS are 5.2% and 2.9 sec, which are found to be less in comparison to the PID controller with the values of 6.1% and 3.8 sec and other existing methods. Similarly, the settling time (sec) of rotor speed with ANFIS is 1.1 sec, which is less than the settling time (2.6 sec) of the PID controller. Another advantage of ANFIS is the reduction of THD (%) of 5.1% with respect to THD (%) of PID controllers of 6.2% and other existing methods. The reduced THD shows the improved version of the voltage profile.

Improved Seven-Level Multilevel DC-Link Inverter with Novel Carrier PWM Technique

Multilevel inverters have emerged as a viable alternative for various power electronic applications. It offers significant features in terms of reduced total harmonic distortion (THD) due to more number of output voltage levels, lower filter size, and voltage stress and reduced switching losses when compared to conventional two-level inverters. The classical topologies such as neutral point clamped, flying capacitor and cascaded H-bridge (CHB) are very popular for industrial applications. All these topologies have limitations in terms of more component count, capacitor voltage balancing for increased number of voltage levels. In this regard, multi-level DC link (MLDCL) inverter has been introduced as an improvement with respect to CHB MLI in terms of reduced switch count and is considered here for the study. This paper presents a single-phase MLDC link inverter with a modified carrier-based level-shifted phase disposition sinusoidal pulse width modulation (LS-PD-SPWM) technique. The proposed novel carrier PWM is compared with the conventional modulation techniques in terms of THD. The performance of the proposed modulation technique is analyzed through simulation studies in MATLAB software. A laboratory prototype model is developed in order to validate the experimental results.

Power quality improvement in single-phase transformerless semi-quasi-Z-source inverters for off-grid photovoltaic systems

The transformerless single-phase semi-quasi-Z-source inverter (SqZSI) provides several advantages over classical PWM converters. Reduced or eliminated leakage current, high power density, and low cost are important features making this topology an attractive choice for PV micro-inverter applications. Two drawbacks of this topology are DC and second harmonic injection in the output AC port, which in some cases prevent the fulfillment of standard requirements. To alleviate this power quality issue, four novel harmonic mitigation algorithms based on PI and PR controllers are proposed, analyzed, and experimentally verified with the 90 W SqZSI in this paper. Moreover, a modified modulation reference waveform strategy is introduced. Consequently, the converter performance, in terms of total harmonic distortion (THDV) is achieved at about 1.27% under full power load. Also, in this paper, the non-ideal state-space model of the SqZSI with the effect of the equivalent series resistance of inductors is developed and the generation origin of DC and second harmonic component is analyzed based on the obtained model. The achieved results confirms the significant THD reduction by more than 75%, the DC component suppression, the second harmonic mitigation, and the power quality improvement.

Analysis and control strategy of standalone PV system with various reference frames

Abstract Renewable energy sources like solar power are the more convenient source of renewable energy. Nowadays, increasing the energy demand may create many disturbances in power system distribution. To overcome the necessity of power demand, all are focusing on generation of more energy from clean technologies with increased development in power distribution systems using the renewable energy sources. This work aims to propose a standalone PV system with an LCL filter, with two cascaded feedback control loops with an appropriate controller for three reference frame. This work concerns the topology for three reference frames such as synchronous, standalone, and natural reference frames with the respective controllers (PI and PR). The topology contains two cascaded feedback control loops such as DC-link voltage control loop (PI) cascaded with the internal current loop (PI and PR). These commonly used controllers are implemented in various well-known reference frames for the PV system and their steady-state performance is also evaluated in terms of total harmonic distortion. Finally, the simulation results from a two-stage 5.5 kW, 440 V (L–L), three-phase standalone PV system are provided to confirm the theoretical analysis and effectiveness of the control schemes.

Parameter Optimization of Bidirectional Three-Phase DC-AC Power Inverter by an Improved Particle Swarm Optimization based Fractional Order PI Controller for the Grid Forming Operation

Nowadays, it is becoming more remarkable for bidirectional power conversion from battery energy sources. These structures can be used for three-phase loads and they also have a common application in Micro-grid systems. This paper is mainly focused on parameter optimization of the system by using improved particle swarm optimization (PSO) in grid forming operation of dual active bridge series resonant converter (DABSRC) topology, in term of total harmonic distortion (THD). Fractional order proportional integral (FOPI) controller is used to simulate DABSRC regarding to THD factor in this system. The results are also compared to genetic algorithm (GA) and conventional PSO. While all algorithms achieved the same optimum control parameters, a significant reduction of computation time has been reported by improved PSO in terms of THD.

Sliding Mode Controller for Parameter-Variable Load Sharing in Islanded AC Microgrid

Controlling voltage, frequency, and current in an islanded microgrid is a challenging problem because the distributed generation sources, stochastic and intermittent in nature, are not connected to the main electricity network to provide stable and clean energy. Therefore, the design of a robust controller to control the output parameters of the islanded microgrid and suppress load variations and disturbances is essential. In this paper, a hysteresis controller is proposed and designed to control the output voltage of an islanded AC microgrid and an improved sliding mode controller (SMC) based on adaptive control principle is designed to control the current of the microgrid. The current controller consists of two parts: An adaptation part, which aims to eliminate disturbances and system uncertainties, and a second part, which aims to deal with the tracking problem of the system under parameter-varying topologies. The adaptation strategy has the advantage of solving the gain tuning problem and chattering reduction. It also requires limited information about disturbance and uncertainties of the system. To validate the proposed control methodology and show its effectiveness, a case study of a simulated islanded microgrid is presented. The results show that the proposed controllers can effectively control the current and voltage underload changes and increase the stability and resilience of the microgrid. The results also reveal that the performance of the proposed controller in terms of total harmonic distortion (THD) and dynamic response overcome the performance of conventional controller by a 4× reduction in THD and 40–200× reduction in settling time.

Most Valuable Player based selective harmonic elimination in a cascaded H-bridge inverter for wide operating range

Abstract Selective Harmonic Elimination PWM (SHEPWM) is a classical method of voltage control of the inverter while eliminating the undesirable lower order harmonics for low-frequency applications. Multivariable non-linear equations often result in SHE modulation scheme. In this work, a Most Valuable Player Algorithm (MVPA) has been applied to solve the non-linear SHE equations for the elimination of lower order harmonics in a cascaded H bridge multilevel inverter. The MVPA algorithm shows better convergence characteristics and wider modulation control compared to some popular meta-heuristic optimization methods. Optimized switching angles have been obtained for 5, 7 and 9 level inverters for different modulation index (MI) from 0.05 to 1. The Total Harmonic Distortion (THD) for the output voltage was found to be smoother compared to the powerful Differential Evolution (DE) algorithm for modulation index greater than 0.6. And for modulation index greater than 0.8, MVPA scores better than DE in terms of THD. Experimentally, the performance of MVPA has also been validated for 1-phase 5, 7 and 9 level cascaded H-bridge inverter and 5th, 5th and 7th, 5th, 7th, and 11th harmonic was eliminated respectively.

Rapid Control Prototyping of Five-Level MMC based Induction Motor Drive with different Switching Frequencies

In this paper, Rapid Control Prototyping (RCP) of five-level Modular Multilevel Converter (MMC) based Induction Motor (IM) drive performance is observed with different switching frequencies. The Semikron based MMC Stacks with two half-bridge each are tested with the switching logic generated by phase and level shifted based Sinusoidal Pulse Width Modulation (SPWM) technique. The switching logic is generated by the Typhoon Hardware in Loop (HIL) 402. The disadvantages of Multilevel Converter like not so good output quality, less modularity, not scalable and high voltage and current rating demand for the power semiconductor switches can be overcome by using MMC. In this work, the IM drive is fed by MMC and the experimentally the performance is observed. The performance of the Induction Motor in terms of speed is observed with different switching frequencies of 2.5kHz, 5kHz, 7.5kHz, 10kHz, 12.5kHz and the results are tabulated in terms of Total Harmonic Distortion (THD) of input voltage and current to the Induction Motor Drive. The complete model is developed using Typhoon HIL 2021.2 Version Real-Time Simulation Software.

Grid-Forming Operation of Energy-Router Based on Model Predictive Control with Improved Dynamic Performance

The focus of this study is on the grid-forming operation of the Energy Router (ER) based on Model Predictive Control (MPC). ER is regarded as a key component of microgrids. It is a converter that interfaces the microgrid (s) with the utility grid. The ER has a multiport structure and bidirectional energy flow control. The ER concept can be implemented in Nearly Zero-Energy Buildings (NZEB) to provide flexible energy control. A concept is proposed where the ER works as a single grid-forming converter. The challenge is to keep the predefined reference voltage and frequency inside the NZEB in all possible modes, including the idle operation mode, current sources, and nonlinear load control. To gain stability and output voltage quality, the MPC is proposed. The design of the modified MPC algorithm with improved dynamics performance is explained. PLECS software is utilized to verify the proposed algorithm. The results demonstrate the suitable performance of the proposed control method in terms of total harmonic distortion of the output voltage. The influence of weighting coefficiencies is evaluated, showing the higher impact of the capacitor filter voltage on lowering the total harmonics distortion of the output voltage. Finally, the capability of the control system toward step change in the reference value is evaluated.

A Multiphase AC–DC Converter With Improved Power Quality for EV Charging Station

This work presents a multiphase ac–dc converter-based electric vehicle (EV) charging station that is designed to meet IEEE-519 power-quality (PQ) standard. The proposed EV charging station draws current from the utility grid at low total harmonic distortion (THD) and high power factor (PF), without using PF corrector and active/passive filter circuits. This study evaluates an 18-phase ac–dc converter for an EV charging station, which consists of three single-phase multiwinding transformers (MWTs) and diode rectifiers. MWTs are connected to enable direct conversion of a three-phase utility supply into an 18-phase power supply that reduces the measured THD in the input line current. The ac–dc conversion stage of the proposed EV charging station is found to be reliable and operates at line-frequency, without the need for high-frequency active switches. For charging an EV in constant current (CC) and constant voltage (CV) mode, a multiphase (interleaved) dc–dc converter is used. MATLAB/Simulink environment is used to evaluate the performance of the proposed EV charging station in terms of THD and PF. The results are validated through an on-the-bench prototype hardware setup of the proposed EV charging station.

Reduced oscillations based perturb and observe solar maximum power point tracking scheme to enhance efficacy and speed of a photovoltaic system

This paper puts forward a reduced oscillation based perturb and observe (ROP&O) maximum power point (MPP) tracking (MPPT) technique to mitigate the probability of loss of tracking direction and to reduce oscillations around MPP when the solar photovoltaic (PV) array is subjected under periodically changing irradiance. The proposed technique retains the structure of conventional perturb and observe (P&O) technique additionally incorporating a unique structure of dynamic step sizing, along with proportional-integral (PI) controller which potently alters the duty cycle (𝐷) of the DC-DC boost power converter (BPC). The ROP&O MPPT technique is compared with conventional P&O and incremental conductance (IC) schemes in terms of tracking efficacy (𝜂), ripples in PV voltage and PV current, convergence time, and the error rates. The efficacy of the proposed scheme lies between 99.06% to 99.80%. Moreover, the time to obtain MPP is 0.018 sec. which is about five times faster than the P&O technique and fifteen times faster than the IC technique. Also, the proposed MPPT technique is benchmarked using three-phase grid integration, and the power quality of the grid current is observed in terms of total harmonic distortion (THD).

A Novel Nearest Level Modulation Method with Increased Output Voltage Quality for Modular Multilevel Converter Topology

The modular multilevel converter (MMC) topology is gaining more interest because of its modular design, high efficiency, and scalable voltage levels in medium- and high-power industrial applications, where the nearest level modulation (NLM) method is frequently preferred. In this paper, a novel NLM method is proposed with increased output voltage quality for MMC topology. In conventional NLM (C-NLM), output voltage is obtained as N + 1 levels, where N is the number of submodules (SMs) per arm. The output voltage is increased to 2N + 1 levels by the proposed NLM method without using any additional SMs. The proposed NLM method is based on the offset term injection, which is optimally determined in terms of the best output performance of MMC. Also, trapezoidal reference signal is used instead of sinusoidal reference, which provides better output voltage quality and controls the modulation process. The proposed NLM method presents simple implementation as in the C-NLM, and it is implemented to the upper and lower arms of the MMC; then, arm voltages are successfully controlled. Furthermore, output voltage returns the value of zero in the C-NLM process for low-modulation-ratio applications in relatively small amount of SM usage of MMC design. However, the proposed NLM method gives promising results instead of zero voltage. In order to validate the superior performance of the proposed NLM method, a comparative study is presented with C-NLM and third-harmonic injected NLM method in terms of total harmonic distortion (THD) and magnitude of the output voltage and current. THD of output waveforms of MMC is significantly reduced, and DC voltage utilization is remarkably increased, thanks to the proposed NLM method. In addition, capacitor voltage balancing for the proposed NLM method is accomplished to keep the capacitor voltage of each SM of MMC constant. Simulation results are presented to verify the effectiveness of the proposed NLM method under various case studies. Finally, experimental validation is carried out using a field programmable gate array (FPGA)-based hardware implementation on the laboratory prototype to show the applicability of the proposed NLM method.

Performance Benchmarking of Active-Front-End Rectifier Topologies Used in High-Power, High-Voltage Onboard EV Chargers

High power onboard battery chargers employed in electric vehicles (EVs) and plug-in hybrid EVs (PHEVs) fed from three-phase mains typically consist of a two-stage structure as AC-DC and DC-DC stages. The AC-DC stage is also known as the active front end (AFE). While the AFE rectifies the mains voltage, maintains the power factor, and provides a constant DC-link voltage to the DC-DC converter, the DC-DC converter stage regulates the charging current considering the charging algorithms in order to extend the battery service life. This study focuses on the selection of cost/performance effective AFE topology that can be used in high power onboard chargers. Four different suitable AC-DC topologies are investigated: (i) 3-phase 2-level rectifier, (ii) 3-phase, 3-level neutral-point-clamped (NPC) rectifier, (iii) 3-phase, 3-level T-type rectifier, and (iv) Vienna rectifier. In this study, the aforementioned AFE topologies have been simulated on the PLECS/SpeedFit environment and compared in terms of efficiency, losses, temperature, the number of switching elements, cost and cost/efficiency metrics. The performance results of the aforementioned topologies have been evaluated under different operating frequencies. The results reveal that the most suitable topology alternatives for the front-end AC-DC converter are 3-phase 2-level PWM rectifier and Vienna rectifier. Although the 3-phase 2-level PWM rectifier is superior with its 12% cost advantage, fewer components, and ease of control advantages, it lags a little behind the Vienna rectifier in terms of total harmonic distortion.