Total Harmonic Distortion Value Research Articles

Hybrid control for capacitor-assisted Z-source inverter in grid-connected photovoltaic system

Renewable energy integration into the power grid is essential for sustainable energy systems, but maintaining efficiency and reliability in such systems remains a key challenge. This study introduces a novel hybrid control topology for a Capacitor-Assisted Extended Boost Z-Source Multilevel Inverter in a grid associated solar photovoltaic (PV) structure. The suggested hybrid technique implies a united implementation of a Gannet Optimization Algorithm and Spiking Deep Residual Network and usually referred as GOA-SDRN technique. Initially, the modelling of the inverter is collected to get the best signal by the proposed controller. The proposed inverter configuration consists of a minimal quantity of diodes, switches, and sources. This configuration also offers advantages like less total harmonic distortion (THD) and reduced electromagnetic interference, making it a favourable choice for PV integration. The GOA is employed to determine the most favourable gain limiting factor based on a variation of power from their regular values. This control method ideally satisfies the load demand while reducing changes in the system limiting factor and external disturbances. The proposed control topology is executed in MATLAB and the concept is contrasted to different techniques. The THD values of existing methods such as Particle Swarm Optimization, Genetic Algorithm, and Grasshopper Optimization Algorithm are 1.36 %,0.89 %, and 1.99 % respectively, while the THD value of the proposedmethod is 0.63 %, demonstrating its optimal performance over existing methods. The proposed GOA-SDRN technique provides an effective solution for enhancing inverter efficiency and reducing distortion in grid-associated PV systems.

Improving the efficiency of a non-ideal grid coupled to a photovoltaic system with a shunt active power filter using a self-tuning filter and a predictive current controller

Introduction. Recently, photovoltaic (PV) systems are increasingly favored for converting solar energy into electricity. PV power systems have successfully evolved from small, standalone installations to large-scale, grid-connected systems. When the nonlinear loads are connected to a grid-tied PV system, the power quality can deteriorate due to the active power supplied by the PV array, there’s a noticeable decline in the quality of power delivered to consumers. Its combination with the shunt active power filter (SAPF) enhances system efficiency. Consequently, this integrated system is adept at not only powering local loads but also at compensating for reactive power and filtering out harmonic currents from the main grid. The novelty of the work describes how an operation of a small scale PV system connected to the low voltage distribution system, and nonlinear load can be achieved, the investigation aims to analyze the system’s behavior and elucidate the advantages of employing various control algorithms. These proposed algorithms are designed to ensure a unity power factor for the utility grid while prioritizing high convergence speed and robustness against load power fluctuations across different levels of solar irradiation affecting the PV modules. The purpose of this work is to enhance the dynamic performance of the SAPF by cooperatively using a self-tuning filter (STF) based instantaneous active and reactive power method (PQ) with a novel predictive current control, enhance the system resilience, ensure optimal management of the total active power between the PV system, the electrical network and the non-linear load by integrating the functionalities of the SAPF under different levels of solar irradiation and maintain the DC-link capacitor voltage constant. Methods. A novel predictive current controller is designed to generate the switching signals piloted the three phase source voltage inverter, also a novel algorithm of instantaneous active and reactive power is developed, based on STF, to extract accurately the harmonic reference under non ideal grid voltage, also the perturb and observe algorithm is used to extract, under step change of solar irradiation, the maximum power point tracking of the PV module and the PI controller is used to maintain constant the DC-link capacitor voltage of the SAPF. Results. The efficacy of the proposed system is primarily centered on the grid side, and the performance evaluation of the control system is conducted using the STF based PQ algorithm and predictive current control. In addition, comprehensive testing encompasses all modes of operation, including scenarios involving distorted voltage sources, step changes in solar radiation, and variations in nonlinear loads. Results highlight superior performance in both transient and stable states, affirming the robustness and effectiveness of the proposed controllers. Practical value. The total harmonic distortion value of the grid current for all tests respects the IEEE Standard 519-1992. References 21, tables 7, figures 25.

Dual Second Order Generalized Integrator – Phase Locked Loop technique applied to a distorted grid-connected solar energy based on a Z-Source Inverter

In this paper, a Dual Second Order Generalized Integrator_Phase Locked Loop (DSOGI_PLL) technique applied to the Photovoltaic (PV) system supplying a Z-Source five-level Inverter (ZSI) is presented. The ZSI assures the increasing voltage of the PV system and provides the desired output DC at the input of the five-level Neutral Point Clamped Inverter (5L_NPCI), without any control which reduces the complexity of the overall system, this is due to the impedance network in its structure. We use Z-Source in order to eliminate the controlled DC bus as well as the use of the DC-DC Boost converter as an intermediary. A DSOGI technique is employed to control and optimize the energy quality, especially in distorted grid conditions and allows one to obtain a very low value of Total Harmonic Distortion (THD) which means lower peak currents, and higher efficiency. Low THD is an essential feature in power systems that international standards such as IEC 61000-3-2, and IEEE-519 set limits on the harmonic currents of various classes of power equipment connected to a distorted three-phase grid. Compared to the classic structure of inverters, the NPC five-level inverter presents a very high performance.

Optimal design of hybrid green energy powered reduced switch converter based shunt active power filter using horse herd algorithm

Renewable energy sources are playing a leading role in today's world. However, integrating these sources into the distribution network through power electronic devices can lead to power quality (PQ) challenges. This work addresses PQ issues by utilizing a shunt active power filter in combination with an Energy Storage System (ESS), a Wind Energy Generation System (WEGS), and a Solar Energy System. While most previous research has relied on complex methods like the synchronous reference frame (SRF) and active-reactive power (pq) approaches, this work proposes a simplified approach by using a neural network (NN) for generating reference signals, along with the design of a five-level reduced switch voltage source converter. The gain values of the proportional-integral controller (PIC), as well as the parameters for the shunt filter, boost, and buck-boost converters in the WEGS and ESS, are optimally selected using the horse herd optimization algorithm. Additionally, the weights and biases for the neural network (NN) are also determined using this method. The proposed system aims to achieve three key objectives: (1) stabilizing the voltage across the DC bus capacitor; (2) reducing total harmonic distortion (THD) and improving the power factor; and (3) ensuring superior performance under varying demand and PV irradiation conditions. The system's effectiveness is evaluated through three different testing scenarios, with results compared against those obtained using the genetic algorithm, biogeography-based optimization (BBO), as well as conventional SRF and pq methods with PIC. The results clearly demonstrate that the proposed method achieves THD values of 3.69%, 3.76%, and 4.0%, which are lower than those of the other techniques and well within IEEE standards. The method was developed using MATLAB/Simulink version 2022b.

A Novel Shunt Zigzag Double-Tap Low-Harmonic Multi-Pulse Rectifier Based on a Three-Stage Power Electronic Phase-Shifting Transformer.

To solve the problem of the large size of traditional industrial frequency phase-shift transformers and the harmonic distortion of multi-pulse wave rectifier systems, this paper proposes a three-stage shunt zigzag power electronic phase-shift transformer based on a double-tap multi-pulse wave rectifier, which combines the power factor correction (PFC) converter with the voltage-type SPWM inverter circuit to form a power electronic converter to realize the frequency boost and power factor correction. Through AC-DC-AC conversion, the frequency of the three-phase AC input voltage is increased, the number of core and coil turns in the transformer is reduced to reduce the size of the phase-shifter transformer, a zigzag structure of the phase-shifter transformer is used to solve the unbalanced distribution of current between the diode bridges, and a passive harmonic suppression method on the DC side is used to generate a loop current by using a group of single-phase rectifier bridges to regulate the input line current of the phase-shifter transformer. The phase-shifted voltage is input into two three-phase diode rectifier bridges to rectify and supply power to the load. Simulation and semi-physical test results show that the proposed method reduces the total harmonic distortion (THD) value of the input current of the phase-shifted transformer to 7.17%, and the THD value of the grid-side input current is further reduced to 2.49%, which meets the harmonic standard and realizes the purpose of power factor correction as well as being more suitable for high-power applications.

Active power compensation circuit for resonance mitigation and harmonic reduction in microgrid system

The nature and behavior of capacitors, transformers, inductors, active compensators, and non-linear loads can produce power resonance. Unfortunately, the presence of a resonance phenomenon can have a negative impact on system stability and lead to catastrophic power system failures. Therefore, even when using modern or conventional techniques to enhance total harmonic distortion (THD) or improve input power factor (IPF), it is necessary to avoid resonance. An active power compensation circuit (APCC) is proposed and designed to function with two categories of linear/non-linear loads. The APCC has been implemented and regulated using an adjusted pulse width modulation technique. The aim of the suggested APCC is to minimize AC side distortions, improve the IPF, and mitigate harmonics resonance at the same time. The simulation results demonstrate that the proposed APCC investigates the aim function of this study by absorbing harmonics, correcting IPF, and eliminating resonance problems under both transient and steady-state operating conditions. The supply voltage and current THD values for the first power circuit type are reduced by 96.7 % and 96.3 %, respectively, at α=30°. Meanwhile, for the second power circuit, the THD is reduced by 91.92 % and 90.4 %. Also, the IPF changed for the first and second power circuits from 0.72 and 0.86 to almost unity. These results demonstrated the effective performance of the APCC circuit and controller in reducing power harmonics, eliminating power resonance, and modifying power factors.

Enhancing power quality in grid-connected hybrid renewable energy systems using UPQC and optimized O-FOPID

Hybrid Renewable Energy Systems (HRES) have recently been proposed as a way to improve dependability and reduce losses in grid-connected load systems. This research study suggests a novel hybrid optimization technique that regulates UPQC in order to address the Power Quality (PQ) problems in the HRES system. The load system serves as the primary link between the battery energy storage systems (BESS), wind turbine (WT), and solar photovoltaic (PV) components of the HRES system. The major objective of the study is to reduce PQ issues and make up for the load requirement inside the HRES system. The addition of an Optimized Fractional Order Proportional Integral Derivative (O-FOPID) controller improves the efficiency of the UPQC. The Crow-Tunicate Swarm Optimization Algorithm (CT-SOA), an enhanced variant of the traditional Tunicate Swarm Optimization (TSA) and Crow Search Optimization (CSO), is used to optimize the control parameters of the FOPID controller. Utilizing the MATLAB/Simulink platform, the proposed method is put into practice, and the system’s performance is assessed for sag, swell, and Total Harmonic Distortion (THD). The THD values for the PI, FOPID, and CSA techniques, respectively, are 5.9038%, 4.9592%, and 3.7027%, under the sag condition. This validates the superiority of the proposed approach over existing approaches.

Analyzing the Nonlinear Performance of Miniature Loudspeakers in Consideration of the Creep Effect

Miniature loudspeakers exhibit pronounced nonlinear characteristics due to physical size limitations and the demand for sufficient sound pressure. The primary nonlinear properties, including the force factor, mechanical stiffness, and mechanical resistance, depend on the displacement or velocity of the voice coil. The creep effect in the loudspeaker’s suspension system, which significantly affects low-frequency displacement, is often neglected in existing studies on nonlinear dynamics. This study enhances the modeling of miniature loudspeakers by incorporating the creep effect into an extended nonlinear model. The voice coil displacement and total harmonic distortion (THD) predicted by the extended model were validated against experimental data. The displacement and THD values predicted by the nonlinear model in consideration of the creep effect corresponded closely to the actual measurement values, substantiating the effectiveness and precision of the model.

A new topology of non-isolated AC-DC quadratic boost converter with enhanced power traits

A novel AC-DC quadratic boost converter (QBC) topology is presented in this paper which can provide higher power factor (PF), lower total harmonic distortion (THD) and higher voltage when compared to a conventional AC-DC boost convertero This is achieved by using additional switched capacitor and switched inductor in the power processing stage. The presented converter is analyzed theoretically, and a voltage gain equation is derived. A simulation model is created to evaluate the converter performance under various duty cycles, switching frequency, and changing output load. The input PF, THD, and voltage gain of the simulated model were compared with conventional converter to determine the validity of the suggested converter circuit. The results show that the efficiency, PF, THD and voltage gain value reaches approximately 97.9%, 0.98, 16.14, and 2.83 respectively at a duty cycle of 50% with fixed output load of 100 Ω. A dual loop voltage and current controller is also arrayed with the proposed circuit which allows further enhancement in PF (0.997) and THD (7.45%). This converter can be a suitable option for systems where isolation is not necessary but high PF, high voltage gain and low THD are required.

Enhancing power conversion efficiency in five-level multilevel inverters using reduced switch topology

This paper presents extensive research on improving the power conversion efficiency of five-level multilevel inverters (MLIs) by utilizing a reduced switch topology. MLIs have received an abundance of focus because of their ability to generate high-quality output waveforms and have better harmonic outcomes than traditional two-level inverters. The high number of switches in MLIs, on the other hand, can result in increased power losses and lower overall efficiency. In this paper, a novel reduced switch topology for five-level MLIs, which is having five switches is proposed with the aim of minimizing power losses while preserving superior performance due to lesser number of switches. To achieve efficient power conversion, the proposed topology employs advanced pulse width modulation control strategies and optimized switching patterns. The simulation results show that the minimized switch topology improves the power conversion efficiency of the five-level MLI, resulting in lower losses and better overall system performance. The total harmonic distortion (THD) value of the output current has been reduced to 7.12% and the efficiency has been achieved to 96.92%. The findings of this investigation help to advance MLI technology, allowing for more efficient and reliable power conversion in a variety of applications such as renewable energy systems, electric vehicles, and industrial drives.

Performance improvement of predictive voltage control for interlinking converters of integrated microgrid

Voltage quality in Renewable Energy System may be harmed by varying power demand and fluctuating energy source outputs. The model predictive voltage (MPV) control approach is suggested in this study. The proposed control strategy enables appropriate power interactions between the AC and DC subgrids while sharing power fluctuations in a coordinated way. Both the AC and DC subgrids support each other in accordance with their normalized relative changes in AC frequency and DC voltage, respectively. A typical photovoltaic (PV) wind-battery-based hybrid AC/DC microgrid is modelled and investigated, and the usefulness of the proposed scheme is validated under the renewable energy variations and load perturbations. MATLAB/Simulink has validated the efficacy of the suggested strategy. A set of comparative tests was conducted between conventional Proportional-Integral (PI) control, Sliding Mode Control (SMC) strategies, and a novel Model Predictive Voltage Control (MPV) approach under diverse conditions. The aim was to comprehensively assess the advantages of the proposed MPV method. Results demonstrate that, in contrast to traditional PI and SMC control strategies, the MPV technique exhibits distinct benefits in terms of superior control performance and achieves exceptionally low Total Harmonic Distortion (THD) values. Ultimately, the proposed solution not only raises the performance standard but also ensures the stable operation of the Renewable Energy System (RES).

The Influence of Solar Irradiance and Temperature on The Pll-Synchronized Inverter Within Grid-Connected PV Systems

This study assesses the influence of solar irradiance and temperature on αβPLL synchronized inverters by investigating their intricate relationship within grid-connected PV systems. The intermittent nature of the DC side of these systems can significantly impact their performance. However, the extent of this impact remains uncertain when employing the stationary reference frame PLL (αβPLL) algorithm for synchronization with the utility grid. Employing simulation in MATLAB 2020a and a Model Based Design approach in the Simscape toolbox of SIMULINK, we conducted this investigation through two test scenarios: one with constant solar irradiance and varying temperature, and the other with varying solar irradiance and constant temperature. Our results indicate that fluctuations in solar irradiance and temperature have minimal effects on the output parameters of grid-connected PV systems when synchronized with the stationary reference frame PLL (αβPLL) algorithm. This conclusion is supported by the total harmonic distortion values, which all fall within the specified limits of IEEE Standard 929- 2000. These findings underscore the potential of αßPLL synchronization as a promising technique, capable of effectively synchronizing grid inverters even in the presence of DC input distortion. This proficiency in grid integration holds promise for enhancing the integration of renewable energy sources into the grid, thereby bolstering power availability for household distribution.

PV Wind Battery Based DC Microgrid with Neural Network MPPT

This Research presents a novel approach to enhancing the performance and efficiency of a PV-wind-battery-based DC microgrid through the integration of a neural network maximum power point tracking (MPPT) system. The proposed system aims to optimize energy harvesting from photovoltaic (PV) panels and wind turbines while efficiently managing energy storage in batteries. By employing neural network algorithms, the MPPT system adapts to varying environmental conditions and load demands, thereby maximizing energy extraction and system stability. Two important RE (Renewable Energy) power sources—photovoltaic cells and wind energy systems—are examined in this technical study under a range of meteorological conditions. Initially, a state-of-the-art intelligent controller system was developed to help monitor the peak power point. For RES, an MPPT (maximum power point tracking) controller is necessary since weather patterns are unpredictable. The purpose of this work is to provide novel ways for power generation using solar and wind energy that are based on MPPT and IDNN (enhanced deep neural network). The integration of a hybrid PV/WES system into microgrids, or MGs, has the potential to lower THD values and enhance power quality. The simulation findings validated that the suggested IDNN system outperforms the current approach in various operating scenarios, as seen by decreased mean square error (MSE) rates, total harmonic distortion (THD), and computational complexity.

Higher performance enhancement of direct torque control by using artificial neural networks for doubly fed induction motor

Recently Direct Torque Control is widely appreciated compared to other conventional control methods due to its numerous advantages, notably its speed and precision. However, despite its qualities, it often encounters torque ripples that limit its operational effectiveness. These variations can be attributed to the use of hysteresis comparators, leading to variable frequency operation and undesirable speed overshoots. To address these challenges and enhance overall motor control, this article introduces a new approach based on neural networks. Direct Torque Control method is specifically designed for Doubly Fed Induction Motors and utilizes an Artificial Neural Network. Unlike conventional methods, this approach eliminates the need for speed controllers, commutation tables, and hysteresis comparators, thus providing a more integrated and efficient solution. Simulations conducted in the Matlab/Simulink environment have demonstrated the significant advantages of this approach with a higher performance enhancement. Not only were torque ripples reduced, but speed overshoot was completely eliminated. Furthermore, significant reductions in Total Harmonic Distortion values of stator and rotor currents were achieved, indicating an overall improvement in system performance.

Performance Characteristics of a Newly Developed Asymmetric Seven-Level Inverter Utilizing Various Hybrid Pulse Width Modulation Strategies

This study unveils a notable breakthrough in inverter technology, holding promise for substantial improvements in voltage quality and the attenuation of harmonic distortions within power systems. This study concentrates on the design and implementation of a novel Seven-Level Asymmetric Inverter (NSLAI) by incorporating various hybrid Pulse Width Modulation (PWM) techniques. The primary goal is to improve the output voltage magnitude while decreasing the Total harmonics compared to conventional PWM methods. The investigation introduces a novel Seven-Level Asymmetric Inverter (NSLAI) with innovative Hybrid Pulse Width Modulation (PWM) strategy. The purpose of this study is to investigate the distinct features of a recently developed asymmetric seven-level inverter, with a focus on exploring its characteristics through the implementation of diverse hybrid pulse width modulation strategies. Hybrid PWM methodology intricately centers on enhancing voltage quality and achieving better harmonious spectral characteristics. The gate signal producing approach for this suggested PWM technology incorporates a hybrid PWM methodology that combines trapezoidal and sinusoidal waveforms, as well as a standard triangular carrier signal enabling NSLAI. The hybrid version of PWM practices is deliberately used to generate switching signals for the NSLAI. An intensive evaluation of numerous indicators of effectiveness across multiple modulation indexes leads in the demonstrating of quantitative findings that compare the unique Hybrid PWM practice with established PWM tactics. Notably, the hybrid reference Carrier Overlapping strategy has emerged as a leading approach surpassing conventional pulse width modulation techniques. It achieves a significantly higher fundamental Root Mean Square voltage output and remarkably lower percentage of Total Harmonic Distortion values compared to all within the hybrid reference Variable Frequency strategy. The principal analytical tool used in the modeling investigation is MATLAB-SIMULINK. This study marks a watershed moment in the development of inverters, claiming significant improvements in battery power quality and distortion caused by harmonics avoidance across power systems, as evidenced by extensive simulation and prototype-based discoveries.

Enhancing grid-connected photovoltaic system performance with novel hybrid MPPT technique in variable atmospheric conditions

This paper proposes an innovative approach to improve the performance of grid-connected photovoltaic (PV) systems operating in environments with variable atmospheric conditions. The dynamic nature of atmospheric parameters poses challenges for traditional control methods, leading to reduced PV system efficiency and reliability. To address this issue, we introduce a novel integration of fuzzy logic and sliding mode control methodologies. Fuzzy logic enables the PV system to effectively handle imprecise and uncertain atmospheric data, allowing for decision-making based on qualitative inputs and expert knowledge. Sliding mode control, known for its robustness against disturbances and uncertainties, ensures stability and responsiveness under varying atmospheric conditions. Through the integration of these methodologies, our proposed approach offers a comprehensive solution to the complexities posed by real-world atmospheric dynamics. We anticipate applications in grid-connected PV systems across various geographical locations and climates. By harnessing the synergistic benefits of fuzzy logic and sliding mode control, this approach promises to significantly enhance the performance and reliability of grid-connected PV systems in the presence of variable atmospheric conditions. On the grid side, both PSO (Particle Swarm Optimization) and GA (Genetic Algorithm) algorithms were employed to tune the current controller of the PI (Proportional-Integral) current controller (inverter control). Simulation results, conducted using MATLAB Simulink, demonstrate the effectiveness of the proposed hybrid MPPT technique in optimizing the performance of the PV system. The technique exhibits superior tracking efficiency, achieving a convergence time of 0.06 s and an efficiency of 99.86%, and less oscillation than the classical methods. The comparison with other MPPT techniques highlights the advantages of the proposed approach, including higher tracking efficiency and faster response times. The simulation outcomes are analyzed and demonstrate the effectiveness of the proposed control strategies on both sides (the PV array and the grid side). Both PSO and GA offer effective methods for tuning the parameters of a PI current controller. According to considered IEEE standards for low-voltage networks, the total current harmonic distortion values (THD) obtained are considerably high (8.33% and 10.63%, using the PSO and GA algorithms, respectively). Comparative analyses with traditional MPPT methods demonstrate the superior performance of the hybrid approach in terms of tracking efficiency, stability, and rapid response to dynamic changes.

Multilevel Inverter with Enhanced THD Value used in Grid Connected Applications

In this work, the relationships among pulse width modulation (PWM), sinusoidal pulse width modulation (SPWM), and space-vector pulse width modulation (SVPWM) for three-phase inverters will be analyzed to better comprehend their differences. detailed comparison of the three modulation schemes under study’s Total Harmonic Distortion (THD). High-power applications are increasingly concentrating on converter technology. This growing importance may be attributed to its improved output waveforms over the 3- carrier-based sinusoidal pulse width modulation (SPWM). To control and modulate multi-level inverters, many techniques are employed. These methods are categorized based on how frequently they switch. The ripple current rating, capacitance value, and voltage balance in the DC bus capacitors are all impacted by the pulse width modulation techniques. It is crucial to select the modulation method based on the current control requirements, as this determines the output voltage waveform’s harmonic content. SVPWM is gradually becoming more and more popular in industries because of its improved dc bus utilization and ease of digital realization. This work examines PWM, Sinusoidal, and SVPWM feeding a load connected to RL. Three different methodologies’ performances are compared as these methods are investigated through simulation with MATLAB/SIMULINK software.

Harmonics mitigation technique for asymmetrical multilevel inverter fed by photovoltaic sources

A multilevel inverter is an electrical device that converts a DC voltage into a higher AC voltage by generating a stepped waveform with several voltage levels. Unlike traditional inverters that produce a square wave or a pulse-width modulated (PWM) waveform with only two voltage levels, multilevel inverters can generate waveforms with three or more levels, resulting in reduced harmonic distortion, improved efficiency, and decreased electromagnetic interference. The design and control of multilevel inverters are active research areas that aim to enhance their performance, reliability, and scalability. In this research, a 31-level asymmetric cascaded multilevel inverter is suggested. The proposed multilevel inverter (MLI) system employs four photovoltaic cells as dc sources with structure of (1:2:4:8) Vdc. The system is modeled by MATLAB/Simulink and total harmonic distortion (THD) values of the output voltage and current are 1.106% for resistive load, and 1.35% and 0.403% for inductive load. These outcomes demonstrate the recommended circuit's efficacy and demonstrate its suitability for medium- and high-power applications.

A PGC demodulation scheme based on the Lissajous ellipse fitting for homodyne interferometer without using second harmonic carrier signal

This paper proposes a phase generated carrier (PGC) demodulation scheme for sinusoidal phase modulation interferometer (SPMI) that does not require a second harmonic carrier signal. In this scheme, an in-phase interference signal component with direct current (DC) bias is obtained by low-pass filtering the original interference signal, and a quadrature interference signal component is obtained by conventional means. The Lissajous figure formed by these two quadrature interference signal components is an ellipse whose center deviates from the origin of the I-Q coordinates. By fitting this ellipse, the major and minor axes and the center coordinates can be obtained. These elliptic parameters are then used to eliminate DC bias and normalize the amplitude of the quadrature signal components. Finally, the phase demodulation of the interference signal can be realized by using arctangent algorithm or differential cross multiplication (DCM) algorithm. The results of simulation and experiment have verified the validity and accuracy of the proposed PGC demodulation scheme, and show that it is insensitive to the phase modulation depth C. Compared with conventional PGC demodulation, this scheme requires lower depth of carrier phase modulation. The vibration measurement results indicate that the average signal-to-noise and distortion Ratio (SINAD) and total harmonic distortion (THD) values of demodulation results in the frequency range of 130 Hz to 250 Hz are 34 dB and -33 dB respectively. The proposed PGC demodulation scheme shows good performance in displacement measurement using SPMI.

A Novel Series 24-Pulse Rectifier Operating in Low Harmonic State Based on Auxiliary Passive Injection at DC Side

To reduce the current harmonics on the input side of a multi-pulse rectifier, this paper proposes a low harmonic current source series multi-pulse rectifier based on an auxiliary passive injection circuit at the DC side. The rectifier only needs to add an auxiliary passive injection circuit on the DC side of the series 12-pulse rectifier, which can change its AC input voltage from 12-step waves to 24-step waves. We analyzed the working mode of the rectifier, optimized the optimal turn ratio of the injection transformer from the perspective of minimizing the total harmonic distortion (THD) value of the input voltage on the AC side, and analyzed the diode open circuit fault in the auxiliary passive injection circuit. Test verification shows that, after using the passive harmonic injection circuit, the THD value of the input voltage of the AC side of the rectifier is reduced from 14.03% to 4.86%. The THD value of the input current is reduced from 5.30% to 2.16%. The input power factor has been increased from 98.86% to 99.83%, and the power quality has been improved.