Voltage Phase Research Articles

An improved nested 3-phase 5-level MLI design with optimized output voltage and total harmonic distortion

Multilevel Inverters (MLIs) have advanced progressively and demonstrated enormous capacity in power electronics. To provide a 5-level voltage output with a 3-phase full-bridge arrangement and an additional bi-directional switch, a dc voltage input was split by two capacitors. This setup has two issues namely the output voltage limiting the magnitude of the input supply voltage and the voltage disparity between the isolating capacitors. This study suggests an improved nested 3-phase 5-level MLI design with a voltage level and total harmonic distortion (THD) that are both optimized. The suggested arrangement has the features of a lower proportion of passive elements and separated DC sources as it is constructed with a cascade linking of nested two-level cells (NTCs). The suggested unit cell was found to produce a 9-level output voltage (line) by producing a 5-level output voltage (phase) with a peak value that is double the level of the input voltage. The output voltage increasing the capacity of the suggested circuit is its prominent advantage, and the efficacy of the suggested design is 95% and validated by the simulated resultsKeywords: Multilevel Inverters (MLIs), Total harmonic distortion (THD), Voltage level.

The Efficiency of the Kalman Filter in Nodal Redundancy

The growing integration of distributed energy resources underscores the critical importance of having precise insights into the dynamics of an electrical power system (EPS). Consequently, an estimator must align with the EPS dynamics to enhance the overall reliability, safety, and system stability. This alignment ensures that operators can make informed decisions during system operations. An initial step in gaining insight into the system’s state involves examining its state vector, which is represented by voltage phasors. These results are derived through the application of a distributed state-estimation process in large-scale systems. This study delved into the effectiveness of Bayesian filters, with a particular emphasis on the extended Kalman filter (EKF) algorithm in the context of distributed state estimation. To analyze the outcomes, the nodal partitioning process was incorporated within the distributed state-estimation framework. The synergy between the EKF algorithm and the partitioning method was evaluated using the IEEE118 test system.

A Novel Inserting Pilot Radio over Fiber System without the Bit Walk-Off Effect for the Generation and Distribution of Frequency 16-Tupling Millimeter Waves by Mach–Zehnder Modulators

A novel inserting pilot scheme to generate and distribute a frequency 16-tupling millimeter wave (MMW) radio over fiber (ROF) system without the bit walk-off effect via Mach–Zehnder modulators (MZMs) is proposed. The operation principle is analyzed and the feasibility of our proposed scheme is verified by simulation test. The main part of our scheme is a ±8th-order sidebands generator (SG), which is constructed by four MZMs connected in parallel. In the back-to-back (BTB) transmission case, by properly adjusting the voltage and initial phase of the radio frequency (RF) drive signals of the MZMs, ±8th-order sidebands are generated by the SG. In the data transmission case, the data signal is first split into two beams, one of which modulates the RF drive signal with an electrical phase modulator (PM) while the other is amplified by an electrical gainer (EG), and then the two beams are combined into one and used as the composite RF drive signal of the MZMs. By adjusting the modulation index of the PM and the gain of the EG, the data signal can only be modulated to the +8th-order sideband of the output of the SG. The optical carrier from the continuous wave (CW) laser is split into two paths: one is sent into the SG, and the other is used as a pilot signal. The output signal of SG is combined with the pilot signal and is transmitted to the base station (BS) via optical fiber. At the BS, the pilot signal is filtered out by a fiber Bragg grating (FBG) and used as the carrier for the uplink for carrier reuse. After filtering out the pilot, the signal from the FBG, which is composed of ±8th-order sidebands, is injected into a photodetector, and a frequency 16-tupling MMW with downlink data is generated. The key parameters’ influence on the bit error rate (BER) and Q factor in the system is also analyzed. Our scheme can not only effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion and greatly increase the fiber transmission distance but can also effectively improve the performance and the tunability of system. Therefore, it has important application prospects in ROF systems.

Realization of synchronized modulations by stator flux trajectory tracking for low‐carrier‐ratio induction motor drives

SummaryCompared with asynchronous voltage modulations, the synchronous space vector modulation (Syn‐SVPWM) can suppress current harmonics for high‐power induction motors (IM) by generating symmetrical voltage pulses. However, it is difficult to build a high‐performance current regulator based on Syn‐SVPWM because of the requirements of fixed voltage phases and the nonsymmetrical switching sequences in Syn‐SVPWM. Therefore, this manuscript proposes the equivalent realization of Syn‐SVPWM by the concept of stator flux trajectory tracking (SFTT). The new method controls the stator flux vector to move along evenly distributed flux samples in the complex plane. Then, the synchronization and symmetries of voltage pulses are maintained by organizing the switching sequence between adjacent flux samples. Meanwhile, the torque can be changed by online updating the control period based on the inverse torque model. Consequently, the proposed method can provide fast torque response with Syn‐SVPWM in a simple manner because it does not have to compensate the phase contradiction and to extract the fundamental of sampled current. Both simulations and experiments have verified the effectiveness of proposed method.

Optimized Design of New 24-pulse Rectifier

Compared with the conventional 24-pulse rectifier, the low-voltage winding of the rectifier transformer must be connected in the y and d modes, so that the voltage phase of the low-voltage side of the transformer is separated by 30° in sequence. This paper uses the phasor method to obtain a set of phase voltages that move towards 15° through the equivalent of three-phase voltages, so that the two sets of voltages produce a phase difference. Then, through decoupling and voltage reduction, the electrical quantity is converted into a signal quantity, the voltage level is reduced, and then the electrical quantity output is obtained to obtain the required voltage value. Finally, the required DC power is obtained through the rectification system. The effectiveness of the reverse model of this paper is verified by comparing the results and efficiency with the conventional 24-pulse rectifier.

Power quality improvement in grid-connected photovoltaic system under partial shading condition

ABSTRACT Solar systems are becoming widely used renewable energy source since photovoltaic cell generates high power output. However, during partial shading conditions (PSC), the existing MPPT techniques failed to determine the actual maximum point of the photovoltaic (PV) cell, and the photovoltaic system is stuck at a local maximum thus output is gradually reduced. The Optimized Grid-Connected Photovoltaic system aims to extract the most power from the solar array under partial shading conditions. It uses an optimisation algorithm named Sovereign Butterfly Optimization Algorithm and a sequence controller to optimize power value selection. The voltage harmonics and phase delay cause the system to be in an unbalanced state, so the proposed model uses an anomaly obliteration filter fusion technique in which the Butterworth filter is utilised for reducing voltage harmonics and removing phase delay completely by avoiding negative sequence by converting three-phase current to dq0 frames. To increase the overall power quality in the photovoltaic system without synchronization problems, a Subsystem Synchronization Control Strategy is applied which effectively synchronizes the active and non-active currents injected into the grid. Simulated results using the proposed model showed high tracking accuracy of 99.23% and minimum power oscillation of 2.53%, thus enhancing the overall power quality.

A Inverter Dead-time Compensation Method Based on Phase current Polarity Determination and Voltage Partitioning

The introduction of the dead time of the inverter solves the straight-arm conduction problem of the upper and lower power devices of the inverter, but also leads to the deviation of the actual output voltage of the inverter from the given voltage. Dead time increases the harmonic components of phase voltage and phase current, which is also an important factor leading to motor torque ripple. In this paper, the mechanism of the deviation of phase voltage and phase current caused by the dead time of voltage space vector modulation is analyzed, and the effect of dead time on phase voltage and phase current harmonic components is studied. A simple and effective dead time compensation method based on phase voltage division and phase current polarity determination is proposed to directly compensate the dead time. This method can suppress the current harmonic and torque ripple in the running state of the motor, and can greatly simplify the calculation process of the traditional dead time compensation method. Through the system modeling and simulation, it is verified that the method can significantly improve the current waveform distortion, and has good practical value.

ANALYSIS OF CIRCUITS WITH UNIFORM PHASE SHIFT OF INVERTER CELLS

ANALYSIS OF CIRCUITS WITH UNIFORM PHASE SHIFT OF INVERTER CELLS

A ground fault location algorithm in double‐circuit transmission lines with T‐off connection to an industrial microgrid by using current and voltage phasors information of a single terminal

AbstractThe paper presents a ground fault location algorithm (GFLA) in double‐circuit transmission lines (DCTL) with a T‐off connection to an industrial microgrid (IMG) containing electric arc furnaces (EAF), renewable distributed generations (RDG), and static VAR compensator (SVC). The design presented utilizes the information on the current and voltage phasors of one side of the transmission lines (TL) during the fault period, and there is no need for the availability of information on the type of faulty phase(s) and even the faulty section. To find the exact location of the fault in this design, the voltage phasor equations governing the fault point in positive, negative, and zero‐sequence (PNZS) domains, the zero‐sequence current (ZSC) equation of the fault point, and the boundary condition equation of the fault point have been used. The simulation system is implemented in Simulink/MATLAB using accurate modelling of all network components. The algorithm has been tested and evaluated in different fault conditions, including various locations, phase types, phase‐to‐ground connection resistance, occurrence time, and microgrid (MG) operation modes. The successful results of various tests of the proposed design as well as the analysis of various sensitivities confirm the satisfying performance of the suggested algorithm.

Measurement uncertainty in on-line bushing monitoring

The high voltage bushing on-line monitoring has been performed for many years to prevent unexpected rapid power network failures. Network unbalance correction, based on separate voltage phase measurement or phasor technique, effectively improves the measurements of bushing dielectric dissipation factor tgδ and capacitance factor C1. The newly implemented monitoring units reveal that the uncertainty of station voltage measuring transformers manifest the greatest influence on the overall uncertainty budget, regardless of the measurement method.

A Contactless Method for Measuring Amplitude and Phase of RF Voltages up to 26.5 GHz

A Contactless Method for Measuring Amplitude and Phase of RF Voltages up to 26.5 GHz

Analysis and suppression of operational overvoltage and inrush current for high‐speed trains by automatic phase‐switching technique

AbstractWhen a high‐speed train approaches the insulated phase‐splitting section embedded between neighbouring power supply arms, the vacuum circuit breaker (VCB) installed on trains must be disconnected to maintain the traction power supply system as a no‐load condition for completing phase‐switching action, as the train passes through the phase‐splitting section depending on its inertia. However, when operating VCBs, the arc is easily triggered between the mobile contacts inside, accompanied by an overvoltage impulse. Herein, to explore the generating mechanism of inrush current and operational overvoltage, a model describing the ‘substation‐catenary‐train’ traction power supply system is launched based on an equivalent circuit modelling technique. Through the analysis of the transient VCB operational process, the phase of catenary voltage is directly related to the characteristics of the VCB switching‐on overvoltage, as the traction current's phase angle is relevant to the amplitude‐frequency characteristics of the VCB switching‐off overvoltage. Inrush current as a noteworthy element is related to the traction transformer's remanence. The automatic phase‐switching technique is utilised to suppress both operational overvoltage and inrush current, as the optimal combination of VCB switching‐on and switching‐off phases considering the balance between overvoltage and inrush current is achieved based on the particle swarm algorithm.

Time-varying coding digital double-layered Huygens' metasurface for high-efficiency harmonic frequency conversion

Time-varying metasurfaces offer an efficient means of controlling nonlinear harmonics by manipulating component geometries and modulating signals. This ability renders them valuable across various fields, such as wireless communication, radar sensing, and biological monitoring. However, most of the energy in time-varying metasurfaces is concentrated in the fundamental wave, as well as scattered at various harmonic orders, which reduces the energy efficiency at the desired harmonic. Existing approaches have employed time-varying coding digital metasurfaces to achieve efficient harmonic conversion but are primarily designed for reflection. Reflection-based designs require a feed source to excite the metasurface, which can cause certain shielding effects and limit their application in specific scenarios. Thus, designing transmissive time-varying coding digital metasurfaces for efficient harmonic conversion is currently an urgent problem that needs to be addressed. To solve this problem, this paper develops a time-varying coding digital double-layered Huygens' metasurface, which achieves efficient conversion of the desired transmitted harmonics. The unit structure of the metasurface consists of a pair of reverse-symmetric split rings located on the upper and lower sides of a dielectric substrate, enabling nearly non-reflective Huygens' resonance. Based on a continuous periodic phase modulation strategy, we achieved efficient conversion of transmitted harmonics by loading a time-varying voltage (phase) modulation signal with a 5-bit resolution bit width onto the designed double-layered Huygens' metasurface. This study presents a solution for designing a transmissive time-varying coding digital metasurface to achieve efficient conversion of harmonics, thereby enhancing the application capabilities of time-varying coding digital metasurfaces.

Incorporating STATCOM into a Hydro-Thermal Optimal Power Flow Algorithm

This paper presents the results of the inclusion of Synchronous Static Compensator (STATCOM) power flow models into a hydro-thermal optimal power flow (HTOPF) algorithm. STATCOM basically introduces the voltage magnitude and phase angle of the source converter into the algorithm. For each incorporated STATCOM, an augmented Lagrangian function was formed. The first and second derivatives of these functions were added to the gradient vector and Hessian matrix of an existing algorithm. The modified algorithm was implemented using MATLAB R2018a and tested on 30 and 57 bus systems. Two and three STATCOMs were, respectively, tested on 30 and 57 bus systems. The results obtained showed that one of the STATCOMs used on 30-bus system injected reactive power that ranges from 8.99 MVAR to 28.22 MVAR while the other one injected reactive power in the range of 8.20 MVAR to 33.20 MVAR. For the STATCOMs placed on the 57-bus system, the range of reactive power absorption by the one placed at bus 5 is 7.83 MVAR to 22.86 MVAR while the one at bus 55 absorbed from 5.06 MVAR to 12.92 MVAR. The STATCOM’s reactive power injection at bus 31 ranges from 4.63 MVAR to 10.35 MVAR. All the lower and higher values were obtained at hours 3 and 7, respectively. While the STATCOMs significantly improved the systems’ voltage profile, the impacts of STATCOM on the total systems daily energy loss, daily energy generations (from both plants), daily fuel cost and hydro plant water worth are insignificant.

Power quality stabilization system for grid connected large-scale solar power system

This paper presents solution to power quality issues when integrating a 1.5 MW photovoltaic array (PVA) with a unified power quality conditioner (UPQC) into the power grid. A modified unit vector template control scheme is used to generate a reference load voltage signal, and a synchronous reference frame (SRF) is created using a low-pass filter to control UPQC. Furthermore, the PVA is interfaced with the grid through a common DC link of shunt and series converters. The series converter mitigates power quality problems allied with the grid side, such as 3rd, 5th, and 7th harmonics, voltage sag, and voltage swell, by introducing signals in phase and out of phase voltage, respectively, at the point of common coupling (PCC). The shunt converter mitigates nonlinear load current harmonics and compensates for reactive power using SRF. The suggested methodology is implemented using MATLAB Simulink with both linear and nonlinear loads under different power quality conditions. Total harmonic distortions are maintained below 5% at PCC, as per IEEE-519 standards.

A Novel Impedance Matching of Class DE Inverter for High Efficiency, Wide Impedance WPT System

In high-frequency wireless power transfer (WPT) applications, Class D, E, and F inverters are most widely used. Class DE inverters combine the respective advantages of Class D and Class E inverters. However, the Class DE inverter is sensitive to changes in impedance, which can easily lead to the loss of soft switching characteristics, thereby reducing efficiency. In this paper, an impedance-matching compensation design method is proposed to expand the high-efficiency region of the Class DE inverter by matching impedance and parameters. The effect of the method on the zero-voltage switching (ZVS) characteristic of Class DE inverters is analyzed in detail. The proposed WPT system maintains a constant voltage and zero phase angle by employing PS/PS compensation topology. Theoretical analysis shows that the impedance can be compressed for the design of resonant network impedance, and the method can expand the high-efficiency region with a reasonable choice of parameters to match the phase. Finally, a 500 kHz, 1 kW WPT prototype was constructed with a coupling factor of 0.25–0.4 and a load range of 30–80 Ω. The inverter’s efficiency exceeds 95%, with optimal efficiency reaching 97.3%. The system efficiency is greater than 87%.

Voltage angle‐based coherency identification in power system

AbstractCoherency detection in power system is vital step for controlled‐islanding. Model‐based slow‐coherency method is the traditional method of detecting coherent areas, which suffers from computational burdens. With the implementation of a wide‐area measurement system (WAMS) in power systems, coherent areas can be detected early after a disturbance that helps to ensure quick separation or remedial action. In this study, a novel Synchrophasor‐based coherency identification method has been proposed with bus voltage angle measurement. A new algorithm is proposed based on the first and second derivatives of the bus voltage phase angle using hierarchical clustering method for coherency detection. The proposed approach leverages hierarchical clustering method and the dynamics reflected in the bus voltage phase angle behavior to achieve automatic and accurate coherency identification. Real time simulation results demonstrate the ability of the proposed algorithm to detect the coherency with three consecutive PMU data from all the system buses and showcase coherent area boundaries. Case studies show robustness of the proposed method and is least affected by the latency in communication network compared to conventional methods. The proposed algorithm has been mathematically formulated and evaluated with different benchmark systems in OPAL‐RT real‐time simulation environment with HYPERSIM platform.

A Novel Higher-Order Numerical Scheme for System of Nonlinear Load Flow Equations

Power flow problems can be solved in a variety of ways by using the Newton–Raphson approach. The nonlinear power flow equations depend upon voltages Vi and phase angle δ. An electrical power system is obtained by taking the partial derivatives of load flow equations which contain active and reactive powers. In this paper, we present an efficient seventh-order iterative scheme to obtain the solutions of nonlinear system of equations, with only three steps in its formulation. Then, we illustrate the computational cost for different operations such as matrix–matrix multiplication, matrix–vector multiplication, and LU-decomposition, which is then used to calculate the cost of our proposed method and is compared with the cost of already seventh-order methods. Furthermore, we elucidate the applicability of our newly developed scheme in an electrical power system. The two-bus, three-bus, and four-bus power flow problems are then solved by using load flow equations that describe the applicability of the new schemes.

Photon Generation Scheme of 32‐Fold Millimeter‐Wave Signal Based on Mach‐Zehnder Modulator

AbstractThis paper proposes a 32‐tupling frequency millimeter‐wave (MMW) filter‐free system based on four Mach‐Zehnder Modulators (MZM) connected in parallel and cascaded with a simple radio‐fiber (RoF) link structure. The four MZMs are all at the maximum transmission point (MATP), and the radio frequency (RF) driving voltage phase difference between MZMs is π /2. The center carrier is suppressed by using an optical attenuator (OATT) and an optical phase shifter (OPS). Two parallel MZMs can generate ±8th order and ±12th order optical sidebands, and the ±4th order optical sidebands can be suppressed by adjusting the modulation index m of the MZM, using cascaded two dual‐parallel MZMS(DPMZM) and the phase difference of the RF signal source is π/4 to generate ±16th order optical sidebands. The theoretical analysis and simulation experiments are performed for the scheme proposed in this paper. The results show that the simulated and theoretical values of the optical sideband suppression ratio (OSSR) for ±16th order optical sideband signals are 60.02 and 59.96 dB, respectively, and the simulated and theoretical values of the RF sideband suppression ratio (RFSSR) for the 32‐tupling MMW signal are 56.34 and 53.94 dB, respectively.

Research on three-level PWM Rectifier without grid voltage sensor

Traditional three-level PWM rectification technology usually uses voltage sensors to sample the grid voltage, and then obtains the angle information of the voltage vector through a phase-locked loop, thereby achieving the d/q axis control function of voltage and current. However, the use of voltage sensors not only increases system costs, but also increases system volume and debugging difficulty. In addition, when the voltage sensor is damaged, it can cause system shutdown and affect system reliability. After analyzing the three-level control method of PWM rectifiers, a sensorless control strategy for grid voltage based on sliding mode observer method is proposed. By using the sliding mode observer method to estimate the amplitude and phase of the power grid voltage at the voltage and current values of each PWM cycle, a phase-locked loop is used to determine the position of its voltage vector. The simulation results all demonstrate that the proposed method can accurately and effectively estimate the voltage vector angle of the power grid, and ensure that the output of the rectification system meets the standard voltage waveform.